chapter 1 introduction: important biomolecules -...

Ashvin B. Padhiyar / Ph. D. Thesis (Physics) / Sardar Patel University - 2010

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Chapter 1

Introduction: Important Biomolecules


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Introduction of Biomolecules

It hardly needs to be emphasized that cell is the fundamental unit of

organization through which life is expressed. This cell or unit of life is a

storehouse of multiple information molecules responsible for bioactions.

Interestingly, it is not known with any degree of certainly as to how cells

were first formed, but there is a good deal of evidence to suggest that variety

of chemical and physical processes taking place on the earth or its

surrounding atmosphere, led to the information of simple molecules

representing the cellular status. These biomolecules entered in to a network

of interaction resulting in more and more complex groupings and structures.

Finally these biomolecules formed a concrete organizational unit which

expressed it self in the form of life.

A large number of biomolecules are in living cells. These include

monosaccharides, disaccharides, polysaccharides, amino acids, proteins,

enzymes, fatty acids, fats and oils, nucleotides, nucleic acids, histones, acidic

proteins, chlorophyll, hemoglobin and a multiple of several other

components of cells It is impossible to pinpoint as to which of the myriads of

biomolecule is living, because none of these ,independently, can be

expressive of life. Viruses are perhaps the simplest of living creatures. These

represent the organization of two important biomolecules including protein

and RNA or DNA.

Meaning of Biomolecules

Biomolecules are complex organic molecules. These molecules form

the basic structural constituent of a living cell. The organic compounds such

as amino acids, nucleotides and monosaccharides serve as building blocks of

complex biomolecules. The important biomolecules are proteins,

carbohydrates and fats, enzymes, vitamins, hormones and nucleic acids.

Some of the biomolecules are polymers. For e.g., starch, proteins, nucleic

acids are condensation polymers of simple sugars, amino acids and


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nucleotides respectively. Most of the biomolecules are very large and

extremely complex. Their reactions involve complex mechanisms.

Biomolecules are related to the living organisms in the following sequence;

Types of Biomolecules

There are several types of biomolecules. Of most importance are the

nucleotides that make up DNA and RNA, the molecules that are involved in

heredity. There are also the lipids which function as the building blocks of

biological membranes and as energy providing molecules. The hormones

serve in the regulation of metabolic processes and many other roles in

organisms. The carbohydrates are also important in the provision of energy

and as energy storage molecules. Amino acids and proteins function in many

capacities in living organisms which include the synthesis of proteins, in the

genetic code and as biomolecules that assist in other processes such as lipid

transport. Vitamins are also necessary to the survival and health of

organisms and though not synthesized by organisms but are important

biomolecules.

- A diverse range of biomolecules exist, including:

Small molecules:

Lipids, phospholipids, glycolipids, sterols, glycerolipids

Carbohydrates, sugars

Vitamins

Hormones, neurotransmitters

Metabolites


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Monomers:

Amino acids

Nucleotides

Monosaccharides

Polymers:

Peptides, oligopeptides, polypeptides, proteins

Nucleic acids, DNA, RNA

Oligosaccharides, polysaccharides (including cellulose)

Cellulose, lignin

Hemoglobin

Areas of Biomolecules

The study of biomolecules is closely related to several fields such as

molecular biology, biochemistry and genetics. Biochemistry is the study of

the structure and function of biomolecules in organisms. This study has

revealed a wealth of information about the biomolecules in living things.

Processes such as glycolysis have been detailed by biochemical studies

which have identified the roles of the biomolecules and their importance. It

was previously thought that the molecules of life, biomolecules, could only

be produced by living organisms. This view was however dispelled with the

synthesis of urea. Today, a focus of biochemistry is the study of enzymes,

biomolecules that are made up of proteins. These biomolecules are essential

to organisms as they speed up reactions that would normally take too long to

sustain life.

Biomolecules obeys the conservation laws of physics for exchange of

energy:

In nature, there is continuous process of exchanging the energy by some kind

of process into the matters; this becomes possible because of some matter

which loses their energy while the others gain the energy.

Straight forword the biomolecules also take part in that process of


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exchanging their energy. This process is very important to growth as well as

to maintain their characteristics to do the living processes. Now the question

is arising into mind that how these processes are possible. To understand it,

we take example of non living molecules and the process of exchange of

energy. Into the non living molecules the exchange of energy is produced by

the chemical process at specific atmospheric condition. Similarly such kind

of process occurs for the biomolecules or living molecules. In such process,

the energy is absorbed by molecules in some form from the environment and

it is utilized for growth of itself. This becomes possible. In the specific

condition of atmosphere means at particular temperature and specific

pressure. That energy which is not utilized by it is released into the

environment.

This utilized energy can do work by molecules at a given specific

condition. Here such kind of biomolecules work differently rather than the

non-bio molecules, e.g. into the non-biological molecules can do this process

under the extreme conditions like high temperature, high pressure, into the

strong electric and magnetic field region as well as into the biomolecules

which are restricted to do that process into such kind of condition.

Biomolecules are consisting of the cells and these cells play

important role to do the different kind of the process including the exchange

of energy by any kind of process. Biomolecules are consisting of cells which

are carrying large numbers of chemicals. This chemical consisting energy is

used to do different kind of activities like growth and repair of biomolecules.

The nonliving or nonbiomolecules got their energy by different

processes, which have different sources of the energy while for the

biomolecules are directly or indirectly got their energy from the sunlight and

that is important source of energy for biomolecules. e. g. The cells of the

plants are grown by gaining their energy from the sunlight. This becomes

possible by the photosynthesis process when it is produced by the cells of the

plant. Into this process, the conversion of carbon dioxide into the water


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provides the different form of energy to the cells of the plant which is

utilized for the different purposes.

The biomolecules are present into the bacteria, plant, animals in

which exchange of energy occur through the environment, so we can say that

the physical rules are also followed by the biomolecules for their growth,

stability, maintenance, repair and for the many type of the other purposes.

1.1.1 Starch and Cyclodextrins (Carbohydrates)

Starch

Starch or amylum is a polysaccharide carbohydrate consisting of a

large number of glucose units joined together by glycosidic bonds. Starch is

produced by all green plants as an energy store. It is the most important

carbohydrate in the human diet and is contained in such staple foods as rice,

wheat, maize (corn), potatoes and cassava.

Pure starch is a white, tasteless and odorless powder that is insoluble in cold

water or alcohol. It consists of two types of molecules: the linear and helical

amylose and the branched amylopectin. Depending on the plant, starch

generally contains 20 to 25% amylose and 75 to 80% amylopectin [1].

Glycogen, the glucose store of animals, is a more branched version of

amylopectin.

Starch can be used as a thickening, stiffening or gluing agent when

dissolved in warm water, giving wheat paste.


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Plants store glucose as the polysaccharide starch. The cereal grains

(wheat, rice, corn, oats, and barley) as well as tubers such as potatoes are

rich in starch.

Starch can be separated into two fractions--amylose and

amylopectin. Natural starches are mixtures of amylose (10-20%) and

amylopectin (80-90%).

Amylose forms a colloidal dispersion in hot water whereas

amylopectin is completely insoluble. The structure of amylose consists of

long polymer chains of glucose units connected by an alpha acetal linkage.

Starch - Amylose: Shows a very small portion of an amylose chain. All of

the monomer units are alpha -D-glucose, and all the alpha acetal links

connect C # 1 of one glucose to C # 4 of the next glucose.

Starch has a few other uses other than food. It's used in pressing

clothes to keep them from wrinkling. It's also used to make a foam packing.

Starch is biodegradable, so starch foam packing is an environmentally-

friendly alternative to Styrofoam packing.


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Starch Coil or Spiral Structure

As a result of the bond angles in the alpha acetal linkage, amylose

Starch Coil

actually forms a spiral much like a coiled spring. See the graphic on the left

which show four views in turning from a side to an end view.

Carbohydrates

Carbohydrates, which include the sugars and polysaccharides, have

many important functions in biological systems.


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Carbohydrates are so named because the structural formula is typically

(CH2O)n, where n is an integer such as 5 (C5H10O5),6 (C6H12O6), etc.

Although this formula might suggest that carbon atoms are joined to

water, the actual molecules are more complicated.

Like most classes of biological molecules, carbohydrates occur as both

monomers and polymers. Small carbohydrates are called sugars, which

commonly include monosaccharides (single sugars) and some disaccharides

(two sugars linked together). Larger carbohydrate is called polysaccharide.

(many sugars linked together).

Functions of carbohydrates include:

• serving as precursors for building many polymers

• storing short-term energy

• providing structural building materials

• serving as molecular "tags" to allow recognition of specific cells and

molecules

Monosaccharides are the simplest form of carbohydrates. They

consist of one sugar and are usually colorless, water-soluble, crystalline

solids. Some monosaccharides have a sweet taste. Examples of

monosaccharides include glucose (dextrose), fructose, galactose, and ribose.

Monosaccharides are the building blocks of disaccharides like sucrose

(common sugar) and polysaccharides (such as cellulose and starch). Further,

each carbon atom that supports a hydroxyl group (except for the first and

last) is chiral, giving rise to a number of isomeric forms all with the same

chemical formula. For instance, galactose and glucose are both aldohexoses,

but they have different chemical and physical properties [8].


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1.1.2 Amino acids and Peptides:

Amino acids

All peptides and proteins are polymers of alpha-amino acids. An

amino acid is a molecule that contains both amino (NH2) and carboxyl

(COOH) functional groups. Alanine is one of the standard amino acids:

Amino acids exist in either D (dextro) or L (levo) form

(stereoisomers). The D and L refer to the absolute confirmation of optically

active compounds. With the exception of glycine, all other amino acids are

mirror images that can not be superimposed. Most of the amino acids found

in nature are of the L-type. Hence, eukaryotic proteins are always composed

of L-amino acids although D-amino acids are found in bacterial cell walls

and in some peptide antibiotics.

Amino acids are molecules containing an amine group, a carboxylic

acid group and a side chain that varies between different amino acids. These

molecules are particularly important in biochemistry, where this term refers

to alpha-amino acids with the general formula H2NCHRCOOH, where R is

an organic substituent. In the alpha amino acids, the amino and carboxylate

groups are attached to the same carbon atom, which is called the α–carbon.

The various alpha amino acids differ in which side chain (R group) is

attached to their alpha carbon. These side chains can vary in size from just a

hydrogen atom in glycine, to a methyl group in alanine, through to a large

heterocyclic group in tryptophan [14].


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Twenty Amino Acids

Grouped table of twenty amino acids' structures, nomenclature, and their

side groups' pKa's.


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Naturally occurring amino acids, their abbreviations, and structural formulas

Essential amino acids

Ala = alanine

CH3CH(NH2)COOH

Arg = arginine

H2N-C(=NH)NHCH2CH2CH2CH(NH2)COOH

Asn = asparagine

H2N-C(=O)CH2CH(NH2)COOH

Asp = aspartic acid

HOOC-CH2CH(NH2)COOH

Cys = cysteine

HS-CH2CH(NH2)COOH

Gln = glutamine

H2N-C(=O)CH2CH2CH(NH2)COOH

Glu = glutamic acid

HOOC-CH2CH2CH(NH2)COOH

Gly = glycine

H2N-CH2COOH

His = histidine *

Ile = isoleucine *

CH3CH2CH(CH3)CH(NH2)COOH

Leu = leucine *

CH3CH(CH3)CH2CH(NH2)COOH

Lys = lysine *

H2N-CH2CH2CH2CH2CH(NH2)COOH

Met = methionine *

CH3-S-CH2CH2CH(NH2)COOH

Phe = phenylalanine *

Pro = proline

Ser = serine

HOCH2CH(NH2)COOH

Thr = threonine *

CH3CH(OH)CH(NH2)COOH

Trp = tryptophan *

Tyr = tyrosine

Val = valine *

CH3CH(CH3)CH(NH2)COOH

Amino acids are critical to life, and their most important function is

their variety of roles in metabolism. One particularly important function is as

the building blocks of proteins, which are linear chains of amino acids.


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Every protein is chemically defined by this primary structure, its unique

sequence of amino acid residues, which in turn define the three-dimensional

structure of the protein. Just as the letters of the alphabet can be combined to

form an almost endless variety of words, amino acids can be linked together

in varying sequences to form a vast variety of proteins.Amino acids are also

important in many other biological molecules, such as forming parts of

coenzymes, as in S-adenosylmethionine, or as precursors for the biosynthesis

of molecules such as heme. Due to this central role in biochemistry, amino

acids are very important in nutrition. Amino acids are commonly used in

food technology and industry. For example, monosodium glutamate is a

common flavor enhancer that gives foods the taste called umami [4].

The term "essential amino acid" refers to an amino acid that is

required to meet physiological needs and must be supplied in the diet.

Arginine is synthesized by the body, but at a rate that is insufficient to meet

growth needs. Methionine is required in large amounts to produce cysteine if

the latter amino acid is not adequately supplied in the diet. Similarly,

phenylalanine can be converted to tyrosine, but is required in large quantities

when the diet is deficient in tyrosine. Tyrosine is essential for people with

the disease phenylketonuria (PKU) whose metabolism cannot convert

phenylalanine to tyrosine. Isoleucine, leucine, and valine are sometimes

called "branched-chain amino acids" (BCAA) because their carbon chains

are branched.

Standard amino acids

Amino acids are the structural units that make up proteins. They join

together to form short polymer chains called peptides or longer chains called

either polypeptides or proteins. These polymers are linear and unbranched,

with each amino acid within the chain attached to two neighbouring amino

acids. The process of making proteins is called translation and involves the

step-by-step addition of amino acids to a growing protein chain by a

ribozyme that is called a ribosome.The order in which the amino acids are


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added is read through the genetic code from an mRNA template, which is a

RNA copy of one of the organism's genes. Twenty-two amino acids are

encoded by the standard genetic code and are called proteinogenic or

standard amino acids.

The amino acid selenocysteine

Non-standard amino acids

Aside from the twenty-two standard amino acids, there are a vast number of

"non-standard" amino acids. Two of these can be specified by the genetic

code, but are rather rare in proteins. Selenocysteine is incorporated into some

proteins at a UGA codon, which is normally a stop codon.Pyrrolysine is used

by some methanogenic archaea in enzymes that they use to produce

methane. Other non-standard amino acids found in proteins are formed by

post-translational modification, which is modification after translation in

protein synthesis. These modifications are often essential for the function or

regulation of a protein; for example, the carboxylation of glutamate allows

for better binding of calcium cations, and the hydroxylation of proline is

critical for maintaining connective tissues. Another example is the formation

of hypusine in the translation initiation factor EIF5A, through modification

of a lysine residue. Such modifications can also determine the localization of

the protein, e.g., the addition of long hydrophobic groups can cause a protein

to bind to a phospholipid membrane [13].


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1.1.3 Fibrous and Globular Proteins:

In general, we can use the conformation of a protein to classify it into

one of two very broad categories. One of those is fibrous, the other is

globular. The fibrous proteins are generally long and insoluble in water. The

globular proteins are tightly folded and most of them are soluble in water.

Some proteins combine the properties of both fibrous and globular within the

same protein.

Fibrous Proteins

- Stringy, physically tough, generally insoluble in water and most solvents

- Elongated, rod- like proteins joined by several types of cross – linkages.

Globular Proteins

- Generally sphericsl or globuler

- Tend to be soluble in water and aqueous solutions

- Polar groups of the side chains are on the outer side

- Nearly all enzymes, antibodies, hormones and transport proteins are

globular

3-dimensional structure of hemoglobin, a globular protein.

Globular proteins or spheroproteins are one of the three main protein

classes, comprising "globe"-like proteins that are more or less soluble in

aqueous solutions (where they form colloidal solutions). This main

characteristic helps distinguishing them from fibrous proteins (the other

class), which are practically insoluble. [9].


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Globular Structure and Solubility

The term globular protein is quite old and is now somewhat archaic

given the hundreds of thousands of proteins and more elegant and

descriptive structural motif vocabulary. The globular nature of these proteins

can be determined without the means of modern techniques, but only by

using ultracentrifuges or dynamic light scattering techniques.

A wide range of roles in the organism

Unlike fibrous proteins which only play a structural function,

globular proteins can act as:

Enzymes, by catalyzing organic reactions taking place in the organism

in mild conditions and with a great specificity. Different esterases fulfill this

role.

Messengers, by transmitting messages to regulate biological

processes. This function is done by hormones, i.e. insulin etc. [7].

Structure of Proteins

Three possible representations of the three-dimensional structure of the protein triose

phosphate isomerase. Left: all-atom representation colored by atom type. Middle: Simplified

representation illustrating the backbone conformation, colored by secondary structure. Right:

Solvent-accessible surface representation colored by residue type (acidic residues red, basic residues

blue, polar residues green, nonpolar residues white).

Most proteins fold into unique 3-dimensional structures. The shape

into which a protein naturally folds is known as its native conformation.

[17].Although many proteins can fold unassisted, simply through the


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chemical properties of their amino acids, others require the aid of molecular

chaperones to fold into their native states [18]. Biochemists often refer to

four distinct aspects of a protein's structure [19].

Primary Structure: the amino acid sequence.

Secondary Structure: regularly repeating local structures stabilized by

hydrogen bonds.

The most common examples are the alpha helix, beta sheet and turns.

Because secondary structures are local, many regions of different secondary

structure can be present in the same protein molecule.

Tertiary Structure: the overall shape of a single protein molecule; the

spatial relationship of the secondary structures to one another. Tertiary

structure is generally stabilized by nonlocal interactions, most commonly the

formation of a hydrophobic core, but also through salt bridges, hydrogen

bonds, disulfide bonds, and even post-translational modifications. The term

"tertiary structure" is often used as synonymous with the term fold. The

Tertiary structure is what controls the basic function of the protein [15]

Quaternary Structure: the structure formed by several protein molecules

(polypeptide chains), usually called protein subunits in this context, which

function as a single protein complex.

Proteins are not entirely rigid molecules. In addition to these levels of

structure, proteins may shift between several related structures while they

perform their functions. In the context of these functional rearrangements,

these tertiary or quaternary structures are usually referred to as

"conformations", and transitions between them are called conformational

changes. Such changes are often induced by the binding of a substrate

molecule to an enzyme's active site, or the physical region of the protein that

participates in chemical catalysis. In solution proteins also undergo variation

in structure through thermal vibration and the collision with other molecules.


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1.1.4 Vitamins & Enzymes

Vitamins

From the beginning, humans ate primarily whole foods or so-called

"natural" foods, which underwent no processing. The nutrient content of

food is decreased when it is processed. Intensive animal rearing,

manipulation of crop production, and food processing have altered the

qualitative and quantitative balance of nutrients of foods consumed by the

Western world. This change is possibly one of the reasons that chronic,

debilitating diseases are rampant in our modem culture. Modem research

suggests that simply taking a synthetic multi-vitamin/mineral formula does

not change this. Research from around the globe asserts that vitamins in their

naturally-balanced state are essential for better assimilation, synergistic

action, and maximum biological effect. And yet most consumers buy

vitamins and minerals that are synthetic, which their bodies usually can't

assimilate properly. The U.S. National Academy of Science, Food and

Nutrition Board, recommends that people meet their daily nutritional needs

through a varied diet rather than through vitamin and mineral

supplementation [6].

A lot of people think vitamins can replace food. They cannot. In fact,

vitamins cannot be assimilated without ingesting food. That is why we

suggest taking them with a meal. Vitamins help regulate metabolism, help

convert fat and carbohydrates into energy, and assist in forming bone and

tissue.

Forms of Vitamins Supplements and how they work?

Over-the-counter vitamin supplements come in various forms,

combinations, and amounts. They are available in tablet, capsule, gel-

capsule, powder, sublingual, lozenge, and liquid forms. They can also be

administered by injection. In most cases, it is a matter of personal preference

as to how you take them; however, due to slight variations in how rapidly the


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supplements are absorbed and assimilated into the body, we will sometimes

recommend one form over another.

Vitamin supplements are usually available as isolated vitamins or in

combination with other nutrients. It is important to select your vitamins

based upon what you really need. A program designed for health

maintenance would be different from one designed to overcome a specific

disorder. If you find one supplement that meets your needs, remember to

make it daily. If it does not contain a large enough quantity of what you

want, you may consider taking more than one.If there is no single

supplement that provides you with what you are looking for, consider taking

a combination of different supplements. Because the potency of most

vitamins may be decreased by sunlight, make sure that the container holding

your vitamins is dark enough to shield its contents properly. Some people

may be sensitive to plastic, and may need to purchase vitamins in glass

containers. Vitamin supplements should be kept in a cool, dark place. All

vitamin supplements work best when taken in combination with food. Unless

specified otherwise, oil-soluble vitamins should be taken before meals, and

water-soluble ones should be taken after meals.

Vitamins have traditionally played the role of coenzymes, organic

molecules that facilitate the chemical reactions catalyzed by enzymes.

However, several vitamins assume additional endocrine-like actions; this

review will discuss four such vitamins. Vitamin K2 is involved in the

gamma-carboxylation of coagulation factors and bone proteins, but it can

also bind and activate the steroid and xenobiotic receptor in order to mediate

transcription in bone tissue, and has been used to treat osteoporosis. Biotin is

critical for some carboxylation reactions, but it also induces epidermal

differentiation and has been used to treat lameness in animals and brittle

nails in humans. Pyridoxal phosphate (the active form of vitamin B6) is

involved in a multitude of reactions, including decarboxylation and

transamination; it can also inhibit DNA polymerases and several steroid


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receptors and may prove useful as an adjunct in cancer chemotherapy.

Finally, nicotinic acid is converted to NAD+ and NADP+, which are used as

hydrogen/electron carriers in redox reactions. However, it also possesses

vasodilatory and antilipolytic activities [8].

Vitamins are miracle workers in the body, but they do not work

alone.Our bodies were created to be able to convert food into energy but in

order to do this it needs three critical elements. Used together, they are

Vitamins, minerals, and enzymes.

Enzymes are tiny elements found in all cell of any living organism,

plant, animal, human. Enzymes are the catalysts, which speed up our body

processes and functions. Think of an enzyme as a specialist. It has one task

to perform, create energy from vitamins in our foods. Here is the next

important bit of information about your friend the Enzyme; he cannot live in

temperatures over 120 degrees. If you cook the foods over that, the enzymes

in the foods will be killed by the heat, and no longer an added source. Foods

that are good tasting, raw, should be eaten as much as possible in the diet.

There are two kinds of Vitamins: Those which dissolve in fat (such

as in eggs and liver); and those which dissolve in water (like in fruits and

vegetables). The fat soluble vitamins are A, D, E, and K. The water soluble

one are C, various B complex, P and others. Vitamins A and D are the two

vitamins which are stored in the liver for future use, as well as some others

we will discuss later. So beware of these levels, as excessive amounts, could

cause trouble. As a general rule of thumb, 50,000 IU or Vitamin A and

4,000 Units of Vitamin D, are considered safe. Please check with your own

physician before taking any medications [7].

As our body uses the vitamin supply by its own activity, what can

you do to help keep your sources of vitamins at higher levels? Replace them

with high vitamin sources of foods, and read the list below. This is only a

small list of items which deplete our vitamins:

Tobacco, alcohol


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salt, sugar, rancid fats

estrogen antibiotics

sleeping pills, tranquilizers

mineral oil

surgery sickness, accidents

emotional strain

fluorides

polluted air or water

pesticides

Vitamins and Minerals

Vitamin A - antioxidant, good for skin, night vision, fighting infections.

Spinach, green leafy veg, peppers, yellow veg, fruit, dried apricots,

watercress, tomatoes, broccoli, and asparagus.

B group - B1- energy production, B2 - converts fats, sugar, proteins to

energy, B3 - energy production, skin, balancing blood sugar, B5 - energy

production, metabolism of fats, healthy skin and hair, B6 - using proteins.

Green leafy veg, avocadoes, mushrooms, currants, watercress, courgette

(zucchini), asparagus, mushrooms, peppers, tomatoes, broccoli, lentils,

onions, seeds and nuts.

B12 - for using proteins.

Seaweed, unpasteurised miso, spirulina, chlorella, fermented foods,

unwashed produce.

Biotin - helps to use essential fats.

Lettuce, tomatoes, almonds.

Vitamin C - antioxidant, protects immune system.

Green leafy veg, peppers, broccoli, parsley, potatoes, watercress, melon,

tomatoes.

Vitamin D - bones, teeth.

Sunlight.


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Vitamin E - antioxidant, helps skin.

Tahini, nuts and seeds, avocadoes.

Folic Acid - brain/nerves

Spinach, asparagus, sesame seeds, hazelnuts, broccoli, avocadoes.

Vitamin K - blood clotting.

Green leafy veg, seaweeds.

Iron - blood, energy.

Avocadoes, dried figs, deep green veg, spinach, parsley, dates, dried

apricots, chickpeas (garbanzo beans), almonds, brazil nuts, sesame seeds.

Calcium - bones, skin, heart, muscles.

Tahini/sesame seeds, green leafy veg, parsley, broccoli, almonds, brazil nuts,

chia seeds.

Zinc - growth, nerves, bones, hair, energy.

Sesame seeds/tahini, almonds, ginger, brazil nuts.

Iodine - thyroid function.

Green leafy veg, seaweeds.

Magnesium - bones, energy.

Green leafy veg, almonds, broccoli, brazil nuts, garlic.

Phosphorus, Sulphur - growth, maintenance, tissues.

Chickpeas (garbanzo beans), many fruits and veg, peas, onion, garlic.

Potassium - nutrient flow, energy, metabolism.

Many fruits and veg (esp. bananas), watercress, parsley, courgettes,

mushrooms, Selenium - antioxidant, metabolism.

Brazil nuts, mushrooms, courgette (zucchini).

Bioflavonoids - aid Vitamin C uptake, bruise healing.

Berries, limes, lemons, peppers, tomatoes, grapes.

Choline - helps break down fat.

Whole grains, nuts, pulses.

Co-Enzyme Q10 - energy, metabolism.

Spinach, sesame seeds.


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Enzymes

A catalytic protein produced by living cells. The chemical reactions

involved in the digestion of foods, the biosynthesis of macromolecules, the

controlled release and utilization of chemical energy, and other processes

characteristic of life are all catalyzed by enzymes. In the absence of

enzymes, these reactions would not take place at a significant rate. Several

hundred different reactions can proceed simultaneously within a living cell,

and the cell contains a comparable number of individual enzymes, each of

which controls the rate of one or more of these reactions. The potentiality of

a cell for growing, dividing, and performing specialized functions, such as

contraction or transmission of nerve impulses, is determined by the

complement of enzymes it possesses. Some representative enzymes, their

sources, and reaction specificities are shown in the table [11].

Characteristics

Enzymes are such efficient catalysts that they accelerate chemical

reactions measurably, even at concentrations so low that they cannot be

detected by most chemical tests for protein. Like other chemical reactions,

enzyme-catalyzed reactions proceed only when accompanied by a decrease

in free energy; at equilibrium the concentrations of reactants and products

are the same in the presence of an enzyme as in its absence. An enzyme can

catalyze an indefinite amount of chemical change without itself being

diminished or altered by the reaction. However, because most isolated

enzymes are relatively unstable, they often gradually lose activity under the

conditions employed for their study.

Chemical Nature

All enzymes are proteins. Their molecular weights range from about

10,000 to more than 1,000,000. Like other proteins, enzymes consist of

chains of amino acids linked together by peptide bonds. An enzyme

molecule may contain one or more of these polypeptide chains. The

sequence of amino acids within the polypeptide chains is characteristic for


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each enzyme and is believed to determine the unique three-dimensional

conformation in which the chains are folded. This conformation, which is

necessary for the activity of the enzyme, is stabilized by interactions of

amino acids in different parts of the peptide chains with each other and with

the surrounding medium. These interactions are relatively weak and may be

disrupted readily by high temperatures, acid or alkaline conditions, or

changes in the polarity of the medium. Such changes lead to an unfolding of

the peptide chains (denaturation) and a concomitant loss of enzymatic

activity, solubility, and other properties characteristic of the native enzyme.

Enzyme denaturation is sometimes reversible.

Many enzymes contain an additional, nonprotein component, termed

a coenzyme or prosthetic group. This may be an organic molecule, often a

vitamin derivative, or a metal ion. The coenzyme, in most instances,

participates directly in the catalytic reaction. For example, it may serve as an

intermediate carrier of a group being transferred from one substrate to

another. Some enzymes have coenzymes that are tightly bound to the protein

and difficult to remove, while others have coenzymes that dissociate readily.

When the protein moiety (the apoenzyme) and the coenzyme are separated

from each other, neither possesses the catalytic properties of the original

conjugated protein (the holoenzyme). By simply mixing the apoenzyme and

the coenzyme together, the fully active holoenzyme can often be

reconstituted. The same coenzyme may be associated with many enzymes

which catalyze different reactions. It is thus primarily the nature of the

apoenzyme rather than that of the coenzyme which determines the specificity

of the reaction [9].

1.1.5 Lipids and Membranes

The boundaries of cells are formed by biological membranes, the

barriers that define the inside and the outside of a cell (shown in below

figure). These barriers prevent molecules generated inside the cell from

leaking out and unwanted molecules from diffusing in; yet they also


25

contain transport systems that allow specific molecules to be taken up and

unwanted compounds to be removed from the cell. Such transport systems

confer on membranes the important property of selective permeability [15].

Membranes are dynamic structures in which proteins float in a sea of

lipids. The lipid components of the membrane form the permeability barrier,

and protein components act as a transport system of pumps and channels that

endow the membrane with selective permeability.

(Red-Blood-Cell Plasma Membrane)

An electron micrograph of a preparation of plasma membranes from

red blood cells showing the membranes as seen “on edge,” in cross section.

In addition to an external cell membrane (called the plasma

membrane), eukaryotic cells also contain internal membranes that form the

boundaries of organelles such as mitochondria, chloroplasts, peroxisomes,

and lysosomes. Functional specialization in the course of evolution has been

closely linked to the formation of such compartments. Specific systems have

evolved to allow targeting of selected proteins into or through particular

internal membranes and, hence, into specific organelles. External and

internal membranes have essential features in common, and these essential

features are the subject of this chapter.

Biological membranes serve several additional important functions

indispensable for life, such as energy storage and information transduction,

that are dictated by the proteins associated with them. In this chapter, we will


26

examine the general properties of membrane proteins—how they can exist in

the hydrophobic environment of the membrane while connecting two

hydrophilic environments—and delay a discussion of the functions of these

proteins to the next.

1.1.6 RNA and DNA – Nucleic acids

- Ribonucleic acid

Ribonucleic acid, or RNA, is a nucleic acid polymer consisting of

nucleotide monomers, which plays several important roles in the processes

of transcribing genetic information from deoxyribonucleic acid (DNA) into

proteins. RNA acts as a messenger between DNA and the protein synthesis

complexes known as ribosomes, forms vital portions of ribosomes, and

serves as an essential carrier molecule for amino acids to be used in protein

synthesis [16]. The three types of RNA include tRNA (transfer), mRNA

(messenger) and rRNA (ribosomal).

- Deoxyribonucleic Acid

DNA

Chemical structure of DNA. Hydrogen bonds shown as dotted lines.

Deoxyribonucleic acid is a nucleic acid that contains the genetic

instructions used in the development and functioning of all known living


27

organisms. The main role of DNA molecules is the long-term storage of

information and DNA is often compared to a set of blueprints, since it

contains the instructions needed to construct other components of cells, such

as proteins and RNA molecules. The DNA segments that carry this genetic

information are called genes, but other DNA sequences have structural

purposes, or involved in regulating the use of this genetic information [11].

DNA is made of four types of bases named cytosine, thymine,

guanine and adenine, which are linked together to form a chain. The bases

are attached to each other in this chain by a sugar-phosphate backbone. Two

of these chains then coil around each other, forming the DNA double helix.

DNA is a long polymer made from repeating units called nucleotides.

The DNA chain is 22 to 26 Angstroms wide (2.2 to 2.6 nanometres), and one

nucleotide unit is 3.3 Å (0.33 nm) long. Although each individual repeating

unit is very small, DNA polymers can be very large molecules containing

millions of nucleotides. For instance, the largest human chromosome,

chromosome number 1, is approximately 220 million base pairs long [14].

In living organisms, DNA does not usually exist as a single molecule,

but instead as a pair of molecules that are held tightly together. These two

long strands entwine like vines, in the shape of a double helix. The

nucleotide repeats contain both the segment of the backbone of the molecule,

which holds the chain together, and a base, which interacts with the other

DNA strand in the helix. A base linked to a sugar is called a nucleoside and a

base linked to a sugar and one or more phosphate groups is called a

nucleotide. If multiple nucleotides are linked together, as in DNA, this

polymer is called a polynucleotide [19].

The backbone of the DNA strand is made from alternating phosphate

and sugar residues [10]. The sugar in DNA is 2-deoxyribose, which is a

pentose (five-carbon) sugar. The sugars are joined together by phosphate

groups that form phosphodiester bonds between the third and fifth carbon

atoms of adjacent sugar rings. These asymmetric bonds mean a strand of


28

DNA has a direction. In a double helix the direction of the nucleotides in one

strand is opposite to their direction in the other strand: the strands are

antiparallel. The asymmetric ends of DNA strands are called the 5′ (five

prime) and 3′ (three prime) ends, with the 5' end having a terminal phosphate

group and the 3' end a terminal hydroxyl group. One major difference

between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being

replaced by the alternative pentose sugar ribose in RNA.

A section of DNA.The bases lie horizontally between the two spiraling strands.

The DNA double helix is stabilized by hydrogen bonds between the

bases attached to the two strands. The four bases found in DNA are adenine

(abbreviated A), cytosine (C), guanine (G) and thymine (T). These four

bases are attached to the sugar/phosphate to form the complete nucleotide, as

shown for adenosine monophosphate [10].

These bases are classified into two types; adenine and guanine are

fused five- and six-membered heterocyclic compounds called purines, while

cytosine and thymine are six-membered rings called pyrimidines. A fifth

pyrimidine base, called uracil (U), usually takes the place of thymine in

RNA and differs from thymine by lacking a methyl group on its ring. Uracil

is not usually found in DNA, occurring only as a breakdown product of


29

cytosine. In addition to RNA and DNA, a large number of artificial nucleic

acid analogues have also been created to study the proprieties of nucleic

acids, or for use in biotechnology [21].

Base pairing

Each type of base on one strand forms a bond with just one type of

base on the other strand. This is called complementary base pairing. Here,

purines form hydrogen bonds to pyrimidines, with A bonding only to T, and

C bonding only to G. This arrangement of two nucleotides binding together

across the double helix is called a base pair. As hydrogen bonds are not

covalent, they can be broken and rejoined relatively easily. The two strands

of DNA in a double helix can therefore be pulled apart like a zipper, either

by a mechanical force or high temperature [22]. As a result of this

complementarity, all the information in the double-stranded sequence of a

DNA helix is duplicated on each strand, which is vital in DNA replication.

Indeed, this reversible and specific interaction between complementary base

pairs is critical for all the functions of DNA in living organisms.

Top, a GC base pair with three hydrogen bonds. Bottom, an AT base pair

with two hydrogen bonds. Non-covalent hydrogen bonds between the pairs

are shown as dashed lines.

The two types of base pairs form different numbers of hydrogen

bonds, AT forming two hydrogen bonds, and GC forming three hydrogen


30

bonds (see Figures). DNA with high GC-content is more stable than DNA

with low GC-content, but contrary to popular belief, this is not due to the

extra hydrogen bond of a GC base pair but rather the contribution of stacking

interactions (hydrogen bonding merely provides specificity of the pairing,

not stability) [16]. As a result, it is both the percentage of GC base pairs and

the overall length of a DNA double helix that determine the strength of the

association between the two strands of DNA. Long DNA helices with a high

GC content have stronger-interacting strands, while short helices with high

AT content have weaker-interacting strands [17]. In biology, parts of the

DNA double helix that need to separate easily, such as the TATAAT

Pribnow box in some promoters, tend to have a high AT content, making the

strands easier to pull apart [18]. In the laboratory, the strength of this

interaction can be measured by finding the temperature required to break the

hydrogen bonds, their melting temperature (also called Tm value). When all

the base pairs in a DNA double helix melt, the strands separate and exist in

solution as two entirely independent molecules [23]. These single-stranded

DNA molecules have no single common shape, but some conformations are

more stable than others.

DNA Structure


31

Components of DNA

Double stranded DNA has two strands

A phosphate-deoxyribose polymer composes the backbone of the DNA

Adjacent sugars are connected by phosphodiester bonds.

Nitrogenous bases are convalently bonded to the 1' carbon of the

deoxyribose.

The two DNA strands are antiparallel

The two strands are held together by hydrogen bonds between

complementary bases

Adenine hydrogen bonds (base pairs) to thymine

Guanine hydrogen bonds to cytosine

When DNA replicates two identical DNA double helices are formed


32

RNA Structure

A hairpin loop from a pre-mRNA. Highlighted are the bases (light green) and backbone (sky blue).

Ribonucleic acid (RNA) is a biologically important type of

molecule that consists of a long chain of nucleotide units. Each nucleotide

consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very

similar to DNA, but differs in a few important structural details: in the cell,

RNA is usually single-stranded, while DNA is usually double-stranded;

RNA nucleotides contain ribose while DNA contains deoxyribose (a type of

ribose that lacks one oxygen atom); and RNA has the base uracil rather than

thymine that is present in DNA [17].

Chemical structure of RNA


33

An important structural feature of RNA that distinguishes it from

DNA is the presence of a hydroxyl group at the 2' position of the ribose

sugar. The presence of this functional group causes the helix to adopt the A-

form geometry rather than the B-form most commonly observed in DNA.

This results in a very deep and narrow major groove and a shallow and wide

minor groove [24].

1.1.7 Fatty acids and Lipids

Fatty Acids

The common fatty acids of plant tissues are C16 and C18 straight-

chain compounds with zero to three double bonds of a cis (or Z)

configuration. Such fatty acids are also abundant in animal tissues, together

with other even numbered components with a somewhat wider range of

chain-lengths and up to six cis double bonds separated by methylene groups

(methylene-interrupted) [26]. The systematic and trivial names of those fatty

acids encountered most often, together with their shorthand designations, are

listed in the table.

The common fatty acids of animal and plant origin

Systematic name

Trivial name Saturated

fatty acids

Shorthand

ethanoic acetic 2:0

butanoic butyric 4:0

hexanoic caproic 6:0

octanoic caprylic 8:0

decanoic capric 10:0

dodecanoic lauric 12:0


34

tetradecanoic myristic 14:0

hexadecanoic palmitic 16:0

octadecanoic stearic 18:0

eicosanoic arachidic 20:0

docosanoic behenic 22:0

Monoenoic fatty acids

cis-9-hexadecenoic palmitoleic 16:1(n-7)

cis-6-octadecenoic petroselinic 18:1(n-12)

cis-9-octadecenoic oleic 18:1(n-9)

cis-11-octadecenoic cis-vaccenic 18:1(n-7)

cis-13-docosenoic erucic 22:1(n-9)

cis-15-tetracosenoic nervonic 24:1(n-9)

Polyunsaturated fatty acids*

9,12-octadecadienoic linoleic 18:2(n-6)

6,9,12-octadecatrienoic γ-linolenic 18:3(n-6)

9,12,15-octadecatrienoic α-linolenic 18:3(n-3)

5,8,11,14-eicosatetraenoic arachidonic 20:4(n-6)

5,8,11,14,17-

eicosapentaenoic EPA 20:5(n-3)

4,7,10,13,16,19-

docosahexaenoic DHA 22:6(n-3)

* all the double bonds are of the cis configuration


35

The most abundant saturated fatty acid in

nature is hexadecanoic or palmitic acid. It can also be designated a "16:0"

fatty acid, the first numerals denoting the number of carbon atoms in the

aliphatic chain and the second, after the colon, denoting the number of

double bonds. All the even-numbered saturated fatty acids from C2 to C30

have been found in nature, but only the C14 to C18 homologues are likely to

be encountered in appreciable concentrations in glycerolipids, other than in a

restricted range of commercial fats and oils [27].

Oleic or cis-9-octadecenoic acid, the most abundant monoenoic fatty

acid in nature, is designated as "18:1", or more precisely as "18:1(n-9)", to

indicate that the last double bond is 9 carbon atoms from the terminal methyl

group.

The latter form of the nomenclature is of special value to

biochemists. Similarly, the most abundant cis monoenoic acids fall into the

same range of chain-lengths, i.e. 16:1(n-7) and 18:1(n-9), though 20:1 and

22:1 are abundant in fish. Fatty acids with double bonds of the trans (or E)

configuration are found occasionally in natural lipids, or are formed during

food processing (hydrogenation) and so enter the food chain, but they tend to

be minor components only of animal tissue lipids, other than of ruminants.

Their suitability for human nutrition is currently a controversial subject.

The C18 polyunsaturated fatty acids, linoleic or cis-9,cis-12-

octadecadienoic acid (18:2(n-6)) and α-linolenic or cis-9,cis-12,cis-15-

octadecatrienoic acid (18:3(n-3)), are major components of most plant lipids,

including many of the commercially important vegetable oils.


36

They are essential fatty acids in that they cannot be synthesised in

animal tissues. On the other hand, as linoleic acid is almost always present in

foods, it tends to be relatively abundant in animal tissues. In turn, these fatty

acids are the biosynthetic precursors in animal systems of C20 and C22

polyunsaturated fatty acids, with three to six double bonds, via sequential

desaturation and chain-elongation steps (desaturases in animal tissues can

only insert a double bond on the carboxyl side of an existing double bond).

Those fatty acids derived from linoleic acid, especially arachidonic acid

(20:4(n-6)), are important constituents of the membrane phospholipids in

mammalian tissues, and are also the precursors of the prostaglandins and

other eicosanoids [28]. In fish, linolenic acid is the more important essential

fatty acid, and polyunsaturated fatty acids of the (n-3) series, especially

eicosapentaenoic acid (20:5(n-3) or EPA) and docosahexaenoic acid (22:6(n-

3) or DHA), are found in greater abundance [24].

Many other fatty acids that are important for nutrition and health do

of course exist in nature, and at present there is great interest in γ-linolenic

acid (18:3(n-6)), the active constituent of evening primrose oil -

- and in conjugated linoleic acid (mainly, 9-cis,11-trans-octadecadienoate) or

'CLA', a natural constituent of dairy products, that is claimed to have


37

remarkable health-giving properties.

Branched-chain fatty acids are synthesised by many microorganisms (most

often with an iso- or an anteiso-methyl branch) and they are synthesised to a

limited extent in higher organisms [29]. They can also enter animal tissues

via the diet, especially those of ruminants.

Phytanic acid, 3,7,11,15-tetramethylhexadecanoic acid, is a

metabolite of phytol and is found in animal tissues, but generally at low

levels only.

Fatty acids with many other substituent groups are found in certain

plants and microorganisms, and they may be encountered in animal tissues,

which they enter via the food chain. These substituents include acetylenic

and conjugated double bonds, allenic groups, cyclopropane, cyclopropene,

cyclopentene and furan rings, and hydroxy-, epoxy- and keto-groups. For

example, 2-hydroxy fatty acids are synthesised in animal and plant tissues,

and are often major constituents of the sphingolipids [30] 12-Hydroxy-

octadec-9-enoic or 'ricinoleic' acid is the main constituent of castor oil.


38

- Lipids

Although lipid analyst tends to have a firm understanding of what is

meant by the term "lipid", there is no widely-accepted definition. General

text books usually describe lipids in woolly terms as a group of naturally

occurring compounds, which have in common a ready solubility in such

organic solvents as hydrocarbons, chloroform, benzene, ethers and alcohols.

They include a diverse range of compounds, like fatty acids and their

derivatives, carotenoids, terpenes, steroids and bile acids [31]. It should be

apparent that many of these compounds have little by way of structure or

function to relate them. In fact, a definition of this kind is positively

misleading, since many of the substances that are now widely regarded as

lipids may be almost as soluble in water as in organic solvents.

While the international bodies that usually decide such matters have

shirked the task, a more specific definition of lipids than one based simply

on solubility is necessary, and most scientist active in this field would

happily restrict the use of "lipid" to fatty acids and their naturally-occurring

derivatives (esters or amides). The definition could be stretched to include

compounds related closely to fatty acid derivatives through biosynthetic

pathways (e.g. prostanoids, aliphatic ethers or alcohols) or by their

biochemical or functional properties [22] (e.g. cholesterol)

“Lipids are fatty acids and their derivatives, and substances

related biosynthetically or functionally to these compounds.”

This treats cholesterol (and plant sterols) as a lipid, and could be

interpreted to include bile acids, tocopherols and certain other compounds. It

also enables classification of such compounds as gangliosides as lipids,

although they are more soluble in water than in organic solvents. However, it

does not include such natural substances as steroidal hormones, petroleum

products, some fat-soluble vitamins, carotenoids or simple terpenes, except

in rare circumstances [17].


39

If "lipids" are defined in this way, fatty acids must be defined also.

They are compounds synthesised in nature via condensation of malonyl

coenzyme. A unit by a fatty acid synthase complex. They usually contain

even numbers of carbon atoms in straight chains (commonly C14 to C24), and

may be saturated or unsaturated, and can contain a variety of substituent

groups.

Fahy et al. (J. Lipid Res., 46, 839-862 (2005)) have developed a

classification system for a lipid that holds promise [33]. While their

definition of a lipid is too broad for my taste, it is based on sound scientific

principles, i.e. Hydrophobic or amphipathic small molecules that may

originate entirely or in part by carbanion-based condensations of thioesters

(fatty acids, polyketides, etc.) and/or by carbocation-based condensations of

isoprene units [11].

The most common lipid classes in nature consist of fatty acids linked

by an ester bond to the trihydric alcohol - glycerol, or to other alcohols such

as cholesterol, or by amide bonds to sphingoid bases, or on occasion to other

amines. In addition, they may contain alkyl moieties other than fatty acids,

phosphoric acid, organic bases, carbohydrates and many more components,

which can be released by various hydrolytic procedures [14].

1.1.8 ADP and ATP

ATP (Adenosine Triphosphate)

Adenosine triphosphate (ATP) is considered by biologists to be the

energy currency of life. It is the high-energy molecule that stores the energy

we need to do just about everything we do. It is present in the cytoplasm and

nucleoplasm of every cell, and essentially all the physiological mechanisms

that require energy for operation obtain it directly from the stored ATP.

(Guyton) As food in the cells is gradually oxidized, the released energy is

used to re-form the ATP so that the cell always maintains a supply of this

essential molecule. Karp quotes an estimate that more than 2 x 1026

molecules or >160kg of ATP is formed in the human body daily! ATP is


40

remarkable for its ability to enter into many coupled reactions, both those to

food to extract energy and with the reactions in other physiological processes

to provide energy to them. In animal systems, the ATP is synthesized in the

tiny energy factories called mitochondria [35].

The structure of ATP has an ordered carbon compound as a backbone,

but the part that is really critical is the phosphorous part - the triphosphate.

Three phosphorous groups are connected by oxygens to each other, and there

are also side oxygens connected to the phosphorous atoms. Under the normal

conditions in the body, each of these oxygens has a negative charge, and as

you know, electrons want to be with protons - the negative charges repel

each other [36,37].These bunched up negative charges want to escape - to

get away from each other, so there is a lot of potential energy here.

If you remove just one of these phosphate groups from the end, so

that there are just two phosphate groups, the molecule is much happier. This

conversion from ATP to ADP is an extremely crucial reaction for the

supplying of energy for life processes. Just the cutting of one bond with the

accompanying rearrangement is sufficient to liberate about 7.3 kilocalories

per mole = 30.6 kJ/mol. Living things can use ATP like a battery. The ATP

can power needed reactions by losing one of its phosphorous groups to form

ADP, but you can use food energy in the mitochondria to convert the ADP

back to ATP so that the energy is again available to do needed work. In

plants, sunlight energy can be used to convert the less active compound


41

back to the highly energetic form. For animals, you use the energy from your

high energy storage molecules to do what you need to do to keep yourself

alive, and then you "recharge" them to put them back in the high energy

state.

Conversion from ATP to ADP

Adenosine triphosphate (ATP) is the energy currency of life and it

provides that energy for most biological processes by being converted to

ADP (adenosine diphosphate). Since the basic reaction involves a water

molecule,

ATP + H2O → ADP + Pi

this reaction is commonly referred to as the hydrolysis of ATP.

The structure of ATP has an ordered carbon compound as a backbone, but

the part that is really critical is the phosphorous part - the triphosphate.

If you remove just one of these phosphate groups from the end, so that there

are just two phosphate groups, the molecule is much happier. If you cut this

bond, the energy is sufficient to liberate about 7000 calories per mole, about

the same as the energy in a single peanut. Food molecules function as fuel

molecules, storing large quantities of energy in a stable form over long


42

periods of time. They are the long-term energy currency of the cell. Such a

molecule is adenosine triphosphate (ATP).

This molecule acts as the short-term energy currency of the cell and

provides the source of energy used in individual synthetic (nonspontaneous)

reactions. ATP collects small packets of energy from the food-burning

power plants of the cell and transports this energy to where it is needed.

Some energy in ATP is released to do work, such as move muscles or force a

seedling out of the ground. At other times, ATP gives up its energy to a

nonspontaneous synthetic reaction, such as the formation of sucrose [15].

When a molecule of fatty acid is burned, energy is given off. Some of

this energy is trapped in molecules of ATP, and some is lost in the form of

heat. Each ATP molecule can then be transported elsewhere within the

cell and used where needed.

Figure

legend:

The ATP-ADP Cycle. Energy is needed for the formation of ATP and is

released as the ATP is converted back to ADP and phosphate.

This cycle is used by cells as a means of converting the large amounts of energy

in food molecules into the smaller amounts of energy needed to drive the

synthetic reactions of cells, such as the formation of sucrose.

The energy-carrying part of an ATP molecule is the triphosphate "tail"


43

[38].Three phosphate groups are joined by covalent bonds. The electrons in

these bonds carry energy.

Within the power plants of the cell (mitochondria), energy is used to add one

molecule of inorganic phosphate (P) to a molecule of adenosine diphosphate

(ADP).

ADP + P + Energy ---> ATP

The amount of energy stored is about 7,300 calories for every mole of

ATP formed. At the energy-requiring site, the last phosphate group in the tail

is broken off and the energy in the bond liberated.

ATP --> ADP + P + Energy

Again, about 7,300 calories of energy per mole is released. The ADP

and the phosphate are then free to return to the power plant and be rejoined.

In this way, ATP and ADP are constantly being recycled.

Energy Storage

The processes of catabolism provide energy which must be made

available for performing useful work. The energy cannot be in the form of

heat because cells function at constant temperature. Heat energy is only

useful when transferred from a hot body to a cold body. The energy from

catabolism must be conserved or transformed into chemical storage. The

major chemical storage is in the form of adenosine triphosphate (ATP). ATP

is the link between exothermic reactions and endothermic reactions.


44

ATP is made of adenosine and ribose bonded to three phosphate

groups through phosphate ester bonds. ATP, ADP, AMP –

The importance of ATP centers on the storage of about 7 kcal/mole of

energy in the phosphorus-oxygen bond between the first and second

phosphate group [41]. The relationship of energy and the formation and

hydrolysis of ATP is illustrated in the following equations: P = PO4-3;

ADP = adenine diphosphate.

a) Hydrolysis: ATP + H2O --> ADP + P + energy

b) Formation: ADP + P + energy --> ATP + H2O

Under certain conditions ATP may be hydrolyzed directly to AMP (adenine

monophosphate).

ATP + H2O --> AMP + PP + energy

There are other metabolic phosphate molecules which store or give

off energy as needed. One further example is the hydrolysis of creatine

phosphate in muscle cells which also releases energy.

1.1.9 Hormones

Hormones are the chemical messengers of the body. They are defined

as organic substances secreted into blood stream to control the metabolic and

biological activities. These hormones are involved in transmission of

information from one tissue to another and from cell to cell. These

substances are produced in small amounts by various endocrine (ductless)

glands in the body. They are delivered directly to the blood in minute

quantities and are carried by the blood to various target organs where these

exert physiological effect and control metabolic activities. Thus frequently

their site of action is away from their origin. Hormones are required in trace

amounts and are highly specific in their functions. The deficiency of any

hormones leads to a particular disease, which can be cured by administration

of that hormone [22].


45

Classification of Hormones

Hormones are classified on the basis of (i) their structure (ii) their site of

activity in the cell.

Steroids on which the below classification is made are compounds

whose structure is based on four-ring network, consisting of 3 cyclohexane

rings and 1 cyclopentane ring.

Hypothalamus functions as master co-ordinator of hormonal action. It

produces atleast 6 releasing factors or hormones.

- Thyrotropin releasing hormone (TRH)

- Corticotropin releasing hormone (CRH)

- Gonadotropin releasing hormone (GnRH)

- Growth hormone releasing hormone (GRH)

- Growth hormone release inhibiting hormone (GRIH)

- Prolactin release inhibiting hormone (PRIH).

Functions of Steroid Hormones

- Sex hormones - are divided into 3 groups

(i) Female sex hormones or estrogens

(ii) Male sex hormones or androgens

(iii) Pregnancy hormones or progestines

Testosterone is the major male sex hormone produced by testes. It is

responsible for male characteristics (deep voice, facial hair, general physical

constitution) during puberty. Synthetic testosterone analogos are used in


46

medicine to promote muscle and tissue growth in patients with muscular

atrophy.

Progesterone is an example of progestin and is responsible for

preparing the uterus for implementation of the fertilized egg. It also has an

important role as birth control agents [28].

Functions of non steroid hormones

1. Peptide Hormones

Insulin has a profound influence or carbohydrate metabolism. It

facilitates entry of glucose and other sugars into the cells by increasing

penetration of cell membranes and augmenting phosphorylation of glucose.

This decreases glucose concentration in blood and insulin is commonly

known as hypoglycamic factor. It promotes anabolic processes and inhibits

catabolic ones. Its deficiency in human beings causes diabetes mellitus.

Insulin isolated from islets of Langerhens or islets tissue of pancreas was the

first hormone to be recognized as protein. Sanger determined the structure of

insulin and was awarded the Nobel prize in 1948 for this achievement.

2. Amino acid Derivatives

The thyroidal hormones e.g., thyroxin and tri-iodothyronine affect

the general metabolism, regardless of their specific activity. It is for this

reason why thyroid gland is known as pace setter of the endocrine system.

Based on the site of activity in the cell hormones are divided into two

categories first category of hormones effect the properties of plasma

membranes. These include all peptide hormones e.g., insulin and hormones

of pituitary gland.

1.1.10 Organometallic Biomolecules

Organometallic compounds have at least one carbon to metal bond,

according to most definitions. This bond can be either a direct carbon to

metal bond (σ bond or sigma bond) or a metal complex bond (π bond or pi

bond). Compounds containing metal to hydrogen bonds as well as some


47

compounds containing nonmetallic (metalloid) elements bonded to carbon

are sometimes included in this class of compounds. Some common

properties of organometallic compounds are relatively low melting points,

insolubility in water, solubility in ether and related solvents, toxicity,

oxidizability, and high reactivity [33].

An example of an organometallic compound of importance years ago

is tetraethyllead (Et44Pb) which is an antiknock agent for gasoline. It is

presently banned from use in the United States [18].

The first metal complex identified as an organometallic compound

was a salt, K(C2H4)PtCl3, obtained from reaction of ethylene with platinum

(II) chloride by William Zeise in 1825. It was not until much later (1951–

1952) that the correct structure of Zeise's compound was reported in

connection with the structure of a metallocene compound known as

ferrocene.

Preparation of ferrocene was reported at about the same time by two

research groups, and a sandwich structure was proposed, based on

ferrocene's physical properties (Kauffman, pp. 185–186). The sandwich

structure was confirmed by x-ray diffraction studies. Since then, other

metallocenes composed of other metals and other carbon ring molecules,

such as dibenzenechromium and uranocene have been prepared.

Possibly the first scientist to synthesize an organometallic compound

was Edward Frankland, who prepared diethylzinc by reaction of ethyl iodide

with zinc metal in 1849. 2 CH3CH2I + 2 Zn → CH3CH2ZnCH2CH3 + ZnI2

In organometallic compounds, most p-electrons of transition metals

conform to an empirical rule called the 18-electron rule. This rule assumes

that the metal atom accepts from its ligands the number of electrons needed

in order for it to attain the electronic configuration of the next noble gas. It

assumes that the valence shells of the metal atom will contain 18 electrons.

Thus, the sum of the number of d electrons plus the number of electrons

supplied by the ligands will be 18. Ferrocene, for example, has 6 d


48

electrons from Fe(II), plus 2 × 6 electrons from the two 5-membered rings,

for a total of 18. (There are exceptions to this rule, however.)

Possibly the earliest biomedical application of an organometallic

compound was the discovery, by Paul Ehrlich, of the organoarsenical

Salvarsan, the first antisyphilitic agent. Salvarsan and other organoarsenicals

are sometimes listed as organometallics even though arsenic is not a true

metal. Vitamin B12 is an organocobalt complex essential to the diet of human

beings. Absence of or deficiency of B12 in the diet (or a body's inability to

absorb it) is the cause of pernicious anemia.

Use as Reagents or Catalysts

Organometallic compounds are very useful as catalysts or reagents in

the synthesis of organic compounds, such as pharmaceutical products. One

of the major advantages of organometallic compounds, as compared with

organic or inorganic compounds, is their high reactivity. Reactions that

cannot be carried out with the usual types of organic reagents can sometimes

be easily carried out using one of a wide variety of available

organometallics. A second advantage is the high reaction selectivity that is

often achieved via the use of organometallic catalysts. For example, ordinary

free-radical polymerization of ethylene yields a waxy low-density

polyethylene, but use of a special organometallic catalyst produces a more

ordered linear polyethylene with a higher density, a higher melting point,

and a greater strength [41]. A third advantage is that many in this wide range

of compounds are stable, and many of these have found uses as medicinals

and pesticides. A fourth advantage is the case of recovery of pure metals.

Isolation of a pure sample of an organometallic compound containing a

desired metal can be readily accomplished, and the pure metal can then be

easily obtained from the compound. (This is generally done via preparation

of a pure metal carbonyl, such as Fe[CO]5 or Ni[CO]4, followed by thermal

decomposition.) Other commonly used organometallic compounds are


49

organolithium, organozinc, and organocuprates (sometimes called Gilman

reagents).

Grignard Reagents

One of the most commonly used classes of organometallic

compounds is the organomagnesium halides, or Grignard reagents (generally

RMgX or ArMgX, where R and Ar are alkyl and aryl groups, respectively,

and X is a halogen atom), used extensively in synthetic organic chemistry.

Organomagnesium halides were discovered by Philippe Barbier in 1899 and

subsequently developed by Victor Grignard.

1.2 Charge Transfer Interactions of Biomolecules and Inclusion

Compounds.

1.2.1 Organic Charge Transfer

A charge-transfer complex (or CT complex, electron-donor-

acceptor-complex) is a chemical association of two or more molecules, or of

different parts of one very large molecule, in which the attraction between

the molecules (or parts) is created by an electronic transition into an excited

electronic state, such that a fraction of electronic charge is transferred

between the molecules. The resulting electrostatic attraction provides a

stabilizing force for the molecular complex. The source molecule from

which the charge is transferred is called the electron donor and the receiving

molecule is called the electron acceptor, hence the alternate name, electron-

donor-acceptor-complex [42].

The nature of the attraction in a charge-transfer complex is not a

stable chemical bond and is much weaker than covalent forces; rather it is

better characterized as a weak electron resonance. As a result, the excitation

energy of this resonance occurs very frequently in the visible region of the

electro-magnetic spectrum. This produces the usually intense colors

characteristic for these complexes. These optical absorption bands are often

referred to as charge-transfer bands, or CT bands. Optical spectroscopy is a

powerful technique to characterize charge-transfer bands [43]. Charge-


50

transfer complexes exist in many types of molecules, inorganic as well as

organic, and in all phases of matter, i.e. in solids, liquids, and even gases.

In inorganic chemistry, most charge-transfer complexes involve

electron transfer between metal atoms and ligands. The charge-transfer

bands in transition metal complexes result from movement of electrons

between molecular orbitals (MO) that are predominantly metal in character

and those that are predominantly ligand in character. If the electron moves

from the MO with ligand like character to the metal like one, the complex is

called ligand-to-metal charge-transfer (LMCT) complex. If the electron

moves from the MO with metal like character to the ligand-like one, the

complex is called a metal-to-ligand charge-transfer (MLCT) complex. Thus,

a MLCT results in oxidation of the metal center whereas a LMCT results in

the reduction of the metal center [43]. Resonance Raman Spectroscopy is

also a powerful technique to assign and characterize charge transfer bands in

these complexes.

Donor-acceptor association equilibrium

Charge-transfer complexes are formed by weak association of

molecules or molecular subgroups, one acting as an electron donor and

another as an electron acceptor. The association does not constitute a strong

covalent bond and is subject to significant temperature, concentration, and

host (e.g., solvent) dependencies [44].

The charge-transfer association occurs in a chemical equilibrium

with the independent donor (D) and acceptor (A) molecules:

Quantum mechanically, this is described as a resonance between the

non-bonded state |D, A> and the dative state |D+...A->. The formation of the

dative state is an electronic transition giving rise to absorption bands [45].

The intensity of charge-transfer bands in the absorbance spectrum is

strongly dependent upon the degree (equilibrium constant) of this association


51

reaction. Methods have been developed to determine the equilibrium

constant for these complexes in solution by measuring the intensity of

absorption bands as a function of the concentration of donor and acceptor

components in solution. The methods were first described for the association

of iodine disolved in aromatic hydrocarbons [46].

Charge-Transfer transition energy

The color of charge-transfer bands, i.e., the charge-transfer transition

energy, is characteristic of the specific type of donor and acceptor entities.

The electron donating power of a donor molecule is measured by its

ionization potential which is the energy required to remove an electron from

the highest occupied molecular orbital [47]. The electron accepting power of

the electron acceptor is determined by its electron affinity which is the

energy released when filling the highest unoccupied molecular orbital.

The overall energy balance (ΔE) is the energy gained in a

spontaneous charge transfer. It is determined by the difference between the

acceptor's electron affinity (EA) and the donor's ionization potential (EI),

adjusted by the resulting electrostatic attraction (J) between donor and

acceptor:

The positioning of the characteristic CT bands in the electromagnetic

spectrum is directly related to this energy difference and the balance of

resonance contributions of non-bonded and dative states in the resonance

equilibrium.

Identification of CT bands

Charge transfer complexes are identified by -

Color: The color of CT complexes is reflective of the relative energy

balance resulting from the transfer of electronic charge from donor to

acceptor.

Solvatochromism: In solution, the transition energy and therefore the


52

complex color varies with variation in solvent permittivity, indicating

variations in shifts of electron density as a result of the transition. This

distinguishes it from the π→ π* transitions on the ligand.

Intensity: CT absorptions bands are intense and often lie in the ultraviolet or

visible portion of the spectrum. For inorganic complexes, the typical molar

absorptivities, ε, are about 50000 L mol-1 cm-1, that are three orders of

magnitude higher than typical ε of 20 L mol-1 cm-1 or lower, for d-d

transitions (transition from t2g to eg). This is because the CT transitions are

not spin or Laporte forbidden as d-d transitions.

Inorganic Charge-Transfer Complexes

Charge-transfer occurs often in inorganic ligand chemistry involving

metals. Depending on the direction of charge transfer they are either

classified as ligand-to-metal (LMCT) or metal-to-ligand (MLCT) charge-

transfer [48].

Charge Transfer Complexes and Color

Many metal complexes are colored due to d-d electronic transitions.

Visible light of the correct wavelength is absorbed, promoting a lower d-

electron to a higher excited state [49]. This absorption of light causes color,

although these colors are usually quite faint. This is because of two selection

rules:

The spin rule: Δ S = 0

On promotion, the electron should not experience a change in spin.

Electronic transitions which experience a change in spin are said to be spin

forbidden.

Laporte's rule: Δ I = ± 1

d-d transitions for complexes which have a center of symmetry are forbidden

- symmetry forbidden or Laporte forbidden [50].

Charge-transfer complexes do not experience d-d transitions. Thus, these

rules do not apply and the absorptions are generally very intense [51].


53

For example, the classic example of a charge-transfer complex is that

between iodine and starch to form an intense purple color.

1.2.2 Studies on charge transfer complexes.

Charge transfer complex between methylviologen and ferrocyanide

has been studied spectrophotometrically at different temperatures. From the

thermodynamic association constants (320 ± 30 M−1, 380 ± 30 M−1 and 460

± 40 M−1 at 15, 25 and 30°C respectively), the enthalpy of formation, ΔH° (−

3.4 ± 1.5 kcal/mole), and the related entropy change, ΔS°(0.4 ± 5 e.u), have

been calculated. The average extinction values of coefficients are 69±6 M−1

cm−1, 70±4 M−1 cm−1 and 72±5 M−1 cm−1 at 15, 25 and 35°C respectively

[52].

X-Ray crystal studies of the titled molecular complexes have

revealed the arrangement of parallel overlap between one of the benzene

rings of the heavily deformed TCNAQ moiety and donor benzene and

pyrene molecules, presumably attributable to the complex formation with

weak charge transfer interactions [53].

Iodine doping of C60 complexes with organic donors were carried

out. The solvent was gradually substituted by the iodine with the formation

of TPDP(C60)2I10, (TMDTDM-TTF)2C60I7.5, and DBTTFC60I9 compounds.

The doping results in strong changes in the donor electron state but only

indirectly affect the C60 electron system [54].

Novel electron acceptors, bithiazole analogues of

tetracyanodiphenoquinodimethane (TCNDQ), were synthesized by using a

Pd-catalyzed coupling reaction of a dibromated precursor with sodium

dicyanomethanide. The new acceptors show strong electron-accepting ability

and small on-site Coulomb repulsion [55].

A fluorometric method is used to study complexes between

thianthrene and various solvents including CCl4, CHCl3, acetone and

dichloroethane. Dichloromethane and dichloroethane are used as solvents


54

and systems are analyzed at 20 and 30°C.

Complex formation constants (Kf) determined in dichloroethane are

corrected for the solvent-thianthrene complex and are seen to be similar to

those determined in dichloromethane. The Stern-Volmer equation is shown

to be an incorrect choice in the analysis despite its yielding a linear plot. The

correct method yields a different value for Kf than does the Stern-Volmer

approach. Enthalpies of complex formation are also determined [56].

The visible and ultra-violet spectra of the charge-transfer complexes,

mesitylenechloranil, durene-chloranil and hexamethylbenzene-chloranil, in

carbon tetrachloride have been measured at 25°, 40°, 55° and 70°C. The

calculated values of equilibrium constants and maximum extinction

coefficients were found to be in disagreement with previous results. The

relationship between the equilibrium constant and the extinction coefficient

is discussed in terms of solvent interaction [57].

It was found that in halogen substitution reactions, bromine monochlonde

acts exclusively as a brominating agent. Formation of chloro-derivatives or

bromide ions could not be detected. Iodine monobromide, on the contrary,

proved to act partly as a lodinating, and partly as a brominating agent, even

in aqueous solutions containing bromide [58].

The complex formation of 1-ethyl-2-pyrrolidinone, 1-benzyl-2-

pyrrolidinone and 1-phenyl-2-pyrrolidinone with iodine, iodine

monobromide and iodine monochloride has been studied by u.v. and visible

spectroscopic methods in carbon tetrachloride, dichloromethane, 1,2-

dichloroethane, n-heptane and cyclohexane. The results show the

equilibrium constants (K), complexation enthalpies (ΔH) and the

wavelengths of maximum absorption bands (λmax) of the complexes to vary

markedly with the solvent. The decrease in the K values with increasing

acceptor number (AN) of the solvent may be due to the competition of the

solvent and the halogen molecule for the amide; for halogenated

hydrocarbon solvents can act as weak electron acceptors. The complex


55

formation ability of the electron donors decreases in the order 1-ethyl-2-

pyrrolidinone 1-benzyl-2-pyrrolidinone 1-phenyl-2-pyrrolidinone, and

the electron acceptor properties decrease in the order iodine monochloride

iodine monobromide iodine [59].

The formation of 1:1 hydrogen-bonded complexes of 2,2,2,-

trichloroethanol and 2,2,2-tribomoethanol with sulfoxides, sulfinamides,

sulfones and sulfonamides has been studied by i.r. spectroscopy in carbon

tetrachloride solution at 288.15, 298.15, 308.15 and 318.15 K. The

equilibrium constants have been measured from the change in intensity of

the free OH-stretching band of alcohols.

The results show that the equilibrium constants (K) and OH-

stretching wavenumber shifts (Δ OH) are in every case greater for the 2,2,2-

trichloroethanol complexes than for the corresponding 2,2,2-tribromoethanol

ones. Furthermore the proton acceptor strengths of sulfoxides and

sulfinamides seem to be of the same order of magnitude, as also the much

lower strengths of sulfones and sulfonamides, in agreement with earlier

suggestion that inductive effects predominate over resonance effects in

determining the polarity of sulfur-oxygen bonds in sulfinamides and

sulfonamides [60].

Complexes between various nitriles and ICl have been studied in

solution by infrared spectroscopic methods. The bond is directed from the

nitrogen to the iodine atom and is probably of the charge transfer type. The

infrared data indicate that in the case of acetonitrile the halogen molecule is

situated on the three-fold symmetry axis. Formation constants (Kc) of these

1:1 complexes in carbon tetrachloride at 28°C were obtained from intensity

changes of the C N stretching bands. The donor strength of the nitriles R-

C N is dependent upon the inductive effects of the substituent R. In the

complexes the C N stretching bands had higher frequencies (v), higher

integrated intensities (B) and generally larger half intensity widths (ν1/2) than


56

those of the free nitriles. Spectral parameters for these bands are given [61].

The vibrational spectra of the charge transfer complex of TTF with

TCNE are explored. It is found that a degree of charge transfer of 0.5,

namely that one electron has migrated from a dimer of TTF to that of TCNE

molecules, characterizes the ground state of the complex. A Holstein-

Hubbard model for a symmetric tetramer with two donor and two acceptor

molecules allows the understanding of the vibronic bands observed in the

infrared and Raman spectra and of the electronic charge transfer excitations

[62].

Charge Transfer (CT) absorption bands are observed in the

interaction of trialkytinhalides and TCNE. Taking account of Person's

restrictions the formation constants Kc of these complexes could be

accurately determined. A relation between the donor-acceptor separation,

rDA, and the size of the donor has been found. Arguments about the CT

absorption maximum, λCT, the formation constants and other spectral

evidence are in favour of the halide lone pairs as preferential donor site in

the organotiniodide molecule [63].

A spectro-photometric study on charge transfer complexes of

totrabromophthalic anhydride with various hydrocarbons has been made in

chloroform and benzene. In each case charge transfer bands characteristic of

the formation of 1 : 1 complexes have been observed. Equilibrium constant

Kc and extinction coefficient c for each of the complexes have been

calculated from the spectrophotometric data. Various predicted regularities

have been tested in the light of these results [64].

Charge transfer complex (CTC) of phenothiazine and iodine (1:2

molar ratio) was prepared by solvent evaporation method in diethyl ether and

its composite with poly(vinyl chloride) was prepared in benzene by diffusion

method. Infra-red spectra showed overlapped peaks for both components and

intensity of individual component was proportional to feed ratio. Optical

photographs and scanning electron microscopy of composites showed


57

template growth and connectivity in insulator matrix was proportional to

wt% of CTC. Mechanical strength of composites was found to increase with

wt% of PVC. The current–voltage study showed percolation threshold of

8 wt% of CTC. The temperature dependence of conductivity showed

semiconducting nature of the materials. Transport property of charges were

explained by regression analysis of σdc vs. T−1/1+n data and meets the basis for

the Mott's 2D, 3D variable range hopping or thermoionic emission model,

depending on temperature and wt% of CTC content. The impedance

spectroscopy was performed between 40 Hz–100 kHz range. Circuit

elements consists only combination of resistance and capacitance, which

showed homogeneous nature of composites. Thermoelectric factor ‘S’ was

also evaluated and has value of <1 at 303 K in all cases [65].

The intermolecular charge-transfer absorption spectra of complexes

of various p-π aromatic electron donor molecules with a series of p-π

aromatic electron acceptor molecules have been measured. The frequencies

of the bands of these complexes may be expressed simply as the sum of two

terms, characteristic of the donor and acceptor molecules respectively. This

relationship fails if the electron donor is weak [66].

A theory for charge transfer between the electrode and the

donor/acceptor molecule coupled through a DNA bridge in solution is

developed. They explore the crossover between the coherent tunneling and

the incoherent sequential transfer regimes by varying the electrode potential

and discuss the effects of single-base mismatches in DNA duplex in both

regimes. In the former regime a single-base mismatch in DNA duplex causes

a reduction in the charge transfer rate simply by decreasing the electron

tunneling matrix element, however, in the latter regime the effects are rather

complicated [67].

The intermolecular charge-transfer (CT) complexes formed between

two poly(amidoamine) dendrimers (PAMAM) from zero (D1) and second

generation (D2) as donor and iodine as σ-acceptor have been studied


58

spectrophotometrically in the chloroform medium. The suggested structures

of the solid iodine charge-transfer complexes investigated by several

techniques using elemental analysis, mid infrared spectra, and thermal

analysis (TGA and DTG) of the solid CT-complexes along with the

photometric titration curves for the reactions. The results indicate the

formation of two CT-complexes [(D1)]–I2 and [(D2)]–2I2 with acceptor:

donor molar ratios of 1:1 and 1:2, respectively. The kinetic parameters (non-

isothermal method) for their decomposition have been evaluated by

graphical methods using the equations of Horowitz–Metzger (HM) and

Coats–Redfern (CR) [68].

Weak interactions between organic donor and acceptor molecules

resulting in cofacially-stacked aggregates ("CT complexes") were studied by

second-order many-body perturbation theory (MP2) and by gradient-

corrected hybrid Hartree-Fock/density functional theory (B3LYP exchange-

correlation functional). The complexes consist of tetrathiafulvalene (TTF)

and related compounds and tetracyanoethylene (TCNE). Density functional

theory (DFT) and MP2 molecular equilibrium geometries of the component

structures are calculated by means of 6-31G*, 6-31G*(0.25), 6-31++G**, 6-

31++G(3df,2p) and 6-311G** basis sets. Reliable molecular geometries are

obtained for the donor and acceptor compounds considered. The geometries

of the compounds were kept frozen in optimizing aggregate structures with

respect to the intermolecular distance. The basis set superposition error

(BSSE) was considered (counterpoise correction). According to the DFT and

MP2 calculations laterally-displaced stacks are more stable than vertical

stacks. The charge transfer from the donor to the acceptor is small in the

ground state of the isolated complexes. The cp-corrected binding energies of

TTF/TCNE amount to -1.7 and -6.3 kcal/mol at the DFT(B3LYP) and

MP2(frozen) level of theory, respectively (6-31G* basis set). Larger binding

energies were obtained by Hobza's 6-31G*(0.25) basis set. The larger MP2

binding energies suggest that the dispersion energy is underestimated or


59

not considered by the B3LYP functional. The energy increases when S in

TTF/TCNE is replaced by O or NH but decreases with substitution by Se.

The charge-transferred complexes in the triplet state are favored in the

vertical arrangement. Self-consistent-reaction-field (SCRF) calculations

predicted a gain in binding energy with solvation for the ground-state

complex. The ground-state charge transfer between the components is

increased up to 0.8 e in polar solvents [69].

UV spectroscopy of charge-transfer complexes (CTCs) with

tetracyanoethylene (TCNE) and iodine has been used to study the relative

donor ability of mono- and bicycloolefins and the stability of the CTCs. The

donor ability of bicycloolefins, characterized by CT(TCNE), increases with

increase in ring strain. The equilibrium constants for complex formation of

bicycloolefins with TCNE are linearly related to the rate constants of the

reaction of epoxidation by tert-butyl hydroperoxide [70].

Charge transfer molecular complexes of some pyrazole donors

(pyrazole, 4-methylpyrazole, 3-methylpyrazole and 3,5-dimethylpyrazole)

with 2,3-dichloro-5,6-dicyano-1,4-p-benzoquinone and tetracyanoethylene

as π-electron acceptors have been studied in CH2Cl2 at 25 °C. Spectral

characteristics and stability constants of the formed charge transfer (CT)

complexes are discussed in terms of the nature of donor and acceptor

molecular structure, as well as in relation to solvent polarity.

Thermodynamic parameters (ΔH, ΔG and ΔS) associated with CT complex

formation are also examined. It was concluded that the formed CT

complexes are of n-π type with 1:1 (D:A) composition [71].

Charge transfer (CT) complexes formed between 2-amino-4-

methoxy-6-methyl-pyrimidine (AMMP), 2-amino-4,6-dimethyl-pyrimidine

(ADMP), 3-amino-pyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-

methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-

methyl-1,3,4-thiadiazole (AMTD) and 3-amino-5,6-dimethyl-1,2,4-triazine

(ADMT) as electron donors with the π-acceptor chloranilic acid (CHA)


60

were investigated spectrophotometrically in ethanol. Minimum–maximum

absorbances method has been used for estimating the formation constants of

the charge transfer reactions (KCT). It has been found that KCT depends on

the pKa of the studied donors. Job’s method of continuous variation and

photometric titration studies were used to detect the stoichiometric ratios of

the formed complexes and they showed that 1:1 complexes were produced.

The molar extinction coefficient (ε), oscillator strength (f), dipole moment

(μ), charge transfer energy (ECT), ionization potential (IP) and the

dissociation energy (W) of the formed complexes were estimated, they

reached acceptable values suggesting the stability of the formed CT-

complexes. The solid CT-complexes were synthesized and characterized by

elemental analyses, 1HNMR and FTIR spectroscopies where the formed

complexes included proton and electron transfer [72].

Molecular charge-transfer complexes of the donor 2,6-

diaminopyridine (2,6-DAPY) with π-acceptors tetracyanoethylene (TCNE),

2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-p-

benzoquinone(chloranil) were studied spectrophotometrically in chloroform

at room temperature. All formed complexes exhibit well resolved charge-

transfer bands in the regions where neither donor nor acceptors have any

absorption. The stoichiometries of the reactions were determined from

photometric titration methods. The results obtained show the formed CT

complexes have the structures [(2,6-DAPY)(TCNE)3], [(2,6-

DAPY)(DDQ)2], and [(2,6-DAPY)(chloranil)]. These three complexes were

isolated as solids and further characterized by elemental analysis and

infrared measurements [73].

Poly(phenylethynyl)copper was prepared by reacting

phenylacetylene with Cu+ ions. Its dc conductivity drastically increases on

doping with iodine and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ).

An investigation using IR and UV spectroscopy, X-ray diffraction and solid

state NMR revealed that on iodine doping structural changes occur caused


61

by a reaction between Cu(I) and the dopant. On the contrary, on doping with

DDQ the structure is preserved. The large conductivity increase with the

latter dopant originates from charge transfer between the polymer chain

(donor) and DDQ (acceptor), evidenced by a transformation from a quinone

into a semiquinone structure of the DDQ molecule [74].

In present study synthesizing and characterizing organic conducting

materials have been focused primarily on the preparation and structure

determination of D-A-D (D = donor, A = acceptor) and A-D-A molecular

units in which donors and acceptors are chemically attached via bridging

atoms or groups. The strategy that motivates the synthetic work is aimed at

gaining control over the architectural features of the solid state structures of

the materials, since gaining control over the three-dimensional structure is a

vital pre-condition for achieving electrical conductivity in organic materials.

Construction of such molecular units predetermines the D-A molar ratio as

well as the maximum degree of charge transfer. Moreover, it is already

shown that this molecular motif has a high propensity to crystallize in the

desired crystallographic arrangement, characterized by segregated stacks of

both donors and/or acceptor, with significant overlap between adjacent units

in the stack. Following this approach we have synthesized two types of

molecules; have been synthesized one contains two donors attached to one

acceptor via -CH2- or S atom bridges, and in the other, two acceptors are

linked to one donor via methylene bridges.

In addition, the importance of introducing heavy atoms in charge-transfer

complexes has long been recognized. Consequently, extensive work has

been carried out on the synthesis of various TTF derivatives, in which Se and

Te atoms replace sulfur or hydrogen atoms in TTF. Recently, we have

synthesized new compounds in which two TTF molecules are linked via

tellurium atoms, are synthesized, e.g. TTF-Te-TTF and TTF-Te-Te-TTF,

and prepared their complexes with TCNQ. They all exhibit high conductivity

at room temperature [76].


62

Interaction of some thiazole and benzothiazole derivatives as donors

with certain di- and trinitrobenzene derivatives as acceptors results in the

formation of 1:1 molecular species. The infrared, NMR and ultraviolet

analysis of the complexes with non-acidic acceptors reveals the presence of

π-π* interaction from a HOMO of the thiazole nucleus or the phenyl moiety

of the benzothiazoles to a LUMO of the benzene ring of the acceptors. The

existence of this type of interaction is supported by HMO calculations on the

donor molecules. On the other hand, the molecular complexes derived from

acidic acceptors are stabilized, in addition to the π-π* interaction, by proton

transfer from the hydroxyl or carboxylic group of the acceptor to the amino

group of the aminothiazole donors. The ionization potentials of donors,

electron affinities of acceptors as well as the energy of the CT complexes

were computed from their u.v. and visible spectra [77].

Formation of the charge transfer complexes between benzo-15-

crown-5, dibenzo-18-crown-6, dibenzo-24-crown-8 and dibenzo-crown-10

and the π-acceptors DDQ and TCNE in dichloromethane solution was

investigated spectrophotometrically. The molar absorptivities and formation

constants of the resulting 1:1 molecular complexes were determined. The

stabilities of the complexes of both π-acceptors varies.All of the resulting

complexes were isolated in crystalline form and characterized. The

influences of potassium ion on the formation and stability of the TCNE

molecular complexes were studied. Effects of the crown ether structure and

the role of the K+ ion on the formation of charge transfer complexes are

discussed [78].

Interactions of diaza-18-crown-6 and diaza-15-crown-5, as electron

donors, with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), as an

electron acceptor, have been investigated spectrophotometrically in

acetonitrile and chloroform solutions. The results indicated immediate

formation of an electron donor-electron acceptor complex


63

DA: which is followed by two relatively slow consecutive

reactions:

The pseudo-first-order rate constants for the formation of the ionic

intermediate and the final product have been evaluated at various

temperatures by computer fitting of the absorbance time data to appropriate

equations. The formation constants of the resulting DA complexes have also

been determined. The influences of both the azacrown’s structure and the

solvent properties on the formation of DA complexes and the rates of

subsequent reactions are discussed [79].

Various studies, such as spectrophotometry, solubility studies and

FT—NMR studies reveal that the interaction of dinitrobenzenes with

anilines is primarily due to charge transfer but in some cases, where very

concentrated solutions are involved, hydrogen bonding may dominate over

charge transfer.

The charge transfer complex (CT-complex) between oxatomide drug

and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was studied

spectrophotometrically in 10 solvents at different temperatures. The donor

oxatomide is found to form stable 1:1 stoichiometric complex with DDQ and

the stoichiometry was unaffected by change in polarity of the solvent

studied. The ΔH°, ΔS° and ΔG° values are all negative, so the studied

complex is reasonably stable and exothermic in nature. The ionization

potential of the drug was determined using the CT-absorption bands of the

complex in all the solvents. The dissociation energy of the charge transfer

excited state for the CT-complex in different solvents was also determined

and is found to be constant. The spectroscopic and thermodynamic

properties were observed to be sensitive to the nature of the solvent [80].

Charge-transfer complexes of some heteroaromatic N-oxides with

tetracyanoethylene, 2,3-dichloro-5, 6-dicyanobenzoquinone, tetrachlorocyclohexa-2,

5-diene-1,4-dione and 7,7,8,8-tetracyanoquinodimethane in methylene chloride were


64

investigated spectrophotometrically. The spectral data, molar extinction

coefficients and transition energies of the complexes formed as well as the

ionization potentials of the donors are reported. B -H and J

methods were applied to the determination of formation and apparent

formation constants, respectively. The effect of temperature and solvent on

the stability of the complexes are discussed [81].

1,4-Naphthalenediol gets converted to 1,4-naphthoquinone on

reaction with 1,4-benzoquinone. In the reaction, 1,4-benzenediol is formed.

The reaction passes through charge delocalisation in the equivalent keto and

enol forms. The spectroscopic and electrochemical studies discern the role of

equivalent charge transfer complex derived from 1,4-naphthoquinone with

1,4-benzenediol. The conversion of 1,4-naphthalenediol to 1,4-

naphthoquinone in the presence of oxidants such as hydrogen peroxide and t-

butylhydroperoxide are catalysed by 1,4-benzoquinone[82].

X-Benzylidenesanthranilic acid molecular complexes with π-

acceptors, tetracyanoethylene, 2,3-dichloro-5,6-dicyano-p-benzoquinone and

chloranil, have been studied. The intramolecular hydrogen bonding that

exists in such compounds greatly inhibits the transition of the nitrogen

azomethine n-electrons. The formation constant values and molar extinction

coefficients of the p-dimethyl-aminobenzylideneanthranilic acid-DDQ CT

complexes have been determined in CH2Cl2, C2H4Cl2 and CHCl3 in the

temperature range 10–30°C. Such CT complexes are of strong n-π type [83].

π-π Molecular complexes of [2.2.2] (1, 2, 4)- as well as 5, 15, 16-

trimethyl [2.2.2] (1, 2, 4) cyclophanes as electron donors with

tetracyanoethylene and 1,4-benzoquinones as acceptors have been studied

spectrophotometrically. The position of λmax of the longest wavelength

charge-transfer band in the visible spectra of the complexes has been used to

discuss the effect of the strain as well as the molecular structure in the tris-

bridged cyclophanes on their complexation with different π-acceptors. The

constitution and apparent formation constants of the molecular complexes


65

formed have been determined, and the effect of solvent on molecular

complexation has been discussed [84].

The interaction of iodine with triphenylamine, triphenylphosphine,

triphenylarsine and triphenystibine has been investigated by electronic

spectroscopy. Transformation of the outer charge-transfer complexes to the

inner complexes (quarternary salts) has been examined. The relations of the

ionization potentials of the donors with the hvc.t have been discussed and

various c.t. parameters have been estimated. Hydrogen bonding of these

donors with phenol have been reported [85].

Complexes of o-carboxyphenylhydrazoneacetoacetanilide

(o-CPHAA) with Cu(II), Ni(II) and Co(II) were studied in dioxane-water

using the Irving and Rossotti method over the temperature range 10–40 °C

and at constant ionic strength (0.1 M). The acid dissociation constant pKH1,2

of the ligand and the stepwise stability constants (log K1 and log K2) of the

complexes formed were computed at various temperatures. The values of the

stepwise and overall changes in ΔG, ΔH and ΔS accompanying the

neutralization of the ligand and complex formation were evaluated. This

study reveals that the ionization of the ligand in the mixed solvent is an

endothermic process, whereas the complex formation is an exothermic

reaction. The optimum conditions for complex formation and the

composition and stability constants (log K1) of the complexes formed in

solution between the ligand and Cu(II), Ni(II) and Co(II) were also

determined (spectrophotometrically) [86].

1.2.3. Earlier studies on charge transfer interactions of biomolecules.

The spectrophotometric and thermodynamic properties of different

substituted methylnaphthalenes charge transfer (CT) complexes with

tetracyanoethylene have been studied in carbon tetrachloride. The spectral

characteristics of the CT bands have also been discussed in relation to the

positions of methyl groups. The formation constants and the spectral

properties of the complexes are markedly affected with the substitution


66

position of the methyl groups. The ionization potentials of the donors are

determined [87].

Charge transfer (CT) complexes of some non-steroidal anti-

inflammatory drugs, naproxen and etodolac which are electron donors with

some π-acceptors, such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-

dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL), have been

investigated spectrophotometrically in chloroform at 21 °C. The coloured

products are measured spectrophotometrically at different wavelength

depending on the electronic transition between donors and acceptors. Beer's

law is obeyed and colours were produced in non-aqueous media. All

complexes were stable at least 2 h except for etodolac with DDQ stable for

5 min. The equilibrium constants of the CT complexes were determined by

the Benesi–Hildebrand equation. The thermodynamic parameters ΔH, ΔS,

ΔG° were calculated by Van’t Hoff equation. Stochiometries of the

complexes formed between donors and acceptors were defined by the Job's

method of the continuous variation and found in 1:1 complexation with

donor and acceptor at the maximum absorption bands in all cases [88].

The interactions of the electron donors 2-aminopyridine (2APY) and

3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE),

2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-

trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-

benzoquinone (chloranil) were studied spectrophotometrically in chloroform

at room temperature. The electronic and infrared spectra of the formed

molecular charge transfer (CT) complexes were recorded. Photometric

titration showed that the stoichiometries of the reactions were fixed and

depended on the nature of both the donor and the acceptor. The molecular

structures of the CT-complexes were, however, independent of the position

of the amino group on the pyridine ring and were formulated as

[(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)].

The formation constants (KCT), charge transfer energy (ECT) and molar


67

extinction coefficients ( CT) of the formed CT-complexes were obtained

[89].

Charge transfer absorptions of linear oligosilanes and

silanorbornadienes, charge transfer induced oligomerization, polymerization

and cycloaddition of tetrasilacyclooctadiyne and its germanium analogues

are described. Photo-induced electron transfer reactions of various types of

organosilicon compounds are discussed in detail, and include photo-induced

chlorinative Si–Si bond cleavage, photo-induced nucleophilic Si–Si bond

cleavage, fluorinative Si–Si bond cleavage via electron transfer, skeletal

rearrangement via photo-induced electron transfer and the structure of a silyl

radical cation [90].

Charge transfer complexes (CTC) of 5,10,15,20-

tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP),

5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-

tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin

(Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various

temperatures in CH2Cl2 and CCl4. The data are discussed in terms of

equilibrium constant (KCT), molar extinction coefficient ( CT),

thermodynamic standard reaction quantities (ΔG°, ΔH° and ΔS°), oscillator

strength (f), and transition dipole moment (μ). The spectrum obtained for

TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main

absorption bands at 475 and 690 nm, which are not due to the absorption of

any of the reactants. These bands are characteristic of an intermolecular

charge transfer involving the overlap of the lowest unoccupied molecular

orbital (LUMO) of the acceptor with the highest occupied molecular orbital

(HOMO) of the donor. The results reveal that the interaction between the

donors and acceptor is due to π–π* transitions by the formation of radical ion

pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the

Job and straight line methods between donors and acceptor with the

maximum absorption bands at wavelengths of 475 and 690 nm. The


68

observed data show salvation effects on the spectral and thermodynamics

properties of CTC. The ionization potential of the donors and the

dissociation energy of the CTC were also determined and are found to be

constant [91].

Charge-transfer molecular complexes of 2-amino-5-X-1,3,4-

thiadiazole (D) (X = H, I; = CH3, II; = phenyl, III) with some π-electron

acceptors (A) have been studied in methanol. It is concluded that these

complexes are predominantly of the π-π type. Solid 1:1 CT complexes of the

donors I–III with π-acceptors DDQ and TCNE have been synthesized and

characterized [92].

The spectrophotometric and thermodynamic properties of different

substituted methylnaphthalenes charge transfer (CT) complexes with

tetracyanoethylene have been studied in carbon tetrachloride. The spectral

characteristics of the CT bands have also been discussed in relation to the

positions of methyl groups. The formation constants and the spectral

properties of the complexes are markedly affected with the substitution

position of the methyl groups. The ionization potentials of the donors are

determined [93].

Simple and sensitive spectrophotometric methods are described, for

the first time, for the determination of sodium salts of phenobarbital (1),

thiopental (2), methohexital (3) and phenytoin (4). The methods are based on

the reaction of these drugs as n-electron donors with the σ-acceptor iodine

and various π-acceptors: 7,7,8,8-tetracyanoquinodimethane; 2,3-dichloro-

5,6-dicyano-1,4-benzoquinone; 2,3,5,6-tetrachloro-1,4-benzoquinone;

2,3,5,6-tetrafluoro-1,4-benzoquinone; 2,5-dichloro-3,6-dihydroxy-1,4-

benzoquinone; tetracyanoethylene and 2,4,7-trinitro-9-fluorenon. Depending

on the solvent polarity, different coloured charge-transfer complexes and

radicals were developed. Different variables and parameters affecting the

reactions were studied and optimized. The formed complexes were examined

by UV/VIS, infrared and 1H-NMR. Due to the rapid development of


69

colours at ambient temperature, the obtained results were used on thin layer

chromatograms for the detection of the investigated compounds. Beer's plots

were obeyed in a general concentration range of 1–400 μg ml−1 for the

investigated compounds with different acceptors. Interference from some co-

formulated drugs was also studied [94].

The stoichiometry of charge transfer complexes formed between

Schiff base donors and aromatic hydrocarbon acceptors was established by

solid-liquid phase equilibrium diagram studies. The thermodynamic

functions of some stable charge transfer complexes were determined by

differential scanning calorimetry and the area under the curve of the

congruent compound is fixed as the criterion to predict the relative strength

of charge transfer complexes on the basis of thermodynamic parameters [95].

The electrical properties of bilayer lipid membranes modified with

strong electron acceptors are examined by the voltammetric method.

Diffusion-limited current-potential curves are obtained in the absence of

exogenous redox agents in the aqueous phase when the membrane is

modified with tetracyanoethylene (TCNE) or tetracyanoquinodimethane

(TCNQ). Other substituted 1,4-benzoquinone modifiers yield either no

response (chloranil) or a current-voltage response indicative of a membrane

limiting charge transfer step. In all cases that demonstrate an eletrical

response, material can be detected leaching into the aqueous phase by

spectroscopic means. Free radicals are detected subsequent to the mixing of

modifier with an organic phase containing lipid; however, the material

detected in the aqueous phase is not a radical [96].

Diaryl ditellurides as electron donors have interacted with bromine

and iodine as electron acceptors in chloroform to form 1: 1 molecular charge

transfer (CT) complexes, which absorb light at 540 and 670 nm,

respectively. The molar ratio methods were used to determine the ratios of

the CT complexes. Diphenyl, di-p-methoxy phenyl and di-p-ethoxy phenyl

ditellurides were reacted with DDQ in chloroform solutions and


70

immediately formed stable solid products which consisted of one molecule

of diaryl ditelluride and two molecules of DDQ. The complexes were

characterized by elemental analyses, IR, UV-visible and mass spectral data

[97].

The reactions of the electron donor 1-methylpiperidine (1MP) with

the π-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ),

tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone

(DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil = CHL) and iodine

(I2) were studied spectrophotometrically in chloroform at room temperature.

The electronic and infrared spectra of the formed molecular charge-transfer

(CT) complexes were recorded. The obtained results showed that the

stoichiometries of the reactions are not fixed and depend on the nature of the

acceptor. Based on the obtained data, the formed charge-transfer complexes

were formulated as [(1MP)(TCNE)2], [(1MP)(DDQ)]·H2O, [(1MP)(CHL)]

and [(1MP)I]I3, while in the case of 1MP–TCNQ reaction, a short-lived CT

complex is formed followed by rapid N-substitution by TCNQ forming the

final reaction products 7,7,8-tricyano-8-piperidinylquinodimethane

(TCPQDM). The five solids products were isolated and have been

characterized by electronic spectra, infrared spectra, elemental analysis and

thermal analysis [98].

The molecular interactions between haloperidol and droperidol as

electron donors and each of iodine; 7,7,8,8-tetracyanoquinodimethane

(TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ);

tetracyanoethylene (TCNE); 2,4,7-trinitro-9-fluorenon (TNF); and 2-3-5-6-

tetrabromo-1,4-benzoquinone (Bromanil) as acceptors have been

investigated spectrophotometrically. Different variables affecting the

reaction were studies and optimized. Beer's law was obeyed in a

concentration limit of 2.5–2500 μg ml−1 for the studied drugs with various

acceptors used. Electron affinities (EA) of the acceptors were found to

correlate with both the time required for maximum colour formation and


71

the molar absorptivities of haloperidol and droperidol. A Job's plot of the

absorbance versus the molar ratio of the drugs to iodine indicated 1:1 ratio

[99].

The reaction of ferric(III) acetylacetonate (donor), Fe(acac)3, with

iodine as a σ-acceptor and with other different π-acceptors have been studied

spectrophotometrically at room temperature in chloroform. The π-acceptors

used in this investigation are 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

(DDQ), p-chloranil and 7,7′,8,8′-tetracyanoquinodimethane (TCNQ). The

results indicate the formation of 1:1 charge-transfer complexes with a

general formula, [Fe(acac)3 (acceptors)]. The iodine complex was shown to

contain the triiodide species, [Fe(acac)3]2I+I3

−, based on the electronic

absorptions as well as on the Far-infrared absorption bands characteristic for

the non-linear triiodide species, I3−, with C2v symmetry. The proposed

structure of this complex is further supported by thermal and middle infrared

measurements [100].

One paper describes the preparation of an organic charge transfer

complex (CTC) based printable enzyme electrode. CTC crystals were

prepared by mixing TCNQ powder with TTF solution (in acetonitrile).

Glucose oxidase (GOD) was adsorbed at the CTC crystal surface in a

monolayer. A printable paste was prepared by mixing GOD-adsorbed

crystals with a binder and a solvent. This paste was applied to an electrode

cavity and vacuum dried. A thin layer of gelatin was cast on the paste filled

dried electrode, and cross-linked with glutaraldehyde in the dry condition.

The sensors were fixed in a flow injection system, and continuously

polarized at 0·15 V and 37°C, and the samples were automatically injected

every 30 min [101].

The interaction of pyrazolones as a donor with iodine as an acceptor

has been studied using spectrophotometric and constant activity methods.

The results indicate the formation of 1:1 molecular complex species ofn–σ*

type. The equilibrium constants of these complexes were determined at


72

different temperatures. The effect of nonpolar solvents are discussed in terms

of the solute–solute and solute–solvent competing equilibria. The

thermodynamic parameters were calculated [102].

Simple, rapid and sensitive spectrofluorimetric methods are

described, for the first time, for the determination of ciprofloxacin (CIP),

norfloxacin (NOR), pefloxacin (PEF) and fleroxacin (FLE). The methods are

based on the charge-transfer (CT) reaction of these drugs as n-electron

donors with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as π-electron

acceptor. TCNQ was found to react with these drugs to produce intensely

transfer reaction complexes and the fluorescence intensity of the complexes

was enhanced in 21–35 fold higher than that of the studied fluoroquinolones

itself. The formation of such complexes was also confirmed by both infrared

and ultraviolet-visible measurements. The different experimental parameters

that affect the fluorescence intensity were carefully studied. At the optimum

reaction conditions, the drug-TCNQ complexes showed excitation maxima

ranging from 277 to 284 nm and emission maxima ranging from 451 to

458 nm. Rectilinear calibration graphs were obtained in the concentration

range of 0.03–0.9, 0.04–1.2, 0.04–1.3 and 0.08–2.4 μg ml−1 for CIP, NOR,

PEF and FLE, respectively [103].

Heterogeneous electron transfer (ET) reactions at the polarised water

1,2-dichloroethane (DCE) interface are studied by in situ UV-Visible

spectroscopy in total internal reflection mode. The reduction of

7,7,8,8-tetracyanoquinodimethane (TCNQ) and the oxidation of

1,1′-dimethylferrocene (DMFc) by the hexacyanoferrate redox couple are

considered. The generation of products in the organic phase is monitored

spectroscopically and correlated to the simultaneous current response. Both

systems exhibit a good correlation between optical and electrochemical

responses, highlighting the ideal behaviour of these redox couples for

electron transfer studies at liquid liquid interfaces. The kinetics of ET

between hexacyanoferrate and TCNQ is analysed also by


73

chronoabsorptometry and potential modulated reflectance spectroscopy

[104].

Copper(II) and nickel(II) biguanides and O-alkyl-1-amidinourea can

act as donors for the formation of charge transfer (CT) adducts with I2 and

tetracyanoquinodimethane (TCNQ) as acceptors. Iodine adducts are

characterized both in solid and solution states whereas TCNQ adducts obtain

only in solution. Appearance of a broad band at 355 nm for iodine adducts

and at 335 nm for TCNQ adducts and shifting of i.r. frequencies support the

formation of donor acceptor associates. Elemental analysis establishes 1:1

stoichiometry of the solid adducts. The K and values determined by

modified Benesi—Hildebrand, Scott and Rose—Drago equations are found

to be of the order of 104 and 103 respectively at 298 K in methanol. The

solvent effect on the K values is discussed in terms of coupled solute-solute

and solute-solvent equilibria [105].

The charge-transfer complex formation of iodine with antipyrine has

been studied spectrophotometrically in chloroform, dichloromethane (DCM)

and 1,2-dichloroethane (DCE) solutions at 25 °C. The results indicate the

formation of 1:1 charge-transfer complexes. The observed time dependence

of the charge-transfer band and subsequent formation of I3− in solution were

related to the slow transformation of the initially formed 1:1 antipyrine:I2

outer complex to an inner electron donor–acceptor (EDA) complex, followed

by fast reaction of the inner complex with iodine to form a triiodide ion. The

values of the equilibrium constant, K, are calculated for each complex and

the influence of the solvent properties on the formation of EDA complexes

and the rates of subsequent reaction is evaluated [106].

The spectral properties of molecular complexes between some [2.2]

paracyclophane-azomethines and both tetracyanoethylene and 1,4-

benzoquinones in methylene chloride have been examined. The probability

of existence of the electronic transanular substituent effect in the

[2.2]paracyclophane-azomethines, as well as the effect of the different


74

substituted aryl groups on complexation have been discussed. The

stoichiometry, transition energy and apparent formation constants of the

molecular complexes formed have been determined spectrophotometrically

[107].

Charge-transfer molecular complexes of 2-amino-5-X-1,3,4-

thiadiazole (D) (X = H, I; = CH3, II; = phenyl, III) with some π-electron

acceptors (A) have been studied in methanol. It is concluded that these

complexes are predominantly of the π-π type. Solid 1:1 CT complexes of the

donors I–III with π-acceptors DDQ and TCNE have been synthesized and

characterized [108].

Spectrophotometric studies on the charge transfer interaction of 2,3

dichloro 5,6 dicyano p-benzoquinone with various hydrocarbons have been

carried out in chloroform. It has been observed that the frequency of the

charge transfer band at its maximum varies almost linearly with the

ionization potential of the donor. The singlet—triplet transition of some of

hydrocarbons has been bound to be coincident with the charge transfer

bands. Charge transfer spectra of all the systems studied are given and from

it λmax max and kc, have been determined [109].

EPR spectra of cobalt (II) complexes of octaethylporphyrin and

tetraphenylporphyrin, CoOEP and CoTPP, are strongly affected by

interactions with π electron donors or acceptors, the effects of the interaction

being generally larger in CoOEP than in CoTPP. Much smaller but still

significant effects of charge transfer complex formations were observed also

on EPR and ENDOR spectra of copper (II) porphyrins, CuOEP and CuTPP.

Direct charge transfer interactions between the metal d orbitals and the π

donors or acceptors make important contributions to the perturbation of the

metal d orbital states by the charge transfer complex formation [110].

Previously it has has been shawned that when glucocorticoids

initially enter rat thymus cells incubated at 37°C. Non-activated hormone-

receptor complexes are formed within 15 s and are then rapidly replaced


75

by activated complexes. Activated and non-activated forms were identified

in cytosols from the cells by DEAE-cellulose chromatography, where they

are eluted with progressively higher salt concentrations in what are referred

to as Peaks I and II [111].

On DNA-cellulose columns dexamethasone-receptor complexes in

cytosols that on DEAE-cellulose give mainly Peak II (the non-activated

complex, referred to as Complex II) are not bound significantly: they are

eluted at the lowest salt concentration along with free steroid, from which

they can be separated by binding to hydroxyapatite. This DNA-cellulose

peak is referred to as Peak a. Complexes in cytosols that give only Peak I on

DEAE, however, on DNA separate into two components. One of these

(Complex Ia) is not bound significantly and appears in Peak a. The other

(Complex Ib, presumably the true activated complex) appears in a later Peak

b. These three complexes have been measured by first adsorbing Ib with

DNA-cellulose, then separating Complexes Ia and II. Which are not

adsorbed on DNA. by means of a DEAE-cellulose column. When

[3H]-dexamethasone is added to cells at 37°C. II is formed within 15 s and is

rapidly replaced by Ib, in agreement with earlier results [112].

1.2.4 Recent studies on charge transfer Interactions of biomolecules

Cloxacillin sodium has been shown to form charge transfer (CT)

complexes of 1:1 stoichiometry with a number of electron acceptors in 50%

(v/v) aqueous ethanol medium. From the trends in the CT absorption bands,

the vertical ionization potential of the drug molecule (cloxacillin sodium) has

been estimated to be 7.89 eV. The enthalpies and entropies of formation of

two such complexes have been determined by estimating the formation

constants spectrophotometrically at five different temperatures. The

oscillator strengths and transition dipole moments of these complexes have

been determined. It has further been noted that the reduction of o-chloranil

by aqueous ethanol is completely inhibited by cloxacillin sodium, a


76

phenomenon that makes the present study of formation equilibrium possible

[113].

Charge transfer complexes between colchicine as donor and

π acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-

p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied

spectrophotometrically in dichloromethane at 21 °C. The stoichiometry of

the complexes was found to be 1:1 ratio by the Job method between donor

and acceptors with the maximum absorption band at a wavelength of 535,

585 and 515 nm. The equilibrium constant and thermodynamic parameters

of the complexes were determined by Benesi–Hildebrand and van’t Hoff

equations. Colchicine in pure form and in dosage form was applied in this

study. The formation constants for the complexes were shown to be

dependent on the structure of the electron acceptors used [114].

A (2) catenane consisting of a π-electron-accepting tetracationic

cyclophane of cyclobis (4,4′-azopyridinium-p-phenylene) and a π-electron-

donating macrocyclic polyether of bis-p-phenylene-34-crown-10 was

synthesized via a template-directed synthesis in 68% yield. The (2) catenane

exhibited charge transfer bands with λmax=526 nm and 566 nm in CH3CN. A

precursor of the cyclophane, bis[4-(4-pyridylazo)pyridinium], spontaneously

formed a charge transfer complex with the macrocyclic polyether. The

investigation of the charge transfer complex using UV-visible and 1H NMR

spectroscopy revealed that the complex had a pseudo-rotaxane structure with

a stability constant (Ka) of 120 dm3 mol-1 at 25°C in CH3CN [115].

Spectrophotometric studies of several substituted benzanilides as

electron donors with tetracyanoethylene (TCNE) and 2,3-dichloro-5,

6-dicyanobenzoquinone (DDQ) as electron acceptors have given results that

are consistent with an interpretation of 1:1 charge-transfer (CT) complexes.

The nature of interaction as well as the substituent effects on the CT

complexation are discussed [116].


77

The charge-transfer (CT) interactions of thiophene, furan, pyrrole

and N-methylpyrrole with tetracyanoethylene, chloranil and maleic

anhydride have been investigated by electronic spectroscopy. In some cases

two CT bands were observed. The association constants of these CT

complexes were compared with those of the H-bonding of these

heterocyclics with phenol [117].

The d.c. electrical properties of polycarbonate (PC) in the dark and

their modification by some charge-transfer (CT) complexes were

investigated. The CT complexes were formed between two low-molecular-

weight additives, trans-stilbene and tetracyanoethylene (TCNE) and between

TCNE and the polymer. The time dependence of current after applying or

removing a step voltage was investigated in the temperature range 77–370 K.

At higher temperatures (above 330 K), three components of the current,

which differ in time and voltage dependence, were distinguished. Their

possible origin is discussed. The conduction current, which is measurable

above room temperature, is increased only slightly by the investigated CT

complexes, in spite of their strong influence on the photoconductivity of PC.

It is concluded that the electrical properties of these systems in the dark are

dominated by the polymer matrix, and that the additives take part in the

photogeneration process, but contribute to the transport of the charge carriers

to only a small extent [118].

Errors and misconceptions arising from Mulliken's treatment of

π-molecular complexes are discussed. Attention is drawn to the common

misuse of the term charge-transfer complex to describe complexes in which

the importance of charge transfer forces has not been established. It is

pointed out that information concerning the importance of charge transfer

forces can best be obtained from measurements of stability constants of

complexes formed by unsubstituted aromatic hydrocarbons. Measurements

of this kind are reported for the complexes formed by fourteen such


78

hydrocarbons with TCNE (tetracyanoethylene). The results do not indicate

any major contribution to binding by charge-transfer forces [119].

The charge-transfer complex formation between an electron donor

polymer, namely poly(2-vinyl pyridine) and low molecular weight acceptors

namely 7,7′,8,8′-tetracyanoquinodimethane and iodine has been investigated

by measuring electronic absorption spectra in dichloroethane at 25°C. The

formation of charge-transfer complexes of 2-picoline with the same set of

acceptors has also been studied as models for comparison. An alternative

method has been proposed to determine the molar ratio and equilibrium

constant for charge-transfer complex formation by electronic spectroscopy.

The equilibrium constant and molar absorptivity for the polymeric

complexes are found to be higher than those for the analogous model

complexes. The charge-transfer complexes undergo an irreversible reaction

to give a final product. The charge-transfer complexes have been studied by

electron spin resonance spectra [120].

Ultraviolet—visible spectral data of iodine complexes of n- and

π-donors have been interpreted by considering that the repulsion energy

responsible for the blue shift of the iodine band is also experienced by the

donor partner which causes the blue shift of the original band of the donor.

This reasoning explains the spectral data of iodine complexes of benzene,

pyridine-N-oxide and stilbazoles. Ultraviolet—vis. spectra of the iodine

complexes of pyridine, aminopyridines and diazines have been

reinvestigated and discussed in the light of the above reasoning. The above

reasoning is extended to the CT spectra of iodine complexes of twin-site

donors such as 1,10-phenanthroline, its methyl and chloro derivatives,

1,7 and 4,7-phenanthrolines, 2,2′-bipyridine and 4,4′-bipyridine. Arguments

are presented which indicate that the donors used in this study form only 1:1

complexes with iodine. The thermodynamic parameters were evaluated for

iodine complexes of the above twin-site donors. The kinetics of


79

transformation of outer CT complexes between the donors and iodine to

inner complexes is presented and discussed [121].

One subject review drawn attention to the peculiarities in behaviour

of bands in the electronic absorption spectra of electron donor–iodine–

solvent systems, the appearance of which is associated with the

intermolecular interaction of molecular iodine with electron donor organic

molecules. The new concept of the bands’ attribution to the isomeric

equilibrium molecular charge-transfer complexes (CTCs) of CTC-I and

CTC-II types is considered. The features of possible phase transitions in the

solid state are discussed on the basis of the thermodynamic properties and

electronic structures of the CTC-I and CTC-II in electron donor–iodine–

solvent systems. The stabilisation of the CTC-II structure with the

temperature lowering coincided in many cases with the electrons’

localisation in the solid state structures having charge-transfer bonds [122].

Spectrophotometric procedures are presented for the determination

of two commonly used antidepressant drugs, fluoxetine (I) and sertraline

hydrochloride (II). The methods are based mainly on charge transfer

complexation reaction of these drugs with either π acceptors chloranil and 2,

3 dichloro-5, 6-dicyanoquinone (DDQ) or σ acceptor iodine. The colored

products are quantified spectrophotometrically at 550, 450 and 263 nm for

fluoxetine and at 450, 455 and 290 nm for sertraline in chloranil, DDQ and

iodine methods, respectively. The molar combining ratio and the optimum

assay conditions were studied. The methods determine the cited drugs in

concentration ranges of 80–640, 16–112 and 7.5–60 μg/ml with mean

percentage recoveries of 99.83, 99.76 and 100.00% and R.S.D. of 1.24, 0.95

and 1.13% in fluoxetine and ranges of 16–160, 15–105 and 6–48 μg/ml with

mean percentage recoveries of 100.39, 99.78 and 99.69% and R.S.D. of 1.02,

0.81 and 0.57% in sertraline for chloranil, DDQ and iodine methods,

respectively [123].


80

Charge transfer (CT) interaction of polyphenylacetylene (PPA) with

iodine, arsenic pentafluoride and 2,3-dichloro-5,6-dicyano-p-benzoquinone

(DDQ) in solution is associated with the formation of broad CT bands

extending beyond the absorption edge of the polymer into the near infra-red

and with a substantial loss of the polymer's effective conjugation. For PPA-I2

and PPA-DDQ in dilute solutions and at low doping levels, the 1:1 CT

complex is susceptible to a Benesi-Hildebrand analysis. The microstructure

of the polymer has a pronounced effect on the observed interaction rates and

equilibrium constants. At high acceptor loadings, there are complicated time-

dependent equilibria involving several complexes of different stoichiometry.

The role of the CT state in this electroactive polymer is discussed in the

context of a band-like model [124].

The charge-transfer interactions between the electron donor 4,

4′-trimethylenedipiperidine (TMDP) and the acceptors 2,3,5,6-tetrachloro-

1,4-benzoquinone (chloranil), 2,4,4,6-tetrabromo-2,5-cyclohexadienone

(TBCHD), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ),

7,7′,8,8′-tetracyanoquinodimethane (TCNQ) and iodine have been studied

spectrophotometrically in CHCI3 solutions. The formed solid charge-transfer

complexes were also isolated and characterized through infrared spectra as

well as thermal and elemental analysis. The stoichiometry of the complexes

was found to be 1:1 in the case of TMDP–chloranil and TMDP–TBCHD

systems and 1:2 in the case of TMDP–DDQ and TMDP–TCNQ systems and

1:3 in the case of TMDP–iodine system. Taking this into consideration along

with infrared spectra and thermal and elemental analysis, the formed

CT complexes have the formulas [(TMDP)(chloranil)], [(TMDP)(TBCHD)],

[(TMDP)(DDQ)2] [(TMDP)(TCNQ)2] and [(TMDP)I]+·I5−, respectively

[125].

The charge transfer donor (D)–acceptor (A) complexes formed

between three classes of vitamin K (all electron acceptors in this study) with

several thiazine psychotropes, used also as antimicrobials, antimalarials,


81

antibiotics, and anticoagulants, were studied by means of alternating current

titrations. The monochloride thiazines formed 2:1 (D:A) complexes,

interacting from 26 to 47.5%; the dihydrochloride formed a 3:1 (D:A)

complex. The antimalarials quinine and its isomer quinidine yielded 2:1

(D:A) complexes, interacting 51 and 60%, respectively. Quinacrine did not

complex with vitamin K. The antibiotics sulfisoxasole and sulfamethisole

gave 1:1 complexes, respectively interacting 6.2 and 11.7% [126].

The electrical properties of some charge transfer complexes, with

stoichiometries 1:1 and 1:2 (donor : acceptor), of 1,5-diaminonaphthalene

and 2,3-diaminonaphthalene with dinitro- and trinitrobenzenes have been

investigated. The positive temperature coefficient of electrical conductivity

(dσ/dT) is evidence for a semiconducting character. The energy gaps (Eg) for

conduction and the charge transfer excitation energies (ECT) have been

discussed. The mechanism of the conduction process is also interpreted

[127].

Inspection of the chemical structure of various drugs suggests that

they might interfere with thyroid metabolism by complexing molecular

iodine in the thyroid gland. Spectroscopic analysis shows that such

compounds form charge transfer complexes with iodine in a 1:1

stoichiometry. Strong donor-acceptor interactions were indicated by the high

values of formation constant Kc for the iodine/drug complexes [128].

The new charge transfer complex t-TTF-TCNQ, whose unsymmetric

cation is intermediate between TTF and HMTTF, presents a regular stacking

of both donor and acceptor chains. They showed that this compound had a

metallic behavior at high temperatures and underwent one metal-insulator

transition near 81 K. Its electrical and magnetic properties are examined in

connection to this phase transition and the effective dimensionality [129].

The iodine charge transfer complexes of thiazole, 4-methylthiazole,

2,4-dimethylthiazole, and benzothiazole in carbon tetrachloride have been

studied by the constant activity method. The equilibrium characteristics of


82

the CT complexes formed were measured. It was concluded that the CT

complexes are of the n-σ* nature and the donating site for the charge transfer

interaction is the lone pair of electrons on the nitrogen atom. Moreover, the

effect of substitution on the CT equilibrium was also studied. The

equilibrium constants have been found to be satisfactorily correlated with the

pK values of the respective thiazole derivatives. This can be attributed to the

lone pair of electrons on nitrogen being more localized on increasing the

donating power of substituent. Hence, the electron density on the nitrogen

atom increases and an increase in equilibrium constant was seen [130].

The solid charge-transfer (CT) complexes of some anthracene

derivatives with nitroaromatic acceptors were prepared. The ionization

potential IP, electron affinity EA and energy of the CT transition for the

donors, acceptors and CT complexes respectively were determined from the

spectrophotometric measurements. In addition, the electrical properties of

the CT complexes were investigated. The positive temperature coefficient of

electrical conductivity (dσ/dT) found for all samples provides evidence of

their semiconducting properties. A correlation between the

spectrophotometric and conductivity parameters was established. The

mechanism of the conduction process in these complexes was also studied

[131].

Charge transfer complexes between iodine and

hexamethylphosphoramide chalcogenides have been investigated

spectrophotometrically. The equilibrium constant increases on passing from

O to Se but not proportionally to the ionization potential of the atoms. A

linear correlation was found between ΔG (or ΔS) and ΔH. The structure of

the complexes is discussed [132].

The interactions of iodine with oxidized cholesterol,

dipalmitoyllecithin and egg lecithin were studied by the monolayer method.

It was found that iodine is incorporated in the hydrophobic region of the

film, unsaturated bonds being essential for the process. No interaction


83

with hydrophilic groups could be detected. The iodide ion had no effect on

the incorporation. The amount of incorporated iodine was the largest for egg

lecithin, and less for oxidized cholesterol, while dipalmitoyllecithin showed

no measurable effect. This tendency is in accordance with the charge-transfer

complexing abilities of the lipids and the effect of iodine on the conduction

of hydrated lipid samples. Our results thus favour the electronic conduction

mechanism in iodine-doped bilayer systems [133].

The naphthoquinone acceptors form stable charge-transfer

complexes in solutions of aprotic solvents with aromatic hydrocarbons as

donors. From the charge-transfer transition energies of the complexes as well

as from the polarographic half-wave reduction potentials of the acceptors

relative electron affinities of the acceptors are determined. In addition, the

association constant, molar extinction coefficients, oscillator strengths, and

enthalpies of formation of the complexes were obtained from charge-transfer

spectral studies with hexamethylbenzene as donor. The average electron

affinities of 2,3-dichloro-(0·90 eV), 2,3-dichloro-5-nitro-(1·18 eV),

2,3,5,6-tetrachloro-7-nitro-(1·30 eV), 2,3-dicyano-(1·53 eV), 2,3-dicyano-

5-nitro-(1·68 eV), and 2,3-dicyano-5,6-dichloro-7-nitro-1,4-naphthoquinone

(1·75 eV) obtained from the charge-transfer spectral studies clearly show the

cumulative effects of electron-withdrawing substituents on the

naphthoquinone -system [134].

Quantum mechanical calculations show that azidopentazole forms

charge transfer complexes with benzene as well as with nitrobenzene. With

the former it reacts as an electron acceptor whereas with nitrobenzene it

functions as an electron donor. The stabilization energy in both cases was

found to be 4.5 kcal/mol [135].

Charge transfer (CT) complexes formed between 2-amino-

1,3,4-thiadiazole as donor and 2,3-dichloro-5,6-dicyano-p-benzoquinone

(DDQ), p-chloranil (p-CHL), o-chloranil (o-CHL), p-bromanil (BRL) and

chloranilic acid (CHA) as acceptors, have been studied


84

spectrophotometrically. Benesi-Hildebrand and Job continuous variation

methods were applied to the determination of association constant (K), molar

extinction coefficients ( ), dipole moment and stoichiometric ratio,

respectively. The solid CT complexes have been synthesized and

characterized by different spectral methods. The spectral changes reveal that

the CT interaction depends on the type of the acceptors. The magnetic

properties of the various complexes were also investigated. The electrical

properties for the solid CT complexes are measured from which the

activation energies are calculated [136].

In the present study CT complexes of 2-, 3- and 4-Picolines with

(DDQ) 2, 3-dichloro-5, 6-dicyano parabenzoquinone (π-acceptor) and (I2)

Iodine (σ-acceptor) have been investigated spectrophotometrically in three

different solvents (CCl4, CHCl3 and CH2Cl2) at six different temperatures.

The formation constants of the CT complexes were determined by the

Benesi-Hildebrand equation. The thermodynamic parameters were calculated

by Van’t Hoff equation. The ΔH°, ΔG° and ΔS° values are all negative

implying that the formation of studied complexes is exothermic in nature

[137].

Charge transfer complexes of substituted-N-aryl-N-4-(-p-anisyl-

5-arylazothiazolyl)thiourea with 2,3-dichloro-5,6-dicyanobenzoquinones

(DDQ), chloranilic acid (CHLA), chloranil (CHL), bromanil (BRL) and

iodanil (IDL) in methylene chloride were investigated

spectrophotometrically to determine association constants (K), molar

extinction coefficients (ε) and stoichiometric ratio. The effect of

thermodynamic parameters (ΔG* and ΔH) on the stability of the complexes

are discussed and the transition energy (E) of the CT complexes are reported.

The solid CT complexes of the substituted-N-aryl-N-4-(-p-anisyl-

5-arylazothiazolyl)thiourea with the above acceptors have been prepared and

investigated by IR, electronic, 1H NMR and ESR spectroscopy. Nonacidic

acceptors yield complexes having π–π* and n–π* bonding. Acidic


85

acceptors yield complexes having π–π* and proton transfer interaction. The

formation of 1:2 (D: A) complexes is also ascertained [138].

The reactions of the electron donor 1- methylpiperidine (1MP) with

the π- acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ),

tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone

(DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil = CHL) and iodine

(I2) were studied spectrophotometrically in chloroform at room temperature.

The electronic and infrared spectra of the formed molecular charge-transfer

(CT) complexes were recorded. The obtained results showed that the

stoichiometries of the reactions are not fixed and depend on the nature of the

acceptor. Based on the obtained data, the formed charge-transfer complexes

were formulated as [(1MP) (TCNE)2], [(1MP)(DDQ)].H2O, [(1MP)(CHL)]

and [(1MP) I] I3, while in the case of 1MP-TCNQ reaction, a short lived CT-

complex is formed followed by rapid N-substitution by TCNQ forming the

final reaction products 7,7,8-tricyano-8-piperidinylquinodimethane

(TCPQDM). The five solids products were isolated and have been

characterized by electronic spectra, infrared spectra, elemental analysis and

thermal analysis [139].

Electron donor–acceptor molecular complexes of a few phenolic

donors with some quinonoid and tetracyanoethylene acceptors have been

prepared by two different methods, i.e., by simple grinding of the respective

component pair in the solid-state and in solution. Both the methods yielded

identical dark colored 1:1 stoichiometric complexes. Spectral studies

revealed that the complexes are ionic in nature. The g values obtained in

ESR spectral studies for all these molecular adducts vary between 2.000 and

2.022, confirming the free radical nature of the adducts. The electronic

absorption spectral studies proved that the donor–acceptor complexes

formed initially, exhibit new electronic transitions at longer wavelengths, are

less stable and disassociate readily into ionic type of adducts. The absorption

maximum at longer wavelengths, i.e. ≥550 nm, are assigned to the charge


86

transfer complexes, while the new transition at around 410 ± 5 nm is

attributed to the anion radical of the adducts [140].

The kinetics and mechanism of the interaction between 2,3-dichloro-

5,6-dicyano-1,4-benzoquinone (DDQ) and ketoconazole and povidone drugs

has been investigated spectroscopically. In the presence of large excess of

donor, the 1:1 CT complex is transformed into a final product, which has

been isolated and characterized by FT-IR and GC–MS techniques. The rate

of formation of product has been measured as a function of time in different

solvents at three temperatures. The thermodynamic parameters, viz.

activation energy, enthalpy, entropy and free energy of activation were

computed from temperature dependence of rate constants. Based on the

spectro-kinetic results a plausible mechanism for the formation of the

complex and its transformation into final product is presented and discussed

[141].

Three simple, rapid and sensitive spectrophotometric procedures

were developed for the analysis of cephapirin sodium (1), cefazoline sodium

(2), cephalexin monohydrate (3), cefadroxil monohydrate (4), cefotaxime

sodium (5), cefoperazone sodium (6) and ceftazidime pentahydrate (7) in

pure form as well as in their pharmaceutical formulations. The methods are

based on the reaction of these drugs as n-electron donors with the σ-acceptor

iodine, and the π-acceptors: 2,3-dichloro-5,6-dicyano-p-benzo-quinone

(DDQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Depending on the

solvent polarity, different coloured charge-transfer complexes and radicals

were developed. Different variables and parameters affecting the reactions

were studied and optimized. The obtained charge-transfer complexes were

measured at 364 nm for iodine (in 1,2-dichloroethane), 460 nm for DDQ (in

methanol) and 843 nm for TCNQ (in acetonitrile). Ultraviolet–visible,

infrared and 1H-nuclear magnetic resonance techniques were used to study

the formed complexes. Due to the rapid development of colours at ambient

temperature, the obtained results were used on thin-layer chromatograms


87

for the detection of the investigated drugs. Beer's plots were obeyed in a

general concentration range of 6–50, 40–300 and 4–24 μg ml−1 with iodine,

DDQ and TCNQ, respectively, with correlation coefficients not less than

0.9989. The proposed procedures could be applied successfully to the

determination of the investigated drugs in vials, capsules, tablets and

suspensions with good recovery; percent ranged from 96.47 (±1.14) to 98.72

(±1.02) in the iodine method, 96.35 (±1.62) to 98.51 (±1.30) in the DDQ

method, and 95.98 (±0.78) to 98.40 (±0.87) in the TCNQ method. The

association constants and standard free energy changes using Benesi–

Hildebrand plots were studied. The binding of cephalosporins to proteins in

relation to their molar absorptivities was studied [142].

The charge transfer (CT) interactions between poly(N-

vinylcarbazole) (PVK) the various electron acceptors such as tetrachloro-o-

benzoquinone (o-chloranil), tetrachloro-p-benzoquinone (p-chloranil),

tetrabromo-o-benzoquinone (o-bromanil), tetracyanoethylene (TCNE),

2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2,4,7-trinitrofluoranone

(TNF), I2 and Br2 have been investigated by X-ray photoelectron

spectroscopy (XPS). The interactions involving halobenzoquinones, DDQ,

I2 and Br2 resulted in the partial localization of negative charges on the

halogen sites; for that involving TCNE, the negative charges were found to

be partially localized on the cyano group. The CT interaction involving Br2

progressed beyond the mere formation of molecular complex [143].

N,N′-Bis(ferrocenylmethylidene)-p-phenylenediamine 1 and N-

(ferrocenylmethylidene) aniline 2 are readily synthesized by Schiff base

condensation of appropriate units. Iodine (I2), 2,3-dichloro-5,6-dicyano-1,4-

benzoquinone (DDQ), tetrachloro-1,4-benzoquinone (CA),

tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ)

form charge transfer complexes with 1 and 2. IR spectroscopy suggests an

increase in the amount of charge transferred from the ferrocenyl ring to the

oxidant in the order, I2<CA<TCNQ<TCNE≈DDQ. EPR spectra of the


88

oxidized binuclear complexes are indicative of localized species containing

iron- and carbon-centered radicals. The larger Fe(II)/Fe(III) ratio at lower

temperatures is best explained by a retro charge transfer from the iodide to

the iron(III) metal center. There is negligible solvent effect on the formation

of the iodine oxidized charge transfer complex of 1[144].

The formation of charge transfer (CT) complexes of

4-acetamidophenol (commonly called ‘paracetamol’) and a series of

quinones (including Vitamin K3) has been studied spectrophotometrically in

ethanol medium. The vertical ionisation potential of paracetamol and the

degrees of charge transfer of the complexes in their ground state has been

estimated from the trends in the charge transfer bands. The oscillator and

transition dipole strengths of the complexes have been determined from the

CT absorption spectra at 298 K. The complexes have been found by Job’s

method of continuous variation to have the uncommon 2:1 (paracetamol:

quinone) stoichiometry in each case. The enthalpies and entropies of

formation of the complexes have been obtained by determining their

formation constants at five different temperatures [145].

One study was interested to develop a simple, rapid and accurate

spectrophotometric method for determination of sodium flucloxacillin (fluc)

in pure form and pharmaceutical formulations. The charge-transfer (CT)

interactions between sodium flucloxacillin as electron donor and chloranilic

acid (CLA), dichloroquinone 4-chloroimide (DCQ), 2,3-dichloro-5,6-

dicyano-p-benzoquinone (DDQ) and 7,7,8,8 tetracyano-p-quinodimethane

(TCNQ), as π-electron acceptors have been investigated

spectrophotometrically. Different variables affecting the reaction were

studied and optimized. Under the optimum conditions, linear relationships

with good correlation coefficients (0.9979–0.9995) were found between the

absorbance and the concentration of the drug in the range 16–880 μg ml−1.

The proposed methods were applied successfully to the determination of the

examined drug either in pure or pharmaceutical dosage forms with good


89

accuracy and precision. The formation of the CT-complexes and the sites of

interaction were confirmed by elemental analysis CHN, UV–vis, IR, 1H

NMR and mass spectra techniques. Based on Job's method of continuous

variation plots, the obtained results indicate the formation of 1:1 charge-

transfer complexes with the general formula [(fluc)(acceptor)]. Statistical

analysis of the obtained results showed no significant difference between the

proposed method and official method [146].

Interactions of some pyrimidine derivatives, 4-amino-2,6-

dimethylpyrimidine, kyanmethin, (4AP), 2-amino-4,6-dimethylpyrimidine

(2AP), 2-aminopyrimidine (AP), 2-amino-4-methylpyrimidine (AMP), 2-

amino-4-methoxy-6-methylpyrimidine (AMMP), and 4-amino-5-chloro-2,6-

dimethylpyrimidine (ACDP) as electron donors, with iodine (I2), as a typical

σ-electron acceptor, have been studied. Electronic absorption spectra of these

interactions in several organic solvents of different polarities have performed

instant appearance of clear charge transfer (CT) bands. Formation constants

(KCT), molar absorption coefficients ( CT) and thermodynamic properties,

ΔH, ΔS, and ΔG, of these interactions have been determined and discussed

[147].

1.2.5 Inclusion Compound

The history of inclusion compounds dates back to the early nineteenth

century, with Humphrey Davy's discovery of chlorine hydrate, but the field

of inclusion phenomena, or host-guest chemistry, a subfield of

supramolecular chemistry, is growing dramatically, particularly in the last 10

years. This can be seen at a glance in Figure 1 which shows the number of

abstracts appearing in Chemical Abstracts under the term “clathrate” and

“inclusion compound” (Figure 1a) and “supramolecular chemistry”

(Figure 1b).


90

Figure 1 (a) Number of abstracts found for the terms “clathrate” and “inclusion

compound,” for the years 1950-2000. (b) Number of abstracts found for

the term “supramolecular,” for the years 1950-2000.

Inclusion Compound (inclusion complex)

A complex in which one component (the host) forms a cavity or, in

the case of a crystal, a crystal lattice containing spaces in the shape of long

tunnels or channels in which molecular entities of a second chemical species

(the guest) are located. There is no covalent bonding between guest and host,

the attraction being generally due to van der Waals forces. If the spaces in

the host lattice are enclosed on all sides so that the guest species is ‘trapped’

as in a cage, such compounds are known as clathrates or ‘cage’ compounds’.

Guest-Host Systems (Inclusion Compounds)

Inclusion compounds are typical representatives of guest-host

systems and serve as models in the field of molecular recognition. They

consist of an almost rigid host lattice with channel- or cage-like cavities

which are able to incorporate various guest molecules of quite different

chemical structure (cycloalkanes, linear alkanes, polymers). Our present

activities are focussed on the characterization of the guest components in

these systems. At present, various types of inclusion compounds (host

components: urea, thiourea, cyclophosphazenes, cyclodextrins and tri-o-

thymotide) are examined in which guests, such as substituted cyclohexanes,

six-membered ring systems and n-alkanes, are incorporated. The various


91

complexes are characterized by differential calorimetry in order to determine

the actual phase behaviour. Afterwards, dynamic solid state NMR

spectroscopy is used to provide quantitative data about the molecular order

(absolute orientation of the guests, orientational disorder, conformational

order) and dynamics (conformational, reorientational and lateral motions) of

the guest species over a large temperature range that might reach from 5 K to

380 K. So far, primarily 2H NMR investigations are performed on inclusion

compounds with selectively deuterated guest compounds. The molecular

parameters can be obtained from the analysis of variable temperature

lineshape studies, relaxation and 2D exchange experiments employing

suitable simulation programs. From this, there is access to molecular motions

that can cover several orders of magnitude. In addition, 13C MAS NMR and

FT IR spectroscopy is used for the evaluation of the conformational

properties of these systems. It is found that both the molecular dynamics and

the molecular order are strongly affected by the surrounding host matrix. In

particular, this can be seen by the changes of the guest properties in the

vicinity of solid-solid phase transitions which usually are accompanied by a

distortion of the host lattice. The above investigations also provide

information about non-bonded interactions between the various species in

such guest-host systems [148].

Cyclodextrin Inclusion Compounds

Inclusion complexes are formed between cyclodextrins and

ferrocene. When a solution of both compounds in a 2:1 ratio in water is

boiled for 2 days and then allowed to rest for 10 hours at room temperature

orange-yellow crystals form. X-ray diffraction analysis of these crystals

reveals a 4:5 inclusion complex with 4 molecules of ferrocene included in

the cavity of 4 cyclodextrine molecules and with the fifth ferrocene molecule

sandwiched between two stacks of ferrocene - cyclodextrine dimers.

Cyclodextrin also forms inclusion compounds with fragrance

molecules. As a result the fragrance molecules have a reduced vapor


92

pressure and are more stable towards exposure to light and air. When

incorporated into textiles the fragrance lasts much longer due to the slow-

release action [149].

Studies on the Inclusion Compounds of Iodine

Molecular iodine gets polarized in the electric field of the permanent

dipole lying on the host molecules. The intermolecular and the

intramolecular distances along a chain of iodine molecules gets nearly

equalized and an individual molecule becomes indistinguishable with the

formation of a long polyiodine chain. There are several inert matrices which

stabilize polyiodine chain, e.g. amylase cyclodextrins, benzamide, etc. In the

actual systems the chains of polyiodide ions are found instead of resonating

polyiodine chain.

Amylose is chemically homogeneous and a helical structure. It

forms a blue complex with iodine and hence is responsible for the blue color

of the well – known starch – iodine complex.

A birefringence of flow was observed in the starch iodine solution

revealing an anisotropic character. The iodine band at 5390 A is found to

shift towards the red part of the optical spectrum up to 6200 A or more on

this complex. The blue color of

The equilibrium for complex formation by pure PVA at room

temperature with low iodine concentration yields the values–150 kJ mol-1

and – 498 J mol-1 K-1 for the enthalpy and entropy of reaction; for a large

excess of iodine the reaction is complete. Variations in the wavelength of

maximum absorbance of the complexes correlate approximately with their

stability. Complex formation occurs through the alcohol groups of the partly

hydrolysed poly (vinyl acetate) polymers and also the residual acetate groups

of these polymers at the higher iodine concentrations [150].

The spectrophotometric and thermodynamic properties of charge—

transfer complexes of iodine and aromatic hydrocarbons have been

reinvestigated in heptane solvent to make a correlation between the


93

oscillator strength of charge - transfer bands and the heats of formation of

the complexes [151].

1.2.6 Inclusion Compounds of Iodine

The maximum absorbance of the complex is proportional to initial

polymer concentration over the range 0–100 mg dm-3 for PVA polymers

with degrees of hydrolysis in the range 75–100 mole-%, in the presence of

an excess of boric acid, iodine and potassium iodide. Within these limits 1-

mg dm-3 solutions of several commercial and laboratory-prepared polymers

have maximum absorbance 0.035 within ± ca. 3% in 1-cm cells. Sources of

error in the determination of PVA are discussed, and the reduction in the

absorbance at low iodine concentration is examined with respect to the mole-

% hydrolysis. Absorbance measurements on two solutions with,

respectively, high and low reagent concentrations allow the determination of

both the concentration of polymer and its % hydrolysis [152].

An attempt has been made to calculate the thermodynamic as well

as spectrophotometric properties of these complexes free from the influence

of iodine—solvent interaction and the results thus obtained show a good

correlation between the oscillator strength of charge—transfer bands and the

heats of formation of the complexes [153].

1.2.7. Electrical, Magnetic and Optical Properties of Biomolecular

Complexes

The electrical and magnetic properties of misfit layered cobaltocene

complexes of composition (PbS)1.18 (TiS2)2(CoCp2)0.28,

(PbS)1.14(TaS2)2(CoCp2)0.28, and (PbSe)1.12(NbSe2)2(CoCp2)0.27 [Cp = C5H5-]

were investigated. All the pristine chalcogenides studied exhibit a metallic

behavior and a magnetic susceptibility virtually independent of temperature.

Moreover, the Ta and Nb compounds the later impurified with NbSe2

undergo a superconducting transition at low temperatures (TC < 4 K). Upon

cobaltocene intercalation, the Ta and Nb systems behave similarly. The

superconducting transition temperature changes very little and the


94

metallic behavior is preserved: the susceptibility is temperature-

independent, whereas the resistivity increases with increasing temperature.

This is consistent with an electron transfer from the metallocene to the host.

The Ti intercalate behaves markedly differently [154].

Charge-transfer complexes formed by reaction of 2,3,7,8-

tetramethoxychalcogenanthrenes(5,10-dichalcogenacyclo-diveratrylenes,

‘Vn2E2’) with 7,7,8,8-tetracyanoquinodimethane (TCNQ) are prepared and

their structures are determined. Spin concentration, mobilities and gap

energies of the polycrystalline samples are evaluated from e.s.r. intensities

and electrical conductivity measurements. The influence of the different

chalcogen atoms on physical properties is discussed [155].

Recently one has studied a charge transfer interaction between

TCNQ and several surfactants in aqueous solutions (1). In this article we will

report an interaction between cationic surfactant such as dodecylpyridinium

chloride and 2, 5-dichloroquinone from the point of a view of charge transfer

interaction and will compare the results with the results of interaction of

TCNQ [156].

The formation of charge-transfer (CT) complex to increase the

conductivity has been the subject of intense research activity for the past

decades. Those CT complexes have been used as organic semiconductors in

field effect transistors (FETs), charge injection and transport materials in

organic light-emitting diodes (OLEDs) and organic photovoltaic (OPV)

cells. A serial was of new CT complexes with polymers as donor and TCNQ

as acceptor were prepared. The polymers are polycarbazoles with various

content of carbazole moiety in the back chain. The X-ray crystal structure of

the model compound 4,4′-bis (N-carbazolyl)-1,1′-biphenyl(CBP)/TCNQ

complex showed the formation of 2:1 stack structure (with 1:1 carbazole

moiety: TCNQ ratio). The polycarbazole/TCNQ complexes form uniform

films by spin-coating. Devices with the structure of ITO/polycarbazole:

TCNQ complex/Mg: Ag were fabricated. The current–voltage


95

characteristics showed that the devices exhibit much higher conductivity

compared to their analogy ITO/polycarbazole/Mg: Ag structure devices

[157].

Two simple, rapid and sensitive spectrophotometric methods have

been proposed for the determination of lisinopril in pure form and

pharmaceutical formulations. The methods are based on the charge transfer

complexation reaction of the drug with 7,7,8,8,tetracyanoquinodimethane

(TCNQ) and p-chloranilic acid (pCA) in polar media. The lisinopril–TCNQ

and lisinopril–pCA charge transfer complexes dissociate in acetone and

methanol, respectively, and yield coloured TCNQ and pCA radical anions

which are measured spectrophotometrically at 743 and 525 nm. Under

optimised experimental conditions, Beer's law is obeyed in the concentration

range of 2–26 and 25–300 μg ml–1 with molar absorptivity of 1.432 × 104

and 1.192 × 104 l mol–1 cm–1 for TCNQ and pCA methods, respectively.

Both the methods have been applied to the determination of lisinopril in

pharmaceutical dosage forms. Results of analysis are validated statistically

[158].

The synthesis and the redox behaviour of electroactive donor

molecules incorporating an azino spacer group between a benzoselenazole

core and another heterocyclic moiety, either a benzoselenazole one or a

thiazole one, are reported. Neutral complexes were obtained with TCNQ

and, for the first time with dithiadiazafulvalene or diselenadiazafulvalene

derivatives, cation radical salts by electrocrystallization. Crystal structures

data of these complexes are presented and their geometries compared with

those deduced from theoretical calculations [159].

The possibility of opening cyclic iminoethers and forming linear

polymers or copolymers under the action of charge transfer complexes has

been studied. The polymerization of 2-methyl-2-oxazoline, acting as donor,

proceeds in the presence of various organic electron-acceptors such as

tetracyanoethylene 7,7,8,8-tetracyanoquinodimethane and


96

2,4,7-trinitrofluorenone. Initiation takes place by charge transfer complexes

formed between the monomer and the acceptor. With acceptors which

possess polymerizable bonds, i.e. tetracyanoethylene and

tetracyanoquinodimethane, copolymers are obtained [160].

The particular study was interested to develop a simple, rapid and

accurate spectrophotometric method for determination of sodium

flucloxacillin (fluc) in pure form and pharmaceutical formulations. The

charge-transfer (CT) interactions between sodium flucloxacillin as electron

donor and chloranilic acid (CLA), dichloroquinone 4-chloroimide (DCQ),

2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and 7,7,8,8 tetracyano-p-

quinodimethane (TCNQ), as π-electron acceptors have been investigated

spectrophotometrically. Different variables affecting the reaction were

studied and optimized. Under the optimum conditions, linear relationships

with good correlation coefficients (0.9979–0.9995) were found between the

absorbance and the concentration of the drug in the range 16–880 μg ml−1.

The proposed methods were applied successfully to the determination of the

examined drug either in pure or pharmaceutical dosage forms with good

accuracy and precision. The formation of the CT-complexes and the sites of

interaction were confirmed by elemental analysis CHN, UV–vis, IR, 1H

NMR and mass spectra techniques. Based on Job's method of continuous

variation plots, the obtained results indicate the formation of 1:1 charge-

transfer complexes with the general formula [(fluc)(acceptor)]. Statistical

analysis of the obtained results showed no significant difference between the

proposed method and official method [161].

Charge transfer complexes of tetracyanoquinodimethane (TCNQ)

(namely TTT-TCNQ and TTT-TCNQ2), are prepared with the radical cation

of tetrathiotetracene (TTT). The two salts are conductive at room

temperature and show (at low temperatures) a quasi constant paramagnetism

and a linear specific heat term. This behaviour which is characteristic of a


97

magnetic ground state as already found in other salts with regular TCNQ

stacks is discussed [162].

Study of the synthesis of four asymmetric partially selenated

tetrathiafulvalenes (TTFs), EDS-TTF Ia (ethylenediselena-TTF), EDS-

DMTTFIb (EDS-dimethyl-TTF),EDS-DCMTTFIIa (EDS-dicarbomethoxy-

TTF) and EDS-DHMTTF IIb (EDS-dihydroxymethyl-TTF), using different

routes is depicted. The preparation of both a charge transfer complex, Ib-

TCNQ (Ib-tetracyanoquinodimethane), and a new radical cation salt, IIb-

ClO4, is presented [163].

The crystal structure for the charge transfer complex of the title

hydrogen-bonded (H-bonded) charge-transfer (CT) complex indicates and

alternated stacking of the naphthalene moiety and chloranil, which contain

no direct H-bonding between the donor and the acceptor. The complex

showed only a little change in stretching frequencies to the applied pressure.

Therefore, as a design strategy for new interesting materials, it seems

important to obtain CT complexes with direct H-bonding between the donor

and acceptor [164].

The 3,6-dicyano-1,2,4,5-tetrazine and the 2,4,6-tricyano- -triazine

are found good electron acceptors for forming charge transfer complexes; the

former gave with tetrathiofulvalene a 1:1 charge transfer complex of good

electric conductivity, thus proving that the attainment of aromaticity in the

radical anion is not a necessary requisite for conductivity [165].

The new charge transfer complex t-TTF-TCNQ, whose unsymmetric

cation is intermediate between TTF and HMTTF, presents a regular stacking

of both donor and acceptor chains. We show that this compound has a

metallic behavior at high temperatures and undergoes one metal-insulator

transition near 81 K. Its electrical and magnetic properties are examined in

connection to this phase transition and the effective dimensionality [166].

The electrical and magnetic properties of misfit layered cobaltocene

complexes of composition (PbS)1.18(TiS2)2(CoCp2)0.28,


98

(PbS)1.14(TaS2)2(CoCp2)0.28, and (PbSe)1.12(NbSe2)2(CoCp2)0.27 [Cp = C5H5-]

were investigated.The complex undergoes a metal semiconducting transition

below 70 K, and the magnetic data are significantly temperature-dependent

[167].

The charge transfer interaction between hexylamine (HA) and

7,7,8,8-tetracyanoquinodimethane (TCNQ) and the fluorescence behaviour

of the charge transfer complex were studied in non-aqueous solvents

(dichloromethane, chloroform, carbon tetrachloride, heptane, iso-octane,

decane and cyclohexane) and in sodium bis(2-ethyl-hexyl)sulphosuccinate

(AOT)-cyclohexane reverse micellar medium and water-AOT-cyclohexane

microemulsion medium. A 1:1 charge transfer complex between HA and

TCNQ was formed, and its binding strength was estimated by the Benesi-

Hildebrand equation. The charge transfer complex was fluorescent; this was

hindered by AOT and by a higher concentration of HA. The results were

analysed using the Stern-Volmer equation [168].

Charge transfer (CT) complexes of tetrathiafulvalene bisannulated

24-crown-8 (1) with tetrafluoro (F4)-, 2,5-dibromo (Br2), 2,5-dichloro (Cl2)-

tetracyanoquinodimethane (TCNQ), and 2,3-dicyano-5,6-dichloro-p-

benzoquinone (DDQ) were prepared. The electronic ground state of the

acceptor varies from the completely ionic to partial charge transfer state.

Within the CT complexes the donor 1 was completely oxidized to the

divalent cationic state 12+. The molecular conformation of 12+ in Cl2-TCNQ

complex was an intra-dimer form folded over the flexible part of

macrocyclic 24-crown-8 [169].

A new charge-transfer compound PANT-TCNQ (PANT=9-

phenylanthracene, TCNQ=7,7,8,8-tetracyanoquinodimethane) has been

prepared from 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 9-

Phenylanthracene in dichloromethane at room temperature. The conductivity

of the compound, at room temperature is 2.08×10−9 S cm−1. The temperature-

dependence of electrical conductivity of the PANT-TCNQ compound


99

exhibits a semiconductor behavior. The optical spectra indicate that the

compound has a direct band gap (2.46±0.15 eV) due to direct transition

[170].

The dielectric constant of the phenothiazine-iodine system in

benzene has been determined at 30°C and 40°C on a dipolemeter operating

at a radiofrequency of 1MHz. Simultaneous determination of density had

been made on a calibrated pyknometer. The dipole moment of the donor, μD

(calc.), has been compared with the dipole moment μN of 1:1 molecular

complex formed between donor-acceptor at two temperatures. The μN values

at 30°C & 40°C are for chloropromazine-I2 13.4 D & 12.6 D;

prochloroperazine -I2, 13.5 D & 11.6 D; promazine-I2, 21.2 D & 17.3 D;

pericyazine -I2, 12.9 D & 10.5 D and thioproperazine -I2, 19.6 D & 12.0 D;.

High values of E HOMO for the donor molecule suggest that the

phenothiazines are good donors and the possibility of molecular association

with σ-acceptor iodine is from the active site at S atom in each donor. The

extent of molecular association decreases with the increase in temperature

[171].

1,5-Dimethoxynaphthalene (1,5-DMN) and 2,3-DMN were

synthesized using the phase transfer catalysis (PTC) technique. Their

fluorescence is quenched by 7,7,8,8 -tetracyanoquinonedimethane (TCNQ)m

picric acid, chloranil and bromanil. The quenching rate constant values kq

were estimated. It was found that the rate of quenching of 2,3-DMN is

slower than that of 1,5-DMN by the same acceptors. The role of the solvent

polarity on the efficiency of fluorescence quenching og 1, 5-DMN with

picric acid was also studied. Spectral studies show that 2,3-DMN forms 1:1

charge transfer complexes (CTCs) with different π-acceptors in

dichloromethane, while 1,5-DMN forms contact CTCs with TCNQ,

chloranil and bromanil and 1:1 CTCs with tetracyanoethylee (TCNE) and

picric acid. The equilibrium constants and thermodynamic standard reaction

quantities of the CTCs were estimated [172].


100

Infrared spectra of the charge transfer complexes between nine

organic sulfides (as well as diethylselenide) with iodine were recorded

between 1500 and 400 cm−1 in CS2 and CCl4 solutions and in the region 600-

50 cm−1 in C6H12 and C6H6 solutions. Raman spectra of the complexes were

recorded below 600 cm−1. For each system, i.r. and Raman bands in the 200-

160 cm−1 were assigned to the I---I stretching mode of the complex.

Additional i.r. bands below 160 cm−1, absent in Raman, were ascribed to

intermolecular S---I stretching vibrations. The integral intensities of these

bands were determined and correlated with the thermodynamic functions.

Some Raman active fundamentals of 1,4-dithiane became i.r. active in the

iodine complex in accordance with a break down of the C2h symmetry. A

force constant calculation was carried out for the dimethylsulfide-iodine

complex and simplified calculations of the three point mass models were

made for all the systems [173].

Optical characterization of the charge transfer complex of

2,9,16,23-tetra neopentoxyphthalocyaninatozinc(II) with 2,3-dichloro-5,6-

dicyano-p-benzoquinone (DDQ) has been carried out using the transmittance

T(λ) and reflectance R(λ) spectra. The optical band gap and Urbach energies

were calculated from the optical absorption spectra. The optical absorption

spectra show that the absorption mechanism is a direct transition. The optical

constants (refractive index n, extinction coefficient k, dielectric constants

ε1, ε2) of the compound were determined. Optical dispersion parameters

Eo and Ed developed by Wemple–DiDmenico were calculated [174].

Formation of molecular charge transfer (CT) complexes of some

polyenes with iodine has been confirmed by spectroscopic studies. The dark

and photoconductive properties of these CT complexes have been

investigated in a sandwich cell. Both the dark and photoconductivity

increases by several orders of magnitude by complex formation. The

measured thermal activation energy is identical for dark and

photoconduction in the complexes. Similar photoconduction action


101

spectra in pure and in iodine-complexed polyenes suggest the same

photocarrier generation mechanism to be operative in both the cases.

Spontaneous generation of carriers by CT interaction and their migration by

trapping and detrapping mechanisms seems to be responsible for electrical

conduction in the CT complexes [175].

It is to be described that how single-molecule sensitive

fluorescence resonance energy transfer (FRET) and photoinduced electron

transfer (PET) reactions can be successfully applied to monitor

conformational dynamics in biopolymers. Single-pair FRET experiments are

ideally suited to study conformational dynamics occurring on the nanometer

scale, e.g. during protein folding or unfolding. In contrast, conformational

dynamics with functional significance, for example occurring in enzymes at

work, often appear on much smaller spatial scales of up to several

Angströms. Our results demonstrate that selective PET-reactions between

fluorophores and amino acids or DNA nucleotides represent a versatile tool

to measure small-scale conformational dynamics in biopolymers on a wide

range of time scales, extending from nanoseconds to seconds, at the single-

molecule level [176].

The charge-transfer (CT) reaction between 7,7,8,8-

tetracyanoquinodimethane (TCNQ) as a π-electron acceptor and cinnarizine,

analgin, norfloxacin as electron donors have been studied by

spectrophotometric method. The charge transfer complexes between TCNQ

and these drugs have stable blue color, therefore a simple, rapid, accurate

and sensitive method for determination of these drugs has been developed.

The optimization of the experimental conditions is described. Beer’s law is

obeyed in the ranges 2–18, 2–18 and 4–32 μg/ml for cinnarizine, analgin and

norfloxacin, respectively. The apparent molar absorptivity of CT complexes

at 743 nm is 1.58×104, 1.71×104 and 8.91×103 l/mol per·cm, respectively.

The composition of all these CT complexes are found to be 1:1 by different

methods. The relative SDs are less than 3% (n=10). The proposed


102

method has been applied to the determination of these drugs in their each

pharmaceutical dosage forms with satisfactory results [177].

The magnetic properties of the charge transfer salts Qn(TCNQ)2,

Cs2(TCNQ)3 and TTF—TCNQ in the form of single crystals and after strong

pressing or grinding to a fine powder, which introduces lattice defects and

increases the surface area. It is found that for the former two compounds

pressing or grinding leads to a non-linear, saturating component in the

magnetisation field curves, whereas the effect is absent for TTF—TCNQ. It

is suggested that this behaviour could arise from strongly coupled localised

spins at the surface, i.e. surface magnetism in these materials [178].

A series of the charge-transfer compounds determined as 1:1

stochiometric ratio by Job method has been prepared with the interaction of

7,7,8,8-tetracyanoquinodimethane (TCNQ) and anthracene, 9-

methylanthracene, 9-bromanthracene in dichloromethane at room

temperature. The values of the optical band gap Eg, and Urbach energy E0

were determined from the optical absorption. The optical absorption

measurements indicate that the absorption mechanism is due to allowed

direct transitions for the compounds and it is evaluated that the optical band

gap and Urbach energy values changes with incorporating R group in the

compounds. The optical constants such as refractive index n, and extinction

coefficient k and real and imaginary part of dielectric constant and optical

conductivity of the compounds were calculated. Eg and E0 reflect the

influence of different types of disorder on the absorption spectra processes.

Thus, a correlation between Eg and E0 was made. Form this correlation, G

value that is proportional to the second-order deformation potential and, Ef

value that depend on local coordination, parameters are found to be 0.29 and

2.37 eV, respectively [179].

In the charge-transfer (CT) solubilization of 7,7,8,8-

tetracyanoquinodimethane (TCNQ) by homogeneous nonionic surfactants,

the amount of solubilized TCNQ and the cloud point and electric


103

conductivity of the CT complex solution were investigated. The amount of

solubilized TCNQ was spectrophotometrically determined by using the color

development due to the CT interaction between TCNQ and the nonionic

surfactant micelle. The cloud point and electric conductivity of the micelle

solutions solubilizing TCNQ increased with increasing TCNQ concentration.

These phenomena were explained in terms of partial ionization in the

hydrophilic portion of nonionic surfactants attributed to the charge transfer

from oxygen atoms in polyethyleneoxide chains to TCNQ [180].

Preparation of conductive polycarbonate and polystyrene films

using tetrathiotetracene (TTT) and TCNQ with different input molar ratio of

TTT: TCNQ even as high as 7:1 i.e. with big excess of the donor (TTT) is

reported. Conductive systems (conductivity of the order of 10−3 − 10−4 S/cm)

containing only 0.037wt.% of TCNQ are obtained. Conducting polymers

with so low content of TCNQ have never been obtained before. The total

additive content (TTT+TCNQ) in these system is also very low (in some

cases less than 0.4wt. %) and the content of 1:1 CT complex is of the order

of 0.1wt. %. Scanning electron microscope pictures show that the conductive

network in these systems consist of very thin (ca.50nm in diameter)

whisker-like crystallites of the additive [181].

The formal of 1:1 charge transfer complex (BTV-TCNQ) have been

studied by the UV-Vis, FT-IR, XPS and ESR spectroscopies. The results

show that partial charge transfers occur between π-donor and π-acceptor, the

room temperature conductivity is 33Scm−1, however, the temperature-

dependence conductivity indicates that the CT complex shows

semiconductor behavior, the activation energy for conduction is 0.06eV

[182].

Copper (II) and nickel (II) biguanides and O-alkyl-1-amidinourea

can act as donors for the formation of charge transfer (CT) adducts with I2

and tetracyanoquinodimethane (TCNQ) as acceptors. Iodine adducts are

characterized both in solid and solution states whereas TCNQ adducts


104

obtain only in solution. Appearance of a broad band at 355 nm for iodine

adducts and at 335 nm for TCNQ adducts and shifting of i.r. frequencies

support the formation of donor acceptor associates. Elemental analysis

establishes 1:1 stoichiometry of the solid adducts. The K and values

determined by modified Benesi—Hildebrand, Scott and Rose—Drago

equations are found to be of the order of 104 and 103 respectively at 298 K in

methanol [183].

Glucose oxidase entrapped in the layer near the electrode surface of

conductive charge-transfer complexes or on glassy carbon electrodes

modified by tetracyano-quinodimethane (or by its K-salt) catalyzes the

electrochemical oxidation of glucose in the interval from −0.05 to 0.4 V

(vs. AgAgCl). When enzyme electrodes operate in a switched-off state the

charge is accumulated in the complexes. The components of the complexes

oxidize the active center of glucose oxidase. A scheme for electrocatalytic

oxidation of glucose by mediators is proposed [184].

Electrical conductivity and spectral properties (UV-VIS absorption

and especially the temperature dependence of IR absorption) are studied for

the simple salt 1-methyl-3-propyl-imidazolium 7,7,8,8-tetracyano-p-

quinodimethane (MPI+ TCNQ−√. The temperature dependence of the IR

absorption coefficient for the bands due to activation of the mode Ag is

discussed in terms of changes in energy level population, geometry, and

electron interactions. The temperature dependence of the absolute number of

the TCNQ dimers in the triplet state is measured independently using the

EPR method. The temperature dependences of the ground (singlet) state

population of the TCNQ dimers and of the singlet—triplet energy separation

J(T) = [(0.18 ± 0.01)-(2.5 ± 0.5) × 10−4 T] eV were determined from this

measurement. These values lead to an unrealistically large value of the linear

temperature expansion coefficient within the framework of the simple

isolated model of dimers. Therefore, the weakly interacting model of dimers

should be preferred [185].


105

The interaction between ketoconazole and povidone drugs with

iodine was found to proceed through initial formation of a charge transfer

(CT) complex as an intermediate. The stoichiometry of the complex was

found to be 1:1 in the case of povidone–iodine system and 1:2 in the case of

ketoconazole–iodine system and the same was confirmed by thermal

(TGA/DSC) studies. The formation of I3− species was confirmed by

electronic and laser Raman spectra. The three peaks appeared in Raman

spectra, of the isolated adducts corresponds to νas(I–I), νs(I–I) and δ(I3−),

confirmed the presence of asymmetric I3− ion. The rate of the interaction has

been measured as a function of time and solvent. The pseudo-first-order rate

constants at various temperatures for the interactions were measured and the

activation parameters (ΔG#, ΔS# and ΔH#) were computed. Based on the

spectral and spectrokinetic evidences a mechanism involving the formation

of a polar intermediate and its conversion to the final product has been

proposed and discussed [186].

The influence of complexing agents such as methanol, ethanol, 1-

propanol, 1-butanol, 1-pentanol, 1-hexanol, cyclohexanol and 2-octanol on

the formation of a blue coloured amylose · iodine complex (pH 4.8), under

suboptimum concentrations of iodine and in the absence of potassium iodide,

is studied by recording the absorbance at 640 nm. A drop in absorbance at

640 nm accompanied by a blue shift in the spectrum (580–640 nm) was

observed at higher concentration of the complexing agents. This behaviour

of amylose partially complexed with iodine appears to be due to ligand-

induced structural changes in the amylose chain. The fall in absorbance at

640 nm observed when the temeprature of amylose · Ioidine complex in the

presence of complexing agents is raised, and the subsequent regeneration of

the absorbance on cooling, indicates the possible helix to random coil

transition of the amylose chain in an aqueous system [187].

The electron donor acceptor complexes of iodine with

phospholipids such as phosphatidylethanolamine (PE),


106

lysophosphatidylcholine (LPC) and sphingomyelin (SM) have been studied

spectrophotometrically in cyclohexane solution as well as in solid film. From

the results, the electron donating properties of phospholipids towards iodine

have been compared including the earlier results of iodine complex with

phosphatidylcholine (PC). Thus the electron donor strengths of the

phospholipids studied are in the order: SM > PC > LPC > PE. The calculated

ionization potentials of phospholipids from the charge-transfer bands are in

the range 6.72–6.79 eV [188].

1.3 Absorption of radiation by semiconductors

The fundamental absorption in a semiconductor refers to interband

(band –to – band) or to exciton transition. There is excitation of an electron

from the valence band to conduction band. There is a rapid increase in

absorption in the band gap region of frequency. There is threshold near Eg

(band gap) and this is called absorption edge.

The moment of a photon is very small compared to the momentum of

the crystal. The phonon absorption process conserves the momentum of an

electron. The absorption coefficient is proportional the probability of

transition and densities of states of initial and final states [189].

1.3.1 Allowed irect transition

In the absorption transitions between two

direct valleys all the momentum

conserving transitions are allowed. The

initial and final states are related by

Ef = h - Ei for parabolic bands as shown

in the Figure 1.

Figure 1


107

(Ef – Eg) = 2 2

e2m *

k and Ei = 2 2

h2m *

k

Therefore, gh E = 2 2 2 2

* *

1 1

2 2h e r

k k

m m m

The density of states is given by

N (h ) d (h ) = 2

3

8

(2 )

k dk

= 3/ 2

1/ 22 3

(2 )( ) ( )

2

rg

mh E d h

where mr is the reduced mass. This shows that (h) = A (h-Eg)1/2, A is a

constant. Thus in allowed direct transition the absorption coefficient is

proportional to (h - Eg)1/2 .

1.3.2 Forbidden direct transition

In some materials, quantum selection rules forbid direct transitions at

k=0 but allow them at k 0. The transition probability increases with k2,

which is proportional to (h - Eg). The density of states is proportional to (h

- Eg)1/2. Thus the absorption coefficient is proportional to (h - Eg)3/2 ,

i .e, h = A (h - Eg)3/2 where A is given by A = B

h, here B is a constant.

Thus,

h = B (h - Eg)3/2.

1.3.3 Indirect transitions

When a transition requires a change in both energy

and momentum and since a photon can not provide momentum, a

two – step process occurs. A phonon is a quantum of lattice

vibration. A phonon of the required momentum change is used in

a two – step process as shown in the Figure 2.

If Ep is the phonon energy, he= Ef - Ei + Ep , ha = Ef - Ei - Ep

for emission and absorption of phonons.


108

The densities of states at Ei and Ef are

given by

N (Ei) = 2 3

1

2 (2mh*)3/2 Ei 1/2 and

N (Ef) = 2 3

1

2 (2me*)3/2 (Ef – Eg)1/2

Figure 2

Thus, N (Ef) = 2 3

1

2 (2me*)3/2 (h- Eg Ep+ Ei)

1/2

By integrating above all possible combinations of states,

a (h) = 2

g p

p

B

A (h - E - E )E

exp 1k T

and e (h) = 2

g + p

p

B

A (h - E E )E

1 expk T

The total is given by = e + a .

a is valid for h Eg – Ep and e is

valid for h Eg + Ep .

Thus there is break in the straight

line plot of 1/2 vs h. There fore

there is a change in slope as indicated

in the Figure 3.

Figure 3

1.3.4 Band tailing

There is a perturbation of the bands by the formation of

tails of states extending the bands into the forbidden energy gap.

This happens due to impurities. An ionized donor exerts

attractive and repulsive forces on electrons and holes,

respectively. The densities of states lead to conduction band

states at lower potential and valence band states at higher


109

potential. At high concentrations of impurities, the impurity

states from a band whose distribution tail in to the energy gap.

Also there is deformation potential. A local mechanical strain is generated by

impurities. Either there is compression or dilation. Compression increases

energy gap and dilation reduces energy gap. Dislocations generate similar

effect.

Because of the above – discussed band tailing effects, one finds an

exponentially increasing absorption edge rather than a sharp cut – off with

step function. It is found that (ln ) 1

( ) B

d

d h K T

and this is called Urbach’s rule.

The final states form an exponential tail described by Nf = No e E/Eo. Here Eo

is called the width of the tail and is calculated by 1

(ln )

( )o

dE

d h

1.5.5 Burstein – Moss shift

If a semiconductor is heavily doped, the Fermi level is inside the band

(the conduction band in an n – type material) by a quantity n as shown in

the Figure 4.

The states below n are already filled, and

transitions to states below Eg + n are

forbidden. Thus absorption edge shift to

higher energies by about n. This shift in

the absorption due to band filling effect is

called Burstein – Moss shift. In n- type

germanium only phonon emission occurs

and edge is shifted to Eg + Ep +n.

Figure 4


110

In heavily doped indirect – gap semiconductors, momentum is conserved by

electron – electron scattering or impurity scattering. The scattering

probability is proportional to the number N of scatters and

= AN (h- Eg - n)2 where A is constant. Heavy doping leads to an

effective shrinkage of the energy gap.

1.3.6 Free – carrier absorption

The Drude model leads to f 2 where f is the absorption by free

carrier and is the wavelength of light. Thus in a metal f is proportional to

2.However, in a semiconductor the absorption by free carrier in a

conduction band occurs in a region h Eg and is proportional to p where p-

can range from 1.5 – 3.5. The electron must make a transition to a higher

energy state within the same valley for absorbing a photon. The transition

requires an additional interaction for conserving momentum. The change in

momentum can be provided by interaction with phonons or ionized

impurities. The collision with the semiconductor lattice results in scattering

by acoustic phonon leading to absorption increasing as 1.5. Scattering by

optical phonons gives a dependence of 2.5while scattering by ionized

impurities gives dependence on 3 or 3.5.

In general, when all the three processes contribute and resultant

absorption coefficient is given by,

f = A 1.5 + B 2.5 + C 3.5 where A, B and C are constants.

The dominant mode of scattering will depend on the impurity concentration.

It is found by experience that f 3 for neutral impurities, f 3.5

for negatively charged impurities, f 4 for positively charged hydrogen –

like impurities and f 5 for impurity band scattering.

From a detailed account of light absorption by electrons [190] in

localized states, 2 2 2 2 4[ 2 *( ]

I

I

E

m E


111

Where IE is the impurity ionization potential. The quantity -1/2 is equal to

the distance at which the probability of locating the electron decreases e

times. increases linearly with frequency for 2 IE and passes through a

maximum then decreases at first slowly 1( ) but much faster in the end.

For IE very less than , 5f or 5

f from the above equation.

The theory of absorption of radiation of the hydrogen atom may be

applied to the localized states with hydrogen – like spectrum, then the

absorption coefficient is given by

410 2 2exp 4 1 arctan 1

2

3 *1 exp 2 1

I I

Iloc

I I

E E

e EN X

ncm E E

where n is refractive index, IE is the impurity ionization energy and *m is the

effective mass. For 4 4,I fE for hydrogen – like impurities from

the above equation.


112

REFERENCES

[01] J Szejtli (1988). "Cyclodextrin Technology" Vol 1. Springer, New

York" ISBN 978-90- 277-2314-7

[02] A Biwer, Antranikian G, Heinzle E. Enzymatic production of

cyclodextrins. Appl Microbiol Biotechnol, 2002; 59: 609-17.

[03] Online Dictionary, Thesaurus and Encyclopediaz.

[04] L Rosenfeld, (Apr 1997). "Vitamine-vitamin. The early years of

discovery. Clin Chem, 43 (4): 680–5.

[05] L E Rohde LE, de Assis MC, Rabelo ER (January 2007). "Dietary

vitamin K intake and anticoagulation in elderly patients". Curr Opin

Clin Nutr Metab Care 10 (1):

[06] Grisham, M Charles; H Reginald Garrett (1999). Biochemistry,

Philadelphia: Saunders College, Pub. pp. 426–7.

[07] D Lilley (2005). "Structure, folding and mechanisms of ribozymes".

Curr Opin Struct Biol 15 (3): 313–23.

[08] The Catalytic Site Atlas at The European Bioinformatics Institute.

Retrieved 4 April 2007.

[09] M V Rodnina, W Wintermeyer (2001). "Fidelity of aminoacyl-tRNA

selection on the ribosome: kinetic and struct. Mechanisms", Annu Rev

Biochem. 70: 415–35.

[10] Boyer, Rodney (2002) [2002]. "6". Concepts in Biochemistry (2nd

ed.). New York, Chichester, Weinheim, Brisbane, Singapore, Toronto,

John Wiley & Sons, Inc.pp. 137–8.

[11] Wagner, L Arthur, 1975. Vitamins and Co -enzymes. Krieger Pub Co.

[12] L Masgrau, A Roujeinikova, L O Johannissen, P Hothi, J Basran, K E

Ranaghan, A J Mulholland, M J Sutcliffe, N S Scrutton, Leys D.

(2006). "Atomic Description of an Enzyme Reaction Dominated by

Proton Tunneling". Science 312 (5771): 237–41.


113

[13] J S Berg, B C Powell, Cheney RE (1 April 2001). "A millennial

myosin census". Mol. Biol. Cell 12 (4): 780–94.

[14] E A Meighen (1 March 1991). "Molecular biology of bacterial

bioluminescence". Microbiol. Rev. 55 (1): 123–42.

[15] N J Faergeman, J Knudsen (April 1997). "Role of long-chain fatty

acyl- CoA esters in the regulation of metabolism and in cell

signalling". Biochem. J. 323 (Pt 1): 1–12.

[16] C M Carr, P S Kim (April 2003). "A spring-loaded mechanism for the

conformational change of influenza hemagglutinin". Cell 73

(4): 823–32.

[17] Cornish-Bowden, Athel. Fundamentals of Enzyme Kinetics.

(3rd edition), Portland Press, 2004.

[18] H Segel Irwin, Enzyme Kinetics: Behavior and Analysis of Rapid

Equilibrium and Steady-State Enzyme Systems. (New Ed. edition),

Wiley-Interscience, 1993.

[19] Fersht, Alan (1999). Structure and mechanism in protein science: a

guide to enzyme catalysis and protein folding. San Francisco:

W H Freeman.

[20] M I Page, and A Williams (Eds.). Enzyme Mechanisms. Royal Society

of Chemistry, 1987.

[21] J Hummel, M Niemann, S Wienkoop, et al. (2007). "ProMEX: a mass

spectral reference database for proteins and protein phosphorylation

sites". BMC Bioinformatics 8: 216.

[22] J R Knowles (1980). "Enzyme-catalyzed phosphoryl transfer

reactions". Annu. Rev. Biochem. 49: 877–919.

[23] Berg, M Jeremy; Tymoczko, John L., & Stryer, Lubert (2007).

Biochemistry (6th ed.). New York: W. H. Freeman. p. 413.

[24] Stryer, Lubert (2002). Biochemistry (5th ed.). New York: W.H.

Freeman and Company.


114

[25] P R Rich (2003). "The molecular machinery of Keilin's respiratory

chain". Biochem. Soc. Trans. 31 (Pt 6): 1095–105.

[26] Maitland, Jr Jones (1998). Organic Chemistry. W W Norton & Co Inc

(Np). p. 139.

[27] E Fahy, Subramaniam S, Brown H A, et al. (2005). "A comprehensive

classification system for lipids". Journal of Lipid Research 46 (5):

839–61.

[28] C W McLaughlin, S Johnson, MQ Warner, D LaHart, J D Wright,

(1993). Human Bio. and Health. Englewood Cliffs, New Jersey, USA:

Prentice Hall

[29] J E Vance, Vance DE. (2002). Biochemistry of Lipids, Lipoproteins

and Membranes. Amsterdam: Elsevier.

[30] F Fezza, C De Simone, D Amadio, M Maccarrone (2008). "Fatty acid

amide hydrolase: a gate-keeper of the endocannabinoid system".

[31] X Wang (2004). "Lipid signaling". Current Opinions in Plant Biology

7 (3): 329–36. K M Eyster (2007). "The membrane and lipids as

integral participants in signal transduction". Advances in Physiology

Edu. 31: 5–16

[32] A Helenius, M Aebi (2001). "Intracellular functions of N-linked

glycans". Science 291: 2364–69.

[33] F L Hoch (1992). "Cardiolipins and biomembrane function".

Biochimica et Biophysica Acta 1113 (1): 71–133.

[34] S White, J Zheng, Y Zhang (2005). "The structural biology of type II

fatty acid biosynthesis". Annual Review of Biochem. 74: 791–831.

[35] J Barciszewski, B Frederic, C Clark (1999). RNA biochemistry and

biotechnology. Springer. pp. 73–87

[36] M S Elliott, R W Trewyn (1983). "Inosine biosynthesis in transfer

RNA by an enzymatic insertion of hypoxanthine". J. Biol. Chem.

259 (4): 2407–10.


115

[37] J M Berg, J L Tymoczko, L Stryer (2002). Biochemistry (5th ed.).

WH Freeman and Company. pp. 118–19, 781–808.

[38] P Ahlquist (2002). "RNA- Dependent RNA Polymerases, Viruses,

and RNA Silencing". Science 296 (5571): 1270–73.

[39] M Mandelkern, J Elias, D Eden, Crothers D (1981). "The dimensions

of DNA in solution". J Mol Biol 152 (1): 153–61

[40] S Gregory; Barlow, KF; McLay, KE; Kaul, R; Swarbreck, D;

Dunham, A; Scott, CE; Howe, KL et al. (2006). "The DNA sequence

and biological annotation of human chromosome 1". Nature 441

(7091): 315–21.

[41] R Wing, H Drew, T Takano, C Broka, S Tanaka, K Itakura, R

Dickerson (1980). "Crystal structure analysis of a complete turn of

B-DNA". Nature 287 (5784): 755–8.

[42] Atkins, P J; Shriver, D F (1999). Inorganic chemistry (3rd ed. ed.).

New York: W.H. Freeman and CO.

[43] H Benesi, J Hildebrand, A Spectrophotometric Investigation of the

Interaction of Iodine with Aromatic Hydrocarbons, J. Am. Chem. Soc.

71(8), 2703-07 (1949).

[44] Mulliken, R S; Person, W. B. (1969). Molecular Complexes. New

York and London: Wiley-Interscience.

[45] Tarr, Donald A; Miessler, Gary L. (1991). Inorganic chemistry

(2nd ed.). Englewood Cliffs, N.J: Prentice Hall.

[46] Kalyanasundaram, K (1992). Photochemistry of polypyridine and

porphyrin complexes. Boston: Academic Press.

[47] Vogler, A; Kunkely, H (2000). "Photochemistry induced by metal-to-

ligand charge transfer excitation". Coord. Chem. Rev. 208: 321.

[48] Robert J Lancashire. "Selection rules for Electronic Spectroscopy".

University of the West Indies, Mona.

[49] Duoli Sun, Sergiy V. Rosokha, Jay K. Kochi (2005). "Through-Space


116

(Cofacial)–Delocalization among Multiple Aromatic Centers: Toroidal

Conjugation in Hexaphenylbenzene-like Radical Cations". Angew.

Chem. Ed. 44 (32): 5133-36.

[50] Y Okamoto and W Brenner Organic Semiconductors, Rheinhold

(1964)

[51] H Akamatsu, H Inokuchi, and Y Matsunaga (1954). "Electrical

Conductivity of the Perylene–Bromine Complex". Nature 173: 168.

[52] Sunanda Aditya, Spectrochimica Acta Part A: Molecular

Spectroscopy, Volume 44, Issue 10, 1988, Pages 941-942

[53] Chizuko Kabuto, Yoshimasa Fukazawa, Takanori Suzuki, Yoshiro

Yamashita, Tsutomu Miyashi, Toshio Mukai Tetrahedron Letters,

Volume 27, Issue 8, 1986, Pages 925-928

[54] R N Lyubovskaya, D V Konarev, E I Yudanova, O S Roschupkina,

Yu.M. Shul'ga, V N Semkin, A Graja Synthetic Metals, Volume 84,

Issues 1-3, January 1997, Pages 741-742

[55] Kazuharu Suzuki, Masaaki Tomura, Shoji Tanaka, Yoshiro

Yamashita, Tetrahedron Letters, Volume 41, Issue 43, 21 Oct. 2000,

Pages 8359-8364

[56] W B Carper, T S Chang, Spectrochimica Acta Part A: Molecular

Spectroscopy, Volume 28, Issue 10, October 1972, Pages 1823-1828

[57] Spectrochimica Acta Part A: Molecular Spectroscopy, Volume 25,

Issue 1, January 1969, Pages 193-197

[58] E Schulek, K Burger, Talanta, Vol.1, Issues 1-2, July 1958,P.147-152

[59] P Ruostesuo, K. Peltola, U Salminen, A -M. Häkkinen Spectrochimica

Acta Part A: Mol. Spectroscopy, Volume 44, Issue 1, 1988, P. 63-67

[60] P Ruostesuo, J Karjalainen, Spectrochimica Acta Part A: Molecular


[61] Else Augdahl, Peter Klaboe, Spectrochimica Acta, Volume 19, Issue

10, October 1963, Pages 1665-1673


117

[62] M Meneghetti, C. Pecile, Synthetic Metals, Volume 86, Issues 1-3, 28

February 1997, Pages 2037-2038

[63] M Slock, S Hoste, L. Verdonck, G P Van der Kelen, Journal of

Molecular Structure, Volume 143, March 1986, Pages 389-394

[64] R D Srivastava, P D Gupta, Spectrochimica Acta Part A: Molecular

Spectroscopy, Volume 24, Issue 4, April 1968, Pages 373-376

[65] S K Singh, R K Gupta, R A Singh, Synthetic Metals, Volume 159,

Issues 23-24, December 2009, Pages 2478-2485

[66] R. Foster, Tetrahedron, Volume 10, Issues 1-2, 1960, Pages 96-101

[67] Akira Okada, Satoshi Yokojima, Noriyuki Kurita, Yasuo Sengoku,

Shigenori, Tanaka Journal of Molecular Structure: THEOCHEM,

Volume 630, Issues 1-3, 25July 2003, Pages 283-290

[68] Moamen S Refat, Akram M El-Didamony, Ivo Grabchev,

Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Volume7, Issue 1, May 2007, Pages 58-65

[69] Rauwolf, Cordula, Mehlhorn, Achim, Fabian, Jürgen, Collection of

Czechoslovak Chemical Communications, 63, 8, pp. 1223-1244

[70] G V Belysheva1, A N Egorochkin1, P G Sennikov1, M A Lopatin1 and

V. V. Voronenkov1 Russian Chemical Bulletin, Volume 39, Number

6 / June, 1990, 1181-1184

[71] A A A Boraei, Spectrochimica Acta Part A: Molecular and

Biomolecular Spectroscopy,Vol. 58,Issue 9, 1July 2002,P. 1895-1901

[72] Amirah S AL-Attas, Moustafa M Habeeb, Doaa S AL-Raim, Journal

of Mole. Structure, Vol. 928, Issues 1-3, 30 June 2009, Pages 158-170

[73] Hassan S Bazzi, Adel Mostafa, Siham Y AlQaradawi, El-Metwally

Nour, Journal of Molecular Structure, Vol. 842, Issues 1-3, 15

October 2007, Pages 1-5

[74] H Krikor, P Nagels Synthetic Metals, Volume 29, Issues 2-3, 21

March 1989, Pages 109-114


118

[75] J Y Becker, J Bernstein, S. Bittner, Y Giron, E Harlev, L Kaufman-

Orenstein, D Peleg, L Shahal, S S Shaik Synthetic Metals, Volume 42,

Issue 3, 29 May 1991, Pages 2523-2528

[76] Ramadan M Ramadan, Ali M El-Atrash, Amany M A Ibrahim,

Spectrochimica Acta Part A: Molecular Spectroscopy, Volume 46,

Issue 9, 1990, Pages 1305-1312

[77] Abolfazl Semnani, Mojtaba Shamsipur, Spectrochimica Acta Part A:

Molecular Spectroscopy, Vol. 49, Issue 3, March 1993, P. 411-415

[78] Masoumeh Hasani, Mojtaba Shamsipur, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Volume 61, Issue 5,

March 2005, Pages 815-821

[79] Pushkin M Qureshi, Rishi K Varshney, Sant Bahadur Singh,

Spectrochimica Acta Part A: Molecular Spectroscopy, Volume 46,

Issue 5, 1990 Pages 731-736

[80] M Pandeeswaran, K P Elango, Spectrochimica Acta Part A: Mol. and

Biomolecular Spectroscopy, Vol. 65,Issue 5,Dec. 2006,P.1148-53

[81] Ahmed M Nour El-Din, Spectrochimica Acta Part A: Molecular


[82] Jyotirekha G Handique, Jubaraj B Baruah, Journal of Molecular

Catalysis A: Chemical, Vol. 184, Issues 1-2, 17 June 2002, P. 85-93

[83] S A El-Gyar, S A Ibrahim, M A El-Gahami, Spectrochimica Acta Part

A: Molecular Spectroscopy, Vol. 45, Issue 9, 1989, P. 977-979

[84 Aboul-fetouh E Mourad, Ahmed M Nour-el-Din, Spectrochimica Acta

Part A: Molecular Spectroscopy, Vol. 39, Issue 3,1983, P 289-292

[85] K R Bhaskar, S N Bhat, Surjit Singh, C N R Rao, Journal of Inorganic

and Nuclear Chemistry, Volume 28, Issue 9, September 1966, P.

1915-1925

[86] Mohamed S Abdel Moez, Basheir A El-Shetary, Mohamed F Eid,

Farouk Zidan, Thermochimica Acta, Vol 128, 15 June 1988, pp. 81-91


119

[87] M. Ayad, Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Vol. 58, No. 1. (1 January 2002), pp. 161-166.

[88] Hulya Duymus, Mustafa Arslan, Mustafa Kucukislamoglu, Mustafa

Zengin, Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Volume 65, Issue 5, December 2006, Pages 1120-1124

[89] Adel Mostafa, Hassan S. Bazzi, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Vol.74, Issue 1,

15 September 2009, P. 180-187

[90] Masahiro Kako, Yasuhiro Nakadaira, Coordination Chemistry

Reviews, Volume 176, Issue 1, 1 September 1998, Pages 87-112

[91] Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Issue 1, January 2008, Pages 216-221Volume 69

[92] M R Mahmoud, M M A Hamed, H M A Salman, Spectrochimica Acta

Part A: Molecular Spectroscopy, Volume 44, Issue 11, 1988,

Pages 1185-1188

[93] M M Ayad, G B El-Hefnawy, G W Bahlol, Spectrochimica Acta Part

A: Molecular and Biomolecular Spectroscopy, Volume 58, Issue 1, 1

January 2002, Pages 161-166

[94] Gamal A Saleh, Talanta, Volume 46, Issue 1, May 1998, P.111-121

[95] H S Randhawa, Sharda Rani, Rajni Sachdeva, S.K. Suri,

Thermochimica Acta, Volume 105, 1 September 1986, P. 303-312

[96] Christopher J Bender, H T Tien, Journal of Electroanalytical

Chemistry, Volume 284, Issue 1, 10 May 1990, Pages 217-227

[97] Ali A H Saeed, Asia H Abed, Rahiem T Mehdi, Polyhedron, Volume

13, Issue 20, October 1994, Pages 2855-2859

[98] Amina A Fakhroo, Hassan S Bazzi, Adel Mostafa, Lamis Shahada.

Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Volume 75, Issue 1, January 2010, Pages 134-141

[99] Hassan F Askal, Talanta, Vol. 44, Issue 10, Oct. 1997, P.1749-1755


120

[100] S M Teleb, M S Refat, Spectrochimica Acta Part A: Molecular and

Biomolecular Spectroscopy, Vol. 60, Issue 7, June 2004, P. 1579-1586

[101] Golam Faruque Khan, Biosensors and Bioelectronics, Volume 11,

Issue 12, 1996, Pages 1221-1227

[102] A A Ibrahim, Microchemical Journal, Volume 58, Issue 2, February

1998, Pages 175-181

[103] Li Ming Du, Hai Yan Yao, Mi Fu, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Vol. 61, Issues 1-2, 1 Jan.

2005, P. 281-286

[104] Zhifeng Ding, David J Fermı ́n, Pierre-François Brevet, Hubert H

Girault Journal of Electroanalytical Chem., Volume 458, Issues 1-2,

30 Oct. 1998, Pages 139-148

[105] T R Bera, D Sen, R Ghosh, Spectrochimica Acta Part A: Molecular


[106] Masoumeh Hasan and Alireza Rezaei, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Volume 65, Issue 5,

December 2006, Pages 1093-1097

[107] Aboul-fetouh E Mourad, Ahmed M Nour-el-Din, Spectrochimica Acta

Part A: Molecular Spectroscopy, Volume 39, Issue 6, 1983, ]Pages

533-536

[108] M R Mahmoud, M M A. Hamed, H M A Salman, Spectrochimica

Acta Part A: Molecular Spectroscopy, Volume 44, Issue 11, 1988,

P. 1185-1188

[109] R D Srivastava, G Prasad, Spectrochimica Acta, Volume 22, Issue 11,

November 1966, Pages 1869-1875

[110] Masamoto Iwaizumi, Yasunori Ohba, Hideki Iida and, Masatoshi

Hirayama, Inorganica Chimica Acta, Volume 82, Issue 1, 1 February

1984, Pages 47-52

[111] Istvan Szundi, Chemistry and Physics of Lipids, Volume 22, Issue 2,


121

Sept. 1978, Pages 153-161

[112] Allan Munck, Rosemary Foley, Journal of Steroid Biochemistry,

Volume 12, January 1980, Pages 225-230

[113] Dalim Kumar Roy, Avijit Saha, Asok K Mukherjee, Spectrochimica

Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 61,

Issue 9, July 2005, Pages 2017-2022

[114] Mustafa Arslan, Hulya Duymus, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Volume 67, Issues 3-4,

July 2007, P. 573-577

[115] Masaru Nakagawa, Masahiro Rikukawa, Kohei Sanui, Naoya Ogata,

Supramolecular Science, Volume 5, Issues 1-2, May 1998, P. 83-87

[116] Aboul-Fetouh E Mourad, Spectrochimica Acta Part A: Molecular


[117] Mohamad M Y Ayad, Saiid A Amer, Raafat M Issa, Thermochimica

Acta, Volume 140, 15 March 1989, Pages 277-285

[118] Z Yoshida, T Kobayashi, Tetrahedron, Vol. 26, Issue 1, 1970,

P. 267-271

[119] J K Jeszka, M. Kryszewski, Journal of Electrostatics, Volume 9, Issue

1, June 1980, Pages 31-40

[120] M J S Dewar, C. C. ThompsonJr, Tetrahedron, Volume 22,

Supplement 7, 1966, Pages 97-114

[121] A C Jambut-Absil, J Buxeraud, J F Lagorce, C Raby, International

Journal of Pharmaceutics, Volume 35, Issues 1-2, February 1987,

Pages 129-137

[122] S Palaniappan, D N Sathyanarayana, Polymer, Volume 31, Issue 8,

August 1990, Pages 1401-1405

[123] N Someswara Rao, G Babu Rao, D. Ziessow, Spectrochimica Acta

Part A: Molecular Spectroscopy, Vol. 46, Issue 7, 1990, P. 1107-1124

[124] Sergey P Abramov, Spectrochimica Acta Part A: Molecular and


122

Biomolecular Spectroscopy, Vol. 55, Issue 6, June 1999, P. 1143-1151

[125] Lories I Bebawy, Naglaa El-Kousy, Jihan K Suddik, Mohamed

Shokry , Journal of Pharmaceutical and Biomedical Analysis, Volume

21, Issue 1, October 1999, Pages 133-142

[126] E T Kang, European Polymer Journal, Vol. 21, Issue 11, 1985,

P. 919-924

[127] Lamis Shahada, Adel Mostafa, El-Metwally Nour, Hassan S. Bazzi,

Journal of Mol. Structure, Volume 933, Issues 1-3, 17 September

2009, Pages 1-7

[138] A Dozal, H Keyzer, H K Kim, W W Wang, International Journal of

Antimicrobial Agents, Volume 14, Issue 3, April 2000, P. 261-265

[129] Mohamad M Y Ayad, Saiid A Amer, Raafat M Issa, Thermochimica

Acta, Volume 140, 15 March 1989, Pages 277-285

[130] A C Jambut-Absil, J Buxeraud, J F Lagorce, C Raby,International

Journal of Pharmaceutics, Volume 35, Issues 1-2, February 1987,

Pages 129-137

[131] G Keryer, J Amiell, S Flandrois, P Delhaes, E Toreilles, J M Fabre

and, L, Giral Solid State Communications,Vol. 26, Issue 8, May 1978,

P. 541-546

[132] Refat Abdel-Hamid, Ahmed A El-Samahy, Mahmd A Abdel-

Rahman, Hussein, El-Sagher Spectrochimica Acta Part A: Molecular

Spectroscopy, Vol 43, Issue 4, 1987, Pages 497-499

[133] Mohamad M Ayad, Mohamad Gaber, Saleh A Azim, Thermochimica

Acta, Volume 147, Issue 1, 15 July 1989, P. 57-64

[134] Paolo Bruno, Maurizio Caselli, Carlo Fragale, Salvatore Magrino,

Journal of Inorganic and Nuclear Chemistry, Vol. 39, Issue 10, 1977,

P. 1757-1759

[135] Istvan Szundi, Chemistry and Physics of Lipids, Volume 22, Issue 2,

September 1978, Page153-161


123

[136] Gaber, Shar S Al-Shihry, Chemistry and Phy. of Lipids, Vol 22,

Issue 2, September 1978, Pages 153-161

[137] Mustafa Arslan, Hulya Duymus, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Vol.67, Issues 3-4, July

2007, P. 573-577

[138] Hulya Duymus, Mustafa Arslan, Mustafa Kucukislamoglu, Mustafa

Zengin, Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, Volume 65, Issue 5, December 2006, Pages 1120-1124

[139] Humaira Razzaq, Rumana Qureshi, Naveed Kausar Janjua, Farhat

Saira, Samia, Saleemi Spectrochimica Acta Part A: Molecular and

Biomolecular Spectroscopy,Vol. 70, Issue 5, Oct. 2008, P. 1034-1040

[140] Adel Mostafa, Hassan S Bazzi, Spectrochimica Acta Part A:

Molecular and Biomolecular Spectroscopy, Vol.74, Issue 1, 15

September 2009, P. 180-187

[141] A Ram Reddy, N V KrishnaMurthy, B Bhudevi, Spectrochimica Acta

Part A: Molecular and Biomolecular Spectroscopy, Volume 63,

Issue 3, March 2006, Pages 700-708

[142] M Pandeeswaran, K P Elango, Spectrochimica Acta Part A: Molecular

and Biomolecular Spectroscopy, Volume 69, Issue 4, April 2008,

P. 1082-1088

[143] Gamal A Saleh, Hassan F Askal, Mohamed F Radwan, Mahmoud A

Omar, Talanta, Volume 54, Issue 6, 6 July 2001, Pages 1205-1215

[144] F C Loh, K L Tan, E T Kang, European Polymer Journal, Volume 27,

Issue 10, 1991, Pages 1055-1063

[145] Sushanta K Pal, K Alagesan, Ashoka G Samuelson, J Pebler, Journal

of Organometallic Chemistry, Vol. 575, Issue 1, 22 February 1999,

P.108-118

[146] F Yakuphanoglu, M Arslan, S Z Yıldız, Optical Materials, Volume 27,

Issue 6, March 2005, Pages 1153-1158


124

[147] A Dozal, H Keyzer, H K Kim, W W Wang, International Journal of

Antimicrobial Agents, Volume 14, Issue 3, April 2000, P. 261-265

[158] Kenneth A Murdoch, Carbohydrate Research, Volume 233,

2 September 1992, Pages 161-174

[149] D P Joshi, Y L Lan-Chun-Fung, J G Pritchard, Analytica Chimica

Acta, Volume 104, Issue 1, 1 January 1979, Pages 153-160

[150] Benoy B Bhowmik, Sankar P Chattopadhyay, Spectrochimica Acta

Part A: Molecular Spectroscopy, Volume 37, Issue 2, 1981,

Pages 135-139

[151] Yu Liu, Rui-Qin Zhong, Heng-Yi Zhang and Hai-Bin A unique

tetramer of 4:5- cyclodextrin–ferrocene in the solid state Song

Chemical Communications, 2005, (17), 2211 - 2213.

[152] D P Joshi, Y L Lan-Chun-Fung, J G Pritchard, Analytica Chimica

Acta, Volume 104, Issue 1, 1 January 1979, Pages 153-160

[153] Benoy B Bhowmik, Sankar P Chattopadhyay, Spectrochimica Acta

Part A: Molecular Spectroscopy, Vol. 37, Issue 2, 1981, P. 135-139

[154] J Morales* and J Santos, Instituto de Ciencias de Materiales de

Madrid, C.S.I.C. Cantoblanco, Spain Chem. Mater., 1999, 11 (10),

p.2737–2742

[155] W Hinrichs, P Berges, G Klar, E Sánchez-Martínez, W. Gunsser,

Synthetic Metals, Volume 20, Issue 3, July 1987, Pages 357-364

[156] Shinya Muto, Kenjiro Meguro, Journal of Colloid and Interface

Science, Volume 49, Issue 3, December 1974, Pages 422-424

[157] Sanchao Liu, Jianmin Shi, Eric W. Forsythe, Steven M. Blomquist,

Dave Chiu, Synthetic Metals, Volume 159, Issue 14, July 2009, Pages

1438-1442

[158] Nafisur Rahman, Nishat Anwar, Mohammad Kashif, Il Farmaco,

Volume 60, Issues 6-7, June-July 2005, Pages 605-611

[159] Zdenko Časar, Ivan Leban, Alenka Majcen-le Marechal, Lidia


125

Piekara-Sady, Dominique Lorcy Comptes Rendus Chimie, Volume

12, Issue 9, September 2009, Pages 1057-1065

[160] A. Tracz, J.K. Jeszka Synthetic Metals, Vol. 42, Issues 1-2, 15 May

1991, Pages 1831-1834

[161] C I Simionescu, Geta David, M. Grigoras, European Polymer Journal,

Volume 23, Issue 9, 1987, Pages 689-693

[162] Moamen S Refat, Akram M El-Didamony, Spectrochimica Acta Part

A: Molecular and Biomolecular Spectroscopy, Volume 65, Issues 3-4,

November 2006, Pages 732-741

[163] P Delhaès, S Flandrois, G Keryer, P Dupuis, Materials Research

Bulletin, Volume 10, Issue 8, August 1975, Pages 825-829

[164] J M Fahre, S Chakroune, A Javidan, M Calas, A Souizi, L Ouahab,

Synthetic Metals, Vol. 78, Issue 1, 15 March 1996, P. 89-92

[165] Kenichi Sugiura, Jiro Toyoda, Jong-Won, Tadaoki Mitani, Kazuhiro

Nakasuji, Tetrahedron Letters, Volume 36, Issue 31, 31 July 1995,

Pages 5535-5538

[166] A Berlin, G A Pagani, F Sannicolo', Synthetic Metals, Volume 19,

Issues 1-3, March 1987, Pages 415-418

[167] G Keryer, J Amiell, S Flandrois, P Delhaes, E Toreilles, J M Fabre

and, L. Giral Solid State Communications,Vol. 26, Issue 8, May 1978,

P.541-546

[168] J Morales* and J Santos, Instituto de Ciencias de Materiales de

Madrid, C.S.I.C. Cantoblanco, Madrid,Spain Chem.

Mater,1999,11(10), p 2737–2742

[169] Christensen, J Becher, Synthetic Metals, Volume 102, Issues 1-3, June

1999, Pages 1599-1600

[170] F Yakuphanoglu, M Arslan, Solid State Communications, Volume

132, Issues 3-4, October 2004, Pages 229-234

[172] Aradhana, A R Saksena, Journal of Mol. Liquids, Volume 26, Issues


126

3-4, October 1983, Pages 197-209

[172] Maged A El-Kemary, Journal of Photochemistry and Photobiology A:

Chemistry, Volume 87, Issue 3, 19 April 1995, Pages 203-207

[173] T Tveter, P Klaeboe, C J Nielsen, Spectrochimica Acta Part A:

Molecular Spectroscopy, Volume 40, Issue 4, 1984, Pages 351-359

[174] F Yakuphanoglu, M. Arslan, S.Z. Yıldız, Optical Materials, Volume

27, Issue 6, March 2005, Pages 1153-1158

[175] P Pal and T N Misra , Spectrosc. Dept., Indian Assoc. for the

Cultivation of Sci., Calcutta, India

[176] P Pal et al 1990 J. Phys. D: Appl. Phys. 23 218-222

[177] Neuweiler H ; Sauer M, Current Pharmaceutical Biotechnology,

Volume 5, Number 3, June 2004 , pp.285-298(14)

[178] Zhao Feng-lin, Xu Bian-zhen, Zhang Zhi-quan, Tong Shen-yang,

Journal of Pharmaceutical and Biomedical Analysis, Volume 21, Issue

2, 1 November 1999, Pages 355-360

[179] K Holczer, G Grüner, M Miljak and, J Cooper, Solid State

Communications, Volume 24, Issue 1, October 1977, Pages 97-100

[180] F Yakuphanoglu, M Arslan, Optical Materials, Volume 27, Issue 1,

October 2004, Pages 29-37

[181] A Tracz, J K Jeszka, Synthetic Metals, Volume 42, Issues 1-2, 15 May

1991, Pages 1831-1834

[182] LianheYu, Daoben Zhu, Physica C: Superconductivity, Volumes

282-287, Part 3, August 1997, Pages 1899-1900

[183] T R Bera, D Sen, R Ghosh, Spectrochimica Acta Part A: Molecular


[184] N K Čenas, J J Kulys, Journal of Electroanalytical Chemistry, Volume

128, 1981, Pages 103-113

[185] Stanislav Ne p rek, Jan Pila , Pavel Schmidt, Miloslav orm,

Vratislav Langer, Andrzej Graja, Ewa Sopa Chemical Physics,


127

Volume 101, Issue 1, 1 January 1986, Pages 81-93

[186] M Pandeeswaran, K P Elango, Spectrochimica Acta Part A: Molecular

and Biomolecular Spectroscopy, Volume 72, Issue 4, May 2009,

Pages 789-795

[187] Shobhana V Bhide, Narayan R Kale, Biochimica et Biophysica Acta

(BBA) - General Subjects, Vol. 444, Issue 3, 22 October 1976,

P. 719-726

[188] Papiya Nandy, Benoy B Bhowmik, Chemistry and Physics of Lipids,

Volume 42, Issue 4, 31 December 1986, Pages 303-309

[189] J I Pankove, Optical process in semiconductors, Prentice – hall Inc;

Englewood Cliffs, New Jersey (1971) and references therein.

[190] R S Kireev, Semiconductor physics, Mir Publishers, Moscow, 1975,

pp. 561 - 567

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