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DISPERSED SYSTEMS

Ingrid Žitňanová

DISPERSED SYSTEMS

Dispersed

phase

(water)Dispersionmedium

(oil)

SOLUTE

(DISPERSED PHASE )

SOLVENT

(DISPERSION MEDIUM )

Solute (NaCl) Solvent (water)

Heterogeneous and Homogeneous Mixtures

Dispersed

systems

Heterogenous

systemsHomogenous

systems

e.g. sugar watere.g. ice in soda

Homogenous Heterogenous

It has a uniform composition It has a non-uniform composition

It has only one phase There are two or more phases

It can’t be separated out physically It can be separated out physically

Examples: sugar water, vinigar,

NaCl in water....

blood, sand in water, ice in soda,

cereal in milk, vegetable soup...

Difference between Homogenous and

Heterogenous dispersions

Classification of the dispersed systems

according to the diameter of dispersed particles

1. Analytical (molecular, true solutions)

2. Colloids

3. Coarse / Crude dispersion (suspension)

< 1 nm

1 – 1000 nm

>1000 nm

SolutionColloidsSolution Coarse dispersion

particle sizeType of dispersion

Properties of the dispersed systems

Dispersion Molecular (true solut.) Colloidal Coarse (crude)

Particles size 1 nm 1 – 1000 nm > 1000 nm (1 μm)

Particles Filterability Cannot be separated by

filtration

Can be separated by

semipermeabile

membrane

Can be separated by

filtration

Diffusion rapid slow No diffusion

Visibility Not visible under the

electrone microscope

Can be visible under

the electrone

microscope

Can be seen under

the low power

microscope or eye

Sedimentation Particals do not sediment Sediment in the

strong centrifugal

field

Sediment under the

influence of gravity

Optical properties Transparent

No Tyndall effect

Tyndall effect Not transparent

Tyndall´s effect

is due to the scattering of light by colloidal particles, while showing

no light in a true solution.

This effect is used to determine whether a mixture is a true solution

or a colloid.

True

solution

Colloidal

solution

• when light is passed

through a colloidal

solution, the substance

in the dispersed phases

scatters the light in all

directions, making it

readily seen

TRUE SOLUTIONS

(Analytical solutions)

SolventsPolar

Nonpolar

Solutes

Polar

Nonpolar

• Polar solutes dissolve well in polar solvents

• Nonpolar solutes dissolve well in non-polar solvents

• Polar and nonpolar do not mix...

– e.g.water, ethanol, methanol,

– e.g. chloroform, hexane, benzene

- ethanol, acetic acid, NaCl

- fats, steroids, waxes

Oil in water

Water

The most important polar solvent

Intracellular fluid ICF – inside cells – 25 - 30L

Extracellular fluid ECF – 15L - blood plasma, intersticial fluid,

lymph, fluid in gastrointestinal tract, urine

Volume of water in body is balanced (intake = output)

Central regulatory organ of water volume – kidneys

Hydrogen

bond

Water – H2O – a polar solvent

O

O

O

O

HH

H

H

H

H

H

H

True solutions

Ionic Molecular

• Solutions of nonelectrolytes

• Contain molecules of compounds in

solution (glucose in water, urea)

• solution of electrolytes in which ions

are present, formed by electrolytic

dissociation of ionic compounds

Na+

Cl-H2OH2O

Cl-

Cl-

Cl-Cl-

Cl-

H2O

NaCl Na+ + Cl-

Electrolytic

dissociation

Hydrated

ions

Ionic strength ( I )

is the concentration of ions in the solution

i – number of particles

ci - the molar concentration of particles (ions)

zi – charge of the particle

Only ionized species contribute to ionic strength in

solution!!!

• Ionic strength of blood is around 0.17 mol/L

Example 1:

Calculate ionic strength of a solution containing 0.02 mol/L

Na2SO4 and 0.1 mol/L glucose.

I1 = 0.5 [(2 x 0.02 × 12 ) + (1 x 0.02 × 22 )] = 0.06 mol/L

1. Na2SO4 = 2Na+ + SO42-

2. Glucose0 no dissociation

I2 = 0.5 x 1 x 0.1 x 02 = 0 mol/L

I = I1 + I2 = 0.06 + 0 = 0.06 mol/L

SO42-2Na+

Solubility

A measure of how much of a solute can be dissolved in a solvent

Factors affecting solubility

• Temperature

• Pressure

• Polarity

Temperature

For most solids and most liquids

Solubility increases when solution temperature increases

Temperature

For gases

Higher temperature reduces solubility of gases –

it drives gases out of solution

Examples:

Carbonated soft drinks are more bubbly if stored in the

refrigerator (more CO2 is inside the drink)

Warm lakes have less O2 dissolved in them than cool

lakes

Pressure

• Little effect on solids and liquids

• Will greatly increase solubility of gases

Polar substances tend to dissolve in polar solvents.

Nonpolar substances tend to dissolve in nonpolar solvents.

Examples

Polarity

Vitamin A is soluble in nonpolar compounds (e.g. fats)

Vitamin C is soluble in water

Vitamin A Vitamin C

Properties of true solutions

Colligative properties don´t depend on the chemical composition of a

solute, but depend only on the number of solute particles (molecules or

ions).

The processes based on colligative properties are:

• Diffusion

• Dialysis

• Osmosis

• Boiling point elevation

• Freezing point depression

Diffusion

is a process of spontaneous movement of particles of a dissolved

compound from a region of higher concentration to a region of lower

concentration, to distribute themselves uniformly = movement of a

substance down a concentration gradient

The rate of diffusion depends on the concentration gradient

Particles move until equilibrium is reached

Diffusion usually happens in a solution in gas or in a liquid.

Examples of diffusion:

A sugar cube is left in a beaker of water for a while.

The smell of food spread in the whole house

Dialysis

Concentrated

sugar solutionDiluted

sugar solution

Movement of low

molecular weight solute to

equal concentrations

Water and low molecular weight LMW compounds (not macromolecules)

are transported across a semipermeable membrane. LMW compounds go from

the more concentrated solution to the less concentrated solution till equilibrium

is reached. Semipermeable membrane

Biomedical importance of dialysis

Dialysis by artificial kidney: In patients with acute kidney injury and

uremia blood is dialyzed in artificial kidneys to eliminate waste products.

Hemodialysis - Blood dialysis

- removal of waste metabolic products (e.g. urea

or creatinine) or toxins, by kidneys

Dialyzing

membrane

Dialysate

- solution isotonic with blood,

- it has the same concentrations of all the

essential substances that should be left in blood

Dialysate

Filtered blood

returning to

bodyBlood flows to

dialyzer

Hemodialyzer

machine

Hemodialyzer

(where filtering takes place)

Osmosis

Osmosis is the flow of solvent across a semipermeable membrane

from a lower solute concentration to a higher solute concentration

semipermeable membrane is permeable only to solvent molecules,

not to solute molecules

Concentrated

solution

Diluted

solution

Semi-permeable

membrane

Osmotic pressure (π)

- external pressure that has to be applied on the more

concentrated solution to stop osmosis

i – number of solute particles in solution to which the compound dissociates

c – amount of substance concentration (mol/L)

R – gas constant – 8.314 J K-1 mol-1

T – temperature in Kelvins (0 °C = -273.15 K)

π = i.c.R.T

π of blood - 780 kPa

π

Movement of solvent (water)

to equal concentrations

Osmolarity (cosm)

molar concentration of all osmotically active particles of solutes in

solution

cosm = i . c

cosm - osmolarity mol/L

i – number of solute particles in solution to which the

compound dissociates

c – amount of substance concentration (mol/L)

Osmolarity (cosm)

Blood serum osmolarity:

πblood = i . c . R . T

cosm

πblood 780 kPa

Blood cosm = = = 0.3 mol/L R . T 8.3 JK-1mol-1 . 310 K

• Osmolarity is kept constant by kidneys

Example 1:

Calculate osmolarity of the solution containing 0.2 mol/L CaCl2

and 0.1 mol/L glucose.

1. CaCl2 = Ca2+ + 2Cl-

2. Glucose no dissociation

cosm = i1 . c1 + i2 . c2

cosm = 3 x 0.2 + 1 x 0.1 = 0.7 mol/L

i1 = 1Ca2+ + 2Cl

- = 3

i2 = 1glucose

Isotonic /isoosmotic solutions

Isotonic solutions are two solutions that have the same

osmolarity.

Hypertonic solution

Hypertonic solution is one of two solutions that has a higher

osmolarity.

Hypotonic solution

Hypotonic solution is one of two solutions that has a lower

osmolarity.

Solution of NaCl with concentration of 0.15 mol/L

Solution of NaCl with osmolarity of 0.3 mol/L

0.9% NaCl solution (9 g NaCl/L)

Physiological solution

Solution which osmotic pressure corresponds to blood plasma:

Any solution added in large quantity into the bloodstream has

to be isotonic!!

hemolysis

Crenation

Cells shrink

Oncotic pressure

Oncotic pressure, or colloid osmotic pressure, is a form

of osmotic pressure exerted by proteins (e.g. albumin) in a blood

that usually tends to pull water into the circulatory system.

Water flow driven by

oncotic pressure

diference

Capilary

lumen

Small molecules and ions can be dialyzed in both directions between

blood and the interstitial compartment

Large protein molecules do not have this ability – their presence

produces excess osmotic pressure of blood (oncotic pressure)

compared to the interstitial fluid.

The hydrostatic pressure of a blood tends to push water out of the

capillary – filtration.

The oncotic pressure pulls the water from the interstitial space back

into the capillary – reabsorption.

Exchange of compounds

between blood and tissues

Donnan equilibrium

High molecular weight

compound

semi-permeable membrane

equilibrium

• According to Donnan´s equilibirium, the products of diffusible electrolytes in

both comparments will be equal

• in the left compartment: Na+ x Cl- = Na+ x Cl- in the right compartment

• in the left compartment: 9 x 4 = 6 x 6 in the right compartment

4Na+, 4Cl-

refers to the uneven distribution of charged particles on one side of a

semipermeable membrane

Donnan equilibrium

equilibrium

1. The products of diffusible electrolytes in both compartments are equal (9x4=6x6)

2. The electrical neutrality of each compartment is maintained (9 + and 9 - in the left)

3. The total number of a particular type of ions before and after the equilibrium is

the same (15 Na+ before, 15 Na+ in the equilibrium)

4. When there is a nondiffusible anion on one side of a membrane, there are

more diffusible cations and less diffusible anions on that side

In summary, Donnan´s equations lead to the following results:

Colloidal dispersions

Colloidal dispersion

is a mixture consisting of large clusters of ions or molecules, or

macromolecules with size of particles 1 – 1000 nm

the dispersed particles do not settle down

particles can be visible under the electrone microscope

particles diffuse slowly

show some unique properties such as Tyndall effect, Brownian

motion

almost all reactions in the organism proceed in colloid

environment

True

solution

Colloid

High–molecular weight (macromolecular) compounds (e.g. proteins,

polysaccharides), in process of dissolution spontaneously form

colloidal solutions

Low–molecular weight compounds may form colloidal solutions as

a consequence of clustering of molecules into aggregates – micelles

(e.g. soap solutions).

Classification of colloids

1. Based on physical state of dispersed phase and

dispersion medium

Sols

Gels

Emulsions

Aerosols

Sols

If the dispersion medium is water, the colloid may be

called a hydrosol; and if air, an aerosol.

Are colloidal solutions made of globular proteins with

normal viscosity

Particles in colloids are isolated

Gels

.

they arise by swelling macromolecular compounds (e.g.proteins) in

solvent – acceptation of water by solid polymers

are formed from fibrous proteins (gelatin from collagen), polysaccharides

(gels – dextran, sephadex).

The wall of the living cells is colloidal, and within the cell there is

a gel (cytoplasm).

Gels undergo aging - particles coagulate, gel volume diminishes and

water is displaced

Protein

moleculesdispersed in

water

waterwater

Protein

molecules

Mechanical

shaking

When particles in colloids are isolated – sol. When they form clusters–gel.

Emulsions

are colloidal dispersions of two immiscible liquids (e.g. oil in water, or

water in oil) when are shaken together.

usually are not stable (e.g. the oil soon separates from the aqueous layer).

can be stabilized by a third component called emulsifying agent

(emulsifiers) (soaps, fats...).

Biologically important emulsions:

lipids in blood – emulsified by proteins

fat emulsions in intestine – emulsified by salts of bile acids

Colloids

LyophilicLyophobic

Micelles

2. Classification of colloids according to their

properties

Macromolecular

compounds Low-molecular

weight compounds

Low-molecular

weight amphipatic

compounds (soaps)

1. Lyophilic colloids

• Solvent attracting, solvent loving particles

• If water is the solvent (dispersing medium), it is known as a

hydrosol or hydrophilic colloids

• particles of a lyophilic colloid are stabilized in solution

(prevention of aggregation) by solvation (hydration) shell, i.e.

oriented solvent molecules

• are formed by spontaneous dissolving of macromolecular substances

(e.g. solutions of proteins, starch...)

1. Lyophilic colloids

The loss of hydration shell after excess of neutral salt (electrolyte) is

added into solution results in irreversible salting out (precipitation)

of particles from solution.

The living cells represent solutions of lyophilic colloids

(as well as coarse dispersions)

• solvent hating colloids, have no affinity for the dispersion medium

2. Lyophobic colloids

• unstable colloid systems in which the dispersed particles:

- tend to repel liquids,

- are easily precipitated

• require protective colloids (lyophilic colloids – gums, gelatin...) to

stabilize in water

Lyophobic soll particle

(particle being protected)

Lyophilic colloidal particle

(protecting particle)

Explanation: The particles of the hydrophobic sol adsorb the particles

of the lyophilic particles. The hydrophobic colloid, therefore, behaves

as a hydrophilic sol and is precipitated less easily by electrolytes.

2. Lyophobic colloids

• are made artificially by aggregation of low molecular weight substances

• Examples: sols of metals and their insoluble compounds like sulphides and

oxides (e.g. gold, silver, platinum in water, cluster of inorganic molecules,

e.g. As2S3)

• Therapy: colloidal systems are used as therapeutic agents in different areas

Silver colloid – germicidal effects

Copper colloid – anticancer effects

Mercury colloid - antisyphilis

Colloidal goldColloidal silver

3. Association colloids – micelles

are formed by dissolving of low-molecular weight amphipathic compounds

Amphipathic compounds contain both polar (hydrophilic) and nonpolar

hydrophobic regions (e.g. fatty acids)

Polar part

Nonpolar part

when mixed with water, amphipatic compounds form colloidal particles –

micelles (e.g. soap, detergents)

Soaps

consist of sodium or potassium salts of higher carboxylic acids

Soaps

Polar -Lyophilic part

lyophilic end of the COO- dips in water, while the lyophobic part stays

away from it

When soap is shaken with water it forms a colloidal dispersion which

contains aggregates of soap molecules - micelles

Nonpolar - Lyophobic part

Dirty cloth

Dirt

Soap molecules

Soap solution

Mechanism of soap action

• The hydrophilic heads (with – charge COO-) interact with water

and the oil drop is stabilized in water.

• The hydrophobic ends attach themselves to the dirt and remove it

from the cloth

Biological importance of colloids

Biological compounds as colloidal particles: the complex molecules of life,

the high-molecular weight proteins, complex lipids and polysaccharides

Blood coagulation: when blood clotting occurs, the sol is converted finally

into the gel.

Biological fluids as colloids: these include blood, milk and cerebrospinal

fluid, lymph, mucus, cytosol, nucleus, cell membranes

Colloidal state is one of the most widespread in nature:

Reaction kinetics

Chemical reaction

Reaction means a change

Chemical reaction is a conversion of reactants to products

A + B C + DReactants Products

Reagents

Reaction kinetics

Kinetics of a chemical reaction can tell us:

How chemicals react to form products (mechanism)

How long it will take for a reaction to reach completion

Effects of catalysts and enzymes

How to control a reaction

A + B C

Rate equation(Guldberg Waage rate law)

The rate of a given chemical reaction (at constant temperature and

pressure) is proportional to product of reactants concentration.

For the general reaction:

aA + bB cC

Rate: v = k . [A]a . [B] b

k = rate constant

[A], [B]= molar concentrations of reactants (mol/L)

Rate constant

k = rate constant

A = Arrhenius constant for each chemical reaction (total number of collisions)

Ea = activation energy

R = gas constant (8.314 J K-1 mol-1)

T = Temperature in Kelvins

e = euler number (2.71828...)

Temperature has a dramatic effect on reaction rate.

For many reactions, an increase of 10°C will double the rate.

Higher T larger k increased rate

Reactant Product

aA bB

When concentration of products and reactants no longer change with time,

the chemical reaction reached equilibrium

equilibrium

Effective collisions

For reactants to make products

They must collide in the correct orientation and with sufficient energy

The energy of collision must be greater than the bond energy

between the atoms

Molecules must collide with the correct orientation and with

enough energy to cause bond breakage and a new bondformation

Activation energy

The minimum amount of energy required to start a chemical reaction

Activation energy

Transition state

(activated complex)

Activation energy

Reactants

Products

Factors which affect the rate of chemical

reactions

Rate of

reaction

The nature of

reactants

Temperature

Concentration

of reactants

Catalysts

Natu

reo

fre

act

an

tsNumber of bonds

• fewer bonds per reactant - faster reaction

Strength of bonds• Breaking of weaker bonds - a faster rate (-C-C- / -C=C-)

The size and shape of a molecule• Complicated molecules or complex ions are often less reactive

Less particles, less frequent

and successful collision

More particles, more frequent

and successful collision

Concentration of reactants

As the concentration of reactants increases, so does the likelihood that reactant

molecules will collide - the reaction rate will increase

Temperature

An increase of about 10°C will often double the rate of a reaction

Catalysts

Catalysts speed up reactions by changing the mechanism of the reaction – they

reduce activation energy of reaction

Catalysts are not consumed during the reaction

Oxidation – reduction reactions

(redox reactions)

Oxidation – reduction reactions

(redox reactions)

Oxidation is the loss of electrons (or hydrogen), the species which loses

the electrons is oxidized, it becomes more positive

Reduction is the gain of electrons (hydrogen), the species which gains

electrons is reduced, becomes less positive.

Na0 → Na+ + 1e-

Cl20 + 2e- → 2Cl-

Oxidation and reduction reactions occur simultaneously

chemical reactions where one of the reactants is oxidized and one of the

reactants is reduced

Decide, in which direction the following reaction is an oxidation and

in which it is a reduction

Oxidation – reduction reactions

(redox reactions)

- electrons are exchanged between chemical species

Na Cl

+ -

-

Na Cl

In these reactions there are changes in the valence shells of atoms

+ -

Oxidizing agent – oxidant - is the chemical species causing the

oxidation. This species is reduced and can also be called the

electron acceptor.

2Na0 + Cl20 2Na+Cl-

oxidant

Reducing agent – reductant- is the species causing the

reduction. This species is oxidized and can be called the electron

donor.

reductant

The number of electrons lost by the reductant must be equal to the

number of electrons gained by the oxidant.

e-

Dismutation (disproportionation)

The special case of oxidation – reduction reaction

a compound of intermediate oxidation state converts to two different

compounds, one of higher and one of lower oxidation states.

Examples:

The dismutation of superoxide free radical to hydrogen peroxide and oxygen,

catalysed in living systems by the enzyme superoxide dismutase

2 O2

.− + 2 H+ → H2O2 + O2

With oxidation numbers:

2 O2. −1 + 2 H+1 → H2

+1 O2-2 + O2

0

The dismutiation of hydrogen peroxide catalysed by the enzyme catalase

2 H2O2-2 → 2 H2O

-2 + O20

Oxidation-reduction reactions

Oxidation – reduction reactions occur together

Fe2+ + Cu2+ Fe3+ + Cu+

This reaction can be described in two half-reactions:

(1) Fe2+ Fe3+ + 1e-

(2) Cu2+ + 1e- Cu+

Which ion is a reducing agent (reductant)?

Reductant – donates electrons

Which ion is an oxidizing agent (oxidant)?

Oxidant – accepts electrons

Electron donor e- + electron acceptor

Conjugate redox pair

Biological oxidation-reduction reactions

In biological systems, oxidation is often synonymous with dehydrogenation

Many enzymes that catalyze oxidation reactions are oxidoreductases, called

dehydrogenases.

O : H ratio1 : 6

O : H ratio1 : 4

O : H ratio1 : 2

More reduced compounds are richer in hydrogen than in oxygen

More oxidized compounds have more oxygen and less hydrogen

The oxidation states of carbon in biomolecules

Most oxidized

Most reduced

Oxidation in organism can occur in one of four different ways:

1. Directly, as transfer of electrons

Fe2+ + Cu2+ Fe3+ + Cu+

2. As transfer of hydrogen atoms

H = H+ + 1e-

AH2↔ A + 2 eˉ + 2 H+

AH2+ B ↔ A + BH2

Hydrogen/electron donor

Reduced

3. As a transfer of hydride ion (Hˉ), which has two electrons (H+ + 2e-)

This occurs in the case of NAD-linked dehydrogenases

4. Through direct combination with oxygen

R−CH3+ ½O2 R−CH2OH

Reduction potentials

When two conjugate redox pairs are together in solution, electron transfer from the electron donor of one pair to the electron acceptor of the other may occur spontaneously.

The tendency for a reaction depends on the relative affinity of the electron

acceptor of each redox pair for electrons.

The standard reduction potential (E0) is the tendency for a chemical

species to be reduced, and is measured in volts at standard conditions

H+ + eˉ ½ H2 E0 = 0 V

The electrode at which this half-reaction occurs is arbitrarily assigned a

standard reduction potential of 0.00V.

Fe2+ + Cu2+ Fe3+ + Cu+

Element with the more positive redox potential has a higher

affinity towards electrons – it has an oxidizing property

Fe0 + Cu2+SO4 → Cu0 + Fe2+SO4

Element with the more negative redox potential has a lower

affinity towards electrons – it can easily donate electrons – it has

an reducing property

Reduction potentials

R is gas constant (8.314 JKˉ1molˉ1

T is temperature (Kelvin degree),

n is the number of electrons transferred per molecule

F is the Faraday constant (9.68 . 104 Cmolˉ1).

The Nerst – Peterson equation:

Reduction potentials in medicine

Known oxidation-reduction potentials of biological redox systems allow to

determine the direction and sequence of oxidation-reduction reactions

in biological systems.

The strict sequence of enzymatic reactions in “respiratory chain” allows a

gradual release of energy during biological oxidation.

Thank you for your attention...