school december 2006 science quarterly journal of science...

Energy Independence 3A.P.J. Abdul KalamHonourable President of India

Nanotechnology – A Primer with FAQ 8Jitendra Singh

Learn more about Nanotechnology and 18Carbon Nano TubesS.V. Sharma

Origins of Colour 23F. Jones

Hard Spots in Teaching Carbohydrates 29V.P. Gupta and Ruchi Verma

Teaching Bioethics at High School 41Methodology and Curriculum DesignS.A. Shaffi and R. Ravichandran

Are We Freezing Ozone? 45S. Hema

Learning Science Hands-on way with 48Discarded Plastic Bottles and Polythene BagsLalit Kishore

Study-habits and Achievement in 54Physics of Students of Class XII–A StudyJagannath K. Dange and Vijayalakshmi

SCIENCE NEWS 58

BOOK REVIEWS 78– Beyond the Barriers by T.V. Krishnan– The Great Aviation Story by R.K. Murthi

VOL. 44 NO. 3DECEMBER 2006QUARTERLY JOURNALOF SCIENCE EDUCATION

CONTENTS

SCHOOLSCIENCE

The intertwined Hansassymbolise the integration ofthree aspects of the work of

the National Council ofEducational Research and

Training (NCERT):(i) Research and

Development, (ii) Training,and (iii) Extension. Thedesign has been adaptedfrom an Ashokan periodrelic of the third century

B.C. found in excavationsnear Maske in the Raichur

district of Karnataka.

The motto has been takenfrom the Isavasya

Upanishad and meanslife eternal through

learning.

LIFE ETERNAL THROUGHLEARNING

3ENERGYINDEPENDENCE

Energy Independence

PRESIDENT, APJ ABDUL KALAM’S ADDRESS**

MALL AIM is a crime”I am indeed delighted to be inKudankulam Nuclear Power

Project, a project of Nuclear PowerCorporation of India. Department ofAtomic Energy has influenced Indiansociety in multiple fields. I understandthat presently the total nuclear powergeneration capacity is 3900 MW using16 nuclear reactor. I am happy to knowthat the nuclear power reactors areworking with an average annualavailability factor of 89%. This was madepossible by adopting innovative fueloptimisation and outage managementtechniques in operating stations. This isa notable contribution of the NuclearPower Corporation towards high qualityoperation and maintenance of powersystems in the country. I extend mygreetings to all the scientists,technologists and staff. I am sure, youwill excel in operational performance inKudankulam Power Plants. When I wasthinking what thoughts I can share withyou since you are in the business ofenergy, I would like to give you a profilewhat should be the energy mix for Indiabetween now to 2020 and 2030. Hence, Ihave selected the topic “EnergyIndependence”.

“S

*Reproduced from Nuclear India Vol- 40/No. 5-6/Nov.-Dec. 2006.**Address of the Honourable President, Dr. A.P.J. ABDUL KALAM at Kudankulam Nuclear Power Project,Kudankulam, Tirunelveli, Tamil Nadu, on 22 September 2006.

Energy Independence

In the field of energy, many innovationsare taking shape. The World EnergyForum has predicted that fossil based oil,coal and gas reserves will last for lessthan ten decades. The energy is animportant parameter for development.Continuously increasing cost of oilsourced from fossil material promptedmany groups in the world to seriouslyconsider the possible energy options.Based on our study, I have discussedabout Energy Independence as part of myIndependence Day Address to the nation,on 15 August 2005. There, I mentionedthat

Energy Independence has to be ournation’s highest priority. Our target isto achieve Energy Security by 2020leading to Energy Independence by2030 and beyond.

Of course there have been manydiscussions nationally as well asinternationally on this subject. I wouldlike to suggest certain actions to be takenon the energy missions for contributingtowards energy independence in Indiaparticularly, it is relevant to atomicenergy scientists and the team of NuclearPower Corporation.

Structure of Energy Sources

Based on the progress visualised for thenation during the next two decades, thepower generating capacity has toincrease to 400,000 MW by 2030 from the

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existing 130,000 MW. This has beenarrived at taking into account the use ofefficient transmission and distributionsystem and minimisation of other losses.Energy independence has got to beachieved through three different sourcesnamely hydel capacity, nuclear powerand non-conventional energy sourcesprimarily through solar energy, apartfrom thermal power. The hydel capacitygenerated through normal water sourcesand inter-linking of rivers is expected tocontribute an additional 50,000 MW.Large scale solar energy farms ofhundreds of megawatts capacity incertain number could contribute around55,000 MW. The nuclear power plantsshould have a target of 50,000 MW ofpower. The balance 115,000 MW has tobe generated through the conventionalthermal plants through coal, gas andother renewable sources of energy suchas wind power, biomass, power throughmunicipal waste and solar thermalpower. The most significant aspect,however would be that the powergenerated through renewable energytechnologies has to be increased to 25%against the present 5%. Let me discussabout the profile of renewable energysystems.

The energy mix for energyindependence envisages use of fourroutes– (a) Hydel + Thermal till coalavailability (b) Solar power using highefficiency CNT based SPV cells(c) Thorium based nuclear reactors(d) Bio-fuel for transportation sector.

As all of you can see the Departmentof Atomic Energy is required to provide50,000 MWs of electric power before 2030contributing to make India energy

independent. Indigenously, we have builtcertain capacity for generating electricitythrough pressurised heavy water route.Let us look at some details which givesus the confidence to take up morechallenging tasks and meet the nationalnuclear energy targets.

India’s first 540 MWe PressurisedHeavy Water Reactor

India’s first 540 MWe Pressurised HeavyWater Reactor (PHWR), built based onindigenous technology at Tarapur,Maharashtra became critical on 6 March2005. It is the largest indigenouslydesigned and built power reactor in thecountry. The commissioning of thisnuclear reactor, has indeed establishedour technological and managerialleadership.

The project at Tarapur comprises ofa twin-unit station of PHWR type, eachof 540 MWe installed capacity and arebeing built adjacent to the existing twounits of smaller size. The first concrete(Grade M-60) was poured on 8 March,2000 and criticality has thus beenachieved in less than 5 years. The designof the reactor incorporates all the basicfeatures of the existing PHWRs. Thesafety features in the existing 220 MWeunits, such as fast acting diverseindependent shutdown systems, highpressure emergency core cooling systems,double containment, supplementarycontrol room along with the safetyobjectives like redundancy diversity,avoidance of common cause failure havebeen incorporated in these 540 MWeunits. However, extensive theoretical andexperimental development followed by

5ENERGYINDEPENDENCE

manufacturing was necessary forimplementing these features. Apart fromthis, there have been additional designinnovations, which were driven with theobjective of maintaining and improvingthe indigenisation of nuclear power plantcomponents. Certain equipment havebeen redesigned so that theirmanufacturing is within the capabilityof Indian industry.

Overall plant execution was done bycontracting out packages of activitiesrather than single activities. Thisapproach simplifies coordination, andtherefore increases speed of execution ofvarious works. This technological andproject management experience will beuseful for our future high-techprogramme.

Completing of this project in a recordtime of less than 5 years is a testimonyto the level of maturity that has beenachieved by the Indian industry and theNPCIL. When I visited project site ofTarapur plant in 2001, I was very happyto see the engineers and staff of NPCILworking round the clock with the pridethat they are going to build the firstIndigenous 540 MWe power station. Theyhave done it and India is proud of them.Similarly, now you are in the process ofcommissioning the first 2 × 1000 MWnuclear power plant using pressurisedheavy water at Kudankulam. I am sure,through your technological capability,dedication and hard work, the plant willbecome critical in time during 2007 andvery soon provide electricity to the grid.As known to the members of NPCIL, Indiahas only limited uranium resourceswhereas, we have plenty of thoriummaterial available in the country. Hence,

the focus of our nuclear scientist in thecoming years has to be in thedevelopment of thorium based nuclearpower plants.

Efficient thorium based nuclear fuel

Going critical of fast breeder reactorwhich is in an advanced stage ofconstruction, development of AdvancedHeavy Water Reactor (AHWR) andAccelerator Driven System (ADS)technologies have to be pursued in anintegrated way. There are many scientificand technological challenges.

Fast Breeder Reactors: Fastbreeder reactors can make a significantcontribution to India’s energyrequirements, but the rate of increasein fast breeder reactor installed capacityhas to follow a certain growth path asplutonium-239, the fuel for the fastreactors gets generated in nuclearreactors. Thus, the rate of new fastreactor capacity addition has to bedetermined by the rate at whichplutonium can be bred. The breedingdepends on the fast reactor design andthe chemical form of plutonium fuel.Metallic fuel gives much higher breedingratio whereas, plutonium in oxide formgives a lower breeding ratio. So our basicresearch has to be on the developmentof metallic fuel on priority. It is only afterwe have established enough fast reactorcapacity, we can shift to thorium basedsystems and continue to get power fromthorium reactors for a long time.

Thorium Technologies: Countryhas already set up a facility forreprocessing thorium and has designedan Advanced Heavy Water Reactor(AHWR), which aims to derive two-third

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of its power from thorium and one thirdfrom plutonium generated from FastBreeder Reactor (FBR). Implementationof the AHWR project and development ofassociated fuel cycle facilities will provideindustrial scale experience in thehandling of thorium. An important basicresearch area would be to develop reactorsystems based on thorium whereinpower derived from thorium can beincreased and external input of fissilematerial can be minimised. It willdefinitely lead to early utilisation ofthorium in power production.

Accelerator Driven Systems: Theother possibility for thorium utilisationis through Accelerator Driven Systems(ADS). ADS have two main components–an accelerator and a reactor. A reactorsystem using only thorium as fuel cannotbecome critical as thorium is not a fissilematerial. To make it critical, an externalsupply of neutrons is needed. A‘spallation’ source can provide anexternal source of neutrons to achievecriticality in an otherwise sub-criticalsystem. The development of anappropriate proton accelerator is the firststep towards the development of ADS.The research results will lead to buildingan accelerator and subsequently the useof accelerator for detachment of neutronsfrom heavy elements. Acceleratortechnology has many other applications.For example, accelerators are useful inhealth care for treatment of cancer andin basic research as tools to studystructure of atom. Accelerators are alsouseful in the industry for chemicalprocessing, where irradiation byaccelerators can be used to improve the

mechanical and electrical properties ofcable insulation. How can we meet theseresearch and development challenges?

I would like to recall two experiences.India’s nuclear programme has alwaysbeen under technological denials fordecades from many countries. Every oneof the nuclear scientists and scienceleaders realised that the self-reliance isthe most promising route. Nuclearscientists have always shown thecountry how nuclear technology can beused for increasing the agriculturalproduce, medical application andnuclear power generation. Let me alsoshare one of my experiences when I waschief of Aeronautical DevelopmentAgency (ADA). It was 1998; Indiaachieved a very important nationalmilestone. This resulted in many nationsimposing technology denials andeconomic sanctions. Particularly, theLight Combat Aircraft programme cameto a halt because of collaboratingcountries breaking the agreements onthe development contracts undertaken.I took an emergency meeting of the ADABoard and we formed a National Teamfor LCA control system with 20 membersdrawn from seven organisations in thecountry with a two years projectschedule. In 18 months, we realised aworld class digital fly by wire controlsystem for the LCA. Now, four LCAaircrafts are flying and the 5th one isgetting ready for flight test. Cumulativeflying hours logged by the four aircraftsis over 500 hours. The batch productionof LCA TEJAS is to commence. Themessage I would like to give to our nuclearscientists is–

7ENERGYINDEPENDENCE

“Nationally we have the best minds,Enlist the national team, The govern-ment and the people are with you,Progress with your vast knowledge andexperience, you will succeed.”

Conclusion

Since I am in the midst of youngscientists of Kudankulam , I would liketo administer an oath on Courage, if youall agree.

COURAGECourage to think different, Courage toinvent,Courage to discover the impossible,

Courage to combat the problems AndSucceed,Are the unique qualities of the scientist.As a scientist of Nuclear Power Plant, Iwill work and work with courage toachieve Success inScientific discoveries andScientific achievements

My best wishes to all the scientistsand technologists of KudankulamNuclear Power Project for success in theirmission of providing all the technologicaland scientific support for making Indiaenergy independent by 2030.

May God bless you.

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NanotechnologyA Primer with FAQ

JITENDRA SINGH

Senior Lecturer, Central Institute ofEducational TechnologyNational Council of EducationalResearch and TrainingNew Delhi-110 016

MAGINE THAT you are able torearrange atoms whichever wayyou want. The properties of the

manufactured products depend on howthose atoms are arranged. If werearrange the atoms in coal, we may getdiamonds. If we rearrange the atoms insand (and add a pinch of impurities), wemay get chips. If we rearrange the atomsin soil, water and air, we may get grass.

Tell us a story

Nobel Prize winner, Physicist Richard P.Feynman may have had the idea fornanotechnology before anyone else. Inthe speech, titled “There’s Plenty of Roomat the Bottom,” Feynman expressed theidea of “manipulating and controllingthings on a small scale,” adding that hewas not referring just to miniaturisation,but the ability to do things such as writingthe entire Encyclopedia Britannica on thehead of a pin. He explained how it couldbe done by shrinking everything downto 1/25,000 of its original size withoutlosing resolution. Although Feynmannever mentioned the word “nano-technology,” he did point out how wecould build incredibly small computers–

I

even miniature surgeons who could goinside our bodies to do their work. Manyscientists at the time took his ideas as ajoke. However, he offered a $1,000 rewardfor the first person to shrink a page to1/25,000 of its size and show that it isstill readable through an electronmicroscope. In 1985, a graduate studentat Stanford named Tom Newman usedan electron beam to write the first pageof A Tale of Two Cities, by CharlesDickens, at 1/25,000 its original size onthe head of a pin. He put together apackage with the pin and the evidencesupporting his work and mailed it toFeynman. Within two weeks, Feynmansent back a cheque.

1. What is Nanotechnology?

The term “nanotechnology” was coinedby Norio Taniguchi of Tokyo ScienceUniversity, Japan in 1974. Nano-technology, really “nanotechnologies” isthe creation of useful materials,structures, devices, and systemsthrough the manipulation of shape andsize of matter on this miniscule scale. Itmatters because familiar materials beginto develop odd properties when they arenanosize. Tear a piece of aluminum foilinto tiny strips, and it will still behavelike aluminum, even after the strips havebecome so small that you need amicroscope to see them. But keepchopping them smaller, and at somepoint, 20 to 30 nanometres, in this case,the pieces can explode. Not all nanosizematerials change properties so usefully,but the fact that some do is a boon. Withthem, scientists can engineer acornucopia of exotic new materials, suchas plastic that conducts electricity and

9NANOTECHNOLOGYA PRIMER WITH FAQ

coatings that prevent iron from rusting.Already, prototype exist of, for instance–a motor as thin as a hair, forceps thatcan hold a single bacterium, and acogwheel only 35 micrometres across, ora hundredth the size of the toothedwheels in a wristwatch. The ongoingquest for miniaturisation has brought usto a point that we are coming closer todoing things only nature can, such asmaking switches using single atoms, orproducing new proteins.

2. It’s a Small WorldSmaller than Small

The main thing to know aboutnanotechnology is that it’s small. Reallysmall. Nano, a prefix that means “dwarf”in Greek, is shorthand for nanometer(10-9), one-billionth of a metre or onemillionth of a millimeter.

This comma, for instance, spansabout half a million nanometers. Ahuman hair is about 80,000 nanometreswide. It’s difficult to imagine anything sosmall, but think of something only1/80,000 the width of a human hair. Tenhydrogen atoms could be laid side-by-sidein a single nanometer. To put it anotherway, a nanometer is the amount a man’sbeard grows in the time it takes him tolift a razor to his face.

To see nanoparticles and manipulatethem, scientists use high-poweredmicroscopes that must be maintainedand operated in a carefully controlledenvironment. The room is kept ultraclean, so particles from the air, and fromthe operators, won’t contaminate thedevice. And to prevent vibrations, theinstrument is anchored to a 5,000 tonblock of concrete 12 metres belowground.

3. Nanotechnology plays bydifferent rules

Much of today’s nanoscale research isdesigned to reach a better understandingof how matter behaves on this smallscale. The factors that govern largersystems do not necessarily apply at thenanoscale. Because nanomaterials havelarge surface areas relative to theirvolumes, phenomena like friction andsticking are more important than theyare in larger systems.

4. Nanodevices: Building Blocks ofNanotechnology

There are two basic approaches forcreating nanodevices. Scientists refer tothese methods as the top-down approachand the bottom-up approach. The top-down approach involves molding or

Fig. 1: Comparison of nanodevices with others on a nanoscale

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etching materials into smallercomponents. This approach hastraditionally been used in making partsfor computers and electronics. Thebottom-up approach involves assemblingstructures atom-by-atom or molecule-by-molecule, and may prove useful inmanufacturing devices used in medicine.

Fig. 3: Approaches to creating nanodevices

4.1 Nanocrystals

Nanocrystals also known as quantumdots, are a semiconductor crystal just afew nanometers in size. Interacting with

such objects in a 3-D landscape insteadof looking at images of them enablesscientists to “easily perceive complexrelationships. Such insight is crucialbecause the properties of basic materialscan radically change when they arenanosize. For instance, scientists havedeveloped glass that can withstandtemperatures up to 982°C for more thantwo hours and tiny gold-plated spheresthat can destroy cancer cells in micewithout harming healthy tissue.

These materials are of hugetechnological interest since many of theirelectrical and thermodynamic propertiesshow strong size dependence, and cantherefore be controlled through carefulmanufacturing processes.

The tiny towers of powering thin-filmsolar panels can be made cheaply in alaboratory beaker. It will cut both of thesolar cells and the equipment needed todeploy them, making solar powereconomical.

Fig. 4a: Nanocrystals

Fig. 2: Nanoscale and Normal scale


Nanocrystals absorb light and thenre-emit it in a different colour. Its sizedetermines the colour.

Fig. 4b: Nanocrystals: six differentquantum dot solutions excited with a

long radiation UV lamp

4.2 Nanotubes

Nature can turn carbon into diamonds.We, humans can turn carbon intonanotubes. Nanotubes are carbon rodsabout half the diameter of a molecule ofDNA. Nanotubes and nanowires arestronger than steel wires, carry athousand times more electricity thancopper wires, and can support morethan a million times their own weight.They’re also the cornerstone of amolecular science that is manipulatingordinary materials so they behave inextraordinary ways.

4.3 Nanoshells

Nanoshells are miniscule beads coatedwith gold. By manipulating the thickness

Fig. 5: Three-Dimensional Carbon nanotube

of the layers making up the nanoshells,scientists can design these beads toabsorb specific wavelengths of light. Themost useful nanoshells are those thatabsorb near-infrared light, which caneasily penetrate several centimeters ofhuman tissue. The absorption of light bythe nanoshells creates an intense heatthat is lethal to cells.

Fig. 6: Nanoshells

4.4 Nanopores

Another interesting nanodevice is thenanopore. Nanopore technology for

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analysis of nucleic acids converts stringsof nucleotides directly into electronicsignatures. Improved methods of readingthe genetic code will help researchersdetect errors in genes. Scientists believenanopores, tiny holes that allow DNA topass through one strand at a time, willmake DNA sequencing more efficient.

Fig.7: Nanopores

4.5 Nanofilters

A strong influence of nanochemistry onwaste-water treatment, air purificationand energy storage devices is to beexpected. Nanoporous membranes aresuitable for a mechanical filtration withextremely small pores smaller than 10nm (“nanofiltration”). Nanofiltration ismainly used for the removal of ions orthe separation of different fluids.Magnetic nanoparticles offer an effectiveand reliable method to remove heavymetal contaminants from waste water.Using nanoscale particles increases theefficiency to absorb the contaminantsand is comparatively inexpensivecompared to traditional precipitation andfiltration methods.

5. Are nanodevices small enough toenter in the biological cell?

Cells are nature’s nanomachines. Mostanimal cells are 10,000 to 20,000nanometers in diameter. The size ofnanomaterials is similar to that of mostbiological molecules and structures. Forinstance, DNA molecule is 2 nm indiameter and proteins range from 5 to50 nm. This means that they can entercells and the organelles inside them bothin vivo and in vitro to interact with DNAand proteins. Tools developed throughnanotechnology may be able to detectdisease in a very small amount of cellsor tissue. They may also be able to enterand monitor cells within a living body.Thus far, the integration ofnanomaterials with biology has led to thedevelopment of diagnostic devices,contrast agents, analytical tools,therapy, and drug-delivery vehicles.

Fig. 8: Nanodevices in a biological cell

6. Nanodevices in medicine

Other challenges apply specifically to theuse of nanostructures within biologicalsystems. Nanostructures can be so smallthat the body may clear them too rapidlyfor them to be effective in detection or


imaging. Larger nanoparticles mayaccumulate in vital organs, creating atoxicity problem. Scientists will need toconsider these factors as they attemptto create nanodevices the body willaccept.

Fig. 9: Nanodevices in human body

6.1 Nanodrugs

Patients will drink fluids containingnanorobots programmed to attack andreconstruct the molecular structure ofcancer cells and viruses to make themharmless. There is even speculation thatnanorobots could slow or reverse theaging process and life expectancy couldincrease significantly.

6.2 Nanodiagnosis

Biological tests measuring the presenceor activity of selected substances becomequicker, more sensitive and more flexiblewhen certain nanoscale particles areput to work as tags or labels. Magneticnanoparticles, bound to a suitableantibody, are used to label specificmolecules, structures or microor -ganisms. Gold nanoparticles tagged withshort segments of DNA can be used fordetection of genetic sequence in a

sample. Multicolour optical coding forbiological assays has been achieved byembedding different-sized quantum dots<http ://en.wik ipedia .org/wik i/Quantum_dots> into polymericmicrobeads.

6.3 Nano drug delivery– Dendrimers

The overall drug consumption and side-effects can be lowered significantly bydepositing the active agent in the morbidregion only and in no higher dose thanneeded. This highly selective approachreduces costs and human suffering. Onesuch molecule with potential to linktreatment with detection and diagnosisis known as a dendrimer. Dendrimers areman-made molecules about the size ofan average protein, and have abranching shape. This shape gives themvast amounts of surface area to whichtherapeutic agents or other biologicallyactive molecules can be attached. Theycould hold small drug moleculestransporting them to the desiredlocation.

Fig. 10: Dendrimer

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6.4 Nanotechnolgy in tissue engineeringNanotechnology can help to reproduceor to repair damaged tissue. This socalled “tissue engineering” makes use ofartificially stimulated cell proliferation byusing suitable nanomaterial-basedscaffolds and growth factors. Tissueengineering might replace today’sconventional treatments, e.g.transplantation of organs or artificialimplants. On the other hand, tissueengineering is closely related to theethical debate on human stem cells<ht tp ://en.wik ipedia .org/wik i/Stem_cells> and its ethical implications.

7. Frequently Asked Questions (FAQ)

#1 What is nanologic?

Response

Nanologic is combining nano-technology and computers. The ideabehind nanologic is to exploit the non-linearities, that nanoscale devices exhibit.

#2 What is nanolaser?

Response

The semiconductor nanowire typically10-100 nanometers wide function as alaser. Lasers made from arrays of thesewires can be used for communicationand sensing devices.

#3 What is quantum computing?

Response

Will we ever have the amount ofcomputing power we need, or want? Ifthe number of transistors on amicroprocessor <http://computer.h o w s t u f f w o r k s . c o m /

microprocessor.htm> continues todouble every 18 months, the year 2020or 2030 will find the circuits on amicroprocessor measured on an atomicscale. And the logical next step will be tocreate quantum computers, which willharness the power of atoms andmolecules to perform memory <http://computer.howstuffworks.com/computer-memory.htm> and processing tasks.Today’s computers work bymanipulating bits that exist in one of twostates– a 0 or a 1. Quantum computersaren’t limited to two states. They encodeinformation as quantum bits, or qubits.A bit can be a 1 or a 0, or it can exist in asuperposition that is simultaneouslyboth 1 and 0 or somewhere in between.Qubits represent atoms <http://comput e r.hows tu f fwo rks . c om/atom.htm> that are working together toact as computer memory <http://computer.howstuffworks.com/computer-memory.htm> and a processor <http://comput e r.hows tu f fwo rks . c om/microprocessor.htm>. Quantumcomputers have the potential to performcertain calculations billions of timesfaster than any silicon-based computer.Because a quantum computer cancontain these multiple statessimultaneously, it has the potential tobe millions of times more powerful thantoday’s most powerful supercomputers.

Fig.11: Nanolaser


#4 What is Smart dust?

Response

Smart dust is a hypothetical networkof tiny microelectromechanicalsensors, computing circuits, robots, ordevices, installed with bidirectionalwireless communications and a powersupply. The devices are intended tobe of the size of a dust <http://en.wikipedia.org/wiki/Dust> particle.These would gather data, runcomputations and communicate usingtwo-way-band radio at distancesapproaching 300 metres.

Fig.12: Smart dust

#5 What will we be able to make withnanotechnology?

Response

Researchers are expanding theboundaries of nanotechnology,discovering unforeseen uses for themanufactured materials. Nano-technology will be impacting the fieldof consumer goods, providing easy-to-clean and scratch-resistant ceramicsand glasses; wrinkle-resistant andstain-repellant nanofibres in textiles;

nanocomposite coating to improve foodprocessing and packaging;antireflective ultrathin optics;cosmetics; and electronics.

Fig.13: Nanogears depicted through acomputer simulation

#6 What will be the impact ofnanotechnology on the medicine?

Response

Nanotechnology may have its biggestimpact on the manufacturing andmedical industry. If we had surgical toolsthat were molecular both in their size andprecision, we could develop a medicaltechnology that for the first time wouldlet us directly heal the injuries at themolecular and cellular level that are theroot causes of disease and ill-health.Nanorobots as molecular surgeons canperform delicate surgeries. That toowithout leaving the scars thatconventional surgery leaves.

With the precision of drugs combinedwith the intelligent guidance of thesurgeon’s sharpest scalpel, we canexpect a quantum leap in our medicalcapabilities.

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#7 How will the nanotechnology impactthe treatment of cancer?

Response

While the existing modes of cancertreatment such as chemotherapy,radiation and surgery are invasive ordebilitating, nanotechnology promisesdeveloping ways to eradicate cancer cellswithout harming healthy, neighbouringcells. Scientists hope to usenanotechnology to create therapeuticagents that target specific cells anddeliver their toxin in a controlled, time-released manner.

Fig. 14: Nanodrugs targeting cancer cells

Scientists link nanoshells toantibodies that recognise cancer cells.They envision letting these nanoshellsseek out their cancerous targets, thenapplying near -infrared light. Inlaboratory cultures, the heat generatedby the light-absorbing nanoshells hassuccessfully killed tumor cells whileleaving neighbouring cells intact.

Fig. 15: Nanoshells in cancer therapy

#8 What is the progress of India in the fieldof Nanoscience and nanotechnology?

Response

● The government of India hasestablished a mission for Nano-science and technology consortium.

● An indigenous nanofilter, that caneliminate contaminants from water,has been developed by an Indianscientist named at the BanarasHindu University.

● An indigenous nano method ofthyphoid diagnosis has beendeveloped by an Indian scientistnamed at DRDO, Indore.

● About eleven patents have beensubmitted for drugs developed by anIndian scientist, named A. K. Mitraof Indian Institute of Science,Bangalore.

#9 What careers might emerge?

Response

Numerous avenues exist for pursuing acareer in nanotechnology, such asmolecular machinery, manufacturing,computation, medicine and so on.


REFERENCES

<http://en>.Wikipedia.org/wiki/Nanotechnologyhttp://science.howstuffworks.com/nanotechnologyKAHN, JENNIFER. 2006. Nano’s Big Future. National Geographic. 98-119FOSTER, LYNN E. 2006. Nanotechnology: Science, Innovation and Opportunity.

Prentice Hall, New YorkHUNT, GEOFFREY AND MEHTA, MICHAEL (eds). 2006. Nanotechnology: Risk Ethics,

and Law. Earthscan, London.Future of Light?Workers expose coloured LEDs, or light-emitting diodes, to high currents,

temperatures, and humidity to test the devices’ long-term reliability at asemiconductor factory. Using nano-engineered molecules to emitlight-generating photons, LEDs are energy efficient.

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Learn more aboutNanotechnology andCarbon Nano Tubes

S.V. SHARMA

Regional Institute of Education (NCERT)Ajmer-305 004, Rajasthan

HE 21st CENTURY in its beginningitself is sparkling with a totallynew kind of technological

revolution whose proper dimensions anddirections are yet to be ascertained. Itwill be now possible to synthesisematerials with tailored properties. Thisis possible because of nano-precisiontechnology known as nanotechnology(NT). What is nanotechnology? It is thetechnology of creation, use ormanipulation of matter on thenanometer (1 nm = 1 0-9 metres) scale–the scale of atoms, molecules and livingcells. It is an emerging, inter disciplinaryfield combining principles of chemistry,physics and biology with the engineeringprinciples of mechanical design,structural analysis, computer science,electrical engineering and systemsengineering. Who has coined the term“nanotechnology”? The term“nanotechnology” was coined by NomoTaniguchi in 1974 in regard to themanufacture of items by mechanicalmachining routes. What doesnanotechnology hold? It holds out thepromise of manufacturing of materials ofprecisely specified composition andproperties which could capitulate

T

structures of exceptional strength andcomputers of amazing compactness andpower. What does one expect from theinnovations of nanotechnology? It isexpected that the innovations ofnanotechnology will lead to fundamentaldiscoveries in the field of science andtechnology. It may also be possible to haverevolutionary methods of atom-by-atommanufacturing based on this technologyfor the processing and rearrangement ofatoms to fabricate customised productsand surgery on the cellular scale.On 29 December 1959, the AmericanPhysicist Richard Feynman delivered alecture in the meeting of AmericanPhysical Society entitled “There is plentyof room at the bottom” (www. Feynman/plenty.html) in which he discussed thebenefits to society that would accumulateif we are able to manipulate matter andmanufacture artifacts with precision onan atomic scale. He very rightly foresawthe impact that miniaturisation wouldhave on the capabilities of electroniccomputers and predicted thedevelopment of the methods that are nowused to make integrated circuits and theemergence of techniques for writingextremely fine patterns with beams ofelectrons. He even mooted thepossibilities of making machines at themolecular scale which would enable usto manipulate chemical and biologicalmolecules. Researchers working in thefield of nanotechnology research havebeen trying to realise some of hisoriginally propounded ideas which werenot foreseen at that time. In order tograsp the idea regarding the scale of ananometre length, consider a human

LEARN MORE ABOUT NANOTECHNOLOGYAND CARBON NANO TUBES

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hair which is typically about 100 μm indiameter. Table 1 visualises a nanometerscale. It can thus be seen that 1 nm isan extremely small dimension to workwith it. However, it is in the close vicinityof researchers to achieve this. In thisarticle, attempts have been made tohighlight the significance ofnanotechnology, its applications andfuture projection. A brief discussion onCarbon Nano Tube (CNT) has also beenpresented to make the learners awareregarding its promising properties.

Current researches innanotechnology

Current research programmes innanotechnology are laying the

foundation for breakthrough develop-ments in manufacturing systems basedon extremely productive nanoscaledevices/tools. These molecularmanufacturing systems can be used tomanufacture complex products withatomic precision, desktop computerswith a billion processors, solar energysystems with very high efficiency,medical devices to destroy pathogens andrepair tissues, superior military systems,and absorbents.

Applications of nanotechnology

Monitoring patients

It is known that the diameter of mostanimal cells is in the range of 10,000 to

TABLE 1Some particles and their size on nano scale

Red blood cells 7,000 nm in diameterWhite blood cells 10,000 nm in diameterA virus 100 nmA hydrogen atom 0.1 nmNano-particles ranges from 1 to 100 nmDNA (width) 2 nmProteins ranges from 5 to 50 nmBacteria ranges from 1000 to 10,000 nmSmoke 10-103 nmColloidal silica 5-80 nmClay 102 to 103 nmMacro particles 104 to 105 nmMicro particles 103 to 104 nmMacro molecules 102 to 103 nmMicro molecules 1 to 80 nmMi-cells 1 to 10 nmPaint pigment 102 to 5 × 103 nmPollens 104 to 105 nmPyrogens 1 to 15 nmQuantum dot 1 to 5 nmSand 105 nmYeast cells 5×103 to 5 × 104 nm

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20,000 nm. This implies that nano scaledevices/tools can enter into cells andinteract with DNA and be able to detectchanges or modifications, if any, due todisease in a very small sample of cells.In order to notice cancer successfully atits earliest stages, researchers must beable to detect molecular changes evenwhen they occur only in small percentageof cells. The potential for nano-structuresto enter and analyse a single cell openup the possibility that they could meetthis need. Nanotechnology baseddevices/tools could be made to moveeasily to different parts in a body andtransmit / take corrective action to repairan organ of body effectively withoutaffecting the healthy cells undisturbed.Researchers are making efforts fordeveloping chimeric peptides containinga nucleic acid building domain linked toa receptor binding domain of neurotrephines to target gene delivery vectorsto tumor cells. Detection in early stagesand the cure for Alzheimer’s disease ishoped to be possible (V.K. Moorthy, 2005)and (M.M.S. Karki, 2005).

Possible use of nano-pores

It is believed that improved methods ofreading the genetic code will helpresearchers to detect error in genes thatcontributes to cancer. Researchersbelieve that nano pores (tiny holes thatallow DNA to pass through one strand ata time) will make DNA sequencing moreefficient. They can monitor the shapeand electrical properties of each base onthe strand when DNA passes through anano pore. They can also use the passageof DNA through a nano pore to decipher

the encoded information including errorsin the code known to be associated withcancer. Nano pores are so small that thebody may clear them too rapidly foreffective detection / imaging. It would bea very challenging task to use nano porescategorically in biological systems andfabricate nano-devices/tools for humanbodies i.e., the living machines.

Electronics

Using’ nanotechnology electroniccomponent and size of the electronicdevices would be reduced drastically. Itis hoped that many complex devices canbe merged to offer multi purpose utilityin a single small chip.

Automobile

It would be possible to run the automobileby using the fuel assembled usingnanotechnology. This may result in themodification of the engines of theautomobiles and their operation stylemay change drastically as compared totraditional ones.

Agriculture

Researchers around the world have beenexploring the possible use of nanoparticles in agriculture for a number ofpurposes other than pesticides; fromenhanced photosynthesis to bettergermination and soil management. Alsouse of nano particles, in particular forcleaning up the soil contamination frommetals has also been explored. They havehinted upon a new technology based onnanotechnology for injecting DNA intomillions of carbon nano fibres.

LEARN MORE ABOUT NANOTECHNOLOGYAND CARBON NANO TUBES

21

Carbon nano tube

Carbon Nano Tube (CNT) is a new carbonallotrope discovered in 1991 by Dr.Sumio-Ijima. It has hollow tubularstructure in nano scale and differentatomic arrangement from graphite,diamond and bucky ball (C6o). Theproperties of three allotropic forms(graphite, diamond and bucky ball) ofcarbon have been reported earlier(Sharma, 2003). The properties of CNTin comparison with some commonmaterials are given in Table 2. Promisingproperties of CNT have attracted theattention of the researchers all over theworld. Carbon Nano Tubes have beenreported useful in broad range oftechnological applications such as–telecommunications, cell phones,rechargeable lithium batteries, medicalimaging equipment, computer display,multifunctional composites for aircraft,bullet proof vests, powered clothes,sensing strain, bucky paper,microcapsules, CNT based field effecttransistor and diode, thermalmanagement, nano silvery washing

machine and refrigerator (V.K. Moorthy,2005) and (M.M.S. Karki, 2005).

Limitations of nanotechnology

Detection of nano particles injected inanimals or human beings because oftheir small sizes is a big problem.Ecological impacts of the nano fibres onthe cells of other organism andinflammation in lungs seems to be moresevere than in cases of silicoses. Hence,use of nanotechnology raises a numberof questions regarding its limitations.

What are environmentalists’ viewsabout nanotechnology?

Nano scale formulation of agriculturalproducts such as pesticides, fertilisersand soil treatment powders should beprohibited from environmental releaseuntil a new regulatory regime specificallydesigned to examine these products andreport them safe. Also all food, feeds andbeverage products that incorporatemanufactured nano particles should berestricted.

TABLE 2Comparison of properties of CNT with some common materials

Material Tensile Strength Yong’s modulus Density(GPa) (g/cc)

Wood 0.008 16 0.6Rubber 0.025 0.05 0.09Steel 0.04 208 7.8Spider silk 1.34 281 1.3Diamond 1.2 1140 3.52Kevlar 2.27 124 1.44CNT 200 1000 2Carbon fibre 2.48 230 2Glass fibre 2.53 87 2.5

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India and nanotechnology

India in its own way is making its wayinto nanotechnology research. Variousfunding agencies like Department ofScience and Technology, UniversityGrants Commission, have launchedmany nano-sciences research pro-grammes. A number of institutions havestarted coordinated nanotechnologyresearch work. Indian nano-sciencesresearch covers a wide spectrum oftopics which includes microelectronicsmechanical systems (MEMS*),synthesis and characterisation of nanomaterials, single and multi walledcarbon nano tubes, carbon nano-tubewire, DNA chips, nano electronics andnanobot.* *

Future scenario of nano technology

Projected scenario in the field ofnanotechnology and nano materialscience research is listed here–

Year Projected Scenario

2010 Nano technology will be visibleeverywhere.

2015 Advances in nano electronics andcomputers based on nano-technology.

2020 Nano materials in plenty.2025 Nanotechnology energy year.

2045 Nano robotics.

It can be concluded that in the daysto come nanotechnology will emerge outas the technology in demand that will beutilised to fabricate substances anddevices/tools to generate newphenomena peculiar to the mingling ofatoms, bits and even genomes. It will alsoprovide a common base to support thedevelopment of advanced materials,information and biotechnologies. It ishoped that potential applications ofnanotechnology will revolutionise everywalk of human life.

* MEMS are micro-electromechanical systems comprising of computers linked to tiny mechanicaland other devices like sensors, valves, gears and actuators embedded in semiconductor chipsbased on silicon.**Nanobot– a microscopic computerised robot uses rotary blades to break up the blockage andsuction nozzles to remove the grey plaque (V.K. Moorthy, 2005) and (M.M.S. Karki, 2005).

REFERENCES

www. Feynman/plenty .htmlwww.icmss.org/LJIYAMA, S. 1991. Nature. 354, 56.KARKI, M.M.S. Jan-Feb 2005. Invention Intelligence. 17.MOORTHY, V.K. Jan-Feb. 2005. Invention Intelligence. 5.SHARMA, S.V. 2003. School Science. XLI -1, 3.

HARD SPOTS IN TEACHINGOF CARBOHYDRATES

29

Hard Spots in Teaching ofCarbohydrates

RUCHI VERMA

Lecturer in Chemistry, NCERTNew Delhi

V.P. GUPTA

Professor of ChemistryRIE, NCERT, Bhopal-462 013

ARBOHYDRATES are essentialnutrients for life like proteins andvitamins. Three essential

requirements of life i.e., food, clothes andshelter, are directly or indirectly linkedwith Carbohydrates. The syllabi ofChemistry at the higher secondary andgraduate level usually envisage a studyof various aspects of carbohydrates suchas their structure and properties.Interaction with students at highersecondary level, collegiate level, teachersand teacher educators have led us toidentify different hard spots from thistopic. An attempt has been made here todiscuss some hard spots of this topicalongwith the chemical reactions involved.

2.0 Identified Hard Spots

● Misconception in definition ofcarbohydrates

● Classification of carbohydrates

● Stereo chemistry of carbohydrates

● Representation of Ring Structure

● Relation between Fischer andHaworth Projection

● Mechanism of Mutarotation

C

2.1 Definition of Carbohydrates

Most of the books at the senior secondaryand collegiate level do not give completedefinition of carbohydrates. This leads tothe misconception about the definition.According to the classical definition, theterm carbohydrate stands for hydratesof carbon, which contain hydrogen andoxygen in the same proportion as in wateri.e 2:1. For example, glucose and fructose[C6H12O6 or C6(H2O)6], sucrose [Cl2H22O11

or Cl2 (H20)1l], and starch (C6H10O5)n or[C6(H2O)6]nare the hydrates of /° carbonand hence they are carbohydrates. Nowthe question arises, whether thefollowing compounds)which alsosatisfy the above definition, are thecarbohydrates?

Fonnaldehyde : HCHO i.e. [C.(H2O)]

Acetic acid : CH3COOH i.e. [C2.H2O)2]

Lactic acid : CH3CH(OH) COOH i.e.[C3.(H2O)3].

Obviously, the answer is No.On the other hand, we also come

across a few Carbohydrates which do notconform to the above definition. Forexample, rhamnose (C6H12O5),rhamnoheptose (C7H14O6) and 2-deoxyribose (C5H10O4), fucose (C6Hl2O5)are carbohydrates but do not satisfy theabove definition. Hence, there is a needto modify the definition keeping in viewthe structure and properties ofcarbohydrates. Structurally, carbo-hydrates contain two types of functionalgroups,– OH and >C=O group can be inthe form of a ketonic group or thealdehydic group.

So, another definition that comes toour mind is, “carbohydrates are

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polyhydroxy aldehydes or ketones or thecompounds, which are converted to theseon hydrolysis.

If we follow the above definition,again we come across another conflict.Whether the following compound, 1, 3Dihydroxypropan-2-one, should beconsidered a carbohydrate.

CH2OH|C=O|CH2OH

To overcome this problem, we willhave to take cognizence of their opticalproperties. Since it is now known thatall naturally occurring carbohydratesare optically active or on hydrolysisproduce optically active compounds.Thus, the correct definition ofcarbohydrates should be read as givenin the box.

Optically active polyhydroxy aldehydesor ketones or the compounds, which areconverted to these on hydrolysis arecalled carbohydrates.

2.2 Classification of Carbohydrates

It was found that generally students getconfused between different classes ofcarbohydrates and their examples. Thefollowing flow chart depicts theclassification of carbohydrates withsuitable examples.

2.3 Stereochemistry of Carbohydrates

Most of the teachers, teacher educatorsand students are found to face difficultyin understanding terminology and thefundamental concepts of carbohydrates’stereochemistry. Some basic termino-logies have been discussed in this

Monosaccharideneespare.They contain upto sixcarbon atoms, They aresweet in taste, soluble inH2O and cannot behydrolysed further.Arabinose, glucose,fructose, mannose are afew examples of thisclass.

Carbohydrates

Oligosaccharides. Thesecontain 2 to 10 units ofmonosaccharides. Forexample, lisaccharides(sucrose, lactose,maltose); Trisaccharides,tetrasaccha-rides etc.Oligosaccharides arehomogeneous: Eachmolecule of a particularoligosaccharide has thesame number of mono-saccharide units joinedtogether in the sameorder as every othermolecule of the sameologosaccharide.

Polysaccharides. Theyhave more than 10 unitsof monosaccharides.Almost always mixturesof molecules having thesimilar but not nece-ssarily the same chainlength. For example,cellulose, starch etc.

▲ ▲ ▲


31

section along with examples.Carbohydrates contain more than oneasymmetric carbon atoms resulting inlarger number of optical isomers. Themaximum number of optical isomers thata carbohydrates can have equals to 2n

where n is the number of asymmetriccarbon atoms. Each optical isomer hasits own optical activity and absoluteconfiguration. If the solution of thecarbohydrate or any substance in theliquid state tilts the path of planepolarised light (The light ray havingvibrations only in one plane) towardsright to its original path, that substanceis said to be dextorotatory and isdesignated as D or (+). On the other hand,the one rotating the path towards left iscalled levorotatory and designated as Lor (–).

Absolute configuration of acompound represents the spatialrelationship of the groups attached to anasymmetric carbon atom. Symbols ‘D’and ‘L’ are used to depict absoluteconfiguration of carbohydrates.Nowadays, it is possible to assignabsolute configuration to each chiralcentre, but in early twentieth century, itwas not possible to assign absoluteconfiguration to the molecule. In 1906,an American Chemist, M.A. Rosanoffsuggested a system of assigning theconfiguration. According to this system,configurational isomers of glyceraldehydewere chosen as the configurationalstandards for the monosaccharides. Heassigned D configuration to (+)glyceraldehyde in which –OH group ofcarbon-2 lies towards right and Lconfiguration to (–) glyceradehyde in

which the –OH group lies towardsleft. For drawing projections ofglyceraldehyde molecule, draw itsstructure in such a way that thealdehyde group is at the top. Tounderstand this, represent theglyceraldelyde molecule on the paperusing Fischer’s projections in whichhorizontal bonds are defined as the onecoming out of the plane of paper towardsthe viewer and vertical bonds going awayfrom the viewer. The form I in which –OHgroup is attached to the asymmetriccarbon atom in the right hand side isassigned D-configuration, whereasthe form II in which –OH group lieson the left hand side is assignedL–configuration as shown in Fig. 1.

D-(+)-Glyceraldehyde L-(–)-Glyceraldehyde

Fig. 1

2.3.1 Isomers of Monosaccharides(Enantiomers andDiastereomers)

Number of isomers goes on increasing aswe go on introducing another asymmetriccarbon atom. Let us illustrate by takingthe examples of isomers of carbohydrateswith molecular formula as C4H804. Dueto two asymmetric carbon atoms, itshould have four isomers (Fig. 2).

CHO

CO

CH2OH

OH

CHO

CHO H

CH2OHMirror

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In the above examples, structure Iand II are non superimposable mirrorimages of each other. These are termedas enantiomers of each other. Structuresshown by III and IV also have the samerelationship. What is the relationshipbetween structure I and III; I and IV; IIand III; and, II and IV? All these pairs ofstructures are not mirror images of eachother. Such optical isomers which arenot mirror images are calleddiastereomers.

Structure I differs from structure IIIand structure II differs from structure IVonly in configuration about carbon No 2.So a new term is used for such a pair ofdiastereomers. Diastereomers whichdiffer in configuration only at carbon 2are called epimers.

“A pair of diastereomers which differin configuration only at one stereo geniccentre i.e., at carbon 2 are calledepimers.

2.4 Unique Behaviour of Carbohydrates

Some important and specific propertiesare highlighted to strengthen thefoundation of structural aspect ofcarbohydrate chemistry. By now, youhave learnt that carbohydrates contain

–OH (hydroxyl) group and >C=O(carbonyl) group. Now the questIon is :whether both the groups show theirunique behaviour/properties incarbohydrates or the properties of onegroup are influenced by the property ofthe other group. Some of the propertiesof Glucose strengthen the later aspect.These are as follows:

(i) Glucose doesn’t show carbonyl(>C=O) absorption in its infra redspectrum.

(ii) Glucose does not give the Schiffstest for aldehydes.

(iii) Glucose does not form an additionproduct with NaHSO3 saturatedsolution although it seems tocontain aldehyde group.

(iv) Glucose penta-acetate does notreact with hydroxyl amine.

(v) Glucose does not react withGrignard’s reagent i.e. no additionproduct is formed which is thecharacteristic reaction of carbonylcompounds.

(vi) Glucose does not react with NH3.

(vii) When glucose is treated withmethanol in presence of dil HCI,dimethyl acetal is not formed, but

CHO|

H—C—OH|

H—C—OH|

CH2OH

CHO|

HO—C—H|

HO—C—H|

CH2OH

CHO|

HO—C—H|

H—C—OH|

CH2OH

CHO|

H—C—OH|

HO—C—H|

CH2OH

C4H8O4

D(–) Erythrose(I)

L(+) Erythrose(II)

D(–) Threose(III)

L(+) Threose(IV)

Fig. 2


33

two isomeric monomethyl glucosidederivatives are obtained.

(viii) Isolation of two crystalline forms ofglucose, the aqueous solutions ofwhich change their specific rotationon keeping overnight.

(ix) Glucose is more stable than thecorresponding alcohol sorbitol.Generally, the stability of aldehydesis less than that of thecorresponding alcohols.

The above abnormalities in thebehaviour of glucose can be understoodon the basis of its ring structure becausein the open chain structure, glucoseseems to contain one free aldehyde groupwhich actually does not remain so in thering structure of glucose. Open chainstructure of glucose is shown in Fig. 3.

CHO|

H—C—OH|

HO—C—H|

H—C—OH|

H—C—OH|

H2C—OH

Open Chain Structure of D( +) - Glucose (V)

Fig. 3

2.5 Representation of Ring Structure

To account for the above behaviour ofglucose and other monosaccharides,Tollens (1883) and Erdman (1885)proposed the two isomeric forms (a&β) ofthese sugars. These two forms arepossible if we assume an oxide cyclicstructure for monosaccharides. We may

take the simplest example of glucose, thetwo configuration of which are shown inFig. 4.

There may be intramolecularinteraction between carbonyl group andone of the –OH groups, resulting in theformation of cyclic hemiacetal. The newstereogenic centre is created at C-l. Inthe cyclic form, two possible positions of–OH group created at C-1 may moveeither to left or right resulting in theformation of two diastereomers. Suchconfigurations differing in position ofatoms/groups at C-l, other positionsremaining same are called annomers.Thus configurations VI and VII areannomers.

A pair of diastereomers differing inconfiguration only at C-1 are calledanomers.

The ring size is decided by Bayer’sbond angle strain theory (five and sixmembered rings have less bond anglestrain, hence more stable than three,four or seven membered rings). Sixmembered ring system (containing fivecarbon atoms and one oxygen atom) is

HO—C—H|

H—C—OH|

HO—C—H|

H—C—OH|

H—C|

CH2OH

(VII)

H—C—OH|

H—C—OH|

HO—C—H|

H—C—OH|

H—C|

CH2OH

(VI)

Fig. 4

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termed as pyran, (Fig. 5) hence the sugarhaving this type of structure is knownas pyranose structure i.e. why the suffixpyranose is used in nomenclature ofstructure VI and Vll. Structure VI isnamed as α – (+) glucopyranose and VIIIas β(+ )-glucopyranose.

Pyran

Fig. 5

Similarly, five membered ring systemcontaining four carbon atoms and oneoxygen atom is termed, as Furan (Fig. 6).The sugar containing this type of ringsystem is known as furanose ringstructure.

Furan

Fig. 6

Ratio of the pyranose and furanoseforms depends on the following factors.

(a) Structure

(b) pH

(c) Solvent composition

(d) Temperature

(e) Structure of polymer (whenmonomers are incorporated intopolysaccharides)

This can be illustrated by data fromNMR studies shown in Table 1. Table 1.Relative amounts of furanose andpyranose (percent) forms

D-ribose exists in solution as amixture of the two ring forms, but inbiological specimen of polysaccharides,specific forms are stabilised. RNAcontains exclusive ribo-furanosewhereas some plant wall polysaccarideshave pentoses entirely in the pyranoseform.

Glucose can be represented as anequilibrium mixture of the cyclic andopen chain forms as shown in Fig. 7.

D-glucose is found to exist as anequilibrium mixture of three forms inaqueous solution, which contains 37%α- anomer, 62% β - anomer and very little(<1%) of the open chain form. It has beenfound that the aqueous solution ofmonosaccharides with five or morecarbon atoms exist for more than 99per cent time in the ring form.

Monosaccharides α - Pyranose β - Phyranose α - Furanose β - Furanose

Ribose 20 56 06 18

Glucose 36 63 a a

Fructose 03 57 09 31

(a denotes much less than 1%)


35

2.6 Relation between Fischer and Haworth Projection

Students have also been foundcommitting mistake in convertingFischer projections to Haworthprojections. Fischer’s structure can beconverted into Haworth’s projections bydrawing pyran as a hexagon with oxygenatom at one of the top comer of thehexagon and other five comers being

occupied by five carbon atoms and thenplacing atoms/groups on L.H.S. in theFischer projection on the upper side ofthe ring and atoms/groups on RH.S. inthe fisher projection below the ring oncarbon atoms 1,2,3,4 and 5. Hydrogenatom attached to carbon 5 is writtenbelow the plane of the ring and the –CH2OH group is placed above the planeof the ring on carbon atom 5. Structureof telrahydropyran and Fischer and

HO—C—H|

H—C—OH|

HO—C—H| O

H—C—OH|

H—C|

CH2OH

Fig. 7

H O C H—C—OH

| HO—C—H

|H—C—OH

| H—C—OH

| CH2OH

H—C—OH|

H—C—OH|

HO—C—H| O

H—C—OH|

H—C|

CH2OH

A - IIβ-D-(+) Glucopyranose

AD-(+) Glucose

A - Iα-D-(+) Glucopyranose

HO—C—H|

H—C—OH|

HO—C—H|

H—C—O|

H—C—OH|

CH2OH

H—C—OH|

H—C—OH|

HO—C—H|

H—C—O|

H—C—OH| CH2OH

A - IIIβ-D-(+) Glucopyranose

A - IVα-D-(+) Glucopyranose

Representations A, A-I, A-II, A-Ill and A-IV are known as Fisher’s Projectionformulae.

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Haworth projections of α-D-(+) Gluco-pyranose and B-D (+) glucophyranose areshown in Fig. 8.

It may be remembered that carbonatoms which constitute the ring are notshown (Fig. 8) in Fischer and Haworthprojections. The point of cross sectionindicates carbon atom.

Above representation indicates thatthe groups on right hand side in theFischer projection go below theplane of the ring and those on lefthand side go above the plane.

Similarly, structure of fructose withthe same molecular formula, C6H12O6,can be tried by students. It may beremembered that glucose contains analdehyde group but fructose contains theketonic group. The position of ketonicgroup is ascertained by the osazoneformation property of glucose and

fructose when both the monosaccharidesare found to form the same osazoneinvolving the two terminal carbon atoms,one of them must be having a carbonylgroup. Since in glucose the aldehydegroup is present at carbon 1, hence, theketone group of fructose responsible forobazone formation must be present atcarbon-2, the other structural portionremains the same as in glucose. Openchain structure of fructose isrepresented as in structure XII andFischer’s projection formulae offructopyranse are represented bystructure XIII and XIV (Fig. 9).

It is amply clear from the structuresshown in Fig. 9 that structures No XIIIand XIV differ in their configuration atC-2. As already stated, suchconfigurations are known as epimers. Itmay be remembered that only one of theabove fructopyranose has been isolatedand assigned the B-configuration.

5

4

3 2

1

Tetrahydrophyran6CH2OH

H

HO4

OH1

H

OH

H

H

OH

5

6CH2OH

H

HO4

OH1

H

OH

H

H

OH

(X)β-D-(+) Glucopyranose

(XI)α-D-(+) Glucopyranose

Fig. 8: Haworth’s Projections


37

However, in the combined state, e.g. insucrose, insulin, etc. i.e. in fructosides,fructose is found to exist in both formsie. as α and β fructosides. Structures ofmethyl fructofuranosides are given as(XV) & (XVI) in Fig. 10.

2.7 Mechanism of Mutarotation

Freshly prepared solution of D(+) glucose(obtained by crystallisation from alcoholand water) shows specific rotation of+110O which on allowing to stand

overnight attains a constant value of+52.5O within approximately 6 hours.Addition of. and an acid or a base orwarming of the solution enhances therate of this change. The solution ofanhydrous D(+)-glucose (crystallisedfrom concentrated solution) showsspecific rotation + 19o which on standingattains the value +52.5o. This change inspecific rotation is called Mutarotationderived from Latin word Mutare meansto change.

1 CH2OH 2| C=O

|HO—C—H

| H—C—OH

| H—C—OH

| CH2OH

1 2HOH2C—C—OH

| HO—C—H

| H—C—OH | O H—C—OH

| H2C

2HO—C—CH2OH

|HO—C—H

| H—C—OH

| H—C—OH

| CH2

(XII)(–)- Fructose

(XIII)α–D-(–) Fructopyranose

(XIV)β–D-(–) Fructopyranose

Fig. 9: Open Chain and ring structures of (-) Fructose containing pyranose andfuranose ring

MeO—C—CH2OH|

HO—C—H| O

H—C—OH|

H—C|

CH2OH

(XV)Methyl ααααα-D-(–) Fructopyranose

HOCH2—C—OMe|

HO—C—H| O

H—C—OH|

H—C—OH|

H—C|

CH2OH

(XVI)Methyl βββββ–D-(–) Fructopyranose

Fig. 10: One can try to draw the corresponding Haworth’s Structures ofStructure No. (XIII), (XIV), (XV) and (XVI).

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Students were found uncomfortableto explain the mechanism ofmutarotation. Through cyclicrepresentation various steps ofmechanisms can be explained with thehelp of chair representation of glucose.Water is an amphiprotic i.e. it acts as anacid as well as a base. Mutarotation is aconcerted process involving thesimultaneous removal of a proton fromthe hydroxyl group and donation ofproton to the oxygen atom by the watermolecule. The Mechanism shown in

Fig. 11 attempts to highlight thisaspect.

Let us consider a typical problem.Mutarotation of glucose solution resultsin equilibrium mixture of ααααα andβββββ-anomers which does not contain equalamounts of the two anomers. Itcontains 62.62% of βββββ- form and only 37%of ααααα -form. Why?

This can be understood by consi-dering the stereochemisry of the cyclicforms. Stereochemistry reveals that 6

Fig. 11

HO

HO HO

H–HOCH2

OH

H

O

O–H

OH2

HO

HO HO

OH

OH

OH

3O

H

CH2OH

+

OH

OH OH

O

OH2

O–H

H

O–OH

[α]D: +19o

CH2OH

[α]D: +110o

Fig. 12

fp

bseq

\ax

eq

ax

axax

bs

fp

ec eq

CC C

C

C C

ax Axial bondseq Equatorial bondsfp Flog-pole bondsbs Bowspr bonds

Boat conformation— Axial bonds— Equatorial bondsChair conformation

(Cyclohexane)


39

membered cyclic forms exist in twodifferent conformations (The differentstructures of a molecule that can beconverted into one another by rotationabout C-C single bond) : chair and boat(Figure 12).

Out of these two conformations, it isfound that the chair conformation ismore stable than the boat conformationby 29.89 k J mol–1 due to combined effectof torsional strain and Van der Waalsrepulsion between flagpole hydrogens.

X-ray studies also support the factthat cyclic forms exist in non-planar chairconformation rather than planar form.

ααααα-Glucopyranose βββββ-Glucopyranose

Fig. 13

From the Figure 13, it can be seenthat -OH groups located at C-2, C-3, C-4and -CH2OH on C-5 occupy theequatorial positions in both thestructures but the -OH group on C-l isaxial in a form and equatorial in β form.

On the basis of stability data ofvarious compounds, it has beengeneralised that chair conformationwith the largest number of bulkysubstituents occupying equatorialposition is preferred.

Test Yourself

After going through this paper you mayattempt to solve the following exercises.

You may consult the books given underbibliography for getting solutions of someof the questions.1. Out of propanoic acid and

2-hydroxypropanoic acid, whichcompound will be optically activeand why?

2. Fructose is supposed to containketonic group but fructose givessilver mirror test and Fehlingsolution test unlike other ketones.Why it is so?

3. Which of the following compoundsdo not satisfy the modern definitionof carbohydrates? Give reasons tosupport your answer.

(a) Starch (b) Lactic acid (c) Sucrose(d) Butan - 2, 3 - dihydroxydioic acid(e) Arabinose (f) 2,6 - Dimethyl-hepta - 2,5 - dien - 4, one

4. Draw (i) Fischer’s projections and(ii) Haworth’s projections of ringstructures of the followingcompounds.(a) ααααα - D - (+) - Glucopyranose(b) β - D- (+) - Glucopyranose

5. Glucose and fructose differ in theirstructures but they form the sameosazone with the same m.p. ontreatment with excess of phenylhydrazine. Why?

6. Draw configurations of differentcompounds corresponding tomolecular formulae, C6H12O6 :

(a) Any two annomers (b) Any twoepimers (c) Any two enantiomers(d) Any two diastereomers

7. List the evidences suggesting thering structure of glucose.

HO

HO e

OH

H

OCH2OH CH2

OHHO

HO HO OH

OHO

e

40 SCHOOLSCIENCE

December2006

8. What are the evidences to suggestthat the five hydroxyl groupspresent in glucose are attached tofive different carbon atoms ?

9. What are the evidences to suggestthat glucose can exist in twodifferent forms?

10. How will you accomplish thefollowing conversions?

(a) Glucose into fructose

(b) Fructose into glucose

(c) Arabinose into glucose

(d) Glucose into arabinose

BIBLIOGRAPHY AND BOOKS FOR FURTHER READING

1. BAHL, B.S. AND ARUN BAHL. 1998. Advanced Organic Chemistry. S. Chand& Co. Ltd., New Delhi.

2. CHAWLA, H.M. AND B. PRAKASH. 1979. Chemistry of Natural Products, Vol. I.Sultan Chand & Sons, Daryaganj, New Delhi.

3. JAIN, J.L. 2001. Fundamentals of Biochemistry, S. Chand and Co Ltd.New Delhi.

4. JAIN, M.K. AND S.C. SHARMA. 2002. Organic Chemistry. Shobhan Lal Naginand Co., Jallandhar.

5. MC MURRY, JOHN. 2005. Organic Chemistry, Indian Edition.6. MORRISON AND BOYD. 2001. Organic Chemistry. Prentice Hall of India,

New Delhi.7. NCERT. 2002. Chemisry – A Textbook for Class XII. NCERT, New Delhi.8. NCERT. 2003. Guidelines and Syllabi for Higher Secondary Stage XI-XII,

NCERT, New Delhi.9. READ, JOHAN AND F.D. GUNSTONE. 1958. A Textbook of Organic Chemistry.

The University Press, Glasgow, U.K.10. ROBERTS JOHN D. AND C. MARJERIE CASERIO. 1965. Basic Principles of Organic

Chemistry. California Institute of Technology, New York.11. SINGH, R.N., S.M.L. GUPTA AND M.M. BOKADIA. 1974. Organic Chemistry.

Vol. I and II. Ratan Prakashan Mandir, Agra.12. STREITWIESER, ANDREW AND H. HEATHCOCK, CLAYTON. Jr. 1989. Introduction to

Organic Chemistry. Macmillan. Publishing Company, New York.13. TALWAR, G.P. AND L.M. SRIVASTAVA. 2002. Textbook of Biochemistry and Human

Biology. Prentice Hall of India, New Delhi.


29

Hard Spots in Teaching ofCarbohydrates

RUCHI VERMA

Lecturer in Chemistry, NCERTNew Delhi

V.P. GUPTA

Professor of ChemistryRIE, NCERT, Bhopal-462 013

ARBOHYDRATES are essentialnutrients for life like proteins andvitamins. Three essential

requirements of life i.e., food, clothes andshelter, are directly or indirectly linkedwith Carbohydrates. The syllabi ofChemistry at the higher secondary andgraduate level usually envisage a studyof various aspects of carbohydrates suchas their structure and properties.Interaction with students at highersecondary level, collegiate level, teachersand teacher educators have led us toidentify different hard spots from thistopic. An attempt has been made here todiscuss some hard spots of this topicalongwith the chemical reactions involved.

2.0 Identified Hard Spots

● Misconception in definition ofcarbohydrates

● Classification of carbohydrates

● Stereo chemistry of carbohydrates

● Representation of Ring Structure

● Relation between Fischer andHaworth Projection

● Mechanism of Mutarotation

C

2.1 Definition of Carbohydrates

Most of the books at the senior secondaryand collegiate level do not give completedefinition of carbohydrates. This leads tothe misconception about the definition.According to the classical definition, theterm carbohydrate stands for hydratesof carbon, which contain hydrogen andoxygen in the same proportion as in wateri.e 2:1. For example, glucose and fructose[C6H12O6 or C6(H2O)6], sucrose [Cl2H22O11

or Cl2 (H20)1l], and starch (C6H10O5)n or[C6(H2O)6]nare the hydrates of /° carbonand hence they are carbohydrates. Nowthe question arises, whether thefollowing compounds)which alsosatisfy the above definition, are thecarbohydrates?

Fonnaldehyde : HCHO i.e. [C.(H2O)]

Acetic acid : CH3COOH i.e. [C2.H2O)2]

Lactic acid : CH3CH(OH) COOH i.e.[C3.(H2O)3].

Obviously, the answer is No.On the other hand, we also come

across a few Carbohydrates which do notconform to the above definition. Forexample, rhamnose (C6H12O5),rhamnoheptose (C7H14O6) and 2-deoxyribose (C5H10O4), fucose (C6Hl2O5)are carbohydrates but do not satisfy theabove definition. Hence, there is a needto modify the definition keeping in viewthe structure and properties ofcarbohydrates. Structurally, carbo-hydrates contain two types of functionalgroups,– OH and >C=O group can be inthe form of a ketonic group or thealdehydic group.

So, another definition that comes toour mind is, “carbohydrates are