Carbohydrates and Carbohydrates and Structural Analysis of Structural Analysis of

PolysaccharidesPolysaccharides

Di Wu2012-11-05

Contents:Contents:- Introdution of carbohydrates- Monosaccharides- Oligosaccharides- Polysaccharides- Structure analysis of polysaccharides

Introdution ofcarbohydrates

Ah! sweet mystery of life . . . —Rida Johnson Young (lyrics) and Victor Herbert (music) “Ah! Sweet Mystery of Life,” 1910

I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit Nature and more time tasting her sweetness and respecting her seniority. —E. B. White, “Coon Tree,” 1977

Four Major Types of Biological Macromolecules

Type of Polymer Monomers making up Polymer Example

I. Carbohydrates (Polysaccharides) Monosaccharides Sugars, Starch,

Cellulose

II. Lipids Fatty acids and glycerol Fats, steroids, cholesterol

III. Proteins Amino acidsEnzymes, structural components

IV. Nucleic Acids Nucleotides DNA, RNA

Proteins:• well defined

• Coded precisely by genes,

hence monodisperse

• ~20 building block residues (amino acids)

• Standard peptide link (apart from proline)

• Normally tightly folded structures

Polysaccharides• Often poorly defined (although some

can form helices)

• Synthesised by enzymes without template – polydisperse, and generally larger

• Many homopolymers, and rarely >3,4 different residues

• Various links etc

• Range of structures (rodcoil

Carbohydrates：Polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. some also

contain nitrogen, phosphorus, or sulfur.

• (CH2O)n

• 70-80% human energy needs (US~50%)• >90% dry matter of plants• Monomers and polymers• Functional properties

– Sweetness– Chemical reactivity– Polymer functionality

There are three major size classes of carbohydrates:

• Monosaccharides – carbohydrates that cannot be hydrolyzed to simpler carbohydrates; eg. Glucose or fructose.

• Oligosaccharides – carbohydrates that can be hydrolyzed into a few monosaccharide units; eg. Sucrose or lactose

• Polysaccharides – carbohydrates that are polymeric sugars; eg Starch or cellulose

• 3-9 carbon atom sugars

-(pentoses 5, hexoses 6 most common in plants)

• have to be obtained by chemical reactions

• only a few are free in plant

-many as polysaccharides

Monosaccharides

The structure and classification of some monosaccharides

Nomenclature

Ketone Aldehyde

4 Tetrose Tetrulose

5 Pentose Pentulose

6 Hexose Hexulose

7 Heptose Heptulose

8 Octose Octulose

Num

ber

of c

arbo

ns

Functional group

Oligosaccharides

• Composed of a few monosaccharide units by glycosidic link from C-1 of one unit and -OH of second unit

• 13, 14, 1 6 links most common but 1 1 and 1 2 are possible

• Links may be or • Link around glycosidic bond is fixed but anomeric

forms on the other C-1 are still in equilibrium

Synthesis

Some Disaccharides

O

CH2OH

OH

OH

OH

O

O

CH2OH

OH

OH

OHH

H

H

H

H

H

H H

O

CH2OH

OH

OH

OH

O

O

CH2OH

OH

OH

OH

H

H

H

H

H

H

H

H

O

CH2OH

OH

OH

H

O

O

CH2OH

OH

OH

OH

H

OH

H

H

H

H

H

H

maltosecellobiose

lactosesucrose

-D-glucosyl-(1->4)--D-glucopyranose)

-D-glucosyl-(1->4)--D-glucopyranose)

-D-galactosyl-(1->4)--D-glucopyranose)

-D-glucosyl-(1->2)--D-fructofuranose)

O

CH2OH

OH

OH

OH

H

H

H

H

OCH2OH

H

H

OH

OH

H

O

CH2OH

Higher Oligosaccharides

Polysaccharides

Polysaccharides are complex carbohydrates made up

linked monosaccharide units.• Nomenclature:

Homopolysaccharide-a polysaccharide is made up of one type of monosaccharide unit

Heteropolysaccharide-a polysaccharide is made up of more than one type of monosaccharide unit

• Starch and glycogen are storage molecules

• Chitin and cellulose are structural molecules

• Cell surface polysaccharides are recognition molecules

Sources of Polysaccharides• Microbial fermentation• Higher plants

– seeds – tree extrudates,– marine plants,

• Chemical modification of other polymers

Polisaccharides

Some types of polysaccharides1.Starch• Starch is a storage compound in plants, and made of glucose

units

• It is a homopolysaccharide made up of two components: amylose and amylopectin.

• Most starch is 10-30% amylose and 70-90% amylopectin

• Amylose – a straight chain structure formed by 1,4 glycosidic bonds between α-D-glucose molecules.

H O

OH

H

OHH

OH

CH 2 OH

HO H

H

OHH

OH

CH 2 OH

H

O

HH H O

OH

OHH

OH

CH 2 OH

HH H O

H

OHH

OH

CH 2 OH

H

OH

HH O

OH

OHH

OH

CH 2 OH

H

O

H

1

6

5

4

3

1

2

a m y lo s e

Structure of Amylose Fraction of Starch

• The amylose chain forms a helix.

• This causes the blue colour change on reaction with iodine.

• Amylose is poorly soluble in water, but forms micellar suspensions

Amylose

Amylopectin-a glucose polymer with mainly α -(14) linkages, but it also has branches formed by α -(16) linkages. Branches are generally longer than shown above.

H O

OH

H

OHH

OH

CH2OH

HO H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH2OH

HH H O

H

OHH

OH

CH2OH

HH

O1

OH

3

4

5

2

amylopectin

Structure of Amylopectin Fraction of Starch

• Amylopectin causes a red-violet colour change on reaction with iodine.

• This change is usually masked by the much darker reaction of amylose to iodine.

Amylopectin

Amylopectin

Starch therefore consists of amylose helices entangled on branches of amylopectin.

2 Glycogen• Storage polysaccharide in animals• Glycogen constitutes up to 10% of liver mass and 1-2% of

muscle mass

• Glycogen is stored energy for the organism

• Similar in structure to amylopectin, only difference from starch: number of branches

• Alpha(1,6) branches every 8-12 residues

• Like amylopectin, glycogen gives a red-violet color with iodine

glycogen

3 Cellulose• The β-glucose molecules are joined by condensation, i.e. the removal

of water, forming β-(1,4) glycosidic linkages.• Note however that every second β -glucose molecule has to flip over to

allow the bond to form. This produces a “heads-tails-heads” sequence.

• The glucose units are linked into straight chains each 100-1000 units long.

• Weak hydrogen bonds form between parallel chains binding them into cellulose microfibrils.

• Cellulose microfibrils arrange themselves into thicker bundles called microfibrils. (These are usually referred to as fibres.)

• The cellulose fibres are often “glued” together by other compounds such as hemicelluloses and calcium pectate to form complex structures such as plant cell walls.

Cellulose

4 pectin

Cell wall polysaccharide

‘smooth’ regions :Partial methylated or not methylated poly-a-(14)-D-galacturonic acid residues;

‘hairy’ regions: due to presence of alternating a -(12)-L-rhamnosyl-a -(14)-D-galacturonosyl sections containing branch-points with side chains (1 - 20 residues) of mainly L-arabinose and D-galactose

Pectin Model

RG-II

• Source: Cell walls of higher plants (citrus rind)• Structure: Largely a linear polymer of polygalacturonic acid with

varying degrees of methyl esterification.  (Also some branches –HAIRY REGIONS)– >50% esterified is a high methoxy (HM) pectin – <50% esterified is a low methoxy (LM) pectin

• Functional Properties: Main use as gelling agent (jams, jellies)

– dependent on degree of methylation

– high methoxyl pectins gel through H-bonding and in presence of sugar and acid

– low methoxyl pectins gel in the presence of Ca2+ (‘egg-box’ model)

Thickeners

Water binders

Stabilizers

Other polysaccharidesOther polysaccharides

• ChitinChitin (poly glucose amine), found in fungal cell walls and the (poly glucose amine), found in fungal cell walls and the exoskeletons of insects.exoskeletons of insects.

• CalloseCallose (poly 1-3 glucose), found in the walls of phloem tubes. (poly 1-3 glucose), found in the walls of phloem tubes.

• Dextran Dextran (poly 1-2, 1-3 and 1-4 glucose), the storage polysaccharide (poly 1-2, 1-3 and 1-4 glucose), the storage polysaccharide in fungi and bacteria.in fungi and bacteria.

• InulinInulin (poly fructose), a plant food store. (poly fructose), a plant food store.

• AgarAgar (poly galactose sulphate), found in algae and used to make agar (poly galactose sulphate), found in algae and used to make agar plates.plates.

• MureinMurein (a sugar-peptide polymer), found in bacterial cell walls. (a sugar-peptide polymer), found in bacterial cell walls.

• LigninLignin (a complex polymer), found in the walls of xylem cells, is the (a complex polymer), found in the walls of xylem cells, is the main component of wood.main component of wood.

Structure analysis of polysaccharides

Information on polysaccharide structures

--Monosaccharide component

--Sugar linkage type

--Sugar sequence

--Monosaccharide configuration(αorβand D or L)

--Molecular weight

--Amount and position of substitute units

--Degree of branching

• Monosaccharide component The polysaccharide samples are hydrolyzed by

HCl/MeOH and TFA, then analyzed by HPLC or GC

HPLC:

High pressure/performance liquid chromatography

• Sugar linkage type Chemical methods:

Periodate Oxidation and Smith degradation

Methylation analysis

GC-MS:Gas chromatography-Mass spectrometer

Physical methods:

NMR(Nuclear Magnetic Resonance)

• Sugar linkage type

• Monosaccharide

configuration

• Substitute units

• Degree of branching

Physical methods:

FT-IR (Fourier transform infrared spectroscopy)

• Monosaccharide

configuration

• Substitute units

Physical methods: MS (Mass spectrometer)

• Sugar linkage type

• Monosaccharide

configuration

• Substitute units

• Degree of branching

• Molecular weight

• Molecular weight

Determination methods Molecular weight range

End group titration < 3×104

Elevation of boiling point < 3×104

Depression of freezing point < 3×104

Vapour pressure Osmometry

< 3×104

Membrane Osmometry 3×104—1.5×106

Light scattering 1×104—1×107

Centrifugation sedimentation velocity

1×104—1×107

Centrifugation sedimentation equilibrium

1×104—1×106

Intrinsic viscosity measurement 1×104—1×107

High performance gel-permeation chromatography

1×102—1×107

E-mail: wud073@nenu.edu.cn