Post on 11-Jan-2016
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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