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CARBOHYDRATESAlso called sugars, they are the most abundant group of biomolecules. Theyhave important biological functions, associated with their formation, theirproperties (alone or in combination with other biomolecules) and theirdecomposition.
From K.P.C.Vollhardt, Organic Chemistry
sucrose
Sugar cane
Carbohydrates are formed by plants from CO2 during photosynthesis. They supply almost all C to living organisms.
Historically the name derives from the empirical formula Cm(H2O)n
Today the term saccharide is replacing the term sugar
polyhydroxyaldheydes and polyhydroxyketones
They are polyfunctional compounds
They are divided into simple sugars (monosaccharides) and complex sugars (disaccharides, oligosaccharides, polysaccharides), composed of the union of several monosaccharides
MONOSACCHARIDES they are not hydrolyzedDISACCHARIDES they are hydrolyzed to 2 units of monosaccharides
OLIGOSACCHARIDES they are hydrolyzed to 3 ÷ 10 units of monosaccharides
POLISACCHARIDES they are hydrolyzed to more than 10 units monosaccharides
NOMENCLATURE
The systematic nomenclature of monosaccharides requires the suffix -ose
monose
a monose with aldheyde function is called aldose a monose with ketone function is called ketose
The number of C atoms (usually 3 to 11) is indicated by a prefix before the suffix -ose
tri-, tetra-, penta-, hexa-, hepta-, etc.
aldohexose means: monose with 6 C atoms and aldehyde function
ketopentose means: monose with 5 C atoms and ketone function
Simplest aldose: 2,3-dihydroxypropanal (glyceric aldehyde) OHH
CH2
CHO
OHaldotriose
simplest ketose: 1,3-dihydroxypropanone (1,3-dihydroxyacetone) C O
CH2
CH2
OH
OH
ketotriose
Aldoses with C atoms from 4 to 6 have trivial names still used by IUPAC. Some ketoses have trivial names
Ketoses are often referred to with the suffix -ulose
hexulose means: ketose with 6 carbon atoms
The suffix -ulose can be preceded by the prefix indicating how many are the C atoms,which is the position of the carbonyl and which is the configuration of the C atoms, thatis indicated with the name of the corresponding aldose.
the most common ketoses are 2-ketoses, therefore the number 2 is often omitted
Fischer notation is used to write monoses
OHHCH2OH
OHHOHHOHH
CHO
CH2OHOHH
CHO
OHHHOH
CHO
CH2OH
OHHOHH
CHO
CH2OH
CH2OHOHHOHHOHH
CHO
CH2OHOHHOHHHOH
CHO
CH2OHOHHHOHOH
CHO
CH2OHOHHHOHHO
CHO
OHHCH2OH
OHHOHHHOH
CHO
OHHCH2OH
OHHOH HH OHCHO
OHHCH2OH
OHHOH HOH H
CHO
OHHCH2OH
OH HOH HOH H
CHO
OHHCH2OH
OH HOHHOHH
CHO
O115HCH2OH
OH HOHH
OH HCHO
OHHCH2OH
OH HOH H
OHHCHO
D-glyceraldehydealdotriose
D-erythrose D-threose
aldotetroses
aldopentoses
D-ribose D-arabinose D-xylose D-lyxose
D-allose D-altrose D-glucose D-mannose D-gulose D-idose D-galactose D-talosealdohexoses
ALDOSES
Mnemonic rule: all altruist gladly make gum in gallon tanks
OHHCH2OH
OHHOHHO
CH2OH
CH2OHO
CH2OH
OHO
CHO
CH2OH
CH2OHOHHOHHO
CH2OH
CH2OHOHHHOHO
CH2OH
OHHCH2OH
OHHOH H
OCH2OH
OHHCH2OH
OH HOHHO
CH2OH
OHHCH2OH
OH HOH H
OCH2OH
dihydroxyacetoneketotriose
D-erythrulose
ketotetrose
ketopentoses
D-ribulose D-xylulose
D-psycose D-fructose D-sorbose D-tagatose
ketohexoses
KETOSES
L-monoses are MIRROR IMAGES of the corresponding D-monoses
OHHCH2OH
OHHOH HH OHCHO
OH HCH2OH
OH HOHHHOH
CHO
D-glucose L-glucose
CH2OHOHHHOHOHH
CHO
CH2OHOH HH OHOH H
CHO
D-xylose L-xylose
Some natural sugars do not have the carbonyl group and are called alditols They are named replacing the suffix -ose with the suffix -itol.
ALDITOLS
OHHCH2OH
H OHHOHOH
CH2OHH
It is present in apples, plums and red berries and finds industrial application as sweetener
NOTICE: Although there is not a more oxidized ending, this alditol is still considered as D-, because it maintains the structure of D-glucoseD-glucitol (D-sorbitol)
NOTICE: if the missing group is replaced by H, the substractive prefix is sufficient. Otherwise, the replacing group must be named
example:
CH2OHOHHOHHHH
CHO
CH2OHOHHOHHOHH
CHO
D-ribose
reference compound
2-desoxy-D-ribose
When an hydroxyl group is missing the SUBTRACTIVE NOMENCLATURE is used. The prefix de(s) indicates that the named group is missing from the reference compound.
OHHCH2OH
OHHOH HH NH2
CHO
D-glucosamineOHH
CH2OH
OHHOH HH OHCHO
D-glucose
2-amino-2-desoxy-D-glucose
ATTENTION! The name 2-amino-D-glucose means that the amino group replaces H (as usual) at position 2 of glucose
OHHCH2OH
OHHOH HNH2 OHCHO
Present in many aminoglycosidic antibiotics
reference compound
CYCLIC FORMS OF MONOSESFormulae considered insofar do not explain all the properties of monoses.
D-glucose exists in two different crystalline form named, a and b that, dissolvedin water, show different optical rotations, when immediately measured. However,with time the values change, converging toward the same value (mutarotation).
a-D-glucose mixture at equilibrium b-D-glucose[a]D +112∞ +52.7∞ +19∞
The carbonyl group of aldoses and ketoses reacts with an alcoholic–OH, giving a stable cyclic hemiacetal .
O
O
COH
CHOHCHOHCHOHCHOHCH2OH
5-membered cyclic hemiacetal FURANOSE
PYRANOSE
furane
pyrane
6-membered cyclic hemiacetal....
Which OH?
Generally, furanosidic rings form rapidly (kinetic control), whereas pyranosidic ringsare more stable and are predominant at the equilibrium (thermodinamic control)
Why D-glucose crystallizes in two form?
C ONu: the formation of cyclic hemiacetal generates anew chiral C, called anomeric carbon
Upon cyclization, TWO diastereomers originate
Diastereomers differing only for the configuration of anomeric C are called
anomers
Mutarotation is the consequence of the rapidly estabilished equilibrium in solution of the two cyclic anomers with the open molecule
a-D-glucoseKa
b-D-glucoseKb
OHHCH2OH
OHHOH HH OHCHO
Different notations can be used to represent the cyclic anomers.
1. Fischer formulaeThe Fisher projection of the open chain is maintained. Also the new chiral C has bonds projected in the form of a cross; O maintains the same position as OH relative to the carbon chain. Bonds appear deformed
COH
CH2OHOH
COH H
CH2OH
OC OHH
CH2OH
O
1
23
45
1 1
Da anomer b anomer
The anomer with the O bridge and the anomeric –OH are on the same side ofthe C atoms chan is called a; b is the anomer where they lay on opposite sides.
COH
OHCH2OH
C OHH
CH2OH
O
COH H
CH2OH
O
1
23
4
5
1 1
Da anomer b anomer6
5 5
Furanosidic form
Pyranosidic form
Analogous is the representation for ketoses:
CH2OH
C O
OHCH2OH
CH2COH
CH2OH
OHO
CH2 C OH
CH2
OH
OOH
CH2COH
CH2
OH
OOH
CH2 C OHOHO
CH2OH
1
23
45
6....
a anomer
D
a anomer
b anomer
b anomer
C 6 is not chiral, but the oxygen bridge is conventionally located on the right of the chain
COH
CH2OHOH
C OHH
CH2OH
OCOH H
CH2OH
O
1
2345
1 1
a anomerL b anomer
Naming a and b anomers follows the same rules: the anomer is called a when anomeric OH and oxygen bridge lay on the same side with respect to the C atoms chain (b when anomeric OH and oxygen bridge lay on opposite sides with rispect the chain).
If the OH acting as the nucleophile is on the left of the C atoms chain in the Fischer projection of the open form, the oxygen bridge must be written on the left side.
2. Haworth formulaeTo write a cyclic monose according to Haworth projections, the rules are as in the following.
a. The ring is represented as a pentagon or a hexagon, drawing them as planar andviewd in perspective. The other bonds are drawn above and below the plane, asvertical segments.
b. The furanosidic ring is oriented so that O occupies the upper vertex with theanomeric C (C1 for aldoses and C2 for ketoses) on the right of it.
c. The pyanosidic ring is oriented so that O occupies the upper right vertex, withthe anomeric C on its right
O
Ofuranosidic anomeric C C1 in aldoses
C2 in ketoses
pyranosidic anomeric C C1 in aldosesC2 in ketoses
Better representation of cyclic structure
Guidelines to convert Fischer formulas into Haworth formulas
For example: a anomer C OHH
CH2OHH
O
C OHH
CH2 H
O
OH
234
1
D6
5
234
1
65
Ø Write the Fischer formula so that all bonds out of the ring lay horizontally, on the left and on the right of the C chain.
ATTENTION! In doing so, be careful to move -CH2OH in the horizontal bond without changing the configuration of the chiral C
Ø All the bonds that in Fisher formula lay horizontally on the left of the C chain must be wtitten above the ring plane in the Haworth notation (and all the bonds on the right must be written below).
C OHH
CH2 H
O
OH
OCH2OH
H
OH
H234
1
65 23
4
5
6
1
NOTICE: following the procedure correctly, the terminal –CH2OH is up in the D series, down in the L series.
OCH2OH
HO
CH2OH
H
D LIn a anomer: CH2OH and OH are always opposite O
CH2OH
H
OH
H OCH2OH
HOH
D, a L, a
Example:CC OHOHH
OH HH OHCH2OH
H
OH
Write the anomers of the aldohexose on the right
Unless otherwise indicated, both pyranosidic AND furanosidic forms must be written
CC OHOHH
OH HH OHCH2OH
H
OH1
23
45
6
....
DH
C OHH
CH2OH
OHHOHH
H
O
OHH
COH H
CH2OH
OHOH
H
O
O
23
4
1
6
5
+ 23
4
1
6
5
ab
HOH
C OHH
CH2OH
OHHOHH
H
OHOH
COH H
CH2OH
OHHOHH
H
O23
4
1
6
5
+
23
4
1
6
5
ba
CHOH
C OHH
CH2OH
OHHOHHO
H CHOH
COH H
CH2OH
OHHOHHO
H
23
4
1
6
5
23
4
1
6
5HOH
C OHH
CH2
OHHOHH
H
O
OHHOH
COH H
CH2
OHHOHH
H
O
OH
234
1
6
5
234
1
65
OH
CH OH
H
OH
HOH
H
CH2
OHOH
OH
CH OH
H
OH
HOH
H
CH2
OHOHb a
OCH2OH
HOH
HOH
H
OH
HOH
H OCH2OH
HOH
HOH
H
OH
H
OH
H23
4
5
6
1
ba
3. Conformational formulas
Piranosidic forms are six-membered rings: the representation closest to the real molecule uses the chair conformations.
OO
Guidelines to pass from Haworth formulas to conformational formulas.ü Groups up in Haworth formula must be written as either axial or equatorial bond, depending on which is above the average ring plane in the chair conformation.
example:
OCH2OH
HOH
HOH
H
OH
HOH
H
H
HCH2OHH
OH
OH OHHH
OHO
OH
OHH
OH
HHH
OH
OH
CH2OH
23
145
6
1
234
5
6
123
45
6
Each pyranose exist in two chair conformations that interconvert: equilibrium is shifted toward the chair with less 1,3-diaxial interactions. Especially important is the -CH2OH, position, beause it is the bulkiest group. Moreover, it is linked to C5 (C-O bond shorter than C-C bond).
OO 1
41
44C1 1C4
1,3-interactions 1,3-interaction
1,3-interaction 1,3-interactions
The two anomers are indicated with 4C1 and 1C4, where C stays for chair , the superscript left number indicates the C above the ring medium plane, the subscript right number indicates the C below the ring medium plane.
OH
OHO
OHOH
CH2OHOH
OH
OHO
OHOH
CH2OH
OHCHOH
OOH CH
OH
CH2
a-D-glucopiranose b-D-glucopiranose b-D-galattopiranose
CH2OH
OH OHOHOH
O
CH2OH
OH
OHOHOH
O
a-D-idopiranose a-D-altropiranose
D-hexapyranoses generally prefer 4C1 conformation.
Examples of preferred 1C4 conformation:
CH2OH
OH
OHOH
OOH a-L-glucopiranose
Back to D-glucose mutarotation, now it is possible to understand the equilibrium composition: the b anomer has all the groups other than H in equatorial positions.
OH
OHO
OHOH
CH2OH
OHHCH2OH
OHHOH HH OHCHO
CH2OH
OHOHO
OHOH
a-D-glucopiranose b-D-glucopiranose
37.3% 0.002% 62.6%
BUT... substituents with electronegative atom linked at the anomeric C prefer the axial position
O
OHO
OHOH
CH2
R
OH CH2
OH
OOHO
OHOH
RROH, H+
R = Me 66% 34%R = H 34% 64%
L-hexapyranoses, with opposite configuration at C5, generally prefer 1C4 conformation.
Anomeric Effect
Anomers with equatorial ORare destabilized by repulsionof electron pairs (or ofaligned dipoles)
OO
RH
.... ..: O
O
RH
Anomers wih axial OR are stabilized byresonance (hyperconjugation)
Or by overlapping of the non-nondingp orbital of ring O with the antibondingle s* orbital of C1-O1 bond
O
O
RO R
O
1 -
+
OR
Oantibonding s* orbital of C1-O1 bond
O non bondingp orbital legante dell'O
with R=H the equatorial anomer predominates, because OH is more solvated than OR. Therefore OH, taking into account the solvation water molecukes, is bulkier than OR.
All the monoses that can form stable rings (5- and 6-membered) undergo mutarotation
Usually, 5-membered rings form faster, 6-membered rings are more stable and predominates at the equilibrium
example: equilibrium composition of an aqueous solution of D-glucose:
CC OH
OH HOHH
H OHCH2OH
H
OHCHO
HH
OH
H
OH
OH
H
CH2OHOH
OC
HH
OH
OH
HOH
OH H
CH2OHH
OC
HH
OH
OH
HOHOH
H
CH2OHH
CHO
HH
OH
H
OH
OH
H
CH2OH
OH OH
H
OHH
OH
OH
H
H
OH
CH2OHO
HH
OHH
OH
OH
H H
OHCH2OH
1
2
3
45
6
D
+
a-D-glucofuranose b-D-glucofuranose<1% <1%
+
a-D-glucopiranose b-D-glucopiranose36% 64%
REACTIONS OF MONOSES1. Reactions in basic medium
The reaction depends on the basicity of aqueous solution.It is advisable to avoid basic media with monoses.
In mild basic solution:
COH
H OH
R
COH
OH
R
H
COH
HOH
R
CO
H
OR
H
Haldose enol
aldose (of different configutation)
ketose
example: keto-enol tautomerism of glucose
OHHCH2OH
OHHOH HH OH
CHO
OHHCH2OH
OHHOH HOH H
CHO
OHHCH2OH
OHHOH H
OCH2OH
OHHCH2OH
OHHOH HH OH
CHO
D-glucose (57%)
NaOH ~10-2M
35°C, 100 h
D-mannose (3%) D-fructose (28%)D-glucosio
+ +
Monoses that differi inconfiguration of ONLY ONE CHIRAL CARBON are called
EPIMERS D-glucosie and D-mannose are a couple of 2-epimers (they differi only for the C2 configurazion)
in strongly basic media:The ketose (from keto-enol tautomerism) undergoes retro-aldol reaction, followed by aldol condensation, yielding 3- and 4-epimers.
OHHCH2OH
OHHOH HH OH
CHO
OHHCH2OH
OHOH H
OCH2OH
H
Ca(OH)2 1%
OHHCH2OH
COH
COH H
C OCH2OH
-+
C OHHCH2OH
COHH
COHH
C OCH2OH
miscela di prodotti
2. Reactions with alcohols (acetal formation)The monose hemiacetal reacts with alcohols in the presence of anhydrous acid catalyst, yielding acetal.
OCH2 OH
OHO
CH2 OOH
CH3CH3OH, H+
The –OR group is called aglycon
a-b interconversion is blocked. In principle, four different glycosides can be isolated.
OOH
OHO
OHCH2OH
CH3
OOH
OH
OOHCH2OH
CH3
O
OHO
OHOH
CH2OH
CH3
OOHO
OHOH
CH2OH
CH3
OH
OHO
OHOH
CH2OH
CHCH
OOH
OH
OHOHCH2OH
O
OHO
OHOH
CH2OH
HH
OOH
OH
OOH
CH2OH
H
H
OHO
OHOH
CH2OH
OOH
OHCH2OH
OH CH3 OH CH3
methyl a-D-glucofuranoside
methyl b-D-glucofuranoside
methyl a-D-glucopiranoside
methyl b-D-glucopiranoside
H+
+
+
- H2O- H2O
++
- H+ - H+
H+H+
- H+ - H+
POLYSACCHARIDESThey are acetals, originating by linking monose units.
A disaccharide is an acetal composed of two units of monosaccharide.This means that at least one of the units is linked through the hemiaceal OH.
Disaccarides are divided in two families:a) the acetal functionality is made with the hemiacetalic OH of one unit and
one alcoholic OH of the second unitglicosylmonose
DISACCHARIDES
glicosylglycoside
b) both units are linked using their hemiacetalic OH.
They are called reducing sugars (the free aldehyde functionality can be oxidized)
They are called non reducing sugars (no free aldehyde functionality present)
Example: 4-O-(b-D-ribofuranosy)-D-glucose One D-ribose unit, in b furanosidic form, is linked to the OH in 4 of D-glucose
OHH
C OHH
CH2OH
OHHHOH
H
OOHH
COH H
CH2OH
OHH
H
OH
C OHH
CH2OH
OHHHOH
H
O
C
OHH
H
CH2OH
OHH
H
OO
4-O-(b-D-ribofuranosyl)-D-glucoseD-glucoseb-D-ribose
- H2O
Glycosylmonoses are named as a derivative of the reductant monose.
Fischer formulas
Haworth formulas
OCH2OH
HH
OHH
OH
OH
H OHHOCH2
OH OH
OHOH OCH2
OH OH
OH OCH2OH
HH
H
OH
OH
H OHH
O
4-O-(b-D-ribofuranosyl)-D-glucose D-glucoseb-D-ribose
- H2O
OCH2
OH OH
OHOHOHOH
OOH OH
CH2
OH CH2
OH
OHOO
OH OHOCH2
OH OH
OH
4-O-(b-D-ribofuranosyl)-D-glucose D-glucoseb-D-ribose
- H2O
the conformation of disaccharide anomeric C remains undetermined, because it undergoes mutarotation (hemiacetal)
Glicosilglicosides are named indicating both units and glycosides and specifying the anomeric configuration.
a-D-ribofuranosyl-b-D-ribofuranosideTwo D-ribose units, in furanose ring, are linked through C 1 of both.
Configurazion of both anomeric C remains fixed (no mutarotation).
Conformational formulas
OHH
COH H
CH2OH
OHH
H
OOHH
CH OH
CH2OH
OHH
H
OOHH
CH O
CH2OH
OHH
H
OOHH
C H
CH2OH
OHH
H
O
b-D-ribosio
- H2O
a-D-ribofuranosyl-b-D-ribofuranosidea-D-ribose
Fischer formulas
OCH2
OH OH
OHOHOCH2
OH OHOH
OHOCH2
OH OH
OH OC
OH OH
OO
b-D-ribose
- H2O
a-D-ribosea-D-ribofuranosyl-b-D-ribofuranoside
or :
OCH2
OH OH
OHOH OCH2
OH OHOH
OH
OCH2
OH OH
OOH
OCH2
OH OH
OH
b a
each monose is the aglycon of the other.
Haworth formulas
SHORTENED NAMING
ó The monose is indicated with the first three letters of the name, except glucose, that is indicated as Glc (or G only) ó Generally, the pyranosidic form is not indicated; hoever, it is better to add p for pyranose, f for furanose. ó Substituents are indicated with additional letters
D-GlcN
examples:
2-amino-2-desoxy-D-glucose
D-GlcA6Et Ethyl D-glucuronate
a-D-Ribf-b-D-Ribf a-D-ribofuranosyl-b-D-ribofuranoside
From two identical hexapyranoses, 11 disaccharides are possible
Prefixes D-, L-, a-, b- precede abbreviations as necessary
DISACCHARIDES MORE PRESENT IN IN NATURE
Maltose4-O-(a-D-glucopyranosyl)-D-glucose
a-D-Glcp-(1 4)-D-Glc
CH2OH
OH
OO
OHOH
CH2OH
OOH
OHOH
From the hydrolysis of starch
CH2
OH
OH
OO
OHOH
CH2OHO
OHOH
OHCellobiose4-O-b-D-glucopyranosyl-D-glucopiranose
b-D-Glcp-(1 4)-D-Glc
From the hydrolysis of cellulose
OHO
OHOH
CH2OH
OH
OO
OHOH
CH2OHLactose4-O-b-D-galactopyranosyl-a-D-glucopiranoseb-D-Galp-(1 4)-D-Glcp
Only In mammals (up to 8.5% in human milk), is obtained commercially as a by-ptoduct in the manufacture of cheese.
OH
O
OH
OHCH2OH O
OHCH2
O OH
OH
OH
Trehalosea-D-glucopyranosyl-a-D-glucopyranosidea-D-Glcp(1 1)-a-D-Glcp
Energy storage in insects and mushrooms (15% of dry weight)present also as a,b and b,b isomers
O
O CH2OH
OH
OHO
OHOH
CH2
CH2 OHOH
OH
21
3
4
5 6
Not written according to Haworth notation
Sucrosea-D-glucopyranosyl-b-D-fructofuranosidea-D-Glcp-(1 2)-b-D-Fruf
Main energy source in plants, soluble in waterIt is used in food industry because, being not reducing sugar, does nor react with amino groups in proteins.
Acid (or enzimatic) hydrolysis produces gluccose and fructose Invert sugar
OH
OHO
OHOH
CH2OH
OCH2OH
HOH
H
H
OHCH2OH
OH
OHO
OHOH
CH2OH
OCH2OH
HOH
H
H
OHCH2OH
Oa
b+ H2O
O
O CH2OH
OH
OHO
OHOH
CH2
CH2OHOH
OH
OCH2OH
HOH
H
H
OHCH2OH
OH
OH
OHO
OH
OH
CH2OH
CH2OH
OH
OHO
OHOH
CH2OH
OHOHO
OHOH
a
b
H2O, H+
orinvertases
+
++
a-D-glucopyranose b-D-glucopyranose
c-D-fruttopyranoseb-D-fructofuranose
18% 32%
16% 34%
[a] + 66.5 + 52.7
- 92,4
- 39.7after hydrolysis
Opt
ical
rota
tion
chan
ges
from
pos
itive
to n
egat
ive
OLIGOSACCHARIDES
tri- and tetra- saccharides occur in nature at concentrations lower than that of disaccharides
OHO
OHOH
CH2
O
O
O CH2OH
OH
OHO
OHOH
CH2
CH2 OHOH
OHraffinose
a-D-Galp-(1 6)-a-D-Glcp-(1 2)-b-D-Fruf
Oligosaccharides can be described with a shortened nomenclature similar to that of monoses.
diffused in plants, by-product of sucrose from molasses of sugar-beet
non reducing sugar
OHO
OHOH
CH2
OCH2
HH
H
O
CH2OH
O
OHO
OHOH
CH2OH
OH
OH
OH
melezitosea-D-Glcp-(1 3)-b-D-Fruf-(2 1)-a-D-Glcp
In honey and in exudation of trees damaged by insects
non reducing sugar
Some cyclic oligosaccharides reached importance in organic chemistry
Cycloheptamaltose: caracterized by a non polar cavity and a polar external surface
O
OH
OHCH2
OH
OO
OH
OH
CH2OH O
O OH
OH
CH2O
O
OHOH
CH2OH
O O
OH
OHCH2OH
O
O
OH
OH
CH2OHO
OO
OHOH
CH2
OH
OH
with 6 units a-cyclodextrine
with 7 units b-cyclodextrinewith 8 units g-cyclodextrine
They can be obtained from starch with the enzyme ceclodetrina transglicolase
OCH3
OCH3
Cl
OCH3Cl
OCH3
Cl
OCH3HOCl
HOCl
b-ciclodextrin
+
96%only product
used in food, cosmetic and pharmaceutical industry
Cyclodextrins can complex small organic molecules, giving “inclusion compounds”, generally crystalline, even if the molecule is volatile. These inclusion compounds show a selectivity different from that of the free molecule.
CH2OHCH2OHCH2OHO
OOH OH
CH2O
OOH OH
OO
OH OHOO
OOH OH
OHetc.
etc.
poly-4-O-(b-D-Gp)Regular polysaccharides (i.e., those constituted by idntical monose units) are indicated adding the suffix -ANE to he name of monose
(1 4)-b-D-glucane
(1 4)-a-D-, (1 6)-a-D-glucane
(1 6)-b-D-glucane
cellulose linear
glycogen
dextrane(in bacterialsecretions)linear
branched
POLYSACCHARIDES
Polysaccharides most common in nature are homopolysaccharides, with a tridimensional structure thaat depends on how monoses are connected.
Ribbon polysaccharides
They are made of several thousands of monoses, with bonds linking monoses almost parallel
Polysaccharides can be described with a shortened nomenclature similar to that of monoses.
examples:
OO
OHOH
CH2
OOO
OHOH
CH2OH
OH
cellulose(1 4)-b-D-glucano
adjacenti glucosidic unities are rotated of 180°; insoluble in water
OOO
OOH
OH
OH OH
O
Glucane in oats is a 1®3, e,e polysaccharide, soluble in water
(1 4)-b-D-xylaneadjacenti xylosidic unities are rotated of 180°.
OO
O
OHCH2
OOO
OH
OHCH2CH3
OH
(1 4)-b-D-mannane
OH
CH2 OH
O CH3
O
CH2OH
OCH3
HH
OH
CH2 OH
O CH3
HH
O
OCH3
CHOHCH2OH
coniferyl alcohol
oxidativepolymerization
(radical reaction)
lignine(representative portion)
Cells of di ripe plants are made of microfibril of cellulose (50%) and xilane(20%) cemented by polymers of coniferyl alcohol (lignine)
Cellulose is the most abundant organic compound on earth. It forms the fibrous component of plant cell walls, together other more flexible ribbon-polysaccharides (xylane and mannane).
OO
OHNHAc
CH2OH
OOO
OHAcHN
CH2OH Chitin(1 4)-2-acetamido-2-desoxi-b-D-glucane
Main component of crustacea shell and insects exoskeleton, It forms rigid sheets, insoluble in water.
Bacterial cell walls contain more than 40% of a peptidoglycane similar to chitin
OO
ONHAc
CH2
OOO
ONHAc
CH2 CH3
HAlaO
OH
OH
Ala
Ala
po
ylsacc
arid
h
n
Peptide
Peptide
Peptide
n = 10-65
very strong network
4) b-D-GlcpNAc(1 4) 3-lactyl b-D-GlcpNAc(1
Polysaccharides "egg-box"
example: pectin
Inserted calcium ions confer the polymers the capability of strong cohesion. Therefore pectins are used as jelling agents in the making of preserves and jellies from fruit .
Ca++ Ca++ Ca++ Ca++ Ca++ Ca++
O
O
O
OH
OHO
OO
O
O
OO
O
H
H
O OO
OH
OHOO
O
O
O
OO
O
H
H
-
-
-
-
.
. ..
. ...
.....
..
..
..
....
..
..... ..
.......
...
...
... .. ......
.. .
..
..
..
...
.... .
....
..
...........
..
Ca++
1,4-Diaxial connections of monose units maintain the connecting bonds psrsllel, but shifted for the length of one monose unit, thus forming hollows bvetween pairs of adjacent monoses. Interactions among atoms of the couple are unfavourable, unless cavities are filled with water or ions
Polymers of galacturonic acid, pectina are found in fruit and in cell walls of several plants.
Helicoidal Polysaccharids
The two connecting bonds have the shape of a VThey tend to form a spiral if hydrogen bonds can exist along the helix axix. In absence of favourable interactions, they present random coils, with continuouslu fluctuating conformations.
usually, they are partially soluble in water.
O
O
O
OH
CH2
H
OH
OO
OHOH
O
O
O
OH
CH2
OOOH
OH
CH2
O
OH OH
CH2
O
O
OH
OHCH2OH
O
O
OHOH
CH2OH
OH
CH2OH OH
OH
hydrogen bond
... ..
gliycogen present in animalsstarch abundant in plants
Starch and glycogen are used as energy storage: hey must form concentrated deposits, but also to be readily available and released, when necessary.
(1 4)-a-D-glucaneStarch is composed of two fractions: amylose and amylopectin
Amylose: long linear chains (1000-2000 units); each coil contains from 4 to 8 glucose units, kept together by hydrogen bonds. The internal hollow tube is hydrophobic. with I2inside the coils, iodine atolms align, giving a dark violet complex
examples:
Amilopectin: 106 glucose units, with branches in position 6 every ca. 20 units. Therefore, extended helicoidal structures are impossible.
amylopectin
a-1,4’-glycosidic bond
a-1,6’-glycosidic bond
glycogen
Glycogen: similar to amylopectin, with branches every 11 units