Page 333 - Carrahers_Polymer_Chemistry,_Eighth_Edition

296 Carraher’s Polymer Chemistry

On the positive side, dextran itself has been refined and employed as a therapeutic agent in restor-

ing blood volume for mass casualties. Natural dextrans are very high molecular weight (on the order
8
9
of 10 –10 Da) and are found to be unsuitable as a blood-plasma substitute. Lower molecular weight
6
(about 10 Da) dextran is suitable and is often referred to as clinical dextran.
Dextran gels are commercially used. The gel formed from reaction with epichlorohydrin gives
a cross-linked material used as a molecular sieve. Commercial cross-linked dextran is know as
Sephadex(TM). Sephadex is formed in bead form from dissolving dextran in sodium hydroxide solu-
tion followed by dispersion in an immiscible organic liquid such as toluene-containing poly(vinyl
acetate) and finally added to epichlorohydrin. Different series of Sephadex are used industrially

and in research. Ionic groups are often incorporated to give anionic and cationic dextrans and ion-
exchange molecular sieves. Sulfate esters of dextran are also used in separations.
Below illustrates some typical units that compose dextrans.

R O
R O H O OH
H O H H O H H
H H H
H O OH H OH H OH R
H HO O HO O HO O
OH H H O
HO H H OH H OH
H OH
OH O OH
H O H O H H H O
H H O H
OH H OH H H H OH
HO H OH H HO H
O O HO H
H OH H OH R H OH
R H OH
O
OH
H O O
H H
OH H O H H O
HO H O
HO H (9.20)
H OH H O H O
H H OH H H R
R OH H OH
O HO H HO H
H OH H OH
H O
H O
OH H
HO H O O
H
H OH H O
O H H O
OH HO H H H H O
H OH OH H H R
H O HO H OH
H H OH HO H
OH H H OH
HO H
H OH
Representative dextran structures appear in 9.20—top left—1→6 linked glucose units with a
1→4 branch; top right—linear 1→6 linked glucose units with a 1→2 branch; middle—linear chain
with both 1→6 and 1→3 linkages; bottom—linear chain of 1→6 linked glucose units with a 1→3
branch. All links are alpha linkages.

9.7.1 FRUCTANS

Fructans are polysaccharides composed of d-fructofuranose units. They are important in short-
term energy reserves for grasses and some plants. Inulin, found in dahlias, and levans from grasses

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