Esterified Polysaccharides

In a similar study of the meningococcal serogroup Y polysaccharide (1.3 mol OAc/Neu5Ac unit) tracing of the positions of the O-acetyl groups was even more difficult since the substituents can be present at C3 or C4 of the Glc units and/or at C7 of the NeuSAc units (Bhattacharjee et al. 1976). 

An interesting phenomenon observed for the a(2-8)- and a(2-9)-linked sialo-polysaccharides upon storage in slightly acidic solutions (pH 3-6) is the formation 

The 13C-NMR spectrum of Neu5Ac2en together with its complete interpretation are described by Eschenfelder et al. (1975) and Czarniecki and Thornton (1977 a). The chemical shift values are summarized in Table 11. 

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Cell wall were isolated (2) and the pectic polysaccharides were extracted according with their solubility on water (highly esterified polysaccharides), imidazolium (ionically linked polysaccharides) and sodium carbonate (covalent linked polysaccharides), as shows figure 1. 

PEP Nondigestible Partially esterified polysaccharides ARCO Chemical Technology (Greenville, Delaware)... 

Hemicellulose-acting esterases may also be utilized in the future for regioselective removal of acetyl, or other esterified groups, in chemically esterified hemicelluloses. Different acetyl xylan esterases have recently been shown to possess distinct regioselective modes of action against cellulose acetate, cleaving the acetyl substituents in the C-2 and/or C-3-position (40). This kind of specificity is difficult to obtain by conventional chemical methods and it will enable the manufacture of more defined esterified polysaccharides. 

Notwithstanding the chemical differences (alcohol groups in guaran, carboxyl groups in xanthan, and partially esterified carboxyl groups in pectin) these three polysaccharides in combination with chitosan in the microspheres appear to be able to bring chitosan into solution. This is particularly interesting if one considers the solubility of these three polysaccharides in water and their important applications in the food and pharmaceutical industries. 

Several natural polysaccharides are esterified with sulfuric or phosphoric acid. Sulfated bacterial polysaccharides are not, however, very common. One example is a polysaccharide from an Arthrobacter species, which is most probably linked to the proteoglycan and contains sulfated D-galactopy-ranosyl residues. An extracellular polysaccharide from a Phormidium spe-... 

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form esterified... 

Natural xylan may occur partially esterified with acetic acid. This possibility arises from the observation that most holocellulose preparations contain a small amount of acetic acid. So far, however, it has not been established which polysaccharides are esterified. Treatment of the holocellulose with the alkaline solutions necessary for xylan extraction brings about complete deacetylation. 

Esterification is not difficult if xylan is first carefully precipitated from solution and dried to a fluffy, non-horny powder, or if the xylan can be highly swollen so as to make the polysaccharide molecules easily accessible to the esterifying reagents. Solechnik101 finds that swollen undried xylan, when treated with acetic anhydride containing sulfuric... 

The phosphate esters and, to lesser extent, the sulphate esters of monosaccharides are very important naturally occurring derivatives. Metabolism of carbohydrates involves the formation and interconversion of a succession of monosaccharides and their phosphate esters of which glucose-1-phosphate and fruc-tose-6-phosphate are important examples. The sulphate esters of monosaccharides or their derivatives (usually esterified at carbon 6) are found in several polysaccharides, notably chondroitin sulphate, which is a constituent of connective tissues. 

The acidic polysaccharides. In Dicotyledons, the major acidic polysaccharides are the pectins (partially methyl-esterified homogalacturo-nans and rhamnogalacturonans) and smaller amounts of arabinoglu-curonoxylans (2). [In growing grass cell walls, the arabinoglucuronoxy-lans usually predominate over pectins.]... 

Some of the acidic and basic polymers of the cell wall bear phenolic side-chains. The acidic polysaccharides carry ferulic and p-coumaric acid and related cinnamate-derivatives, esterified to specific hydroxy groups... 

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