Polysaccharides acetyl-substituted

A similar procedure was adopted for synthesis of nanoparticles of cellulose (CelNPs). The polysaccharide nanoparticles were derivatised under ambient conditions to obtain nanosized hydrophobic derivatives. The challenge here is to maintain the nanosize even after derivatisation due to which less vigorous conditions are preferred. A schematic synthesis of acetyl and isocyanate modified derivatives of starch nanoparticles (SNPs) is shown in scheme 3. The organic modification was confirmed from X-ray diffraction (XRD) pattern which revealed that A- style crystallinity of starch nanoparticles (SNPs) was destroyed and new peaks emerged on derivatisation. FT-IR spectra of acetylated derivatives however showed the presence of peak at 3400 cm- due to -OH stretching indicating that the substitution is not complete. 

The floss silk from Chorisia speciosa furnished a polysaccharide with a main chain of (1 -> 4) linked P-Xylp substituted at 0-2 by 5 % of uronic acid. The xylan structure also was interposed with a-Rhap units in small amounts. The defatted seeds furnished on aqueous extraction a major fraction, ((9-acetyl, 10 % and protein, 45 %) wich was hydrolysed and analysed by p.c. and GLC, showing Rha (20 %), Ara (16 %), Gal (64 %) and also uronic acids (45 %). Partial hydrolysis gave rise to a polysaccharide free of arabinose, with 46 % of uronic acids. Methylation analysis (GLC -MS) indicated a chain of (1 4) - linked Gal/ (42 % of 2,3,6-Me3-Gal). 

Observation of displacement effects resulting from O-substitution, and use of standards, led to the assignment of the chemical structure of the polysaccharide of Neisseria meningitidis serogroup 29e, which consists of 2-acetamido-2-deoxy-D-galactosyl and partly acetylated 3-deoxy-D-manno-octulosylonic acid (KDO) residues.166 The 13C-n.m.r. spectrum of the O-deacetylated polymer (see Fig. 36,B) contained 15 signals out of the possible 16 expected from an alternating structure. Comparison of these resonances with those of the anomers of 2-aceta-... 

D-Giucosamine and o-gaiactosamine, usually as A-acetyl derivatives, are part of the structures of several natural polysaccharides, whilst other uncommon aminosugars are components of the aminoglycoside antibiotics. We have also noted the occurrence of A-glycosides, where the nitrogen substitution is at the anomeric centre (see Box 12.3). 

As with agar and carrageenan, substitution in the Xanthomonas polysaccharide structure inhibits the interaction with galactomannan. Thus, removal of the acetyl groups by saponification yields a product that interacts much better with galactomannans.211 Less locust-bean gum is required to gel deacetylated Xanthomonas polysaccharide, and mixtures of locust-bean gum and deacetylated Xanthomonas polysaccharide form a gel at lower, total-polysaccharide concentrations. 

D-Galacturonic acid (35) is a common polysaccharide component in the plant kingdom. Its a-(l —> 4)-linked polymer forms the building unit of pectins.123 Some of the carboxyl groups are esterified with methanol and some units are substituted with 2-0- or 3-O-acetyl groups. 

Serotype B contains capsular polysaccharide, 60% of which consists of a (1— 3)-linked a-D-mannopyranosyl main-chain, two of every three units being substituted at 0-2 by /3-D-xylopyranosyl side-chains, the other being disubstituted, at 0-4 with /3-D-xylopyranosyl and at 0-2 with j8-D-glucopyranosyluronic acid units (40). The polysaccharide contains 3 acetyl groups for every 7 sugar residues.169 As serotype C polysaccharide is similar, except for 2 of every 3 units being disubstituted,170 and as serotype D polysaccharide contains 1 of every 3 man-nosyl residues unsubstituted (and no disubstituted residues171), the reclassification appears to be confirmed. 

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