Acetyl groups, determination polysaccharides

Amino and sulfoamino groups react with nitrous acid, and this has been made the basis of a method for the determination of amino, N-sul-fate, and IV-acetyl groups in polysaccharides. 

Rha, Ara and Gal are the neutral sugar components from all the fractions. Xyl is not present in Fla and is significantly present in the hemicellulose fractions, indicating that this monosaccharide is component of hemicellulosic polymers. Chemical composition of the water fractions were determined (Table V). High protein contents and the presence of O-acetyl-groups were observed in four aqueous fractions. Neutral sugar and uronic acid composition points to inclusion of these polymers in the class of pectic polysaccharides. 

C-N.m.r.-spectroscopic analyses have been successfully made for determination of the position of O-acetyl groups in sialic acids, using the 9-O-acetyl- and 4,9-di-O-acetyl derivatives of Neu-/3-Me methyl ester as model compounds,9 1 or in the sialic acid residues of polysaccharide antigens ofN. meningitidis.166 1... 

Acetyl and Feruloyl Esters in Pectin. A colorimetric method for determining degrees of acetylation in pectins from various sources ( ), has been shown to be rapid and quite sensitive. Hydroxy-lamine is reactive toward both the methyl and acetyl esters in pectin, and ferric ion complexes with the resulting hydroxamic acids are red. The pectin complex is insoluble and removed by filtration the intensity at 520nm in the soluble fraction, consisting of the ferric complex with acetohydroxamic acid, is a measure of acetyl content. The accuracy of the method was demonstrated in determinations of 0-acetyl levels in standard per-ace-tylated polysaccharides. Another method ( ) involves alkaline hydrolysis of the acetyl groups from pectin, followed by distillation of acetic acid and its titration with standard base. 

Acyl (for example, O-acetyl) groups are common structural features in bacterial polysaccharides. The proportion and position of O-acyl groups can be determined by a method devised by de Beider and Norrman. ... 

All of the free hydroxyl groups are protected as acetals by reaction with methyl vinyl ether. The 0-acyl groups are then split off by treatment with alkali, and the resulting material is methylated (see Scheme 20). After hydrolysis of the methylated material, and analysis of the hy-drolyzate as alditol acetates by g.l.c.-m.s., it is possible to determine the positions and proportions of O-methyl groups and, hence, the substitution pattern of the 0-acyl groups. This procedure has been used to locate 0-acetyl groups in bacterial polysaccharides and wood polysaccharides. ... 

Acetic acid, liberated from the O- and A-acetyl groups of bacterial lipo-polysaccharides, has been determined by g.l.c. analysis. ... 

As regards the nature of the glycosidic bonds in a polysaccharide molecule, it may be determined by derivatization (formation of methyl ethers) prior to acid hydrolysis. As a consequence of this process, the —OH groups formerly involved in bonding are transformed into acetyl esters, whereas the free hydroxy groups occur as methyl ethers (analyzed by GLC). 

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