Polysaccharides acyl groups

Another microbial polysaccharide-based emulsifier is Hposan, produced by the yeast Candida lipolytica when grown on hydrocarbons (223). Liposan is apparentiy induced by certain water-immiscible hydrocarbons. It is composed of approximately 83% polysaccharide and 17% protein (224). The polysaccharide portion consists of D-glucose, D-galactose, 2-amino-2-deoxy-D-galactose, and D-galacturonic acid. The presence of fatty acyl groups has not been demonstrated the protein portion may confer some hydrophobic properties on the complex. 

Acyl groups are common in bacterial polysaccharides. The parent acids are fatty acids, hydroxy acids, and amino acids. The simplest acid, formic acid, has only been found as the amide. The occurrence of O-formyl groups had been reported, but proved to be incorrect. A-Formyl groups have been found in different polysaccharides for example, in the 0-specific side-chains of the LPS from Yersinia enlerocolitica 0 9, which are composed of 4,6-dideoxy-4-formamido-D-mannopyranosyl residues. The formyl group can assume two main conformations, s-cis (41) and s-trans (42), which are... 

F.a.b.-m.s. has been applied to three types of problem in the bacterial polysaccharide area assigning compositions (including the number and type of O-acyl groups), sequencing, and identifying cyclic structures. The last application is covered in Section VI,5. 

O-Acylation also provides a frequent modification of monosaccharide residues in bacterial polysaccharides, and, in most cases, substitution with acyl groups is only partial. 

Although most polysaccharides may be acylated without degradation, acyl derivatives of xylans29 are often unsatisfactory for molecular-weight determinations owing to their poor solubility characteristics. Mixed esters of xylans143 are often superior in this respect, but there are obvious difficulties in the differential analysis of acyl groups. Hemicellulose nitrates have been used for measurements of molecular size,168 but xylan nitrates,29 like xylan acetates, are reported to have poor solubility characteristics. 

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. ... 

A special publication of the Royal Society of Chemistry on Magnetic Resonance in Food Science discusses many aspects of the use of conventional and less conventional NMR methods in food analysis (such as oil, meat, beer, wine, moisture in biopolymers) including multivariate analysis of time domain NMR (TD-NMR) °, the use of an NMR-MOUSE (mobile universal surface explorer) for portable NMR and a review of the challenges in transferring NMR technology to the on-line industrial situation . Quantitative analysis methods of mixtures of fatty compounds by H -NMR are reviewed. Rapid simultaneous determination by H NMR of unsaturation and composition of acyl groups have also been reported in vegetable oils. The use of IR, Raman, NMR, and MS was reviewed for the analysis of polysaccharides related to food. ... 

Disaccharides to have been examined are two D-ribofuranosyl-D-ribitols produced from two bacterial capsular polysaccharides, and several aa-trehalose derivatives prepared as model bacterial cord factors [F.D. cationization with cesium iodide gave intense (M + Cs) ions]. The same group of workers have also reported on this method applied to the natural cord factor of Corynebacterium diphtheriae, and they found at least 22 species differing in the chain lengths of the two trehalose acyl substituents. A further report describes the determination of the sites of substitution of the acyl groups.Daunosamine-containing disaccharides have been examined by negative ion, positive ion, chemical ionization, and electron-impact methods. 

Alkyl halide, sodium hydride in DMSO 2.5.1 General, substances insoluble in common organic solvents, polysaccharides, lipopolysaccharides, peptides, sterically hindered functions, amides, amino acids Esters, and as stated for procedure 2.4 peptides containing sulfur-amino acids, histidine and arginine 132] O-Acyl groups are replaced with O-alkyl groups. For N-isopropyl amino acids, isopropyl ester formation, (see Chapter 2)... 

Note The important difference between the alkylation procedures involving sodium hydride in polar apiotic solvents and those involving alkyl halides and metal salts is that 0-acyl groups are completely replaced by 0-alkyl groups [30], N-Acyl groups survive and N-ulkyl-N-acylamido derivatives are produced. This alkylation can be performed on an extremely small amount of material and, thus, the procedure provides a rapid means for methylation linkage analysis in the polysaccharide [30], lipopolysaccharide [31] and peptide [20, 32] fields. 

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