Polysaccharides derivatives

Xanthan gum [11138-66-2] is an anionic heteropolysaccharide produced by several species of bacteria in the genus Aanthomonas A. campestris NRRL B-1459 produces the biopolymer with the most desirable physical properties and is used for commercial production of xanthan gum (see Gums). This strain was identified in the 1950s as part of a program to develop microbial polysaccharides derived from fermentations utilizing com sugar (333,334). The primary... 

Every polysaccharide contains glycosyl units with unsubstituted hydroxyl groups available for esterification or etherification. Polysaccharide derivatives are described by their degree of substitution (DS), which is the average number of substituent groups per glycosyl unit. Because each monomeric unit of cellulose molecules has free hydroxyl groups at C-2, C-3, and C-6, the maximum DS for cellulose, and all polysaccharides composed exclusively of neutral hexosyl units, the majority of polysaccharides, is 3.0. 

Polysaccharide derivatives for chromatographic separation of heterocyclic enantiomers 98AG(E)1021. 

The type of CSPs used have to fulfil the same requirements (resistance, loadabil-ity) as do classical chiral HPLC separations at preparative level [99], although different particle size silica supports are sometimes needed [10]. Again, to date the polysaccharide-derived CSPs have been the most studied in SMB systems, and a large number of racemic compounds have been successfully resolved in this way [95-98, 100-108]. Nevertheless, some applications can also be found with CSPs derived from polyacrylamides [11], Pirkle-type chiral selectors [10] and cyclodextrin derivatives [109]. A system to evaporate the collected fractions and to recover and recycle solvent is sometimes coupled to the SMB. In this context the application of the technique to gas can be advantageous in some cases because this part of the process can be omitted [109]. 

Maurice Stacey s work, 15 nomenclature, 84-86 polysaccharide derivatives, 166 Amylose, 340-349 derivatives, 347-349... 

Uronic acid definition, 51 nomenclature, 108-110 polysaccharide derivatives, 165... 

L-arabinose molecules combine together in the furanose form to produce an araban. Since enzymes capable of hydrolysing pectic acid to n-galacturonic acid are known to be present in certain plant juices, and since the comparatively low temperature and slightly acid condition of plant materials would tend to favor the transformation of arabinose into the furanose form, the occurrence of the furanose structure in the polysaccharide derived from arabinose is not altogether unexpected. 

Among optically active polymers, polysaccharide derivatives are particularly valuable. Polysaccharides such as cellulose and amylose are the most readily available optically active polymers and have stereoregular sequences. Although the chiral recognition abilities of native polysaccharides are not remarkable, they can be readily converted to the esters and carbamates with high chiral recognition abilities. The chiral recognition mechanism of these derivatives has been clarified to some extent. 

Lithium salts in organic solvents with high solubility parameters have been previously used to dissolve strongly hydrogen-bonded polyamidesfciy and polysaccharides /for viscosity studies and for preparation of films or fibers. We are not aware of any previous attempts to utilize these solvent systems to prepare ester or carbamate polysaccharide derivatives... 

Viscosity data are reported in Table I for a number of the polysaccharide derivatives in 5% LiCl/N,N-dimethylacetamide solutions. At low concentrations of polymers, an upward curvature in the DSp/c (reduced viscosity) vs c (concentration) plot was observed. Additionally, nonlinear increases in solvent viscosity were observed for increased lithium ion concentrations in the absence of polymer. Therefore, reduced viscosities at 0.25 dl/g are reported. 

Hydrolysis studies have been conducted under acidic, basic, and neutral conditions for the polysaccharide derivatives. 

More recent developments in the field of the Pirkle-type CSPs are the mixed r-donor/ r-acceptor phases such as the Whelk-Of and the Whelk-02 phases.The Whelk-Of is useful for the separation of underiva-tized enantiomers from a number of families, including amides, epoxides, esters, ureas, carbamates, ethers, aziridines, phosphonates, aldehydes, ketones, carboxylic acids, alcohols and non-steroidal anti-inflammatory drugs.It has been used for the separation of warfarin, aryl-amides,aryl-epoxides and aryl-sulphoxides. The phase has broader applicability than the original Pirkle phases. The broad versatility observed on this phase compares with the polysaccharide-derived CSPs... 

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