Glucose conformational behaviour

The conformational behaviour of monosaccharides in solution is complicated. In solution, acyclic D-glucose readily converts into cyclic five-member (f, furanose) and/or six-member (p, pyranose) rings (Figure 1.36). Furanose (f) and pyranose (p) rings always exist as pairs of anomers (o or jd). These a and p anomers differ from each other only in their hydroxyl group... 

Extracellular polysaccharides composed of o-glucose, pyruvic acid, and succinic acid have been isolated from a number of strains of Agrobacterium. The conformational behaviour of the extracellular gel-forming polysaccharides from Arthrobacter species has been investigated by nuclear magnetic resonance relaxation and optical rotation techniques. " A number of the polysaccharides studied showed evidence of an ordered conformation which could be melted out on heating. O-Deacetylation destroyed the ordered conformation of two A. viscosus polysaccharides, whilst O-deacylation of the A. stabilis polysaccharide stabilized the ordered structure. 

At about 55 % the slope of the Ago curve shows a sudden change. This indicates the occurrence of a polymer-solvent compound with 6 molecules acetone per glucose-unit, in conformity with X-ray investigations It is to be noted in this connection, that the entropy of mixing in the system cellulose nitrate-acetone becomes negative in the limit of very low concentrations of acetone. This is explained by Schulz on the assumption that the solvent molecules are absorbed by the cellulose nitrate on to localised sites (perhaps in an orientated state), to which one would have to attribute a lower entropy. A behaviour of this type is, of course, not accounted for in Huggins and Flory s theory of the entropy of mixing. 

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