Saccharides solid-state structures

Additional evidence on the selection of conformations by the exo-ano-meric effect is derived from the solid-state structures of saccharides. It was earlier observed that the actual orientation of the anomeric alkoxyl group in pyranosides in the solid state corresponds to the (+sc, +sc) or ap, —sc) conformer, and thus proved that these conformers respectively represent the most stable axial and equatorial forms. As already noted, a particularly clear illustration of the operation of the exo-anomeric effect comes from the nonreducing disaccharide 0 ,a-trehalose, in which the most stable orientation about both exocyclic, C-0 bonds corresponds to the (+sc, +sc) conformer. Analyses of carbohydrate structures - revealed regularities in the distribution of the torsional angle O that are consistent with a restriction of rotation about the exocyclic C-O bond. The torsional angle for equatorial isomers varies from — 50° to — 110 , with a mean value of—79.4°. For the axial isomers, the range is 30-130°, with a mean value of 84.5 ° (see Ref. 29). 

Electroanalytical innovation and development of novel sensor electrodes are often driven by progress in materials chemistry. In particular for boron-based structures and assemblies the detection of saccharides plays a very prominent role. Monomeric as well as polymeric borate and boronic esters are reactive towards diols and lead to novel electroanalytical tools as well as new signal amplification strategies. There are many new opportunities arising and this overview will cover some of the recent developments in solid state, surface, and molecular boron structures with application in electroanalysis. 

Reviews have been published on progress over the last 20 years in computional methods for studying oligo- and poly-saccharide conformations in the solid state and in solution, and on the newer techniques of H-n.m.r. spectroscopy which have proved useful in the elucidation of oligosaccharide structures. A review and a symposium report have appeared on the conformational analysis of oligosaccharides in solution by n.m.r. methods combined with... 

An optical rotation-based method of conformational analysis has been applied to methyl P-xylobioside and a semi-empirical model of saccharide optical activity has been used to calculate the NaD rotation of this same compound. Calculated values of optical rotation based on the crystal structures of a series of 1,6-anhydro-p-D-pyranoses of galactose, talose and mannose suggest that solution conformations are very similar to those found in the solid state. However, significant differences were detected for methyl 3,6-anhydro-a- and p-pyranosides of glucose, galactose and mannose. 

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