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Flexibility of the pyranose ring in \alpha and \beta -glucoses

Joshi, NV and Rao, VSR (1979) Flexibility of the pyranose ring in \alpha and \beta -glucoses. In: Biopolymers, 18 (12). pp. 2993-3004.


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Conformational energies of \alpha and \beta -D-glucopyranoses were computed by varying all the ring bond angles and torsional angles using semiempirical potential functions. Solvent accessibility calculations were also performed to obtain a measure of solvent interaction.The results indicate that the $4C_1$ (D) chair is the most favored conformation, both by potential energy and solvent accessibility criteria. The $4C_1$ (D) chair conformation is also found to be somewhat flexible, being able to accommodate variations up to 10 Deg in the ring torsional angles without appreciable change in energy. Observed solid-state conformations of these sugars and their derivatives lie in the minimum-energy region, suggesting that the substituents and crystal field forces play a minor role in influencing the pyranose ring conformation. Theory also predicts the variations in the ring torsional angles, i.e., CCCC < CCCO < CCOC, in agreement with the experimental results. The boat and twist-boat conformations are found to be at least $5 kcal mol^{-1}$ higher in energy compared to the $4C_1$ (D) chair, suggesting that these forms are unlikely to be present in a polysaccharide chain. The $1C_4$ (D) chair has energy intermediate between that of the $4C_1$ (D) chair and that of the twist-boat conformation. The calculated energy barrier between $4C_1$ (D) and $1C_4$ (D) conformations is high-about $11 kcal mol^{-1}$.

Item Type: Journal Article
Publication: Biopolymers
Additional Information: The copyright belongs to John Wiley & Sons, Inc.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 09 Dec 2005
Last Modified: 19 Sep 2010 04:21
URI: http://eprints.iisc.ac.in/id/eprint/4286

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