Conformational analysis of (1. -->. 4)-. beta. -D-mannan triacetate
In wood, algae, and tubers, glucomannans have varying mannose-to-glucose ratios (M/G). Since diffraction on glucomannans of widely varying M/G do not show significant change in unit-cell base plane dimensions, the authors have suggested that isomorphous replacement may occur in glucomannans. To further investigate this point, it has been undertaken conformational analysis of glucomannan triacetate in which the X-ray fiber diagram suggests that two nonequivalent residues make up the asymmetric unit. X-ray fiber diagrams of the triacetate of glucomannan from Tubera salep show twofold symmetry along the chain axis with a fiber repeat of 1.6 nm. This implies that the asymmetric unit is composed of two pyranose rings since the virtual bond length of a single pyranose ring cannot be greater than approximately 0.54 nm. By using empirical potential functions, it could be shown that the minimum internal energy of a mannan triacetate chain corresponds to a state where contiguous mannose triacetate units are not conformationally equivalent. This supports the hypothesis of mannobiose hexaacetate as the asymmetric unit. Furthermore, introduction of glucose triacetate into the backbone did not change the minimum energy conformation, thereby lending support to the isomorphous replacement concept in crystalline glucomannans. 19 references, 13 figures, 2 tables.
- Research Organization:
- Xerox Research Centre of Canada, Mississauga, Ontario
- OSTI ID:
- 6971366
- Report Number(s):
- CONF-8205234-Vol.1
- Journal Information:
- J. Appl. Polym. Sci.: Appl. Polym. Symp.; (United States), Conference: 9. cellulose conference, Syracuse, NY, USA, 24 May 1982
- Country of Publication:
- United States
- Language:
- English
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