Molecular and crystal structure of (1----3)-alpha-D-glucan triacetate.
A crystal and molecular structure for GTA I, the low temperature polymorph of (1----3)-alpha-D-glucan triacetate, is proposed on the basis of X-ray diffraction analysis of well-oriented films, combined with stereochemical model refinement. The unit cell is monoclinic with parameters a = 30.17 A, b = 17.42 A, c (fibre axis) = 12.11 A, and beta = 90 degrees C. The probable space group is P2(1) with b axis unique. Six molecular chains pass through the unit cell with alternating polarity and with three independent chains comprising the asymmetric unit. The chain axes are located in a hexagonal packing arrangement. The chain backbone conformation is a left-handed, three-fold helix, but all nine O(6) acetyl groups of the asymmetric unit are in non-equivalent rotational positions. The most probable structure is indicated by X-ray residuals R = 0.261 and R" = 0.283, based on 62 reflection intensities (41 observed and 21 unobserved).
Yui
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Chemistry Department, State University of New York, College of Environmental Science and Forestry, Syracuse 13210.
Sarko
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A
D005936:Glucans / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D014961:X-Ray Diffraction
D005936:Glucans