Molecular and crystal structure of the regenerated form of (1→3)-α- d-glucan

Abstract

The crystal structure of a regenerated form of (1→3)-α- d-glucan, obtained by solid state deacetylation of the triacetate derivative, has been determined by combined X-ray diffraction analysis and stereochemical model refinement. The structure crystallizes in an orthorhombic unit cell with parameters a = 16.46 A ̊ , b = 9.55 A ̊ and c (fibre repeat)=8.44 Å, and space group P2 12 12 1. The chain conformation is nearly completely extended and is very close to a 2/1 helix, even though the dimer residue is the crystallographic repeat unit. An intramolecular O(2)   O(4)′ hydrogen bond stabilizes the conformation and extensive intermolecular hydrogen-bonding abilizes the packing. The resulting structure is sheet-like, with an alternating polarity of chain directions within the sheet. In its sheet-like character, extensive hydrogen-bonding, and insolubility in water, this polymorph of (1→3)-α- d-glucan resembles regenerated cellulose. The reliability of the structure analysis is indicated by the X-ray residual R=0.206.