Conformation and crystalline structure of (2→1)-β-D-fructofuranan (inulin)

Abstract

The crystalline conformation of inulin a (2 .fwdarw. 1)-.beta.-D-fructofuranan was determined based on conformational analysis coupled with X-ray and electron diffraction data. The energy contour maps as a function of 3 torsional angles in the backbone were calculated taking into account van der Waals, torsional and electrostatic interactions. Although several minima were observed, only 2 models are possible considering the information obtained from the diffraction data. The 2 models correspond to 5-fold helices, one 54 (left-handed) and the other 51 (right-handed) with an advance per monomer of 2.16 .ANG. but with different conformational angles. Compared to the crystalline state torsion angles of polyethylene oxide analogs of inulin, large differences are noted. Steric interactions of the substituents and the exoanomeric effect may be responsible for the observed conformational differences.