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

Abstract

The crystalline conformation of inulin a (2→1)-β-D-fructofuranan has been determined based on conformational analysis coupled with X-ray and electron diffraction data. The energy contour maps as a function of three torsional angles [Formula: see text], ψ, ω in the backbone were calculated taking into account van der Waals, torsional, and electrostatic interactions. Although several minima were observed, only two models are possible when one considers the information obtained from the diffraction data. The two models correspond to five-fold helices, one 5 4 (left-handed) and the other 5 1 (right-handed) with an advance per monomer of 2.16 Å, but with different conformational angles: ω = 60° and 180° respectively. 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 are believed responsible for the observed conformational differences.