Role of van der Waals, electrostatic, and hydrogen-bond interactions for the relative stability of cellulose Iβ and II crystals

Abstract

Naturally occuring cellulose Iβ with its characteristic parallel orientation of cellulose chains is less stable than cellulose II, in which neighbouring pairs of chains are oriented antiparallel to each other. While the distinct hydrogen-bond patterns of these two cellulose crystal forms are well established, the energetic role of the hydrogen bonds for crystal stability, in comparison to the van der Waals and overall electrostatic interactions in the crystals, is a matter of current debate. In this article, we investigate the relative stability of cellulose Iβ and II in molecular dynamics simulations and energy minimizations. We find that the larger stability of cellulose II results from clearly stronger electrostatic interchain energies that are only partially compensated by stronger van der Waals interchain energies in cellulose Iβ. A decomposition of the electrostatic interchain energies into interaction energies of neutral subgroups of atom leads to a consistent multipole description of hydrogen bonds and to interchain hydrogen-bond energies that account for roughly 80% of the interchain electrostatics in cellulose II.