Modelling the feasibility of intramolecular dehydrodiferulate formation in grass walls

Abstract

Molecular modelling is a useful tool for predicting and visualising molecular interactions, eg providing a means of predicting the feasibility of covalent bond formation between macromolecules. Molecular modelling was used to evaluate the feasibility of intramolecular diferulate formation. Two ferulates were positioned at various locations along the backbone of an arabinoxylan (16 xylose residues) and the optimised structure generated using MM2 parameters. For ferulates separated by several xylose residues, diferulates could only form if the xylan backbone relaxed allowing chain folding to bring the two ferulates within spatial proximity for bonding. In positions that would allow overlap of ferulates, one or both of the ferulates would have to rotate along the xylan backbone for radical coupling. In both cases high-energy barriers prevented the complete rotation to allow bond formation. It therefore seems unlikely that intramolecular dehydrodiferulates form readily within grass cell walls. When two xylose residues separate two arabinose moieties containing ferulate units it is feasible for rotation to a position allowing the formation of the 5–5 linked diferulate with no relaxation of the backbone. This is the only diferulate that can form without bond strain when the ferulates are positioned three xylose residues apart on the same xylan backbone. This suggests restricted positioning of ferulates for 5–5 coupling. © 1999 Society of Chemical Industry