Probing the structural chirality of crystalline cellulose with induced circular dichroism

Abstract

There is mounting evidence of twists in the crystalline regions of cellulose, but direct imaging of the twist is hindered by the small crystal sizes in cellulose nanocrystals from wood and plant sources. Here the structural chirality of cellulose nanocrystals is determined experimentally using induced circular dichroism of optically inactive Congo red. Time Dependent Density Functional Theory B3LYP 6-31G calculations indicate right-handed twisted cellulose surfaces induce positive Cotton effects in adsorbed Congo red and left-handed surfaces induce negative Cotton effects. Consistent with directly observed twists, conventional wood cellulose nanocrystals are estimated to have a right-handed 800 nm per half-twist demonstrating the crystalline regions are not uniformly flat, but rather right-handed twisted crystalloids.