A DFT study shows that metal ions prefer to approach between the two glucose rings in α/β-D-cellobiose while interacting/chelating with hydroxyl oxygen atoms of the disaccharide in aqueous medium. In the series of Li+, K+, Mg2+, Ca2+, Sn2+, Zn2+ and La3+ chlorides studied, ZnCl2 was identified as the most strongly interacting metal salt.
Understanding interactions of metal ions with cellulose is an important step in the development of efficient catalytic methods for processing cellulose. In this study, density functional theory methods were used to identify oxygen atoms interacting or chelating with selected metal chlorides of Li+, K+, Mg2+, Ca2+, Sn2+, Zn2+ and La3+ with cellulose model compound D-cellobiose. Calculated metal-oxygen distances of energy minimized D-cellobiose : metal chloride 1 : 2 mixtures revealed that the metal ions approach between the two glucose rings in α/β-D-cellobiose, and O4, O9 are the preferred interaction/chelation points. DFT study supported a previous 13C NMR chemical shift change based experiments. ZnCl2 showing the shortest metal-oxygen distances in approach to α/β D-cellobiose is known to produce the largest 13C NMR chemical shift changes in D-cellobiose. In α-anomer, average closest metal-oxygen distances and NMR shift changes co-related at 95 % confidence interval with liner regression R2=0.8582 and Sy.x=0.5722.
Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Harshica Fernando, Ananda S. Amarasekara