Docking Structures Induced by Substitution Motifs of Softwood Xylan at Various Cellulose Surfaces

To understand xylan-cellulose interactions in softwood, the adsorption behavior of hexameric softwood xylan proxies with various substitutions was analyzed on the three surfaces of a hexagonal cellulose microfibril. The study found that all surfaces could bind xylan motifs, showing equally high affinity for the hydrophilic (110) and hydrophobic (100) surfaces and significantly lower affinity for the hydrophilic (11̅0) surface. Unsubstituted xylose hexamers had the highest affinity and most ordered adsorption structures, while substitutions generally reduced the affinity and regularity. An exception was a motif with two glucuronic acids two residues apart, which displayed high affinity and increased tendency to adopt a 2-fold screw on hydrophilic surfaces. Surface affinity correlated with the tightness of xylan-cellulose associations and the ratio of the xylan-cellulose to xylan-water interaction energies. Novel methods to quantify backbone conformations were proposed. Future work should address differences in simulation models and explore the competition between xylan and glucomannan for cellulose surfaces.