Top-Down Grafting of Xyloglucan to Gold Monitored by QCM-D and AFM;Enzymatic Activity and Interactions with Cellulose

摘要

This study focuses on the manufacture and characterization of model surfaces consisting of end-grafted xyloglucan (XG),a naturally occurring polysaccharide,onto a gold substrate.The now well-established XET-technology was utilized for enzymatic incorporation of a thiol moiety at one end of the xyloglucan backbone.This functionalized macromolecule was subsequently top-down grafted to gold,forming a thiol-bonded xyloglucan brushlike layer.The grafting was monitored in situ with QCM-D,and a significant difference in the adsorbed/grafted amount between unmodified xyloglucan and the thiol-functionalized polymer was observed.The grafted surface was demonstrated to be accessible to enzyme digestion using the plant endo-xyloglucanase TmNXGl.The nanotribological properties toward cellulose of the untreated crystal,brush-modified surface,and enzyme-exposed surfaces were compared with a view to understanding the role of xyloglucan in friction reduction.Friction coefficients obtained by the AFM colloidal probe technique using a cellulose functionalized probe on the xyloglucan brush showed an increase of a factor of 2 after the enzyme digestion,and this result is interpreted in terms of surface roughness.Finally,the brush is shown to exhibit binding to cellulose despite its highly oriented nature.