title: Top-down grafting of xyloglucan to gold monitored by QCM-D and AFM: enzymatic activity and interactions with cellulose.
abstract: 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 TmNXG1. 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.
authors.affiliation: Department of Chemistry, Surface Chemistry, Royal Institute of Technology, Drottning Kristinas väg 51, SE-100 44 Stockholm, Sweden.
authors.forename: Niklas
authors.initials: N
authors.lastname: Nordgren
authors.forename: Jens
authors.initials: J
authors.lastname: Eklöf
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Harry
authors.initials: H
authors.lastname: Brumer
authors.forename: Mark W
authors.initials: MW
authors.lastname: Rutland
mesh_terms: D002482:Cellulose / Q000737:chemistry*; D003460:Crystallization; D005936:Glucans / Q000737:chemistry*; D006026:Glycoside Hydrolases / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D015335:Molecular Probes / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D011791:Quartz / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties; D014990:Xylans / Q000737:chemistry*
chemical_list: D005936:Glucans; D015335:Molecular Probes; D013438:Sulfhydryl Compounds; D014990:Xylans; D011791:Quartz; C029353:xyloglucan; D006046:Gold; D002482:Cellulose; D006026:Glycoside Hydrolases; C072818:xyloglucan endo(1-4)-beta-D-glucanase