Formation of self-assembled monolayers by chemisorption of derivatives of oligo(ethylene glycol) of structure HS(CH2)11(OCH2CH2)mOH on gold

Abstract

This paper describes the preparation of oligo(ethylene glycol)-terminated alkanethiols having structure HS- (CHz)'l(OCH2CHz),nOH (m = 3-7) and their use in the formation of self-assembled monolayers (SAMs) on gold. A combination of experimental evidence derived from X-ray photoelectron sp€ctroscopy (XPS), measurement of contact angles, and ellipsometry implies substantial disorder in the oligo(ethylene glycol)-containing segment. The order in the -(CHz)r- group is not defined by the available evidence. The SAMs are moderately hydrophilic: du(H2O) = 34-38o; d,(H2O) = 22-25. A study of monolayers containing mixtures of HS(CH2)rrCHr and HS(CH2)rr(OCH2CH 2)6OH suggests that the oligo(ethylene glycol) moieties are eflective at preventing underlying methylene groups from influencing wetting by water. A limited study demonstrates that these oligo(ethylene glycol)-containing SAMs resist the adsorption of protein from solution and suggests that SAMs will be a useful model system for studying the adsorption of proteins onto organic surfaces.