INFRARED STUDY OF THIOL MONOLAYER ASSEMBLIES ON GOLD - PREPARATION, CHARACTERIZATION, AND FUNCTIONALIZATION OF MIXED MONOLAYERS

We report on the preparation and characterization of self-assembling monolayers (SAM's) on polycrystalline gold surfaces. The aim of the work is to develop model surfaces for applications in biomolecule interaction studies. Our attention is primarily focused on mixed monolayers of alkanethiols with different chain lengths and tail groups. Mixed monolayers of 16-thiohexadecanol (HS-(CH2)16OH) and n-alkanethiols (HS-(CH2)n-CH3) forM the basis for this study, and are primarily analyzed in terms of composition and distribution of functional groups (OH), by using infrared reflection-absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS). IRAS data of HS-(CH2)16-OH:HS-(CH2)15-CH3 monolayers prepared at mole fractions chi(sol)OH less-than-or-equal-to 0.5 exhibit no traces of intermolecular interactions (hydrogen bonding) between neighboring OH groups, an observation which clearly favors true molecular mixing rather than single component domain or island formation. Furthermore, the distribution of OH functions as well as their accessibility and reactivity have been studied in more detail by reacting them with trifluoroacetic anhydride (TFAA). The main purpose with this procedure is to enhance the OH signature in monolayers prepared at low mole fractions chi(sol)OH, by forming a strongly IR absorbing trifluoromethyl ester group on the surface. We discuss also routes to introduce biologically important substituents like phosphates and sulfates as tail groups on the surface.