AMIDE AND ESTER SURFACE ATTACHMENT REACTIONS FOR ALKANETHIOL MONOLAYERS AT GOLD SURFACES AS STUDIED BY POLARIZATION MODULATION FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The modification of alkanethiol monolayers via amide and ester formation reactions is demonstrated as a methodology for attaching monolayer and submonolayer coverages of specific chemical species onto metal electrodes. A monolayer of 11-mercaptoundecanoic acid (HSC10H20COOH) is used as a surface bifunctional linking agent on polycrystalline gold surfaces. The reaction of these adsorbed molecules with gaseous thionyl chloride converts the carboxylic acid group to an acid chloride which can then be reacted further with an amine or alcohol to form an amide or ester linkage. The attachment of alkyl, aromatic, and electrochemically active species to the surface is reported to demonstrate the versatility of this surface derivatization chemistry. Polarization modulation Fourier transform infrared (PM-FTIR) spectroscopy is employed as the primary method for monitoring the chemical structure of the adsorbed monolayers, and additional X-ray photoelectron spectroscopy (XPS) and electrochemical measurements are used to verify the elemental composition, oxidation state, and surface coverage of the adsorbed molecules.