Preparation and characterization of mixed monolayer assemblies composed of thiol analogues of cholesterol and fatty acid

Mixed self-assembled monolayers provide an attractive model system for investigating the role of different molecules in biological membranes. This paper describes the preparation and characterization of a novel type of mixed monolayer assemblies composed of thiol analogues of cholesterol and fatty acid. The mixed monolayers are prepared by coadsorbing 11-mercaptoundecanoic acid (MUA) and thiocholesterol (cholest-5-ene-3β-thiol, TC) from solution directly onto evaporated gold surfaces. The influence of TC on the molecular composition and conformation in the mixed monolayer is analyzed by using a combination of infrared reflection−absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurement, and cyclic voltammetry. The results indicate that the TC molecules maintain their conformation in the mixed monolayers, whereas the MUA molecules display a significantly more disordered conformation as compared to the MUA molecules in the pure monolayer. Cyclic voltamme...