Hydrophobic Gaps of Steroid Size in a Surface Monolayer Collect 1,2-trans-Cyclohexanediol and Glucose from Bulk Water

Mixed monolayers made of steroid thiol molecules lying nat on the surface and thin octadecanethiol walls have been prepared on gold by subsequent chemisorption and self-assembly procedures. Cyclo-voltammetry of ferricyanide in bulk water showed 30% of the peak current observed for naked gold electrodes. 1,2-trans-Cyclohexanediol interrupted ferricyanide penetration into the steroid membrane gaps almost quantitatively; its 1,2-cis diastereomer, on the other hand, had practically no blocking effect. Glucose, galactose, and mannose were also efficient blockers for ion penetration into the hydrophobic gaps. Infrared spectroscopy, quartz balance, radioactivity, impedance, and contact angle measurements on the monolayers and its physisorbed entrapments were used to characterize the membrane system and the unique physisorption process of the highly water-soluble compounds in hydrophobic gaps. A model based on the fitting of polyols with a cyclohexane skeleton and equatorial OH-groups into icelike water clusters and the slowdown of diffusion processes in such rigid and shielded clusters is proposed.