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 surf ace and thin octadecanethiol walls have been prepared on gold by subse quent chemisorption and self-assembly procedures. Cyclo-voltammetry of ferricyanide in bulk water showed 30% of the peak current observed fo r naked gold electrodes. 1,2-trans-Cyclohexanediol interrupted ferricy anide penetration into the steroid membrane gaps almost quantitatively ; its 1,2-cis diastereomer, on the other hand, had practically no bloc king effect. Glucose, galactose, and mannose were also efficient block ers for ion penetration into the hydrophobic gaps. Infrared spectrosco py, quartz balance, radioactivity, impedance, and contact angle measur ements 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 bas ed on the fitting of polyols with a cyclohexane skeleton and equatoria l OH-groups into icelike water clusters and the slowdown of diffusion processes in such rigid and shielded clusters is proposed.