Partial Electron Transfer in Octadecanethiol Binding to Gold?

Langmuir-Blodgett transfer of octanedecanethiol (Cl&H) containing monolayers onto gold-coated glass slides under potentiostatic conditions leads to a quantitative characterization of Cl&H chemisorption on gold. The thiol-gold bond involves a partial electron transfer from sulfur to the gold substrate. The CL$H partial charge number was determined to vary linearly with the potential of gold substrates from 0.30 at -0.30 V to 0.45 at 0.70 V vs SCE. Only ca. 81% of Cl&H molecules appear to chemisorb upon LB transfer at 20 mNlm. This is likely a result of some orientational restrictions (e.g. tilt and registry with the gold surface lattice) imposed on the system by the lateral pressure during LB transfer. The requirement of monolayer charge neutrality, stemming from a negligible capacitance of the Au/LB monolayer interface, results in a dissociation of thiol's proton to an extent equal to the charge transferred due to C&H chemisorption.