Effects of water-soluble alcohols on the surface conductance of lipid monolayers: Bimodal action

We (Yoshida et al. J. Phys. Chem. B 2000, 104, 1249) devised a submersible horizontal electrode for estimation of the conductance of surface monolayers. The effects of 1-propanol on the electrical conductance of surface monolayers of stearic, elaidic, and oleic acids were estimated. The effects depend on the structures of the hydrophobic part of the monolayers. The surface electrical conductance of a stearic acid monolayer increased 18-fold by the addition of I-propanol. However, the response of an oleic acid monolayer was almost negligible. The result suggests that alcohol effects on the surface electrical conductance depend strongly on the packing of the monolayers, therefore it is affected by changes in the alkyl tails. Because alcohol molecules in water anchor to the monolayer surface, sandwiched water molecules between the alcohol and monolayer form two-dimensional structures. The solid condensed form of the stearic acid membrane tends to form two-dimensional structures of sandwiched water. The magnitude of their structures depends on the condensability of the monolayer. We contend that the proton flow through the hydrogen-bond network of water (electrical conductance) increases.