Monolayer characteristics of valinomycin in the presence of various salts in aqueous subphase.

Abstract The surface pressure-molecular area, surface potential-molecular area and Brewster reflectivity-molecular area isotherms for valinomycin monolayers (states II and III) at various aqueous salt subphases were measured. Two additional states of valinomycin monolayers were observed in the presence of K + and Rb + as compared to the other alkali metal cations. This phenomenon correlates with the strong complexation between the valinomycin and these cations in bulk. State II corresponds to the very special ‘bangle’ conformation of the polypeptide ring of valinomycin, in which all carbonyl and carboxyl groups of the amino-acid residues are coordinated to the cation inside the polypeptide ring. State III corresponds to the vertical orientation of the ‘bangle’ conformation of valinomycin molecules with respect to the interface. An influence of the anion size on the stability of valinomycin-cation complexes at the interface was found.