Determination of the Viscosity of Valinomycin Monolayers as a Function of Surface Density and a Comment on Conformation

The surface viscosity of valinomycin spread on aqueous substrates buffered to pH 6.7 ±0.1 with trisphosphate has been determined over the surface pressure range 7–30 dyn/cm (area 360–160 Ų/molecule). Four series of measurements were made: buffer alone, buffer with 0.1 M NaCl, and buffer with 0.1 M and 1 M KCl. The surface viscosity remained essentially constant at 1.8 (mdyn s)/cm over the entire compressional range, regardless of the presence of Na⁺or K⁺. Apparently, the polar groups do not form an intermolecular network by hydrogen bonding as the polar groups of lecithin or the fatty alcohols appear to do. The surface pressure-molecular area diagrams (II-A) in all cases, with and without Na⁺ or K⁺ ions in the water, are monotonic and nearly identical. None of the diagrams display a signature that can be attributed to either a phase change, a conformation change, or a unique molecular area. It is concluded that all monolayers studied in this research had essentially the same conformation.