Penetration of 1-alkanols into monolayers of α-helical polypeptides with hydrophobic side chains

Abstract

Penetration of 1-alkanols into monolayers of α-helical polypeptides with hydrophobic side chains at two different compressional states is studied by surface potential and surface pressure measurements. It was found that at an initial surface pressure of 3.0 mN m −1 there existed a time difference in achieving the final equilibrium between the surface potential and the surface pressure for poly (γ-dodecyl-L-glutamate) (PDOLG) and poly (γ-methyl-L-glutamate) (PMLG) monolayers after adsorption of 1-alkanol. This disagreement was accounted for by the time-dependent reorientation of polypeptide side chains at the interface after adsorption. The free energies of adsorption per CH 2 group of 1-alkanol to the monolayers spread at the initial surface pressures of 3.0 and 13.5 mN m −1 were −2.90 and −2.46 kJ mol −1 for PDOLG, and −2.70 and −2.57 kJ mol −1 for PMLG, respectively. The affinity of 1-alkanol to the PDOLG monolayer was stronger than that of the PMLG monolayer.