Electric potential developed across Langmuir–Blodgett preparations of proteins

Abstract

Langmuir–Blodgett (LB) preparations of up to 18 layers of bovine haemoglobin or bovine serum albumin have been found to develop an electric potential, measured between aluminium electrodes placed above and below the preparations. The magnitude of the potential increased with the surface pressure at which the protein monolayers were held during manufacture of the LB preparations, and which was in the range 10–25 mN m^–1. The potential increased linearly with the number of layers, the rate of increase being, in the middle, of the range of preparation pressure, ca. 33 mV per layer for haemoglobin and ca. 23m V per layer for serum albumin. The potential developed as a relaxation process; the time constant of the process at laboratory temperature and humidity was some hours, but it decreased substantially if the temperature or relative humidity were increased. The observed phenomena have been interpreted in terms of layers of orientated dipoles, rather than a Schottky depletion layer. Values inferred from measurements of the potentials and of capacitances of the preparations are a relative permittivity of ca. 17.7 for solid protein in layered LB preparations and dipole moments of 1.67 × 10^–27 C m (500 D) for haemoglobin and 8.67 × 10^–28 C m (260 D) for serum albumin.