Dielectric studies on water in solutions of purified lecithin vesicles

Abstract

The complex permittivity of sonicated aqueous solutions of purified dimyristoylphosphatidylcholine has been measured as a function of frequency between 3 kHz and 40 GHz. The dielectric spectrum of the samples shows two dispersion/absorption regions, one centered at about 80 MHz the other at about 20.GHz (30°C). Otherwise than in previous studies no additional dispersion/absorption process has been found at frequencies below 10 MHz. The complex dielectric spectrum of the samples is discussed with respect to the dynamical state of solvent water in solutions of single-bilayer vesicles. The main relaxation time of the solvent water, τ 1 ((2 πτ 1) −1 ≈ 20 GHz), is smaller than that of pure water, τ W , at the same temperature. This effect results from the action of internal depolarizing fields which obviously overcompensate and enhancement of τ 1 due to specific solute/solvent interactions (hydration) as had been previously found with micellar solutions of lysolecithins. It cannot be excluded, that some solvent water shows unusual dynamical behaviour. If there exists a substantial amount of such motionally perturbed water, however, it must be characterized by a relaxation time close to that of the phosphorylcholine zwitterions, τ 2 ((2 πτ 2) −1 ≈ 80 MHz).