Dielectric constant and refractive index of lipid bilayers

Abstract

In order to elucidate the thickness of lipid bilayers, dielectric constants and refractive indices both for an oriented hydrocarbon assembly in bulk phase and for an oriented hydrocarbon monolayer of infinite extent are calculated on the basis of Kirkwood's theory of dielectric polarization. Dielectric constant is obtained as a function of the distance between the hydrocarbon chains and the thickness of the molecular layer. Dielectric constants of an oriented hydrocarbon assembly in bulk phase parallel and perpendicular to the hydrocarbon chains, ϵ | bulk and ϵ τ bulk, are 2·4879 and 1·7435 (for the interchain distance, a, of 4472 Å), and are 2·2709 and 1·5143 (for a = 5·000 A ̊ ), respectively. Dielectric constants of an oriented hydrocarbon monolayer, ϵ | layer and ϵ τ layer are 2·6079 and 4·0277 (for a = 4·472 A ̊ and the layer thickness h of 60 Å), and are 2·2708 and 2·2762 (for a = 5·000 A ̊ h = 60 A ̊ ), respectively.