The Oil/Water Interface, with and without Monomolecular Film, as a Model of the Living Cell Membrane.1

Abstract

Summary. 1 An oil/water interface (benzene/salicylic acid solution) has been employed as a model of a cell membrane. 2 The velocity of penetration of salicylic acid from the aqueous into the non-aqueous phase, and the influence of interposed mono-molecular interfacial films (gliadin, sodium cetyl sulphate) on the penetration velocity have been investigated. 3 The penetration constants found were of the order of 106cm2sec-1. An effect of interfacial films on the penetration could not be demonstrated. 4 The reasons for the failure of the interfacial films to affect the penetration are discussed. The influence of the unstirred layers around the phase boundary is found to be negligible. It is concluded that the penetration velocity is principally determined by an “energy barrier” situated in the phase boundary, which must be overcome by the penetrating molecules. 5 The order of magnitude of the penetration constants found in model systems is the same as that observed for living cell membranes. The kinetics of penetration through the latter may therefore be considered as determined by the conditions at the phase boundary as well as by the pore dimensions etc.