Monolayer and Interfacial Permeation

Abstract

Transport across physical-chemical interfaces is considered in connection with three particular problems of biological interfaces: the structure and properties of cell membranes, the properties of the lung surfactant, and the effects of ionic currents across excitable membranes. With regard to cell membranes, studies of monolayer permeation suggest that permselectivity on the basis of size is a property of bilayer structure and probably gives rise to the observed dependence of the permeability on partition coefficients. The permeabilities of lipid and protein monolayers are consistent with the bimolecular leaflet (BML) model of the membrane and not with mosaic models. Experiments with the lung surfactant indicate that, in addition to its surface tension-lowering properties, it is unusual in its ability to form a strong two-dimensional network, which probably contributes to alveolar stability. Finally, the results of studies of interfacial ionic transference suggest a new way of accounting for the ionic fluxes in excitable membranes during an action potential without assuming ion-selective pores or carriers. In the suggested mechanism, it is possible to account for the change in ionic selectivity and the proper phasing of the fluxes, as well as other aspects of excitation in natural membranes.In this paper, I would like to present the results of investigations of flow and exchange across physical-chemical interfaces and to relate the results to specific problems of biologic interfaces. The three problems that I wish to touch upon in connection with these model studies are (a) the problem of general membrane permeability, i.e. the apparent porosity of the plasma membrane; (b) the permeation barrier in the lung and the problem of alveolar stability; and (c) the effects of stimulating currents through excitable membranes.These are large topics, and the information that I shall present must, of necessity, deal with limited aspects of the problems. However, the main advantage in studying models is that experiments with very simple systems are easily interpreted and often give an insight into factors that are important in more complex systems. I shall try to present the results of the model studies from a point of view that will suggest new approaches to the general biological problems.

Effect of Fatty Alcohol Monolayers on the Rate of Bromine Transfer across the Water/Air Interface: Assessment of Candidate Models Using Scanning Electrochemical Microscopy

“…Early work by Blank and co-workers showed that the presence of various long chain alcohol monolayers reduced the uptake rate of oxygen and carbon dioxide by water. The permeability of monolayers to several substances has also been measured for a small range of amphiphiles, at a few surface pressures and temperatures. ,− It was found that the least permeable monolayers were formed from saturated, straight-chain fatty acids or alcohols, with a long carbon chain and a close-packed incompressible structure.…”