Contribution to the physico-chemical study of the electrostatic interactions between ions and polyions of synthetic or biological origin at the air-water interface, comparison with the behavior of charged sites carried by nerve membranes

One method for studying the interfacial behavior of membrane constituents has long been that of monomolecular layers at the air/water interface. This work focuses on the study of such model systems: films spread at the air/water interface of hydrophobic synthetic or biologically charged macromolecules. We use classic techniques to measure surface potential, surface pressure and ion exchange at the interface using radioactively labeled ions. The interest of these conventional methods, although insufficient, remains a first approach and will be developed in chapter II. Our main focus is on studying the surface potential of the films studied. The theoretical interpretation in two specific cases is presented in chapter III. It provides an insight into the distribution of the electric potential in the interfacial region and helps us to understand ion exchange reactions and the role of electrostatic versus hydrophobic interactions. In Chapter V, a synthetic hydrophobic polyacid is used to simulate a highly simplified physicochemical model of a protein system close to the axon membrane. We then study a hydrophobic basic protein extracted from myelin, a type of membrane 'structural' protein: the 'FOLCH-LEES' proteolipid apoprotein. After characterizing its behavior in the pure state at the air/water interface in chapter VI, its interactions with an acidic phospholipid, Phosphatidyl Inositol monophosphate, extracted from wheat germ, are studied in Chapter VII, as a more general model of lipoprotein interactions. The results obtained, compared with those of physiologists, seem to lead to some interesting conclusions. They confirm and clarify earlier work on the role of Calcium ions in the extracellular environment in relation with the potential of the external interface of the axonic membrane at the moment of nerve excitation. They also highlight the possible role of charge/charge interactions between lipids and proteins in the interfacial electric field, leading to changes in molecular structures and perhaps to the creation of the pores required for ionic transport across membranes