Macromolecular Switches for Bilayer Membranes

Abstract

Controlled polyelectrolyte adsorption provides a powerful tool for use in the design of thin molecular films. The adsorption of polyelectrolyte chains would be expected to cause large changes in the delicate balance of forces that determines the structural and functional properties of organized assemblies, including monolayer, bilayer and multilayer films. But in addition, polyelectrolyte adsorption is exceedingly sensitive to environment, e.g., to pH, temperature and ionic strength. Controlled adsorption can therefore serve as a molecular switching mechanism, rendering film properties sensitive to selected chemical and physical stimuli. We have used this approach to effect molecular switching in mixtures of poly(2-ethyl acrylic acid) with bilayer vesicles of natural or synthetic phosphatidylcholines. In particular, we have prepared phosphatidylcholine vesicles that release their contents rapidly and quantitatively in response to changes in pH, temperature or glucose concentration. The design and preparation of responsive bilayer membranes, and the kinetics and mechanisms of the associated molecular switching processes, are discussed herein.