Interactions and Kinetics in Membrane Mimetic Systems

Membrane mimetic chemistry has become a vitally important area of research (1-5). It is directed to the development of chemistries based on membrane-mediated processes in organized surfactant assemblies and molecular hosts. Aqueous and reversed micelles, microemulsions, mono­ layers, organized multilayers, bilayer or black lipid membranes (BLMs), and vesicles are considered to constitute the organized surfactant as­ semblies (1, 6). Molecular hosts include naturally occurring cyclodextrins (7) and synthetic crown ethers, cryptands, and spherands, collectively referred to as cavitands (8, 9). Organization and compartmentalization in membrane mimetic systems are exploited for reactivity control (2), transport (1 , 10), recognition (1 , 9, 1 1), drug delivery (12-14), and artificial photosynthesis (15-18). Reactivities' in the microheterogeneous environments of membrane mimetic systems cannot be described in terms of homogeneous kinetics. Attention has to be given to the partitioning of the reactants between the organized assembly and the bulk phase and to the structural and dynamic features of the system. Different kinetic treatments have been proposed for fast and slow reactions occurring in the different membrane mimetic systems. The important factor is, of course, the rate of reaction relative to the rates of reactant(s) and surfactant assembly reorganizations. A large variety of diverse approaches have been taken. Physical organic chemists . have focused their attention on reactions whose rates were appreciably slower than the time scale needed for the reorganization of the membrane