Physicochemical Characterization of Phospholipid Solubilized Mixed Micelles and a Hydrodynamic Model of Interfacial Fluorescence Quenching

Mixed micelles of solubilized dimyristoyl phosphatidylcholine (DMPC) and the zwitterionic detergent dodecyldimethylammoniopropane sulfonate are characterized employing time-resolved fluorescence quenching (TRFQ), electron spin resonance (ESR), and surface tensiometry toward the goal of investigating interfacial reactions using these micelles as host reaction media. The properties measured are the micelle aggregation numbers, interfacial hydration index, microviscosity, and the critical micelle concentrations for various molar fractions, XDMPC, of DMPC, 0 ≤ XDMPC < 0.35. A complementary interpretation of the experimental results from TRFQ and ESR within the framework of a polar shell model for the mixed micelle yields some microstructural features, including the micelle core radius, polar shell thickness, and the fraction of the total hydrocarbon that overlaps with the micelle−water interface. The results of the characterization are applied in investigating an interfacial reaction; namely, micellar fluorescence quenching. A bulk hydrodynamic model when modified appropriately so as to be applicable to reaction within the interface is shown to describe micellar fluorescence quenching kinetics and also provides some insight into the location of guest molecules in micelles.