The goal of this work is to describe specific ion and pH effects on the apparent pKa's of micellized surfactants with head groups that model those of membrane phospholipids. Potentiometric titrations will be carried out on four different micellized subfactants with increasingly complex head groups using a variety of counterion concentrations and types. Specific ion electrodes will be used to monitor the distribution of each counterion and micellar bound spectrophotometric indicators to distinguish between site bound protons and the proton """"""""concentration-in-the-immediate-vicinity"""""""" of the micelle surface. The experimental results should provide crucial tests of current models for the structure of charged aqueous interfaces. If successful, it will be possible to describe, quantitatively, the observed shifts in the apparent pKa's of the titratable phosphate, carboxyl and amino functional groups attached to the surfactant head group and the apparent pKa's of micellar bound indicators over a wide range of experimental conditions, using a single value for the intrinsic pKa's of the functional groups and bound indicators and independently verifiable constants for the distribution of counterions between the micellar and aqueous phase. These results should provide a clearer picture of the structure of the electrical double layer around functionalized micelles as a function of surface charge density; a more detailed understanding of the relationship between head group structure, specific ion binding and surface pH; aid in the interpretation of the catalytic activity of functional micelles; increase the utility of spectrophotometric indicators as probes of surface pH of membranes and membrane mimetic agents; and clarify how the electrical double layer influences structural properties of phospholipid vesicle such as phase transition temperature, fusion and domain formation. The dynamic response of bilayer structure to its environment mediates a number of important functions of biological membranes such as excitability, active and passive transport, fluidity, the absorption of anesthetics and the activity of membrane bound enzymes. A clear picture of the specific interactions between the components of biological membranes may be important in understanding diseases, such as Tay-Sachs, which are caused bydefects in the catabolism of certain classes of phospholipids.
