This proposal presents a plan to study the thermodynamics of transfer of common lipid membrane components between gel and fluid phases of a reference bilayer, dipalmitoylphosphatidylcholine, using differential scanning calorimetry as the primary technique. The experimental protocols involve carrying out the measurements in very dilute solutions of the solute components in the bilayer, and then using the regular solution model to evaluate the free energy proposed for evaluation of the enthalpy of transfer of the solute, so that the entropy change can also be determined. In the end a complete thermodynamic description of the transfer process will allow comparisons between a variety of lipid classes that are important in membrane biophysics. By systematically varying the structures of solute molecules, a set of parameters can be devised that will relate structural features of the solutes to the overall thermodynamic transfer characteristics. Molecules such as the phospholipids, fatty acids, sphingolipids and steroids will be studied. %%% Interactions between the lipid components of biological membranes determine the physical and chemical characteristics of the components in the membrane. Evaluation of the thermodynamics of these interactions is fundamental to understanding the behavior of molecules in the bilayer membrane environment. It has been difficult to devise methods to evaluate the thermodynamic properties of membrane components because of the limitations of models and techniques that can be used to study the interactions.
