Measurement of intermolecular forces in biomimetic systems

The intermolecular forces in two model biological membrane systems were measured by a variety of experimental techniques. In the study of monolayer domain morphology of the mixed Langmuir monolayer of Dimyristoyl-phosphatidyl-choline/Dihydrochloesterol, domain growth via the Ostwald ripening mechanism was followed by fluorescence microscopy. The domains in the monolayer were found to remain polydisperse over an extended time period. Parallel theoretical calculations showed that at thermodynamic equilibrium the system can either be at one-phase polydisperse state or two-phase state with macroscopically separated phases. The morphology of the domains was found to be very sensitive to the combined effects of the attractive line tension and electric dipole repulsion. In the second study of a model myelin membrane system, the interactions of lipid-lipid and lipid-protein were characterized experimentally. The results provided a consistent picture of the roles of different molecules such as lipids and myelin basic protein (MBP), as well as different interaction forces on the morphology of myelin membranes. The bare membranes showed no adhesion. Upon addition of MBP, lateral reorganization of the membrane was observed. MBP induced adhesion between apposing membranes. The degree of adhesion was mediated by the composition of the membrane. These results imply that changes in lipid composition of the membrane can moderate the non-specific interactions between the membrane and its resident proteins, which in turn determine the overall adhesion between two apposing membranes as in myelin.