ORIENTATIONAL BEHAVIOR OF PHOSPHATIDYLCHOLINE BILAYERS IN THE PRESENCE OF AROMATIC AMPHIPHILES AND A MAGNETIC-FIELD

A number of aromatic-containing additives which can influence the orie ntation of fragments of lipid bilayer membranes by a magnetic field ha ve been investigated. Two properties of these additives prove importan t: (1) sufficient detergency to facilitate reorganization of bilayer c omponents and (2), sufficient anisotropy in magnetic susceptibility to alter the preferred direction of fragment orientation. Triton X-100 i s identified as effective in terms of facilitating magnetic field orde ring of bilayer fragments but does not alter the preferred direction o f orientation A combination of the detergent CHAPSO (3-[(3-cholamidopr opyl)-dimethylammonio]-1-propane sulfonate) and the aromatic alcohol 1 -naphthol facilitates both ordering and alters the preferred direction of bilayer orientation. As mixtures of dimyristoylphosphatidylcholine (DMPC) and CHAPSO, which orient with bilayer normals perpendicular to the magnetic field, were titrated with 1-naphthol, the assemblies und erwent transitions, first to random orientation, and then to an orient ation with bilayer normals parallel to the field. Based on temperature -induced phase transitions and the extent of motional averaging of the P-31 shielding tensor of the DMPC headgroup, the DMPC in these orient ed samples appears to maintain a bilayer morphology during transitions . The insight provided in this study regarding factors which influence fragment stability and orientation lays the groundwork for the design of improved field-oriented media for spectroscopic investigation of m embrane components.