RARELY OBSERVED PHASE-TRANSITIONS IN A NOVEL LYOTROPIC LIQUID-CRYSTALSYSTEM

This Letter presents neutron diffraction data from a novel, biological ly relevant, lyotropic membrane system which is highly alignable (less than or equal to 1.0 degrees mosaic) in a magnetic field and gives ri se to a number of well-defined Bragg reflections. The system, composed of two different phosphorylcholine lipids, undergoes a rare nematic - -> smectic phase transition upon doping the system with paramagnetic i ons (e.g., 2.7 wt% Tm3+). In addition, the isotropic phase occurs at a lower temperature than the smectic phase, in contrast to other lyotro pic systems and in contrast to the phase behavior predicted by the McM illan model [Phys. Rev. A 4, 1238 (1971)] of smectic ordering.