Orientational Order of the Polyene Fatty Acid Membrane Probe trans-Parinaric Acid in Langmuir−Blodgett Multilayer Films

Abstract

trans-Parinaric acid, a polyene fatty acid, is widely used as a fluorescent membrane probe in photophysical and biophysical studies. We have worked on the orientational order of this molecule in Langmuir−Blodgett multilayer films of both gel-phase dipalmitoylphosphatidylcholine and arachidic acid at room temperature. Namely, orientational density probability functions were calculated using the maximum entropy method. Because liquid-crystal lipids do not deposit forming multilayers by Langmuir−Blodgett techniques, we have used Brownian dynamics methods to simulate a trans-parinaric acid molecule in a liquid-crystal bilayer environment. Orientational density probability functions are also achieved under the ergodic hypothesis. In the gel phase, trans-parinaric acid is highly ordered (narrow density probability function) and almost perpendicular (78°) to the multilayer planes. In the liquid-crystal phase, the density probability function broadens and the average orientation is not so close to the multilayer ...