TEMPERATURE-COMPOSITION PHASE DIAGRAM AND MESOPHASE STRUCTURE CHARACTERIZATION OF THE MONOVACCENIN/WATER SYSTEM. Martin Caffrey and Hong Qiu, Department of Chemistry, The Ohio State University, Columbus, OH 43210

The temperature-composition phase diagram of monovaccenin (a C18:1c11 monoacylglycerol) in water was constructed using small- and wide-angle x-ray scattering/diffraction in the range of ca. 0 deg.C to 110 deg.C and ca. 0 % (w/w) to 60 % (w/w) water in the heating direction. The phases identified in this system include the lamellar crystalline phase, the lamellar liquid crystalline, phase, the fluid isotropic (FI) phase, two inverted cubic phases (Q^230, Ia3d; Q²²⁴, Pn3m), and the inverted hexagonal (H_II) phase. The monovaccenin/water phase diagram reported herein is remarkably similar to that of the monoolein (a C18:1c9 monoacylglycerol)/water system. There are some important differences however that will be highlighted in the presentation. Since our long term objective is to establish the relationship between lipid molecular structure and lyotropic/thermotropic mesophase propensity by comparing phase diagrams for an homologous series of lipids, every effort has been taken to ensure that the current phase diagram represents equilibrium behavior and that the assorted phase boundaries have been determined accurately. The interpreted phase diagram is based on close to 500 discrete measurements in temperature-composition space recorded as a function of temperature in 5 deg.C increments and of composition in 4 % (w/w) water increments on average.