Chiral discrimination in monolayers of monoglycerides

The influence of chirality on the structure of high- and low-temperature phases of monoglyceride monolayers has been studied by Brewster angle microscopy (BAM) and grazing incidence X-ray diffraction (GID). While there is no effect of the chiral center of monopalmitoylglycerol on the monolayer structure at 20 degrees C, an influence of chirality has been found for monostearoylglycerol at 5 degrees C. At low temperature the latter compound has an oblique lattice of the molecule chains at all investigated surface pressures, while the racemic mixture exhibits a rectangular structure. Additionally, it can clearly be visualized by BAM that the racemic mixture exhibits a phase transition between 6 and 12 mN/m at 5 degrees C characterized by a change of the tilt azimuth. By using GID, this transition could be identified as a change of the azimuthal tilt angle from a nearest neighbor (NN) direction to a next nearest neighbor direction (NNN).