[Evaluation of phase transition models in lipid-aqueous systems by the optical analogy method]

There are two models of phase transition in mesomorphic lipid-water systems. The first one describes the transition in terms of trans-gauche isomerisation, the second-by the appearance of gauche-trans-gauche isomers (kinks). Both were argumented theoretically, but experiments cannot as yet offer an unambiguous decision. We have tried to evaluate each of the assumptions based on the qualitative analysis of X-ray and optical diffraction pictures from models and real objects. We have had in mind the early proved reason in the application of optical modeling of liquid crystal structures in a range of which our dipalmitoyllecithin-water system could be included. Results of comparing optical diffraction of laser beam (gamma = 630 nm) on two-dimensional models with our X-ray pictures of the system mentioned in L alpha and L beta modifications have shown that high-temperature L alpha phase consists of molecules with gauche-conformation of aliphatic fragments. In view of these data the kink model seems less realistic.