Phase Behavior Of Mixed Binary Monolayers Consisted Of Ursolic Acid And Lipid Molecules At Interface

With the development of science and the increasingly improved experimental techniques, the study of biomembrane system has been extended to medicine, biophysics and biochemistry, and other interdisciplinary fields beyond the life sciences, and gradually became popular and frontier topics of each fields. Study found that many life activities are closely linked with the structure and function of biomembrane systems. Biomembrane in vitro simulation technology is one of the simple and effective methods to research the physical and chemical characteristics of biomembrane system.1,2-dipalmitoyl-sn-glycero-3-phosphor-choline (DPPC) and1,2-dihexadecanoyl-sn-glycerol-3-phosphoethanolamine phosphatidyl-ethanolamine (DPPE) were chosen as the skeleton of the artificial membrane. The phase behavior of the binary mixtures system monolayer consisted of ursolic acid and the two lipid molecules at the air-water interface has been studied by π-A isotherm measurement and analysis based on the Langmuir monolayer technique. The thermodynamic properties of binary mixed monolayer (such as elastic modulus, the average and excess area per molecule, excess Gibbs free energy and interaction parameters) was investigated based on molecular fusion level. The theoretical analysis of the thermodynamics and kinetics of the mixed monolayer was indicated by the study of surface morphology of the artificial membrane using the Langmuir-Blodgett (LB) film technology combined with atomic force microscopy(I) In the binary mixtures of ursolic acid/1,2-dipalmitoyl-sn-glycerol-3-phosphor-choline (UA/DPPC) monolayer. With the gradually increased molar faction of ursolic acid, the arrangement of the π-A isotherms of shown regularity. When the faction of ursolic acid is small, the agglutination occurs in the mixed monolayer and the thermodynamically of mixed monolayer is more stable. The interaction between the two molecules is attraction. With the increase of surface pressure, the arrangement of ursolic acid molecules changed, which would affect the properties of the mixed monolayer. At lower surface pressure, a small amount of ursolic acid can easily access into the DPPC area, the attraction between the molecular on monolayer makes the appearance of aggregation morphology. At this time, ursolic acid plays the same role as cholesterol. Differed from the cholesterol, at high surface pressure, ursolic acid molecules overturned, which could increase the arrange order of the molecules in the mixed monolayer, and the shortage of the distance between molecules. The aggregation between two molecules may induce the formation of dimers. The detection of the mixed monolayer surface morphology using atomic force microscopy indicated this phenomenon.(II) Langmuir monolayer π-A isotherms of ursolic acid/1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine phosphatidyl-ethanolamine (UA/DPPE) binary mixtures at the air-water interface showed a regular distribution. There has interaction between molecules in the air-water interface and the two molecules can be mixed. The interaction of molecular on the UA/DPPE monolayer is weak than on the UA/DPPC. The interaction of different molecules on the mixed monolayer has relationship with the molar fraction and the surface pressure. When the mole fraction of ursolic acid is small, the morphology of monolayer appears defective film. With the increase of the fraction of ursolic acid on the monolayer, obviously aggregation can be found. As the increase of surface pressure, the distribution and arrangement of the lipid molecules and ursolic acid molecules will change. Correspondingly, the surface morphology of monolayer also changes.This article investigated the phase behavior of binary mixed monolayer consisted of ursolic acid and two different lipid molecules in the air-water interface. Interactions exist between ursolic acid and two different lipid molecules. At low surface pressure, ursolic acid played the same role as cholesterol-an important components of the biomembrane. At high surface pressure, as the molecular arrangement more closely, the molecular spacing decreases, the interaction force changed because the characteristic structure of ursolic acid. Comparative analysis found that, the interaction of ursolic acid with two kinds of lipid molecules is different.