Study on Higher Order Phase Transition of Phospholipid Bilayrs and Stability of Emulsion Formed with These Disperisons

本文研究了分散在水中的二肉豆蔻酰磷脂酰胆碱（DMPC）和二肉豆蔻酰磷脂酰甘油（DMPG）层状液晶及其与十六烷形成的乳状液的热性质。对该脂质分散体进行了恒压热容、水平衡表观压力、X射线衍射分析、ESR谱、DSC和zeta-电位的测定，结果表明，在（L_ +H_2O）层状液晶中，（L_<alpha>+H_2O）双分子层在高于其凝胶-液相转变温度（Tm ; DMPC为23.5 ℃，DMPG为23.7 ℃）几度时发生高级相变。DMPC分散体在29.0 ℃下观察到这些脂质的高阶相变，DMPG分散体在31.7 ℃下观察到这些脂质的高阶相变。这些磷脂的物理和表面化学性质被发现， ...更多信息 随后，在低于和高于T^**&gt;温度下研究了十六烷与DMPC分散体的乳化。结果表明，DMPC分散液在T^**&gt;时的热性质变化，使乳液的粒径、zeta电位和热稳定性发生变化。特别是，在Tm ~ T^**&gt;温度范围内，DMPC与正十六烷乳化时，乳液表面被DMPC的三层结构所覆盖，而在T^**&gt;温度以上，乳液表面由DMPC的单层结构所组成。对DMPC稳定的十六烷乳液的聚结动力学的精确研究支持了这一观察结果。结果表明，在T^&lt;**&gt;以下发生的乳液聚结活化能比T^&lt;**&gt;以上发生的乳液聚结活化能大一倍。这可以解释为什么DMPC形成的乳液在高于Tg时变得不太稳定。少

This work was carried out to make clear the thermal properties of lamellar liquid crystals of dimyristoylphosphatidylcholine (DMPC) and dimyristoryphosphatidylglycerol (DMPG) dispersed in water, and emulsions of hexadecane formed with these lipids. Main measurements for the lipid dispersions were made on the temperature dependence of heat capacity at constant pressure, equilibrium apread pressure on water, X-ray diffraction analysis, ESR spectra, DSC,and zeta-Potential.As a result, it was confirmed from these experiments that in the lamellar liquid crystals of the (L_<alpha>+H_2O) phase a higher order phase transition of bilayr occurred at the temperatures several degrees higher than their gel-liquid crystral transition temperatures (Tm ; 23.5ﾟC for DMPC and 23.7ﾟC for DMPG). The higher order phase transition for these lipids were observed at 29.0ﾟC for DMPC dispersion and at 31.7ﾟC for DMPG dispersion. The physical and surface-chemical properties of these phospholipids were found to d … More iffer incredibly below and above T^<**>.Subsequently, the emulsification of hexadecane with DMPC dispersion was investigated below and above T^<**> temperature. It was found that the particle size, zeta-potential, and thermal stability of emulsion were changed in paralell with the variation of the thermal properties of DMPC dispersion at T^<**>. Especially, a new finding was that when hexadecane wa emulsified with DMPC at a temperature between Tm and T^<**>, the emulsion surface was covered and stabilized with the triple layrs of DMPC,but above T^<**> the surface of emulsion was composed of a monolayr of DMPC as a usual surfactant. This observation was supported by the precise study on the coalescence kinetics for the DMPC stabilized hexadecane emulsion. The conclusion was that the activation energy for coalescence of the emulsion taking place below T^<**> was twice lager than that for coalescence above T^<**>. This may explain why the emulsion formed with DMPC above T^<**> became less stable. Less