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

研究了双肉豆蔻基磷脂酰胆碱(DMPC)和双肉豆蔻基磷脂酰甘油(DMPG)层状液晶在水中的分散及其与十六烷形成乳状液的热性质。实验结果表明，在(Lα+H_2O)相的层状液晶中，在高于凝胶-液晶相转变温度(Tm；23.5ﾟC，DMPG为23.7ﾟC)的温度下，双分子发生了高阶相变。DMPC分散体的高阶相变温度为29.0ﾟC，DMPG分散体的高阶相变温度为31.7ﾟC。这些磷脂的物理和表面化学性质被发现是d…在此基础上，对十六烷与DMPC分散体系的乳化进行了研究。结果表明，随着DMPC分散体系热性能的变化，乳液的粒径、Zeta电位和热稳定性也发生了相应的变化。特别是，当十六烷与DMPC在Tm和Tm之间乳化时，乳状液表面覆盖并稳定了DMPC的三层，但在Tm以上，乳状液表面是由单层DMPC组成的。对DMPC稳定的十六烷乳液聚并动力学的精确研究支持了这一观察结果。结果表明，乳状液在T^lt；**&gt；以下的聚合活化能比高于T^lt；**&gt；的聚合活化能大一倍。这可能解释了为什么DMPC高于T^&lt；**&gt；形成的乳状液变得不太稳定。较少

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