Castresana J, Nieva J L, Rivas E, Alonso A
Department of Biochemistry, University of the Basque Country, Bilbao, Spain.
Biochem J. 1992 Mar 1;282 ( Pt 2)(Pt 2):467-70. doi: 10.1042/bj2820467.
The gel-to-fluid and lamellar-to-HII-hexagonal thermotropic phase transitions of egg-yolk phosphatidylethanolamine have been examined by Fourier-transform infrared spectroscopy under a variety of conditions, namely excess water at pH 5.0, excess water at pH 9.5 and low hydration. The various lamellar and hexagonal phases have been characterized by X-ray diffraction. At pH 5.0, gel-fluid and lamellar-hexagonal transitions were detected at 10 and 32 degrees C respectively, in accordance with previous data. At pH 9.5, only the first of these two transitions was detected. In the partially hydrated sample a single phenomenon was observed, probably encompassing both transitions, so that, in practice, a gel-HII-hexagonal transition appears to occur. The region of the i.r. spectrum corresponding to the phospholipid phosphate group reveals that the lamellar-hexagonal, but not the gel-fluid, transition is accompanied by a weakening in the shell of hydrogen-bonded water, thus providing direct evidence that, in a pure lipid/water system, hexagonal phase formation requires partial dehydration of the phospholipid phosphate group. X-ray diffraction data support this conclusion, since, at least in the low-hydration system, the average surface area per lipid polar group decreases with the thermotropic lamellar-hexagonal transition.
利用傅里叶变换红外光谱，在多种条件下，即pH 5.0的过量水、pH 9.5的过量水和低水合作用条件下，研究了蛋黄磷脂酰乙醇胺的凝胶态到流体态以及片层态到HII - 六方热致相变。通过X射线衍射对各种片层相和六方相进行了表征。在pH 5.0时，凝胶态到流体态以及片层态到六方态的转变分别在10℃和32℃被检测到，这与先前的数据一致。在pH 9.5时，仅检测到这两个转变中的第一个。在部分水合的样品中观察到单一现象，可能包含了这两个转变，因此实际上似乎发生了凝胶态到HII - 六方态的转变。红外光谱中对应磷脂磷酸基团的区域显示，片层态到六方态的转变（而非凝胶态到流体态的转变）伴随着氢键结合水层的减弱，从而提供了直接证据，即在纯脂质/水体系中，六方相的形成需要磷脂磷酸基团的部分脱水。X射线衍射数据支持这一结论，因为至少在低水合体系中，每个脂质极性基团的平均表面积随着热致片层态到六方态的转变而减小。
