Lewis R N, Sykes B D, McElhaney R N
Department of Biochemistry, University of Alberta, Edmonton, Canada.
Biochemistry. 1988 Feb 9;27(3):880-7. doi: 10.1021/bi00403a007.
The thermotropic phase behavior of dioleoylphosphatidylcholine and six of its longer chain homologues was studied by differential scanning calorimetry and 31P nuclear magnetic resonance (NMR) spectroscopy. Aqueous dispersions of these compounds all exhibit a single endotherm upon heating but upon cooling exhibit at least two exotherms, both of which occur at temperatures lower than those of their heating endotherm. The single transition observed upon heating was shown by 31P NMR spectroscopy to be a net conversion from a condensed, subgel-like phase (Lc phase) to the liquid-crystalline state. Aqueous ethylene glycol dispersions of these compounds also exhibit single endotherms upon heating and cooling exotherms centered at temperatures lower than those of their corresponding heating endotherm. However, the behavior of the aqueous ethylene glycol dispersions differs with respect to their transition temperatures and enthalpies as well as the extent of "undercooling" observed, and there is some evidence of discontinuities in the cooling behavior of the odd- and even-numbered members of the homologous series. Like the aqueous dispersions, 31P NMR spectroscopy also shows that the calorimetric events observed in aqueous ethylene glycol involve net interconversions between an Lc-like phase and the liquid-crystalline state. However, the Lc phase formed in aqueous ethylene glycol dispersions exhibits a considerably broader powder pattern than that observed in water. This, together with the fact that the transition enthalpies of the aqueous ethylene glycol dispersions are considerably higher than those of the aqueous dispersions, indicates that these lipids form more ordered Lc phases in aqueous ethylene glycol.(ABSTRACT TRUNCATED AT 250 WORDS)
通过差示扫描量热法和31P核磁共振（NMR）光谱研究了二油酰磷脂酰胆碱及其六种较长链同系物的热致相行为。这些化合物的水分散体在加热时均表现出单一吸热峰，但在冷却时表现出至少两个放热峰，这两个放热峰均出现在低于其加热吸热峰的温度下。31P NMR光谱显示，加热时观察到的单一转变是从凝聚的、亚凝胶状相（Lc相）到液晶态的净转变。这些化合物的乙二醇水分散体在加热时也表现出单一吸热峰，冷却放热峰的中心温度低于其相应加热吸热峰的温度。然而，乙二醇水分散体的行为在转变温度和焓以及观察到的“过冷”程度方面有所不同，并且有证据表明同系物系列中奇数和偶数成员的冷却行为存在不连续性。与水分散体一样，31P NMR光谱也表明，在乙二醇水溶液中观察到的量热事件涉及Lc样相和液晶态之间的净相互转化。然而，在乙二醇水分散体中形成的Lc相表现出比在水中观察到的更宽的粉末图谱。这一点，再加上乙二醇水分散体的转变焓远高于水分散体的转变焓，表明这些脂质在乙二醇水溶液中形成了更有序的Lc相。（摘要截短至250字）
