Salonen I S, Eklund K K, Virtanen J A, Kinnunen P K
Department of Membrane Physics, KSV Research Laboratories, University of Helsinki, Finland.
Biochim Biophys Acta. 1989 Jul 10;982(2):205-15. doi: 10.1016/0005-2736(89)90056-4.
The phase behaviour of liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphatidyl-sn-1'-glycerol (1'-DMPG) and the corresponding sn-3' stereoisomer (3'-DMPG) were studied by DSC as a function of NaCl concentration. The melting of the metastable gel phase to the liquid-crystalline phase was similar for both lipids. However, in the presence of salt and at 6 degrees C (T less than Tp) the gel phase of both stereoisomers of DMPG was shown to be metastable and a new phase nominated here as the highly crystalline phase was formed as the stable state. However, significant differences in the formation and melting of the highly crystalline phase were evident between the two polar headgroup stereoisomers. For 3'-DMPG in the presence of 300 mM NaCl the melting enthalpy of this phase is approx. 82 kJ/mol and the transition temperature about 11 degrees higher (at 33.6 degrees C) than for the gel to liquid-crystalline phase transition (25 kJ/mol at 23.0 degrees C). In the presence of 0.15-1.2 M NaCl at 6 to 10 degrees C the formation of the highly crystalline phase of 3'-DMPG is complete within 2 to 5 days, increasing [NaCl] facilitates the rate. For a 1:1 mixture of 1'- and 3'-DMPG the formation of the highly crystalline phase requires several weeks and melts at about 20 degrees higher than the gel phase (at approx. 40 degrees C). For 1'-DMPG partial conversion into the highly crystalline phase requires several months. For 3'-DMPG several intermediate phases appeared as endothermic peaks between the main phase transition temperature and the melting temperature of the highly crystalline phase. In contrast, for 1'-DMPG and the 1:1 mixture the subgel phase appears to be the only metastable intermediate phase. Different monovalent cations differ in their effect on the metastable behaviour.
通过差示扫描量热法（DSC）研究了1,2-二肉豆蔻酰-sn-甘油-3-磷脂酰-sn-1'-甘油（1'-DMPG）和相应的sn-3'立体异构体（3'-DMPG）脂质体的相行为随氯化钠浓度的变化。两种脂质从亚稳凝胶相到液晶相的熔化过程相似。然而，在有盐存在且温度为6℃（T小于Tp）时，DMPG的两种立体异构体的凝胶相显示为亚稳态，并且形成了一种在此命名为高度结晶相的新相作为稳定状态。然而，两种极性头基立体异构体在高度结晶相的形成和熔化方面存在明显差异。对于在300 mM氯化钠存在下的3'-DMPG，该相的熔化焓约为82 kJ/mol，转变温度比凝胶到液晶相转变的温度（23.0℃时为25 kJ/mol）高约11℃（在33.6℃）。在6至10℃下，当存在0.15 - 1.2 M氯化钠时，3'-DMPG高度结晶相的形成在2至5天内完成，增加[NaCl]可加快形成速率。对于1'-DMPG和3'-DMPG的1:1混合物，高度结晶相的形成需要数周时间，且熔化温度比凝胶相高约20℃（约40℃）。对于1'-DMPG，部分转化为高度结晶相需要数月时间。对于3'-DMPG，在主相变温度和高度结晶相的熔化温度之间出现了几个作为吸热峰的中间相。相比之下，对于1'-DMPG和1:1混合物，亚凝胶相似乎是唯一的亚稳中间相。不同的单价阳离子对亚稳行为的影响不同。
