Chang Henry H, Bhagat Ramesh K, Tran Rosalie, Dea Phoebe
Department of Chemistry, Occidental College, Los Angeles, California 90041, USA.
J Phys Chem B. 2006 Nov 9;110(44):22192-6. doi: 10.1021/jp055178s.
It is known that when bilayers of some saturated phosphatidylcholines are stored for 3 or more days at approximately 0 degrees C, a lamellar subgel (Lc) phase is detected at temperatures below the pretransition by differential scanning calorimetry (DSC). However, the subgel (Lc) phase and the corresponding subtransition (Lc--> Lbeta') for dimyristoylphosphatidylcholine (DMPC) has not been clearly characterized. In this study, using the temperature jump protocol first developed by Tristram-Nagle et al. for the dipalmitoylphosphatidylcholine (DPPC) system, new and accurate data characterizing the subgel formation and subtransition of DMPC were obtained through DSC and fluorescence spectroscopy with 1,6-diphenyl-1,3,5-hexatriene (DPH). It was discovered that the formation of the DMPC subgel phase requires incubation at temperatures of -5 degrees C or lower for 2 h or more. Kinetics of the subgel formation indicate that it is a very complex process and demonstrates that the planar gel phase is merely metastable below the subtransition, and not the thermodynamically stable phase. The subgel growth of DMPC is proven to be the dehydration of the headgroup region, and the subtransition is a process in which poorly hydrated DMPC becomes hydrated.
已知当某些饱和磷脂酰胆碱的双层膜在约0摄氏度下储存3天或更长时间时，通过差示扫描量热法（DSC）在低于预转变温度时可检测到层状亚凝胶（Lc）相。然而，二肉豆蔻酰磷脂酰胆碱（DMPC）的亚凝胶（Lc）相和相应的亚转变（Lc→Lβ'）尚未得到明确表征。在本研究中，使用Tristram-Nagle等人最初为二棕榈酰磷脂酰胆碱（DPPC）系统开发的温度跳跃方案，通过DSC和使用1,6-二苯基-1,3,5-己三烯（DPH）的荧光光谱法获得了表征DMPC亚凝胶形成和亚转变的新的准确数据。发现DMPC亚凝胶相的形成需要在-5摄氏度或更低温度下孵育2小时或更长时间。亚凝胶形成的动力学表明这是一个非常复杂的过程，并表明平面凝胶相在亚转变温度以下仅仅是亚稳态的，而不是热力学稳定相。DMPC的亚凝胶生长被证明是头基区域的脱水过程，而亚转变是水合不良DMPC变得水合的过程。
