Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, PR China.
J Phys Chem B. 2010 Feb 18;114(6):2158-64. doi: 10.1021/jp9107014.
Knowledge on the synchronicity or cooperativity of changes in different parts of the amphiphilic molecules is important to understand the molecular mechanisms of phase transformations of self-assembled aggregates. A long-standing and challenging question is to understand the roles individual groups/portions in an amphiphilic molecule play during phase transitions. To address this question, we selected a lysophospholipid, 1-stearoyllysophosphatidylcholine (SLPC), to study the transition mechanisms between its lamellar phase and micellar phase by using differential scanning calorimetry, small-angle X-ray scattering, Fourier transform infrared spectroscopy, and two-dimensional correlation analysis. It was found that during the lamellar to micellar transition the interfacial C=O groups and the lipid acyl tails change evidently with the former changing a little earlier, but the lipid headgroups remain unchanged in the hydration and conformation state. This means that the head, interface, and tail of SLPC molecules change nonsynchronously. Moreover, the results show that the lamellar to micellar transition is initiated by the interfacial groups. The molecular mechanism of the slow formation kinetics of the lamellar state from the micellar state was also discussed in the context of the nonsynchronicity phenomenon. The markedly different behaviors of the head and interface/tail groups during phase transitions are explained as the retention of the intermolecular attractive forces between the neighboring polar headgroups of the amphiphiles.
关于两亲性分子不同部分变化的协同性或协同性的知识对于理解自组装聚集体的相转变的分子机制非常重要。一个长期存在且具有挑战性的问题是要了解在相转变过程中，两亲性分子中各个基团/部分的作用。为了解决这个问题，我们选择了溶血磷脂酰胆碱 1-硬脂酰基（SLPC），通过差示扫描量热法、小角 X 射线散射、傅里叶变换红外光谱和二维相关分析来研究其层状相与胶束相之间的转变机制。结果发现，在从层状相到胶束相的转变过程中，界面 C=O 基团和脂质酰基尾部变化明显，前者变化稍早，但脂质头部在水合和构象状态保持不变。这意味着 SLPC 分子的头、界面和尾部变化不同步。此外，结果表明，层状到胶束的转变是由界面基团引发的。还根据非同步现象讨论了从胶束态缓慢形成层状态的动力学的分子机制。在相变过程中头部和界面/尾部基团的明显不同行为可以解释为保留了两亲分子相邻极性头部之间的分子间吸引力。
