Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing, P R China.
J Phys Chem B. 2011 Jul 7;115(26):8559-68. doi: 10.1021/jp200733y. Epub 2011 Jun 13.
We have a long-standing interest to explore the answer of the question: Which part of the amphiphilic molecule triggers the phase transition of the self-assembled aggregates consisting of these amphiphiles? This is an important issue regarding the phase transition kinetics of amphiphiles. To this end, we studied the phase transition behaviors of dipalmitoylphosphatidylcholine (DPPC) by differential scanning calorimetry, synchrotron X-ray scattering, Fourier transform infrared spectroscopy, and image analysis. We found that different parts (head, interface, and tail) of DPPC molecules all exhibit nonsynchronous changes during the sub-, pre-, and main transitions. Particular efforts have been devoted to studying the isothermal subgel (L(c')) formation process. It was found that only the lipid interface and tail regions change, and only when the rearrangement of the lipid hydrocarbon chain packing reaches a certain extent can the interfacial C═O groups be induced to undergo vibrational environment changes. The result means that the hydrocarbon tail is the part that triggers the gel (L(β')) to L(c') phase transition. The present work deepens our understanding on the phase transition mechanisms of DPPC and may shed light on those of other phospholipids and other types of amphiphiles.
两亲分子的哪一部分触发了由这些两亲分子组成的自组装聚集体的相转变？这是关于两亲物相转变动力学的一个重要问题。为此，我们通过差示扫描量热法、同步辐射 X 射线散射、傅里叶变换红外光谱和图像分析研究了二棕榈酰磷脂酰胆碱 (DPPC) 的相转变行为。我们发现，DPPC 分子的不同部分（头、界面和尾）在亚相、预相和主相转变过程中均表现出不同步的变化。我们特别致力于研究等温亚凝胶 (L(c')) 形成过程。结果发现，只有脂质界面和尾部发生变化，只有当脂质烃链堆积的重排达到一定程度时，才能诱导界面 C═O 基团发生振动环境变化。这意味着烃尾是触发凝胶 (L(β')) 到 L(c') 相转变的部分。本工作加深了我们对 DPPC 相转变机制的理解，可能为其他磷脂和其他类型两亲物的相转变机制提供启示。
