Wu Fu-Gen, Chen Lin, Yu Zhi-Wu
J Phys Chem B. 2009 Jan 29;113(4):869-72. doi: 10.1021/jp810820d.
The metastable crystal usually appears first during crystallization from solution, and it will then transform into the stable form. This metastable crystal-to-stable crystal phase transition process is important in the field of crystal growth and engineering. Crystallization behaviors of amphiphiles such as phospholipids are special as they have preassembled structures prior to crystallization, and the fundamental mechanisms regarding the transformation details of their polymorphic forms at the molecular level are not well understood. In this work, by using Fourier transform infrared spectroscopy combined with the hydrogen/deuterium (H/D) exchange method, we have demonstrated that water plays a critical role in mediating the metastable crystal-to-stable crystal phase transition process of a representative phospholipid, dilauroylphosphoethanolamine (DLPE). The H/D exchange method applied here is a powerful and simple approach to probe if water is involved in the crystal-to-crystal transformation process. The results indicate that water works like a catalyst for the physical process. Furthermore, the conformational changes of the lipid molecules during the crystal-to-crystal transition process have been examined. Understanding the details of the transition from a metastable crystal to a stable crystal will shed light on the crystal growth theory and engineering of the self-assembled amphiphiles in aqueous solutions.
亚稳晶体通常在从溶液中结晶的过程中首先出现，然后会转变为稳定形式。这种亚稳晶体到稳定晶体的相变过程在晶体生长和工程领域中很重要。两亲分子如磷脂的结晶行为很特殊，因为它们在结晶前具有预组装结构，而且关于其多晶型形式在分子水平上转变细节的基本机制尚未得到很好的理解。在这项工作中，通过使用傅里叶变换红外光谱结合氢/氘（H/D）交换方法，我们证明了水在介导代表性磷脂二月桂酰磷脂酰乙醇胺（DLPE）的亚稳晶体到稳定晶体的相变过程中起着关键作用。这里应用的H/D交换方法是一种强大且简单的方法，用于探测水是否参与了晶体到晶体的转变过程。结果表明，水在这个物理过程中起到了催化剂的作用。此外，还研究了晶体到晶体转变过程中脂质分子的构象变化。了解从亚稳晶体到稳定晶体的转变细节将为水溶液中自组装两亲分子的晶体生长理论和工程提供启示。
