Infrared spectroscopy reveals the nonsynchronicity phenomenon in the glassy to fluid micellar transition of DSPE-PEG2000 aqueous dispersions.
Infrared spectroscopy reveals the nonsynchronicity phenomenon in the glassy to fluid micellar transition of DSPE-PEG2000 aqueous dispersions.
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DOI：
10.1021/la101539z
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发表时间：
2010-08
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影响因子：
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通讯作者：
Fulin Wu;Jun-jie Luo;Zhi‐Wu Yu
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文献类型：
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作者：
Fulin Wu;Jun-jie Luo;Zhi‐Wu Yu
关于两亲分子相变机理的一个具有挑战性的问题是寻找两亲分子的各个基团/部分在相变过程中所起的作用。为了解决这个问题，我们选择了一种聚乙二醇接枝磷脂，distearoylphosphatidylethanolamine-N-[methoxy(poly(ethylene-PEG2000，用差示扫描量热法和傅里叶变换红外光谱研究了它的玻璃态到流体胶束的相转变。FTIR结果表明，在玻璃态到流体胶束的转变过程中，脂酰尾发生了明显的构象重排，但在堆积状态下只发生了轻微的改变。对于脂界面区，C=O基团的水合状态变化不大，而脂头基团(NHCO和PO(4)(-))的构象和水化状态保持不变。因此，DSPE-PEG2000分子的头部、界面和尾部区域在转变过程中不同步地变化。对于位于胶束外表面的块状聚乙二醇电晕，受热后水化状态没有明显变化，其行为与水化后的游离聚乙二醇2000分子基本相同。发生相变的自组装两亲性聚集体的不同部分之间的这种不同步变化可能是一个需要广泛认识的普遍现象。
One challenging question regarding the phase transition mechanism of amphiphiles is to seek the roles individual groups/portions of the amphiphilic molecule play during the transformation. To address this question, we selected a poly(ethylene glycol)-grafted phospholipid, distearoylphosphatidylethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG2000), to study its glassy to fluid micellar phase transition by using differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. FTIR results revealed that during the glassy to fluid micellar transition, the lipid acyl tails have evident conformational rearrangements but undergo only slight modifications in the packing state. For the lipid interface region, small changes in the hydration state of C=O groups were observed, whereas for the lipid headgroups (NHCO and PO(4)(-)), their conformation and hydration states remain unchanged. Thus, the head, the interface, and the tail regions of DSPE-PEG2000 molecules change nonsynchronously during the transition. As to the bulky PEG corona residing at the outer micellar surface, no evident hydration state change was observed upon heating, and its behavior is almost the same as that of the hydrated free PEG2000 molecules. Such a nonsynchronous change in different parts of the self-assembled amphiphilic aggregates undergoing phase transition could be a common phenomenon that needs to be widely recognized.