Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University , Beijing 100084, P. R. China.
Langmuir. 2011 Mar 15;27(6):2349-56. doi: 10.1021/la1049474. Epub 2011 Feb 17.
We have characterized the structure and phase behavior of dioctadecyldimethylammonium bromide (DODAB) aqueous dispersions by using conventional and high-sensitivity nano-differential scanning calorimetry, microscopy, cryogenic transmission electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, and electric conductivity measurements. Special attention has been paid to the formation and transformation of the subgel phase. An almost pure subgel can be obtained in the dilute region (below 7.5 mM), while an almost pure coagel phase can be obtained in the concentrated region (above 6.7 wt %). We found that unilamellar vesicles were spontaneously formed in the subgel phase of a 5 mM DODAB dispersion. Infrared spectroscopic data reveal that the only significant change during the gel to subgel phase transition is the ordering in the lipid alkyl chain packing. That is, the head and tail parts of the DODAB molecules change nonsynchronously upon the gel to subgel transition, and the subgel phase is triggered only by the change of the lipid tail part. We propose that the morphological change (from curled membranes in the gel phase to unilamellar vesicles with faceted surface in the subgel phase) is coupled to the change of alkyl chain packing state during the gel to subgel transition. Finally, a full picture of the phase transition sequences for the dilute and concentrated DODAB dispersions is given.
我们通过常规和高灵敏度纳米差示扫描量热法、显微镜、低温传输电子显微镜、衰减全反射傅里叶变换红外光谱和电导率测量来研究了双十八烷基二甲基溴化铵（DODAB）水溶液的结构和相行为。特别关注了亚凝胶相的形成和转变。在稀溶液区（低于 7.5 mM）几乎可以得到纯亚凝胶相，而在浓溶液区（高于 6.7 wt %）几乎可以得到纯凝聚相。我们发现，在 5 mM DODAB 分散体的亚凝胶相中，自发形成了单层囊泡。红外光谱数据表明，在凝胶到亚凝胶相转变过程中，唯一显著的变化是脂质烷基链堆积的有序化。也就是说，在凝胶到亚凝胶转变过程中，DODAB 分子的头和尾部分是非同步变化的，只有脂质尾部的变化才能引发亚凝胶相的形成。我们提出，形态变化（从凝胶相中卷曲的膜到亚凝胶相中具有多面表面的单层囊泡）与凝胶到亚凝胶转变过程中烷基链堆积状态的变化相关。最后，给出了稀溶液和浓溶液中 DODAB 分散体的完整相变序列图。
