季铵盐型双子表面活性剂C14-s-C14·2Br的聚集行为

用1H NMR弛豫、2D NOESY研究了双子表面活性剂14-s-14胶束在重水溶液中的聚集行为. 1H NMR自旋-晶格、自旋-自旋弛豫实验表明, 联结基团质子及其邻近的亚甲基质子的运动受到严重限制, 表明这些质子形成胶束疏水核的壳层；而远离极性头的疏水质子的运动则相对自由, 说明其位于胶束的内部. 14-s-14系列(s=2, 3, 4)的弛豫实验结果还表明, 联结基团越短, 分子的碳氢链在疏水核中的排列越紧密. 与14-4-14的对应单链表面活性剂TTAB相比, 它们的分子运动更受限制. 14-4-14的2D NOESY 谱给出了与16-4-16类似的交叉峰信息, 这表明14-4-14同16-4-16一样, 形成了表面不平滑的球形胶束. 因此, 烷烃链的长短对胶束中分子的排列方式没有影响.

Aggregation Behavior of Quaternary Ammonium Dimeric Surfactant C14-s-C14·2Br Micelles

The aggregation behavior of gemini surfactants 14-s-14 micelles in heavy water solutions was studied using 1H NMR relaxation and two-dimensional nuclear Overhauser enhancement spectroscopy(2D NOESY).Spin-lattice and spin-spin relaxation measurements of the protons showed that the motion of the spacer protons and a part of the methylene protons next to the polar head group was seriously restricted.Therefore,these protons should be involved in the formation of the surface layer of the hydrophobic micellar core.The hydrophobic protons that were away from the polar head group were situated internal in the micellar core and moved relatively freely.Relaxation measurements of the 14-s-14 series(s=2,3,4)also showed that the molecules were more tightly packed as the length of the spacer decreased.Their motion was relatively more restricted than those of TTAB,the monomeric homologue of 14-4-14.2D NOESY spectrum of 14-4-14 exhibited the same pattern as that of 16-4-16.This showed that the micelles of 14-4-14 were spherical,the surface of which exhibited a saw-toothed form,similar to that of 16-4-16.Consequently,the length of the alkyl chain did not have any effect on the relative arrangement of molecules in the micelles.