NMR方法监测季铵型双子表面活性剂的胶束交换动力学（英文）

Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by Nuclear Magnetic Resonance

本文应用DNMR的方法测量了双子表面活性剂12—s—12和14—s—14（s=2，3，4）单体在溶液和胶束间的分子交换动力学参数．根据DNMR理论的简化公式，变温条件下测量了表面活性剂分子的逸出速率常数（k^-），根据阿伦尼乌斯公式拟台得到了逸出活化能（Ea^-）．结果显示14—s—14和12—s—12的逸出速率常数分别在10^1和10^3s^-1数量级，逸出活化能分别为54．04-73．64kJ／mol和33．42-47．09kJ／mol．随着联结基团长度的增大，14—s—14和12—s—12的逸出速率常数增大，逸出活化能减小．结合荧光探针实验测量微极性的结果，揭示了双子表面活性剂分子从胶束中逸出时经历了构象变化，支持了双子表面活性剂的两步分子交换机制．

The dynamic NMR （DNMR） method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14 （s 2, 3 and 4）. The escape rate constant, k^- , was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, Ea^- , was obtained based on the Arrhenius equation through temperature variation experiments. Results show that the orders of magnitude of k^- for 14-s-14 and 12-s-12 are respectively 10 and 103 s-1, Ea^- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/rnol. Furthermore, k increases and Ea^- decreases with the spacer length growing. In combination with the rnicro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the rnicelles. The two-step molecular exchange mechanism for Gemini surfactants was therefore supported.