摘要
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.
作者
刘君
杜有如
毛诗珍
刘买利
Jun Liu;You-ru Du;Shi-zhen Mao;Mai-li Liu(State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China;National Engineering Laboratory of Wheat & Corn Further Processing, Henan University of Technology, Zhengzhou 450000, China)
基金
supported by the National Natural Science Foundation of China (No.21375145)
关键词
双子表面活性剂
动态NMR
分子交换
交换速率常数
表观活化能
两步交换机制
Gemini surfactants
Dynamic nuclear magnetic resonance
Molecular exchange,Exchange rate constant
Apparent activation energy
Two-step exchange mechanism