波谱学杂志 ›› 2005, Vol. 22 ›› Issue (3): 235-243.

• 研究论文 •    下一篇

表面活性剂CTAB水溶液中的T2弛豫分散研究

  

  1. 1.波谱与原子分子物理国家重点实验室(中国科学院 武汉物理与数学研究所),湖北 武汉 430071;  2. 中国科学院 研究生院,北京 100049
  • 收稿日期:2005-05-25 修回日期:2005-06-02 出版日期:2005-09-05 发布日期:2005-09-05
  • 基金资助:

    国家自然科学基金资助项目(10234070, 30370419).

Millisecond-Scale Molecular Dynamics in Aqueous Solution of Surfactant CTAB Studied by NMR Transverse Relaxation Dispersion

  1. 1.State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics (Wuhan  Institute of Physics and Mathematics, Chinese Academy of Sciences), Wuhan 430071, China; 2.Graduate School of the Chinese Academy Sciences, Beijing 100049, China
  • Received:2005-05-25 Revised:2005-06-02 Online:2005-09-05 Published:2005-09-05
  • Supported by:

    国家自然科学基金资助项目(10234070, 30370419).

摘要:

用CPMG脉冲序列测定了表面活性剂十六烷基三甲基溴化铵(CTAB)分子中的氮甲基(N-CH3)质子的横向弛豫时间(T2表观),并发现测得的T2表观\}与序列中的重聚脉冲间隔时间的一半τ cp有关,说明存在横向弛豫分散现象. 当在τcp≤1 ms时,T2表观与τ2cp}呈线性关系;而当τcp≥4.6 ms时,T2表观变得与τcp无关. 利用Luz-Meiboom两体化学交换模型计算了不同浓度的CTAB溶液中的N-CH3质子的本征横向弛豫时间(T2本征)和化学交换速率kex,发现kexT2本征和自扩散系数D一样,在临界胶束浓度(CMC)附近发生突变. 这个突变反映了CTAB分子在从单体到胶束的转变过程中其动力学特性发生了改变. 

关键词: 核磁共振波谱, 弛豫分散, 表面活性剂, CTAB, 临界胶束浓度

Abstract:

Apparent proton transverse relaxation times of the hydrophilic group (N-CH3) were measured in aqueous solution of surfactant CTAB with different concentrations using the CPMG pulse sequence, and found to be dependent on the interpulse delay between the refocusing pulses (τcp). This indicates that diffusion and/or chemical exchange contribute to the transverse relaxation process of the N-CH3 protons. It was observed that the apparent transverse relaxation time has a linear relationship with τ2cp when τcp≤1 ms, but becomes independent on τcp when τcp≥4.6 ms. Using the Luz-Meiboom two-site chemical exchange model, the chemical exchange rates of the N-CH3 protons at different concentrations were calculated and found to change from 1.57 ms-1 to 1.15 ms-1 at the critical micelle concentration (CMC), behaving similarly as the intrinsic transverse relaxation time and selfdiffusion coefficient D. Change of the chemical exchange rate at CMC is probably a reflection of alteration of the exchange dynamics of adjacent CTAB molecules when micelles are formed.

Key words: NMR spectroscopy, transverse relaxation dispersion, surfactant, CTAB, critical micelle concentration

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