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(NCH3)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τcp有关,说明存在横向弛豫分散现象.当在τcp≤1ms时,T2表观与τ2cp呈线性关系;而当τcp≥4.6ms时,T2表观变得与τcp无关.利用LuzMeiboom两体化学交换模型计算了不同浓度的CTAB溶液中的NCH3质子的本征横向弛豫时间(T2本征)和化学交换速率kex,发现kex与T2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.
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 τ^2cp 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 intrin- sic 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.
出处
《波谱学杂志》
CAS
CSCD
北大核心
2005年第3期235-243,共9页
Chinese Journal of Magnetic Resonance
基金
国家自然科学基金资助项目(10234070
30370419).
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
NMR spectroscopy, transverse relaxation dispersion, surfactant, CTAB, critical micelle concentration
