CAJ | 학술논문

已知两位置交换分子运动速率对于静态13C NMR谱的影响是由一简单代数关系决定,它已成为分析固体中分子运动的常规方法.慢速的魔角旋转可以保留边带,所产生的边带型原则上也可用来分析分子运动,只是缺乏象静态谱那样的简单的关系,以至于在实际应用上是不可行的.本文给出作者所发现的存在分子运动时魔角旋转核磁共振自由诱导衰减信号的解析表达式的理论推导,提供分析固体分子运动的理论谱计算公式.我们选择二甲砜(dimethyl sulfone)作为模型化合物,记录其不同温度下13C NMR谱,又计算了两个甲基做两位置交换运动的理论谱.理论谱与实验谱定性一致.定量上,边带强度存在一些差别,但边带宽度符合很好.通过理论谱与实验谱的比较,得到交换速率与温度的对应关系.虽然本文限于化学位移各向异性相互作用两位置交换问题,但容易推广到偶极作用多位置交换问题.
이지량위치교환분자운동속솔대우정태13C NMR보적영향시유일간단대수관계결정,타이성위분석고체중분자운동적상규방법.만속적마각선전가이보류변대,소산생적변대형원칙상야가용래분석분자운동,지시결핍상정태보나양적간단적관계,이지우재실제응용상시불가행적.본문급출작자소발현적존재분자운동시마각선전핵자공진자유유도쇠감신호적해석표체식적이론추도,제공분석고체분자운동적이론보계산공식.아문선택이갑풍(dimethyl sulfone)작위모형화합물,기록기불동온도하13C NMR보,우계산료량개갑기주량위치교환운동적이론보.이론보여실험보정성일치.정량상,변대강도존재일사차별,단변대관도부합흔호.통과이론보여실험보적비교,득도교환속솔여온도적대응관계.수연본문한우화학위이각향이성상호작용량위치교환문제,단용역추엄도우겁작용다위치교환문제.
An exact solution of a magic-angle-spinning free-induction-decay under two-site exchange has been derived. The expression has been confirmed by comparing the calculated spinning sideband patterns for powdered crystalline dimethyl sulfone at different exchange rates with experimentally measured CP/MAS 13C NMR spectra at various temperatures. The information of the mode and the site exchange rate constants of molecular motion can be provided by spectral line fitting between calculated and experimental spectra. The numerical calculations with this algorithm show that the exchange effect results in a slight narrowing of the centerband and a slight broadening of sidebands compared to the equal linewidths without exchange.