Département de Chimie, UMR 7203 CNRS, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France.
J Chem Phys. 2010 Jul 21;133(3):034506. doi: 10.1063/1.3445777.
Relaxation processes induced by the antisymmetric part of the chemical shift anisotropy tensor (henceforth called anti-CSA) are usually neglected in NMR relaxation studies. It is shown here that anti-CSA components contribute to longitudinal relaxation rates of the indole (15)N nucleus in tryptophan in solution at different magnetic fields and temperatures. To determine the parameters of several models for rotational diffusion and internal dynamics, we measured the longitudinal relaxation rates R(1)=1/T(1) of (15)N, the (15)N-(1)H dipole-dipole (DD) cross-relaxation rates (Overhauser effects), and the cross-correlated CSA/DD relaxation rates involving the second-rank symmetric part of the CSA tensor of (15)N at four magnetic fields B(0)=9.4, 14.1, 18.8, and 22.3 T (400, 600, 800, and 950 MHz for protons) over a temperature range of 270<T<310 K. A good agreement between experimental and theoretical rates can only be obtained if the CSA tensor is assumed to comprise first-rank antisymmetric (anti-CSA) components. The magnitude of the hitherto neglected antisymmetric components is of the order of 10% of the CSA.
在 NMR 弛豫研究中，通常会忽略化学位移各向异性张量的反对称部分（简称反 CSA）引起的弛豫过程。本文表明，反 CSA 分量会影响溶液中色氨酸中吲哚（15）N 核在不同磁场和温度下的纵向弛豫率。为了确定几个用于旋转扩散和内部分子动力学的模型的参数，我们测量了（15）N 的纵向弛豫率 R(1)=1/T(1)、（15）N-（1）H 偶极-偶极（DD）交叉弛豫率（Overhauser 效应）以及涉及 CSA 张量二阶对称部分的交叉相关 CSA/DD 弛豫率在四个磁场 B(0)=9.4、14.1、18.8 和 22.3 T（质子的 400、600、800 和 950 MHz）下，温度范围为 270<T<310 K。只有假设 CSA 张量包含一阶反对称（反 CSA）分量，才能得到实验和理论速率之间的良好一致性。迄今为止被忽略的反对称分量的大小约为 CSA 的 10%。
