高分辨率 NMR 研究 T1 磁弛豫弥散。II. 自旋-自旋耦合对多自旋体系中纵向自旋弛豫弥散的影响。
High resolution NMR study of T1 magnetic relaxation dispersion. II. Influence of spin-spin couplings on the longitudinal spin relaxation dispersion in multispin systems.
机构信息
Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
出版信息
J Chem Phys. 2010 Nov 21;133(19):194502. doi: 10.1063/1.3495988.
Effects of scalar spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of coupled multispin systems were analyzed. Taking spin systems of increasing complexity we demonstrated pronounced influence of the intramolecular spin-spin couplings on the NMRD of protons. First, at low magnetic fields where there is strong coupling of spins the apparent relaxation times of the coupled spins become equal. Second, there are new features, which appear at the positions of the nuclear spin level anticrossings. Finally, in coupled spin systems there can be a coherent contribution to the relaxation kinetics present at low magnetic fields. All these peculiarities caused by spin-spin interactions are superimposed on the features in NMRD, which are conditioned by changes of the motional regime. Neglecting the effects of couplings may lead to misinterpretation of the NMRD curves and significant errors in determining the correlation times of molecular motion. Experimental results presented are in good agreement with theoretical calculations.
分析了标量自旋-自旋相互作用对耦合多自旋体系核磁共振弛豫弥散(NMRD)的影响。通过分析越来越复杂的自旋体系,我们证明了分子内自旋-自旋耦合对质子 NMRD 的显著影响。首先,在磁场较弱时,自旋的强耦合使得耦合自旋的表观弛豫时间变得相等。其次,在核自旋能级交叉点的位置出现了新的特征。最后,在耦合自旋体系中,在低磁场下可能存在与弛豫动力学相干的贡献。所有这些由自旋-自旋相互作用引起的特殊现象都叠加在由运动状态变化引起的 NMRD 特征上。忽略耦合的影响可能导致对 NMRD 曲线的误解,并在确定分子运动的相关时间时产生显著误差。实验结果与理论计算吻合良好。