Gan Z
Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
J Magn Reson. 2000 Mar;143(1):136-43. doi: 10.1006/jmre.1999.1971.
Polarization inversion spin exchange at the magic angle (PISEMA) [J. Magn. Reson. A 109, 270 (1994)] is an important experiment in NMR structural characterization of membrane proteins in oriented lipid bilayers. This paper presents a theoretical and experimental study of the spin dynamics in PISEMA to investigate the line-narrowing mechanism. The study focuses on the effect of neighboring protons on the spin exchange of a strongly coupled spin pair. The spin exchange is solved analytically for simple spin systems and is numerically simulated for many-spin systems. The results show that the dipolar couplings from the neighboring protons of a strongly coupled spin pair perturb the spin exchange only in the second order, therefore it has little contribution to the linewidth of PISEMA spectra in comparison to the separated-local-field spectra. The effects from proton resonance offset and the mismatch of the Hartmann-Hahn condition are also discussed along with experimental results using model single-crystal samples.
魔角极化反转自旋交换（PISEMA）[《磁共振杂志A》109, 270 (1994)]是在定向脂质双层中对膜蛋白进行核磁共振结构表征的一项重要实验。本文对PISEMA中的自旋动力学进行了理论和实验研究，以探究谱线变窄机制。该研究聚焦于相邻质子对强耦合自旋对自旋交换的影响。对于简单自旋系统，自旋交换通过解析求解，对于多自旋系统则进行数值模拟。结果表明，强耦合自旋对相邻质子的偶极耦合仅在二阶上扰动自旋交换，因此与分离局部场谱相比，它对PISEMA谱线宽度的贡献很小。还结合使用模型单晶样品的实验结果，讨论了质子共振偏移和哈特曼 - 哈恩条件失配的影响。
