Explanation of spin-lattice relaxation rates of spin labels obtained with multifrequency saturation recovery EPR
Explanation of spin-lattice relaxation rates of spin labels obtained with multifrequency saturation recovery EPR
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DOI：
10.1021/jp044671l
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发表时间：
2005-05-12
影响因子：
2.9
通讯作者：
Robinson, BH
中科院分区：
文献类型：
--
作者：
Mailer, C;Nielsen, RD;Robinson, BH
电子顺磁共振（EPR）脉冲饱和恢复（PSR）的自旋晶格弛豫速率的测量已被嵌入脂质双层中的含氮氧自由基的脂肪酸由Hyde和同事。已经收集了一些自旋标记的脂肪酸在几个微波光谱仪频率（从2到35 GHz）的数据。我们比较这些自旋晶格弛豫率预测的Redfield理论结合几种机制。在低光谱仪频率下的主要弛豫机制是电子-核偶极（END）过程，自旋旋转（SR）、化学位移各向异性（CSA）和广义自旋扩散（GSD）机制都有贡献。光谱仪频率的广泛使用清楚地表明，动力学不能充分建模的刚体各向同性旋转运动。刚体各向异性旋转运动的动力学足以解释实验误差内的实验弛豫率。可以考虑更精细的运动模型，我们的分析并不排除它们。然而，结果表明，仅在两个适当选择的光谱仪频率的测量是足够的，以区分各向异性从各向同性运动。结果表明，各向异性驱动的自旋-晶格弛豫的主要机制是很好地理解的液体制度。
Electron paramagnetic resonance (EPR) pulsed saturation recovery (pSR) measurements of spin-lattice relaxation rates have been made on nitroxide-containing fatty acids embedded in lipid bilayers by Hyde and co-workers. The data have been collected for a number of spin-labeled fatty acids at several microwave spectrometer frequencies (from 2 to 35 GHz). We compare these spin-lattice relaxation rates to those predicted by the Redfield theory incorporating several mechanisms. The dominant relaxation mechanism at low spectrometer frequencies is the electron-nuclear dipolar (END) process, with spin rotation (SR), chemical shift anisotropy (CSA), and a generalized spin diffusion (GSD) mechanism all contributing. The use of a wide range of spectrometer frequencies makes clear that the dynamics cannot be modeled adequately by rigid-body isotropic rotational motion. The dynamics of rigid-body anisotropic rotational motion is sufficient to explain the experimental relaxation rates within the experimental error. More refined models of the motion could have been considered, and our analysis does not rule them out. However, the results demonstrate that measurements at only two suitably chosen spectrometer frequencies are sufficient to distinguish anisotropic from isotropic motion. The results presented demonstrate that the principal mechanisms responsible for anisotropically driven spin-lattice relaxation are well understood in the liquids regime.