Nuclear spin relaxation in paramagnetic complexes of S=1:: Electron spin relaxation effects
Nuclear spin relaxation in paramagnetic complexes of S=1:: Electron spin relaxation effects
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DOI：
10.1063/1.479876
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发表时间：
1999-10-01
影响因子：
4.4
通讯作者：
Parigi, G
中科院分区：
文献类型：
--
作者：
Bertini, I;Kowalewski, J;Parigi, G
S=1系统的电子自旋弛豫及其在静态零场分裂（ZH）存在下的场依赖性已经被描述，并被纳入溶液中顺磁性复合物的核自旋-晶格弛豫模型中，该模型是由佛罗伦萨的小组早先提出的。慢重定向是假设和电子自旋能级结构（在任何方向的分子相对于实验室的框架）描述的塞曼相互作用和静态电子自旋。电子自旋弛豫被假定为由描述为畸变（或伪旋转）运动的复合物的变形调制的瞬态电子自旋弛豫引起，并且Redfield理论被用于导出电子自旋弛豫矩阵。在电子自旋弛豫的描述中，我们忽略了涉及通过重定向调制的机制的任何贡献，例如静态自旋和不太重要的塞曼相互作用，因为我们将自己限制在慢旋转极限（即，τ（R）远大于τ（S））。这通常包括蛋白质和大分子的行为。分解（DC）近似，这意味着再取向运动和电子自旋动力学被假定为是不相关的。这不是一个严重的问题，由于慢旋转的条件，因为重新定向和扭曲运动的时间尺度分离。由此产生的核磁弛豫色散（NMRD）的配置文件使用佛罗伦萨模型计算和比较与瑞典的方法，这可以被认为是基本上准确的假设的相互作用和动态过程的给定的一组内的计算。该理论不受Redfield极限的限制，因此可以处理慢运动状态下的电子自旋弛豫，这是没有明确定义任何电子自旋弛豫时间的结果。此外，没有调用DC近似，此外，电子自旋弛豫描述的重取向调制的静态电子自旋和塞曼相互作用，除了扭曲调制的瞬态电子自旋。与佛罗伦萨模型计算的曲线显示出令人满意的协议，这些更精确的计算的瑞典的方法，特别是轴对称的静态张量，提供信心的电子自旋弛豫模型的充分条件下的缓慢旋转。就电子自旋弛豫及其与核自旋系统相互作用的物理意义而言，这种比较也是很有启发性的。(C)1999年美国物理学会。[S0021-9606（99）00532-2]。
Electron spin relaxation for an S=1 system and its field dependence in the presence of static zero-field splitting (ZFS) has been described and incorporated in a model for nuclear spin-lattice relaxation in paramagnetic complexes in solution, proposed earlier by the group in Florence. Slow reorientation is assumed and the electron spin energy level structure (at any orientation of the molecule with respect to the laboratory frame) is described in terms of the Zeeman interaction and of the static ZFS. The electron spin relaxation is assumed to be caused by a transient ZFS modulated by the deformation of the complex described as a distortional (or pseudorotational) motion and the Redfield theory is used to derive the electron spin relaxation matrices. In the description of the electron spin relaxation we neglect any contribution from mechanisms involving modulation by reorientation, such as those of the static ZFS and the less important Zeeman interaction, as we limit ourselves to the slow-rotation limit (i.e., tau(R)much greater than tau(S)). This in general covers the behavior of proteins and macromolecules. The decomposition (DC) approximation is used, which means that the reorientational motion and electron spin dynamics are assumed to be uncorrelated. This is not a serious problem, due to the slow-rotation condition, since reorientational and distortional motions are time-scale separated. The resulting nuclear magnetic relaxation dispersion (NMRD) profiles obtained using the Florence model are calculated and compared with the calculations of the Swedish approach, which can be considered essentially exact within the given set of assumed interactions and dynamic processes. That theory is not restricted by the Redfield limit and can thus handle electron spin relaxation in the slow-motion regime, which is a consequence of not explicitly defining any electron spin relaxation times. Furthermore, the DC approximation is not invoked, and in addition, the electron spin relaxation is described by reorientationally modulated static ZFS and Zeeman interaction besides the distortionally modulated transient ZFS. The curves computed with the Florence model show a satisfactory agreement with these more accurate calculations of the Swedish approach, in particular for the axially symmetric static ZFS tensor, providing confidence in the adequacy of the electron spin relaxation model under the condition of slow rotation. The comparison is also quite instructive as far as the physical meaning of the electron spin relaxation and of its interplay with the nuclear spin system are concerned. (C) 1999 American Institute of Physics. [S0021-9606(99)00532-2].