Max-Planck Institute for Multidisciplinary Sciences, 37070 Göttingen, Germany(1).
J Magn Reson. 2023 May;350:107414. doi: 10.1016/j.jmr.2023.107414. Epub 2023 Mar 7.
Saturation-recovery (SR)-EPR can determine electron spin-lattice relaxation rates in liquids over a wide range of effective viscosity, making it especially useful for biophysical and biomedical applications. Here, I develop exact solutions for the SR-EPR and SR-ELDOR rate constants of N-nitroxyl spin labels as a function of rotational correlation time and spectrometer operating frequency. Explicit mechanisms for electron spin-lattice relaxation are: rotational modulation of the N-hyperfine and electron-Zeeman anisotropies (specifically including cross terms), spin-rotation interaction, and residual frequency-independent vibrational contributions from Raman processes and local modes. Cross relaxation from mutual electron and nuclear spin flips, and direct nitrogen nuclear spin-lattice relaxation, also must be included. Both the latter are further contributions from rotational modulation of the electron-nuclear dipolar interaction (END). All the conventional liquid-state mechanisms are defined fully by the spin-Hamiltonian parameters; only the vibrational contributions contain fitting parameters. This analysis gives a firm basis for interpreting SR (and inversion recovery) results in terms of additional, less standard mechanisms.
饱和恢复（SR）-EPR 可以在广泛的有效粘度范围内确定液体中的电子自旋晶格弛豫率，使其特别适用于生物物理和生物医学应用。在这里，我开发了作为旋转相关时间和光谱仪工作频率函数的 N-氮氧自由基自旋标记物的 SR-EPR 和 SR-ELDOR 速率常数的精确解。电子自旋晶格弛豫的明确机制包括：N-超精细和电子-Zeeman 各向异性的旋转调制（特别是包括交叉项）、自旋-旋转相互作用以及来自 Raman 过程和局部模式的剩余频率独立振动贡献。来自电子和核自旋翻转的交叉弛豫以及直接的氮核自旋晶格弛豫也必须包括在内。后两者都是电子-核偶极相互作用（END）的旋转调制的进一步贡献。所有常规的液态机制都完全由自旋哈密顿参数定义；只有振动贡献包含拟合参数。该分析为根据附加的、不太标准的机制解释 SR（和反转恢复）结果提供了坚实的基础。
