Livshits V A, Páli T, Marsh D
Centre of Photochemistry, Russian Academy of Sciences, Moscow, 117427, Russian Federation.
J Magn Reson. 1998 Sep;134(1):113-23. doi: 10.1006/jmre.1998.1471.
The dependence on spin-lattice (T1) relaxation of the first-harmonic absorption EPR signal (V'1) detected in phase quadrature with the Zeeman modulation has been investigated both theoretically and experimentally for nitroxide spin labels. Spectral simulations were performed by iterative solution of the Bloch equations that contained explicitly both the modulation and microwave magnetic fields (T. Páli, V. A. Livshits, and D. Marsh, 1996, J. Magn. Reson. B 113, 151-159). It was found that, of the various non-linear EPR displays, the first-harmonic out-of-phase V'1-signal, recorded under conditions of partial saturation of the microwave absorption, is particularly favorable for determining spin-lattice relaxation enhancements because of its superior signal intensity and relative insensitivity to spin-spin (T2) relaxation. By varying the Zeeman modulation frequency it is also possible to tune the optimum sensitivity of the V'1-signal to different ranges of the T1-relaxation time. A Zeeman modulation frequency of 25 kHz appears to be particularly suited to spin label applications. Calibrations are given for the dependence on T1-relaxation time of both the amplitude and the second integral of the V'1-signal recorded under standard conditions. Experiments on different spin labels in solution and in membranes demonstrate the practical usable sensitivity of the V'1-signal, even at modulation frequencies of 25 kHz, and these are used to investigate the dependence on microwave field intensity, in comparison with theoretical predictions. The practicable sensitivity to spin-lattice relaxation enhancements is demonstrated experimentally for a spin-labeled membrane system in the presence of paramagnetic ions. The first-harmonic out-of-phase V'1-signal appears to be the non-linear CW EPR method of choice for determining T1-relaxation enhancements in spin-labeled systems.
对于氮氧自旋标记物，已经从理论和实验两方面研究了与塞曼调制正交相位检测的一次谐波吸收电子顺磁共振信号（V'1）对自旋晶格（T1）弛豫的依赖性。通过对包含调制磁场和微波磁场的布洛赫方程进行迭代求解来进行光谱模拟（T. Páli、V. A. Livshits和D. Marsh，1996年，《磁共振杂志B》113卷，151 - 159页）。研究发现，在各种非线性电子顺磁共振显示中，在微波吸收部分饱和条件下记录的一次谐波异相V'1信号，因其优越的信号强度和对自旋 - 自旋（T2）弛豫相对不敏感，特别有利于确定自旋晶格弛豫增强。通过改变塞曼调制频率，还可以将V'1信号的最佳灵敏度调整到不同的T1弛豫时间范围。25 kHz的塞曼调制频率似乎特别适合自旋标记应用。给出了在标准条件下记录的V'1信号的幅度和二次积分对T1弛豫时间依赖性的校准。对溶液中和膜中的不同自旋标记物进行的实验表明，即使在25 kHz的调制频率下，V'1信号也具有实际可用的灵敏度，并且与理论预测相比，这些实验用于研究对微波场强度的依赖性。在存在顺磁性离子的情况下，通过实验证明了自旋标记膜系统对自旋晶格弛豫增强具有切实可行的灵敏度。一次谐波异相V'1信号似乎是用于确定自旋标记系统中T1弛豫增强的首选非线性连续波电子顺磁共振方法。
