Dependence of Saturation-Transfer EPR Intensities on Spin–Lattice Relaxation

T. Páli , V.A. Livshits , D. Marsh
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引用次数: 19

Abstract

The intensities of saturation-transfer EPR (ST-EPR) spectra from nitroxyl spin labels have proved a sensitive means for studying slow exchange processes (both Heisenberg spin exchange and physical/chemical exchange) and weak interactions with paramagnetic ions, via the dependence on the effective spin–lattice relaxation rate (D. Marsh,Appl. Magn. Reson.3, 53, 1992). The dependences of the second-harmonic EPR absorption intensities detected in phase quadrature with the field modulation (V2) on the microwaveH1field, and on the effective relaxation times, were studied both theoretically and experimentally. Power-saturation curves and normalized integrated intensities (IST) of theV2spectra were determined as a function of the concentration of a spin-labeled phospholipid in lipid membranes and of the concentration of paramagnetic Ni2+ions in the aqueous phase as a means of varying the effective relaxation times. The results were correlated with progressive-saturation measurements of the double-integrated intensities of the conventional EPR spectra. Intensities of theV2spectra were calculated from the Bloch equations incorporating the modulation and microwave fields (K. Halbach,Helv. Phys. Acta27, 259, 1954), and the results were fitted to the experimental data. The ST-EPR intensities depend approximately linearly on the effectiveT1, but with a nonzero intercept. On the basis of the theoretical calculations and experimental correlations, relations betweenISTandT1are suggested that may improve precision in the application of this alternative form of ST-EPR spectroscopy to biological systems.

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饱和转移EPR强度与自旋晶格弛豫的关系
来自硝基自旋标签的饱和转移EPR (ST-EPR)光谱强度已被证明是研究缓慢交换过程(包括海森堡自旋交换和物理/化学交换)和与顺磁离子弱相互作用的敏感手段,通过依赖于有效自旋-晶格弛缓速率(D. Marsh, appll。粉剂。共振。3,53,1992)。本文从理论和实验两方面研究了用场调制(V ' 2)相正交检测到的二次谐波EPR吸收强度与微波h1field和有效弛豫时间的关系。它们的v ' 2光谱的功率饱和曲线和归一化积分强度(IST)被确定为脂膜中自旋标记磷脂的浓度和水相中顺磁性Ni2+离子的浓度的函数,作为改变有效松弛时间的手段。结果与常规EPR光谱双积分强度的渐进式饱和测量结果相关。它们的v ' 2光谱强度是根据结合调制和微波场的布洛赫方程计算出来的(K. Halbach,Helv。理论物理。Acta27, 259, 1954),结果与实验数据拟合。ST-EPR强度近似线性依赖于有效t1,但具有非零截距。在理论计算和实验关联的基础上,提出了istandt1之间的关系,可以提高这种替代形式的ST-EPR光谱在生物系统中的应用精度。
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