A probability distribution of rate constants contained within an exponential-like saturation recovery (SR) electron paramagnetic resonance signal can be constructed using stretched exponential function fitting parameters. Previously (Stein et al. Appl. Magn. Reson. 2019.), application of this method was limited to the case where only one relaxation process, namely spin-lattice relaxations due to the rotational diffusion of the spin labels in the intact eye-lens membranes, contributed to an exponential-like SR signal. These conditions were achieved for thoroughly deoxygenated samples. Here, the case is described where the second relaxation process, namely Heisenberg exchange between the spin label and molecular oxygen that occurs during bimolecular collisions, contributes to the decay of SR signals. We have further developed the theory for application of stretched exponential function to analyze SR signals involving these two processes. This new approach allows separation of stretched exponential parameters, namely characteristic stretched rates and heterogeneity parameters for both processes. Knowing these parameters allowed us to separately construct the probability distributions of spin-lattice relaxation rates determined by the rotational diffusion of spin labels and the distribution of relaxations induced strictly by collisions with molecular oxygen. The later distribution is determined by the distribution of oxygen diffusion concentration products within the membrane, which forms a sensitive new way to describe membrane fluidity and heterogeneity. This method was validated in silico and by fitting SR signals from spin-labeled intact nuclear fiber cell plasma membranes extracted from porcine eye lenses equilibrated with different fractions of air.

中文翻译：

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饱和恢复EPR在晶状体纤维细胞质膜中的输氧参数

可以使用扩展的指数函数拟合参数来构造包含在指数状饱和恢复（SR）电子顺磁共振信号中的速率常数的概率分布。以前（Stein等人，Appl。Magn。Reson。2019.），这种方法的应用仅限于只有一个弛豫过程的情况，即由于自旋标记在完整的眼睛中旋转扩散而引起的自旋晶格弛豫。晶状体膜，形成类似指数的SR信号。对于完全脱氧的样品，达到了这些条件。这里，描述了第二弛豫过程，即在双分子碰撞期间发生的自旋标记和分子氧之间的海森堡交换，导致SR信号衰减的情况。我们进一步发展了应用扩展指数函数来分析涉及这两个过程的SR信号的理论。这种新方法允许分离拉伸指数参数，即两个过程的特征拉伸速率和异质性参数。知道了这些参数后，我们就可以分别构造由自旋标记的旋转扩散确定的自旋晶格弛豫速率的概率分布以及严格地由与分子氧的碰撞引起的弛豫分布。后面的分布由膜中氧扩散浓度产物的分布决定，这形成了描述膜流动性和异质性的灵敏新方法。