Poluektov O G, Paschenko S V, Utschig L M
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA.
Phys Chem Chem Phys. 2009 Aug 21;11(31):6750-6. doi: 10.1039/b906521k. Epub 2009 Jun 23.
Spin-dynamics of the spin-correlated radical pair (SCRP) P(700)(+)A(1A)(-) in the photosystem I (PSI) reaction center protein have been investigated with high-frequency (HF), time-resolved EPR spectroscopy. The superior spectral resolution of HF EPR enables spin-dynamics for both the donor and acceptor radicals in the pair to be monitored independently. Decay constants of each spin were measured as a function of temperature and compared to data obtained at X-band EPR. Relaxation times, T(1), and decay rates, k(S), are the same at both X- and D-band magnetic fields. The spin-dynamics within the radical pair were determined from theoretical simulation of experimental time-resolved HF EPR spectra. At low temperatures, T < 60 K, the decay of the SCRP from the singlet state, k(S), is the predominant process, while at high temperatures, T > 130 K, the T(1) relaxation is much faster than k(S). The recombination rate k(S) was observed to decrease as the temperature is increased. These EPR spectral results are in agreement with previously reported optical measurements of P(700)(+)A(1)(-) radical pair recombination.
利用高频（HF）时间分辨电子顺磁共振光谱研究了光系统I（PSI）反应中心蛋白中自旋相关自由基对（SCRP）P(700)(+)A(1A)(-)的自旋动力学。HF EPR卓越的光谱分辨率能够独立监测该自由基对中供体和受体自由基的自旋动力学。测量了每个自旋的衰减常数随温度的变化，并与在X波段EPR获得的数据进行比较。在X波段和D波段磁场下，弛豫时间T(1)和衰减率k(S)相同。自由基对中的自旋动力学是通过对实验时间分辨HF EPR光谱的理论模拟确定的。在低温下，T < 60 K，SCRP从单重态的衰减k(S)是主要过程，而在高温下，T > 130 K，T(1)弛豫比k(S)快得多。观察到复合率k(S)随温度升高而降低。这些EPR光谱结果与先前报道的P(700)(+)A(1)(-)自由基对复合的光学测量结果一致。
