Kulik L V, Lubitz W, Messinger J
Max Planck Institute for Bioinorganic Chemistry, 45470 Mülheim/Ruhr, Germany.
Biochemistry. 2005 Jul 5;44(26):9368-74. doi: 10.1021/bi050411y.
The temperature dependence of the electron spin-lattice relaxation time T1 was measured for the S0 state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)2 bipy4]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for Mn(II)Mn(III)(mu-OH)(mu-piv)2(Me3 tacn)22 between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the S0 state of photosystem II, the T1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S2 state of photosystem II indicates that the Orbach relaxation process is dominant for the S0 state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.
利用反转恢复法，通过脉冲电子顺磁共振测量了光系统II中析氧复合物（OEC）的S0态以及两种双核锰模型配合物的电子自旋-晶格弛豫时间T1的温度依赖性。对于[Mn(III)Mn(IV)(μ-O)2 bipy4]ClO4，在低于50 K的温度下，拉曼弛豫过程占主导。相比之下，在4.3至9 K之间，发现Mn(II)Mn(III)(μ-OH)(μ-piv)2(Me3 tacn)22存在奥尔巴赫型弛豫。对于后一种配合物，确定了基态与第一激发电子态之间的能量间隔为24.7 - 28.0 cm(-1)。在光系统II的S0态中，T1弛豫时间在4.3 - 6.5 K范围内测量。与两种模型配合物以及光系统II的S2态的弛豫数据（速率和指数前因子）进行比较表明，对于S0态，奥尔巴赫弛豫过程占主导，并且其第一激发态比基态高21.7±0.4 cm(-1)。结合光系统II中OEC的结构对结果进行了讨论。
