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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Energetics of Primary Charge Separation in Bacterial Photosynthetic Reaction Center Mutants: Triplet Decay in Large Magnetic Fields
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Energetics of Primary Charge Separation in Bacterial Photosynthetic Reaction Center Mutants: Triplet Decay in Large Magnetic Fields

机译：细菌光合反应中心突变体中主电荷分离的能量学：大磁场中的三重态衰减。

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摘要

The triplet state of aromatic molecules forms and decays by intersystem crossing, as originally demonstrated by Kasha and Lewis. By contrast, the triplet state of the primary electron donor, ~3P, in photosynthetic reaction centers is formed exclusively by spin- and magnetic-field-dependent charge recombination of the initially formed radical ion pair. ~3P decays by intersystem crossing at low temperatures; however, at higher temperatures, it can also decay by activated re-formation of the radical ion pair from which it was born, followed by a spin- and magnetic-field-dependent pathway that leads ultimately to the ground state. The discovery of this activated decay pathway leads to an approach for obtaining information on the relative energies of the radical pair and ~3P state (Chidsey et al. Proc. Natl. Acad. Sci. U.S.A. 1985, 82, 6850-6854); with knowledge of the absolute energy of ~3P from its phosphorescence, the energy of the initial charge separation reaction can be obtained. In this paper, we present the first data on the temperature and magnetic field dependence of the formation and decay of ~3P for Rb. sphaeroides reaction center mutants in a background that contains no carotenoid. The mutations have been studied in other contexts and were designed to perturb the redox potential of the primary electron donor or acceptor. The measured trends are in the same direction as expected from chemical intuition; however, the quantitative changes are typically smaller than expected. Possible reasons for this finding are discussed. Improved values are obtained for the enthalpy and free energy change associated with primary charge separation in wild-type reaction centers.
机译：最初由Kasha和Lewis证明，芳香分子的三重态通过系统间交叉形成和衰减。相比之下，光合作用中心的一次电子供体的3t态〜3P仅通过最初形成的自由基离子对的自旋和磁场相关的电荷重组而形成。在低温下，系统间交叉导致〜3P衰减;然而，在更高的温度下，它也可能因其所生的自由基离子对的活化重塑而衰减，随后是自旋和磁场相关的途径最终导致基态。该活化衰变途径的发现导致一种获得关于自由基对和〜3P状态的相对能量的信息的方法（Chidsey等人，Proc.Natl.Acad.Sci.U.S.A.1985，82，6850-6854）;通过从其磷光了解〜3P的绝对能量，可以获得初始电荷分离反应的能量。在本文中，我们提供了有关Rb〜3P形成和衰减的温度和磁场依赖性的第一个数据。 sphaeroides反应中心突变体的背景中不含类胡萝卜素。已经在其他情况下对突变进行了研究，并将其设计为干扰初级电子供体或受体的氧化还原电势。测得的趋势与化学直觉所预期的方向相同;但是，数量变化通常小于预期。讨论了此发现的可能原因。获得了与野生型反应中心中的一次电荷分离相关的焓和自由能变化的改进值。

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