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首页> 外文期刊>Applied Magnetic Resonance >The Transient EPR Spectra and Spin Dynamics of Coupled Three-spin Systems in Photosynthetic Reaction Centres
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The Transient EPR Spectra and Spin Dynamics of Coupled Three-spin Systems in Photosynthetic Reaction Centres

机译：光合反应中心中三自旋系统的瞬时EPR谱和自旋动力学

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The concept of introducing an additional. stable paramagnetic species into photosynthetic reaction centres to increase the information content of their spin polarized transient EPR spectra is investigated theoretically. The light-induced electron transfer in such systems generates a series of coupled three-spin states consisting of sequential photoinduced radical pairs coupled to the stable spin which acts as an "observer". the spin polarized transient EPR spectra are investigated using the coupled three-spin system P~+I~-Q_A~- in pre-reduced bacterial reaction centres as a specific example which has been studied experimentally. The evolution of the spin system and the spin polarized EPR spectra of P~+I~-Q_A~- and Q_A~- following recombination of the radical pair (P = primary donor, I = primary acceptor, Q_A = quinone acceptor)are calculated numerically by solving the equations of motion for the density matrix. The net polarization of the observer spin is also calculated analytically by perturbation theory for the case of a single, short-lived, charge-separated state. The result bears a close resemblance to the chemically induced nuclear polarization (CIDNP) generated in photolysis reactions in which a nuclear spin plays the role of the observer interacting with the radical pair intermediates, However, because the Zeeman frequencies of the three electron spins involved are usually quite similar, the polarization of the electron observer spin in strong magnetic fields can reflect features of the CIDNP effect in both, high and low magnetic fields. The dependence of the quinone spin polarization on the exchange couplings in the three-spin system is investigated by numerical simulations, and it is shown that the observed emissive polarization pattern is compatible with either sign, positive or negative, for a range of exchange couplings, J_(PI), in the primary pair. The micro-wave frequency and orientation dependence of the spectra are discussed as two of several possible criteria for determining the sign of J_(PI).
机译：引入了额外的概念。从理论上研究了稳定的顺磁性物质进入光合反应中心，以增加其自旋极化瞬态EPR光谱的信息含量。在这样的系统中，光诱导的电子转移产生一系列耦合的三自旋态，该三自旋态由与作为“观察者”的稳定自旋耦合的顺序的光致自由基对组成。以偶合三旋系统P〜+ I〜-Q_A〜-在预​​先还原的细菌反应中心为研究对象，对自旋极化瞬态EPR谱进行了研究。计算了自由基对（P =主要供体，I =主要受体，Q_A =醌受体）重组后自旋系统的演化以及P〜+ I〜-Q_A〜-和Q_A〜-的自旋极化EPR光谱通过求解密度矩阵的运动方程进行数值计算。对于单个的，短暂的，电荷分离的状态，观察者自旋的净极化也通过微扰理论进行解析计算。结果与光解反应中产生的化学感应核极化（CIDNP）极为相似，在核解中，核自旋扮演着观察者与自由基对中间体相互作用的角色，但是，由于所涉及的三个电子自旋的塞曼频率是通常情况下，在强磁场中电子观测器的自旋极化可以反映高低磁场中CIDNP效应的特征。通过数值模拟研究了醌自旋极化对三轴系统中交换耦合的依赖性，结果表明，对于一系列交换耦合，观察到的发射极化图与正负符号兼容， J_（PI），在主要对中。作为确定J_（PI）的符号的几种可能标准中的两个，讨论了频谱的微波频率和方向依赖性。

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