Department of Chemical and Forensic Science, Faculty of Science, Botswana International University of Science and Technology, Private Bag 16, Palapye, Botswana.
Molecules. 2021 May 4;26(9):2699. doi: 10.3390/molecules26092699.
The S state produces two basic electron paramagnetic resonance signal types due to the manganese cluster in oxygen-evolving complex, which are influenced by the solvents, and cryoprotectant added to the photosystem II samples. It is presumed that a single manganese center oxidation occurs on S → S state transition. The S state has readily visible multiline and g4.1 electron paramagnetic resonance signals and hence it has been the most studied of all the Kok cycle intermediates due to the ease of experimental preparation and stability. The S state was studied using electron paramagnetic resonance spectroscopy at X-band frequencies. The aim of this study was to determine the spin states of the g4.1 signal. The multiline signal was observed to arise from a ground state spin ½ centre while the g4.1 signal generated at ≈140 K NIR illumination was proposed to arise from a spin 52 center with rhombic distortion. The 'ground' state g4.1 signal was generated solely or by conversion from the multiline. The data analysis methods used involved numerical simulations of the experimental spectra on relevant models of the oxygen-evolving complex cluster. A strong focus in this paper was on the 'ground' state g4.1 signal, whether it is a rhombic 52 spin state signal or an axial 32 spin state signal. The data supported an X-band CW-EPR-generated g4.1 signal as originating from a near rhombic spin 5/2 of the S state of the PSII manganese cluster.
S 态由于放氧复合体中的锰簇产生两种基本的电子顺磁共振信号类型，这两种信号类型受溶剂和添加到光系统 II 样品中的冷冻保护剂的影响。据推测，S → S 态跃迁时单个锰中心发生氧化。S 态具有明显的多线和 g4.1 电子顺磁共振信号，因此它是所有 Kok 循环中间态中研究最多的一种，因为它易于实验制备和稳定。使用 X 波段频率的电子顺磁共振光谱研究了 S 态。本研究的目的是确定 g4.1 信号的自旋态。多线信号是由基态自旋为 1/2 的中心产生的，而在 ≈140 K NIR 光照下产生的 g4.1 信号被认为是由具有菱形畸变的自旋为 52 的中心产生的。“基态”g4.1 信号仅由多线信号产生或由其转换产生。所使用的数据分析方法涉及对放氧复合体簇相关模型的实验光谱进行数值模拟。本文的一个重点是“基态”g4.1 信号，它是菱形 52 自旋态信号还是轴向 32 自旋态信号。数据支持 X 波段 CW-EPR 产生的 g4.1 信号源自 PSII 锰簇 S 态的近菱形自旋 5/2。
