Characterizing the photosystem II (PSII) sample, continuous wave electron paramagnetic resonance (CW-EPR) simulations of the S2 ML signal at X-band frequencies was our focus. This can help increase our understanding of how the manganese (Mn) atoms in the catalytic site of the PSII magnetically interact using ML signals. It can also be used to further the understanding of possible water-splitting mechanisms in the oxygen-evolving complex (OEC). The question that remains is how much does each manganese (Mn) ion contribute to the ML signal through its hyperfine interactions in the OEC? Currently, there are two proposals for the average oxidation states of the Mn ions, denoted the ‘high’ oxidation paradigm (HOP) and the ‘low’ oxidation paradigm (LOP). Majority of PSII researchers favour the HOP. Various experiments have been conducted to investigate the two alternative oxidation states, including EPR (Jin et al. in Phys Chem Chem Phys 16(17):7799–7812, https://doi.org/10.1039/c3cp55189j, 2014; Baituti in Hyperfine Interact 238(1), https://doi.org/10.1007/s10751-017-1440-8, 2017; Ioannidis et al. in Biochemistry, https://doi.org/10.1021/bi060520s, 2006). The S2 ML EPR signal simulation using the 55Mn hyperfine coupling constants, with one very large, one medium, and two small hyperfine values, fits the experimental data. The Mn1 has a large hyperfine coupling, which agrees well with earlier data by Jin et al. [19]. Three large fractional anisotropy observed on three Mn centers (Mn1,3,4), suggests the presence of three MnIII ions, and Mn2 center is likely to be MnIV ion, hence favouring the LOP (MnIII MnIV MnIII MnIII).

中文翻译：

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锰离子的两种替代氧化态分配：S2 CW-EPR 多线 (ML) 信号模拟揭示了什么？

表征光系统 II (PSII) 样品，X 波段频率下 S2 ML 信号的连续波电子顺磁共振 (CW-EPR) 模拟是我们的重点。这有助于增加我们对 PSII 催化位点中的锰 (Mn) 原子如何使用 ML 信号进行磁性相互作用的理解。它还可以用于进一步了解析氧复合物 (OEC) 中可能的水分解机制。剩下的问题是每个锰 (Mn) 离子通过其在 OEC 中的超精细相互作用对 ML 信号有多大贡献？目前，对于锰离子的平均氧化态有两种建议，分别表示“高”氧化范式 (HOP) 和“低”氧化范式 (LOP)。大多数 PSII 研究人员支持 HOP。已经进行了各种实验来研究两种替代氧化态，包括 EPR（Jin 等人在 Phys Chem Chem Phys 16(17):7799–7812, https://doi.org/10.1039/c3cp55189j, 2014; Baituti in Hyperfine Interact 238(1)，https://doi.org/10.1007/s10751-017-1440-8，2017；Ioannidis 等，生物化学，https://doi.org/10.1021/bi060520s，2006）。S2 ML EPR 信号模拟使用 55Mn 超精细耦合常数，具有一个非常大、一个中等和两个小的超精细值，符合实验数据。Mn1 具有大的超精细耦合，这与 Jin 等人的早期数据非常吻合。[19]。在三个 Mn 中心 (Mn1,3,4) 上观察到的三个大的分数各向异性表明存在三个 MnIII 离子，而 Mn2 中心可能是 MnIV 离子，因此有利于 LOP（MnIII MnIV MnIII MnIII）。