Photosystem II (PSII) contains Ca²⁺, which is essential to the oxygen-evolving activity of the catalytic Mn₄CaO₅ complex. Replacement of Ca²⁺ with other redox-inactive metals results in a loss/decrease of oxygen-evolving activity. To investigate the role of Ca²⁺ in this catalytic reaction, we investigate artificial Mn₃[M]O₂ clusters redox-inactive metals [M] ([M] = Mg²⁺, Ca²⁺, Zn²⁺, Sr²⁺, and Y³⁺), which were synthesized by Tsui et al. (Nat Chem 5:293, 2013). The experimentally measured redox potentials (E_m) of these clusters are best described by the energy of their highest occupied molecular orbitals. Quantum chemical calculations showed that the valence of metals predominantly affects E_m(Mn^III/IV), whereas the ionic radius of metals affects E_m(Mn^III/IV) only slightly.

光系统II (PSII) 含有Ca ²⁺ ，这对于催化Mn ₄ CaO ₅络合物的放氧活性至关重要。用其他氧化还原惰性金属替代Ca ²⁺会导致放氧活性的损失/降低。为了研究 Ca ²⁺在此催化反应中的作用，我们研究了人工 Mn ₃ [M]O ₂簇氧化还原惰性金属 [M] ([M] = Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Sr ^{2 +}和 Y ³⁺ )，由 Tsui 等人合成。 (《自然化学》5:293, 2013)。通过实验测量的这些团簇的氧化还原电位（ E _m ）可以通过其最高占据分子轨道的能量来最好地描述。量子化学计算表明，金属的价态主要影响E _m (Mn ^III/IV )，而金属的离子半径对E _m (Mn ^III/IV )影响很小。