Inorganic species in OEC

Inorganic species are at the centre of the OEC. Moreover, inorganic model chemistry has played an important and synergistic role in studies of the OEC. 

Manganese appears to be unique in catalyzing 02 evolution in all aerobic pho-totrophs. No other metal ion has been found to date that can replace it. Manganese was probably selected via evolution for this function because of its ability to exist in multiple oxidation states (Mn2+, Mn3+, Mn4+, Mn5+) and to form strong bonds with oxygen ligands [29], 

Ca2+ is an essential ion in the photoassembly reaction in all PSII OECs examined to date. The experimental data indicated that Ca2+ is involved in accelerating the final step in the S-state catalytic cycle, involving the 0-0 bond formation reaction [29], 

To build the Mn4Ca cluster from its free metal ions, it is necessary to deprotonate four or more aqua ligands attached to the initially bound Mn2+ [29]. 

Bicarbonate ion is important not only as a substrate for carbon fixation in the Calvin cycle but also for its role in PSII ET efficiency and photoassembly of the OEC cluster in PSII [29], 

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