DFT Calculations for Mössbauer Properties on Dinuclear Center Models of the Resting Oxidized Cytochrome c Oxidase.

Mössbauer isomer shift and quadrupole splitting properties have been calculated using the OLYP-D3(BJ) density functional method on previously obtained (W.-G. Han Du, et al., Inorg Chem. 2020, 59, 8906-8915) geometry optimized Fe a3 3+ -H 2 O-Cu B 2+ dinuclear center (DNC) clusters of the resting oxidized (O state) "as-isolated" cytochrome c oxidase (CcO). The calculated results are highly consistent with the available experimental observations. The calculations have also shown that the structural heterogeneities of the O state DNCs implicated by the Mössbauer experiments are likely consequences of various factors, particularly the variable positions of the central H 2 O molecule between the Fe a3 3+ and Cu B 2+ sites in different DNCs, whether or not this central H 2 O molecule has H-bonding interaction with another H 2 O molecule, the different spin states having similar energies for the Fe a3 3+ sites, and whether the Fe a3 3+ and Cu B 2+ sites are ferromagnetically or antiferromagnetically spin-coupled.