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_a3³⁺ -H₂ O-Cu_B²⁺ 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 H₂ O molecule between the Fe_a3³⁺ and Cu_B²⁺ sites in different DNCs, whether or not this central H₂ O molecule has H-bonding interaction with another H₂ O molecule, the different spin states having similar energies for the Fe_a3³⁺ sites, and whether the Fe_a3³⁺ and Cu_B²⁺ sites are ferromagnetically or antiferromagnetically spin-coupled.