Comparison of Experimental and Broken Symmetry Density Functional Theory Calculated Electron Paramagnetic Resonance Parameters for the Manganese Catalase Active Site in the Superoxidized Mn^III/Mn^IV State

Abstract

Broken symmetry density functional theory has been used to calculate g-tensor, Mn,N, and O hyperfine couplings for active site models of superoxidized Mn/Mn manganese catalase both in its native and azide-inhibited form. While a good agreement is found between the calculated and experimental g-tensor and Mn hyperfine couplings for all models, the active site geometry and Mn ion oxidation state can only be readily distinguished based on a comparison of the calculated and experimentalN azide and O HFCs. This comparison shows that only models containing a Jahn-Teller distorted 5-coordinate (Mn) site and a 6-coordinate (Mn) site can satisfactorily reproduce the experimental N andO hyperfine couplings.

Mechanism of Radical Initiation and Transfer in Class Id Ribonucleotide Reductase Based on Density Functional Theory

“…It is indicated that the Mn ions in 2 a are antiferromagnetically coupled, whereas the Mn ions in 2 b and 2 c are ferromagnetically coupled possibly due to the presence of the hydroxyl group. The Heisenberg exchange coupling constant J = −70.1 cm –1 in 2 a is in good agreement with the BS-DFT results of MnCat ( J = −71 cm –1 ) with a comparable Mn–Mn distance . Rose et al experimentally found that the Mn ions in complexes 2 is antiferromagnetically coupled .…”

“…be seen that, after the dimanganese cofactor is oxidized to the superoxidized state (Mn III -(μ-oxo) 2 -Mn IV ), the Mn1 III −Mn2 IV distance is shortened from 3.69 to 2.72 Å. The Mn1 III −Mn2 IV , Mn1 III −O1, Mn1 III −O2, Mn2 IV −O1, and Mn2 IV −O2 distances are in good agreement with the results by BS-DFT and the experimental data of the manganese catalase (MnCat) 62,63. The Mn1 III site is five-coordinated, and the Mn2 IV site is sixcoordinated.…”

“…The Heisenberg exchange coupling constant J = −70.1 cm −1 in 2 a is in good agreement with the BS-DFT results of MnCat (J = −71 cm −1 ) with a comparable Mn−Mn distance. 62 Rose et al experimentally found that the Mn ions in complexes 2 is antiferromagnetically coupled. 17 It is suggested that, among the three model systems, only the model system 2 a can reflect the structure of complex 2.…”

“…However, it can be seen that the calculated g-values are in good agreement with the data of the oxobridged dinuclear manganese complexes in the superoxidized state. 25,27,60,62 3.1.1.4. 55 Mn Hyperfine Couplings.…”

“…The Mn1 III −Mn2 IV , Mn1 III −O1, Mn1 III −O2, Mn2 IV −O1, and Mn2 IV −O2 distances are in good agreement with the results by BS-DFT and the experimental data of the manganese catalase (MnCat). 62,63 The Mn1 III site is five-coordinated, and the Mn2 IV site is sixcoordinated. The binding patterns of Glu67 and Glu97 with the Mn ions are changed from bi-dentate to mono-dentate in the model system 2 a , and the binding pattern of Glu195 turns from tri-dentate to bi-dentate (Figures 1b, 2, and 3a).…”