Protonation state of the Cu4S2 CuZ site in nitrous oxide reductase: redox dependence and insight into reactivity

Citation:
Johnston, E. M., S. Dell'acqua, S. R. Pauleta, I. Moura, and E. I. Solomon. "Protonation state of the Cu4S2 CuZ site in nitrous oxide reductase: redox dependence and insight into reactivity." Chem Sci. 6 (2015): 5670-5679.

Abstract:

Spectroscopic and computational methods have been used to determine the protonation state of the edge sulfur ligand in the Cu4S2 CuZ form of the active site of nitrous oxide reductase (N2OR) in its 3CuICuII (1-hole) and 2CuI2CuII (2-hole) redox states. The EPR, absorption, and MCD spectra of 1-hole CuZ indicate that the unpaired spin in this site is evenly delocalized over CuI, CuII, and CuIV. 1-hole CuZ is shown to have a mu2-thiolate edge ligand from the observation of S-H bending modes in the resonance Raman spectrum at 450 and 492 cm-1 that have significant deuterium isotope shifts (-137 cm-1) and are not perturbed up to pH 10. 2-hole CuZ is characterized with absorption and resonance Raman spectroscopies as having two Cu-S stretching vibrations that profile differently. DFT models of the 1-hole and 2-hole CuZ sites are correlated to these spectroscopic features to determine that 2-hole CuZ has a mu2-sulfide edge ligand at neutral pH. The slow two electron (+1 proton) reduction of N2O by 1-hole CuZ is discussed and the possibility of a reaction between 2-hole CuZ and O2 is considered.

Notes:

Johnston, Esther MDell'Acqua, SimonePauleta, Sofia RMoura, IsabelSolomon, Edward IR01 DK031450/DK/NIDDK NIH HHS/United StatesEnglandChemical scienceChem Sci. 2015 Oct 1;6(10):5670-5679. Epub 2015 Jul 3.

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