title: Protonation state of the Cu4S2CuZsite in nitrous oxide reductase: redox dependence and insight into reactivity.
abstract: Spectroscopic and computational methods have been used to determine the protonation state of the edge sulfur ligand in the Cu4S2CuZform 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 CuZindicate that the unpaired spin in this site is evenly delocalized over CuI, CuII, and CuIV. 1-hole CuZis shown to have a μ2-thiolate edge ligand from the observation of S-H bending modes in the resonance Raman spectrum at 450 and 492 cm-1that have significant deuterium isotope shifts (-137 cm-1) and are not perturbed up to pH 10. 2-hole CuZis 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 CuZsites are correlated to these spectroscopic features to determine that 2-hole CuZhas a μ2-sulfide edge ligand at neutral pH. The slow two electron (+1 proton) reduction of N2O by 1-hole CuZis discussed and the possibility of a reaction between 2-hole CuZand O2is considered.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Esther M
authors.initials: EM
authors.lastname: Johnston
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Dell'Acqua
authors.affiliation: UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Sofia R
authors.initials: SR
authors.lastname: Pauleta
authors.affiliation: UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Moura
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon