Further evidence supporting an inner sphere mechanism in the NO reduction of the copper(II) complex Cu(dmp)22+ (dmp=2,9-dimethyl-1,10-phenanthroline)

Nitrite and Nitric Oxide Interconversion at Mononuclear Copper(II): Insight into the Role of the Red Copper Site in Denitrification

Nitrite (NO2 - ) and nitric oxide (NO) interconversion is crucial for maintaining optimum NO flux in mammalian physiology. Herein we demonstrate that [L2 CuII (nitrite)]+ moieties (in 2 a and 2 b; where, L = Me2 PzPy and Me2 PzQu) with distorted octahedral geometry undergo facile reduction to provide tetrahedral [L2 CuI ]+ (in 3 a and 3 b) and NO in the presence of biologically relevant reductants, such as 4-methoxy-2,6-di-tert-butylphenol (4-MeO-2,6-DTBP, a tyrosine model) and N-benzyl-1,4-dihydronicotinamide (BNAH, a NAD(P)H model). Interestingly, the reaction of excess NO gas with [L2 CuII (MeCN)2 ]2+ (in 1 a) provides a putative {CuNO}10 species, which is effective in mediating the nitrosation of various nucleophiles, such as thiol and amine. Generation of the transient {CuNO}10 species in wet acetonitrile leads to NO2 - as assessed by Griess assay and 14 N/15 N-FTIR analyses. A detailed study reveals that the bidirectional NOx -reactivity, namely, nitrite reductase (NIR) and NO oxidase (NOO), at a common CuII site, is governed by the geometric-preference-driven facile CuII /CuI redox process. Of broader interest, this study not only highlights potential strategies for the design of copper-based catalysts for nitrite reduction, but also strengthens the previous postulates regarding the involvement of red copper proteins in denitrification.

Nitric oxide reactivity of copper(II) complexes of bidentate amine ligands: effect of substitution on ligand nitrosation

Three copper(ii) complexes with bidentate ligands L(1), L(2) and L(3) [L(1), N,N(/)-dimethylethylenediamine; L(2), N,N(/)-diethylethylenediamine and L(3), N,N(/)-diisobutylethylenediamine], respectively, were synthesized as their perchlorate salts. The single crystal structures for all the complexes were determined. The nitric oxide reactivity of the complexes was studied in acetonitrile solvent. The formation of thermally unstable [Cu(II)-NO] intermediate on reaction of the complexes with nitric oxide in acetonitrile solution was observed prior to the reduction of copper(II) centres to copper(I). The reduction was found to result with a simultaneous mono- and di-nitrosation at the secondary amine sites of the ligand. All the nitrosation products were isolated and characterized. The ratio of the yield of mono- and di-nitrosation product was found to be dependent on the N-substitution present in the ligand framework.