Marie M. Melzer

A copper(II) thiolate from reductive cleavage of an S-nitrosothiol.

S-Nitrosothiols RSNO represent circulating reservoirs of nitric oxide activity in the plasma and play intricate roles in protein function control in health and disease. While nitric oxide has been shown to reductively nitrosylate copper(II) centers to form copper(I) complexes and ENO species (E = R(2)N, RO), well-characterized examples of the reverse reaction are rare. Employing the copper(I) β-diketiminate [Me(2)NN]Cu, we illustrate a clear example in which an RS-NO bond is cleaved to release NO(gas) with formation of a discrete copper(II) thiolate. The addition of Ph(3)CSNO to [Me(2)NN]Cu generates the three-coordinate copper(II) thiolate [Me(2)NN]CuSCPh(3), which is unstable toward free NO.

Reversible RS–NO bond cleavage and formation at copper(I) thiolates

Two coordinate copper(I) thiolates IPrCu-SR undergo rapid, reversible transnitrosation with S-nitrosothiols RSNOs without catalyzing the loss of NO(gas) from these biological carriers of NO.

Reductive Cleavage of O-, S-, and N-Organonitroso Compounds by Nickel(I) β-Diketiminates

An electron-rich nickel(I) beta-diketiminate cleaves the E-NO bond of O-, S-, and N-organonitroso species to give the nickel nitrosyl [Me 3NN]NiNO along with dimeric nickel(II) alkoxide or thiolate complexes {[Me 3NN]Ni} 2(mu-E) 2 or the mononuclear nickel(II) amide [Me 3NN]NiNPh 2. This diamagnetic three-coordinate amide exhibits temperature-dependent NMR spectra due to a low-lying triplet state.

A motif for reversible nitric oxide interactions in metalloenzymes

Nitric oxide (NO) participates in numerous biological processes, such as signalling in the respiratory system and vasodilation in the cardiovascular system. Many metal-mediated processes involve direct reaction of NO to form a metal-nitrosyl (M-NO), as occurs at the Fe(2+) centres of soluble guanylate cyclase or cytochrome c oxidase. However, some copper electron-transfer proteins that bear a type 1 Cu site (His2Cu-Cys) reversibly bind NO by an unknown motif. Here, we use model complexes of type 1 Cu sites based on tris(pyrazolyl)borate copper thiolates [Cu(II)]-SR to unravel the factors involved in NO reactivity. Addition of NO provides the fully characterized S-nitrosothiol adduct [Cu(I)](κ(1)-N(O)SR), which reversibly loses NO on purging with an inert gas. Computational analysis outlines a low-barrier pathway for the capture and release of NO. These findings suggest a new motif for reversible binding of NO at bioinorganic metal centres that can interconvert NO and RSNO molecular signals at copper sites.