Dynamics of Dinitrosyl Iron Complex (DNIC) Formation with Low Molecular Weight Thiols.

Dinitrosyl iron complexes (DNICs) are ubiquitous in mammalian cells and tissues producing nitric oxide (NO) and have been argued to play key physiological and pathological roles. Nonetheless, the mechanism and dynamics of DNIC formation in aqueous media remain only partially understood. Here, we report a stopped-flow kinetics and density functional theory (DFT) investigation of the reaction of NO with ferrous ions and the low molecular weight thiols glutathione (GSH) and cysteine (CysSH) as well as the peptides WCGPC and WCGPY to produce DNICs in pH 7.4 aqueous media. With each thiol, a two-stage reaction pattern is observed. The first stage involves several rapidly established pre-equilibria leading to a ferrous intermediate concluded to have the composition FeII(NO)(RS)2(H2O)x (C). In the second stage, C undergoes rate-limiting, unimolecular autoreduction to give thiyl radical (RS•) plus the mononitrosyl Fe(I) complex FeI(NO)(RS)(H2O)x following the reactivity order of CysSH > WCGPC > WCGPY > GSH. Time course simulations using the experimentally determined kinetics parameters demonstrate that, at a NO flux characteristic of inflammation, DNICs will be rapidly formed from intracellular levels of ferrous iron and thiols. Furthermore, the proposed mechanism offers a novel pathway for S-nitroso thiol (RSNO) formation in a biological environment

Reactions of platinum(O) complexes with carbazole

Reaction of carbazole with zerovalent [Pt(L)(n)] gives oxidative insertion into the N-H rather than into a C-N bon

Mononuclear copper(I) complexes of O-t-butyl-1,1-dithiooxalate and of O-t-butyl-1-perthio-1-thiooxalate

Described are the syntheses and structures of a phosphonium salt of the anionic ligand O-t-butyl-1,1-dithiooxalate, [PPh 3Bz][i-dto tBu] ([PPh 3Bz][1]), and of two Cu(I) complexes of this anion, Cu(PPh 3) 2(\u3b7 2-i-dto tBu) (2) and Cu(dmp)(PPh 3)(\u3b7 1-i-dto tBu) (3, dmp = 2,9-dimethyl-1,10-phenanthroline). In addition, it was found that the reaction of CuBr 2 with i-dto tBu - gives a O-t-butyl-1-perthio-1-thiooxalato complex of copper(I), [BzPh 3P][Cu(Br)(S-i-dto tBu)] ([BzPh 3P][4]), where [S-i-dto tBu] - is a disulfide-containing anionic ligand. The electronic structure and absorption spectrum of this species were investigated by time dependent DFT methods

Dinitrosyl iron complexes with cysteine. Kinetics studies of the formation and reactions of DNICs in aqueous solution.

Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO4, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe2(μ-CysS)2(NO)4, a Roussin's red salt ester (Cys-RSE), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe(NO)2(CysS)2(-) (Cys-DNIC) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both Cys-RSE and Cys-DNIC are formed via a common intermediate Fe(NO)(CysS)2(-). Cys-DNIC and Cys-RSE interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the Cys-RSE formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant kNO = 6.9 × 10(7) M(-1) s(-1). In contrast, photolysis of the mononuclear-DNIC species Cys-DNIC formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS(•) radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes

Correction to Dinuclear PhotoCORMs: Dioxygen-Assisted Carbon Monoxide Uncaging from Long-Wavelength-Absorbing Metal-Metal-Bonded Carbonyl Complexes.

Page 6102. A clerical error led to the submission of the wrong CIF file for compound 4, (CO)5ReMn(CO)3(L), where L = 1,10-phenanthroline-4-carboxaldehyde. The correct CIF file is attached here. All of the structural data for 4 in the published article and Supporting Information were based on the correct CIF file

Dinuclear PhotoCORMs: Dioxygen-Assisted Carbon Monoxide Uncaging from Long-Wavelength-Absorbing Metal-Metal-Bonded Carbonyl Complexes.

We describe a new strategy for triggering the photochemical release of caged carbon monoxide (CO) in aerobic media using long-wavelength visible and near-infrared (NIR) light. The dinuclear rhenium-manganese carbonyl complexes (CO)5ReMn(CO)3(L), where L = phenanthroline (1), bipyridine (2), biquinoline (3), or phenanthrolinecarboxaldehyde (4), each show a strong metal-metal-bond-to-ligand (σMM → πL*) charge-transfer absorption band at longer wavelengths. Photolysis with deep-red (1 and 2) or NIR (3 and 4) light leads to homolytic cleavage of the Re-Mn bonds to give mononuclear metal radicals. In the absence of trapping agents, these radicals primarily recombine to reform dinuclear complexes. In oxygenated media, however, the radicals react with dioxygen to form species much more labile toward CO release via secondary thermal and/or photochemical reactions. Conjugation of 4, with an amine-terminated poly(ethylene glycol) oligomer, gives a water-soluble derivative with similar photochemistry. In this context, we discuss the potential applications of these dinuclear complexes as visible/NIR-light-photoactivated CO-releasing moieties (photoCORMs)

Catalytic disassembly of an organosolv lignin via hydrogen transfer from supercritical methanol

A novel approach to disassembling biomass-derived lignin into processible units is described. This transformation is achieved in supercritical methanol, using a Cu-doped porous metal oxide as the catalyst, at a relatively mild temperature (300 °C). Hydrogen transfer from methanol to an organosolv lignin results in the complete hydrogenolysis of phenyl ether bonds, coupled with the hydrogenation of aromatic rings. The product is a complex mixture composed principally of monomeric substituted cyclohexyl derivatives with greatly reduced oxygen content and negligible aromatics. Notably, no char formation was observed. We also describe operational indices based on the 1H NMR spectra that facilitate holistic evaluation of the product distribution in this and other biomass transformations.

Dinitrosyl Iron Complexes with Cysteine. Kinetics Studies of the Formation and Reactions of DNICs in Aqueous Solution

Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO₄, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe₂(μ-CysS)₂(NO)₄, a Roussin’s red salt ester (<b>Cys-RSE</b>), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe­(NO)₂(CysS)₂^– (<b>Cys-DNIC</b>) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both <b>Cys-RSE</b> and <b>Cys-DNIC</b> are formed via a common intermediate Fe­(NO)­(CysS)₂^–. <b>Cys-DNIC</b> and <b>Cys-RSE</b> interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the <b>Cys-RSE</b> formed from Fe­(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant <i>k</i>_NO = 6.9 × 10⁷ M^–1 s^–1. In contrast, photolysis of the mononuclear-DNIC species <b>Cys-DNIC</b> formed from Fe­(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS^• radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes