An effective procedure for selective reduction of O2 to H2O2 exploring the use of hydrogen sulfide, an obnoxious industrial pollutant as reductant is reported herein. The reduction of [Ru(III)(EDTA)pz](-) (EDTA(4-) = ethylenediaminetetraacetate; pz = pyrazine) by hydrogen sulfide resulting in the formation of a red [Ru(II)(EDTA)pz](2-) complex (λmax = 462 nm) has been studied spectrophotometrically and kinetically using both rapid scan and stopped-flow techniques. The time course of the reaction was followed as a function of [HS(-)]i, pH (5.5-8.5), and temperature. Alkali metal ions were found to have a positive influence (K(+) > Na(+) > Li(+)) on the reaction rate. Kinetic data and activation parameters are interpreted in terms of a mechanism (admittedly speculative) involving outer-sphere electron transfer between the reaction partners. Reaction of the red [Ru(II)(EDTA)pz](2-) complex with molecular oxygen regenerates the [Ru(III)(EDTA)pz](-) species in the reacting system along with the formation of H2O2, a partially reduced product of dioxygen (O2) reduction. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented.

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Reported is the first example of a ruthenium(III)-complex, Ru(III)(EDTA) (EDTA(4-) = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [Ru(III)(EDTA)(NO(+))](0). However, at pH below 5.0, the coordinated nitrite ion in the [Ru(III)(EDTA)(NO2)](2-) complex undergoes proton-assisted decomposition, resulting in the formation of a [Ru(III)(EDTA)(NO(+))](0) species.

A series of copper (II) (1 and 3) and cobalt (II/III) (2, 4 and 5) complexes comprising different imino-phenolate ligands DCH, DTH and DBH 2 (where DCH = 2,4-dichloro-6-((mesitylimino)methyl)phenol, DTH = 2,4-di-tert-butyl-6-((mesitylimino)methyl) phenol and DBH 2 = 2,4-dibromo-6-((mesitylimino) methyl)phenol) have been prepared with excellent yield and high purity. By utilizing different spectroscopic tools such as UV-visible, electrospray ionization (ESI)-mass, Fourier-transform infrared (FTIR) spectrometry and elemental analysis, the prepared complexes (1-5) were thoroughly characterized. The molecular structure of the synthesized complexes was ascertained by using single-crystal X-ray diffraction studies (SCXRDs). The experiment reveals that Complexes 1-5 bind to calf thymus DNA (CT-DNA) through non-intercalative way with good interacting abilities. However, 1-5 are excellent quenchers of the fluorescence intensity of bovine serum albumin (BSA) following the static pathway. Additionally, they had shown remarkable cytotoxic potential against MCF-7 (mammary gland adenocarcinoma) and A549 (lung adenocarcinoma) cell lines. The IC 50 values associated with these complexes were much lower than the conventional drug cisplatin. Apoptosis-induced cell death was confirmed from the DNA fragmentation studies and Hoechst 33342 staining. The 2 0 ,7 0-dichlorofluorescein diacetate (DCFDA) assay indicates that the complex mediated reactive oxygen species (ROS) generation is accountable for governing the apoptosis mechanism via oxidative cell distress. Apart from these studies, by carrying out density functional theory (DFT) method, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap calculations and optimized structures of the synthesized complexes were accomplished.