Hydrogen Peroxide Decomposition by Pyrite in the Presence of Fe(III)-ligands

The decomposition of hydrogen peroxide (H2O2) by pyrite in the presence of Fe(III)-ligands (sulfosalicylate (SSAL), ethylenediaminetetraacetate (EDTA), and phosphate) has been investigated in aqueous acidic media (pH 1) at 25 °C. It was found that H2O2 decomposition by pyrite was inhibited by the presence of EDTA, SSAL and phosphate. On the other hand, pyrite oxidation by H2O2 does not seem to be affected by the presence of Fe(III)-ligands. The experimental results demonstrate that H2O2 decomposition in the presence of Fe(III)-ligands is catalyzed by pyrite surface (a heterogeneous process). This process is first order with respect to [H2O2]. It is expected that the rate-determining step of the reaction mechanism of H2O2 decomposition in the presence of Fe(III)-ligands is one of the following two reactions: ≡FeHO22+ → ≡Fe2+ + HO2• ≡Fe(OH)(HO2)+ → ≡Fe2+ + HO2• + HO- where ≡ denotes pyrite surface

A highly reactive precursor in the iron sulfide system

Iron sulfur (Fe–S) phases have been implicated in the emergence of life on early Earth due to their catalytic role in the synthesis of prebiotic molecules. Similarly, Fe–S phases are currently of high interest in the development of green catalysts and energy storage. Here we report the synthesis and structure of a nanoparticulate phase (FeSnano) that is a necessary solid-phase precursor to the conventionally assumed initial precipitate in the iron sulfide system, mackinawite. The structure of FeSnano contains tetrahedral iron, which is compensated by monosulfide and polysulfide sulfur species. These together dramatically affect the stability and enhance the reactivity of FeSnano

The use of structural alerts to avoid the toxicity of pharmaceuticals

In order to identify compounds with potential toxicity problems, particular attention is paid to structural alerts, which are high chemical reactivity molecular fragments or fragments that can be transformed via bioactivation by human enzymes into fragments with high chemical reactivity. The concept has been introduced in order to reduce the likelihood that future candidate substances as pharmaceuticals will have undesirable toxic effects. A significant proportion (∼78–86%) of drugs characterized by residual toxicity contain structural alerts; there is also evidence indicating the formation of active metabolites as a causal factor for the toxicity of 62–69% of these molecules. On the other hand, the pharmacological action of certain drugs depends on the formation of reactive metabolites. Detailed assessment of the potential for the formation of active metabolites is recommended to characterize a biologically active compound. Although many prescribed drugs frequently contain structural alerts and form reactive metabolites, the vast majority of these drugs are administered in low daily doses. Avoiding structural alerts has become almost a norm in new drug design. An in-depth review of the biochemical reactivity of these structural alerts for new drug candidates is critical from a safety point of view and is currently being monitored in the discovery of drugs. The chemical strategies applied to structural alerts in molecules to limit the toxicity are: • partial replacement or full replacement of the structural alert; • reduction of electronic density; • introduction of a structural element of metabolic interest (metabolic switching); • multiple approaches.Therefore, chemical intervention strategies to eliminate bioactivation are often interactive processes; their success depends largely on a close working relationship between drug chemists, pharmacologists and researchers in metabolic science. Keywords: Structural alerts, Active metabolites, Toxicit