Oxidation of Sodium Hypophosphite by Oxygen in Alcoholic Solutions of Ferrum (III)

<p>Hypophosphites are widely used as reducers in the metal protection coating, as reagents in the synthesis of various organophosphorus compounds, in analytical chemistry, and in many other fields. NaH₂PO₂ difficultly reacts with many oxidizers without catalysts despite of the significant reduction potential. The kinetics and the mechanism of hypophosphite oxidation in aqueous acid solution of the metal and nonmetal salts are studied in detail. The reactivity of hypophosphite in the organic solvents was not almost studied. In this work the basic possibility of synthesis dialkylphosphites from cheap, accessible and harmless NaH₂PO₂ and alcohols is shown. Sodium hypophosphite is oxidized by oxygen in alcoholic solutions of FeCl₃ at 50-80 °С to dialkylphosphites. Kinetic and mechanism of the reaction are investigated by methods of volumetry, redox-potentiometry, GC, IR-, UV-, EPR-, Mössbauer- and NMR ³¹Р-spectroscopy and X-ray powder diffraction analysis, optimum conditions are found, kinetic and activation parameters of the reaction are calculated. It is shown, that the process follows redox-mechanism and consists of two key stages: reduction of Fe (III) by hypophosphite with formation of dialkylphosphite and reoxidation of Fe (II) by oxygen. The coordination mechanism of reduction reaction of Fe (III) by hypophosphite is proposed. According to this mechanism the dialkylphosphite forms through innersphere redox-decomposition of intermediate alcoxyhypophosphite complex of Fe (III). The coordination mechanism of the process is confirmed by low values of Е^≠ and negative activation entropies ∆S^≠. The availability in an inner sphere of Fe (III) bromide, low-molecular alcohols, water, characterized by high acidity, increases the reaction rate of oxidative alcoxylation of hypophosphite and promotes the further transformation of dialkylphosphite to di- and trialkylphosphate.</p>

Electron transfer in human cytochrome P450 reductase

Cytochrome P450 reductase (CPR) is a diflavin enzyme responsible for electron donation to mammalian cytochrome P450 enzymes in the endoplasmic reticulum. Dissection of the enzyme into functional domains and studies by site-directed mutagenesis have enabled detailed characterization of the mechanism of electron transfer using stopped-flow and equilibrium-perturbation methods, and redox potentiometry. These studies and the mechanism of electron transfer in CPR are reported herein.

Electron Transfer and Binding of thec-Type Cytochrome TorC to the TrimethylamineN-Oxide Reductase inEscherichia coli

Reduction of trimethylamineN-oxide (E′0(TMAO/TMA)= +130 mV) inEscherichia coliis carried out by the Tor system, an electron transfer chain encoded by thetorCADoperon and made up of the periplasmic terminal reductase TorA and the membrane-anchored pentahemicc-type cytochrome TorC. Although the role of TorA in the reduction of trimethylamineN-oxide (TMAO) has been clearly established, no direct evidence for TorC involvement has been presented. TorC belongs to the NirT/NapCc-type cytochrome family based on homologies of its N-terminal tetrahemic domain (TorCN) to the cytochromes of this family, but TorC contains a C-terminal extension (TorCC) with an additional heme-binding site. In this study, we show that both domains are required for the anaerobic bacterial growth with TMAO. The intact TorC protein and its two domains, TorCNand TorCC, were produced independently and purified for a biochemical characterization. The reduced form of TorC exhibited visible absorption maxima at 552, 523, and 417 nm. Mediated redox potentiometry of the heme centers of the purified components identified two negative midpoint potentials (−177 and −98 mV) localized in the tetrahemic TorCNand one positive midpoint potential (+120 mV) in the monohemic TorCC. In agreement with these values, thein vitroreconstitution of electron transfer between TorC, TorCN, or TorCCand TorA showed that only TorC and TorCCwere capable of electron transfer to TorA. Surprisingly, interaction studies revealed that only TorC and TorCNstrongly bind TorA. Therefore, TorCCdirectly transfers electrons to TorA, whereas TorCN, which probably receives electrons from the menaquinone pool, is involved in both the electron transfer to TorCCand the binding to TorA.