Catalysts of water oxidation for artificial photosynthesis, formed from the binuclear oxysulfate ruthenium(IV) complex K 4 [Ru 2 (SO 4 ) 2 (μ-SO 4 ) 2 (μ-O) 2 ] · 2H 2 O, are studied via chromatography-mass spectrometry. It is shown that these new catalysts do not contain organic ligands and are more stable and active than the familiar blue dimer [(bpy) 2 Ru(OH) 2 ] 2 O 4+ and its analogues. It is found that adamantane-like tetra-nuclear and octanuclear ruthenium clusters are active catalysts that oxidize water to oxygen and oxozone O 4 , respectively.

The kinetics and mechanism of water oxidation with cerium(IV) compounds catalyzed by a tetranuclear ruthenium complex containing two polyoxotungstate ligands are reported. Four water molecules are oxidized via an eight-electron process to form two oxygen molecules.

Изучены кинетика и механизм окисления воды соединениями Се(IV), катализированного четырехъядерным комплексом рутения с двумя полиоксовольфраматными лигандами. Показано, что четыре молекулы воды окисляются в восьмиэлектронном процессе с образованием двух молекул кислорода.

The mechanisms of the many-electron oxidation of water by a chemical model of the manganese oxidase cofactor in photosynthesis photosystem II (manganese(IV) clusters) and nitrogen reduction in chemical models of nitrogenase cofactor (vanadium(II) and molybdenum(III) clusters) were considered. The hypothesis was suggested according to which polynuclear enzyme cofactors and their functional chemical models performed two important functions, catalyzed noncomplementary processes and effected many-substrate concerted reactions with decreased activation energies.

It was shown earlier that the hydrolysis of the (CuATP2−)2 dimeric complex to CuADP− and inorganic phosphate P i was an irreversible reaction. The main intermediate hydrolysis product, the formation of which should be taken into account at comparatively early hydrolysis stages, was the IntK pentacovalent intermediate. It was formed in parallel with hydrolysis to CuADP− and P i through the common intermediate product (CuATP2−)2OH− — DOH−. We studied the influence of the addition of various concentrations of Mg2+ ions to the reaction mixture at pH 7.1–7.2, a range for which the kinetics of hydrolysis is sensitive to the rate constants of deactivation of DOH− active centers (conjugated with CuADP− formation and occurring via the formation of IntK). The conversion of ATP above which stationary hydrolysis regime was observed decreased as the concentration of Mg2+ grew. The DOH− \(\underset{{OH^ - }}{\overset{{OH^ - }}{\longleftrightarrow}}\) IntK equilibrium according to the conversion of ATP was established more rapidly, and it was to a greater extent shifted toward IntK. It was assumed that hydrated Mg2+ linked as a second metal ion with ATP β and γ phosphate groups hydrated IntK much stronger than DOH−. The Cu · OH2 · AMP complex played the role of a common acid catalyst and hydrated DOH− better than Mg2+ · OH2. The selective hydration of DOH− by the CuOH2 · AMP complex at early hydrolysis stages directed the process toward the formation of IntK, which caused the appearance of an induction period in the formation of CuADP−.

The kinetics of methane oxidation by methane monooxygenase is simulated numerically. Literature data on the distribution of products of the oxidation of deuterated methane CH 4 − n D n (CH 3 D, CH 2 D 2 , and CHD 3 ), as well as on the kinetic isotope effect in the competitive oxidation of CH 4 and CD 4 by methane monooxygenase, are analyzed in the framework of a nonradical multistep mechanism. Kinetic schemes whose first step involves two hydrogen atoms of the oxidation substrate are considered. The kinetic models suggested for methane oxidation are in good agreement with experimental data.

In order to identify common and distinctive features in the catalytic behavior of natural and artificial nitrogen-fixation clusters, the kinetics of the catalytic reduction of C2H2 in the presence of Mg-Mo-cluster (1) was investigated and compared with the kinetics of acetylene reduction catalyzed by the cluster FeMoco (2) isolated from the enzyme nitrogenase we studied previously. The reactions were conducted in the presence of Zn/Hg and Eu/Hg as reducing agents and PhSH and C6F5SH as proton donors, i.e., under the same conditions as had been used in the case of 2. Both polynuclear Mg-Mo-complex and the europium amalgam-reduced FeMoco have multiple interdependent binding sites for substrates and/or inhibitors. Carbon monoxide inhibits the acetylene reduction much less efficiently in systems with cluster 1 than in systems with cluster 2, although the type of inhibition is mixed in both systems: CO binds to multiple sites of the cluster and affects both C2H2 complexation to the reduced cluster and decomposition of the catalyst-substrate complex to give the products. Unlike isolated FeMoco, the Mg-Mo-cluster efficiently catalyzes the reduction of molecular nitrogen. The reaction is greatly inhibited by acetylene, while no inhibiting effect of N2 is observed in acetylene reduction, as was found earlier for a system with the natural cluster as the catalyst.

The kinetics and mechanism of the reduction of KMnO4 in sulfuric acid solutions were studied. It was demonstrated that the Mn(VII)-containing compounds formed from KMnO4 in 18 M sulfuric acid decompose unimolecularly to yield molecular oxygen. In 12 M sulfuric acid, KMnO4 is reduced by water via two parallel routes: four-electron oxidation of water to oxygen and the six-electron oxidation to ozone, which decomposes almost completely in the reaction medium into molecular oxygen.

The study of water oxidation by Mn n IV clusters, which are functional chemical models of the manganese cofactor (enzyme that oxidizes water in photosystem II of natural photosynthesis) has demonstrated that a Mn 2 IV cluster oxidizes two water molecules to form one oxygen molecule, Mn 4 IV oxidizes four water molecules to form two O2 molecules, and Mn 8 IV oxidizes eight water molecules to form four O2 molecules. A Mn 6 IV cluster oxidizes six water molecules to two ozone molecules, whereas Mn 12 IV oxidizes twelve water molecules to four ozone molecules. The six-electron oxidation of water to ozone is also observed in photosynthesis in red and brown sea algae under conditions of water deficit. It is hypothesized that, in the case of water deficit in algae, the manganese cofactor with four manganese ions turns into the cofactor with six manganese ions.

Published data on the kinetic isotope effects of the hydroxylation of deuterium-substituted methane molecules (CHD 3 , CH 2 D 2 , and CH 3 D) by methane monooxygenase are examined in the framework of the two-step nonradical mechanism through the intermediate formation of a complex containing pentacoordinate carbon. The kinetic schemes with the first step involving one, two, and three hydrogen atoms of the oxidized substrate are considered. Contrary to the widely accepted oxygen rebound mechanism, the experimental results obtained for the oxidation of various substrates by methane monooxygenase and cytochrome P450 can be explained from the viewpoint of the dynamics of a general nonradical mechanism.

According to the mechanism of alkane hydroxylation, whose main postulate is the formation of an intermediate complex containing pentacoordinated carbon, the hydroxylation of methane and ethane by methane monooxygenase was kinetically simulated by the numerical method. The published data on the kinetic isotope effects of oxidation of deuterium-substituted methane molecules (CHD 3 , CH 2 D 2 , and CH 3 D) and the distribution of products of chiral ethane ( R - and S -MeCHDT) oxidation by methane monooxygenase were examined. The kinetic models proposed for the oxidation of isotopically substituted methane and ethane are in good agreement with experimental data.

A new mechanism for the catalytic reduction of N2 was proposed. According to the mechanism, reduction is preceded by the oxidation step with the formation of N2O. The mechanism allows the participation of weaker reducing agents than those in purely reductive processes. Probable individual steps are considered, in particular, the oxygen atom transfer from the superoxide radical anion O2–· in a cyclic complex containing the N2 molecule in the coordination sphere of a metal. The proposed mechanism can explain N2 reduction involving recently discovered nitrogenase in which O2–· acts as an electron donor and N2 reduction in purely chemical systems including the air nitrogen and relatively weak reducing agents.