Mechanism Of Intermediate Formation Research Articles

DFT Study on Mechanism of Olefin Hydroalumination by XAlBui2 in the Presence of Cp2ZrCl2 Catalyst. I. Simulation of Intermediate Formation in Reaction of HAlBui2 with Cp2ZrCl2

The mechanism of intermediate formation in the reaction of HAlBui2 with Cp2ZrCl2 has been studied by DFT calculations. Stationary points have been localized on the potential energy surface of the r...

A Comparative Study of the Activity of Oxide Catalysts in the Oxidation of Methane and 1,1-Dimethylhydrazine

The catalytic oxidation of methane and 1,1-dimethylhydrazine ((CH3)2N–NH2, unsymmetrical dimethylhydrazine (UDMH)) with air on oxide catalysts was studied. Two pairs of perovskites (Ca0.7Sr0.3FeO2.5(3.0) and La0.7Sr0.3CoO2.5(3.0), stoichiometric and superstoichiometric with respect to oxygen) and a supported spinel (20%(Cu x Mg1 – x Cr2O4)/γ-Al2O3, IC-12-73) were used as catalysts. The experiments were performed using two laboratory flow-type systems: in a catalytic fixed-bed reactor (the oxidation ofCH4) and in a gradientless vibrationally fluidized bed reactor (the oxidation of CH4 and UDMH) at 150–700°C. In the oxidation of CH4, the IC-12-73 catalyst was more active than the perovskite catalysts, although particular perovskite catalysts can exhibit higher activity in the region of low temperatures. In the oxidation of UDMH, the activity of perovskites in the test temperature region was lower than that of IC-12-73; this correlates with the higher activity of IC-12-73 in the oxidation of CH4. The Ca0.7Sr0.3FeO3.0 and La0.7Sr0.3CoO2.5(3.0) perovskites exhibited similar activities in the deep oxidation of UDMH, which were higher than the activity of Ca0.7Sr0.3FeO2.5. A comparison between the selectivities of the conversion of fixed nitrogen, which is a constituent of UDMH, into nitrogen oxides $$\left( {S_{NO_x }^N } \right)$$ demonstrated that, on all of the perovskites, S N NO was higher and $$S_{N_2 O}^N $$ was lower than the corresponding values on IC-12-73. Additional information on the possible mechanisms of intermediate formation in the adsorption and oxidation of UDMH on IC-12-73 was obtained using Fourier transform IR spectroscopy.

The separate effects of E60Q in Lactobacillus casei thymidylate synthase delineate between mechanisms for formation of intermediates in catalysis.

X-Ray crystal structures of Lactobacillus casei thymidylate synthase (TS) mutant complexes of E60D with dUMP, and E60Q with dUMP or FdUMP, as well as ternary complexes with folate analog inhibitor CB3717, are described. The structures we report address the decrease in rate of formation of ternary complexes in the E60 mutants. Structures of ternary complexes of L.casei TS mimic ligand-bound TS just prior to covalent bond formation between ligands and protein. Ternary complex structures of L.casei TS E60Q show the ligands are not optimally aligned for making the necessary covalent bonds. Since CB3717 is an analog of the open, activated form of the cofactor, these structures suggest that the slow rate of ternary complex formation in E60 mutants is at least partly the result of impaired alignment of ligands in the active site after binding and activation of the cofactor. Binary complexes of TS E60Q and TS E60D with substrate (dUMP) show no change in dUMP position or occupancy. These results are consistent with the fact that Kd(dUMP) and Km(dUMP) are almost the same, and the rates of folate-independent debromination of 5-bromo-dUMP are even higher than for wild type TS.