The new transition metal oxo‐thiostannate {[Ni(cyclen)]6[Sn6S12O2(OH)6]} · 2(ClO4) · 19H2O ( 1 ) was prepared under hydrothermal conditions using Na4SnS4 · 14H2O and [Ni(cyclen)](ClO4)2 as reactants. In the crystal structure the rare [Sn6S12O2(OH)6]10– anion is observed, which is composed of SnS2O(OH)3 and SnS4O2 octahedra, and SnS4 tetrahedra sharing edges and corners. The anion is expanded by six Ni2+ centered complexes via Ni–S and Ni–OH bonds. The photocatalytic properties for the visible light driven hydrogen evolution reaction shows that 26.6 mmol · g–1 H2 were evolved after 3 h. 相似文献
Crystals of copper halide and pseudohalide compounds with pyrazine are synthesized under hydrothermal conditions. The title compound, [Cu3Cl2CNPz] (1) (Pz = pyrazine), is a new copper compound exhibiting an unusual -(Cu3Cl2)- polymeric stair structural motif and three-coordinate cyanide. Compound 1 crystallizes in the monoclinic space group P2(1)/m, with a = 3.6530(7) A, b = 17.160(3) A, c = 6.9800(14) A, beta = 90.58(3) degrees, and Z = 2. In addition, the series of complexes [Cu2X2Pz] for X = Cl (2), Br (3), and I (4) are also crystallized under hydrothermal conditions. The inorganic polymer [Cu2Br2Pz] (3) belongs to the triclinic space group P1, with a = 6.9671(14) A, b = 7.849(2) A, c = 8.099(2) A, alpha = 71.69(3) degrees, beta = 70.71(3) degrees, gamma = 85.43(3) degrees, and Z = 2. The structure of 3, is similar to the recently reported structure for [Cu2Cl2Pz] (2) (Kawata, S.; Kitagawa, S.; Kumagai, H.; Iwabuchi, S.; Katada, M. Inorg. Chim. Acta 1998, 267, 143). The third member of the series, [Cu2I2Pz], is found to be isostructural on the basis of X-ray powder diffraction results. The lattice parameters are refined from indexed reflections to a = 7.115(10) A, b = 8.321(19) A, c = 8.378(17) A, alpha = 71.1(3) degrees, beta = 67.3(1) degrees, and gamma = 83.0(2) degrees. Electronic spectra show that compounds 1-4 have optical band gaps in the range 2.2-2.4 eV. The infrared and Raman spectra as well as the thermal properties of all compounds are presented. 相似文献
Large-gel two-dimensional gel electrophoresis (2-DE) is the method of choice for high-resolution proteome analysis of complex
protein mixtures. Until now, however, the advantages of large 2-DE in combination with multiplexed fluorescence dye protein
labelling has been complicated by the separate handling and analysis of the second-dimension gels. Therefore, we adapted the
large 2-DE procedure allowing us to run “one-piece” large 2-DE gels (40 cm × 30 cm) in the second dimension for high resolution
proteome analysis. Here, we show that in combination with fluorescence dye protein saturation labelling “one-piece” large
2-DE enables analysis of small amounts of sample (3 μg protein) for high-resolution proteome analysis. 相似文献
The new thiostannate Na4Sn2S6 was prepared by directed crystal water removal from the hydrate Na4Sn2S6 ⋅ 5H2O at moderate temperatures. While the structure of the hydrate comprises isolated [Sn2S6]4− anions, that of the anhydrate contains linear chains composed of corner-sharing SnS4 tetrahedra, a structural motif not known in thiostannate chemistry. This structural rearrangement requires bond-breakage in the [Sn2S6]4− anion, movements of the fragments of the opened [Sn2S6]4− anion and Sn−S−Sn bond formation. Simultaneously, the coordination environment of the Na+ cations is significantly altered and the in situ formed NaS5 polyhedra are joined by corner- and edge-sharing to form a six-membered ring. Time-dependent in situ X-ray powder diffraction evidences very fast rehydration into Na4Sn2S6 ⋅ 5H2O during storage in air atmosphere, but recovery of the initial crystallinity requires several days. Impedance spectroscopy demonstrates a mediocre room-temperature Na+ ion conductivity of 0.31 μS cm−1 and an activation energy for ionic transport of Ea=0.75 eV. 相似文献
An iterative solver has been recently developed to solve very large systems of linear equations. The application of such a solver in commercial finite element software is not yet accepted. The purpose of the paper is to describe the new iterative solver and report on the practical application of this capability in different fields of interest.
The iterative solver uses the conjugate gradient method and employs two types of preconditioning: the traditional Jacobi and the incomplete Cholesky decomposition method. An option has been added for diagonal scaling to handle matrices whose entries greatly differ in magnitude. This paper illustrates the reduction possible in both central processor time and disk storage for problems with very large, well-conditioned matrices. Problems arising in electromagnetic analysis as well as in structural analysis have been solved with different options available in the iterative solver and compared with the standard, direct solver results. Guidelines on the use of the new solver and the status of research on even more efficient preconditioners are given. 相似文献
Dihydroorotase (DHO) is a zinc metalloenzyme, although the number of active site zinc ions has been controversial. E. coli DHO was initially thought to have a mononuclear metal center, but the subsequent X-ray structure clearly showed two zinc ions, α and β, at the catalytic site. Aquifex aeolicus DHO, is a dodecamer comprised of six DHO and six aspartate transcarbamoylase (ATC) subunits. The isolated DHO monomer, which lacks catalytic activity, has an intact α-site and conserved β-site ligands, but the geometry of the second metal binding site is completely disrupted. However, the putative β-site is restored when the complex with ATC is formed and DHO activity is regained. Nevertheless, the X-ray structure of the complex revealed a single zinc ion at the active site. The structure of DHO from the pathogenic organism, S. aureus showed that it also has a single active site metal ion.
Results
Zinc analysis showed that the enzyme has one zinc/DHO subunit and the addition of excess metal ion did not stimulate catalytic activity, nor alter the kinetic parameters. The metal free apoenzyme was inactive, but the full activity was restored upon the addition of one equivalent of Zn2+ or Co2+. Moreover, deletion of the β-site by replacing the His180 and His232 with alanine had no effect on catalysis in the presence or absence of excess zinc. The 2.2 Å structure of the double mutant confirmed that the β-site was eliminated but that the active site remained otherwise intact.
Conclusions
Thus, kinetically competent A. aeolicus DHO has a mononuclear metal center. In contrast, elimination of the putative second metal binding site in amidohydrolyases with a binuclear metal center, resulted in the abolition of catalytic activity. The number of active site metal ions may be a consideration in the design of inhibitors that selectively target either the mononuclear or binuclear enzymes.