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91.
Ram C. Maurya Dinesh C. Gupta Rajesh Shukla Raj K. Shukla Nalmas Anandam Mannar R. Maurya 《Transition Metal Chemistry》1986,11(12):463-464
Summary A new series of cyano-substituted nitrosylchromium(I) complexes having octahedral stereochemistry around the metal ion, and of general formula, [CrNO(CN)2(L)2(H2O)] (L =o-,m- andp-phenetidines oro-,m-, andp-anisidines) have been isolated in the solid state by interaction of potassium pentacy-anonitrosylchromate(I) monohydrate with the appropriately substituted aniline. The complexes, which have been characterised by elemental analysis, conductance, molecular weight determination, magnetic measurements, e.s.r. and i.r. spectral studies, contain chromium(I) in a low-spin d5-configuration. 相似文献
92.
Balderas-Hernández P Rojas-Hernández A Galván M Ramírez-Silva MT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):569-577
The detailed analysis of the experimental spectrophotometric data obtained from solutions containing the acid-base indicator thymol blue (TB) and mercury(II) (Hg(II)) coupled with data processing by means of the SQUAD program, a chemical model was determined that includes the formation of complexes indicator-metal ion (HgTB and HgOTB), dimer species (H3TB2 and H4TB2) and monomer species (HTB and TB). The values of the overall formation constants (log beta) were calculated for the chemical equilibria involved: TB+Hg<-->HgTB log beta=16.047 +/- 0.043, TB+Hg+H2O<-->HgOHTB+H log beta=7.659 +/- 0.049, 2TB+4H<-->H4TB2 log beta=31.398 +/- 0.083, 2TB+3H<-->H3TB2 log beta=29.953 +/- 0.084 and H+TB<-->HTB-log beta=8.900. To compliment the present research, the values of the absorptivity coefficients are included for all the species involved, within a wide range of wavelengths (250-700 nm). The latter were used subsequently to carry simulations of the absorption spectra at various pH values, thus corroborating that the chemical model proposed is fully capable to describe the experimental information. Voltammetric study performed evidenced the formation of a complex with a 1:1 stoichiometry Hg(II):TB. 相似文献
93.
Mixed valency in the high-temperature phases of transition metal molybdates, A MoO4 ( A =Fe, Co, Ni)
Transition metal molybdates of the formulaAMoO4 whereA=Fe, Co or Ni exhibit a first-order phase transition between 670K–970K. An investigation of the lowtemperature (lt) and high-temperature (ht) phases by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, magnetic susceptibility and other physical methods
shows that the phase transition is associated with a valence change of the typeA
2++Mo6+αA
3++Mo5+ in the cases of iron and cobalt molybdates.
Contribution No. 311 from the Solid State and Structural Chemistry Unit. 相似文献
94.
Ramón Serrano Roberto Gaxiola Gabino Ríos Javier Forment Oscar Vicente Roc Ros 《Monatshefte für Chemie / Chemical Monthly》2003,11(3):1445-1464
We have performed functional genomics of salt stress by overexpression of gene libraries in yeast and selection for salt tolerance. Thirty halotolerance genes were isolated from yeast, Arabidopsis, and sugar beet. The results indicate that Na+ transport (uptake, efflux, and compartmentation), sulfate activation, RNA processing, and protein synthesis are crucial for salt tolerance. 相似文献
95.
Submerged culture fermentation studies were carried out in batch mode for optimizing the environmental parameters and carbon
source requirement by Pseudomonas elodea for the production of gellan gum. The maximum production of gellan gum was obtained with 16-h-old culture and 8% inoculum
at 30°C and pH 7.0 after 52 h of incubation (6.0 g/L). Of the various carbon sources tested, 2% sucrose, glucose, and soluble
starch yielded considerably high amounts of gellan. Studies on the concentration of various carbohydrates on gellan gum production
indicated that the optimum concentration of glucose and starch was 3%, whereas for sucrose it was 4%. The addition of glucose
in the medium above 3% had a detrimental effect on gellan yield. The investigation of intermediate two-step addition of glucose
under identical conditions of fermentation showed an enhanced production of gellan (8.12 g/L) as compared with the control
(6.0 g/L). To optimize the recovery of gellan from fermented broth, different solvents were tested for precipitation of gellan
gum. Among the various solvents tested, tetrahydrofuran gave better recovery of gellan (82%) as compared with the conventional
solvent isopropanol (49%). 相似文献
96.
Chary KV Sagar GV Naresh D Seela KK Sridhar B 《The journal of physical chemistry. B》2005,109(19):9437-9444
A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2. 相似文献
97.
Bassil BS Nellutla S Kortz U Stowe AC van Tol J Dalal NS Keita B Nadjo L 《Inorganic chemistry》2005,44(8):2659-2665
The 15-cobalt-substituted polyoxotungstate [Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}](5-) (1) has been characterized by single-crystal XRD, elemental analysis, IR, electrochemistry, magnetic measurements, and EPR. Single-crystal X-ray analysis was carried out on Na(5)[Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}].37H(2)O, which crystallizes in the hexagonal system, space group P6(3)/m, with a = 19.8754(17) A, b = 19.8754(17) A, c = 22.344(4) A, alpha= 90 degrees, beta = 90 degrees, gamma = 120 degrees, and Z = 2. The trimeric polyanion 1 has a core of nine Co(II) ions encapsulated by three unprecedented (beta-SiW(8)O(31)) fragments and two Cl(-) ligands. This central assembly {Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}(17-) is surrounded by six antenna-like Co(II)(H(2)O)(5) groups resulting in the satellite-like structure 1. Synthesis of 1 is accomplished in a simple one-pot procedure by interaction of Co(II) ions with [gamma-SiW(10)O(36)](8-) in aqueous, acidic NaCl medium (pH 5.4). Polyanion 1 was studied by cyclic voltammetry as a function of pH. The current intensity of its Co(II) centers was compared with that of free Co(II) in solution. Our results suggest that 1 keeps its integrity in solution. Magnetic susceptibility results show the presence of both antiferro- and ferromagnetic coupling within the (Co(II))(9) core. A fully anisotropic Ising model has been employed to describe the exchange-coupling and yields g = 2.42 +/- 0.01, J(1) = 17.0 +/- 1.5 cm(-1), and J(2) = -13 +/- 1 cm(-(1). Variable frequency EPR studies reveal an anisotropic Kramer's doublet. 相似文献
98.
Barluenga J Ballesteros A Bernardo De La Rúa R Santamaría J Rubio E Tomás M 《Journal of the American Chemical Society》2003,125(7):1834-1842
Cyclization reactions of group 6 Fischer carbene complexes with cyclopentanone and cyclohexanone enamines are described. Enamine 3a undergoes thermal alpha,beta,beta'-annulation with alkenylcarbene complexes 1 and 2 (THF, 60 degrees C), affording semibullvalenes 5. The metalate intermediates 6, resulting from beta,beta'-annulation of the enamines 3a and 4a, were quantitatively formed by running the reaction in hexane at room temperature. Acid-promoted demetalation of 6 afforded endo-2-bicyclo[3.2.1]octen-8-ones 7 and endo/exo-2-bicyclo[3.3.1]nonen-9-ones 8 (endo/exo = 5:1). Using (S)-methoxymethylpyrrolidine-derived enamines 3b and 4b,c allowed highly enantioenriched cycloadducts endo-(+)-7 as well as endo-(-)-8 and exo-(-)-8 to be accessed. The non-heteroatom-stabilized carbene complex 10 was formed from complex 6 by Me(3)SiOTf-promoted elimination of the methoxy group, characterized by (13)C NMR, and transformed into the organic compounds 7, 7-d, and 11 as well as into bicyclo[3.2.1]octan-2,8-diones 14 and cycloheptanones 15. On the basis of this sequence, enantioenriched cycloheptanones (+)-15 were efficiently prepared in one pot from carbene complexes 2 and enamine 3b (51-55% yield, 91-96% ee). Extension of this work to simple Fischer carbene complexes 16 allowed an appropriate way to generate the nonstabilized pentacarbonyl[(phenyl(alkyl)carbene]tungsten complex 17 to be designed, for which the thermal and chemical behavior leading to compounds 18-21 is described. 相似文献
99.
In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order M?ller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies. 相似文献
100.
A mild and new procedure for the selective cleavage of an alkoxycarbonyl group (Boc, CBz) in N,N-dicarbamoyl-protected amino compounds is described. The method is based on the use of lithium bromide in acetonitrile and is compatible with a large range of other functionalities present in the substrates. Compared with other reported methodologies, the procedure is particularly useful for the Cbz-selective cleavage in N,N-Ts,Cbz-diprotected amines. A rationalization of the selectivity supported by ab initio calculations is also presented. 相似文献