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991.
Komaragiri V McCarter B Bililign S Hagebaum-Reignier D Ledentu V Jeung GH 《The Journal of chemical physics》2005,123(2):24303
Quenching mechanisms of the Li3p and Li4p states in collision with the nitrogen molecule are studied by laser-induced fluorescence spectroscopy and by a quantum chemical calculation. The Li3p state is observed to be efficiently quenched to the Li3s state detected as intense 3s-->2p emission. The Li4p state is efficiently quenched to the Li4s and Li3d states detected as 4s-2p and 3d-2p emissions, respectively. The potential-energy surfaces for the Li(2s-4p)N2 states show a large number of conical intersections and avoided crossings resulting from the couplings between the ionic [Li+(N2)-] and covalent configurations. There are a large number of stable excited states, and we give here the spectroscopic constants for the lowest two stable isomers correlating to Li2p+N2. 相似文献
992.
Aamer Saeed 《Chemistry of Heterocyclic Compounds》2007,43(8):1072-1075
An efficient, rapid, microwave-accelerated one-step synthesis of some 5-aryl-2-(2-hydroxy-phenyl)-1,3,4-oxadiazoles by reaction
of salicylic hydrazide with carboxylic acids in the presence of thionyl chloride under neat conditions is described.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1264–1267, August, 2007. 相似文献
993.
Zhou J Kelly WL Bachmann BO Gunsior M Townsend CA Solomon EI 《Journal of the American Chemical Society》2001,123(30):7388-7398
Using a single ferrous active site, clavaminate synthase 2 (CS2) activates O(2) and catalyzes the hydroxylation of deoxyguanidinoproclavaminic acid (DGPC), the oxidative ring closure of proclavaminic acid (PC), and the desaturation of dihydroclavaminic acid (and a substrate analogue, deoxyproclavaminic acid (DPC)), each coupled to the oxidative decarboxylation of cosubstrate, alpha-ketoglutarate (alpha-KG). CS2 can also catalyze an uncoupled decarboxylation of alpha-KG both in the absence and in the presence of substrate, which results in enzyme deactivation. Resting CS2/Fe(II) has a six-coordinate Fe(II) site, and alpha-KG binds to the iron in a bidentate mode. The active site becomes five-coordinate only when both substrate and alpha-KG are bound, the latter still in a bidentate mode. Absorption, CD, MCD, and VTVH MCD studies of the interaction of CS2 with DGPC, PC, and DPC provide significant molecular level insight into the structure/function correlations of this multifunctional enzyme. There are varying amounts of six-coordinate ferrous species in the substrate complexes, which correlate to the uncoupled reaction. Five-coordinate ferrous species with similar geometric and electronic structures are present for all three substrate/alpha-KG complexes. Coordinative unsaturation of the Fe(II) in the presence of both cosubstrate and substrate appears to be critical for the coupling of the oxidative decarboxylation of alpha-KG to the different substrate oxidation reactions. In addition to the substrate orientation relative to the open coordination position on the iron site, it is hypothesized that the enzyme can affect the nature of the reactivity by further regulating the binding energy of the water to the ferrous species in the enzyme/succinate/product complex. 相似文献
994.
The relativistic ground and low-lying excited state potential energy curves of AgH and AuH in the presence of a cylindrical
harmonic confining potential were calculated using the multi-state multi-reference perturbation theory with the spin-free
no-pair Hamiltonian obtained via the third-order Douglas–Kroll transformation, incorporated with the full two-electron Breit–Pauli
spin–orbit operator. The spectroscopic parameters were obtained for both the scalar- and quasi-relativistic potentials. The
spin–orbit coupling constants were calculated for several strengths of the confining potential, and the effects of the applied
potential on the coupling constants were analyzed using configuration interaction.
This paper is dedicated to Serafín Fraga—colleague, mentor, and friend. 相似文献
995.
The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube
filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to
simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results
of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the
order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective
flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon
floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc.
The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from
a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation
distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing
that deviation. 相似文献
996.
Ordered aggregation of thiol-passivated Au nanoparticles in a diblock copolymer polystyrene-b-poly(methyl methacrylate) has been observed. The morphology of the diblock copolymer/Au-nanocomposite was dependent on the composition of the thiol modifier. For the thiol modifier that does not preferentially interact with one of the blocks, a perpendicular (relative to the substrate) lamellar morphology is maintained. However, for a thiol with a surfactant structure similar to one of the blocks, we observed a parallel lamellar morphology and speculate that the nanoparticles have localized at the microdomain interface. These conclusions are based on transmission electron microscopy, angle-dependent X-ray photoelectron microscopy and tensiometry. These results are consistent with theoretical predictions on the hybrid systems composed of block copolymers and nanoparticles. 相似文献
997.
Antonio Doménech María Teresa Doménech-Carbó María Luisa Vázquez de Agredos Pascual 《Journal of Solid State Electrochemistry》2007,11(9):1335-1346
The preparation of indigo from Indigofera suffruticosa following the procedures attributed to ancient Mayas was electrochemically monitored using the voltammetry-of-microparticles
approach. The mechanism formation of indigotin and indirubin from its precursors, indican and isatan, is discussed. Comparison
of voltammetric profiles for differently prepared and commercial indigos and genuine Maya Blue samples suggests that the preparation
procedure of indigo changed during the Late Classical Maya period.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
998.
Ikhsan J Angove MJ Johnson BB Wells JD 《Journal of colloid and interface science》2005,284(2):400-407
Data from acid-base titrations at 25 degrees C of Zn(NO(3))(2) and 2-, 3-, or 4-aminopyridine in 10 mM KNO(3) as background electrolyte suggested that soluble complexes ZnL(2+) and Zn(OH)L(+) form, where L represents aminopyridine. Zinc-hydroxyaminopyridine complexes have not been reported previously. The cosorption of Zn(II) with each of the aminopyridines to K-saturated Wyoming (SWy-K) and Texas (STx-K), and Ca-enriched Texas (STx-Ca) montmorillonites was measured at 25 degrees C, with 10 mM KNO(3) or 3.3 mM Ca(NO(3))(2) as background electrolyte. Comparison with previous data for sorption of Zn(II) and the aminopyridines separately and surface complexation modeling of the cosorption data showed that under acid conditions competition between Zn(2+) and aminopyridinium ions for the permanent negatively charged sites of montmorillonite results in suppression of the uptake of each sorbate by the other, but only when a large excess of the competing sorbate is present. Under alkaline conditions the sorption of Zn(II) was not affected by the presence of even a large excess of aminopyridine, but the sorption of 4-aminopyridine in particular was slightly enhanced when a large excess of Zn(II) was present. The enhancement was attributed to the formation of metal-bridged ternary surface complexes at the variable-charge sites on the edges of the montmorillonite crystals. 相似文献
999.
Zhang C Staunton E Andreev YG Bruce PG 《Journal of the American Chemical Society》2005,127(51):18305-18308
Polymer electrolytes, salts dissolved in solid polymers, hold the key to realizing all solid-state devices such as rechargeable lithium batteries, electrochromic displays, or SMART windows. For 25 years conductivity was believed to be confined to amorphous polymer electrolytes, all crystalline polymer electrolytes were thought to be insulators. However, recent results have demonstrated conductivity in crystalline polymer electrolytes, although the levels at room temperature are too low for application. Here we show, for the first time, that it is possible to raise significantly the level of ionic conductivity by aliovalent doping. The conductivity may be raised by 1.5 orders of magnitude if the SbF6- ion in the crystalline conductor poly(ethylene oxide)6:LiSbF6 is replaced by less than 5 mol % SiF6(2-), thus introducing additional, mobile, Li+ ions into the structure to maintain electroneutrality. 相似文献
1000.
JongHwa Moon SangHoon Kang YongSam Chung OkHee Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):155-158
Instrumental neutron activation analysis was used to assess the concentration of the inorganic trace elements in Korean women’s
blood serums. It was found that a high concentration of Na and Cl incurs an analytical interference, but the 12 elements such
as Br, Ca, Cl, Co, Cr, Cs, Fe, K, Na, Rb, Se and Zn could be determined under the condition of an interference minimization.
Serum samples collected from 63 women were analyzed and the concentration level and range of the elements were evaluated.
NIST SRMs were analyzed simultaneously for quality control. The average values of the Na and Cl determined in the serum samples
were 3,365 and 3,533 mg/l, Ca was 96.4 mg/l and K was 191 mg/l. Besides, Br, Se and Zn have a concentration level of 6.46,
0.13 and 0.98 mg/l, respectively. It was found that there is no significant difference between the present values and the
reported values. 相似文献