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931.
Kokh DB Buenker RJ Liebermann HP Pichl L Whitten JL 《The journal of physical chemistry. B》2005,109(38):18070-18080
Configuration interaction calculations of the ground and excited states of the H2CO molecule adsorbed on the Ag(111) surface have been carried out to study the photoinduced dissociation process leading to polymerization of formaldehyde. The metal-adsorbate system has been described by the embedded cluster and multireference configuration interaction methods. The pi electron-attachment H2CO- and n-pi* internally excited H2CO* states have been considered as possible intermediates. The calculations have shown that H2CO* is only very weakly bound on Ag(111), and thus that the dissociation of adsorbed formaldehyde due to internal excitation is unlikely. By contrast, the H2CO- anion is strongly bound to Ag(111) and gains additional vibrational energy along the C-O stretch coordinate via Franck-Condon excitation from the neutral molecule. Computed energy variations of adsorbed H2CO and H2CO- at different key geometries along the pathway for C-O bond cleavage make evident, however, that complete dissociation is very difficult to attain on the potential energy surface of either of these states. Instead, reneutralization of the vibrationally excited anion by electron transfer back to the substrate is the most promising means of breaking the C-O bond, with subsequent formation of the coadsorbed O and CH2 fragments. Furthermore, it has been demonstrated that the most stable state for both dissociation fragments on Ag(111) is a closed-shell singlet, with binding energies relative to the gas-phase products of approximately 3.2 and approximately 1.3 eV for O and CH2, respectively. Further details of the reaction mechanism for the photoinduced C-O bond cleavage of H2CO on the Ag(111) surface are also given. 相似文献
932.
Ka-Man Cheung Ka-Wang Chan Ian D. Williams 《Journal of organometallic chemistry》2005,690(12):2913-2921
Treatment of [Ir(ppy)2(μ-Cl)]2 and [Ir(ppy)2(dtbpy)][OTf] (ppy = 2-(2′-pyridyl)phenyl; dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridine; OTf = triflate) with pyridinium tribromide in the presence of Fe powder led to isolation of [Ir(4-Br-ppy)(μ-Br)]2 (1) and [Ir(4-Br-ppy)2(dtbpy)][OTf] (2), respectively. Pd-catalyzed cross-coupling of 2 with RB(OH)2 afforded [Ir(4-R-ppy)2(dtbpy)][OTf] (R = 4′-FC6H4 (3)), 4′-PhC6H4 (4), 2′-thienyl (5), 4′-C6H4CH2OH (6). Treatment of 4 with B2(pin)2 (pin = pinacolate) afforded [Ir{4-(pin)B-ppy}2(dtbpy)][OTf] (7). The alkynyl complexes [Ir(4-PhCC-ppy)2(dtbpy)][OTf] (8) and [Ir{4-Me2(OH)CC-ppy}(4-Br-ppy)(dtbpy)][OTf] (9) were prepared by cross-coupling of 2 with PhCCSnMe3 and Me2C(OH)CCH, respectively. Ethynylation of [Ir(fppy)2(dtbpy)][OTf] (fppy = 5-formyl-2-(2′-pyridyl)phenyl) with Ohira’s reagent MeCOC(N2)P(O)(OEt)2 afforded [Ir{5-HCC-ppy}2(dtbpy)][OTf] (10). The solid-state structures of 2, 5, 7, and 10 have been determined. 相似文献
933.
Hedstrom JA Toney MF Huang E Kim HC Volksen W Magbitang T Miller RD 《Langmuir : the ACS journal of surfaces and colloids》2004,20(5):1535-1538
Materials with nanometer size heterogeneities are commonplace in the chemical and biological sciences (e.g, polymer blends, microemulsions, gels) and often exhibit complex morphologies. Although this morphology has a dramatic effect on the materials' properties, it is often difficult to accurately characterize. We describe a method, using small-angle X-ray scattering data, of generating representative three-dimensional morphologies of isotropic two-phase materials where the morphology is disordered, and we apply this to thin films containing nanometer sized pores with a range of porosities (4-44%). These representations provide a visualization of the pore morphology, give the pore size scale and extent of interconnection, and permit the determination of the transitions from closed pore to interconnected pores to bicontinuous morphology. 相似文献
934.
Bruce S. Dien Nick Nagle Kevin B. Hicks Vijay Singh Robert A. Moreau Melvin P. Tucker Nancy N. Nichols David B. Johnston Michael A. Cotta Quang Nguyen Rodney J. Bothast 《Applied biochemistry and biotechnology》2004,115(1-3):937-949
Approximately 9% of the 9.7 billion bushels of corn harvested in the United States was used for fuel ethanol production in 2002, half of which was prepared for fermentation by dry grinding. The University of Illinois has developed a modified dry grind process that allows recovery of the fiber fractions prior to fermentation. We report here on conversion of this fiber (Quick Fiber [QF]) to ethanol. QF was analyzed and found to contain 32%wt glucans and 65%wt total carbohydrates. QF was pretreated with dilute acid and converted into ethanol using either ethanologenic Escherichia coli strain FBR5 or Saccharomyces cerevisiae. For the bacterial fermentation the liquid fraction was fermented, and for the yeast fermentation both liquid and solids were fermented. For the bacterial fermentation, the final ethanol concentration was 30 g/L, a yield of 0.44 g ethanol/g of sugar(s) initially present in the hydrolysate, which is 85% of the theoretical yield. The ethanol yield with yeast was 0.096 gal/bu of processed corn assuming a QF yield of 3.04 lb/bu. The residuals from the fermentations were also evaluated as a source of corn fiber oil, which has value as a nutraceutical. Corn fiber oil yields were 8.28%wt for solids recovered following prtetreatment. 相似文献
935.
DESTRUCTION OF PHOTOREACTIVATING ENZYME BY 365 nm RADIATION* 总被引:3,自引:0,他引:3
Abstract— Following the observation that in vivo photoreactivation of 365-nm-induced pyrimidine dimers could not be observed chemically, a study was made of the inactivation of photoreactivating enzyme activity by this near-ultraviolet wavelength. It was observed that: (1) Dimers induced in extracted bacterial DNA by 365 nm radiation are completely photoreactivable and are monomerized as an exponential function of the photoreactivation time. (2) Photoreactivability of 254-nm-induced damage in Escherichia coli B/r Hcr is progressively destroyed in vivo as a function of the dose of 365 nm radiation. (3) The ability of the yeast photoreactivating enzyme to monomerize dimers induced at 365 nm in bacterial DNA is destroyed in vitro as a function of the dose of 365 nm radiation, and at a rate comparable to killing of E. coli. These results are consistent with biological measurements which indicate that photoreactivability of ultraviolet (near and far) lethal damage is reduced by exposure of the bacteria to 365 nm radiation. 相似文献
936.
Robert W. Lenz Lars C. Westfelt 《Journal of polymer science. Part A, Polymer chemistry》1976,14(9):2147-2153
The cationic polymerization of p-chloro-α-methylstyrene was investigated for the effect of initiator and solvent on polymer tacticity, molecular weight, and molecular weight distribution. The products were generally crystalline polymers of 80–90% syndiotactic content with fairly high molecular weights and broad molecular weight distributions. Tacticities and molecular weight distributions followed similar patterns suggesting that the effect of reaction conditions on ionpair end-group structures was the dominant factor. 相似文献
937.
A spectrophotometric and a photometric titration method in a two-phase system for the determination of gold with ferroin is reported. Both methods are rapid and reproducible with an accuracy of ±1%. In the spectrophotometric determination Co2+, Cu2+, Ni2+ , Fe3+, Zn2+, Mn2+ and Cr3+ do not interfere with the determination of gold and Pt4+, Pd2+, Hg2+, Ir4+ and Os4+ can be tolerated up to a ratio of 1:1. The titrations can also be carried out in the presence of a number of diverse ions, e.g. Ni2+, Cu2+, Co2+, Fe3+, Zn2+, Cr3+, Mn2+, without interference; the platinum metals and Hg2+ cause interference but, by the use of the spectrophotometric procedure, this can be reduced. 相似文献
938.
Seymour Siegel Robert J. Champetier A. R. Calloway 《Journal of polymer science. Part A, Polymer chemistry》1966,4(9):2107-2120
The ultraviolet (λ = 2537 A.) photolysis of a degassed mixed phenyl and methyl polysiloxane liquid is examined in terms of gas and crosslinking yields. Results are compared to the published values obtained by ionizing irradiation of this type of molecule. It is shown that ultraviolet radiation is less efficient by two orders of magnitude in producing decomposition (i.e., gaseous products) than is ionizing radiation. The comparisons for crosslinking efficiencies are less certain, but the yields seem to have much more similar values in this case based on a spectroscopic estimation of crosslinking (i.e., analysis for substituted phenylcyclohexadiene formation). The gas quantum yields were ?H2 = 2.6 × 10?5, ?CH4 = 0.63 × 10?5, ?C2H6 ≈ 0.12 × 10?5, and ?C2H2 ≈ 0.06 × 10?5. 相似文献
939.
Freezing temperatures of dilute aqueous solutions of ethyl acetate and mixtures with myo-inositol, D-mannitol, formamide, 1,3,5-trioxane, 1,4-dioxane, acetamide, hexamethylenetetramine, and methyl formate have been measured. In addition, freezing temperatures of dilute aqueous solutions of methyl formate and mixtures with the above solutes have been measured. From these data, the pairwise molecular Gibbs energies of interaction between the molecules were calculated. Using the additivity principle, the pairwise functional group Gibbs energies of interaction were calculated for ester group interactions with a variety of other functional groups. 相似文献
940.