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71.
The extent of electron quasilocalization in the high density gases is greater in ethane than in methane. However, the density required for quasilocalization in methane is n/nc > 0.1, while that in ethane is n/nc > 0.4, where nc is the critical density. The mobilities in methane and ethane cross at n = 6 × 1021 molecules/cm3, in the respective fluids along their vapor/liquid coexistence curves. 相似文献
72.
William T. Speck Amy J. Behrman Pnina G. Rosenkranz Doria Gordon Herbert S. Rosenkranz 《Photochemistry and photobiology》1980,31(5):513-517
Abstract— The unfertilized oocytes and spermatozoa of the American sea urchin ( Arbacia punctulata ) were exposed to phototherapy lights in order to determine the effect of this treatment regimen on post-irradiation fertilization and embryonic development. Light treatment revealed dose-dependent abnormalities in fertilization and subsequent embryonic development. 相似文献
73.
Huang Y Triscari JM Pasa-Tolic L Anderson GA Lipton MS Smith RD Wysocki VH 《Journal of the American Chemical Society》2004,126(10):3034-3035
Analysis of fragmentation patterns from 5654 unique doubly charged tryptic peptides is obtained. Great variability of average relative abundance of bond cleavage is found between different amino acid combinations. There exist similarities as well as differences between b and y ions. Strong enhancement or suppression of cleavage gives insight into possible chemical interactions at reactive conformations formed by preferred phi-psi angles. 相似文献
74.
Ruthenium(II) complexes of monodonor ligands: efficient reagents for asymmetric ketone hydrogenation
Xu YA Clarkson GC Docherty G North CL Woodward G Wills M 《The Journal of organic chemistry》2005,70(20):8079-8087
[Chemical reaction: See text] A series of BINOL-derived ligands have been prepared and incorporated into ruthenium(II) complexes containing a diamine ligand. The complexes have proven to be excellent catalysts for the asymmetric hydrogenation of ketones, giving reduction products with enantiomeric excesses of up to 99%. 相似文献
75.
Abstract— Chlorophyll, pheophytin and bacteriochlorophyll sensitize a one-electron transfer in the presence of quinones in ethanol, to produce a ternary complex of ground state porphyrin analog, alcohol cation radical and semiquinone anion radical as the primary photo-product at low temperature. A similar photo-oxidation of alcohol to produce a binary complex is caused by direct excitation of quin-one in the absence of chlorophyll. The mechanisms of these reactions and their implications for photosynthesis are discussed. 相似文献
76.
Regioselective ortho lithiation of 2-, 3-, and 4-halopyridines is achieved with lithium diisopropylamide (?78°, tetrahydrofuran) to afford, upon quenching with electrophilic reagents, 2,3- and 3,4-disubstituted pyridines in good to excellent yield. 相似文献
77.
Gordon G. Cash 《Journal of mathematical chemistry》1995,18(2):115-119
A fast computer algorithm is described which brings computation of the permanents of sparse matrices, specifically, chemical adjacency matrices, within the reach of a desktop computer. Examples and results are presented, along with a discussion of the relationship of the permanent to the Kekulé structure count. Also presented is a C-language implementation which was deliberately written for ease of translation into other high-level languages. 相似文献
78.
Formulae for calculating the analytic gradients of the exchange-repulsion energy in the general effective fragment potential (EFP2) method are derived and implemented using a direct differentiation approach. The timings for the exchange repulsion gradient evaluations are approximately three times longer than the energy evaluations, orders of magnitude faster than a previous implementation. Since the direct differentiation approach is not approximate, the gradients can be used with confidence in molecular dynamics and Monte Carlo simulations with the EFP2 method. 相似文献
79.
E L White M S Uhrig T J Johnson B M Gordon R D Hicks M F Borgerding W M Coleman J F Elder 《Journal of chromatographic science》1990,28(8):393-399
Eight compounds from a Kentucky 1R4F reference cigarette smoke condensate have been determined by selected ion monitoring-mass spectrometry (SIM-MS) to confirm the validity of multidimensional gas chromatography (MDGC) as a quantitative tool in complex mixture analyses. Four electrostatically precipitated smoke condensate samples of 100 cigarettes each are dissolved individually in 25 mL of 2-propanol. The 2-propanol contains two methyl esters (C8 and C14) and seven deuterium-labeled compounds used as internal standards (IS). Analysis of the compounds of interest, pyridine; acetamide; acrylamide; phenol; o-, m-, and p-cresol; and quinoline, is accomplished by using two heartcuts. Heartcut times of the MDGC analysis are selected such that at least one IS is transferred with each group of compounds being analyzed. This study shows that the MDGC technique previously developed and described can be used for quantitative analyses. A comparison is made between the two types of internal standards. The results obtained for both types of internal standards agree within 20% of each other, on the average, with higher standard deviations for approximately 60% of the compounds where methyl esters are used as internal standards. 相似文献
80.
The electronic absorption spectra of a series of alkoxy-styryl substituted terthiophenes, their corresponding sexithiophenes, and the oxidation products of both have been measured. The terthiophenes studied sigma-dimerize to sexithiophenes during the oxidation process and there is clear evidence of sexithiophene radical cations, dications, and pi-dimers in the electronic absorption spectra. The oxidation of concentrated solutions produces predominantly pi-dimer bands, as expected. The absorption spectrum of the styryl-functionalized sexithiophene dication without alkoxy substitution closely resembles that of unsubstituted sexithiophene, while alkoxy substitution induces changes in the wavelength of the dication band maximum and the overall band shape. Time-dependent density functional theory (TDDFT) calculations have shown that styryl-based molecular orbitals are important in the transitions of the neutral molecules as well as the charged species, the dication in particular. Kinetics analyses confirm the stabilization effect induced by the alkoxy substituents. The presence of a reversible pi-dimer equilibrium was verified by cyclic voltammetry. It is clear from the experimental observations and the theoretical calculations that both the styryl and alkoxy groups are influencing the electronic properties of this class of molecules. 相似文献