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101.
William T. Simpson 《Theoretical chemistry accounts》1972,23(4):295-308
For a particular model with two electronic states, each with two vibrations, the dipole correlation function governing electronic absorption is e ?iωOt cosγt with spectrum ω 0±γ. The function starts as e ?iωOt (γ?ω 0), with Fourier transform peaking around ω 0 instead of ω 0±γ, and this is associated with vertical excitation. After a time t~2/γ the spectrum goes over into the normal one. As a generalization, a procedure is outlined for characterizing the state reached first after interaction with light is initiated. Finally it is suggested that one can understand aspects of internal conversion by analogy with the case of vertical excitation. 相似文献
102.
The reaction of phenyl lithium acetylide () with 2,6-diphenylpyrylium perchlorate () is solvent dependent. With diethyl ether as solvent, the isolated product differed from that previously reported and is reassingned as 2,6-diphenyl-4-phenylacetylenyl-4-pyran (). On the other hand, in THF the title compound () was obtained; its structure confirmed by single-crystal x-ray crystallography. 相似文献
103.
Samuel K Yin W Stearns RA Tang YS Chaudhary AG Jewell JP Lanza T Lin LS Hagmann WK Evans DC Kumar S 《Journal of mass spectrometry : JMS》2003,38(2):211-221
Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. 相似文献
104.
Marc Henry 《Journal of Cluster Science》2003,14(3):267-287
Among Achim Müller's prolific crystal structure database, we have selected two crystalline phases in order to perform a whole and complete characterization of water structure at the nanometer scale. The first chosen example involves the Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24] 76H2O compound synthesized and characterized in 1994. Some very interesting yet unnoticed water clusters may be evidenced in the voids generated by the stacking of the polyanionic units. Among them, we have been able to characterized a pure water crown (H2O)18, a loose association of three strongly solvated ammonium ions [H3N–HOH2]+ mediated by two water dimers and one water molecule, a perfectly planar alternating six-member ring [(NH4)3(H2O)3]3+, a puckered chair-shaped hexagonal ring [(NH4)2(H2O)4]3+ and two triangular pyramidal water tetramers (H2O)4. It was also shown that the crown and the chair ring was involved through further hydrogen bonding into the formation of a quite novel supramolecular layer modeling the structure of water in contact with a polyelectrolyte. The second example involves the (gua)32[Mo132O372(H2O)72(SO4)10(H2PO2)20(gua)20]nH2O compound synthesized and characterized in 2002. Here, we provide for the first time a complete structural analysis of all the various hydrogen bond patterns encountered in this system. Among them we may cite, an intramolecular web covering the internal cavity, an intramolecular finite system involving the guanidinium cations and the nine-member ring pores of the Mo132 shell and a central pure water cluster of one hundred water molecules. In this last case, the evolution of the hydrogen bond strengths on a per H-bond basis or within supramolecular aggregates ([H2O]20, [H2O]40, and [H2O]100) is quantitatively studied from standpoints involving both geometry (H–OO bond angles distribution) and energy (partition functions). A survey of other crystalline phases involving water clusters is also presented. It is hoped that the study of these new clusters in a very next future will allow us to solve the well-known water puzzling behaviors. 相似文献
105.
The copper-catalyzed pyrolysis of 1-diazo-3-(pyrrol-1-yl)-2-propanone (1a) and 1-diazo-4-(pyrrol-1-yl)-2-butanone (1b) in benzene solution gave 1 H-pyrrolizin-2-(3H)-one (4a) and 5,6-dihydroindolizin-7 (8H)-one (4b) , respectively, in quantitative yield. Similar pyrolysis of 1-diazo-4-(3-methylindol-1-yl)-2-butanone (9) was less efficient giving 1-methylbenzo[b]-5,6-dihydroindroindolizin-7 (8H)-one (10) and 4-(3-methylindol-1-yl)-but-l-en-3-one (11) in 7% and 24% yield, respectively. 相似文献
106.
Zhu H Chai J Chandrasekhar V Roesky HW Magull J Vidovic D Schmidt HG Noltemeyer M Power PP Merrill WA 《Journal of the American Chemical Society》2004,126(31):9472-9473
The reaction of beta-diketiminated aluminum(I) monomer LAl with a large bulky azide N3Ar' (L = HC(CMeNAr)2, Ar' = 2,6-Ar2C6H3, Ar = 2,6-iPr2C6H3) in the temperature range from -78 degrees C to room temperature affords two different isomers 2 and 3, which have been characterized by spectroscopic and X-ray structural analyses, as well as elemental analysis. The variable-temperature 1H NMR kinetic studies of this reaction indicate the existence of the monomer LAlNAr' (1) at low temperature and the thermal stability of the compounds increases in the order of 1 < 2 < 3. 相似文献
107.
A systematic optimization strategy for reverse-phase h.p.l.c. is used to produce complete separation of all components of a mixture containing two coumarins, umbelliferone and scopoletin, and the cis-trans isomers of two cinnamic acids, p-coumaric and ferulic. A series of experiments gives retention time data for each of these substances in four citric acid-buffered mobile phases. A mathematical model fitted to this data gives model parameters that provide the basis for a window diagram of relative retentions vs. mobile phase pH. The window diagram gives an estimate of the mobile phase pH required for optimum separation. 相似文献
108.
Marshall M. Siegel Rushung Tsao William Bouley Theodore Kornas Glen Brubaker 《Journal of the American Society for Mass Spectrometry》1993,4(6):504-506
An inexpensive multisample fast-atom bombardment (FAB) probe assembly was designed for high-throughput analysis of samples on a VG ZAB-SE mass spectrometer. The system consists of a vacuum lock system and a FAB probe whose tip contains five or more sample wells. The probe enters the mass spectrometer source region perpendicular to the secondary ion beam axis, The probe is maintained at high voltage on contact with a spring clip attached to the screen plate of the source block. Sample throughput with the multisample probe is twice that of a coaxial probe, with about twice the sensitivity and no sample cross contamination. 相似文献
109.
2,5-Dihydro-5-oxo-1,2,4-triazine and some of its alkylated derivatives have been prepared. Nmr spectroscopic analysis has established that the 2,5-dihydro-5-oxo tautomers are preferred over the 4,5-dihydro-5-oxo ones. This preference, and the behavior of 1,2,4-triazines in some other chemical reactions has been interpreted in terms of electron-electron repulsions between the lone pairs of electrons of N1 and N2 in this ring system. 相似文献
110.
William R. Dolbier Jr. Jian-Xin Duan Xiao X. Rong 《Journal of fluorine chemistry》2007,128(10):1091-1093
Selective, high yield partial fluorination of p-bis-(trichloromethyl)benzene to p-bis-(chlorodifluoromethyl)benzene has been accomplished by warming a slurry of the p-bis-(trichloromethyl)benzene in anhydrous HF which also contains a small quantity of inert solvent, such as 1,2-dichloroethane. 相似文献