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1.
Qun Dang Zhibo Zhang Bingyu Tang Yang Song Ling Wu Tongqian Chen Stephane Bogen Vinay Girijavallabhan David B. Olsen Peter T. Meinke 《Tetrahedron letters》2014
To discover novel nucleosides as potential antiviral agents, 2′-spirolactam and 2′-spiropyrrolidine-containing nucleoside analogs were envisioned. Efficient synthetic routes were developed with an epoxide opening as the key step to establish the quaternary center at the 2′ position, leading to the design and synthesis of uridine analogs 8 and 21, prodrugs 13–16, and cytidine analog 11. 相似文献
2.
Qun Dang Zhibo Zhang Shuangsheng He Yaohong Liu Tongqian Chen Stephane Bogen Vinay Girijavallabhan David B. Olsen Peter T. Meinke 《Tetrahedron letters》2014
To discover novel nucleosides as potential antiviral agents, 4′-spirocyclic phosphono-nucleosides were designed to mimic the monophosphate of R-1479, a known nucleoside inhibitor of HCV NS5B. Bypassing the first kinase step to nucleoside monophosphate is viewed as advantageous since this phosphorylation is often observed as the rate-limiting transformation to the active NTP for many nucleosides. Efficient synthetic routes were developed with a triphenylphosphine–iodine cyclization reaction as the key step to form the tetrahydrofuran 4′-spirocycle. The desired 4′-spirocyclic phosphono-cytidine analogs 12a, 12b, and 16 were prepared in 11 steps. 相似文献
3.
Analyses have been made for trace metals in surface waters from lakes known to be sensitive to inputs of acidic deposition. Electrothermal atomic-absorption spectrometry was used for direct measurement of the low metal concentrations. The studies revealed non-spectral interferences resulting from small amounts of inorganic material in the sample matrix that prevent accurate measurements of Mn and Pb. Several types of interferences were identified by means of a computer coupled to the atomic-absorption spectrometer and procedures to overcome them were evaluated. Matrix modification with nitric acid is required for the determination of Mn. Atomization from a platform inserted within the graphite tube is necessary for interference-free Pb determination. 相似文献
4.
Global fallout plutonium, most of which was produced by large thermonuclear tests injecting submicron particles into the stratosphere, can be readily extracted from soil by strong acid leaching. Some nuclear tests conducted at the Nevada Test Site (NTS) produced fallout in offsite regions that does not yield its total plutonium content to an acid leach. We theorize that those detonations occurred near the desert surface and incorporated fused silicate soil particles, many >1 m, into the mushroom cloud and stem. We have assembled a radiochemical procedure to insure the complete dissolution of plutonium in 50g of acid leached soil residue. The results of a complete analysis of the leachate and leached residue from soil collected near NTS and the eastern United States illustrate the impact of these particles on the plutonium values obtained by the two methods. 相似文献
5.
The oxidation of Co(poly) and Co(100) surfaces has been investigated using AES within the temperature range 300–700 K. It is found that at both surfaces the initial step — dissociative adsorption of oxygen — exhibits identical kinetics, independent of temperature. Approaching the oxide layer formation regime, temperature and surface structure of the substrate as well determine the oxygen uptake. With the aid of sputter profiling through the oxidized surface layers it is seen that at both, single crystal and polycrystal, oxygen is present even far below the actual surface. The diffusion of oxygen into the bulk is found to be faster at the polycrystalline sample. 相似文献
6.
The absolute intensity of a vacuum sliding spark (length 2–10 cm, half cycle 0,8 μsec) has been measured in the spectral region between 0,4 and 3μ. From the long wavelength radiation emitted from an optically thick layer, one gets the temperature, from the short wavelength radiation emitted from an optically thin layer, one obtains the density. Using polyethylene as an insulator we reached a temperature of 4·105 °K at electron densities of 8·1018 cm?3 and current densities of 1.2·106 A/cm2. The temporal development of temperature and density has been determined. The maximum intensity at λ=0.43 μ was found to be 5·104 (7·1010 W/cm3 ster) as large as that of the positive crater of a properly driven carbon arc. At λ=3 μ this same parameter turned out to be 300 times as large (5·107 W/cm3 ster). 相似文献
7.
8.
An efficient method for calculating the Lagrange multipliers and the analytical gradients of one state included in a state average MCSCF wave function is presented. It is demonstrated that the state average energy of an ‘equal-weight’ scheme is invariant to rotations within the state average subspace and that the corresponding rotations should be eliminated from the Lagrangian equations. Finally, a diagnostic is presented, which gauges the energy difference between a state defined by a state average calculation and the corresponding fully variational multi-configurational SCF state. 相似文献
9.
A set of N-substituted benzoperylene monoimide (BPI) fluorophores was synthesized and characterized structurally and photophysically. Condensation of benzo[ghi]perylene-1,2-dicarboxylic anhydride in the presence of "swallow tail" alkyl amines produced fluorophores that are soluble in a range of organic solvents, highly absorbing in the near-UV (ε(334) = 79,000 M(-1) cm(-1)), and fluorescent in the visible range. Photophysical behavior of the compounds was studied with steady-state and time-correlated single photon counting. The synthesized BPIs exhibit positive solvachromatic emission (λ(em) (hexane) = 469 nm; λ(em) (ethanol) = 550 nm) as a function of solvent polarity with little change in their excited-state lifetime (9.6-6.5 ns) and fluorescence quantum yield (0.27-0.44) over the polarity range studied. Solvachromatic shifts were analyzed using the Lippert-Mataga approach. In nonpolar hydrocarbon solvents evidence of dual emission from closely spaced (562 cm(-1)) S(1) and S(2) excited states is observed. Preliminary peak assignments for the anomalous S(2) emission are made. 相似文献
10.
ChemInform Abstract: X-Ray Structural Studies of the Polymorphic Elpasolites K2LiAlF6 and Rb2LiGaF6.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献