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901.
Barrett AG Ahmed M Baker SP Baugh SP Braddock DC Procopiou PA White AJ Williams DJ 《The Journal of organic chemistry》2000,65(12):3716-3721
4-Alkenyl-2-azetidinone systems were converted to the corresponding ethyl 2-?4-alkenyl-2-oxo-1-azetidinyl-4-pentenoates. In addition, 4-(2-propenyl-1-oxy)-, 4-(2-propenyl-1-thio)-, 4-?N-(2-propenyl)-(4-toluenesulfonyl)- and (3S, 4R)-4-(2-propenyl)-3-?(1R)-1-(tert-butyldimethylsilyloxy)ethyl-++ +azeti din-2-one were converted into beta-lactam dienes via sequential N-alkylation, Ireland-Claisen ester enolate rearrangement and esterification. Ring-closing metathesis using the Schrock ?(CF(3))(2)MeCO(2)Mo(=CHCMe(2)Ph)(=NC(6)H(3)-2,6-iso-Pr(2)) (1) or Grubbs Cl(2)(Cy(3)P)(2)Ru=CHPh (2) carbenes gave a series of ?5.2.0 and ?6.2.0 bicycles. Subsequent elaboration of the analogous (2R,7R, 8S)-tert-butyl 8-?(1R)-(tert-butyldimethylsilyloxy)ethyl-1-aza-9-oxobicyclo++ +?5.2. 0non-4-ene-2-carboxylate (15), via selenation and desilylation, gave (+)-(2S,7R,8S)-tert-butyl 8-?(1R)-hydroxyethyl-1-aza-9-oxobicyclo?5.2.0nona-2, 4-diene-2-carboxylate (18), a novel type of bicyclic beta-lactam. Diels-Alder cycloaddition further afforded tetracyclic systems exemplified by tert-butyl (1R,4S,5R,7S)-4-?(1R)-1-hydroxyethyl-3,9, 11-trioxo-10-phenyl-2,8,10,12-tetraazatetracyclo?5.5.2.0.(2, 5)0(8, 12)tetradec-13-ene-1-carboxylate (19). 相似文献
902.
Preston MA Kornbrekke R White LR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(22):9832-9842
The standard equations developed to describe the electrophoretic motion of a charged particle immersed in an electrolyte subjected to an oscillating electric field are solved numerically with a new technique suitable for stiff systems. The focus of this work is to use this solution to determine the dynamic particle mobility, one of several quantities that can be extracted from these equations. This solution is valid from low frequencies to indefinitely high frequencies and has no restriction on zeta potential, double-layer thickness, or electrolyte composition. The solution has been used to calculate the dynamic electrophoretic mobility of a particle for a wide range of double-layer thicknesses and zeta potentials. The solution agrees with analytic approximations obtained previously by other authors under the conditions of a thin double layer and low zeta potential. The results are also consistent with calculations valid at frequencies where the ion diffusion length extends a significant distance beyond the double layer as obtained by another numerical technique. 相似文献
903.
Izo I. Abram Robin M. Hochstrasser James E. Kohl Myron G. Semack David White 《Chemical physics letters》1980,71(3):405-408
Hydrogen crystals were pumped by stimulated Raman gain into coherent superpositions of the ground and 2 v = 1 vibrational exciton state and its amplitude monitored by coherent anti-Stokes scattering. The resulting non-exponential and temperature independent (1.6–4.2 K) decays, for o-H2 concentrations between 0.22 and 2.7%, were attributed to compositional scattering. 相似文献
904.
Gas chromatography/mass spectrometry (GC/MS) with negative ion chemical ionization permits detection of underivatized patulin in apple juice extracts while minimizing co-extractive responses. The technique has been used with a variety of capillary columns in quadrupole, ion trap, and magnetic sector GC/MS instruments to confirm presumptive findings of patulin in apple juice at concentrations ranging from 68 to 3700 micrograms/L. The demonstrated ability to use any of these 3 mass spectrometers and several capillary columns to confirm the identity of patulin are significant strengths of the technique. 相似文献
905.
906.
A method for the titration of arsenite and thiosulphate with iodine is recommended in which the iodine is extracted as Ph3MeAsl3 at the end-point. The method is satisfactory for titration with , and iodine solutions, in the presence of coloured ions of molar concentrations up to 200 times that of the iodine solution. Copper(II) ions interfere. A stable tri-iodide Ph3MeAsl3 has been prepared by two different methods. 相似文献
907.
Examination of selected cyclohexene derivatives which are fixed into the boat conformation reveals structural deviations from "normal" C-C bond distances consistent with the early stages of the retro Diels-Alder reaction. 相似文献
908.
T. L. White T. L. White K. B. Martin K. B. Martin L. N. Oji L. N. Oji D. P. DiPrete D. P. DiPrete W. R. Wilmarth 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(1):65-69
Summary One waste remediation process used at the Savannah River Site was the in-tank precipitation of the beta-emitting 137Cs from high-level waste (HLW) using sodium tetraphenylborate (NaTPB) followed by processing the resulting decontaminated
filtrate into grout at the Saltstone Production Facility (SPF). A simple method was developed for the monitoring of tetraphenylborate
(TPB) in high-level waste (HLW) containing up to 0.38 Ci/gal of 137Cs. Separation was achieved by extraction of the high sodium-bearing waste with acetonitrile followed by analysis using reversed-phase
high performance liquid chromatography (HPLC). The sample preparation method allowed for the handling of an organic extraction
layer that had 94% less acitivity than the HLW sample. The subsequent HPLC analysis of the extraction layer determined the
TPB concentration in HLW waste to 0.8 mg/l with a %rsd of 8. 相似文献
909.
Calculations of van der Waals forces in 2-dimensionally anisotropic materials and its application to carbon black 总被引:5,自引:0,他引:5
We present calculations of the van der Waals force for carbon black dispersions in both aqueous and nonaqueous media using Lifshitz theory. The microstructure and composition of carbon black are complex, but an initial approximation to the shell-like microstructure of carbon black allows the local interaction of carbon black particles to be approximated as oriented domains of graphite. The dielectric spectra for graphite, which has a 2-dimensional anisotropy due to its the layered microstructure, is required for the Lifshitz theory van der Waals force calculations. The anisotropic dielectric spectra of graphite (which behaves as a semiconductor) was constructed by modeling the conduction or free charge response separately from the polarization or bound charge response. The free charge response was modeled using the Drude model, while the dielectric spectra for the bound charge response was constructed from the spectroscopic data directly according to the Kramers-Kronig relation for the dielectric function, epsilon(omega). The expressions for calculating the fully retarded van der Waals force for half spaces with 2-dimensional dielectric anisotropy were derived as well as. The construction for the dielectric spectra of polystyrene from recent spectroscopic data from the literature according to the method outlined in (Dagastine, R. R., Prieve, D. C., and White, L. R., J. Colloid Interface Sci.231, 351 (2000)) is also presented. 相似文献
910.
Parsons JG Stachurska-Buczek D Choi N Griffiths PG Huggins DA Krywult BM Marino ST Nguyen T Sheehan CS James IW Bray AM White JM Boyce RS 《Molecules (Basel, Switzerland)》2004,9(6):449-458
The synthesis of (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methoxyphenyl)- propionic acid, (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methylphenyl)propionic acid and (2S)-2-benzyl-oxymethyl-3-(2,4-dimethylphenyl)propionic acid has been achieved by TiCl4 mediated alkylation of the corresponding (4R)-4-benzyl-3-[3-(2-fluoro-4-methoxyphenyl-, 2-fluoro-4-methylphenyl-, 2,4- dimethylphenyl-)propionyl]-2-oxazolidinones, followed by hydrolysis of the chiral auxiliary. The stereochemistry of the alkylation reaction was confirmed by an X-ray crystal structure of (4R)-4-benzyl-3-[(2S)-2-benzyloxymethyl-3-(2- fluoro-4-methylphenyl)propionyl]-2-oxazolidinone. 相似文献