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141.
The 3,3′,5,5′-tetramethylenebiphenyl tetraanion, prepared in good yield by metallation-elimination, gives tetrasubstituted biphenyl derivatives, e.g., with H2O, D2O, methyl iodide, and trimethylsilyl chloride. The reaction sequence, starting from alkylated cyclohexanones, provides a general synthetic route to symmetrical polysubstituted biphenyls. 相似文献
142.
Clark SM Leaist DG Konermann L 《Rapid communications in mass spectrometry : RCM》2002,16(15):1454-1462
This work describes a novel approach for monitoring analyte diffusion in solution that is based on electrospray ionization mass spectrometry (ESI-MS). A mass spectrometer at the end of a laminar flow tube is used to measure the Taylor dispersion of an initially sharp boundary between two solutions of different analyte concentration. This boundary is dispersed by the laminar flow profile in the tube. However, this effect is diminished by analyte diffusion that continuously changes the radial position, and hence the flow velocity of individual analyte molecules. The steepness of the resulting dispersion profile therefore increases with increasing diffusion coefficient of the analyte. A theoretical framework is developed to adapt the equations governing the dispersion process to the case of mass spectrometric detection. This novel technique is applied to determine the diffusion coefficients of choline and cytochrome c. The measured diffusion coefficients, (11.9 +/- 1.0) x 10(-10) m(2) s(-1) and (1.35 +/- 0.08) x 10(-10) m(2) s(-1), respectively, are in agreement with the results of control experiments where the Taylor dispersion of these two analytes was monitored optically. Due to the inherent selectivity and sensitivity of ESI-MS, it appears that the approach described in this work could become a valuable alternative to existing methods for studying diffusion processes, especially for experiments on multicomponent systems. 相似文献
143.
Synthesis of a new fluorescent probe specific for catechols 总被引:1,自引:0,他引:1
[reaction: see text] The synthesis of a new fluorescent probe, specific for the catechol moiety, has been conducted by preparation of alpha,alpha-dibromomalonamides containing an appropriate fluorophore. N,N'-Bis-anthracen-9-ylmethyl-2,2-dibromomalonamide reacted with various catechols in the presence of cesium carbonate to generate highly fluorescent derivatives. 相似文献
144.
Tripathi S Armstrong DS Christy ME Clark JH Gorringe TP Hasinoff MD Kovash MA Wright DH Zołnierczuk PA 《Physical review letters》2002,89(25):252501
We report the first observation of double radiative capture on pionic hydrogen. The experiment was conducted at the TRIUMF cyclotron using the RMC spectrometer and detected gamma-ray coincidences following pi(-) stops in liquid hydrogen. We found the branching ratio for double radiative capture to be [3.05+/-0.27(stat)+/-0.31(syst)]x10(-5). The measured branching ratio and angle-energy distributions support the theoretical prediction of a dominant contribution from the pipi-->gammagamma annihilation mechanism. 相似文献
145.
Aubert B Boutigny D Gaillard JM Hicheur A Karyotakis Y Lees JP Robbe P Tisserand V Palano A Chen GP Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Reinertsen PL Stugu B Abbott B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Clark AR Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kluth S Kolomensky YG Kral JF LeClerc C Levi ME Liu T Lynch G Meyer AB Momayezi M Oddone PJ Perazzo A Pripstein M Roe NA Romosan A Ronan MT Shelkov VG Telnov AV Wenzel WA Zisman MS 《Physical review letters》2002,88(10):101805
The branching fractions of the exclusive decays B0-->K(*0)gamma and B+-->K(*+)gamma are measured from a sample of (22.74+/-0.36)x10(6) BB decays collected with the BABAR detector at the PEP-II asymmetric e(+)e(-) collider. We find B (B0-->K(*0)gamma) = [4.23+/-0.40(stat)+/-0.22(syst)]x10(-5), B(B+-->K(*+)gamma) = [3.83+/-0.62(stat)+/-0.22(syst)]x10(-5) and constrain the CP-violating charge asymmetry to be -0.170K(*)gamma)<0.082 at 90% C.L. 相似文献
146.
In order to correlate/predict electrophoretic mobility data in the mixture of water+organic modifier four equations have been presented and examined. The experimental mobilities of five analytes were determined in a water-methanol mixture. These data have been used to assess the accuracy and predictability of the models. Also, some previously published mobility data in water-organic modifier mixtures has been employed for further evaluation of the models. The models produced accurate results and the means of percentage deviations were in the range of 0.66-1.30. 相似文献
147.
Joseph A. Clark 《Physics letters. A》1981,83(3):139-141
A new mechanism for exciting cavitation has been identified. Surface-reflected shock waves can produced localized spalling in liquids. This spalling mechanism forms cavities which then collapse under the influence of gravity and atmospheric pressure. The form of the closure pulses generated by cavity collapse characterizes this new type of cavitation. 相似文献
148.
The global stability of the uniform ground state of nuclear matter is tested relative to a π0-condensed state characterized by static spin-(isospin-) waves. Strong nuclear correlations are introduced into the trial wave functions for each phase, thereby permitting models of the realistic two-nucleon force to be employed. In low cluster-order comparison, the uniform phases of symmetrical nuclear matter and neutron matter are emphatically favored over the entire density range considered. 相似文献
149.
The hyperfine structure of 161Dy and 163Dy for five transitions hasbeen measured with a tunable dye laser and a thermal velocity atomic beam. Values for the magnetic dipole and electric quadrupole coupling constants have been determined for the relevant excited states. The hyperfine anomaly parameters, Δ, which are extracted are interpreted in terms of available atomic wave functions. 相似文献
150.
Syntheses are described for the “slow reacting substances” 11--leukotriene C (3) (previously known as leukotriene C-2) and leukotriene D (4), the cys-gly analog of leukotriene C (2). The synthesized leukotrienes 3 and 4 were instrumental in the assignment of structure to these members of the family of naturally occuring slow reacting substances which includes also 2. 相似文献