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991.
Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br?2 · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO2H=CR'CO2H) in aqueous solution. 相似文献
992.
Summary Two high-performance liquid chromatography (HPLC) techniques were developed for the determination of binding constants in
the interaction of serum albumin with L-tryptophan: internal calibration and external calibration. The results obtained were
compared with those obtained by the classical method of equilibrium dialysis and by gel filtration. While all the methods
are equally reliable, the internal and external calibration techniques seem to be superior in their simplicity, speed and
convenience. 相似文献
993.
We describe a space of functions contained inxxLx
(D)C(D G) but not necessarily inU. We give a representation of these functions as bounded multiplication operators on the Bergman spacexxLx
a
2
and identify the subspace consisting of functions which induce compact multiplication operators. We also describe a newC
*-subalgebra ofxxLx
(D) which we conjecture to be a proper super-set ofU.Most of this research was done while the second author was visiting Cleveland State University. He would like to thank the Mathematics Department for its hospitality. He would also like to thank the NNSFC for partial support. 相似文献
994.
995.
996.
997.
998.
Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Wang P Zoeller MM Crawford G Fulton R Gan KK Kagan H Kass R Lee J Malchow R Morrow F Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Skubic P Snow J Bortoletto D Brown DN Dominick J McIlwain RL Miao T Miller DH Modesitt M Schaffner SF Shibata EI Shipsey IP Battle M Ernst J Kroha H Roberts S Sparks K Thorndike EH Wang C Artuso M Goldberg M Haupt T Horwitz N Kennett R Moneti GC Playfer S Rozen Y Rubin P 《Physical review D: Particles and fields》1992,46(11):4822-4827
999.
Sun Huibin Liu Yunzuo Zhou Jiewen Wu Yaodong 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(2):141-144
Theγ-rays emitted in theβ-decay of182Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in182W observed in theβ-decay of182Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of182Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 2 + →2 1 + ) deexciting theβ-band head in182W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements. 相似文献
1000.
Shao-Chen Yang Qihuang Gong Zongju Xia Y. H. Zou Y. Q. Wu D. Qiang Y. L. Sun Z. N. Gu 《Applied physics. B, Lasers and optics》1992,55(1):51-53
The nonlinear third-order optical susceptibility of C70 in a toluene solution is measured for the first time by the method of degenerate four-wave mixing using 10 ns laser pulses at 1.06 m. The third-order susceptibility X
in
(3)
is 5.6×10–12 esu for a C70 toluene solution at a concentration of 0.476 g/l. The correspondent magnitude of the hyperpolarizability 1111 of the C70 molecule is 1.2×10–30 esu which is in a good agreement with the prediction given by the model of a free electron in a spherical box. 相似文献