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131.
Grosnick D Wright SC Bolton RD Cooper MD Frank JS Hallin AL Heusi PA Hoffman CM Hogan GE Mariam FG Matis HS Mischke RE Piilonen LE Sandberg VD Sanders GH Sennhauser U Werbeck R Williams RA Wilson SL Hofstadter R Hughes EB Ritter MW Highland VL McDonough J 《Physical review letters》1986,57(26):3241-3244
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The upper limit of momentum transfer by a proton to K-shell electrons is calculated in a restricted three-body classical model. The model shows that the infinite upper limit used in practice, is generally good except for low energy protons passing through an extremely rarefied gas. 相似文献
137.
R. J. Smith P. J. Woods R. Chapman J. L. Durell J. N. Mo B. R. Fulton R. A. Cunningham 《Zeitschrift für Physik A Hadrons and Nuclei》1986,324(3):283-287
The ground-state masses of35Si and34Si have been measured using the reactions64Ni(36S,35,34Si)65,66Zn at a36S beam energy of 198 MeV.34,35Si14+ ions were analysed and identified in a QMG/2 magnetic spectrometer and gas-filled focal-plane detector. The experimental mass excess of35Si was determined to be ?14.58± 0.12 0.07 MeV while that of34Si was measured as ?19.961±0.034 MeV. A comparison is made with the results of mass model predictions. 相似文献
138.
In an effort to exploit the enhancement in catalytic activity which might be derived through hydrophobic interactions between polymeric catalyst and substrate, 1-methyl-5-vinylimidazole (1-Me-5-VIm), 1-methyl-4-vinylimidazole (1-Me-4-VIm), 1-butyl-5-vinylimidazole (1-Bu-5-VIm), and 1-butyl-4-vinylimidazole (1-Bu-4-VIm) have been synthesized and polymerized. In 28.5% ethanol-water, poly(1-alkyl-5-vinylimidazoles)proved to be efficient catalysts for the hydrolysis of various 3-nitro-4-acyloxybenzoic acids (Sn-, where n denotes the acyl chain length). Order of magnitude rate enhancements, as compared to the model compound, 1,5-dimethylimidazole (1,5-DMIm) were observed in the poly(1-alkyl-5-vinylimidazole)-catalyzed solvolysis of S12- and S18-. Poly(1-Me-5-VIm) catalyzes the hydrolysis of S18-88 times faster than does 1,5-DMIm. The poly(1-Me-5-VIm)-catalyzed hydrolysis of S18- in ethanol-water was analyzed in terms of a simple Michaelis-Menten type mechanism. Vmax and Km were determined to be 40.2 X 10(-7) M min-1 and 2.20 X 10(-5) M, respectively. 相似文献
139.
In earlier work we nave described and partially characterized two histone kinases from regenerating rat liver and other tissues which catalyze the transfer of the γ-phosphoryl group from ATP to histones. The histone phosphates thus formed were observed to be acid-labile and base-stable. In the present study we report on the specificity of one of these enzymes, namely, the kinase which is optimally active at pH 9. This enzyme appears to be relatively specific for the two histidine residues of histone H4. These histidines occur at positions 18 and 75, and both are phosphorylated. However, when regenerating rat liver was the source of enzyme, the product was 1-phosphohistidine, whereas the enzyme from Walker-256 carcinosarcoma catalyzed the formation of 3-phosphohistidine. 相似文献
140.
Macomber RS Constantinides I Bauer JK Smith G Button A Lindstrom DO 《The Journal of organic chemistry》1996,61(2):727-734
The reaction of the title diketone (3) with phenyl Grignard produces (with rate constant k(1)) the conjugate base (6-M) of 10-hydroxy-10-phenylcyclooctadecanone (6), which is subsequently converted (with rate constant k(2)) to the conjugate base of the title diol, as a mixture of the cis (7, 55%) and trans (8, 45%) isomers. The ratio k(2)/k(1), 2.2 +/- 0.4, indicates that the carbonyl group in 6-M is 4.4 times as reactive as each carbonyl in 3. Competition experiments further demonstrate that the relative rates (per carbonyl) for addition of phenylmagnesium bromide to 3, 10-methylenecyclooctadecanone (11), and cyclopentadecanone (12) are 1.0:0.60:1.92. Possible reasons for this order of reactivity are discussed. Diols 7 and 8 undergo facile double dehydration to form the title diene 13, which is predicted by molecular mechanics calculations to be the most stable of the four possible symmetrical diene isomers. The structures of 7, 8, and 13 were secured by single-crystal X-ray studies. 相似文献