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Noora Virtanen Ville Nevalainen Taru Lehtinen Satu Mikkola 《Journal of Physical Organic Chemistry》2007,20(1):72-82
Transesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H2O and D2O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pKa), as the buffer concentration increases. The kinetic solvent deuterium isotope effect kH/kD, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Ruthenium (III) tris acetylacetonate is an efficient catalyst for the isomerization of O-deuterated alkylvinyl carbinols allowing thus a facile route to the title compounds. 相似文献
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The perfect matchings in the n-cube have earlier been enumerated for n?≤?6. A dynamic programming approach is here used to obtain the total number of perfect matchings in the 7-cube, which is 391 689 748 492 473 664 721 077 609 089. The number of equivalence classes of perfect matchings is further shown to be 336 in the 5-cube, 356 788 059 in the 6-cube and 607 158 046 495 120 886 820 621 in the 7-cube. The techniques used can be generalized to arbitrary bipartite and general graphs. 相似文献
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Dr. Alexia Ville Dr. Julien Annibaletto Dr. Sébastien Coufourier Prof. Christophe Hoarau Dr. Rodolphe Tamion Dr. Guillaume Journot Dr. Cédric Schneider Dr. Jean-François Brière 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):13961-13965
An efficient primary-amine-directed, palladium-catalyzed C−H halogenation (X=I, Br, Cl) of phenylalanine derivatives is reported on a range of quaternary amino acid (AA) derivatives thanks to suitable conditions employing trifluoroacetic acid as additive. The extension of this original native functionality-directed ortho-selective halogenation was even demonstrated with the more challenging native phenylalanine as tertiary AA. 相似文献
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We consider a tier of weakened bonds along the center line of a two-dimensional Ising ferromagnet strip as a model of a grain boundary. When an interface traverses such a strip at an angle, whether or not there is a continuous pinning-depinning transition at subcritical temperature depends on this angle and the degree of bond weakening. We also study the relaxation of such a system to its equilibrium state using continuous time Monte Carlo simulation with Kawasaki dynamics; this reveals a matter transport mechanism confined to the grain boundary. 相似文献
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F. Schilling Oskar Rudolf Adler William Küster Kratter Jeserich Popp Piettre J. Ville und E. Derrien 《Fresenius' Journal of Analytical Chemistry》1905,44(8-9):582-585
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The diffraction of sound from an edge of a thin chipboard panel was measured in an anechoic chamber, and compared to simulations based on the diffraction formulation developed by Svensson et al. [Svensson UP, Fred RI, Vanderkooy J. An analytic secondary source model of edge diffraction impulse responses. J Acoust Soc Am 1999;106(5):2331-44]. The measurements and simulations were performed for a line of receiver positions below the panel to include cases for which the direct sound had an unobstructed propagation path to the receivers, as well as cases for which the direct sound was occluded by the panel. Comparison of the measured and simulated responses is provided in both the time and frequency-domains, and shows that the differences between them are small over the entire audible frequency range. This case study verifies that the applied diffraction-modeling method gives accurate results, and that the assumptions of ideal source and wedge characteristics inherent in the method do not preclude its use in simulations of realistic scenarios. 相似文献