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991.
Jacob St-Gelais Émilie Côté Danny Lainé Prof. Paul A. Johnson Prof. Denis Giguère 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(59):13499-13506
In this work, we synthesized all mono-, di-, and trifluorinated glucopyranose analogues at positions C-2, C-3, C-4, and C-6. This systematic investigation allowed us to perform direct comparison of 19F resonances of fluorinated glucose analogues and also to determine their lipophilicities. Compounds with a fluorine atom at C-6 are usually the most hydrophilic, whereas those with vicinal polyfluorinated motifs are the most lipophilic. Finally, the solvation energies of fluorinated glucose analogues were assessed for the first time by using density functional theory. This method allowed the log P prediction of fluoroglucose analogues, which was comparable to the C log P values obtained from various web-based programs. 相似文献
992.
Joshua W. M. MacMillan Katherine M. Marczenko Prof. Dr. Erin R. Johnson Prof. Dr. Saurabh S. Chitnis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(71):17134-17142
The addition of Sb−H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring open-shell neutral intermediates. Density-functional theory (DFT) calculations are consistent with this model, predicting an activation barrier that is in agreement with the experimental value (Eyring analysis) and a rate limiting step that is congruent with the experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring SbII and SbIII intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a synthetic methodology. 相似文献
993.
994.
The proton and carbon-13 NMR spectra of 2,3,6 -tri-O-methyl-β-cyclodextrin in deuteriochloroform have been fully and unambiguously assigned using homonuclear and selective heteronuclear spin decoupling and two-dimensional homo- and heteronudear correlation NMR spectroscopy. Corrections are made to some earlier literature assignments. 相似文献
995.
996.
David C. Johnson II 《Tetrahedron letters》2004,45(46):8483-8487
The benzyl groups of β-hydroxy-N-benzyl sulfonamides are labile toward hydrogenolysis-unlike N-benzyl sulfonamides lacking the β-hydroxy moiety. We find that N-acyl-N-benzyl sulfonamides undergo hydrogenolysis under very mild conditions. Based upon these observations, we developed a reversible safety-catch method using tert-butoxycarbonyl moieties to activate N-benzyl sulfonamides toward hydrogenolysis. We also explored the utility of the safety-catch activation method for other nitrogen-based functionality such as N-benzyl carboxamides, imides, and related functionality. 相似文献
997.
998.
N. Hayashi I. Sakamoto E. Johnson L. Graabak P. Børgesen B. M. U. Scherzer 《Hyperfine Interactions》1988,42(1-4):989-992
γ (fcc)→α (bcc) phase transformation in type 304 stainless steel has been observed after irradiation of He+ and H+ ions up to fluence levels of 1017 and 1019 ions/cm2, respectively. Depth selective conversion Mössbauer spectroscopy and surface-sensitive X-ray diffractometry were employed to study the effect of irradiation. It is shown that the amount of the ion induced phase is highly sensitive to the fluence, the ion species and depth from the surface. It is worth noting that H+ ion irradiation is rather ineffective in inducing the transformation. 相似文献
999.
Use of a urea and guanidine-HCl-propanol solvent system to purify a growth inhibitory glycopeptide by high-performance liquid chromatography 总被引:1,自引:0,他引:1
Reversed-phase high-performance liquid chromatography was used to purify an inhibitory glycopeptide where resolution and recovery were enhanced by using urea or guanidine-HCl-isopropanol-water as a solvent system. Isopropanol alone or other solvent systems that have been proposed for such purification steps were not effective in eluting hydrophobic proteins from the reversed-phase column. The application of the urea or guanidine-HCl solvent systems in the separation and purification of membrane proteins, and other hydrophobic macromolecules, could greatly enhance recovery and efficiency of purification. 相似文献
1000.
Summary From kinetic studies of18O-exchange between aqueous solutions of K12V18O42 · 16H2O and water it is concluded that [V18O42]12– exists as a discrete ion in this medium. The rate of exchange is relatively slow (t1/2
ca. 6×104s at 0°C) and obeys the McKay equation within the precision obtainable. The sensitivity of the ion to its environment in the solid state, leading to induced exchange, prevented a decision as to whether all oxygens are kinetically equivalent. It is clear, however, that the ions remains intact for long periods in solution in the absence of air. 相似文献