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211.
Joel D. Smith George Durrant Daniel H. Ess Benjamin S. Gelfand Warren E. Piers 《Chemical science》2020,11(39):10705
The synthesis and characterization of an iridium polyhydride complex (Ir-H4) supported by an electron-rich PCP framework is described. This complex readily loses molecular hydrogen allowing for rapid room temperature hydrogen isotope exchange (HIE) at the hydridic positions and the α-C–H site of the ligand with deuterated solvents such as benzene-d6, toluene-d8 and THF-d8. The removal of 1–2 equivalents of molecular H2 forms unsaturated iridium carbene trihydride (Ir-H3) or monohydride (Ir-H) compounds that are able to create further unsaturation by reversibly transferring a hydride to the ligand carbene carbon. These species are highly active hydrogen isotope exchange (HIE) catalysts using C6D6 or D2O as deuterium sources for the deuteration of a variety of substrates. By modifying conditions to influence the Ir-Hn speciation, deuteration levels can range from near exhaustive to selective only for sterically accessible sites. Preparative level deuterations of select substrates were performed allowing for procurement of >95% deuterated compounds in excellent isolated yields; the catalyst can be regenerated by treatment of residues with H2 and is still active for further reactions.The synthesis and characterization of an iridium polyhydride complex (Ir-H4) supported by an electron-rich PCP framework and capable of mild hydrogen/deuterium exchange catalysis is described. 相似文献
212.
C. T. LIN Y. G. CHYAN G. C. KRESHECK HERBERT C. BITTING JR M. A. EL-SAYED 《Photochemistry and photobiology》1989,49(5):641-648
Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism. 相似文献
213.
Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2392-2395
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218.
M.C. Durrant H.W. Kroto D. McNaughton J.F. Nixon 《Journal of Molecular Spectroscopy》1985,109(1):8-14
The new long-chain molecule 1-cyano-4-phosphabutadiyne has been produced by copyrolysis of phosphorus trichloride, PCl3, and 1-cyanoprop-1-yne, CH3CCCN at 1000°C in a flow system. The species was detected by microwave spectroscopy, which indicated that the yield was low and that several other linear species were also produced. The ground state lines as well as vibrational satellites (up to v9 = 4 and v8 = 2) in the region 26.5–40 GHz have been assigned, and structural parameters have been estimated. B0 = 873.48034(27) MHz and D0 = 0.01282(35) KHz. 相似文献
219.
Nonlinear Faraday rotation with counter-propagating light beams was investigated in a rubidium vapor cell. Observations across all hyperfine and crossover resonances of the D2 line of 87Rb atoms were made. Additionally, rotation spectra as a function of pump and probe intensity, pump polarization and external magnetic field strength were studied.The investigations were performed in a regime where the pump beam power was sufficiently low relative to the probe power to avoid polarization rotation due to pump-induced anisotropy. Our results are analyzed in the context of Bennett structures and coherent optical processes. 相似文献
220.
Abstract Humic substances are the major organic constituents of soils and sediments. They also occur in small concentrations in natural surface waters and groundwaters. They form through the breakdown of plant and animal tissues by chemical and biological processes that tend to produce complex chemical structures that are more stable than the original material from which they were derived. One of the more important characteristics of humic substances is their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and various organic compounds such as alkanes, fatty acids, and toxic organic substances such as pesticides. 相似文献