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201.
W. A. SUMMERS JR. C. ENWALL J. G. BURR R. L. LETSINGER 《Photochemistry and photobiology》1973,17(5):295-301
Abstract— Quantum yields for 254 nm ultraviolet photoaddition of the nucleophiles hydrazine, HCN, HSO3 - , methyl amine, and BH4 - to uracil have been measured; the quantum yields for hydrazine, HCN, and HSO3 - additions are pH-dependent. The nucleophiles sulfide, azide, chloride, bromide, iodide, nitrite and thiocyanate failed to photo–add under similar conditions. These reactions are interpreted as 1,4-additions to the conjugated enone system of the anti-aromatic compound, uracil; as suggested by S. Y. Wang (Wang and Nnadi, 1968). The nuclear magnetic resonance (NMR) spectrum of the photohydrate of uracil-5-d-showed that the proton was added to the 5-position in a stereochemically random manner. The photoaddition of HSO3 - takes place at much lower concentrations than required for the thermal addition of this anion and is also stereochemically random. 相似文献
202.
The effects of hetero atoms within the substrate molecule and the number of available hydrogen atoms in the hydrogen abstraction reaction are considered. Chlorodifluoromethyl radicals are generated by the photolysis of 1,3-dichlorotetrafluoroacetone and the substrate molecules used are dimethyl ether, trimethylamine and tetramethylsilane. The Arrhenius parameters for the hydrogen abstraction reaction have been calculated and compared with those obtained using other radicals. The role of secondary radical decomposition is considered. 相似文献
203.
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
204.
The integrated ion current method is applied to the determination of mug quantities of mercury(II) chloride. The mass spectra of both mercury(I) and (II) chlorides indicate that the analytical reagent grade chemicals contain traces of mercury(II) bromide and iodide. 相似文献
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206.
F. Rupp E. Lehmann St. kramovský R. Uzel G. Spacu V. Armeanu M. Stschigol G. Denigès und Vl. Majer 《Fresenius' Journal of Analytical Chemistry》1936,106(1-2):64-68
Ohne Zusammenfassung 相似文献
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Schuster DI Wallraff A Blais A Frunzio L Huang RS Majer J Girvin SM Schoelkopf RJ 《Physical review letters》2005,94(12):123602
We have performed spectroscopy of a superconducting charge qubit coupled nonresonantly to a single mode of an on-chip resonator. The strong coupling induces a large ac Stark shift in the energy levels of both the qubit and the resonator. The dispersive shift of the resonator frequency is used to nondestructively determine the qubit state. Photon shot noise in the measurement field induces qubit level fluctuations leading to dephasing which is characteristic for the measurement backaction. A crossover in line shape with measurement power is observed and theoretically explained. For weak measurement a long intrinsic dephasing time of T2>200 ns of the qubit is found. 相似文献