Water, photolysis spectroscopy

In comparison, photolysis of 83 in protic solvents such as methanol, ethanol, and water yields 84 as expected, but 84 forms mainly 87 rather than 85. Furthermore, in these solvents, the transient absorption (Amax 425 nm) due to 84 decays not with a second-order rate law but by biexponential decay. For example, the decay of transient absorption of 84 (A ax 420 nm) in water at pH 7 had rate constants of 2 x 10 and 3 x lO s Subsequent to the decay of 84, a transient absorption was formed with Amax 330 nm and a weak absorption band at 740 nm. However, this transient was formed much slower than 84 decayed. The absorption at 330 nm was described as a biexponential growth with rate constants of 584 and 21 s h The authors assigned this absorption to 88. Since 84 and 88 do not form and decay at the same rate, the authors theorized that 84 decays into 87, which then furnishes 88. Even though intermediate 87 does not absorb in the near UV, the authors characterized it with time-resolved IR spectroscopy. The authors demonstrated that, in hexane and a strongly acidic or basic aqueous solution, the photorelease from 83 goes through the formation of 87, whereas in near neutral aqueous solution, formation of 85 predominates. The authors concluded that the dehydration of intermediates 85 and... 

Recently, isolable bis (triphenylstannyl)-substituted butatrienylidene complexes of manganese (13) were obtained by photolysis of alkynyl(triphenylstannyl)vinylidene complexes 12 (Scheme 3.9) [4, 5]. Treatment of the resulting bis(stannyl)butatrie-nylidene complexes 13 with tetrabutylammonium fluoride and water afforded the first characterizable butatrienylidene complexes (14) containing an unsubstituted [M=C=C=C=CH2] moiety (Scheme 3.9). In contrast to 13, complexes 14 were unstable above —5 °C and were therefore characterized in solution only by NMR spectroscopy at —40°C. Complexes 14 were also formed instantaneously when solutions of 12 were treated at — 30 °C with one equivalent of tetrabutylammonium fluoride. 

Levenson, M. D., and Eesley, G. L. 1979. Polarization selective optical heterodyne detection for dramatically improved sensitivity in laser spectroscopy. Appl. Phys. 19 1-17. Librizzi, R, Viapianni, C., Abbruzzetti, S., and Cordone, L. 2002. Residual water modulates the dynamics of the protein and of the external matrix in trehalose-coated MbCO An infrared and flash-photolysis study. J. Chem. Phys. 116 1193-1200. 

EPA. 1995. Draft guidelines Direct photolysis rate in water by sunlight. OPPTS 835.2210 maximum direct photolysis rate in air from UV/VIS spectroscopy. OPPTS 835.2310. U.S. Environmental Protection Agency, Washington, D.C. 

Binding of the components in a neutral aqueous solution was confirmed by potentiometric titrations. The feasibility of electron transfer between the components was predicted by cyclic voltammetry and an efficient outer-sphere fast electron transfer was foreseen. Fluorescence spectroscopy measurements showed that the formation of a defined donor-acceptor complex worked even in water at neutral pH. Electron transfer as the quenching mechanism was proved by laser flash photolysis. 

The guanine moiety has the lowest ionization potential of any of the DNA bases or of the sugar-phosphate backbone. As a result, radiation-produced holes are stabilized as dG for hydrated DNA irradiated at 77 K There is an extensive literature describing the role of dG in the radiation chemistry of DNA as studied by pulse radiolysis, flash photolysis, and product analysis. In order to explicate the oxidative reaction sequence in irradiated DNA and to more firmly identify the relevant radical intermediates, ESR spectroscopy was employed to investigate y-irradiated hydrated DNA (T = 12 2). Some experiments were also performed on hydrated (T = 12 2) DNA in which an electron scavenger [thallium(ni) (TP )] was employed to isolate the oxidative path. Oxygen-17 isotopically enriched water was also used to confirm a proposed water addition step to G and the subsequent transformations that follow These experiments were run in oxygen-free samples under conditions for which indirect effects were unimportant. 

Carabine and Norrish found results somewhat different from those of the other studies. Furthermore, they also found that a small amount of O3 accelerated the non-explosive reaction, but did not raise the upper ignition limit. They studied the flash photolysis of B2H6-O2 mixtures with radiation below 2000 A. Intermediates BH, OH, BO, and BO2 were monitored by absorption spectroscopy. Water was not a final product of the reaction unless the B2H6 was completely consumed. Almost surely it was produced, but was removed in a rapid reaction with B2H6. 

Laser-flash photolysis of (203) in solution affords the ketene (204) and this is the first time that this ketene has been observed using time-resolved IR spectroscopy, Although other workers have previously reported the formation of this species. The present work reports the kinetics of the reaction of the ketene with water, methanol and diethylamine. The products obtained from the irradiation of a series of AT-acetoacetyl-a-amino acids have been identified by gas chromatography and chemical ionization mass spectrometry. ... 

The structure of oxidized radicals obtained by reaction in water of hy-droxypyrimidines with HO, 0 , S04 , Br2 (generated by in situ photolysis or radiolysis) have been determined by EPR spectroscopy. 2-Hydroxypyrimidine... 

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