Laser flash photolysis studies

Lu, C. Y. Lui, Y.Y. (2002). Electron transfer oxidation of tryptophan and tyrosine by triplet states and oxidized radicals of flavin sensitizers a laser flash photolysis study. Biochimica et Biophysica Acta (BBA) - General Subjects, Vol. 1571, No.l, (May 2002), pp. 71-76, ISSN 0304-4165... 

Despite the above, there is also considerable evidence to suggest that oxazole formation proceeds via an intermediate nitrile ylide, particularly in the catalysed reactions (see below). Nitrile ylides have been detected in laser flash photolysis studies of diazo compounds in the presence of nitriles, and stable nitrile ylides can be isolated in some cases.<94CRV1091>... 

Gratzel and Serpone and co-workers recently reported on a picosecond laser flash photolysis study of TiO. They observed the absorption spectrum immediately after the 30 ps flash and attributed it to electrons trapped on Ti" " ions at the surface of the colloidal particles. The absorption decayed within nanoseconds, the rate being faster as the number of photons absorbed per colloidal particle increased. This decay was attributed to the recombination of the trapped electrons with holes. 

El-Agamey, A. and McGarvey, D.J. 2003. Evidence for a lack of reactivity of carotenoid radicals towards oxygen A laser flash photolysis study of the reactions of carotenoids with acylperoxyl radicals in polar and non-polar solvents. J. Am. Chem. Soc. 125 3330-3340. 

Mortensen, A. 2000. Mechanism and kinetics of scavenging of the phenylthiyl radical by carotenoids. A laser flash photolysis study. Asian Chem. Lett. 4 135-143. 

Ikegami M, Arai T (2000) Laser flash photolysis study on hydrogen atom transfer of 2-(2-hydn>xyphenyl)benzoxazole and 2-(2-hydroxyphenyl)benzothiazole in the triplet excited state. Chem Lett 9 996-997... 

Alvaro, M., Atienzar, P., Bourdelande, J.L., and Garda, H. (2004) An organically modified single wall carbon nanotube containing a pyrene chromophore Fluorescence and diffuse reflectance laser flash photolysis study. Chem. Phys. Lett. 384, 119-123. 

Schnapp, K.A., and Platz, M.S. (1993) A laser flash photolysis study of di-, tri- and tetrafluorinated phe-nylnitrenes Implications for photoaffinity labeling. Bioconjugate Chem. 4, 178-183. 

Platz, M.S. Maloney, V.M. Laser Flash Photolysis Studies of Triplet Carbenes. In Kinetics and Spectroscopy of Carbenes and Biradicals, M.S. Platz, Ed. Plenum New York, 1990 ... 

Jackson, J.E. Platz, M.S. Laser Flash Photolysis Studies of Ylide-Forming Reactions of Carbenes. In Advances in Carbene Chemistry, U.H. Brinker, Ed. JAI Greenwich, CT, 1994 pp 89-160. 

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

Bhattacharyya, A.K., Lipka, J.J., Waskell, L. and Tollin, G. (1991) Laser flash photolysis studies of the reduction kinetics of NADPH cytochrome P-450 reductase. Biochemistry, 30 (3), 759-765. 

Previous studies of the photochemistry of alkylchlorodiazirines have shown that the yield of trappable carbene is sensitive to the alkylcarbene structure. A laser flash photolysis study of phenanthridenes (91), precursors of alkylchlorocarbenes, in the presence of pyridine, has ruled out the intermediacy of a carbene-pyridine complex which partitions between pyridine-ylide formation and [1,2]-H shift. ... 

Laser flash photolysis studies were performed on 2-cyano (8c), 4-cyano (8e) and 2,6-dicyanophenyl (8f) azide. The results are given in Table 6. In pentane the barrier to cyclization of orr/io-cyanophenylnitrene is the same, within experimental error, to that of parent phenylnitrene. The barrier to cyclization of 2,6-dicyanophenylnitrene (8f) is about 1 kcahmol larger than that of parent phenylnitrene ( PN). Variation of solvent has only a small effect on the kinetics. 

In the early 1990s, singlet aryl nitrenes had never been detected and the influence of structure on reactivity was only dimly appreciated. Laser flash photolysis studies in combination with theory has provided insight and has led to a comprehensive theory of substituent effects. We have been proud to be part of this process. 

A laser flash photolysis study of phenylacyloxycarbene (75) allowed the measurement of the rate of 1,2-acyl shift of between 105 and 106 s 1 in pentane at room temperature.82 The activation parameters were in good agreement with calculations. High-level calculations supported a carbanion-like attack by the carbene lone pah on the carbonyl (76) whereas the effects of substituents on the rate suggested an acyl anion-like transition state (77). The electron-donating, stabilizing effect of OAc slows the 1,2-C and 1,2-H shifts in alkylacetoxycarbenes (78),83 allowing 1,2-acetyl shifts to compete. 

Laser Flash Photolysis Studies of Benzophenone in Supercritical C02... 

Hug GL, Bonifacic M, Asmus K-D, Armstrong DA (2000a) Fast decarboxylation of aliphatic amino adds induced by 4-carboxybenzophenone triplets in aqueous solutions. A nanosecond laser flash photolysis study. J Phys Chem B 104 6674-6682 Hug GL, Carmichael I, Fessenden RW (2000b) Direct EPR observation of the aminomethyl radical during the radiolysis of glycine. J Chem Soc Perkin Trans 2 907-908 Hunter EPL, DesrosiersMF, Simic MG (1989) The effect of oxygen, antioxidants and superoxide radical on tyrosine phenoxyl radical dimerization. Free Rad Biol Med 6 581-585 Ito O (1992) Flash photolysis study for reversible addition reactions of thiyl radicals with olefins and acetylenes. Trends Phys Chem 3 245-266... 

Ito T, Shinohara H, Hatta H, Nishimoto S-l (1999) Radiation-induced and photosensitized splitting of C5-C5 -linked dihydrothymine dimers product and laser flash photolysis studies on the oxidative splitting mechanism. J Phys Chem A 103 8413-8420 ItoT, Shinohara H, Hatta H, Fujita S-l, Nishimoto S-l (2000) Radiation-induced and photosensitized splitting of C5-C5 -linked dihydrothymine dimers. 2. Conformational effects on the reductive splitting mechanism. J Phys Chem A 104 2886-2893 ItoT, Shinohara H, Hatta H, Nishimoto S-l (2002) Stereoisomeric C5-C5 -linked dehydrothymine dimers produced by radiolytic one-electron reduction of thymine derivatives in anoxic solution structural characteristics in reference to cyclobutane photodimers. J Org Chem 64 5100-5108 Jagannadham V, Steenken S (1984) One-electron reduction of nitrobenzenes by a-hydroxyalkyl radicals via addition/elimination. An example of an organic inner-sphere electron-transfer reaction. J Am Chem Soc 106 6542-6551... 

A picosecond laser flash photolysis study appeared on 268a-b (94CPL (230)249). After excitation at 355 nm of 268a, the absorption maximum at ca. 560 nm is ascribed to the closed form and the depletion below 450 nm is due to the bleaching of the open-form, respectively. 

Such reactions are, of course, unimolecular decompositions, not free radical chain processes. This fact made perfluorodiacyl peroxides ideal precursors for the laser flash photolysis studies which will be described in Sect. 4. Kinetics for the thermal decomposition of a number of perfluorodiacyl peroxides have been measured and their AH+ values were approximately 24 kcal/mol, about 5 kcal/mol... 

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