Radiolytic studies

The high values of E generally characteristic of the decomposition reactions of metal oxyhalides are widely interpreted as evidence that the initial step in anion breakdown is the rupture of the X—O bond and that the energy barrier to this reaction is not very sensitive to the properties of the cation present. Information of use in the formulation of reaction mechanisms has been obtained from radiolytic studies of oxyhalogen salts [887-889],... 

Because anhydrous nitric acid is of low thermal stability even at room temperature, very few photochemical and radiolytic studies have been carried out with it. A flash photolytic study of nitric acid vapour by Husain and Norrish250 has provided evidence for a primary photochemical split into OH and N02, viz. 

Halo-alkenes are common pollutants. Therefore, there is an ongoing study on plausible approaches to the dehalogenation of halo-alkanes. One of these approaches involves their electrocatalytic reduction. NinL2 + (L = a tetraaza macrocyclic ligand) complexes were proposed as plausible electrocatalysts (150). A pulse radiolytic study on the mechanism and kinetics of the reaction ... 

Radiolytic studies have been used to provide insight into the mechanisms involved in the TiO2-catalyzed photo-oxidation of a variety of organic substrates... 

Radiolytic studies have now demonstrated that the Wheland intermediate type 1 does in fact form and that earlier work had neglected the possibility that rapid desilylation by bases present in the mass spectrometric study would compete effectively with, and prevent, deprotonation, i.e. that reaction 2 is faster than reaction 3. This would therefore give the appearance that an Si—C bond was not formed62 - 65. If a nitrogen-centred base... 

Meyerstein D (1971) Trivalent Copper. I. A pulse radiolytic study of the chemical properties of the aquo complex. Inorg Chem 10 638-641... 

Aruoma Ol (1994) Deoxyribose assay for detecting hydroxyl radicals. Methods Enzymol 233 57-66 Ashton L, Buxton GV, Stuart CR (1995) Temperature dependence of the rate of reaction of OFI with some aromatic compounds in aqueous solution. J Chem Soc Faraday Trans 91 1631-1633 Asmus K-D, Mockel H, Flenglein A (1973) Pulse radiolytic study of the site of OFI radical attack on aliphatic alcohols in aqueous solution. J Phys Chem 77 1218-1221... 

In radiolytic studies, C02 is often used with some advantage the superoxide radical, 02 [reaction (26) Chap. 8.4], as a precursor of... 

Fang X, Wu J, Wei G, Schuchmann H-P, von Sonntag C (1995) Generation and reactions of the disulfide radical anion derived from metallothionein a pulse radiolytic study. Int J Radiat Biol 68 459-466... 

If this mechanism is strictly followed the chain length and hence the value of 02-uptake (see below) increases linearly with the substrate concentration and (initiation rate)"1/2 (i.e., in radiolytic studies the dose rate) and in charged polymers also on the pH (cf. Ulanski et al. 1996a). In polymers, the chain reaction may mainly proceed intramolecularly (Ulanski et al. 1996a Janik et al. 2000). An example for an efficient intramolecular autoxidation is poly(acrylic acid) [reactions (34)-(36) Ulanski et al. 1996a], In these autoxidation reactions, hydroperoxides are formed which, in some cases, are quite unstable [e.g. reaction (37) see also Leitzke et al. 2001],... 

Rush JD, Bielski BHJ (1985) Pulse radiolytic studies of the reactions of H02/02 with Fe(ll)/Fe(lll) ions. The reactivity of H02/02 with ferric ions and its implication on the occurrence of the Haber-Weiss reaction. J Phys Chem 89 5062-5066... 

Based on a pulse-radiolytic study, it has been concluded that 17% of OH add to the C(8)-position of dGuo (see above). The ensuing reactions are complex and seem to involve a number of equilibria, P-fragmentation and 1,2-H-shift reactions as depicted in reactions (94)-(104). 

Bianchini F, Hall J, Donato F, Cadet J (1996) Monitoring urinary excretion of 5-hydroxymethyluracil for assessment of oxidative DNA damage and repair. Biomarkers 1 178-184 Bienvenu C, Wagner JR, Cadet J (1996) Photosensitized oxidation of 5-methyl-2 -deoxycytidine by 2-methyl-1,4-naphthoquinone characterization of 5-(hydroperoxymethyl)-2 -deoxycytidine and stable methyl group oxidation products. J Am Chem Soc 118 11406-11411 Bothe E, Behrens G, Schulte-Frohlinde D (1977) Mechanism of the first order decay of 2-hydroxypro-pyl-2-peroxyl radicals and of O2 formation in aqueous solution. Z Naturforsch 32b 886-889 Bothe E, Deeble DJ, Lemaire DGE, Rashid R, Schuchmann MN, Schuchmann H-P, Schulte-Frohlinde D, Steenken S, von Sonntag C (1990) Pulse-radiolytic studies on the reactions of S04 with uracil derivatives. Radiat Phys Chem 36 149-154... 

Crich D, Huang W (2001) Dynamics of alkene radical cations/phosphate anion pair formation from nucleotide C4 radicals. The DNA/RNA paradox revisited. J Am Chem Soc 123 9239-9245 Das S, Deeble DJ, Schuchmann MN, von Sonntag C (1984) Pulse radiolytic studies on uracil and uracil derivatives. Protonation of their electron adducts at oxygen and carbon. Int J Radiat Biol 46 7-9... 

JellinekT, Johns RB (1970) The mechanism of photochemical addition of cysteine to uracil and formation of dihydrouracil. Photochem Photobiol 11 349-359 Jiang Y, Lin W-Z, Yao S-D, Lin N-Y, Zhu D-Y (1999a) Pulse radiolytic study of electron transfer reaction for fast repair of the one-electron oxidized radicals of dAMP and dGMP by hydroxycinnamic acid derivatives. Radiat Phys Chem 54 349-353... 

O Neill P (1983) Pulse radiolytic study of the interaction of thiols and ascorbate with OH-adducts of dGMP and dG. Implications for DNA repair processes. Radiat Res 96 198-210 O Neill P (1984) Hydroxyl radical damage potential repair by sulphydryls, ascorbate and other antioxidants. Life Chem Rep Suppl Ser 2. In Rotilio G, Bannister JV (eds) Oxidative damage and related enzymes. Life Chem Rep 1 337-341... 

O Neill P, Chapman PW (1985) Potential repair of free radical adducts of dGMP and dG by a series of reductants. A pulse radiolytic study. Int J Radiat Biol 47 71-80 O Neill P, Davies SE (1987) Pulse radiolytic study of the interaction of SO4" with deoxynucleosides. 

Sessler, J.L. et al. (2001) Pulse Radiolytic Studies of Metallotexaphyrins in the Presence of Oxygen Relevance of the Equilibrium with Superoxide Anion to the Mechanism of Action of the Radiation Sensitizer Motexafin Gadolinium (Gd-Tex2+, Xcytrin), J. Phys. Chem. B 105, 1452-1457. 

Decay of Organocobalt Complexes The dramatic effect of the nature of the alkyl group on the mechanism of decomposition of macrocyclic Co(III) complexes containing a Co-C bond was demonstrated in an early pulse radiolytic study of the formation and decay of LComR,18 where L is rac -Me6-diene. 

Fig. 8.3. An example of a gas chromatogram of the base-damage to DNA after exposure to hydroxyl radicals (generated radiolytically) - study of the trimethyl-silylated acidic hydrolysate of the modified DNA (modified from Dizdaroglu, 1988 with permission). Peaks I, phosphoric acid II, thymine III and Ilia, cytosine IV and IVa adenine V and Va guanine I uracil 2 5,6-dihydrothymine 3 5-hydroxy-5,6-dihydrothymine 4 5-hydroxyuracil 5 5-hydroxy-5,6-dihydrouracil 6 5-hydroxycytosine 7 cis-thymine glycol 8 /ra .s-thymine glycol 9 5,6-dihydroxyuracil 10 4,6-diamino-5-formamidopyr-imidine 11 8-hydroxyadenine 12 2,6-diamino-4-hydroxy-5-formamidopyrimidine 13...

Jiang Y, Lin W, Yao S, Lin N, Zhu D. (1999) Fast repair of oxidizing OH adducts of DNA by hydroxycinnamic acid derivatives. A pulse radiolytic study. Radiat Phys Chem 54 355-359. 

Thermal polymerizations of vinylic crystalline monomers giving isotactic or syndiotactic crystalline polymers are rare. More frequent are photolytical and radiolytical studies. The crystallographic packing requirements are most stringent. Clearly, the polymer chains cannot exit the crystal. They must therefore be able to accommodate with the monomer structure. Despite enormous efforts only a few... 

Several recent publications indicate that the role of intermediate complexes in ionic reactions is still controversial (21, 24, 25). Our interest in this and earlier observations of persistent complexes in alkyl halides already mentioned prompted us to study ionic reactions in ethyl chloride. The previously noted mass spectrometric investigations of alkyl halides did not include the chlorides, and radiolytic studies of these compounds have been limited to the propyl and butyl chlorides which apparently isomerize (39). The present investigation consists of two phases. In the initial phase, the ion-molecule reactions for ethyl chloride were probed by the sensitive mass spectrometric methods which we have applied in recent studies of a similar nature (3,12, 28, 43). In the latter part of this study, the gas-phase radiolysis and vacuum-ultraviolet photolysis of ethyl chloride have been studied to identify those products which arise from ionic precursors. More specifically, we wished to define the behavior under radiolytic conditions of those intermediate ionic species which the spectrometric studies suggested were important, and we hoped to arrive at a reasonable conciliation of the ionic reaction information derived from these different but complementary techniques. 

For production of the superoxide radical in radiolytic studies, HO, e q, and H are all utilized via oxygen-saturated formate solutions. The solvated electron and the hydrogen atom produce 02 equivalents by direct reactions with O2 (reactions 43 and 44). 

The notion that AO molecules reduced to different degrees may exhibit distinct reactivities can be ruled out because experiments starting with the fully oxidized enzyme and ending with less than 5% oxidized Tl sites yielded essentially identical intramolecular ET rates (33). Also, no difference in these internal ET rate constants was observed with enzymes activated or pulsed" by turning over 1 mM ascorbate in the presence of 0.25 mM O2 prior to the determination of the intramolecular ET rates. In contrast to these experiments, which were all performed under anaerobic conditions, a more recent pulse-radiolytic study employed AO solutions containing small and controlled concentrations of O2 (15-65 fxm), and conspicuous differences in the kinetic behavior were observed. A new and faster intramolecular ET phase was discovered which... 

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