- Reactions of Ni(II) and its complexes with free radicals derived from thymine
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The effects of nickel(II) ions and its complexes on the products arising from the γ-radiolysis of thymine were studied.The decomposition of the pyrimidine base and formation of different radiolytic products indicate that nickel(II) ions or its complexes have little effect on the radiosensitivity of thymine.The transient hydroxyl adduct of thymine reacts with Ni(II) with the formation of a complex having a nickel-carbon bond.The rate constants for the reactions are of the order of 106 dm3mol-1s-1.Possible mechanisms for the formation of different products in the radiolysis of thymine in the presence of nickel(II) compounds are discussed.
- Chakrabarti, S.,Mandal, P. C.,Bhattacharyya, S. N.
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p. 307 - 312
(2007/10/02)
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- Far ultraviolet induced decomposition of thymine in deaerated and aerated aqueous solutions
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Thymine in aqueous solution was decomposed with quantum yields of 0.3 and 0.4 under N2-saturated and aerated conditions by far-ultraviolet light (>180 nm, far-uv), and quantum yields of 2E-4 and 3E-4 by near-ultraviolet light (>220 nm, near-uv), respectively.The main photolytic products by far-uv were 5,6-dihydrothymine (DHT) (selectivity: S(DHT) = 0.2) and 5-hydroxymethyluracil (HMU) (S(HMU) = 0.1) under N2-saturated conditions. cis- and trans-5,6-Dihydroxy-5,6-dihydrothymine (TG), 6(5)-hydroperoxy-5(6)-hydroxy-5,6-dihydrothymine (HTP) (S(TG) + S(HTP) = 0.2), and N1-formyl-N2-pyruvylurea (FPU) (S(FPU) = 0.4) were obtained under aerated conditions.These products were attributed to the reactions of thymine with the radical H and radical O produced by photolysis of water.
- Ohtani, Bunsho,Nagasaki, Hiroshi,Nishimoto, Sei-ichi,Sakano, Koichi,Kagiya, Tsutomu
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p. 2297 - 2300
(2007/10/02)
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- Radiation-induced Reduction of Thymine Derivatives in Aqueous Solution. Part 4. Promoted Transformation of Thymine Glycol into Thymine by Aromatic Amines and Low-valent Transition Metal Salts
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The radiation induced reduction of thymine glycol in aqueous solution containing sodium formate (pH 7.0) has been studied under deaerated and N2O-satureted conditions at room temperature.For comparison, the radiolysis of (1a) has also been performed with alcohols as a scavenger of OH and H, instead of formate. γ-Irradiation of the deaerated formate solution gave thymine (2), 5,6-dihydrothymine (3), and 6-hydroxy-5,6-dihydrothymine (4) along with a minor product, 5-methylbarbituric acid (5).The radiolytic transformation of (1a) into these products was inefficient under N2O, indicating that CO2- as a primary active species produced by irradiation has much less ability to reduce (1a) compared with e-aq.The presence of either inorganic salts (6a-c) or aromatic amines (7e-f) greatly promoted the total formation of (2) + (3), which depressed those of (4) and (5).The sum of the G values (=molecules/100eV of absorbed energy) of (2) and (3) > increased and that of (4) > decreased, respectively, in the sigmoidal forms with decreasing one-electron oxidation potential of the amines.The ratio G/G increased upon increasing the concentration of o-phenylenediamine (7e).In the absence of added reductants, (6a-e) or (7a-g), the yields of (2) +(3) and (4) changed either with the formate concentration or with variation of alcohols used as radical scavengers.The mechanism involving consecutive one-electron reductions of (1a) and an intermediate 6-hydroxythymin-5-yl radical (8) is discussed and compared with the reduction of 5-bromo-6-hydroxy-5,6-dihydrothymine (1b).
- Nishimoto, Sei-ichi,Ide, Hiroshi,Otsuki, Nobuaki,Nakamichi, Kikumi,Kagiya, Tsutomu
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p. 1127 - 1134
(2007/10/02)
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- RADIOLYSIS OF DIHYDROURACIL AND DIHYDROTHYMINE IN AQUEOUS SOLUTIONS CONTAINING OXYGEN; FIRST- AND SECOND-ORDER REACTIONS OF THE ORGANIC PEROXYL RADICALS; THE ROLE OF ISOPYRIMIDINES AS INTERMEDIATES
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The nature and yields of the products of radiolysis of aqueous solutions of dihydrouracil containing both N2O and O2 strongly depend on pH and dose rate.At a dose rate of 0.3 Gy s-1 and at pH 3, the major products are barbituric acid (G 2.4), labile material (G 2.8), and uracil (G 0.1).The labile material is converted into uracil upon treatment with acid and is largely composed of 5,6-dihydro-6-hydroxyuracil.At pH 7 barbituric acid is absent and uracil becomes the major product (G 4.5); some labile material is also formed (G 0.7).At pH 5 the pattern of the product distribution changes as a function of dose rate.With increasing dose r ate G(uracil) decreases whereas G(barbituric acid) increases.The predominant radical formed in the dihydrouracil system is the 6-peroxyl radical, and it has been found, using pulse radiolysis with both optical and conductometric detection, that this peroxyl radical can eliminate O2-. to give uracil via an unstable isomeric form of the pyrimidine (isouracil).The elimination is base-catalysed so that, under alkaline conditions, uracil is the major radiolysis product.At lower pH, and also at higher dose rates, bimolecular decay of the peroxyl radical competes with the O2-. elimination process, barbituric acid being a specific product of the bimolecular decay route.The mechanism of these processes are discussed.Irradiation of dihydrothymine-N2O-O2 solutions gave similar results.
- Al-Sheikhly, Mohamed I.,Hissung, Alfred,Schuchmann, Heinz-Peter,Schuchmann, Man Nien,Sonntag, Clemens von,et al.
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p. 601 - 608
(2007/10/02)
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- PROMOTION EFFECT OF 2,2,6,6-TETRAMETHYLPIPERIDINE-1-OXYLS ON THE RADIOLYTIC HYDROXYLATION OF THYMINE IN DEAERATED AQUEOUS SOLUTION
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Remarkable promotion of the hydroxylation of thymine to give thymine glycol with almost complete depression of side reactions by 2,2,6,6-tetramethylpiperidine-1-oxyl (TMPO.) derivatives was observed in the γ-radiolyses of the N2- and N2O-saturated aqueous solutions.In the O2-saturated solution, TMPO. depressed the thymine conversion close to the level under N2 while promoted the formation of thymine glycol to some extent by decreasing side reactions.
- Kagiya, Tsutomu,Kimura, Ryoji,Komuro, Chikara,Sakano, Koichi,Nishimoto, Sei-ichi
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p. 1471 - 1474
(2007/10/02)
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- RADIATION-INDUCED REDUCTIVE CONVERSION OF 5-BROMO-6-HYDROXYTHYMINE TO THYMINE PROMOTED BY TRANSITION METAL SALTS IN DEAERATED AQUEOUS SOLUTION
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The radiation-induced reduction of 5-bromo-6-hydroxythymine to produce thymine (2) in deaerated aqueous solution was remarkably promoted by the addition of lower-valent transition metal salts (K4Fe(CN)6 (3a), CuCl (3b), K2PtCl6 (3c), and FeSO4 (3d)).It is suggested that the possible intermediate hydroxythymine-5-yl radical undergoes one-electron reduction by 3a-d to the corresponding anion which eliminates OH- to produce 2.
- Nishimoto, Sei-ichi,Ide, Hiroshi,Nakamichi, Kikumi,Otsuki, Nobuaki,Kagiya, Tsutomu
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p. 1441 - 1444
(2007/10/02)
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