- Reactions of cobalt(III) complexes with free radicals derived from thymine
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The nature of interaction of Co(III) complexes such as Co(III)EDTA and Co(III)NTA with transient adducts of thymine such as TOH·, T·-, and TH· formed in the gamma radiolysis of thymine were studied. The study shows that TOH radicals do not undergo electron transfer reaction with Co(III) complexes whence no radiosensitization of thymine by Co(III) complexes was observed. Electron transfer however, takes place from T·- and TH· to Co(III) complexes. A plausible mechanism of radiolysis of thymine in presence of Co(III) complexes is discussed.
- Chakrabarti,Mandal,Bhattacharyya
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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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- 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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- Hydroxyl radical-induced cross-linking of thymine and lysine: Identification of the primary structure and mechanism
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Hydroxyl radical-induced formation of a cross-link of thymine (Thy) and lysine (Lys) in the γ-radiolysis of N2O-saturated aqueous solution was studied. A Thy-Lys cross-link (I) of the formal structure that OH radical and 4-carbon-centered Lys radical added respectively to C(5) and C(6) positions of Thy was isolated by a preparative HPLC and identified by a FAB-HRMS. The primary cross-link I was dehydrated by treatment with HCl at 120°C to yield the secondary structure (II) possessing a C(5)-C(6) double bond in the Thy moiety: the latter structure II was reported previously (Dizdaroglu, M.; Gajewski, E. Cancer Res. 1989, 49, 3463-3467). A pulse radiolysis study with a redox titration method indicated that 4-carbon centered Lys radical intermediate was of neutral redox reactivity in contrast to reducing reactivity of 5-hydroxy-5,6-dihydrothymin-6-yl radical intermediate. The cross-link I could be formed by a conventional radical recombination mechanism, but not by an ionic recombination mechanism involving a redox reaction between the radical intermediates.
- Morimoto, Syota,Hatta, Hiroshi,Fujita, Shin-Ichi,Matsuyama, Tomochika,Ueno, Toru,Nishimoto, Sei-Ichi
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p. 865 - 870
(2007/10/03)
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- 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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- Photoreduction of Thymine Glycol sensitized by Aromatic Amines in Aqueous Solution
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Photolyses (λex > 280 nm or λex 300 nm) of thymine glycol (TG) (1mM) in the absence and presence of aromatic amines (1mM) have been performed in aqueous solution at pH 7.0.The photoconversion of TG was quite inefficient without aromatic amines, but was remarkably promoted by the addition of the amines .The main products in the amine-sensitized photolysis were thymine (T) and 6-hydroxy-5,6-dihydrothymine (6HODHT).With the exception of NNN'N'-tetramethyl-p-phenylenediamine (TMPD), the amine-sensitized reaction of TG was quenched by a triplet quencher, biacetyl.The yield of T increased on decreasing the half-wave oxidation potencial (Eox1/2) of the aromatic amines.The yield of 6HODHT in the photolysis with aniline increased on increasing the concentration of sodium formate added as a hydrogen-atom donor.The effects of Eox1/2 and sodium formate on the product yields were consistent with an intermediacy of 6-hydroxythymin-5-yl radicals (6HOT) produced by reductive dehydroxylation of TG.
- Ide, Hiroshi,Otsuki, Nobuaki,Nishimoto, Sei-ichi,Kagiya, Tsutomu
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p. 1387 - 1392
(2007/10/02)
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- RADIATION-INDUCED HYDROXYLATION OF THYMINE SENSITIZED BY NITRO COMPOUNDS IN N2O-SATURATED AQUEOUS SOLUTION
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Hydroxylation of thymine (1) to give thymine glycol (3) is remarkably promoted by the addition of nitro compounds (2a-f) in the γ-radiolysis of the N2O-saturated aqueous solution, although overall decomposition of 1 is depressed to some extent.The G-value of 3 increases linearly with increasing the one-electron reduction potential of 2a-f.
- Wada, Takeshi,Ide, Hiroshi,Nishimoto, Sei-ichi,Kagiya, Tsutomu
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p. 1041 - 1044
(2007/10/02)
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