- Sonochemical transformation of thymidine: A mass spectrometric study
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Abstract Ultrasound is extensively used in medical field for a number of applications including targeted killing of cancer cells. DNA is one of the most susceptible entities in any kind of free radical induced reactions in living systems. In the present work, the transformation of thymidine (dT) induced by ultrasound (US) was investigated using high resolution mass spectrometry (LC-Q-ToF-MS). dT was subjected to sonolysis under four different frequencies (200, 350, 620 and 1000 kHz) and at three power densities (10.5, 24.5 and 42 W/mL) in aerated as well as argon saturated conditions. A total of twenty modified nucleosides including non-fully characterized dT dimeric compounds were detected by LC-Q-ToF-MS. Out of these products, seven were obtained only in the argon atmosphere and two only in the aerated conditions. Among the identified products, there were base modified products and sugar modified products. The products were formed by the reaction of hydroxyl radical and hydrogen atom. Under aerated conditions, the reactions proceed via the formation of hydroperoxides, while in argon atmosphere disproportionation and radical recombinations predominate. The study provides a complete picture of sonochemical transformation pathways of dT which has relevance in DNA damage under ultrasound exposure.
- Chandran, Jisha,Aravind, Usha K.,Aravindakumar
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p. 178 - 186
(2015/06/02)
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- Synthesis and stereochemical assignment of DNA spore photoproduct analogues
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Investigation of the DNA repair process performed by the spore photoproduct (SP) lyase repair enzyme is strongly hampered by the lack of defined substrates needed for detailed enzymatic studies. The problem is particularly severe because the repair enzyme belongs to the class of strongly oxygen-sensitive radical (S)-adenosyl-methionine (SAM) enzymes, which are notoriously difficult to handle. We report the synthesis of the spore photoproduct analogues 1a and 1b, which have open backbones and are diastereoisomers. In order to solve the problem of stereochemical assignment, two further derivatives 2a and 2b with closed backbones were prepared. The key step of the synthesis of 2a/b is a metathesis-based macrocyclization that strongly increases the conformational rigidity of the synthetic spore photoproduct derivatives. NOESY experiments of the cyclic isomers furnished a clear cross-peak pattern that allowed the unequivocal assignment of the stereochemistry. The results were transfer red to the data for isomers 1a and 1b, which were subsequently used for enzymatic-repair studies. These studies were performed with the novel spore photoproduct lyase repair enzyme from Geobacillus stearothermophilus. The studies showed an accordance with a recent investigation performed by us with the spore photoproduct lyase from Bacillus subtilis,[1] in that only the 5 isomer la is recognized and repaired. The ability to prepare a defined functioning substrate now paves the way for detailed enzymatic studies of the SP-lyase lesion recognition and repair process.
- Friedel, Marcus G.,Pieck, J. Carsten,Klages, Jochen,Dauth, Christina,Kessler, Horst,Carell, Thomas
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p. 6081 - 6094
(2007/10/03)
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- Release of superoxide from nucleoside peroxyl radicals, a double-edged sword?
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5,6-Dihydrothymidin-5-yl (1) and 2'-deoxyuridin-1'-yl (3) were independently generated in solution under aerobic conditions. The release of superoxide (O2.-) from the respective peroxyl radicals derived from 1 and 3 was determined spectrophotometrically. Competition studies enable one to estimate that the rate constant for elimination of O2.- from the peroxyl radical (4) derived from 3 is ~1 s-1. This process is competitive with the anticipated rate of trapping of 4 in DNA by glutathione. Relative rate studies indicate that O2.- generation reslting from the formation of 1 under aerobic conditions competes effectively with trapping of the peroxyl radical by Bu3SnH. Superoxide elmination from the peroxyl radical of 1 (2) restores the damaged nucleoside to its unaltered form, implying that this reactive intermediate has a naturally occurring detoxification pathway available to it. However, the freely diffusible superoxide can react further to generate other reactive species capable of damaging nucleic acids, suggesting that the eliminations of O2.- from 2 is a potential double- edged sword.
- Tallman, Keri A.,Tronche, Christopher,Yoo, Dong Jin,Greenberg, Marc M.
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p. 4903 - 4909
(2007/10/03)
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- Radiation-Induced Degradation of Purine and Pyrimidine 2'-Deoxyribonucleosides in Aqueous KBr Solutions
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Steady-state γ-radiolysis of 5E-4 M pyrimidine and purine 2'-deoxyribonucleosides in aqueous solutions saturated with N2, N2O and O2, respectively, have been carried out in the presence of 0.1 M KBr.The main final degradation products have been isolated and characterised by various spectroscopic measurements including 1H and 13C NMR, UV, C.D. and mass spectrometry.The radiation-induced decomposition of thymidine is mostly accounted for by an ionic mechanism involving Br2, the decay product of Br2, as the reactive oxidising specie.On the other hand the degradation of the purine ring of 2'-deoxyadenosine and 2'-deoxyguanosine may be accounted for by the action of Br2 or Br3. - Keywords: 2'-Deoxyribonucleosides, Inorganic Radical, γ-Irradiation, Radical Reactions, Thymidine Oxidation
- Cadet, J.,Voituriez, L.,Berger, M.,Myers, L. S., (Jr.)
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p. 1643 - 1651
(2007/10/02)
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