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'Pulse Radiolysis' in keywords Facet   Publication Year 1982  [X]
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1982[X]
1Author    R. K. Broszkiewicz+, T. Söylemez, D. Schulte-FrohlindeRequires cookie*
 Title    Reactions of OH Radicals with Acetylacetone in Aqueous Solution. A Pulse Radiolysis and Electron Spin Resonance Study  
 Abstract    Pulse radiolysis experiments monitoring optical absorbance as well as conductivity and in-situ ESR radiolysis studies show that the OH radical reacts with the enol (k = 8.6 x 10 9 M _1 s _1) and the enolate (k = 7.4 X 10 9 M _1 s -1) forms of acetylacetone by addition to the C = C double bond in aqueous N2O saturated solution. The OH reaction with enol leads to equal amounts of two radicals, CH3COCHOHCOHCH3 (2) and CH3COCHC(OH)2CH3 (4), as determined by scavenger reactions. At pH less than 1 the radical CH3COCHCOCH3 (1) is observed by ESR spectroscopy showing that radical 2 and/or 4 eliminate water by proton catalyzed reactions. Under alkaline condition the OH adducts to the enolate eliminate OH -with rate constants larger than 10 5 s -1 leading to radical 1. G(OH") is determined to be 5.6 showing that addition is the main reaction of OH with enolate. To a much smaller degree the OH radical is proposed to abstract an H atom from that CH3 group which is attached to the C —C double bond in enol and enolate, producing substituted allyl radicals which absorb in the visible region. The reaction of OH with the keto form has not been observed indicating that the rate constant of this reaction is significantly smaller than those with enol and enolate. 
  Reference    Z. Naturforsch. 37b, 368—375 (1982); received August 19 1981 
  Published    1982 
  Keywords    Pulse Radiolysis, OH Radicals, Acetylacetone, Reaction Mechanisms 
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 TEI-XML for    default:Reihe_B/37/ZNB-1982-37b-0368.pdf 
 Identifier    ZNB-1982-37b-0368 
 Volume    37 
2Author    Z. NaturforschRequires cookie*
 Title    Über die oxidative Hauptkettenspaltung einiger Nukleinsäuren — Pulsradiolytische Untersuchungen  
 Abstract    O n the O xidative M ain-C hain Scission o f N u cleic A cids — P ulse R adiolysis S tudies O tm ar D enk und W olfram Schnabel Polyriboadenylic acid, polyribocytidylic acid and polyribouridylic acid were irradiated with 16 MeV electrons in aqueous solution. Part of the OH radicals generated during the radiolysis of water reacted with the sugar moieties of the polynucleotides. Subsequently formed peroxyl radicals reacted with each other thus forming oxyl radicals whose's decay led to main-chain scissions with the consequence of a decrease of the light scattering intensity (LSI). In the case of single-stranded polynucleotides, the analysis of the LSI decay curves revealed the occurrence of two processes. The rapid mode was assigned to the intramolecular and the slow mode to the intermolecular reaction of peroxyl radicals. For the rate constant of the rapid process (activation energy: 5 kcal/mol) a pronounced kinetic salt effect was observed. In the case of double-stranded polynucleotides (polyA and polyC at pH 4, poly(A+U) at pH 8) the same effects were observed as with native calf thymus DNA in a former study [9]: The LSI decreased only after a critical dose was surpassed. A rapid process was followed by a slow one. The slow process is assigned to the melting of H-bridges located at bases between main-chain scissons in the double helix. The rapid process corresponds to the separation of fragments formed by two single strand breaks laying very close to each other on opposite sites in the double helix. 
  Reference    Z. Naturforsch. 37c, 405—412 (1982); received February 1/M arch 16 1982 
  Published    1982 
  Keywords    Nucleic Acids, Main-Chain Scission, Peroxyl Radicals, Intra-and Intermolecular Reactions, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-0405.pdf 
 Identifier    ZNC-1982-37c-0405 
 Volume    37