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1990 (2)
1983 (1)
1Author    Eberhard Bothe, G. Ali, Ureshi, D. Ietrich, S. Ch, Lte-F Ro, H. Lin DRequires cookie*
 Title    Rate of OH Radical Induced Strand Break Formation in Single Stranded DNA under Anoxic Conditions. An Investigation in Aqueous Solutions Using Conductivity Methods  
 Abstract    Single stranded D N A (ssD N A) in aqueous N 20-satu rated solution was pulse-irradiated with electrons or irradiated under steady-state conditions with 60Co-y rays. The conductivity increase after irradiation was measured as a function o f concentration, pH, temperature, metal cation content and additives. The conductivity increase could be shown to be due to the release o f associated counterions (N a+ or H+) as a result o f the formation o f chain breaks. At 28 mg I-1 D N A ~ 8 sodium ions are liberated per 100 eV absorbed energy (G (N a +) = 8.3). On the basis o f G value for single-strand breaks (ssb) o f G(ssb) = 0.55, it is calculated that 8.3/0.55 = 15 sodium ions per strand break are set free. The release o f N a+ monitored by 23N a-N M R at pH 7 as a function o f dose corresponds to that o f the conductivity increase. The rate o f the conductivity increase does not depend on d ose/p u lse (range 2 -2 0 J kg-1) and shows at least two components. The rate constant o f the fast and dom inant com ponent is constant above pH 8.5 (A: = 38 s— 1, 20 °C) and increases linearly with proton concentration below pH 7. Values o f 13kcal/m ol for the activation energy and 5 x 10" s_1 for the frequency factor were obtained at pH 7.3. Addition o f p-benzoquinone (pBQ) increases the rate constant o f the fast component proportionally to the concentration o f pBQ. From these results the rate-determining step o f the fast conductivity increase is concluded to be the splitting o f D N A radicals. The pH dependence and the m agnitude o f the activation energy agree with results from low molecular weight model com pounds for the C-4' m echanism ; this m echanism involves a heterolytic splitting o f the phosphoric acid ester bond starting from the 4' radical o f D N A . 
  Reference    Z. Naturforsch. 38c, 1030—1042 (1983); received Septem ber 19 1983 
  Published    1983 
  Keywords    DNA, Formation o f Strand Breaks, Electrical Conductivity, Pulse R adiolysis, Rate Constants 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-1030.pdf 
 Identifier    ZNC-1983-38c-1030 
 Volume    38 
2Author    DavidJ. Deebleab, Eberhard Bothea, Heinz-Peter Schuchmanna, BarryJ. Parsonsb, GlynO. Phillips ', Clemens Von SonntagaRequires cookie*
 Title      
 Abstract    Hydroxyl radicals were generated radiolytically in N 20 -and N 20 / 0 2(4: l)-saturated aqueous solutions o f hyaluronic acid. The hydroxyl radicals react rapidly with hyaluronic acid mainly by abstracting carbon-bound H atom s. A s a consequence o f subsequent free-radical reactions, chain breakage occurs the kinetics o f which has been followed using the pulse radio­ lysis technique. In the absence o f oxygen, strand breakage was followed by the change in conductivity in­ duced by the release o f cationic counterions condensed at the surface o f hyaluronic acid which is a polyanion consisting o f subunits o f glucuronic acid alternating with N-acetyl-glucosamine. It appears that strand breakage is not due to one single first-order process, however, the con ­ tributions o f the different com ponents cannot be adequately resolved. At pH 7 the overall half-life is 1.4 ms, in both acid and basic solutions the rate o f free-radical induced strand breakage is accelerated (at pH 4.8, / 1/2 = 0.6 ms; at pH 10, r1/2 = 0.18 ms). In the absence o f oxygen there is no effect o f dose rate on the kinetics o f strand breakage. In the presence o f oxygen in addition to conductom etric detection, strand breakage was also followed by changes in low-angle laser light-scattering. These two techniques are com plem en­ tary in that in this system the conductom etry requires high doses per pulse while the light-scat­ tering technique is best operated in the low -dose range. In the presence o f oxygen a pro­ nounced dose-rate effect is observed, e.g. at pH 9.7 after a dose o f 9.4 Gy the overall half-time is approx. 0.5 s, while after a dose o f 6.6 Gy the half-time is approx. 0.23 s. Both the yield and the rate o f strand breakage increase with increasing pH, e.g. at pH 7 G(strand breaks) = 0.7 x 10"7 mol J" 1 and at pH 10.4, 4.8 x 10"7 mol J"7. The radiolytic yields o f C 0 2, H 20 2, organic hydroperoxides, 0 2'~ and oxygen consum ption have been determined in y-irradiated N 20 / 0 2(4: l)-saturated solutions o f both hyaluronic acid and ß-cyclodextrin. 
  Reference    Z. Naturforsch. 45c, 1031—1043 (1990); received M ay 10 1990 
  Published    1990 
  Keywords    Hyaluronic Acid, Strand Breakage, Pulse R adiolysis, Hydroxyl Radical, Superoxide Radical 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-1031.pdf 
 Identifier    ZNC-1990-45c-1031 
 Volume    45 
3Author    Shailesh Phulkar, Balijepalli Sethu, M. Adhava Rao, Heinz-Peter Schuchmann, Clemens Von SonntagRequires cookie*
 Title    Radiolysis of Tertiary Butyl Hydroperoxide in Aqueous Solution. Reductive Cleavage by the Solvated Electron, the Hydrogen Atom, and, in Particular, the Superoxide Radical Anion  
 Abstract    The reactions o f the solvated electron, the H atom, the OH radical and the superoxide radi­ cal anion with /-butylhydroperoxide (/-BuOOH) have been studied in aqueous solutions using y-radiolysis and pulse radiolysis to generate these radicals. The solvated electron reacts rapidly with r-BuOOH (k = 5 x 109 dm 3 m ol" 1 s~') yielding /-BuO ' and OH in a ratio o f 4:1. The yield o f r-BuO' has been determined by measuring its fragmentation product, acetone. The H atom reacts more slowly with r-BuOOH (k = 5x 107 dm 3 m o l-1 s"1). There is very little H-abstraction from the methyl and the hydroperoxyl groups (about 3%), the main reac­ tion again being the scission o f the hydroperoxyl function with a branching ratio /-BuO'/'OH o f about unity. The OH radical reacts with /-BuOOH considerably more slowly (k = 8 x 107 dm3 m o l" 1 s ' 1) than with /-butanol (k = 5 X 108 dm3 m o l-1 s"1) with an approximate preference o f 8:1 o f ab­ stracting a methyl hydrogen over a hydroperoxyl hydrogen atom. The carbon-centered radical undergoes y-cleavage (k ~ 102 s"1) thereby reforming an OH radical. The resulting chain reac­ tion is rather short (maximum yield G (2-methyl-1,2-epoxypropane), 26 x 10"7 mol / ' at low dose rate) due to H-abstraction at the hydroperoxyl function o f r-BuOOH by the OH radical. The superoxide radical anion also reacts with /-BuOOH by cleaving the hydroperoxyl func­ tion. Its reactivity is, however, rather low (k = 5 dm3 m ol" 1 s"1). 
  Reference    Z. Naturforsch. 45b, 1425—1432 (1990); received May 9 1990 
  Published    1990 
  Keywords    /-Butyl Hydroperoxide, Solvated Electron, H Atom, Superoxide Radical, Hydroxyl Radical, Pulse R adiolysis, Chain Reaction 
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 TEI-XML for    default:Reihe_B/45/ZNB-1990-45b-1425.pdf 
 Identifier    ZNB-1990-45b-1425 
 Volume    45