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1Author    Nien Man, Clemens Schuchmann, Von SonntagRequires cookie*
 Title    Hydroxy! Radical-Induced Oxidation of Diisopropyl Ether in Oxygenated Aqueous Solution. A Product and Pulse Radiolysis Study  
 Abstract    In the radiolysis of N 2 0/0 2 (4:1)-saturated aqueous solutions of diisopropyl ether(10~ 3 mol dm ~ 3), OH radicals abstract H-atoms, thereby producing radicals at C(2) (1 = 78%) and to a lesser extent at C(l) (2 — 22%) which are converted by oxygen into the corresponding peroxyl radicals 3 and 4. Some 0 2 radicals are formed by the reaction of radiolytically produced H atoms with oxygen. Methyl radicals formed in the course of the bimolecular decay of 3 and 4 give rise to methylperoxyl radicals 5. At high dose rate as delivered by 2.8 MeV electron pulses the products (G values in parentheses) are: isopropyl acetate (2.6), acetone (1.1), isopropanol (1.1), 2-iso-propoxypropanal (1.4, estimated), formaldehyde (2.0), organic hydroperoxides (0.4), organic acids (0.5) and hydrogen peroxide (1.9). At low dose rates (<0.39 Gy s -1) G(acetone) is consid-erably increased and is no longer balanced by an equivalent yield of isopropanol. This is thought to be due to an intramolecular H-abstraction of radical 3. Pulse radiolysis studies revealed that 3, 4 and 5 decay by second order kinetics. At the early stages the bimolecular decay is faster (2k = 6 x 10 7 dm 3 moP's" 1) than toward the end (2k = 2 x 10 7 dm 3 mor I s" 1). It is suggested that the faster decay at the beginning is due to a preponderance of termination by the primary peroxyl radical 4 with the tertiary peroxyl radical 3 while at later stages termination is mainly governed by the reaction of 3-1-3 which produces 5. The rate constants k(5 + 3) and k(5 + 5) are very likely much higher than 2k(3 + 3), hence 2k(3 + 3)<2 x 10 7 dm 3 moP's" 1 . In 0 2 -saturated solutions 0 2 plays a considerable role in the termination reactions, and organic hydroperoxides which are unimportant in N 2 0/0 2 -saturated solutions at high dose rates are now the major products. 
  Reference    Z. Naturforsch. 42b, 495—502 (1987); received November 7 1986 
  Published    1987 
  Keywords    Diisopropyl Ether, Hydroxyl Radicals, Peroxyl Radicals, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_B/42/ZNB-1987-42b-0495.pdf 
 Identifier    ZNB-1987-42b-0495 
 Volume    42 
2Author    W. A. Prütz, S. VogelRequires cookie*
 Title    Specific Rate Constants of Hydroxyl Radical and Hydrated Electron Reactions Determined by the RCL Method  
 Abstract    Relative rate constants of OH radical and eaq~ reactions have been determined by comparing, under steady x-irradiation, the effect of various solutes upon the radiation-induced chemiluminescence (RCL) of aqueous dye (DH) solutions, [DH + -OH] + eaq --> DH* + OH -. The results abundantly confirm other published data. RCL changes upon addition of phosphates indicate prototropic reactions with the oxidized dye, D'-f^PO^ ^ DH-+ + HPO4 2-, promoting or inhibiting the formation of semioxidized dye (DH-+) as the most efficient RCL precursor. The RCL enhancement commonly observed upon addition of halides and pseudo halides is discussed at some length on the base of previous and present results in order to focus attention to the possible correlation between such RCL enhancement and the effect of halogen-sensitization in radiobiology. RCL results suggest that the halide transients formed from OH radicals, X -+ -OH X 1 -f OH -, are very powerful oxidizing agents reacting with aromatics by electron-abstraction rather than by addition or H-abstraction. The common application of I -and SCN -as competitors for the estimation of OH radical reactivities is being commented in the context. 
  Reference    (Z. Naturforsch. 31b, 1501—1510 [1976]; received July 12 1976) 
  Published    1976 
  Keywords    Hydrated Electron, Hydroxyl Radical, Luminescence, Radiation Chemistry, Rate Constants 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-1501.pdf 
 Identifier    ZNB-1976-31b-1501 
 Volume    31 
3Author    Mohamed Al-Sheikhly, Clemens Von SonntagRequires cookie*
 Abstract    The y-radiolysis of N20-saturated aqueous solutions generates OH radicals and a small amount of H atoms. In 1,3-dimethyluracil solutions (10 -3 M) these radicals add mainly to the 5-position of the C(5) -C(6) double bond of the solute. The resulting products have been identified by GC-MS after trimethylsilylation. The major products (G values in brackets) are dimers of the C(5)-OH-adduct radicals (3.4), 5,6-dihydro-5,6-dihydroxy-1,3-dimethyl-uracil (0.85), 5,6-dihydro-5-hydroxy-1,3-dimethyluracil (0.75), dimer of the C(5)-0H-adduct with the C(5)-H-adduct radical (0.2) and 5,6-dihydro-6-hydroxy-l,3-dimethyl-uracil (0.2). G(1,3-dimethyluracil consumption) has been found to be 5.7. The major reaction in this system is the dimerisation of the primary radicals. To a small extent the primary radicals also disproportionate by electron transfer to give the glycol 5,6-dihydro-5,6-dihydroxy-l,3-dimethyluracil as one of the products. Radiolytically formed H202 which could oxidise the C(5)-0H-adduct radical does not contribute to the formation of the glycol because the H202 yield is not reduced with respect to its expected "molecular yield" (G = 0.75). In contrast to the uracil system where it has been reported that drastic changes in radiolytic yields occur on going from neutral to alkaline irradiation conditions no such changes have been observed with 1,3-dimethyluracil. However, an acid-catalysed rearrangement from the C(5)-OH-adduct to the C(6)-0H-adduct radical is observed in the present system. 
  Reference    Z. Naturforsch. 38b, 1622—1629 (1983); received June 27 1983 
  Published    1983 
  Keywords    Hydroxyl Radicals, Electron Transfer Reactions, Radical Reactions, DNA Model Systems 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-1622.pdf 
 Identifier    ZNB-1983-38b-1622 
 Volume    38 
4Author    M. Aurice, B. Erger, JeanC. AdetRequires cookie*
 Title    Isolation and Characterization of the Radiation-Induced Degradation Products of 2 -Deoxyguanosine in Oxygen-Free Aqueous Solutions  
 Abstract    The bulk o f the radiation-induced degradation products o f 2'-deoxyguanosine in oxygen-free aqueous solution have been separated by high performance liquid chrom atography and charac­ terized by various spectroscopic techniques including fast atom bom bardm ent mass spectrom etry, 'H NM R and circular dichroism. The two main decom position products result from the opening o f the imidazole ring and further rearrangement o f the sugar m oiety. In addition, the formation o f six other nucleosides was shown to involve sugar radicals with subsequent epim erization, re­ arrangement or cyclization reactions. 
  Reference    Z. Naturforsch. 40b, 1519—1531 (1985); received June 18 1985 
  Published    1985 
  Keywords    2'-D eoxyguanosine, Gamma Irradiation, Hydroxyl Radicals, 'H N M R Spectra, M odified N ucleosides 
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 TEI-XML for    default:Reihe_B/40/ZNB-1985-40b-1519.pdf 
 Identifier    ZNB-1985-40b-1519 
 Volume    40 
5Author    OliverJ. Mieden, Clemens Von Sonntag, D. Ruhr, F.R GRequires cookie*
 Title    Peptide Free-Radicals: The Reactions of O H Radicals with Glycine Anhydride and its Methyl Derivatives Sarcosine and Alanine Anhydride. A Pulse Radiolysis and Product Study  
 Abstract    The reactions of radiolytically generated O H radicals and H atoms with the cyclic dipeptides of glycine, alanine and sarcosine in deoxygenated aqueous solutions and the subsequent reactions of the transient peptide radicals were studied in the absence and presence of K,Fe(CN)ft as oxidant by pulse radiolysis and product analysis. Hydroxyl radicals and H atoms react with glycine anhydride and alanine anhydride by abstract­ ing an H atom bound at C-3; there is no evidence for any other site of attack at these two peptides. The resulting radicals have pKa values of 9.8 and 10.6, respectively. In the absence of an oxidant the radicals decay by second order (2k = 7.Ox 10s dm3 m ol-1 s" ' and 2k = 4.4x 108 dm3 mol ' 1 s_ l, resp.), the main fraction (94% of the glycine anhydride-derived radicals, 90% of the alanine anhydride-derived radicals) yielding dehydrodimers (G = 0.58 /<mol J~l and 0.56 ,«mol 7-1 (in monomer units), resp.). A small portion however disproportionates via abstraction of a C-6 -bound H atom followed by isomerization to 2,5-dihydroxypyrazines (pKa values of the parent 2,5-dihydroxvpyrazine at about 7.9 and 10.1) and subsequent addition of water to 2,5-diketo-3-hydroxypiperazines, thus indicating that the transfer of a carbon-bound hydrogen atom is prefered to the transfer of a nitrogen-bound hydrogen atom. No disproportionation products but three different dehydrodimers (G = 0.36, 0.18 and 0.04 ^m ol J~l (in monomer units)) were found after irradiation of sarcosine anhydride. In this case a dose rate and solute concentration dependence of dehydrodimer formation indicates a radical-solute reaction converting part of the N-methyl radicals (21% of 'initial' attack) into the C-3-yl radicals. A rate constant of k = 600 ± 50 dm3 m o l 1 s" 1 was obtained for this reaction by measuring and computing the dehydrodimer yields as a function of dose rate and solute concen­ tration. Thus the observed transient spectrum accounts only for about 79% of the radicals from the 'initial' attack at C-3. The rate of oxidation of the glycine anhydride-derived radicals by Fe(CN)63~ reflects the pKa of the transient radical. The rate constant for oxidation of the (protonated) radical derived from glycine anhydride is: k = l.O x lO 8 dm3 mol-1 s-1, the corresponding radical anion is oxidized with k = 3.1 x 108 dm 3 m ol-1 s-1. No change with pH was observed in the case of the alanine anhydride-derived radicals (k = 7.9x 108 dm3 m ol" 1 s ' '). In contrast to the disproportionation, oxidation by Fe(CN) 63 leads to the removal of a proton from the heteroatom, a carbocation being the inter­ mediate. The resulting dehydropiperazines rapidly add water to yield the corresponding 2,5-diketo-3-hydroxypiperazines (G = 0.61 ,wmol J 1 after oxidation of the glycine anhydride-derived radicals, G — 0.58 //mol after oxidation of the alanine anhydride-derived radicals). The radicals derived from sarcosine anhydride are readily oxidized with k = 4 .0 x l0 8 dm3 mol 1 s"1, independent of pH. !H and 13C {'H } NMR-spectroscopic and mass-spectroscopic data of the products are given. 
  Reference    Z. Naturforsch. 44b, 959 (1989); received March 23 1989 
  Published    1989 
  Keywords    Glycine Anhydride, Alanine Anhydride, Sarcosine Anhydride, Pulse Radiolysis, Hydroxyl Radical, Peptide Radicals 
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 TEI-XML for    default:Reihe_B/44/ZNB-1989-44b-0959.pdf 
 Identifier    ZNB-1989-44b-0959 
 Volume    44 
6Author    DavidJ. Deebleab, Eberhard Bothea, Heinz-Peter Schuchmanna, BarryJ. Parsonsb, GlynO. Phillips ', Clemens Von SonntagaRequires cookie*
 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 
7Author    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