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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    Nien Man, Clemens Schuchmann, Von SonntagRequires cookie*
 Title    Determination of the Rate Constants of the Reactions C02 -f-OH~ -> HC03 — and Barbituric Acid -> Barbiturate Anion + Using the Pulse Radiolysis Technique  
 Abstract    The kinetics of the reactions of CO2 + OH --»HCO3 -(i) and barbituric acid ^barbi-turate anion -j-H + (ii) have been remeasured using as a new approach the pulse radiolysis technique with optical and conductivity detection. The rate constants obtained in the present study, ki (21 °C) = 6900 ± 700 M^s" 1 and ku (19 °C) = 22 ± 2s-1 agree within experimental errors with values obtained earlier by other methods. 
  Reference    Z. Naturforsch. 37b, 1184—1186 (1982); received March 29 1982 
  Published    1982 
  Keywords    Fast Reaction Kinetics, Pulse Conductometry, Peroxyl Radicals, Radiation Chemistry 
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 TEI-XML for    default:Reihe_B/37/ZNB-1982-37b-1184.pdf 
 Identifier    ZNB-1982-37b-1184 
 Volume    37 
3Author    Eberhard Bothe, Nien Man, Dietrich Schuchmann, Schulte-Frohlinde, Clemens Von SonntagRequires cookie*
 Title    Hydroxyl Radical-Induced Oxidation of Ethanol in Oxygenated Aqueous Solutions. A Pulse Radiolysis and Product Study  
 Abstract    y-Radiolysis of N20-saturated water or photolysis of aqueous H2O2 provided a source of OH radicals. These radicals react with ethanol by preferentially abstracting an H atom at C-l. In the presence of oxygen these radicals are converted into the corresponding peroxyl radicals. The a-hydroxyethylperoxyl radicals decay by first order kinetics (k = ki + k2 [OH -]) acetaldehyde and H02/H+ + 01 being the products (ki (20 °C) = 50 ± 10 s" 1 , Ea = 66 ± 7 kJ-mol -1 , k2= (4± 1) X 10 9 M -1 s -1). In competition (favoured by low pH, low tem-perature and high dose rate) they also decay by second order kinetics (2k3 = (7 ^ 2) x 10 8 M~ 1 s _1). The most important route in the bimolecular decay leads to acetaldehyde, acetic acid and oxygen (ca. 75%). This route might largely be concerted (Russell mech-anism), but there might also be a contribution from the disproportionation of oxyl radicals within the solvent cage. There is also a concerted route that leads to two molecules of acetic acid and to hydrogen peroxide (ca. 10%). Another pathway (ca. 15%) yields two oxyl radicals and oxygen. The former may either decompose into formic acid and methyl radicals (ca. 5%) or rearrange into 1,1-dihydroxyethyl radicals (ca. 10%). These radicals add oxygen and the resulting peroxyl radicals rapidly decompose into acetic acid and HO2. The reaction of a-hydroxyethylperoxyl radicals with H02/02 radicals appears to be slow (k» 10 7 M-is-i). 
  Reference    Z. Naturforsch. 38b, 212—219 (1983); received September 28 1982 
  Published    1983 
  Keywords    Pulse Conductometry, Peroxyl Radicals, Oxyl Radicals, Radical Rearrangements, Radiation Chemistry 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-0212.pdf 
 Identifier    ZNB-1983-38b-0212 
 Volume    38 
4Author    Heinz-Peter Schuchmann, Clemens Von SonntagRequires cookie*
 Title    Methylperoxyl Radicals: A Study of the y-Radiolysis of Methane in Oxygenated Aqueous Solutions  
 Abstract    A product study has been made of the y-radiolysis of aqueous methane solutions that also contained nitrous oxide and oxygen. Formaldehyde (G = 2.8), hydrogen peroxide (G = 2.1), methanol (G = 1.5), methylhydroperoxide (G = 0.8), formic acid (G = 0.3), and dimethylper-oxide (G = 0.1) were found. In alkaline solutions (pH 8, 10-3 M phosphate buffer), the formal­ dehyde yield rises to G = 3.2, while the formic acid yield falls to almost zero (G = 0.05). The initial precursor of the carbon-containing products is the methylperoxyl radical. The methyl­ peroxyl radicals decay through a short-lived tetroxide along various pathways. The most promi­ nent one leads to formaldehyde, methanol and oxygen. Methoxyl radicals (and oxygen) are also formed and, after rearrangement into hydroxymethyl radicals and their conversion into hy-droxymethylperoxyl radicals, eventually yield formic acid and probably further formaldehyde. A route to formaldehyd and hydrogen peroxide is also envisaged. Methylhydroperoxide is formed in the reaction of methylperoxyl radicals with H 0 2 / 0 27 radicals (from radiolytic H atoms and the unimolecular decay of the hydroxymethylperoxyl radical). 
  Reference    Z. Naturforsch. 39b, 217 (1984); received September 19 1983 
  Published    1984 
  Keywords    Autoxidation, Peroxyl Radicals, Oxyl Radicals, Radical Rearrangements, Radiation Chemistry 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-0217.pdf 
 Identifier    ZNB-1984-39b-0217 
 Volume    39 
5Author    Alicja Piesiak, M. An, Nien Schuchmann, Henryk Zegota, Clemens Von SonntagRequires cookie*
 Title    ß-Hydroxyethylperoxyl Radicals: A Study of the y-Radiolysis and Pulse Radiolysis of Ethylene in Oxygenated Aqueous Solutions  
 Abstract    Hydroxyl radicals (and H atom s) generated in the radiolysis of N20-co n tain in g w ater add to ethylene forming /3-hydroxyethyl radicals (and ethyl radicals). In the presence of oxygen these are converted into the corresponding peroxyl radicals which decay bim olecularly (2 k — 2 x 108 M ~'s-1) as m easured by pulse radiolysis. The m ajor products (G values in brackets) are glycolaldehyde (3.3), form aldehyde (1.6), ethylene glycol (0.8), acetaldehyde (0.5), organic peroxidic m aterial (0.5), and hydrogen peroxide (2.4) (dose rate 0.26 Gy s-1, pH 5.6). A m aterial balance has been obtained with respect to the primary w ater radicals (6.0) and oxygen uptake (4.8). The products and their yields can be accounted for if in the rate determ ining step atetro x id e is form ed which decomposes via three m ajor pathways leading to; (i) H 20 2 and two m olecules of glycolaldehyde (ca. 45%), (ii) 0 2, glycolaldehyde and ethylene glycol (ca. 30%), and (iii) 0 2, two molecules of form aldehyde and two C H 2OH radicals (ca. 15%). A 1,2-H shift of interm ediate oxyl radicals is unim portant in this system. 
  Reference    Z. Naturforsch. 39b, 1262—1267 (1984); received March 5 1984 
  Published    1984 
  Keywords    Peroxyl Radicals, Oxyl Radicals, Pulse Radiolysis, Ethylene, Reaction Kinetics 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-1262.pdf 
 Identifier    ZNB-1984-39b-1262 
 Volume    39 
6Author    Nien Man, Henryk Schuchmann, Zegota, Clemens Von SonntagRequires cookie*
 Title    Acetate Peroxyl Radicals, 0 2 CH 2 C0;: A Study on the y-Radiolysis and Pulse Radiolysis of Acetate in Oxygenated Aqueous Solutions  
 Abstract    Hydroxyl radicals from the radiolysis of N 2 0/0 2 (4:1 v/v)-saturated aqueous solutions have been reacted with acetate ions (1CT 2 M). As measured by pulse radiolysis, the resulting "CH 2 C0 2 radicals react with oxygen yielding the corresponding peroxyl radicals, 0 2 CH 2 C0 2 (k = 1.7 x 10 9 M-V 1). These peroxyl radicals decay bimolecularly (2k = 1.5 x 10 8 M _1 s _1) giving rise to the products (G values in brackets) glyoxylic acid (2.7), glycolic acid (0.7), formaldehyde (1.4), carbon dioxide (1.4), organic hydroperoxide (0.7) and hydrogen peroxide (2.5). Oxygen is consumed with a G value of 5.3. Aided by data from pulse radiolysis it is concluded that the intermediate tetroxide formed upon the bimolecular decay breaks down by various routes to yield: (i) hydrogen peroxide and two molecules of glyoxylic acid (ca. 27%); (ii) oxygen, glycolic acid and glyoxylic acid (ca. 25%); (iii) hydrogen peroxide and two molecules of formaldehyde, carbon dioxide and OH~ (25%). These reactions do not involve free radicals as intermediates; (iv) There is some 0 2 (G = 0.5) formed in the decay of the peroxyl radicals, which is attributed to the decay of intermediate oxyl radicals (tetroxide —* • 0 2 + 2 0CH 2 C0 2) by 1,2-H shift, oxygen addition and H0 2 elimination, a reaction sequence which gives rise to glyoxylic acid (10%); (v) The reaction of 0 2 with the organic peroxyl radical yields the hydroperoxide (13%). Reaction (iii) is a novel peroxyl radical reaction. 
  Reference    Z. Naturforsch. 40b, 215—221 (1985); received October 24 1984 
  Published    1985 
  Keywords    Acetic Acid, Peroxyl Radicals, Oxyl Radicals, Superoxide Radicals, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_B/40/ZNB-1985-40b-0215.pdf 
 Identifier    ZNB-1985-40b-0215 
 Volume    40 
7Author    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