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1Author    Leopold Horner, Engelbert PliefkeRequires cookie*
 Title    Die Autoxidation von metallischem Kupfer und Kupfer(I)-Verbindungen Investigation on Autoxidation of Metallic Copper and Copper(I) Compounds by Different Methods  
 Abstract    The corrosion of copper granules under controlled conditions (2.5% NaCl solution, pH 4 buffer, Og) was studied using a) the rate of uptake of oxigen and b) the pH stat method. Cu 2+ ions catalyse the corrosion of copper. The surface area of the copper and the temperature influence the rate of corrosion in the expected manner. Experiments in light and dark showed little variation in the results. The results obtained by measuring the O2 uptake and using the pH stat method were confirmed and complemented by electrochemical measurements. (Steady potential/time curves, current/voltage curves, measurement of the polarisation resistance and estimation of Cu 2+ during corrosion via a Cu 2+ sensitive electrode.) The influence on the corrosion of F~, CI -, Br -and I~, mineral acid concentration and other inorganic ions was also studied under standard conditions. To ensure the correctness of the interpretation of the results (see reaction scheme), the autoxidation of CuCl and CU2O was also studied under standard conditions. The experimental results are consistent with the steps (l)-(4) in the reaction scheme. The fastest step is clearly the oxidation of Cu 1+ , which is continuously supplied via the copper surface. The interpretation here presented forms the basis for the understanding of the inhibition of corrosion exhibited by a number of organic compounds. 
  Reference    Z. Naturforsch. 36b, 713—720 (1981); eingegangen am 19. Dezember 1980 
  Published    1981 
  Keywords    Copper(I) Compounds, Autoxidation, Electrochemical Investigation 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0713.pdf 
 Identifier    ZNB-1981-36b-0713 
 Volume    36 
2Author    A. M. El-Wakil, M. S. Soliman, A. B. FaragRequires cookie*
 Title    Quantum Chemical Interpretation of the Photoinitiated Autoxidation of Sulphite Catalysed by Ferric Ions  
 Abstract    Autoxidation of sulphite is the first well known chain reaction proceeding through free radicals in solutions. Dark and photochemical autoxidation of sulphite were stated to take place by the same mechanism except in the initial steps. It was found that the formation of sulphite radicals in photoinitiated autoxidation of sulphite which is a metal catalysed reaction as well as the classical thermal reaction is due to the absorption of photons by ferrisulphite complexes rather than sulphite itself. Confirmation of this finding was achieved spectrophotometrically as well as by the fact that such complexes are specified by very high stability constants. The present work is a further evidence for the presence of such complexes and to cover the gap present before in the literature data. Quantum mechanical calculations using the extended Hückel molecular orbital method has proved that the range of absorption by sulphite lies in a region at which sulphite alone does absorb at all, and the absorption process is thus due to the formation of ferrisulphite complexes. 
  Reference    Z. Naturforsch. 38b, 858—860 (1983); received March 11 1983 
  Published    1983 
  Keywords    Photoinitiation, Autoxidation, Sulphite Ferric Ion, Sensitization, Quantum Chemical Interpretation 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-0858.pdf 
 Identifier    ZNB-1983-38b-0858 
 Volume    38 
3Author    VitalyA. Roginsky3, TatjanaK. Barsukova3, Gernot Brucheltb, HartmutB. StegmanncRequires cookie*
 Title    The Oxidation of Catecholamines and 6-Hydroxydopamine by Molecular Oxygen: Effect of Ascorbate  
 Abstract    Comparative kinetic studies on the oxidation of catecholamines (CA) (dopamine (DA), epi­ nephrine (EP). norepinephrine (NEP)) serving as a neurom ediator in the sympathetic nervous system, 3,4-dihydroxyphenylalanine (DOPA) and 6-hydroxydopamine (6-OHDA), a well-known neurotoxic agent, were perform ed in the presence of ascorbate (A scH -) in 50 mM phos­ phate buffer, pH 7.40, at 37 °C by using a Clark electrode, EPR and the absorption spectros­ copy. The oxidation of CA and DOPA alone was found to be a self-accelerating process, with quinone products (Q) acting as autocatalysts. The rate of oxygen consumption (Rox) increased with time and reached a steady-state level. A starting value of Ro x increased in the order: EP < DOPA « NEP « DA « 6-OHDA, whereas a steady-state value of Ro x changed in the or­ der: DOPA < DA < NEP « EP « 6-OHDA. The changes in R0x with time were found to correlate with the resistance of primary Q to the intramolecular cyclization. The effect of A scH -on CA oxidation depended dramatically on whether A scH -was added to non-oxidized or preoxidized CA. Added to non-oxidized CA and DOPA, A scH -inhibited their oxidation (but not that of 6-OHDA). For the case of DA, a pronounced lag period was observed by both a Clark electrode and spectrophotometrically. The addition of A scH -to preoxidized CA. DOPA and 6-OHDA induced an increase in R0 x a°d a steady-state concentration of the ascorbyl radical. The kinetic behaviour of the systems was deter­ mined by two major factors: 1) A scH -suppressed the formation of Q, a catalyst for CA oxidation, most likely due to the reaction of A scH -with the semiquinone formed from CA; 2) Q derived both from CA and 6-OH D A catalyzed A scH -oxidation. The elevated cytotox­ icity of 6-OHDA was found to be in part caused by the condition that 6-OHDA oxidation was not inhibited by A scH -and by the high efficiency of 6-OHDA as a redox cycling agent in combination with A scH ". These observations explain the very pronounced and prolonged cytotoxicity of 6-OHDA even at low concentrations that increases at elevated concentrations of A scH -. 
  Reference    Z. Naturforsch. 52c, 380—390 (1997); received November 7. 1996/ 
  Published    1997 
  Keywords    birthday Catecholamines, 6-Hydroxydopamine, Ascorbate, Autoxidation, Redox Cycling 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0380.pdf 
 Identifier    ZNC-1997-52c-0380 
 Volume    52 
4Author    Nien Man, Clemens Schuchmann, Von SonntagRequires cookie*
 Title    Free Radical Induced Oxidation of Neutral Aqueous Solutions of D-Glucose in the Presence of Oxygen -a Non-Chain Process  
 Abstract    Oxygenated 1 M aqueous solutions of 2-methyltetrahydrofuran (MTHF) or D-glucose were y-irradiated, and G(total peroxide) was determined as a function of dose rate and temperature. Whereas MTHF was oxidized by a chain process, D-glucose was not. The peroxyl radicals derived from D-glucose rapidly eliminate H02". At natural pH H02' (pK = 4.75) is largely deprotonated. O2— does not propagate a chain. 
  Reference    Z. Naturforsch. 33b, 329—331 (1978); received November 25 1977 
  Published    1978 
  Keywords    Autoxidation, D-Glucose, 2-Methyltetrahydrofuran, a-Hydroxyalkylperoxyl Radicals, y-Irradiation 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-0329.pdf 
 Identifier    ZNB-1978-33b-0329 
 Volume    33 
5Author    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 
6Author    W. Erner, H. K. Alusa, W. Illiam, G. Filby, RuthM. ÜnznerRequires cookie*
 Title    Chemical Aspects of the Mutagenic Activity of the Ascorbic Acid Autoxidation System  
 Abstract    It has been proposed that the mutagenic activity associated with the ascorbic acid autoxidation system may involve hydrogen peroxide and peroxide radicals. We report here that the mutagenic effect may also partially reside in as yet unknown secondary products. The observed mutagenicity of 2,3-diketogulonic acid, one o f the main oxidation products, reflects its ability to form hydrogen peroxide. 
  Reference    Z. Naturforsch. 37c, 40—45 (1982); received September 16 1981 
  Published    1982 
  Keywords    Ascorbic Acid, Autoxidation, Hydrogen Peroxide, Mutagenic Effect, Oxidation Products 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-0040.pdf 
 Identifier    ZNC-1982-37c-0040 
 Volume    37