| | 1 | Author
| R. K. Broszkiewicz+, T. Söylemez, D. Schulte-Frohlinde | Requires 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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| default:Reihe_B/37/ZNB-1982-37b-0368.pdf | | | | Identifier
| ZNB-1982-37b-0368 | | | | Volume
| 37 | |
| 2 | Author
| Nien Man, Clemens Schuchmann, Von Sonntag | Requires 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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| default:Reihe_B/42/ZNB-1987-42b-0495.pdf | | | | Identifier
| ZNB-1987-42b-0495 | | | | Volume
| 42 | |
| 3 | Author
| Alfred Hissung, Clemens Von Sonntag | Requires cookie* | | | Title
| Radiolysis of Cytosine, 5-Methyl Cytosine and 2'-Deoxycytidine in Deoxygenated Aqueous Solution A Pulse Spectroscopic and Pulse Conductometric Study of the OH Adduct | | | | Abstract
| Using the pulse radiolysis technique the OH adducts of cytosine, 5-methyl cytosine and 2'-deoxycytidine were investigated in alkaline N20 saturated aqueous solutions. Ab-sorption spectra were recorded and their change with time was correlated with the change in conductivity. An OH -induced reaction (1.4 • 10 8 1 • mol -1 • s -1) was observed with OH adducts of cytosine and 5-methyl cytosine leading to radicals (pK = 10.3), the G-values of which were 3.2 and 1.6 respectively (conductivity measurements). These intermediates were assigned to the C-5 OH radical adducts. After completion of the free radical reactions (2k = 6 • 10 8 1 • mol -1 • s -1) the resulting product mixture showed pK-values of 8.3 (cytosine, G = 0.6), 10.5 (5-methyl cytosine, G = 0.8), 10.7 (cytosine, G=1.5; 2'-deoxycytidine, G=1.5) and 12.4 (cytosine, no G-value, determinable with optical detection). Ammonia, which is a product measured after y-radiolysis of all the three compounds investigated (G(NHs) = 0.6 ± 0.1), is not released within 15 ms after the pulse. | | | |
Reference
| Z. Naturforsch. 33b, 321—328 (1978); received November 25 1977 | | | |
Published
| 1978 | | | |
Keywords
| Cytosine, G-Values, pK-Values, Absorption Spectra, Pulse Radiolysis | | | |
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| default:Reihe_B/33/ZNB-1978-33b-0321.pdf | | | | Identifier
| ZNB-1978-33b-0321 | | | | Volume
| 33 | |
| 5 | Author
| Alicja Piesiak, M. An, Nien Schuchmann, Henryk Zegota, Clemens Von Sonntag | Requires 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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| default:Reihe_B/39/ZNB-1984-39b-1262.pdf | | | | Identifier
| ZNB-1984-39b-1262 | | | | Volume
| 39 | |
| 6 | Author
| Nien Man, Henryk Schuchmann, Zegota, Clemens Von Sonntag | Requires 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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| default:Reihe_B/40/ZNB-1985-40b-0215.pdf | | | | Identifier
| ZNB-1985-40b-0215 | | | | Volume
| 40 | |
| 7 | Author
| BarryJ. Parsons, Dietrich Schulte-Frohlinde, Clemens Von Sonntag | Requires cookie* | | | Title
| Reaction of Br3' 2 -with 2-Deoxy-D-ribose. A Preferred Attack at C-l | | | | Abstract
| In the photolysis of 5-bromouracil containing DNA Br atoms are expected inter mediates. In order to evaluate the possible site of attack of the Br atom at the sugar moiety of DNA the reaction of 2-deoxy-D-ribose with the Br atom (complexed with two bromide ions) was investigated. Hydroxyl radicals generated by the radiolysis of N20 saturated aqueous solutions were converted into Br3 -2_ radicals by 1 M bromide ions. Br3-2-reacts with 2-deoxy-D-ribose (k = 3.7 • 10 4 M -1 s -1 , pulse radiolysis). The major product is 2-deoxy-D-erythro-pentonic acid (G = 2.4, y-radiolysis). It is formed by hydrogen abstraction from C-l and oxidation of this radical by other radicals. An alternative route via the radical at C-2 is neglible. It follows that Br3-2 ~ reacts preferentially at C-l of 2-deoxy-£>-ribose. | | | |
Reference
| Z. Naturforsch. 33b, 666—668 (1978); received March 15 1978 | | | |
Published
| 1978 | | | |
Keywords
| Pulse Radiolysis, y-Radiolysis, 2-Deoxy-D-ribose, G-values, Radical Reactions | | | |
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| default:Reihe_B/33/ZNB-1978-33b-0666.pdf | | | | Identifier
| ZNB-1978-33b-0666 | | | | Volume
| 33 | |
| 8 | Author
| Xian-Ming Pan, Eugenie Bastian, Clemens Von Sonntag | Requires cookie* | | | Title
| The Reactions of Hydroxyl Radicals with 1,4-and 1,3-Cyclohexadiene in Aqueous Solution A Pulse Radiolysis and Product Study | | | | Abstract
| The reactions of radiolytically generated hydroxyl radicals and H atoms with 1,4-and 1,3-cyclohexadiene were studied by pulse radiolysis and product analysis. Hydrogen abstraction from these substrates by the OH radical yields the cyclohexadienyl radical (f (310 nm) = 4400 dm 1 mol" 1 cm"' from the reaction of the H atom with benzene) with an efficiency of 50% (0.29 ,«moI /"') in the case of 1,4-cyclohexadiene and 25% (0.15,«mol /"') in the case of 1,3-cyclohexadiene as determined by pulse radiolysis. The remaining OH radicals add to the olefin. In 1,4-cyclohexa-diene the yield of the resulting adduct radicals has been determined in a steady-state "'Co-y-irradiation experiment by reducing it with added 1,4-dithiothreitol (DTT) to 4-hydroxycyc-lohexene. There are two sites of OH radical attack in the case of 1,3-cyclohexadiene, and only the alkyl radical is reduced quantitatively by DTT (G(3-hydroxycyclohexene) = 0.15 ,«mol J '). From material balance considerations it is concluded that the allylic radical must be formed with a G value of 0.28 «mol J~ x but largely escapes reduction by DTT (G(4-hydroxycyclohexene) = 0.03 ,«mol y 1). H atoms add preferentially to the double bonds of 1,4-and 1,3-cyclohexadiene (78% and 93%, respectively), while the O t radical (the basic form of the OH radical) undergoes mainly H-abstraction (92% and 83%. respectively). The radicals formed in these systems decay bimolecularly (2k = 2.8xl0 4 dm' mop 1 s~'). In their combination reactions the cyclohexadienyl radicals form the four possible dimers in propor-tions such that the dienyl radical moiety shows a 2:1 preference to react from its central (la) rather than from a terminal carbon atom (lb). Cyclohexadienyl radicals and the OH-and H-adduct radicals also cross-terminate by disproportionation and dimerization. Material balance has been obtained for the 1,4-cyclohexadiene system in N : 0-saturated solution (10 : mol dm 3) at a dose rate of 0.14 Gy s" 1 , the products (G values in «mol J ') being: benzene (0.085), 4-hydroxycyclohexene (0.25), cyclohexadienyl-dimers (0.144), cyclohexadienyl-OH-adduct-dimers (0.02), OH-adduct-dimers (0.02). Some of the 4-hydroxycyclohexene is formed in an H-abstraction reaction by the OH-adduct radical from 1,4-cyclohexadiene. | | | |
Reference
| Z. Naturforsch. 43b, 1201—1205 (1988); received April 13 1988 | | | |
Published
| 1988 | | | |
Keywords
| 1, 4-Cyclohexadiene, 1, 3-Cyclohexadiene Hydroxyl Radical, Cyclohexadienyl Radical, Pulse Radiolysis | | | |
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| default:Reihe_B/43/ZNB-1988-43b-1201.pdf | | | | Identifier
| ZNB-1988-43b-1201 | | | | Volume
| 43 | |
| 9 | Author
| OliverJ. Mieden, Clemens Von Sonntag, D. Ruhr, F.R G | Requires 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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| default:Reihe_B/44/ZNB-1989-44b-0959.pdf | | | | Identifier
| ZNB-1989-44b-0959 | | | | Volume
| 44 | |
|
