ZfN: Search Results

1	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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	TEI-XML for	default:Reihe_B/40/ZNB-1985-40b-0215.pdf
	Identifier	ZNB-1985-40b-0215
	Volume	40

2	Author	DavidJ. Deebleab, Eberhard Bothea, Heinz-Peter Schuchmanna, BarryJ. Parsonsb, GlynO. Phillips ', Clemens Von Sonntaga	Requires 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

3	Author	Shailesh Phulkar, Balijepalli Sethu, M. Adhava Rao, Heinz-Peter Schuchmann, Clemens Von Sonntag	Requires 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