19186-12-0Relevant academic research and scientific papers
Singlet dioxygen formation in ozone reactions in aqueous solution
Mun?oz,Mvula,Braslavsky,Von Sonntag
, p. 1109 - 1116 (2007/10/03)
In ozone reactions, singlet dioxygen [O2(1Δg)] is formed when ozone reacts by O-atom transfer. O2(1Δg) yields were determined for more than 50 compounds using as reference the reaction of hydrogen peroxide with hypochlorite. Close to 100percent yields were found in the reaction of O3 with sulfides, disulfides, methanesulfinic acid, and nitrite. In accordance with this, the only products are: methionine sulfoxide, methanesulfonic acid, and nitrate for the reaction of O3 with methionine, methanesulfinic acid, and nitrite, respectively. In the case of aliphatic tertiary amines (trimethylamine, triethylamine, and DABCO), the O2(1Δg) yields range between 70 and 90percent, the aminoxide being the other major product. With EDTA and nitrilotriacetic acid (NTA), the O2(1Δg) yield is around 20percent. The interpretation of the data with DABCO required the determination of the quenching constant of O2(1Δg) by this amine, kq = 1.8 × 109 dm3 mol-1 s-1 in H2O and D2O, two orders of magnitude lower than previously reported. Aromatic tertiary amines give even lower O2(1Δg) yields [N,N-dimethylaniline (7percent), N,N,N′,N′-tetramethylphenylenediamine (9percent)]. Substantial amounts of O2(1Δg) are also formed with the DNA model compounds, 2′-deoxyguanosine (40percent) and 2′-deoxyadenosine (15percent, in the presence of tert-butyl alcohol as ·OH scavenger). The pyrimidine nucleobases only yield O2(1Δg) when deprotonated at N(1). O2(1Δg formation is also observed with hydrogen sulfide (15percent), azide (17percent), bromide (56percent), iodide (12percent), and cyanide ions (20percent). The O2(1Δg yield from the reaction of O3 with phenols and phenolates is typically around 20percent, but may rise closer to 50percent in the case of pentachloro-and pentabromo-phenolate. Low O2(1Δg yields are found with unsaturated acids such as dihydroxyfumarate (6percent), muconate (2percent), and acetylenedicarboxylate (15percent). With saturated compounds, also, no O2(1Δg (e.g. with propan-2-ol, acetaldehyde, acetaldehyde dimethylacetal and glyoxal) or very little O2(1Δg (formic acid; 6percent, at high formate concentrations) was detected. As shown with some examples, knowledge of the O2(1Δg yield (in combination with that of other products) is a prerequisite for the elucidation of the mechanisms of O3 reactions in aqueous solutions.
The Radiolysis of Uracil in Oxygenated Aqueous Solutions. A Study by Product Analysis and Pulse Radiolysis
Schuchmann, Man Nien,Sonntag, Clemens von
, p. 1525 - 1532 (2007/10/02)
Hydroxyl radicals are generated by the radiolysis of N2O-O2 (4:1 v/v)-saturated aqueous solutions of uracil.They add to the 5,6-double bond of the substrate .These radicals are converted by oxygen into the corresponding peroxyl radicals (I) and (II), respectively.Peroxyl radical (I) undergoes a base-induced O2(1-.) elimination (kobs 8x1E3 s-1 at pH 10.5).As an intermediate 5-hydroxy-isopyrimidine is formed which rearranges into isobarbituric acid and adds water forming 5,6-dihydro-5,6-dihydroxyuracil.Competing with this base-induced reaction of radical (I) there is a bimolecular decay of radicals (I) and (II).These processes become predominant at low pH.For this reason a strong pH dependence of G (products) is observed.The major products are (G values at pH 3 and 10 in parentheses) 5,6-dihydroxy-5,6-dihydrouracil (1.1; 2.4), isobarbituric acid (0; 1.2), N-formyl-5-hydroxyhydantoin (1.6; 0.2), 5-hydroxybarbituric acid (0.9; 0.2). 5-Hydroxybarbituric acid is formed in its keto form.Its deprotonation (k 4.4 s-1) has been followed by pulse conductometry.Details of the reaction mechanism, e.g. the involvement of oxyl radicals in the bimolecular decay of (I) and (II), are discussed.
