41596-66-1Relevant articles and documents
The oxidation of 6-hydroxydopamine in aqueous solution. Part 3. Kinetics and mechanism of the oxidation with iron(III)
Jameson, Guy N.L.,Linert, Wolfgang
, p. 569 - 575 (2001)
The kinetics of the oxidation of 6-hydroxydopamine [5-(2-aminoethyl)benzene-1,2,4-triol, protonated form H3LH+] by iron(III) under anaerobic conditions are presented. A complex mechanism whereby the o- (oQ), p- (pQ), and triketoquinones (tQ) are formed via parallel inner- and outer-sphere electron transfer mechanisms has been established. The outer-sphere mechanism is particularly fast (nearly diffusion limiting) and predominates. By following the dependence of the rate on ionic strength it has been shown that a deprotonated form of 6-hydroxydopamine reacts via an outer-sphere reaction with all species of iron. Like the other catecholamines [3,4-dihydroxy-1-(2-amino-ethyl)benzenes], but to a much smaller extent, complex formation occurs by FeOH2+ reacting with the fully protonated form of 6-hydroxydopamine. Three different semiquinones are initially produced; two of them, the triketo- and p-semiquinones, are tautomers. The o- and triketo-semiquinones react quickly with another iron atom to form their respective quinones. The p-semiquinone, however, is seemingly stable, partly reacting with more iron and partly disproportionating to form pQ and reforming 6-hydroxydopamine. At pHs above 2.5. pQ and oQ are in equilibrium via a deprotonated quinone Q-. The biological implications of this mechanism are discussed.
A novel hydrogen peroxide-dependent oxidation pathway of dopamine via 6-hydroxydopamine
Manini, Paola,Panzella, Lucia,Napolitano, Alessandra,D'Ischia, Marco
, p. 2215 - 2221 (2003)
In the presence of excess H2O2, oxidation of dopamine was diverted from the usual pigment-forming pathway to afford 6-hydroxydopamine and then a colorless reaction mixture comprising a polar non-extractable product. The latter was obtained in 20% yield by oxidation of 6-hydroxydopamine and was tentatively formulated as the novel 5-(2-aminoethyl)-2-hydroxy-5-(3-hydroxy-2-oxotetrahydro-1aH-oxireno[2,3] cyclopenta[1,2-b]pyrrol-3a(4H)-yl)cyclohex-2-ene-1,4-dione by extensive spectral analysis and conversion to a tetraacetyl derivative. Mechanistic experiments suggested that formation of the product proceeds via 6-hydroxydopamine by H2O2-dependent epoxidation and cyclization steps followed by dimerization and ring contraction with decarboxylation.
Kinetics of oxidation of hydroquinones by molecular oxygen. Effect of superoxide dismutase
Roginsky, Vitaly,Barsukova, Tatyana
, p. 1575 - 1582 (2007/10/03)
The kinetics of the autoxidation of sixteen hydroquinones (QH2) (substituted 1,4-hydroquinones and 1,4-dihydroxynaphthalenes as well as 9,10-dihydroxyphenanthrene) were studied using the Clark electrode technique in aqueous solution, pH 7.40, at 37°C both with and without added superoxide dismutase (SOD). QH2 oxidation occurs typically with a self-acceleration. A maximum rate of oxidation, RMAX, was found to be the most indicative parameter characterizing QH2 oxidizability. A kinetic scheme of QH2 autoxidation was developed; computer simulations carried out on the basis of this scheme reproduce the main kinetic features of the studied process. QH2 autoxidation is suggested to be a free-radical chain process with semiquinone (Q-) and superoxide (O2-) as chain-carrying species. The oxidation is initiated by reaction (1) Q + QH2→2Q- + 2H+. The addition of SOD results in two main effects: shifting the equilibrium (2) Q- + O2?Q + O2- (K2) to the right and suppressing reaction (3) QH2 + O2-→Q- + H2O2. The net effect of SOD depends basically on K2. When K2 2 > 0.1, the more SOD inhibits the oxidation, the higher K2. The concentration of SOD causing the 50%-effect on RMAX ([SOD]50), both inhibitory and stimulatory, decreases dramatically when K2 increases. At [SOD] ? [SOD]50 the rate of QH2 autoxidation is definitively determined by the rate of reaction (1). For the majority of QH2, [SOD]50 is significantly less than the physiological values of [SOD] and thus QH2 autoxidation in biological environment is expected to occur in the above kinetically simple mode.
