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Upstream product

• 51-61-6 dopamine 
• 1199-18-4 6-Hydroxydopamin 
• 7732-18-5 water 
• 28094-15-7 Oxidopamine hydrochloride 
• 62-31-7 dopamine hydrochloride 
• 636-00-0 6-hydroxydopamine hydrobromide 

Relevant academic research and scientific papers

The oxidation of 6-hydroxydopamine in aqueous solution. Part 3. Kinetics and mechanism of the oxidation with iron(III)

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.

The oxidation of 6-hydroxydopamine in aqueous solution. Part 1. The formation of three metastable quinones at low pH

1H and 13C NMR investigations have been carried out in order to elucidate the products of oxidation of 6-hydroxy-dopamine [5-(2-aminoethyl)benzene-1,2,4-triol, protonated form H3LH+]. Stopped-flow, NMR kinetic experiments, and quantum mechanical calculations were employed as additional aids to the interpretation of the results. Evidence is provided that, at low pH, three quinones are produced that are in metastable equilibrium, namely the p- (pQ), o- (oQ), and triketo-quinones (tQ). Results obtained with sodium periodate and iron(III) are compared and discussed. At higher pHs (>2.5) the quinones reach rapid equilibrium because they start to deprotonate, all giving rise to the same species (Q-), which is the only species detectable above a pH of about 6 and which is stable over a large pH range.

A novel hydrogen peroxide-dependent oxidation pathway of dopamine via 6-hydroxydopamine

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.

Inhibition of the Fe(III)-catalyzed dopamine oxidation by ATP and its relevance to oxidative stress in Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic cells, which implicates a role of dopamine (DA) in the etiology of PD. A possible DA degradation pathway is the Fe(III)-catalyzed oxidation of DA by oxygen, which produces neuronal toxins as side products. We investigated how ATP, an abundant and ubiquitous molecule in cellular milieu, affects the catalytic oxidation reaction of dopamine. For the first time, a unique, highly stable DA-Fe(III)-ATP ternary complex was formed and characterized in vitro. ATP as a ligand shifts the catecholate-Fe(III) ligand metal charge transfer (LMCT) band to a longer wavelength and the redox potentials of both DA and the Fe(III) center in the ternary complex. Remarkably, the additional ligation by ATP was found to significantly reverse the catalytic effect of the Fe(III) center on the DA oxidation. The reversal is attributed to the full occupation of the Fe(III) coordination sites by ATP and DA, which blocks O2 from accessing the Fe(III) center and its further reaction with DA. The biological relevance of this complex is strongly implicated by the identification of the ternary complex in the substantia nigra of rat brain and its attenuation of cytotoxicity of the Fe(III)-DA complex. Since ATP deficiency accompanies PD and neurotoxin 1-methyl-4-phenylpyridinium (MPP+) induced PD, deficiency of ATP and the resultant impairment toward the inhibition of the Fe(III)-catalyzed DA oxidation may contribute to the pathogenesis of PD. Our finding provides new insight into the pathways of DA oxidation and its relationship with synaptic activity.

Kinetics of oxidation of hydroquinones by molecular oxygen. Effect of superoxide dismutase

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.

Iron-mediated generation of the neurotoxin 6-hydroxydopamine quinone by reaction of fatty acid hydroperoxides with dopamine: A possible contributory mechanism for neuronal degeneration in parkinson's disease

Exposure of dopamine to an excess of linoleic acid 13-hydroperoxide (13- hydroperoxyoetadecadienoic acid) in the presence of ferrous ions in Tris buffer, pH 7.4, resulted in a relatively fast, oxygen-independent reaction exhibiting first-order kinetics wi