Mechanism of the oxidation of dopamine by the hydroxyl radical in aqueous solution

Journal Article · Wed Aug 10 00:00:00 EDT 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00354a041· OSTI ID:7119133

Richter, H W ^[1]; Waddell, W H

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1. Carnegie-Mellon Univ., Pittsburgh, PA

The hydroxyl radical (HOin equilibrium) reacts with dopamine (4-(2-aminoethyl)-1,2-benzenediol) via one-electron oxidation producing o-semiquinone and o-semiquinone anion radicals, k = 5.9 x 10/sup 9/ M/sup -1/ s/sup -1/. Reaction of HO. with protonated dopamine (H/sup +/QH/sub 2/) proceeds via addition to the aromatic ring, while reaction with deprotonated dopamine (H/sup +/QH/sup -/) proceeds via direct, one-electron oxidation. The isomeric hydroxycyclohexadienyl radicals formed via addition of HO. to H/sup +/QH/sub 2/ yield three kinetically distinguishable groups (1- and 2-, or 3- and 6-, or 4- and 5-hydroxycyclohexadienyl radicals) with regard to rates of water elimination to produce semiquinone radicals; dehydration is ''very fast'' (addition of HO. ipso to an OH group), ''fast'', or ''slow''. The fast and slow reactions are acid and base catalyzed, with minimal rates at pH 4-5. Acid catalysis appears to be specific, while base catalysis is general. Spectra were determined for the initial products of HO. reaction with H/sup +/QH/sub 2/ at pH 3.1 and 4.7. Deprotonation of the HO. adducts is the rate-controlling step in the base-catalyzed water loss at pH less than or equal to 8.5. For the slow water elimination, rate constants for proton transfer from the adducts to H/sub 2/O, HPO/sub 4//sup 2 -/, HO/sup -/, and PO/sub 4//sup 3 -/ were 1.7 x 10/sup 2/, 6.5 x 10/sup 8/, less than or equal to1.5 x 10/sup 11/, and less than or equal to7.0 x 10/sup 11/ M/sup -1/ s/sup -1/, respectively; for the fast reaction, rate constants for H/sub 2/O and HPO/sub 4//sup 2 -/ were 1.1 x 10/sup 3/ and 2.2 x 10/sup 8/ M/sup -1/ s/sup -1/, respectively.

• OSTI ID: 7119133
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:16; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400600* -- Radiation Chemistry
AMINES
AQUEOUS SOLUTIONS
AROMATICS
AUTONOMIC NERVOUS SYSTEM AGENTS
CARDIOTONICS
CARDIOVASCULAR AGENTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
DISPERSIONS
DOPAMINE
DRUGS
HYDROXY COMPOUNDS
HYDROXYL RADICALS
KINETICS
MIXTURES
NEUROREGULATORS
ORGANIC COMPOUNDS
OXIDATION
PHENOLS
POLYPHENOLS
RADICALS
REACTION KINETICS
SOLUTIONS
SYMPATHOMIMETICS
YIELDS