Fe(III)-coordination properties of neuromelanin components: 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid.
The Fe(III)-coordination chemistry of neuromelanin building-block compounds, 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and 5,6-dihydroxy-N-methyl-indole (Me-DHI), and the neurotransmitter dopamine were explored in aqueous solution by anaerobic pH-dependent spectrophotometric titrations. The Fe(III)-binding constants and pH-dependent speciation parallel those of catechol in that mono, bis, and tris FeLx species are present at concentrations dependent on the pH. The bis FeL2 dihydroxyindole species are favorable for L = DHI and DHICA under neutral to mildly acidic conditions. DHI and DHICA are stronger Fe(III) chelates than catechol, dopamine, and Me-DHI at pH values from 3 to 10. Oxidation studies reveal that iron accelerates the air oxidation of DHI and DHICA.
Charkoudian
Louise K
LK
Department of Chemistry, Duke University, P.O. Box 90346, Durham, North Carolina 27708, USA.
Franz
Katherine J
KJ
D004298:Dopamine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008543:Melanins / Q000737:chemistry*; D019636:Neurodegenerative Diseases / Q000209:etiology; D010100:Oxygen / Q000737:chemistry; D010300:Parkinson Disease; D013057:Spectrum Analysis; D017186:Titrimetry
D007211:Indoles; D008543:Melanins; C014121:neuromelanin; C030692:5,6-dihydroxy-2-indolylcarboxylic acid; D007501:Iron; D010100:Oxygen; D004298:Dopamine; C033871:5,6-dihydroxyindole