Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry |
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Authors: | Nare Alpheus Mautjana Joshua Estes John R Eyler Anna Brajter‐Toth |
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Institution: | Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL, 32611‐7200, USA |
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Abstract: | Dopamine DA]+ (m/z 154), DA dimer 2DA‐H]+ (m/z 307) and DA quinone DAQ]+ (m/z 152) are detected in positive ion mode electrospray ionization mass spectrometry (ESI MS) of dopamine in 50/1/49 (vol%) water/acetic acid/methanol. H/D exchange experiments support a covalent structure of DA dimer. Thus, ESI of DA may involve 1e?, 1H+ oxidation processes followed by rapid radical dimerization. The DA quinone signal is low in ESI MS, which indicates a low efficiency of the 2e?, 2H+ oxidation reaction. On‐line electrochemistry ESI MS (EC/ESI MS) with low electrochemical cell voltage floated on high ES voltage increases electrospray current and improves sensitivity for DA. The DA quinone signal increases and DA dimer signal decreases. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity of ESI and EC/ESI MS measurements. A DA quinone‐cysteine adduct DAQ+Cys]+ was detected in solutions of DA with cysteine (Cys). ESI MS and EC/ESI MS indicate formation of the DA quinone‐cysteine adduct by 1e? pathway. Oxidation pathways in ESI MS are relevant to biological reactivity of DA and Cys. |
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Keywords: | Antioxidant Dopamine On‐line electrochemistry Electrospray ionization Mass spectrometry |
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