Antioxidant Pathways and One-Electron Oxidation of Dopamine and Cysteine in Electrospray and On-Line Electrochemistry Electrospray Ionization Mass Spectrometry

✍ Scribed by Nare Alpheus Mautjana; Joshua Estes; John R. Eyler; Anna Brajter-Toth

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 445 KB
• Volume: 20
• Category: Article
• ISSN: 1040-0397
• DOI: 10.1002/elan.200804279

✦ Synopsis

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.