Stable Parent Anions of Dopamine and Adrenaline: A New Form of Neurotransmitters.

Previously, dopamine and adrenaline were only known to exist in three closed-shell forms: neutral molecules (including zwitterions), protonated cations, and deprotonated anions. In the present work, stable open-shell parent anions of dopamine and adrenaline were generated in the gas phase and characterized by a combination of anion photoelectron spectroscopy and calculations. These anions were formed as a result of an enol-keto-type tautomerization initiated by the attachment of excess electrons. Calculations showed that hydrogen atoms on the hydroxyl groups of dopamine and adrenaline migrated to adjacent carbon atoms under the influence of the additional electron, breaking the aromaticity of the benzene ring and resulting in the formation of the rare anionic tautomers. We speculate that the secondary electrons generated in scenarios such as radiotherapy could produce the anions reported in this work, providing a potential new depletion channel of these molecules in vivo.