A Metastable Semiquinone Molecular Switch Modulated by Ascorbate/O: A Study from a System Far-From-Equilibrium to Biological Assays in Mitochondria.

A molecular switch based on the metastable radical anion derived from a substituted heteroaryl quinone is described. Pyrrolyl quinone thiocyanate (PQ 9) showed an interaction with the fluoride anion that was visible to the naked eye and quantified by UV/vis and 1H and 13 C NMR. The metastable quinoid species formed by the interaction with F ("ON" state) showed a molecular switching effect autocontrolled by the presence of ascorbate ("OFF" state) and back to the "ON" state by an autooxidation process, measured by visible and UV/vis spectroscopy.