What drives the redox properties of model green fluorescence protein chromophores?

K.M. Solntsev, D. Ghosh, O. Amador, M. Josowics, and A.I. Krylov
J. Phys. Chem. Lett. 2, 2593 – 2597 (2011)

We report the first experimental determination of the oxidation potentials E_ox⁰ (relative to standard hydrogen electrode, SHE) of the model GFP chromophores, para-, meta- and ortho- methylated 4-hydroxybenzylidene-2,3-dimethylimidazolinone (MeOBDI). E_ox⁰ of the three isomers are -1.31, -1.52, and -1.39 V, respectively. The electronic structure calculations reproduce the observed differences between the isomers and reveal that E_ox⁰ follow the trend of ionization energies (IE), i.e., p-MeOBDI has the lowest IE (6.96 eV in the gas phase) due to the resonance stabilization of its cation, while the resonance is detuned in m-MeOBDI resulting in more negative E_ox⁰.

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