Screening of how aromatic substitutions and cycling ion affects the electrochemistry of quinones and catechols
In this project we will focus on the redox chemistry of quinones to further understand of how the quinone redox chemistry is affected by the cycling ion and by substitutions on the quinone ring. In addition we will expand the investigation to include substituted catechols with particular emphasis on cycling of divalent cations at the proximity of the two oxygens would allow for charge compensation by one doubly charged di-cation.
We know from previous, combined experimental and computational studies that the large difference in reduction potentials of quinones when protons, lithium and non-coordination ions are cycled is due to the different charge stabilizing effect that the different ions show. In addition we have seen that the effects of substitution on the aromatic ring are quite different for different cycling chemistries and that the cycling ion also strongly affects the relative energies of the nine involved states in quinone redox conversion leading to dispropostionation of intermediate redox states for some cycling ions while some cycling chemistries lead to stable radical intermediates. We have suggested that the difference in behavior can be traced to the coulombic interaction between successively induced charges and we have introduced an interaction term to account for this effect. The interaction term is readily accessible from computational studies and in this proposal we want to explore the possibility to expand the concept to a large set of cycling ions, such as protons, lithium, sodium, potassiun, zink, calcium and manganese. In addition we want to expand the screening to include, not only substituted quinones, but also to include the catechol-family of compounds with the two oxygens in orto-positions to each other.
By employing first-principles theory based on density functional theory (DFT), we will investigate how the nature of substituents, cucling ion and solvent affects the redox potential of quinones and catechols. The redox potentials in solution will be calculated by combining DFT and self-consistent reaction field methods where the free energies (including all internal energy and entropic contribution) are calculated using the Born–Haber thermodynamic cycle. Explicit solvent effect will be assessed by carrying out ab-initio molecular dynamics (MD) simulations. A sequential MD/DFT scheme will be used to determine the electronic structure at a given temperature. In this approach, snapshots of the MD simulations are selected to carry out high-accurate single point DFT calculations, and subsequently, the obtained electronic structures are averaged. We will explore the Born-Oppenheimer molecular dynamics as implemented in the Vienna Ab-initio Simulation Package (VASP).
 H. Wang, R. Emanuelsson, A. Banerjee, R. Ahuja, M. Strømme, M. Sjödin, The Journal of Physical Chemistry C 2020, 124, 13609-13617.