title: Enhancing the Reduction Potential of Quinones via Complex Formation.
abstract: Quantum calculations are used to study the manner in which quinones interact with proton-donating molecules. For neutral donors, a stacked geometry is favored over a H-bond structure. The former is stabilized by charge transfers from the N or O lone pairs to the quinone's π* orbitals. Following the addition of an electron to the quinone, the radical anion forms strong H-bonded complexes with the various donors. The presence of the donor enhances the electron affinity of the quinone. This enhancement is on the order of 15 kcal/mol for neutral donors, but up to as much as 85 kcal/mol for a cationic donor. The increase in electron affinity is larger for electron-rich quinones than for their electron-deficient counterparts, containing halogen substituents. Similar trends are in evidence when the systems are immersed in aqueous solvent.
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322-0300, United States.
authors.forename: Binod
authors.initials: B
authors.lastname: Nepal
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322-0300, United States.
authors.forename: Steve
authors.initials: S
authors.lastname: Scheiner