Electrochemical Reduction of Quinones: Interfacing Experiment and Theory for Defining Effective Radii of Redox Moieties

Abstract

Using cyclic voltammetry, we examined the dependence of the reduction potentials of six quinones on the concentration of the supporting electrolyte. An increase in the electrolyte concentration, resulting in an increase in the solution polarity, caused positive shifts of the reduction potentials. We ascribed the observed changes in the potentials to the dependence of the solvation energy of the quinones and their anions on the media polarity. Analysis of the reduction potentials, using the Born solvation energy equation, yielded unfeasibly small values for the effective radii of the quinone species, that is, the experimentally obtained effective radii were up to 4-fold smaller than the radii of the solvation cavities that we calculated for the quinones. The nonspherical shapes of the quinones, along with the uneven charge density distribution in their anions, encompassed the underlying reasons for the discrepancies between the obtained experimental and theoretical values for the radii of these redox species. The generalized Born approach, which does not treat the solvated species as single spheres, provided means for addressing this discrepancy and yielded effective radii that were relatively close to the measured values.

Amyloid Histology Stain for Rapid Bacterial Endospore Imaging

“…7). As previously reported, an increase in the medium viscosity causes an increase in the ThT fluorescence quantum yield (82), which is expected given the properties of chromophores, such as ThT, classified as molecular rotors (4,81). A viscosity-induced increase in the emission quantum yield of ThT amounts to about three orders of magnitude (82).…”

“…1), ThT is a molecular rotor (24,73,74,81). Similar to other chromophores that are molecular rotors (3,4,28,39) within the lifetime of the lowest singlet-excited state of the dye, a viscous microenvironment slows and/or completely restrains the attainment of ThT conformers (i.e., rotamers) that have the density of vibrational states allowing efficient internal conversion to the ground state. Such viscosity-induced suppression of efficient nonradiative deactivation results in an increase in the emission quantum yield of ThT, as demonstrated by photophysical studies of this staining agent for solvent media with differing viscosities (82).…”

Bioinspired molecular electrets: bottom-up approach to energy materials and applications

“…The data points (the circles) represent E ð0Þ for four neat solvents, obtained from extrapolation to zero electrolyte concentration. 72,73 The dashed lines are least-square data fits using E ¼ a þ b∕ε, as expected from the Born solvation energy. 74 (c) Zero-to-zero energy of Aa residues.…”

“…72,73 The half-wave potentials, E ð1∕2Þ , were determined from the midpoints between the cathodic and anodic peak potentials for reversible oxidation and from the inflection points of the anodic waves for irreversible oxidation. For each residue, CV was carried out for different solvents at different electrolyte concentrations (tetrabutylammonium hexafluorophosphate was used for the electrolyte with concentration varying between 25 to 200 mM).…”

Building blocks for bioinspired electrets: molecular-level approach to materials for energy and electronics

“…To elucidate the media effects on the electronic properties, we focus on the dependence of the Aa electrochemical potentials on the solvent polarity [64][65][66][67][68] polarity that have electrochemical windows extending over the expected potentials needed for the oxidation of the Aa residues: chloroform (CHCl 3 ), dichloromethane (DCM), benzonitrile (PhCN), acetonitrile (MeCN), and propylene carbonate (PC).…”