ABSTRACT
Grid-scale energy storage applications, such as redox flow batteries, rely on the solubility of redox-active organic molecules. Although redox-active pyridiniums exhibit exceptional persistence in multiple redox states at low potentials (desirable properties for energy storage applications), their solubility in non-aqueous media remains low, and few practical molecular design strategies exist to improve solubility. Here we convey the extent to which discrete, attractive interactions between C-H groups and π electrons of an aromatic ring (C-H···π interactions) can describe the solubility of N-substituted pyridinium salts in a non-aqueous solvent. We find a direct correlation between the number of C-H···π interactions for each pyridinium salt and its solubility in acetonitrile. The correlation presented in this work highlights a consequence of disrupting strong electrostatic interactions with weak dispersion interactions, showing how minimal structural change can dramatically impact pyridinium solubility.
ABSTRACT
Successful application of emerging bioelectrocatalysis technologies depends upon an efficient electrochemical interaction between redox enzymes as biocatalysts and conductive electrode surfaces. One approach to establishing such enzyme-electrode interfaces utilizes small redox-active molecules to act as electron mediators between an enzyme-active site and the electrode surface. While redox mediators have been successfully used in bioelectrocatalysis applications ranging from enzymatic electrosynthesis to enzymatic biofuel cells, they are often selected using a guess-and-check approach. Herein, we identify structure-function relationships in redox mediators that describe the bimolecular rate constant for its reaction with a model enzyme, glucose oxidase (GOx). Based on a library of quinone-based redox mediators, a quantitative structure-activity relationship (QSAR) model is developed to describe the importance of mediator redox potential and projected molecular area as two key parameters for predicting the activity of quinone/GOx-based electroenzymatic systems. Additionally, rapid scan stopped-flow spectrophotometry was used to provide fundamental insights into the kinetics and the stoichiometry of reactions between different quinones and the flavin adenine dinucleotide (FAD+/FADH2) cofactor of GOx. This work provides a critical foundation for both designing new enzyme-electrode interfaces and understanding the role that quinone structure plays in altering electron flux in electroenzymatic reactions.
