Physicochemical and Electrochemical Investigation of Naturally Occurring Quinones for Application toward Electrochemically Mediated Carbon Dioxide Capture

Abstract

The physicochemical and electrochemical characteristics of two naturally occurring quinone families were studied in the context of electrochemical CO 2 capture. Due to their dissimilar lipophilic isoprenoid side chains and quinone redox centers, Vitamin K and Coenzyme Q homologues possess intrinsically adjustable physicochemical properties that were characterized using the Hansen solubility/log P lipophilicity parameters, and experimentally quantified using hydrophobic interaction chromatography and viscosity/diffusivity measurements, with an especially large polarity difference noted between Coenzymes Q 10 and Q 0 . Cyclic voltammetry experiments revealed CO 2 -dependent redox behavior that supported the proposed ECEC mechanism for complex formation between electroreduced 1,4-naphthoquinone-/1,4-benzoquinone-derived nucleophiles and the Lewis acidic CO 2 , with the Coenzyme Q adducts exhibiting less negative cathodic peak potentials than the parasitic dioxygen/superoxide half-reaction. Further investigation of Coenzyme Q anions suggested that their CO 2 complexation is potentially affected by both electronic and steric/polarity effects via the presence and length of the side chain substituent, respectively. Inspired by the electron transport role of Coenzyme Q 10 in mitochondrial membranes, the enhanced lipophilicity of the nonpolar Coenzyme Q 10 compared to the chain-less Q 0 was leveraged to facilitate the heterogeneous CO 2 -selective electrochemical response of a Coenzyme Q 10 composite in aqueous media, thus illustrating the potential of natural/bioinspired compounds for future redox-active applications.