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

The physicochemical and electrochemical characteristics of two naturally occurring quinone families were studied in the context of electrochemical CO2 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 Q10 and Q0. Cyclic voltammetry experiments revealed CO2-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 CO2, 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 CO2 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 Q10 in mitochondrial membranes, the enhanced lipophilicity of the nonpolar Coenzyme Q10 compared to the chain-less Q0 was leveraged to facilitate the heterogeneous CO2-selective electrochemical response of a Coenzyme Q10 composite in aqueous media, thus illustrating the potential of natural/bioinspired compounds for future redox-active applications.