Physicochemical\nand Electrochemical Investigation\nof Naturally Occurring Quinones for Application toward Electrochemically\nMediated Carbon Dioxide Capture

The\nphysicochemical and electrochemical characteristics\nof two\nnaturally occurring quinone families were studied in the context of\nelectrochemical CO<sub>2</sub> capture. Due to their dissimilar lipophilic\nisoprenoid side chains and quinone redox centers, Vitamin K and Coenzyme\nQ homologues possess intrinsically adjustable physicochemical properties\nthat were characterized using the Hansen solubility/log <i>P</i> lipophilicity parameters, and experimentally quantified\nusing hydrophobic interaction chromatography and viscosity/diffusivity\nmeasurements, with an especially large polarity difference noted between\nCoenzymes Q<sub>10</sub> and Q<sub>0</sub>. Cyclic voltammetry experiments\nrevealed CO<sub>2</sub>-dependent redox behavior that supported the\nproposed ECEC mechanism for complex formation between electroreduced\n1,4-naphthoquinone-/1,4-benzoquinone-derived nucleophiles and the\nLewis acidic CO<sub>2</sub>, with the Coenzyme Q adducts exhibiting\nless negative cathodic peak potentials than the parasitic dioxygen/superoxide\nhalf-reaction. Further investigation of Coenzyme Q anions suggested\nthat their CO<sub>2</sub> complexation is potentially affected by\nboth electronic and steric/polarity effects via the presence and length\nof the side chain substituent, respectively. Inspired by the electron\ntransport role of Coenzyme Q<sub>10</sub> in mitochondrial membranes,\nthe enhanced lipophilicity of the nonpolar Coenzyme Q<sub>10</sub> compared to the chain-less Q<sub>0</sub> was leveraged to facilitate\nthe heterogeneous CO<sub>2</sub>-selective electrochemical response\nof a Coenzyme Q<sub>10</sub> composite in aqueous media, thus illustrating\nthe potential of natural/bioinspired compounds for future redox-active\napplications.