Electrochemical Studies of Vitamin K₁Microdroplets: Electrocatalytic Hydrogen Evolution

Abstract

The voltammetry of a basal-plane pyrolytic graphite electrode modified with a random ensemble of unsupported microdroplets of vitamin K, is investigated when the electrode is immersed in aqueous electrolytes. It is shown that in dilute acidic solutions, electroreduction occurs in a single two-electron two-proton process to yield the corresponding hydroquinone at the electrode\vitamin K1 microdroplet\aqueous-electrolyte three-phase boundary. On addition of ionic alkali-metal salts to the aqueous acidic phase, the electrochemical reduction of vitamin K1 to the quinol is accompanied by catalytic hydrogen evolution within and alkali-metal-cation insertion into the organic microdroplets. In strongly alkaline solutions, electrochemical reduction of vitamin K1 at the triple-phase junction is proposed as being a single two-electron process with concomitant uptake of alkali-metal cations in order to maintain electroneutrality within the oil phase. Surprisingly, the relative ease of cation insertion into the oil phase is demonstrated to be governed by the degree of ion-pair formation rather than by the Gibbs transfer energy of the cation across the liquid\liquid interface.

A Comparison of the Solvation Properties of 2-Nitrophenyloctyl Ether, Nitrobenzene, and n-Octanol as Assessed by Ion Transfer Experiments

“…[33][34][35][36][37] Whereas Compton and his group used three-phased electrodes to study the electrochemistry of electroactive liquids, 32,[38][39][40] Scholz and co-workers [28][29][30][31][33][34][35][36][37] developed the technique of determining the Gibbs energies of ion transfer with the help of solutions of electroactive compounds in droplets of organic solvents immobilized on electrode surfaces.…”

Voltammetric Insights in the Transfer of Ionizable Drugs Across Biomimetic Membranes - Recent Achievements

“…Compton et al [40][41][42][43] obtained significant data for biologically active compounds by exploring the redox and lipophilic properties of vitamin K1 [40], p-chloranil [41], and vitamin B-12 [42] with immobilized electroactive organic droplets. Inverse experiments for the evaluation of lipophilic parameters in water droplets immobilized on organic electrodes subsequently submersed into organic electrolyte solutions have also been used [43].…”

pEDOT:Vitamin K1 Composites: An Electrochemical Study on Stable, Water‐Permeable, Proton‐Bonding Thin‐Film Electrodes

“…These methods fit under the category of being diffusive methods of looking at transfer; where because the quinoid is solubilised, diffusion kinetics play a factor into the analysis of the behaviour of the quinoid. Diffusive methods of this nature include electrochemical investigation of microdroplet electrodes . Furthermore, solubilisation of the quinoid by using an organic co‐solvent is considered to be less reflective of the biological environment.…”