Distribution of Cytochrome c in LCST-Type Ionic Liquid/Water Mixtures Controlled by Applied Potential and Temperature

Ionic liquid (IL)/water biphasic systems have received a large amount attention because of their application as extraction media for many compounds; in particular, IL/water mixtures with lower critical solution temperature (LCST)-type phase transitions have been successfully applied to the selective extraction of proteins. However, the reversible control of protein distribution in IL/water biphasic mixtures has not yet been explored. This study investigates the change in distribution of cytochrome c (cyt c) in a mixture of tetrabutylphosphonium 2,4,6-trimethylbenzenesulfonate ([P-4,P-4,P-4,P-4][TMBS]), which has LCST behavior, and a potassium phosphate buffer (PKB) with temperature variation. Absorbance measurements of cyt c in the two phases show that oxidized cyt c was transferred into the [P-4,P-4,P-4,P-4] [TMBS] phase via the LCST behavior, whereas reduced cyt c remained in the PKB phase. Based on the distribution of cyt c in the [P-4,P-4,P-4,P-4][TMBS]/PKB mixture, which depends on the redox state, we propose a system to reversibly transfer cyt c in the biphasic mixture by applying potential and temperature gradients. The calculated redox potentials suggest that oxidized cyt c is more stable than its reduced form in the [P-4,P-4,P-4,P-4][TMBS]/PKB mixture. (C) 2018 The Electrochemical Society.