Fluorescence Mapping of α-Tocopherol Redox Activity in Supported Lipid Bilayers

Abstract

Lipid membranes have gained wide attention as assembly scaffolds, owing to their ability to self-assemble into well-defined fluid structures, allowing the compartmentalization and direct assembly of components of interest in a fluid platform. Model lipid membranes offer the opportunity to mimic and study processes occurring across these fluid mosaics such as respiration, transport and signaling.Armed with a spectroelectrochemistry microscopy setup, in this study we have explored redox reactions within lipid membranes, proof of concept experiments intended to address the response of membrane embedded redox systems. Experimentally, a supported lipid bilayer was formed on top on an indium tin oxide (ITO)-coated glass. H4BPMHC, a redox sensitive fluorogenic probe bearing the chromanol moiety of α-tocopherol (Vitamin E), and a BODIPY tail segment was incorporated within the lipid membrane. The electrochemical and optical properties were next studied using our total internal reflection fluorescence (TIRF) microscopy based spectro-electrochemical (SEC) setup, that enables monitoring emission while minimizing background by virtue of sampling a small ~ 300 nm region above the glass water interface, while also controlling the redox potential at the basal leaflet of the lipid membrane.Our results are consistent with oxidation of the chromanol moiety of the probe into a chromanone moiety through an irreversible process that elicits fluorescence, and further thermally induced rearrangement of the newly formed chromanone into a chromoquinone. We will discuss the general methodology, results, and implications of the work in the context of electron transport through relay redox systems.