Fluorescence-Amplified Detection of Redox Turnovers in Supported Lipid Bilayers Illuminates Redox Processes of α-Tocopherol

Abstract

Electron-transfer processes in lipid membranes are key to biological functions, yet challenging to study because of the intrinsic heterogeneity of the systems. Here, we report spectroelectrochemical measurements on indium tin oxide-supported lipid bilayers toward the selective induction and sensing of redox processes in membranes. Working at neutral pH with a fluorogenic α-tocopherol analogue, the dynamics of the two-electron oxidation of the chromanol to a chromanone and the rapid thermal decay of the latter to a chromoquinone are recorded as a rapid surge and drop in intensity, respectively. Continuous voltage cycling reveals rapid chromoquinone two-electron, two-proton reduction to dihydrochromoquinone at negative bias, followed by slow regeneration of the former at positive bias. The kinetic parameters of these different transitions are readily obtained as a function of applied potentials. The sensitivity and selectivity afforded by the reported method enables monitoring signals equivalent to femtoampere currents with a high signal-to-background ratio. The study provides a new method to monitor membrane redox processes with high sensitivity and minimal concentrations and unravels key dynamic aspects of α-tocopherol redox chemistry.

Singlet Oxygen Flux, Associated Lipid Photooxidation, and Membrane Expansion Dynamics Visualized on Giant Unilamellar Vesicles

“…Here, 1 O 2 molecules are produced and consumed within the same lipid membrane microenvironment, minimizing the detrimental role that quenching by water may have on product yield (rate of probe activation). Extended irradiation times under the abovementioned conditions lead to a decrease in the emission intensity of the activated probe, possibly due to the reaction of 1 O 2 with the BODIPY core or degradation of H 4 BPMHC ox to less emissive products …”

“…Extended irradiation times under the abovementioned conditions lead to a decrease in the emission intensity of the activated probe, possibly due to the reaction of 1 O 2 with the BODIPY core or degradation of H 4 BPMHC ox to less emissive products. 36 The effect that different degrees of lipid unsaturation have on the rates of enhancement was also explored by recording the response to 1 O 2 of an H 4 BPMHC analogue that differs in the degree of BODIPY methylation and sensitivity, H 2 BPMHC. 18 Results were obtained working with liposomes prepared with either DMPC, POPC, or EggPC (a mixture of natural lipids).…”

Electrochemical and Spectroscopic Characterization of Oxidized Intermediate Forms of Vitamin E

“…One area of research that requires considerably more attention to fully understand the biological properties of vitamin E and possibly its oxidized forms, is the exact location that the compound resides within the lipid bilayers. Existing experiments that have been used to probe vitamin E’s position within membranes have required the use of fluorescent probes attached to the structure and/or model membranes, which will likely affect its exact orientation to a greater of lesser extent [ 31 , 32 , 33 , 129 , 130 , 131 ]. It is significant that the α–TTP specifically targets the RRR –chiral form, which is likely because of the exact geometry that is adopts.…”