Monitoring Chemical and Biological Electron Transfer Reactions with a Fluorogenic Vitamin K Analogue Probe

Abstract

We report herein the design, synthesis, and characterization of a two-segment fluorogenic analogue of vitamin K, B-VK, prepared by coupling vitamin K, also known as menadione (a quinone redox center), to a boron-dipyrromethene (BODIPY) fluorophore (a lipophilic reporter segment). Oxidation-reduction reactions, spectroelectrochemical studies, and enzymatic assays conducted in the presence of DT-diaphorase illustrate that the new probe shows reversible redox behavior on par with that of vitamin K, provides a high-sensitivity fluorescence signal, and is compatible with biological conditions, opening the door to monitor remotely (i.e., via imaging) redox processes in real time. In its oxidized form, B-VK is non-emissive, while upon reduction to the hydroquinone form, B-VK, BODIPY fluorescence is restored, with emission quantum yield values of ca. 0.54 in toluene. Density functional theory studies validate a photoinduced electron transfer intramolecular switching mechanism, active in the non-emissive quinone form and deactivated upon reduction to the emissive dihydroquinone form. Our results highlight the potential of B-VK as a fluorogenic probe to study electron transfer and transport in model systems and biological structures with optimal sensitivity and desirable chemical specificity. Use of such a probe may enable a better understanding of the role that vitamin K plays in biological redox reactions ubiquitous in key cellular processes, and help elucidate the mechanism and pathological significance of these reactions in biological systems.

A Synthetic Isoprenoid Lipoquinone, Menaquinone-2, Adopts a Folded Conformation in Solution and at a Model Membrane Interface

“…Investigation of the conformation of a particular MK derivative’s location and conformation will also allow for a more realistic interpretation of data obtained with the novel fluorogenic probe, a vitamin K analog, reported to fluoresce after reduction to the quinol. 92 Studies with this new probe may help provide information on the role that vitamin K plays in key redox processes. Accurate information obtained from the use of this probe would provide better quality data regarding photosynthesis and cellular respiration, and future consideration of MK derivatives location and conformation will be important for proper interpretation of the results obtained from the use of this probe.…”

Spectroelectrochemical Sensing: Current Trends and Challenges

“…Therefore, most of the reactant is transformed, allowing us to obtain a clean photoluminescence signal but, at the same time, the ohmic drop resistance is common in this type of setups. Epifluorescence SEC can be also performed under semi‐infinite diffusion conditions , Figure .a. Confocal microscopy , Figure .b. In this case, the microscope includes a spatial pinhole placed at the confocal plane of the lens to remove light coming from outside of the focus plane.…”

“…Confocal microscopy , Figure .b. In this case, the microscope includes a spatial pinhole placed at the confocal plane of the lens to remove light coming from outside of the focus plane.…”

Quinone-based fluorophores for imaging biological processes

“…An activatable fluorescent analogue of vitamin K was synthesized via coupling of a BODIPY core to menadione to render a fluorogenic probe showing 70-fold fluorescence increase upon reduction of the quinone moiety. 47 The probe functioned as an electron shuttle in the presence of a NAD(P)H:quinone oxidoreductase, either NADP or NADPH and cytochrome C. Other protein complexes, such as intracellular complex I, can be also detected by monitoring the redox state with Q/HQ pairs. Long et al described the synthesis and application of bioconjugates containing Q/HQ pairs attached to QDs for the monitoring of complex I levels in human neuroblastoma SH-SY5Y cells.…”