Fluorescent Flippers: Small‐Molecule Probes to Image Membrane Tension in Living Systems

Abstract

Flipper probes have been introduced as small molecule fluorophores to image physical forces, that is, membrane tension in living systems. Their emergence over one decade is described, from evolution in design and synthesis to spectroscopic properties. Responsiveness to physical compression in equilibrium at the ground state is identified as the ideal origin of mechanosensitivity to image membrane tension in living cells. A rich collection of flippers is described to deliver and release in any subcellular membrane of interest in a leaflet‐specific manner. Chalcogen‐bonding cascade switching and dynamic covalent flippers are developed for super‐resolution imaging and dual‐sensing of membrane compression and hydration. Availability and broad use in the community validate flipper probes as a fine example of the power of translational supramolecular chemistry, moving from fundamental principles to success on the market.

Recent Development of Advanced Fluorescent Molecular Probes for Organelle-Targeted Cell Imaging

“…For example, high-resolution methods can assist in distinguishing the different modes of mitochondrial fission; this may explain how other organelles participate in modulating the fission process in cells [ 188 ]. Furthermore, a series of novel probes that can monitor the membrane tension on the plasma membrane and other organelles were developed recently and promote the understanding of mechanobiological processes, thus indicating the importance of mechanoforce as an interesting parameter in the regulation of bioactivities [ 189 , 190 , 191 , 192 ]. Therefore, it is critical for scientists in different fields to exchange their cutting-edge knowledge to discover the most suitable molecular probes, thus advancing the growth of science.…”

Fluorogenic In Situ Thioacetalization: Expanding the Chemical Space of Fluorescent Probes, Including Unorthodox, Bifurcated, and Mechanosensitive Chalcogen Bonds

“…Flipper 15 was synthesized in 12 steps from commercially available starting materials following reported procedures. 33 Weakening of the push−pull system in 15 by the aldehyde acceptor in 7 was correctly reflected by the emission changing from orange to green. As initial targets for donor junctions, 1,3-dioxolane 16 and thioacetals 17−20 were selected to probe for accessibility of the central motifs from popular starting materials like reduced asparagusic acid 65,66 or dithiothreitol 67,68 (DTT, Figures 3 and 4a).…”

“…Fluorescent flippers have been introduced as small-molecule fluorescent probes to image membrane tension in living systems (Figure 1a−c). 33 For the imaging of biomembrane function, 34−47 membrane tension 48−50 is particularly interesting but also particularly demanding because physical forces are detectable only through the suprastructural changes they cause. 33 Inspired by nature, 51 we have considered the concept of planarizable push−pull probes to tackle this challenge.…”

“…33 For the imaging of biomembrane function, 34−47 membrane tension 48−50 is particularly interesting but also particularly demanding because physical forces are detectable only through the suprastructural changes they cause. 33 Inspired by nature, 51 we have considered the concept of planarizable push−pull probes to tackle this challenge. 52 The resulting flipper probes are built around two dithienothiophenes, 53,54 one electron rich and one electron poor.…”

“…33,55−57 Moreover, donors D are needed in planarized flippers II to generate a strong push−pull system accounting for large red-shifts, but they are incompatible with twisted flippers I because the decoupled donor side oxidizes. 33 Flippers such as 1 with simple alkoxy donors are not stable for this reason (Figure 1d). Sulfide donors, like in 2, that turn on only when attached to electron-deficient aromatics obtained by the planarization of flippers, did not afford the spectroscopic properties needed for bioimaging.…”