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

Progress with fluorescent flippers, small-molecule probes to image membrane tension in living systems, has been limited by the effort needed to synthesize the twisted push-pull mechanophore. Here, we move to a higher oxidation level to introduce a new design paradigm that allows the screening of flipper probes rapidly, at best in situ. Late-stage clicking of thioacetals and acetals allows simultaneous attachment of targeting units and interfacers and exploration of the critical chalcogen-bonding donor at the same time. Initial studies focus on plasma membrane targeting and develop the chemical space of acetals and thioacetals, from acyclic amino acids to cyclic 1,3-heterocycles covering dioxanes as well as dithiolanes, dithianes, and dithiepanes, derived also from classics in biology like cysteine, lipoic acid, asparagusic acid, DTT, and epidithiodiketopiperazines. From the functional point of view, the sensitivity of membrane tension imaging in living cells could be doubled, with lifetime differences in FLIM images increasing from 0.55 to 1.11 ns. From a theoretical point of view, the complexity of mechanically coupled chalcogen bonding is explored, revealing, among others, intriguing bifurcated chalcogen bonds.

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

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.