Torsion-induced π-conjugation Offers an Approach to Small Coumarin-based Color-changing Fluorescent Sensors of Esterase Activity

Document Type

Article

Publication Date

1-1-2025

Abstract

Fluorescent sensors for esterase activity include a diverse array of compounds that utilize intramolecular charge transfer induced by the unmasking of the electron-donating hydroxyl group through esterase action. These sensors exhibit different outcomes, ranging from turn-on fluorescence to fluorescence color changes. In this work, we demonstrate the application of torsion-induced fluorescence changes in designing esterase-dependent chemosensors. We present a method for detecting esterase activity based on the torsion-induced geometrical changes between the ester and carboxylate forms of a fluorophore. Our approach shows that aligning electronic interactions between the C7 heteroatom and the C4 ester substituents within a small coumarin core stabilizes the planar geometry of the coumarin ester, leading to fluorescence emission above 570 nm. Upon esterase-mediated hydrolysis, the coumarin exhibits a blue shift in emission to 460 nm, corresponding to the carboxylate form. This shift occurs due to the nonplanar orientation of the carbonyl relative to the fluorophore. As a result, C4-coumarin ester emissions can be observed in the red fluorescence channel, while carboxylate emissions are detected in the blue/green fluorescence channels. Consequently, we introduce small, highly permeable aryl and acetoxymethyl coumarin esters as indicators of esterase activity and as tools to differentiate between live and dead cells.

Publication Title

Chemistry A European Journal

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