New pyridoxal based chemosensor for selective detection of Zn2+: Application in live cell imaging and phosphatase activity response

Abstract Although a variety of fluorescence based chemosensors have been utilized for selective detection of Zn 2+ , pyridoxal containing simple Schiff bases still remained less explored. Here, we combine pyridoxal hydrochloride and 1,2-diaminocyclohexane to generate a new sensor molecule, H 4 PydChda [5-Hydroxymethyl-4-({2-[5-hydroxymethyl-2-methylpyridin-3-hydroxy-4-ylethylene)-amino]-cyclohexylimino}-methyl-2-methylpyridin-3-ol]. Chemosensor H 4 PydChda exhibits selective turn-on type response in presence of Zn 2+ in ethanol-water mixture at physiological pH. Appreciable fluorescence enhancement occurs upon addition of Zn 2+ to H 4 PydChda as a result of inhibited C N isomerisation and excited state intramolecular proton transfer (ESIPT) leading to efficient chelation enhanced fluorescence (CHEF). The relevant properties, including reversibility, life time measurements and detection limit have been determined for the sensor system. The experimental and theoretical supports in terms of 1 H and 13 C NMR spectroscopy and DFT/TDDFT study are provided to establish the binding mode of H 4 PydChda to Zn 2+ . H 4 PydChda was employed as a sensor for detection of Zn 2+ in Human gastric adenocarcinoma (AGS) cells. Moreover, the resulting probe-Zn 2 + complex shows convincing phosphatase activity (k cat  = 21.59 s −1 ), opening a promising avenue for further research.