Invited feature article New pyridoxal based chemosensor for selective detection of Zn 2+ : Application in live cell imaging and phosphatase activity response Senjuti Mandal a , Yeasin Sikdar a , Dilip K. Maiti a , Ria Sanyal a , Debasis Das a , Abhishek Mukherjee b , Sushil Kumar Mandal c , Jayanta Kumar Biswas c , Antonio Bauzá d , Antonio Frontera d , Sanchita Goswami a, * a Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700009, India b Drug Development Diagnostic and Biotechnology Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700032, India c Department of Ecological Engineering & Environmental Management, University of Kalyani, Kalyani, Nadia 741235, West Bengal, India d Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Baleares), Spain A R T I C L E I N F O Article history: Received 18 February 2016 Received in revised form 5 October 2016 Accepted 27 October 2016 Available online 10 November 2016 Keywords: Chemosensor Schiff base Fluorimetry Live cell imaging Phosphatase activity DFT A B S T R A C T 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]-cyclohexy- limino}-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 C¼N 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. ã 2016 Elsevier B.V. All rights reserved. 1. Introduction Among many biologically significant metal ions, Zn 2+ is the second most abundant metal ions in human body as it is involved in a number of biochemical processes [1]. However, both its deficiency and excess can induce human health disorders in the form of Alzheimer’s disease, Parkinson’s disease etc. [2]. Therefore, generation of efficient chemosensors specific for Zn 2+ detection is the need of the hour. Analytical methods for detection of Zn 2+ such as atomic absorption spectrometry [3(a)], inductively coupled plasma mass spectroscopy (ICPMS) [3(b)], inductively coupled plasma-atomic emission spectrometry (ICPAES) [3(c)], and vol- tammetry [3(d)] require expensive instrumentation and large sample amount. As a result, fluorescence based chemosensors have attracted significant attention due to high sensitivity, easy visualization, short response time for detection and most importantly they can be implemented for real time bio-imaging [4]. In recent years, a large number of probes based on fluorescence detection have been reported for selective detection of Zn 2+ [5–8]. In an attempt to make the chemosensor design simple and biocompatible, we have undertaken a strategy to generate pyridoxal containing Schiff bases as sensors, coupling the two prerequisites [9]. General signaling mechanism prevalent in such systems is based on chelation enhanced fluorescence (CHEF) induced by restricted C¼N isomerisation and excited state intramolecular proton transfer (ESIPT). The binding of analyte disables the non-radiative decay pathways involving C¼N isomer- isation and ESIPT, thereby restoring the fluorescence (Scheme 1) [9 (c)–(e)]. In particular, we have demonstrated that the occurrence pyridoxal-3-pyridone tautomerism triggered by Zn 2+ binding, imparts additional specificity to the system [9][9(c)][10,11]. This combined mechanistic rationale has not been explored much in literature (Chart 1 in supporting information). Our goal is to carry out extensive research on pyridoxal Schiff base chemosensors in a * Corresponding author. E-mail address: sgchem@caluniv.ac.in (S. Goswami). http://dx.doi.org/10.1016/j.jphotochem.2016.10.038 1010-6030/ã 2016 Elsevier B.V. All rights reserved. Journal of Photochemistry and Photobiology A: Chemistry 334 (2017) 86–100 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journal home page : www.elsevier.com/locat e/jphotochem