A highly potential acyclic Schiff base fluorescent turn on sensor for Zn2+ ions and colorimetric chemosensor for Zn2+, Cu2+ and Co2+ ions and its applicability in live cell imaging

Anjitha Jayaraj; M S Gayathri; Gandhi Sivaraman; Chinna Ayya Swamy P

doi:10.1016/j.jphotobiol.2021.112371

A highly potential acyclic Schiff base fluorescent turn on sensor for Zn²⁺ ions and colorimetric chemosensor for Zn²⁺, Cu²⁺ and Co²⁺ ions and its applicability in live cell imaging

J Photochem Photobiol B. 2022 Jan:226:112371. doi: 10.1016/j.jphotobiol.2021.112371. Epub 2021 Dec 2.

Authors

Anjitha Jayaraj¹, M S Gayathri¹, Gandhi Sivaraman², Chinna Ayya Swamy P³

Affiliations

¹ Main group Organometallics Materials, Supramolecular Chemistry and Catalysis lab, Department of Chemistry, National Institute of Technology, Calicut 673601, India.
² Department of Chemistry, Gandhigram Rural Institute (Deemed to be University), Gandhigram 624302, India.
³ Main group Organometallics Materials, Supramolecular Chemistry and Catalysis lab, Department of Chemistry, National Institute of Technology, Calicut 673601, India. Electronic address: swamy@nitc.ac.in.

PMID: 34906923
DOI: 10.1016/j.jphotobiol.2021.112371

Abstract

Herein, we report two acyclic Schiff base receptors CS-1 and CS-2 capable of being selective fluorescent turn on for Zn²⁺ions and colorimetric chemosensor for Zn²⁺, Cu²⁺, and Co²⁺ ions by showing a colour change from colourless to yellow in 1:1 ratio of acetonitrile and HEPES buffer (1:1, v/v, pH 7.4) without the interference from other metal ions screened (Cd²⁺, Hg²⁺, Sn²⁺, Ni²⁺, Cr³⁺, Mn²⁺, Pb²⁺, Ba²⁺, Al³⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺). The fluorescence turn on enhancement towards Zn²⁺ ions is ascribed to PET blocking, suppression of -C=N- isomerisation, and the ESIPT process. The selectivity, competitivity and reversibility of the synthesised probes (CS-1 and CS-2) made them promising chemosensors for the detection of Zn²⁺, Cu²⁺, and Co²⁺ ions. The density functional theory (DFT) calculations have theoretically endorsed the colorimetric changes in the examined absorption spectra and binding mode of both CS-1/CS-2 with metals ions. In addition, ¹H NMR titrations were also consistent with the recognition mechanism of Zn²⁺ ions with the CS-1/CS-2. Further, the Jobs plot analysis infers a 1:1 stoichiometric ratio for both evaluating receptors CS-1 and CS-2 with Zn²⁺, Cu²⁺ and Co²⁺ ions and was supported by DFT, NMR (only for Zn²⁺ ions), UV-Visible, and fluorescence spectroscopic studies. Moreover, the detection limits of CS-1 and CS-2 for Zn²⁺ ions were determined to be 7.69 and 5.35 nM, respectively, which is less compared to the detection limit of Cu²⁺, Co²⁺ ions as well as the limit approved by the United State Environmental Protection Agency (US EPA). The probes CS-1 and CS-2 found to show high fluorescence quantum yields at pH = 7 during the titration with Zn²⁺ as compared with other pHs (5-6 and 8-11). Gratifyingly, fluorescence microscopy imaging in HeLa cells revealed that the pair of receptors can be employed as an excellent fluorescent probe for the detection of Zn²⁺ions in living cells, indicating that this facile chemosensor has a huge potential in cellular imaging.

Keywords: Bioimaging; Colorimetric sensors; Fluorescent turn on; Schiff bases; Selectivity; Zn(2+) ions.

MeSH terms

Cobalt* / chemistry
Colorimetry* / methods
Copper* / analysis
Copper* / chemistry
Density Functional Theory
Fluorescent Dyes* / chemistry
HeLa Cells
Humans
Schiff Bases* / chemistry
Spectrometry, Fluorescence*
Zinc* / analysis
Zinc* / chemistry

Substances

Schiff Bases
Fluorescent Dyes
Zinc
Copper
Cobalt