A new pyridoxal based fluorescence chemo-sensor for detection of Zn(ii) and its application in bio imaging

Abstract

This paper describes the activity of a Schiff base ligand, derived from pyridoxal, as a promising fluorescence probe for biologically important Zn(II) ion sensing. A physiologically compatible pyridoxal based chemosensor PydDmen was synthesized and evaluated for its fluorescent response towards metal ions. Chemosensor PydDmen exhibits a selective turn-on type response in the presence of Zn²⁺ in ethanol–water mixture. The addition of EDTA quenches the fluorescence of receptor PydDmen-Zn²⁺, making the chemosensor PydDmen reversible. The response is specific for Zn(II) ions, and remains almost unaffected by the presence of alkali and alkaline earth metals but is suppressed to varying degrees by transition metal ions. The selectivity mechanism of PydDmen for Zn²⁺ is the combined effects of proton transfer between the prevailing tautomeric forms, CN isomerization and CHEF. The DFT optimized structure of the complex is compatible with elemental analysis, mass spectrometry, FT-IR, electronic and NMR spectra. The experimental and theoretical support in terms of NMR spectroscopy and DFT are provided to establish the existence of Zn²⁺ induced transformation of PydDmen to a 3-pyridone tautomeric form.