Quinoline-based bio-compatible fluorophore employing a dual sensor for Mg(ii) and Zn(ii): insights from single crystal structures and spectroscopic, DFT and cell imaging studies

Abstract

The quinoline-based Schiff base HQNP (E)-3-((2-(4,6-dimethylpyrimidin-2-yl)hydrazono)methyl)quinolin-2-ol was designed and synthesized as a fluorescent probe for the dual detection of Zn²⁺ and Mg²⁺ ions. The structure of the probe was confirmed using different spectroscopic techniques, such as single crystal X-ray diffraction (SCXRD), ¹H & ¹³C NMR, FT-IR and ESI-MS spectra. The probe HQNP showed an excellent ‘turn on’ fluorescence response with Zn²⁺ at 446 nm and with Mg²⁺ at 442 nm, with detection limits of 6.6 × 10⁻⁸ M and 4.6 × 10⁻⁸ M, respectively. The photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) sensing mechanism and binding mode of HQNP with these two cations were established by UV-Vis, fluorescence, ESI-MS spectra, Job's plot, lifetime study and DFT studies. Importantly, the 1 : 1 complexation of HQNP with Zn²⁺ is confirmed by the SCXRD study. The probe can sense Zn²⁺ and Mg²⁺ reversibly against the chelating agent EDTA several times. Moreover, HQNP can detect Zn²⁺ and Mg²⁺ in different solvents and different counter cationic and anionic environments with minimal interference. Further, excellent cell imaging performance of HQNP with the mentioned ions in TPC-1 and HtH-7 cell lines is observed without marked cytotoxicity.