Chemoselective detection based on experimental and theoretical calculations of Cu2+ ions via deprotonation of chromone derived probe and its application

Abstract

A new Schiff base chemosensor 2-Ethoxy-3-(((2‑hydroxy-4-nitrophenyl)imino)methyl)-2H-chromen-4-ol (CANP) was synthesized and characterized by 1HNMR , FT-IR, HRMS, FE-SEM spectral techniques for the detection of cupric ions through colorimetric and fluorimetric response in THF. Colorimetric change from yellow to orange and fluorescence turn-off behavior was observed for chemosensor in presence of cupric ions over the rest of metal ions. This turn-off behavior was observed due to the paramagnetic nature of cupric ions. Job's plot indicated that complex formed in 2:1 (CANP:Cu2+) ratio and binding stoichiometry was confirmed by HRMS spectral technique. The binding constant was obtained as 2.84 × 104 M − 1 and 1.71 × 104 M − 1 via absorbance and fluorimetric titrations respectively. The LOD values were obtained as 4.93 × 10−6 M and 2.06 × 10−6 M via absorbance and fluorimetric titrations respectively. Selectivity of chemosensor towards cupric ions was observed in pH range 6–11. The reversibility effect was observed on the addition of sodium salt of EDTA. No interference from other competitive metal ions confirmed the selectivity of chemosensor for cupric ions. The probe and its cupric ion complex was found to be stable over a span time period. Theoretical calculations based on DFT were performed for a better understanding of the optical character of CANP and the effect of cupric ions titration; moreover, these results validated the experimental data. Time decay data illustrated that complex of chemosensor formed with cupric ions was stable. FESEM analysis of chemosensor CANP and its complex confirmed the formation of complex as morphology changed after complex formation. Additionally, this chemosensor was successfully used for the detection of cupric ions in environmental water samples. Also, it was applied to recognize cupric ions in human blood serum with micromolar detection limits.