A Sensitive “Turn-off” Fluorescent Chemosensor for Hg(II) Detection based on a Vanillin-derived N-phenylpyrazoline

Abstract

Even in small quantities, Hg(II) is one of the most dangerous heavy metals because of its harmful effects on human health. Therefore, Hg(II) monitoring in environmental samples is essential. In this study, vanillin was chemically modified to create new fluorescent chemosensing agents for Hg(II) ions. Vanillin was modified via an etherification reaction, and the intermediate was then subjected to a Claisen-Schmidt reaction and cyclocondensation to produce the pyrazoline in 91.60% yield. The properties of the products were characterized by spectroscopic methods. MPP had a LoD of 1,920 nM, showing that the phenyl group in pyrazoline lowers the LoD and increases sensitivity for detecting Hg(II). Hg(II) ions were shown to be chelated with two nitrogen atoms of pyrazoline structures and two oxygen atoms of vanillin and styrene through experimental evidence using Job's plot, FT-IR, and 1H-NMR analyses. This finding is useful for designing pyrazolines as metal-ion chemosensors.