A Schiff Base and Its Copper(II) Complex as a Highly Selective Chemodosimeter for Mercury(II) Involving Preferential Hydrolysis of Aldimine over an Ester Group

Abstract

The syntheses of a new Schiff base, diethyl-5-(2-hydroxybenzylidene)aminoisophthalate (HL), and a copper complex, [Cu(L2)] (1), imparting L(-), have been described. Both the ligand HL and complex 1 have been thoroughly characterized by elemental analyses, electrospray ionization mass spectrometry, FT-IR, NMR ((1)H and (13)C), electronic absorption, and emission spectral studies and their structures determined by X-ray single-crystal analyses. Distinctive chemodosimetric behavior of HL and 1 toward Hg(2+) has been established by UV/vis, emission, and mass spectral studies. Comparative studies further revealed that the chemodosimetric response solely originates from selective hydrolysis of the aldimine moiety over the ester group and 1 exhibited greater selectivity toward Hg(2+) relative to HL while the sensitivity order is reversed. Further, these followed different hydrolytic pathways but ended up with the same product analyzed for diethyl-5-aminoisophthalate (DEA). Hg(2+)-induced displacement of Cu(2+) and subsequent hydrolysis of the -HC═N- moiety in 1 affirmed the identity of the actual species undergoing hydrolysis as HL. The occurrence of Cu(2+) displacement and Hg(2+) detection via hydrolytic transformation has been supported by various physicochemical studies.

Fluorescent and colorimetric sensors for environmental mercury detection

“…98 A new Cu 2+ compound 79 ( Figure 41) with a Schiff base and naphthol as the Hg 2+ -binding sites was synthesized as a highly selective fluorescence chemosensor for the detection of Hg 2+ . 100 Hg 2+ induces displacement of Cu 2+ and subsequent hydrolysis of the -HC=N− moiety in 80. On addition of Hg 2+ , the Cu 2+ is displaced and an Hg 2+ complex is formed, turning on the fluorescence, with a significant increase in the emission intensity at about 530 nm.…”

“…Another Cu 2+ compound, 80, was designed for the recognition of Hg 2+ based on selective hydrolysis of the aldimine moiety over the ester group. 100 Hg 2+ induces displacement of Cu 2+ and subsequent hydrolysis of the -HCvNmoiety in 80. Gradual addition of Hg 2+ leads to hypochromic shifts of the absorption bands at 392 and 281 nm.…”

An Azo Dye Based D‐π‐A Chromogenic Probe for Selective Naked‐Eye Detection of Hg2+ Ion: Application in Logic Gate Operation

“…The upfielding of the H b signal upon Hg 2+ binding to aldehydic oxygen may be explained through a partial delocalization of incipient positive charge through a reversible nucleophilic binding of water molecule resulting in a tetrahedral intermediate. Similar Hg 2+ assisted nucleophilic attack to C=N system and further hydrolysis has been reported . (iii) The water peak in DMSO‐ d 6 which appeared at δ 3.33 ppm is found to be deshielded progressively with increase in Hg 2+ content.…”

A new nano‐sized mononuclear Cu (II) complex with N,N‐donor Schiff base ligands: sonochemical synthesis, characterization, molecular modeling and biological activity

“…This element due to its participation in the biological process, like enzyme hydrolysis, electron transfer, is a good catalyst for redox reactions . Schiff bases transition metal complexes (especially copper complexes) are more and more important as textile materials, catalitical, anticancer, anti‐convulsant, analytical, antimicrobial, and biochemical reagents . The Schiff bases complexes of copper (II) derived from 4‐amino acids and hydroxysalicylaldehyde have been shown to have stronger anticancer activities …”