Schiff bases as analytical tools: synthesis, chemo-sensor, and computational studies of 2-aminophenol Schiff bases

Abstract

Schiff bases of 2-((2-hydroxybenzylidene)amino)phenol (MJ₁) and 4-bromo-2-(((2-hydroxyphenyl)imino)methyl)phenol (MJ₂) were synthesized from 2-aminophenol and screened for the detection of some biologically important metal ions. UV-vis spectroscopy screening, electrochemical studies, and theoretical calculations of the ligands (MJ₁ and MJ₂) revealed the sensing properties of the probes. The binding interactions of probes MJ₁ and MJ₂ with Cu²⁺, Zn²⁺, and Ni²⁺ resulted in redshifts in the absorption maxima. MJ₁ exhibited reversibility of its metal complexes with Cu²⁺ and Zn²⁺ in an EDTA solution. The electrochemical behavior of both probes with Cu²⁺, Zn²⁺, Ni²⁺, Cr³⁺ resembled voltammograms with one or two quasi-reversible redox processes, indicating complex formation between the probes and metal ions. The electrochemical screening showed none or insignificant binding interactions between the probes with Cr³⁺. The change in electro-activeness of ligands MJ₁ and MJ₂ upon complexation with metal ions (Cu²⁺, Zn²⁺, and Ni²⁺) suggested a metal-to-ligand charge transfer (MLCT) and intramolecular charge transfer binding mechanism. The complex formed between the sensor and ligand was determined using density functional theory employing the B3LYP functional and the LANL2DZ and 6-311+G(d,p) basis sets. Atomic charge and molecular orbital analyses of the frontier molecular orbitals also support the MLCT mechanism. The global reactivity descriptor parameters show that MJ₂ may be a better electron acceptor than MJ₁.