Unraveling the Potential of Mononuclear Zn(II) and Cu(II) Schiff Base Metal Complexes: Microwave-Aided Synthesis, Theoretical Analysis and Application in Biomimetic Catalysis, CT-DNA Interaction, and In Vitro Biological Assays

Abstract

Given the widespread and diverse effects of transition metal ions such as copper and zinc in multiple biological processes, this research endeavor addresses herein the microwave-aided synthesis of two novel tetradentate ONNO (L1) and tridentate NNO (L2) donor Schiff base ligands derived from 4,5-dimethyl-1,2-phenylenediamine and 4-bromo-2-hydroxybenzaldehyde in a 1:2 ratio and from 4,5-dimethyl-1,2-phenylenediamine and 5-methoxy-2-hydroxybenzaldehyde in a 1:1 ratio, with their respective zinc, ZnL1(1) and ZnL2(3), and copper, CuL1(2) and CuL2(4), Schiff base metal complexes, which are comprehensively characterized utilizing physiochemical and analytical techniques, along with geometry optimization using the DFT approach. Spectrophotometric analyses have been used to assess the biomimetic activity in the conversion of 3,5-DTBC to 3,5-DTBQ with turnover numbers 53.4 and 78 h⁻¹ in methanol for 2 and 4, whereas the zinc complexes are found to be ineffective. With CT-DNA, possible modes of interaction with the synthesized complexes have been explored using absorption spectroscopy, where the associated binding constants ranged between 1.541 × 10⁵ and 2.186 × 10⁵ M⁻¹. EtBr-bound DNA was used in the fluorescence quenching experiments with Stern–Volmer constant (K_sv) values in the range 4.084 × 10⁴ and 3.402 × 10⁴ M⁻¹, showing a stronger association with CT-DNA. The compounds' ability to inhibit bacterial strains was also examined in vitro, as well as their ability to reduce inflammation, through the protein denaturation method and the DPPH assay for antioxidant activity have been performed. Furthermore, molecular docking simulations have been carried out to obtain a deeper comprehension of the molecular-level interactions with CT-DNA and cyclooxygenase-2 (COX-2).