Comprehensive In Vitro and In Silico Biological Evaluation of Chloro, Nitro-Substituted Hydroxamic Acid, and Its Zn(II) Complex: TGA, Electrochemical Behavior, and DFT Calculations

Abstract

A mononuclear zinc(II) complex formulated as [Zn(2-Cl-5-NO₂BzH)₂] {where 2Cl-5-NO₂BzHK = potassium 2-chloro-5-nitrobenzohydroxamate(2Cl-5-NO₂C₆H₃CONHO) (KHL)} was synthesized and analyzed by physicochemical (elemental analysis and molar conductivity) and spectroscopic (FTIR, UV–visible, ¹H NMR, and ¹³C NMR) techniques. Spectroscopy and density functional theory (DFT) analysis together unveiled the complex's distorted tetrahedral structure defined by O,O coordination (carbonyl and hydroxamic oxygens). DFT calculations using Orca 4.2.1 program along with the B3LYP hybrid exchange-correlation functional and Def2-SVP basis set (B3LYP/Def2-SVP) demonstrate the complex's enhanced stability over the ligand, based on chemical reactivity parameters and Mulliken charge analysis. The nitro group's characteristic R-NHOH/R-NO redox behavior, a ligand-centric trait, was established by cyclic voltammetry. Up to 800°C, thermal gravimetric analysis meticulously displayed the complex's four-stage decomposition. To determine their antimicrobial potency, compounds were assayed against selected bacteria (Staphylococcus aureus, Salmonella typhi, Escherichia coli, and Shigella flexneri) and fungi (Rhizoctonia solani, Alternaria alternata, and Fusarium sambucinum) employing minimum inhibitory concentration (MIC) method, comparative with standard tetracycline and amphotericin B. Molecular docking employing Autodock pinpointed key interactions supporting the ligand and complex's efficacy. In vitro MTT assay on L₂₀B and Rhabdomyosarcoma RD cells and in silico DNA binding investigations then converged to reveal potent cytotoxic activity and unveil the complex's mechanism of action. In silico toxicity predictions were performed using ProTox-3.0 for both the ligand and complex.

A novel Zinc(II) complex containing ligand potassium 2-chloro-5-nitrobenzohydroxamate moiety was synthesized in 1:2 M ratio. Physicochemical, spectral, and DFT studies inferred O,O coordination and distorted tetrahedral geometry around zinc. DFT studies revealed the complex to be more stable than the ligand. Electrochemical and thermal analyses were also studied. The ligand and the complex were screened in vitro for their antimicrobial and cytotoxic properties revealing efficient activities fortified by in silico investigations using molecular docking.