SYNTHESIS, CHARACTERISATION AND BIOLOGICAL ACTIVITY OF COPPER (II) COMPLEX LIGAND DERVIDED FROM BENZOTHIOPHENE-2-CARBOHYDRAZIDE SCHIFF BASE

This study reports the synthesis, characterization, and antimicrobial evaluation of a novel Schiff base ligand (L) derived from benzothiophene-2-carbohydrazine and its corresponding copper(II) complex. The successful complex formation was confirmed by Fourier Transform Infrared (FTIR) spectroscopy, which revealed a significant bathochromic shift in the azomethine (C=N) stretching vibration from 1620-1640 cm⁻¹ in the free ligand to a lower wavenumber in the complex, alongside the emergence of new bands in the far-IR region attributable to ν(Cu–N) and ν(Cu–O) vibrations. The complex exhibited a markedly superior and broad-spectrum antimicrobial profile compared to the ligand. The results demonstrated that the copper(II) complex was highly effective against both Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria, as well as fungal strains (Candida albicans, Tricophytum rubrum), showing potent, dose-dependent activity in the susceptibility assay. Crucially, minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) analyses revealed exceptional potency, particularly against S. aureus, where the complex exhibited a bactericidal MIC/MMC value of 3.125 µg/mL, outperforming the ligand (MIC/MMC >50 µg/mL) and the standard drug ciprofloxacin (MIC/MMC = 5 µg/mL). The dramatic enhancement in efficacy upon complexation is attributed to the synergistic effect of increased lipophilicity, facilitating microbial membrane penetration, and the redox-active copper center enabling reactive oxygen species generation. These findings conclusively validate the copper(II) complex as a highly promising candidate for further development as a broad-spectrum antimicrobial agent.