ANTIBACTERIAL POTENTIAL OF THE HOT-WATER CRUDE EXTRACT OF RINOREA OBLONGIFOLIA COMPLEXED WITH COPPER SULPHATE

Antimicrobial resistance has become a major global health concern, leading to an urgent search for safer, more effective, and naturally derived anti-bacterial agents. Medicinal plants such as Rinorea oblongifolia have long been used in traditional medicine for treating infections, largely due to their diverse phytochemical constituents with known anti-bacterial activity. In this study, the antimicrobial potential of copper sulphate complexed with the hot water crude extract of Rinorea oblongifolia leaves was evaluated to determine whether metal complexation enhances the biological activity of the plant extract. The study was aimed at assessing the antimicrobial potency of the copper–extract complex and comparing its efficacy with that of the crude extract. The leaves of R. oblongifolia were collected, authenticated, air-dried, and extracted using hot water, yielding 5.42 ± 0.1%. The extract was then complexed with copper sulphate and characterized using physicochemical and spectroscopic methods. Physicochemical analysis revealed a decrease in pH from 6.2 in the control to 4.7 in the complex, an increase in electrical conductivity from 547 µS/cm to 743 µS/cm, and a change in colour from deep green to green, confirming complex formation. Fourier Transform Infrared (FTIR) spectroscopy showed notable shifts in absorption peaks, including a shift of the hydroxyl (O–H) stretch from 3099.83 cm⁻¹ to 3197.32 cm⁻¹ and the emergence of a new Cu–O band at 550.28 cm⁻¹, indicating successful coordination between copper ions and the phytochemicals in the extract. Antimicrobial susceptibility testing demonstrated that the copper–extract complex exhibited significantly higher zones of inhibition compared to the crude extract alone, with Staphylococcus aureus showing 26 ± 1.75 mm at 25 mg/ml for the complex compared to 7.0 ± 0.81 mm for the extract. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values ranged from 25 to 50 mg/ml, suggesting that the complex possessed bactericidal activity. These findings indicate that complexation with copper sulphate enhances the antimicrobial efficacy of Rinorea oblongifolia extract by improving its stability, solubility, and metal–ligand interactions. The study concludes that the copper–Rinorea oblongifolia complex is a promising candidate for developing potent plant-based antimicrobial agents. It is recommended that further work be carried out to isolate the active compounds, evaluate toxicity and pharmacological safety, and develop suitable formulations for therapeutic and industrial applications.