SYNTHESIS, CHARACTHERISATION, AND ANTIBACTERIAL POTENTIAL OF A Pt(II) COMPLEX WITH A NOVEL LINEAR SULFONAMIDE LIGAND TERMINATED BY BENZIMIDAZOLYL MOIETIES

Abstract

Platinum complexes have been extensively studied for their antibacterial and anticancer properties, primarily due to their ability to bind to DNA and proteins. In recent years, there has been growing interest in the development of novel N donor ligands to enhance these biological activities. This study aimed to synthesise and characterise a novel N,N′,N″-donor linear sulfonamide ligand terminated with benzimidazolyl rings, along with its corresponding platinum(II) complex, to investigate their potential biological applications. The compounds were characterised using 1H and 1H–1H ROESY NMR, FTIR, UV–Visible, and fluorescence spectroscopy. The 1H and ROESY NMR spectra reveal that the methylene protons, which appear as singlets in the free ligand (L), split into two doublets in the platinum complex, indicating bidentate coordination to the Pt(II) centre, forming a symmetrical complex. This coordination restricts the free rotation of the methylene group, leading to the observed spectral changes. Tridentate binding is considered unlikely, as literature evidence suggests that similar N,N′,N″ donor linear sulfonamide ligands do not coordinate to Pt(II) in a tridentate fashion due to electronic and steric restrictions. The resulting yellow solid of the platinum complex is soluble in chloroform but insoluble in polar solvents such as water. Spectroscopic and literature data collectively support the formation of a Pt(L)Cl₂ type complex, featuring an eight-membered chelate ring. Notably, complexation results in significant fluorescence quenching compared to the free ligand. The potential antibacterial activity of both the ligand (L) and the complex (C) was evaluated against gram-positive, Staphylococcus aureus ATCC25923, and gram negative, Escherichia coli ATCC25922, using the agar well diffusion method. Both compounds exhibited minimal to no antibacterial activity even at 4000 ppm, suggesting limited interaction with bacterial cellular components. Nevertheless, further cytotoxicity studies on mammalian cell lines are warranted to assess their potential as anticancer agents.