Mammalian Cell Cytotoxicity, Antibacterial Activity and the Properties of Methylenebis(Hydroxybenzoic Acid) and Its Related Zinc(II) Complex

Formaldehyde, sulfuric acid and salicylic acid were combined to create a 3,3′-methylenebis(2-hydroxybenzoic acid) (MHB) ligand, which was subsequently permitted to bind with zinc(II) ions. The ligand and its zinc(II) complex (Zn–MHB) have been described by a combination of elemental analyses, spectral analyses (UV–Vis, IR, MS and NMR), XRD, TEM, as well as TGA measurement. The ligand has been suggested to coordinate to the zinc center in a tetradentate manner forming the binuclear tetrahedral complex. An X-ray analysis indicated a considerable difference between MHB (crystalline) and Zn–MHB (amorphous). The UV–Vis spectra were used to determine the optical properties such as bandgap, refractive index, optical conductivity and penetration depth. The possibility of employing the samples for optoelectronic applications was indicated from the band gap values which underlie the range of semiconductors. TEM revealed the spherical shapes and mutation of ligand particles into the nano-scale by complexation. The antimicrobial potential of the MHB towards Gram-positive and Gram-negative bacterial growths has been investigated. The results suggested that it would be possible to employ MHB to prevent bacterial development, particularly that of salmonella typhimurium. The cytotoxicity of the MHB was assessed against two types of mammalian cells: VERO (the kidney of an African green monkey) and HFB4 (human skin melanocytes). Lower sensitivity was observed in VERO cells.