Salicylaldehyde-based Schiff bases and their transition metal complexes: an overview on synthesis and biological activities
Md. Sohel Rana, Noor Mohammad Azbar Rayhan, Abu Hurayra Emad, Md. Iqbal Hossain, M. M. I. Shah, Md. Kudrat‐E‐Zahan, Md. Faruk Hossen, Md. Ali Asraf
Abstract
Due to their varied biological actions, salicylaldehyde-based Schiff bases and their transition metal complexes have received interest. The imine and hydroxyl groups of Schiff bases are essential in the mechanism of biological activities. Phenyl-derived metal complexes have increased antimicrobial activity owing to lipophilicity and delocalized p-electrons. Chelation lessens metal ion polarity and increases lipophilicity, allowing cell penetration and enzyme inhibition to cause higher antimicrobial and anticancer activity. A positive charge on the metal atom in salicylaldehyde-based Schiff-base metal complexes enhances the acidity of proton-containing Schiff-base metal complexes that promote stronger hydrogen bonding and increased anticancer activity. The t-butyl group substituents of the metal complexes improve hydrophobicity and anticancer action. Diorganotin(IV) and Ru(III) complexes have higher anticancer activity. Salicylaldehyde-based Schiff bases act as antioxidants by providing protons and electrons to remove free radicals that are improved by the electron-donating substituent. The complexes formation of the ligand develops antioxidant effectiveness, and nitro-substituted Cu(II) complexes, phenyl-containing diorganotin(IV) complexes, and Ru(III) complexes having d5 electronic configurations are more antioxidant. More investigation is needed to understand the biological activities of salicylaldehyde-based Schiff base and their transition metal complexes. This review summarizes synthetic methods, biological activities, and structure-activity relationships.