Synthesis, spectroscopic characterization and in vitro antibacterial activity studies of Cu(II) complexes derived from 6- hydroxyflavone Schiff bases

Abstract

This study reported the synthesis of the ligands (E) – 4 – ((2-hydroxyphenyl)imino -2-phenyl-4H- chromen-6-o1 (L¹) and (E) – 2 – ((6-hydroxy-2-phenyl-4H-chromen-4-ylidene)amino)benzaldehyde (L²). These two Schiff base ligands were synthesized by refluxing equimolar amount of 6- hydroxyflavone with 2-aminophenol and 2-aminobenzoic acid as ligands L¹ and L² respectively. The synthesized Schiff bases were subsequently reacted with Cu(II) acetate to form the corresponding metal complexes C₁ and C₂. The compounds were characterized using FT-IR, molar conductance, melting point and decomposition temperature studies, solubility test, magnetic susceptibility studies and gravimetric analysis. The purity of the compounds were analysed using TLC. The spectroscopic data indicated that the Schiff base ligands acted as tridentate and coordinated to the metal via imine nitrogen and deprotonated phenolic oxygen atoms. The Schiff base ligands have melting point between 166 – 185 C, whereas the Cu(II) complexes decomposes in the range 161 – 202 ^oC. Magnetic susceptibility studies showed that the complexes are paramagnetic in nature with the µeff values are in the range of 1.9 - 2.1 BM. Molar conductance values of the complexes were found to be in the range of 20.4 - 33.5 Ω^-1cm² mol^-1 indicating that they are non-electrolytic in nature. The solubility test of the compounds indicated that they are soluble in most organic solvents except water, acetone and tetrachloro methane in which are completely insoluble. The Cu(II) acetate, synthesized ligands and their metal complexes were studied for their in vitro antibacterial activity against two gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two gram negative bacteria (Escherichia coli and Salmonella typhi) using agar well diffusion method and the results indicated that the complexes were more active than the ligands and the Cu(II) acetate but less active compared to standard drug (ciprofloxacin).

Keywords: 6-hydroxyflavone, 2-aminophenol, 2-aminobenzoic acid, Schiff bases and antibacterial activity