Mechanochemical Synthesis, Characterization and In-vitro Anti-Microbial Studies of Binuclear Cu(II) and Zn(II) Complexes with Schiff Base Derived from Phenylalanine and Vanillin

Abstract

Schiff base derived from phenylalanine and vanillin and its corresponding binuclear Cu(II) and Zn(II) complexes have been synthesized by  mechanochemical synthesis. The composition and structure of the complexes were characterized by elemental analysis, Infrared spectroscopy, ESI-  mass spectrometry, thermogravimetric analysis, conductivity, and magnetic susceptibility measurements. The presence of a new band at 1660 cm-1  in the IR spectrum of the ligand due to ʋ(C=N) co nfirms the formation of the Schiff base and the shifts of this band (1660 cm^-1) to higher  frequencies in the spectra of the metal(II) complexes indicate complexation. The experimental results showed that the Schiff base binds to the metal  ion in a tridentate (O, N, O) manner, resulting in the formation of binuclear metal(II) complexes. The copper and zinc ions are all six  coordinated and coordinates through the azomethine nitrogen, carboxylic and phenolic oxygen in addition to oxygen from three coordinated water  molecules respectively. The copper(II) and zinc(II) complexes have the general formula[M2L3(H2O)6] xH2O (where x = 3 or 0 and M = Cu or Zn). ESI-  MS analysis showed m/z =376.03, 1166.77 and 1171.44 correspond to singly charged ions which confirms the molecular weight of the Schiff base  and the binuclear Cu(II) and Zn(II) complexes respectively. The molar conductance of the complexes measured is low in the range 20.01-23.68 Ω-1  cm2 mol-1, indicating their non-electrolytic nature. TGA analysis showed the gradual loss of water of hydration, coordinated water molecules,  followed by the stepby- step decomposition of the Schiff base into its metal oxide residue. The magnetic susceptibility measurements indicate a  diamagnetic binuclear Zn(II) complex, while Cu(II) complex was found to be paramagnetic. The percentage yield of the synthesized compounds was  found to be greater than 90%. The anti-fungal and antibacterial activities of the Schiff base and their corresponding metal complexes were  investigated in vitro using the disc diffusion method against Staphylococcus aureus, Streptococcus pneumoniae, Salmonella typhi, Escherichia coli,  Tinea capitis, and Trichophyton rubrum. Both Schiff base and metal complexes were found to be active against all selected bacterial and fungal  species but a much enhanced activity was observed for the complexes.