Synthesis, Structural and Biological Investigations of Vanadium(V) Complexes with N and O Donor Ligands

Abstract

In last two decades vanadium coordination chemistry has grasp the interest of chemists due to its importance from catalysis and medicinal point of view. Vanadium plays significant role in different biological systems, actively serving in vanadium dependent haloperoxidase and nitrogenase enzymes. It also exhibits insulin-mimetic (anti-diabetic) activity. The present study is carried out in order to synthesize new vanadium (V) complexes with N and O donor hydrazide ligands and reveal their biological importance in terms of antioxidant activities and different enzyme inhibition activities. On the basis of spectral, elemental and physical data, synthesized vanadium (V) complexes are tentatively assigned to have an octahedral geometry with two hydrazide ligands and two oxo groups forming a negatively charged sphere complex with ammonium as counter ion. This is further verified by the conductivity studies of the complexes. In synthesized vanadium (V) complexes hydrazides act as bidentate ligands and are found to be attached with O of C=O and N of NH2, and these attachments are evident from IR and NMR spectra of these complexes.

The inhibitory potential of vanadium (V) complexes of hydrazides against oxidative enzymes including xanthine oxidase and lipoxygenase is determined. In addition, non-enzymatic radical scavenging activities of these complexes were also determined. Results show that hydrazide ligands (1-12) and their respective vanadium (V) complexes (1c-12c) posses scavenging and inhibition potential against DPPH and lipoxygenase, respectively. However, contrary to that uncoordinated ligands showed no activity against nitric oxide, superoxide and xanthine oxidase whereas their complexes showed varying degree of activity. It is interesting that V(V) complexes are more active for all enzymatic and radical scavenging studies reported here except for lipoxygenase enzyme which demonstrates the difference in the interaction of metal complexes with metalloenzymes. Furthermore enzyme inhibition potential of all the synthesized ligands, metal salt and vanadium (V) hydrazide complexes has also evaluated against tyrosinase, urease and carbonic anhydrase enzymes. Results obtained during the course of this study reveal that hydrazide ligands show moderate inhibition against tyrosinase, but found to be inactive against urease and carbonic anhydrase enzymes. Vanadium (V) hydrazide complexes show variable degree i.e. excellent, moderate to weak activity against all of these studied enzymes.

These studies indicate that geometry of complex, nature and position of substituent groups play a vital role in scavenging and inhibition potential of these compounds and demonstrate the difference in the interaction of metal complexes with metalloenzymes. Further pharmacological and toxicological studies are required to evaluate the bioactive vanadium complexes to find out their potential for use as drugs.