Synthesis, Spectroscpic Studies and Reactivity of Chromium(111) Complexes with Aroyl Hydrazines

Abstract

Chromium in biological tissues is mostly present in trivalent form and helps to maintain the normal metabolism of glucose, proteins and fats. Literature suggests that chromium(III) complexes have a number of biological activities but some are cytotoxic in nature. So it is necessary to investigate new non-toxic chromium(III) complexes. Aroylhydrazines are biologically important chemical substances and their activities are known to be more improved after complexation with certain metal ions. In order to reveal the chemistry and biochemistry of chromium(III) complexes, the present work explains the synthesis of chromium(III) complexes with aroylhydrazine ligands, their structural and spectroscopic studies. Another significant contribution of this study is the evaluation of the cytotoxic activity, antioxidant nature, antiglycation property and carbonic anhydrase inhibition activities of synthesized chromium(III)-aroylhydrazine complexes. Aroylhydrazine ligands (1-12) with different substituents and their chromium(III) complexes (1a-12a) were synthesized and characterized by using analytical (C, H, N, Cr and Cl- analysis), physical (conductivity measurements) and spectral (EI-Mass, ESI-Mass, FTIR and UV-visible) methods. These physical, analytical and spectral data support that all chromium(III)-aroylhydrazine complexes exhibit an octahedral geometry in which ligand exhibits as a bidentate coordination and two water molecules coordinated at equatorial positions with general formula [Cr(L)2(H2O)2]Cl3. FTIR study demonstrated that in chromium(III)-aroylhydrazine complexes, the ligands were coordinated in a bidentate fashion through carbonyl oxygen and terminal amino nitrogen. ESI-Mass spectra showed that all chromium(III)-aroylhydrazine complexes produce fragments which were assigned to three chlorides and two water molecules from chromium(III) complexes. UV-visible study showed that there are three absorption bands and they also confirmed octahedral geometry of chromium(III)-aroylhydrazine complexes. UV-visible solution study of chromium(III)-aroylhydrazine complexes were evaluated that all of the aroylhydrazine ligands generate stronger ligand field strength than DMSO. Moreover, viii Time dependent stability study of chromium(III)-aroylhydrazine complexes in DMSO showed the decomposition of complex with the passage of time. Some chromium(III) complexes are reported to exhibit cytotoxicity. However, our studies show that chromium(III)-aroylhydrazine complexes reported here were not found to be toxic against normal cells so these compounds were further studied for other biological activities. All chromium(III)-aroylhydrazine complexes were screened for in vitro diphenyl dipicryl hydrazine (DPPH), superoxide dismutase and nitric oxide radical scavenging activities. Majority of the chromium(III)-aroylhydrazine complexes were found to be more effective scavengers as compared to free aroylhydrazine ligands. Studies showed that both steric hindrance and electron inductive effect play an important role in antioxidant activities. Aroylhydrazine ligands and their chromium(III) complexes were also investigated for carbonic anhydrase (CA II) inhibition activity and it was found that all aroylhydrazine ligands were inactive whereas chromium(III)-aroylhydrazine complexes showed excellent carbonic anhydrase inhibition. Chromium(III)-aroylhydrazine complexes with substituents meta position showed higher inhibition potential which may indicate better orientation of these complexes with interactive sites of enzymes. These studies also justified that slight alteration in the structure of the ligands may enhance the biological activities of chromium(III)-aroylhydrazine complexes. Aroylhydrazine ligands and their chromium(III) complexes were also examined for their antiglycation activity in which ligands were found inactive whereas chromium(III)-aroylhydrazine complexes showed significant inhibition of the process of protein glycation. Antiglycation potential of these complexes are dependent upon various factors such as metal-ligand complexation, binding pattern of ligands in the complexes, presence of nitrogen and nature of the ligands. This study provides the opportunity for future researchers to work in this area in order to find more Cr(III)-based antioxidant & antiglycating agents for controlling of diabetes.