Transition metal complexes with N, S donor ligands as synthetic antioxidants: Synthesis, characterization and antioxidant activity

Abstract

Transition metal complexes containing bidentate N, S donor ligands i.e., carvone thiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one thiosemicarbazone (IPMCHTSC)] and carvone N¹-phenylthiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one phenylthiosemicarbazone (IPMCHPhTSC)] have been synthesized. All the metal complexes (1–8) have been characterized by elemental analysis, molar conductance measurement and various spectral studies [infrared (IR), electronic, fast-atom bombardment (FAB) mass and NMR (for ligands)] and thermogravimetric analysis. FAB mass spectroscopic studies of (1), (3), (4), (5), (6) (7), and (8) suggest their monomeric nature. Metal complexes are [M(LH)Cl₂] and [M(LH)₂Cl₂] type, where M = Fe(III), Co(II), and Cu(II) and LH = IPMCHTSC and IPMCHPhTSC. The proposed geometries of the complexes were octahedral for 1:2 complexes, square planar for 1:1 complexes and distorted octahedral for Cu(II) complexes (1:2). The free radical scavenging activity of ligands (IPMCHTSC and IPMCHPhTSC) and their metal complexes have been determined at the concentration range of 10–400 μg/mL by means of their interaction with the stable free radical 2,2′-diphenyl-1-picrylhydrazyl and 5–200 μg/mL by 2,2′-Azinobis-3-ethylbenzothiazoline-6-sulphonic acid. All the compounds have shown encouraging antioxidant activities.

Keywords::

• Molar conductance
• FAB mass
• radical scavenging activity
• DPPH
• ABTS

Acknowledgements

The authors are thankful to Defence Institute of Bio-Energy Research, Pithoragarh (Uttrakhand), for carrying out antioxidant activity and also grateful to Zydus Research Center, Ahmedabad for recording FAB Mass, TGA, elemental analysis and electronic spectra. One of the authors (R.S.) is grateful to CSIR, New Delhi for the award of Research Associateship to her.

Declaration of interest

The authors report no conflicts of interest.