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Phosphorus‐based Schiff bases and their complexes as nontoxic antioxidants: Structure–activity relationship and mechanism of action
Author(s) -
Al Zoubi Wail,
Kim Min Jun,
Salih AlHamdani Abbas Ali,
Kim Yang Gon,
Ko Young Gun
Publication year - 2019
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.5210
Subject(s) - chemistry , schiff base , ligand (biochemistry) , metal , octahedron , octahedral molecular geometry , medicinal chemistry , infrared spectroscopy , metal ions in aqueous solution , stereochemistry , crystallography , inorganic chemistry , crystal structure , organic chemistry , biochemistry , receptor
Phosphorus‐based Schiff base were synthesized by treating bis{3‐[2‐(4‐amino‐1.5‐dimethyl‐2‐phenyl‐pyrazol‐3‐ylideneamino)ethyl]‐indol‐1‐ylmethyl}‐phosphinic acid with paraformaldehyde and characterized as a novel antioxidant. Its corresponding complexes [(VO) 2 L(SO 4 ) 2 ], [Ni 2 LCl 4 ], [Co 2 LCl 4 ], [Cu 2 LCl 4 ], [Zn 2 LCl 4 ], [Cd 2 LCl 4 ], [Hg 2 LCl 4 ], [Pd 2 LCl 4 ], and [PtLCl]Cl 2 were analyzed by Fourier transform‐infrared, ( 1 H and 13 C) nuclear magnetic resonance, and mass and UV–Vis spectroscopy. Experimental data showed that the ligand coordinated with the metal ions via donor atoms such as nitrogen to form an octahedral arrangement of the Schiff base around the central transition‐metal atom. The nature of these complexes was identified using the molar ratio and Job's methods, with the results agreeing with a metal‐to‐ligand (M:L) molar ratio of 2:1, expect for Pt, whose M:L was 1:1. Thermodynamic activation parameters such as ∆E*, ∆H*, ∆S*, ∆G*, and K were determined from the thermogravimetric analysis curve using the Coats–Redfern method. The antioxidant activities of the prepared compounds were assessed by using 1.1‐diphenyl‐2‐picrylhydrazyl as the free radical, and the results show that the complex Schiff bases were found to possess potent antioxidant activity. The structure–activity relationship of the ligand and its complexes indicates that the presence of electron‐donating moieties, such as Co(II) and Ni(II), in the chemical structure increases the antioxidant activity, whereas the Pt(IV) and Pd(II) complexes diminished the antioxidant activity, indicating the superior activity of the hydroxyl radical (OH · ) over the superoxide radical.