Phosphorus‐based Schiff bases and their complexes as nontoxic antioxidants: Structure–activity relationship and mechanism of action

Abstract

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-toligand (M:L) molar ratio of 2:1, expect for Pt, whose M:L was 1:1. Thermodynamic activation parameters such as ΔE*, ΔH*, ΔS*, ΔG*, 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.

Synthesis, Characterization, and Thermal Analysis of a New Acidicazo Ligand's Metal Complexes

“…In the produced complexes spectra, it is noticed with a slight modification in form and moved to higher frequencies 1676-1670 cm -1 . 32,33 These variances point to hydrogen bonding between the carboxylic group's C=O and the orthogonal OH group. The azo group was shifted toward lower frequencies in their complexes spectra, and the primary amine group appeared within the (3436-3325) cm -1 region, as well as the disappearance of the resorcinol hydroxyl group.…”

Synthesis and Characterization of Some Metals Complexes with New Acidicazo Ligand 4-[(2-Amino-4-Phenylazo)-Methyl]-Cyclohexane Carboxylic Acid

“…The azo group was shifted toward lower frequencies in their complex's spectra, and the primary amine group appeared within the 3440 cm -1 region, as well as the disappearance of the resorcinol hydroxyl group. These findings can be explained by the participation of NH &azo-nitrogen in coordination with metallic ions, as seen in complexes spectra [20][21][22][23][24]29,30]. 4 contains information on the thermal degradation process.…”

Phosphorus Schiff base ligand and its complexes: Experimental and theoretical investigations

“…Regarding bio‐applications, the formation of coordination complexes brings extensive changes in the biological properties of Schiff bases and also in those of transition metal ions upon chelation which could be applied in therapy for many diseases. Recently, we have reported the biological importance of various heteroatom‐based Schiff bases and their metal complexes . A review of Schiff bases and their antimicrobial activities elaborated the importance of this functional group in medicinal chemistry.…”