Antioxidant Activity and DFT Calculations of Metal Complexes Derived from a Schiff Base Ligand: Synthesis, Characterization, and Biological Evaluation

Herein, a Schiff base ligand, (Z)-2-(((4-chlorophenyl)imino)methyl)naphthalen-1-ol HL, is synthesized via condensation reaction between 2-hydroxy-1-naphthaldehyde and 4-chloroaniline in methanol with formic acid as catalyst. The ligand reacts with Mn(II), Ni(II), and Cu(II) to form complexes C1–C3. Characterization techniques confirm the formation of ON-type complexes. Antioxidant activity testing reveals C1’s superior scavenging ability compared to the ligand, complexes, and ascorbic acid. DFT analysis supports experimental findings.

Abstract

Metal complexes derived from Schiff bases are known to have a wide range of applications, spanning the areas of material and medicinal sciences. Herein, a Schiff base ligand, (Z)-2-(((4-chlorophenyl)imino)methyl)naphthalen-1-ol HL, was synthesized via a condensation reaction between 2-hydroxy-1-naphthaldehyde and 4-chloroaniline using methanol as a solvent in the presence of a catalytic amount of formic acid. The obtained ligand was further reacted with Mn(II), Ni(II), and Cu(II) using their acetate salts in a 1 : 2 stoichiometric ratio of metal to ligand to afford complexes C1–C3, respectively. Physicochemical and analytical techniques consisting of FTIR, UV-Vis, elemental (CHN and metal content), TGA, HRMS, 1H, and 13 C NMR spectroscopy were deployed to establish the formation of the compounds. Results show that the ligand coordinated with the metal ions through the oxygen and nitrogen atoms of the phenolate and azomethine moieties, respectively, forming ON-type complexes. Furthermore, the free ligand and its complexes were evaluated for their antioxidant activity compared to the standard (ascorbic acid) using an in vitro DPPH radical scavenging assay. From this investigation, C1 demonstrated higher radical scavenging activity than the free ligand, the complexes, and the standard (ascorbic acid). But the ligand has better scavenging activity than C2 and C3 at higher concentrations. DFT was also used to examine the electronic properties of the compounds, and the data obtained corroborated well with the experimental study.

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