Executing a Series of Zinc(II) Complexes of Homologous Schiff Base Ligands for a Comparative Analysis on Hydrolytic, Antioxidant, and Antibacterial Activities

Abstract

Six zinc(II) complexes, namely, [Zn(HL 1 H)Cl 2 ] (1), [Zn(HL 1 H)Br 2 ] (2), [Zn 2 (HL 1 H) 2 (OH)I 2 ]•I (3), [Zn(HL 2 )-Cl] (4), [Zn 2 (HL 2 )Br 3 ] (5), and [Zn(HL 2 )I] (6) have been manufactured by using two homologous Schiff base ligands H 2 L 1 and H 2 L 2 for the purpose of perlustrating their phosphatase-like activity, antioxidant activity, and antibacterial activity. Complexes 1, 2, 4, and 5 have been reported earlier by us, whereas complexes 3 and 6 have been synthesized and structurally characterized by regular physicochemical methods The hydrolytic property of the six complexes has been evaluated by checking the hydrolysis of the P−O bond of a widely used substrate, namely, disodium salt of (para-nitrophenyl)phosphate (PNPP) in 97.5% (v/v) mixture of N,N-dimethylformamide and water (DMF−water). Complexes 2− 5 have profound efficiency toward hydrolysis of phosphate ester bonds, and complexes 1 and 6 were noted to be inactive toward hydrolysis. Complex 3 displayed the highest efficacy among the six complexes. Additionally, antioxidant and antibacterial activities of the complexes were studied thoroughly. A detailed study of their antioxidant property revealed that complex 3 manifested superior radical scavenging activity, thus exhibiting the highest antioxidant property. The antibacterial activity was tested using four investigating bacteria, specifically Listeria monocytogenes ATCC19111, Staphylococcus aureus ATCC 700699, Salmonella typhimurium ATCC 23564, and Escherichia coli ATCC 25922 by determining minimum inhibitory concentration (MIC) values using the microdilution method. Here as well, complex 3 exhibited the highest activity to both Gram positive and Gram negative bacteria. The chemistry behind these experimental findings has been manifested by shedding light upon the structural features of the complexes. The suitable choice of ligand H 2 L 1 where one methylene group is less than its homologous ligand and metal precursor (ZnI 2 ) imparts a unique hydroxo-bridged molecular geometry and 2D hydrogen bonding network which in turn probably enhances the hydrolytic and biological activities of complex 3.

Recent Progress in Metal‐Incorporated Acyclic Schiff‐Base Derivatives: Biological Aspects

“…Structures of ligand H 2 L L26 and its Zn II complex 44 (Reproduced from Ref. [88]. Copyright (2020) ACS.…”

“…Das and co‐workers obtained the dinuclear Zn II complex, [Zn 2 (HLH) 2 (OH)I 2 ]⋅I 44 from the Schiff‐base ligand H 2 L L26 which showed very high anti‐bacterial activity against both Gram‐positive ( L. monocytogenes , MIC value: 158.8 μg mL −1 and S. aureus , MIC value: 50.99 μg mL −1 ) and Gram‐negative bacteria ( E. coli , MIC value: 163.61 μg mL −1 and S. typhimurium , MIC value: 79.11 μg mL −1 ) (Figure 19). [88] The anti‐bacterial activity of the complex was suggested to arise from the unique hydroxo‐bridged geometry of the complex along with its 2D hydrogen bonding molecular network.…”

“…The dinuclear Zn II complex, [Zn 2 (HL 1 H) 2 (OH)I 2 ]⋅I 44 synthesized by Das and co‐workers from the Schiff‐base ligand H 2 L 1 ( L26 ) (Figure 19) showed high antioxidant activity which was confirmed through its high scavenging effect on DPPH⋅ and ABTS⋅ (2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid)) radicals (Figure 42). [88] The dimeric structure of complex 44 containing two protonated amino groups was responsible for its ability to liberate protons in close proximity to DPPH⋅ radical leading to high radical scavenging activity. The ample positive charge density due to the presence of two Zn II ions, was responsible to attract ABTS⋅ radical.…”

Chromone‐Appended Zn(II) tRNA‐Targeted Potential Anticancer Chemotherapeutic Agent: Structural Details, in vitro ct‐DNA/tRNA Binding, Cytotoxicity Studies And Antioxidant Activity

“…The pliability of Zinc metal's coordination number along with the formation of hydrogen bonds by the coordinating water molecules with nucleobases is responsible for the trapping of the phosphodiester linkage, leading to greater binding of complexes with ct-DNA/tRNA. [35] The in vitro comparative bind- ing studies of Zn(II)-based complex 1 with ct-DNA/tRNA were ascertained by a battery of different spectroscopic techniques such as UV-visible, Fluorescence, 1 H NMR titration, circular dichroism and cyclic voltammetry.…”

Synthesis, X-ray Structure and Evaluation of Bactericidal Activity of an o-vanillin Functionalized Schiff Base

“…Furthermore, among the various aromatic aldehydes, vanillin or 3-methoxybenzaldehyde is a constituent of fruits and obtained from the plant Vanilla Planifolia. Moreover, o-vanillin (aromatic hydroxyaldehydes) functionalized Schiff bases show high stability in the ligand backbone and facilitate the formation of metal complex of varied functionalities [16][17][18]. The chelating behaviour of o-vanilin functionalized Schiff bases is found good and well documented in scientific literatures [19,20].…”