Designing, spectroscopic characterization, biological screening and antioxidant activity of mononuclear transition metal complexes of bidentate Schiff base hydrazones

Antioxidant activity of Schiff base ligands using the DPPH scavenging assay: an updated review

Schiff base ligands, formed from primary amines and carbonyl compounds, are potential antioxidants because they scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals via hydrogen atom transfer (HAT) and single electron transfer (SET) routes. This review aims to help design, synthesize, and discuss the antioxidant activity of Schiff base ligands based on their structure. This study critically discussed the solvent effect and the structural changes of Schiff base ligands responsible for DPPH scavenging activity, such as proton donating, electron-donating, and electron-withdrawing substituents, conjugation and ring structure. The ligands with electron-donating substituent groups in the phenolic ring demonstrated greater activity by readily stabilizing the radical and some of them showed higher activity than the standard. The activity also depends on the solvent used; the activity increases in those solvents that promote the proton and electron donation of the Schiff base. Schiff bases are most important due to their versatile applications, which can be explained by their antioxidant activity. The data led to the conclusion that the Schiff base ligand will serve as a source of synthetic antioxidants. There should be lots of scope for research on the antioxidant activity of Schiff bases. This review will assist researchers in studying Schiff base-based antioxidants and their applications. All the data analyzed in this paper was found from in vitro tests; for more clearance supplementary tests and in vivo investigations are crucial.

Manganese(II) and Zinc(II) metal complexes of novel bidentate formamide-based Schiff base ligand: synthesis, structural characterization, antioxidant, antibacterial, and in-silico molecular docking study

A new bidentate Schiff base ligand (C16H16Cl2N4), condensation product of ethylene diamine and 4-chloro N-phenyl formamide, and its metal complexes [M(C16H16Cl2N4)2(OAc)2] (where M = Mn(II) and Zn(II)) were synthesized and characterized using various analytical and spectral techniques, including high-resolution mass spectrometry (HRMS), elemental analysis, ultraviolet-visible (UV-vis), Fourier-transform infrared (FTIR) spectroscopy, AAS, molar conductance, 1H NMR, and powder XRD. All the compounds were non-electrolytes and nanocrystalline. The synthesized compounds were assessed for antioxidant potential by DPPH radical scavenging and FRAP assay, with BHT serving as the positive control. Inhibitory concentration at 50% inhibition (IC50) values were calculated and used for comparative analysis. Furthermore, the prepared compounds were screened for antibacterial activity against two Gram-negative bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-positive bacteria (Escherichia coli and Salmonella typhi) using disk-diffusion methods, with amikacin employed as the standard reference. The comparison of inhibition zones revealed that the complexes showed better antibacterial activity than the ligand. To gain insights into the molecular interactions underlying the antibacterial activity, the ligand and complexes were analyzed for their binding affinity with S. aureus tyrosyl-tRNA synthetase (PDB ID: 1JIL) and S. typhi cell membrane protein OmpF complex (PDB ID: 4KR4). These analyses revealed robust interactions, validating the observed antibacterial effects against the tested bacterial strains.

Biological and computational investigation of transition metal(II) complexes of 2-phenoxyaniline-based ligands

Aim: In the 21st century, we are witness of continuous onslaughts of various pathogen deformities which are a major cause of morbidity and mortality worldwide. Therefore, to investigate the grave for these deformities, antioxidant, anti-inflammatory and antimicrobial biological activities were carried out against newly synthesized Schiff base ligands and their transition metal complexes, which are based on newly synthesized 2-phenoxyaniline and salicylaldehyde derivatives. Materials & methods: The synthesized compounds were characterized by various physiochemical studies, demonstrating the octahedral stereochemistry of the complexes. Results: The biological assessments revealed that complex 6 (3.01 ± 0.01 μM) was found to be highly active for oxidant ailments whereas complex 14 (7.14 ± 0.05 μM, 0.0041-0.0082 μmol/ml) was observed as highly potent for inflammation and microbial diseases. Conclusion: Overall, the biological and computational studies demonstrate that the nickel(II) complex 14 can act as an excellent candidate for pathogen deformities.

Investigation of antituberculosis, antimicrobial, anti-inflammatory efficacies of newly synthesized transition metal(II) complexes of hydrazone ligands: structural elucidation and theoretical studies

Tuberculosis disease is a serious threat to humans and spreading quickly worldwide, therefore, to find a potent drug, the synthesis of hydrazone ligands endowed Co(II), Ni(II), Cu(II), Zn(II) metal complexes were carried out and well characterized by numerous spectral and analytical techniques. The octahedral geometry of the complexes was confirmed by spectral analysis. Further, in vitro antituberculosis efficacy of the compounds (1-10) revealed that complexes (6), (9), (10) have highest potency to control TB malformation with 0.0028 ± 0.0013-0.0063 ± 0.0013 µmol/mL MIC value while Zn(II) complex (10) (0.0028 ± 0.0013 µmol/mL) has nearly four time potent to suppress TB disease in comparison of streptomycin (0.0107 ± 0.0011 µmol/mL). The antimicrobial and anti-inflammatory evaluations revealed that the complex (10) is more active with lowest MIC (0.0057-0.0114 µmol/mL) and IC50 (7.14 ± 0.05 µM) values, correspondingly which are comparable with their respective standard drugs. Furthermore, the theoretical studies such as molecular docking, DFT, MESP and ADMET were employed to authenticate the potency of HL2 hydrazone ligand (2) and its metal complexes (7-10) which revealed that the zinc(II) complex (10) might be utilized as novel drug candidate for tuberculosis dysfunctions. So, the present research gives a new insight for in vivo investigation of the compounds.

Synthesis of novel coumarin-hydrazone hybrids as α-glucosidase inhibitors and their molecular docking studies

Diabetes mellitus is a metabolic disorder and more than 90% of diabetic patients suffer from type-2 diabetes, which is characterized by hyperglycemia. α-Glucosidase inhibition has become an appropriate approach to tackle high blood glucose levels. The current study was focused on synthesizing coumarin-hydrazone hybrids (7a-i) by using facile chemical reactions. The synthesized compounds were characterized by using 1H-NMR, 13C-NMR, and IR. To evaluate their anti-diabetic capability, all of the conjugates were screened for in vitro α-glucosidase inhibitory activity to reveal their therapeutic importance. All of the compounds (except 7b) demonstrated significant enzyme inhibitory potential with IC50 values ranging between 2.39-57.52 μM, as compared to the standard inhibitor, acarbose (IC50 = 873.34 ± 1.67 μM). Among them, compound 7c is the most potent α-glucosidase inhibitor (IC50 = 2.39 ± 0.05 μM). Additionally, molecular docking was employed to scrutinize the binding pattern of active compounds within the α-glucosidase binding site. The in silico analysis reflects that hydrazone moiety is an essential pharmacophore for the binding of compounds with the active site residues of the enzyme. This study demonstrates that compounds 7c and 7f deserve further molecular optimization for potential application in diabetic management.

Green synthesis of nanosized N,N'-bis(1-naphthylidene)-4,4'-diaminodiphenylmethane and its metal (II) complexes and evaluation of their biological activity

Condensation of ecofriendly synthesized 4,4'-methanedianiline with 2-hydroxy-1-naphthaldehyde produced a (1:1) octopus-like Schiff base mixed ligand. Reaction with Co(OAc)2⋅H2O, NiCl2⋅6H2O, Cu(OAc)2⋅H2O and Zn(OAc)2⋅2H2O metals furnished their complexes in high yield and purity. All new structures were fully characterized by various spectroscopic and spectrometric measurements. The complexes exhibited high thermal stability up to 700 °C, leaving nearly 40% of their mass as residues. Antimicrobial screening results exhibited moderate activities towards all studied microbes. Antioxidant screening was concentration dependent, and their activities were in the order Ni(II) > Zn(II) > Cu(II) > Co(II) complexes. The NO inhibitory effect revealed that the nickel complex exhibited the highest activity, whereas the cobalt complex showed the lowest inhibition. All compounds showed a significant lipid peroxidation inhibitory effect against oxidative stress. The complexes significantly diminished the TBARS level, and the nickel complex exhibited the highest inhibition at p < 0.01. Antioxidants stress the oxidative damage induced by iron, indicating that the nickel complex has the highest reducing activity. The inhibitory effect against acetylcholine esterase showed that the copper complex has the highest activity. Membrane stabilization activities clearly indicated that most compounds can improve the integrity of the cells and stability of their membrane, and this result may be related to their antioxidant capacity to protect against cytotoxicity. The nickel complex exhibited a stronger total antioxidant capacity than the other complexes. The biological and antioxidant capacities of these complexes may make them promising candidates in pharmaceutical applications.

Transition metal complexes of triazole-based bioactive ligands: synthesis, spectral characterization, antimicrobial, anticancer and molecular docking studies

In the present research work, four new heterocyclic Schiff base ligands (1–4) were synthesized by the condensation of 4-(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)phenol with salicylaldehyde derivatives in 1:1 molar ratio. The synthesized Schiff base ligands were allowed for complexation with Co(II), Ni(II), Cu(II), Zn(II) metal ions. The structure of the newly synthesized compounds (1–20) was elucidated with the help of various spectral and physicochemical techniques. Spectroscopic data confirm the tridentate nature of ligands which coordinate to the metal via deprotonated oxygen, azomethine nitrogen and thiol sulphur. Conductivity data showed the non-electrolytic nature of complexes. Furthermore, the synthesized compounds were evaluated for their in-vitro antimicrobial activity against four pathogenic bacterial strains and two pathogenic fungal strains. The observed results of microbial activity reveals that compound 3 and its complexes (13–16) were found most potent against the pathogenic strains. In addition, the anticancer activity of all the synthesized compounds was evaluated against human carcinoma cell lines i.e. HCT-116, DU145 and A549 using MTT assay. Among the tested compounds 12, 19, and 20 were found to show promising potency against the cancer cell lines. To rationalize the preferred modes of interaction of most potent compounds with the active site of human EGFR protein (PDB id: 5XGM), molecular docking studies were performed.