Synthesis, characterisation, in vitro antimicrobial, antioxidant and anti-inflammatory activities of diorganotin(IV) complexes derived from salicylaldehyde Schiff bases

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.

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.

Pincer Complexes Derived from Tridentate Schiff Bases for Their Use as Antimicrobial Metallopharmaceuticals

Within the current challenges in medicinal chemistry, the development of new and better therapeutic agents effective against infectious diseases produced by bacteria, fungi, viruses, and parasites stands out. With chemotherapy as one of the main strategies against these diseases focusing on the administration of organic and inorganic drugs, the latter is generally based on the synergistic effect produced by the formation of metal complexes with biologically active organic compounds. In this sense, Schiff bases (SBs) represent and ideal ligand scaffold since they have demonstrated a broad spectrum of antitumor, antiviral, antimicrobial, and anti-inflammatory activities, among others. In addition, SBs are synthesized in an easy manner from one-step condensation reactions, being thus suitable for facile structural modifications, having the imine group as a coordination point found in most of their metal complexes, and promoting chelation when other donor atoms are three, four, or five bonds apart. However, despite the wide variety of metal complexes found in the literature using this type of ligands, only a handful of them include on their structures tridentate SBs ligands and their biological evaluation has been explored. Hence, this review summarizes the most important antimicrobial activity results reported this far for pincer-type complexes (main group and d-block) derived from SBs tridentate ligands.

Synthesis, characterization and SAR studies of bis(imino)pyridines as antioxidants, acetylcholinesterase inhibitors and antimicrobial agents

In this study we synthesized a series of sixteen bis(imino)pyridines (BIPs) starting from 2,6-diaminopyridine and various aromatic aldehydes, and evaluated their antioxidant, antibacterial, antifungal and acetylcholinesterase (AChE) inhibitory activity. The chemical structures were elucidated by FTIR, elemental analysis, ESR and HRMS. ¹H and ¹³C NMR spectra couldn't be acquired due to the formation of stable, carbon-centered radical cations in a solution, as confirmed by ESR spectroscopy and DFT calculations. The in vitro antioxidant potency was evaluated using four assays: free radical scavenging activity (DPPH and ABTS), reducing power and total antioxidant capacity assay. BIPs demonstrated excellent antioxidant properties, and two derivatives proved to be more potent than reference antioxidants (ascorbic acid and Trolox) in all assays. DFT calculations on ωB97XD/6-311++g(d,p) level of theory provided valuable insights into the radical scavenging mechanism of BIPs. For hydroxyl-substituted BIPs, hydrogen atom transfer (HAT) is a predominant mechanism, while the single electron transfer coupled with proton transfer (SET-PT) governs the antioxidant activity of other derivatives. Intramolecular hydrogen bonding (IHB) plays an important role in the mechanism of antioxidant activity as revealed by noncovalent interaction analysis and rotational barrier calculations. The spin density of radical cations is localized on carbon atoms of a pyridine ring, which corroborates with g-factors and multiplicity obtained from ESR analysis. The most potent BIP exhibited moderate inhibitory activity toward AChE (IC₅₀ = 20 ± 4 μM), while molecular docking suggested binding at the peripheral anionic site of AChE with the MMFF94 binding enthalpy of -43.4 kcal/mol. Moderate in vitro antimicrobial activity of BIPs have been determined against several pathogenic bacterial strains: Pseudomonas aeruginosa, Escherichia coli, Enterococcus faecalis, Staphylococcus aureus and clinical isolate of methicillin resistant S. aureus (MRSA). The antifungal activity of BIPs toward Candida albicans was also confirmed. The similarity ensemble approach combined with molecular docking suggested leucyl aminopeptidase as the probable antimicrobial target for the three most potent BIP derivatives.