A treatise on benzimidazole based Schiff base metal(II) complexes accentuating their biological efficacy: Spectroscopic evaluation of DNA interactions, DNA cleavage and antimicrobial screening

Sustainable synthesis of benzimidazole-based Schiff base using reusable CaAl2O4 nanophosphors catalyst: Insights into metal(II) complexes and DNA interactions

This article presents a new and facile method for the synthesis of Schiff base compounds with a benzimidazole group using a low-cost and reusable calcium aluminate nanophosphorus catalyst (CaAl2O4). This approach avoids harmful solvents and reactants, supporting a more environmentally friendly synthesis process. The catalyst maintained its activity and heterogeneity over four cycles with minimal loss of efficiency. The synthesis process was straightforward and eliminated the need for column chromatography. The Schiff base ligand (HL=(E)-N-((6-(thiophen-2-yl)pyridin-2-yl)methylene)-1H-benzo[d]imidazol-2-amine)) was synthesized by the reaction of 6-(thiophen-2-yl)pyridine-2-carbaldehyde with 1H-benzimidazole-2-amine. Subsequently, metal(II) complexes of Co(II), Ni(II), and Cu(II) were prepared using this ligand. Structural analysis of both the ligand and its metal complexes was carried out using various physicochemical and spectroscopic methods. Ni(II) and Co(II) complexes were found to adopt an octahedral geometry, while the Cu(II) complex exhibited a square-planar structure. Binding studies with calf thymus DNA (CT-DNA) at pH 7.2 were performed using UV-visible spectroscopy, viscosity measurements, and thermal denaturation studies and showed that the metal complexes intercalate into the DNA and produced a distinct binding pattern. Molecular docking simulations with AutoDock Vina provided insights into the interaction of these complexes with the B-DNA dodecamer. Furthermore, the ligand and its metal complexes showed UV-visible photonuclease activity against pUC19 DNA. Agarose gel electrophoresis showed that the metal complexes exhibit photoinduced nuclease activity, confirming their ability to cleave DNA upon exposure to light.

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

DNA-binding, cleavage, antibacterial and in vitro anticancer activity of copper(II) mixed ligand complexes of 2-(((6-chloro-1H-benzo[d]imidazol-2-yl)methyl)amino)aceticacid and polypyridyl ligands

A tridentate ligand(A), 2-(((6-chloro-1H-benzo[d]imidazol-2-yl)methyl)amino) aceticacid (Cl-BIGH) was synthesised by the Phillips condensation of 4-chlorobenzene-1,2-diamine and iminodiaceticacid in 1:2 molar ratio. Its Cu(II) mixed ligand complexes[Cu(II)-A-L] were obtained by involving other co-ligands(L): 2,2΄-bipyridine(L₁), 4,4΄-dimethyl-2,2΄-bipyridyl(L₂), 5,5΄-dimethyl-2,2΄-bipyridyl(L₃) and 1,10 phenanthroline(L₄). The complexes were characterized by elemental analysis, thermal analysis, molar conductance, magnetic moment measurements, X-ray diffraction, FTIR, UV-Visible, ESR spectroscopy, mass spectrometry and cyclic voltammetry. From the spectral and analytical data, the ternary complexes [Cu(Cl-BIGH)(L_1-4)]ClO₄ were found to form in 1:1:1(Cu(II): Cl-BIGH: L) molar ratio. The geometry of the mixed-ligand complexes were found to be 5-coordinated square pyramidal or trigonal bipyramidal with polycrystalline natures. The DNA binding and cleaving abilities, antibacterial and the in vitro cytotoxicity of the complexes were explored. The molecular docking was used to predict the efficiency of binding of the metal complexes with COX- 2.Communicated by Ramaswamy H. Sarma.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Discovery of metal-based complexes as promising antimicrobial agents

The antimicrobial resistance (AMR) is an intractable problem for the world. Metal ions are essential for the cell process and biological function in microorganisms. Many metal-based complexes with the potential for releasing ions are more likely to be absorbed for their higher lipid solubility. Hence, this review highlights the clinical potential of organometallic compounds for the treatment of infections caused by bacteria or fungi in recent five years. The common scaffolds, including antimicrobial peptides, N-heterocyclic carbenes, Schiff bases, photosensitive-grand-cycle skeleton structures, aliphatic amines-based ligands, and special metal-based complexes are summarized here. We also discuss their therapeutic targets and the risks that should be paid attention to in the future studies, aiming to provide information for researchers on metal-based complexes as antimicrobial agents and inspire the design and synthesis of new antimicrobial drugs.

In Vitro Evaluation of the Potential Pharmacological Activity and Molecular Targets of New Benzimidazole-Based Schiff Base Metal Complexes

Metal-based drugs, including lanthanide complexes, have been extremely effective in clinical treatments against various diseases and have raised major interest in recent decades. Hence, in this work, a series of lanthanum (III) and cerium (III) complexes, including Schiff base ligands derived from (1H-benzimidazol-2-yl)aniline, salicylaldehyde, and 2,4-dihydroxybenzaldehyde were synthesized and characterized using different spectroscopic methods. Besides their cytotoxic activities, they were examined in human U-937 cells, primate kidney non-cancerous COS-7, and six other, different human tumor cell lines: U251, PC-3, K562, HCT-15, MCF-7, and SK-LU-1. In addition, the synthesized compounds were screened for in vitro antiparasitic activity against Leishmania braziliensis, Plasmodium falciparum, and Trypanosoma cruzi. Additionally, antibacterial activities were examined against two Gram-positive strains (S. aureus ATCC® 25923, L. monocytogenes ATCC® 19115) and two Gram-negative strains (E. coli ATCC® 25922, P. aeruginosa ATCC® 27583) using the microdilution method. The lanthanide complexes generally exhibited increased biological activity compared with the free Schiff base ligands. Interactions between the tested compounds and model membranes were examined using differential scanning calorimetry (DSC), and interactions with calf thymus DNA (CT-DNA) were investigated by ultraviolet (UV) absorption. Molecular docking studies were performed using leishmanin (1LML), cruzain (4PI3), P. falciparum alpha-tubulin (GenBank sequence CAA34101 [453 aa]), and S.aureus penicillin-binding protein 2a (PBP2A; 5M18) as the protein receptors. The results lead to the conclusion that the synthesized compounds exhibited a notable effect on model membranes imitating mammalian and bacterial membranes and rolled along DNA strands through groove interactions. Interactions between the compounds and studied receptors depended primarily on ligand structures in the molecular docking study.

Investigation of redox mechanism and DNA binding of novel 2-(x-nitrophenyl)-5-nitrobenzimidazole (x = 2, 3 and 4)

The present study describes the investigation of the binding modes of potential anti-cancerous nitrophenyl derivatives of 2-(x-nitrophenyl)-5-nitrobenzimidazole with calf thymus DNA. The -2-(x-nitrophenyl)-5-nitrobenzimidazoles under investigation differ only in position x of nitro group in nitrophenyl substituent relative to benzimidazole moiety leading to 1-NPNB (x = 2), 2-NPNB (x = 3) and 3-NPNB (x = 4). The DFT calculations predicted that derivatives were electrochemically reducible which was then confirmed by cyclic voltammetry. In cyclic voltammetry, the second reversible peak was dependent on first irreversible reduction. This revealed that electrochemical irreversible process was governed by some other process which was then followed by reversible second electron transfer. Thus, ECE (electron transfer leading to coupled chemical reaction followed by another electron transfer process) mechanism was attributed for electrochemical reduction. Experimental results based on UV-Vis spectroscopy vaguely showed intercalation of 1-NPNB, 2-NPNB and 3-NPNB into DNA which was assisted by cyclic voltammetry. However, thermal melting and florescence spectroscopy unambiguously established intercalation for all three compounds. Molecular docking analysis ascertained in pocket stacking of 5-nitrobenzimidazole moiety in 1-NPNB and 2-NPNB while nitro phenyl substitution in 3-NPNB stacks between DNA base pair during intercalation which was in agreement with DFT computed molecular geometry. Therefore, the relative positions of nitro group and 5-nitrobenzimidazole moieties in 2-(x-nitrophenyl)- 5-nitrobenzimidazole influenced the DNA binding pattern of compounds during intercalation. The cytotoxicity of these compounds was comparable to standard drug doxorubicin against both cancerous (MCF-7) and normal (MCF-10A) breast cells which depicts their anti-cancerous potential.

Benzimidazole Schiff base derivatives: synthesis, characterization and antimicrobial activity

A series of Schiff bases (3.a–f) bearing benzimidazole moiety was successfully synthesized in ethanol by refluxing Oct-2-ynoic acid (1,3-dihydrobenzimidazole-2-ylidene)amide with substituted amines. Fourier transform infrared (FTIR), ultra violet light (UV–VIS), elemental analysis, proton (¹H) and carbon (¹³C) nuclear magnetic resonance spectroscopy were used to characterize the newly synthesized Schiff bases. Micro dilution method was used to determine the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of the Schiff bases, against 14 human pathogenic bacteria (8 Gram negative and 6 Gram positive) and against 7 fungal strains (5 Aspergillus and 2 Fusarium) representatives. Antimalarial activity against Plasmodium falciparum and antitrypanosomal property against Trypanosoma brucei was studied in vitro at a single dose concentration of the Schiff bases. Cytotoxicity of the Schiff bases was assessed against human cervix adenocarcinoma (HeLa) cells. Results obtained show that the newly synthesized Schiff bases are very potent antimicrobial agents. Gram negative bacteria Klebsiella pneumonia and Escherichia coli were more affected on exposure to Compounds 3.c–f (MIC 7.8 µg/mL) which in turn exhibited more antibacterial potency than nalidixic acid reference drug that displayed MICs between 64 and 512 µg/mL against K. pneumonia and E. coli respectively. The test compounds also demonstrated high cytotoxic effect against Aspergillus flavus and Aspergillus carbonarius as they displayed MFC 7.8 and 15.6 µg/mL. Compound 3.c exhibited the highest fungicidal property from this series with MFC alternating between 7.8 and 15.6 µg/mL against the investigated strains. The malarial activity revealed Compounds 3.c and 3.d as the more potent antiplasmodial compounds in this group exhibiting 95% and 85% growth inhibition respectively. The IC₅₀ of Compounds 3.c and 3.d were determined and found to be IC₅₀ 26.96 and 28.31 µg/mL respectively. Compound 3.a was the most cytotoxic agent against HeLa cells in this group with 48% cell growth inhibition. Compounds 3.c, 3.d and 3.f were biocompatible with HeLa cells and displayed low toxicity. With a very low cytotoxic effect against HeLa, compound 3.c stands out to be a very good antiparasitic agent and consideration to further evaluate the candidate drug against others cell lines is necessary.

Exploiting the biological efficacy of benzimidazole based Schiff base complexes with l-Histidine as a co-ligand: Combined molecular docking, DNA interaction, antimicrobial and cytotoxic studies

Four new metal complexes were synthesized and screened for their cytotoxic activity after sufficient assertion from the preliminary DNA binding studies. The metal complexes could bind to CT-DNA through intercalation binding mode. This has also been confirmed by the molecular docking studies. The DNA cleavage efficiencies of these complexes with pBR322 DNA were investigated by gel electrophoresis. The complexes were found to promote the cleavage of pBR322 DNA from the supercoiled form I to the open circular form II in the presence of an oxidizing agent (H₂O₂). The in vitro chemosensitivity of the studied complexes exhibits significant cytotoxic effects, compared to those reported for cisplatin. These findings represent a prompting to search for the probable interaction of these complexes with other cellular elements of fundamental consequence in cell proliferation. The in vitro anticancer activities indicate that the Cu(II) complex is active against the selected human tumor cell lines, and the order of in vitro anticancer activities is consistent with the DNA-binding affinities. Towards noncancerous cell line, Cu(II) complex exhibits very low toxicity. On the other hand all the complexes have been found to exhibit cytotoxic effects against cancerous cell lines with potency more than that of the widely used drug cisplatin and hence they have the potential to act as promising anticancer agents. Captivatingly, they are non-toxic to normal cell lymphocytes revealing that they are selective in killing only the cancer cells.