Synthesis, structural characterization and biological studies of some nalidixic acid–metal complexes: Metalloantibiotic complexes of some divalent and trivalent metal ions

Refashioning of the drug-properties of fluoroquinolone through the synthesis of a levofloxacin-imidazole cobalt (II) complex and its interaction studies on with DNA and BSA biopolymers, antimicrobial and cytotoxic studies on breast cancer cell lines

Levofloxacin (HLVX), a quinolone antimicrobial agent, when deprotonated (LVX-) behaves as a bidentate ligand, and it coordinates to Co2+ through the pyridone oxygen and the carboxylate oxygen. Along with two imidazole (ImH) ligands, levofloxacin forms a Co(II)-Levofloxacin-imidazole complex, [CoCl(LVX)(ImH)2(H2O)]·3H2O (abbreviated henceforth as CoLevim) which was isolated and characterized by 1H and 13C NMR spectroscopy, UV-visible and FT-IR spectroscopy, powder X-ray diffraction and thermal analysis methods. CoLevim shows promise in its antimicrobial activities when tested against microorganisms (Bacillus cereus, Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus, Salmonella typhimurium and Escherichia coli). Fluorescence competitive studies with ethidium bromide (EB) revealed that CoLevim can compete with EB and displace it to bind to CT-DNA through intercalative binding mode. In addition, CoLevim exhibited a good binding propensity to BSA proteins with relatively high binding constants. The antioxidant activities of the free ligands and CoLevim were determined in vitro using ABTS+ radical (TEAC assay). The Co-complex showed a better antioxidant capacity with inhibitory concentrations (IC50) of 40 μM than the free ligands. CoLevim also showed noteworthy apoptotic potential and behaved as an efficient resistant modifying agent when its antiproliferative potential was examined by MTT assay using the breast cancer cell lines (MCF7, MCF7Dox/R and MCF7Pacli/R cells).

Anticancer properties of complexes derived from bidentate ligands

Cancer is the abnormal division and multiplication of cells in an organ or tissue. It is the second leading cause of death globally. There are various types of cancer such as prostate, breast, colon, lung, stomach, liver, skin, and many others depending on the tissue or organ where the abnormal growth originates. Despite the huge investment in the development of anticancer agents, the transition of research to medications that improve substantially the treatment of cancer is less than 10%. Cisplatin and its analogs are ubiquitous metal-based anticancer agents notable for the treatment of various cancerous cells and tumors but unfortunately accompanied by large toxicities due to low selectivity between cancerous and normal cells. The improved toxicity profile of cisplatin analogs bearing bidentate ligands has motivated the synthesis of vast metal complexes of bidentate ligands. Complexes derived from bidentate ligands such as β-diketones, diolefins, benzimidazoles and dithiocarbamates have been reported to possess 20 to 15,600-fold better anticancer activity, when tested on cell lines, than some known antitumor drugs currently on the market, e.g. cisplatin, oxaliplatin, carboplatin, doxorubicin, and 5-fluorouracil. This work discusses the anticancer properties of various metal complexes derived from bidentate ligands, for possible application in chemotherapy. The results discussed were evaluated by the IC50 values as obtained from cell line tests on various metal-bidentate complexes. The structure-activity relationship study of the complexes discussed, revealed that hydrophobicity is a key factor that influences anticancer properties of molecules.

Synthesis, Spectral Characterization and Potential Fluorescent Properties of Three Lanthanide(III) Ions Complexes with Nalidixic Acid

Three new solid lanthanide complexes with nalidixic acid (HNal) with the stoichiometry [Ln(Nal)₃]·5·.5H₂O (Ln = Tb, Dy and Ho) were synthesized applying the green synthesis method from the aqueous solutions without the organic solvent addition and fully characterized by the elemental analysis, XRF, complexometric titration, gravimetric analysis, molar conductivity and solubility measurements, powder X-Ray diffraction, UV-Vis and infrared (FT-IR) spectroscopies. Moreover, the luminescent properties of the Tb(III), Dy(III), and Ho(III) complexes in the solid state and in the solutions were investigated. On the basis of the detailed spectral analysis, it was concluded that the nalidixate ligands bind to the lanthanide ions by the bidentate carboxylate and carbonyl groups while water molecules belong to the outer coordination sphere. At the excitation of UV light, the complexes exhibited characteristic emission of central lanthanide ions, the intensity of which depends significantly on the excitation wavelength and/or the solvent. Thus, the application of nalidixic acid (apart from biological activity) for the synthesis of luminescent lanthanide complexes was confirmed which can find potential applications in the field of photonic devices and/or bioimaging agents.

Computational and optoelectronic quantification of semi-conducting, warm ruby red color emanating Eu3+ complexes with hetro-cyclic ligands

Six Eu³⁺ complexes were synthesised with β-keto acid as main ligand and secondary ligands through liquid assisted grinding method. These complexes were characterised by various techniques such as spectroscopic technique, XRD, EDAX, SEM analysis, thermal technique, Urbach energy and optical band gap investigation. The luminous photophysical properties were studied by PL spectroscopy in solid as well as solution phase and some theoretical calculation was done to investigate the radiative (A_rad) & non-radiative (A_nrad) transition rate, quantum efficiency (ɸ), Judd Ofelt parameters for ⁵D₀ → ⁷F_2,4 transitions in both states. Judd Ofelt parameters were also calculated by the JOES software and the outcomes are well harmonised with theoretical values. The complexes have CIE color coordinate value in ruby red region and above 88.65% color purity in both phases, which made them attractive candidates for red light-emitting displays. ⁵D₀ → ⁷F₂ transition was proposed as a laser emission transition owing to their high branching ratio (67.18-74.24%) in solid and (60.09-74.40%) in solution phase. Computational methods were employed to determine the structure and energy of various molecular orbitals. Antimicrobial assay of complexes was also rationalised and found that the complexes are pertinent as good bactericidal and fungicidal agents in pharmaceutical industry.

Computational analysis, Urbach energy and Judd-Ofelt parameter of warm Sm3+ complexes having applications in photovoltaic and display devices

In this work, six reddish orange Sm3+ complexes were synthesized using organic ligand (L) and secondary ligands having hetero atoms by a one-step significant liquid-assisted grinding method and were characterized by spectroscopic techniques. The Urbach energy and band gap energy of the complexes were inspected by a linear fit. Using a least square fitting method, the Judd-Ofelt parameter and radiative properties were also determined. Thermal analysis, colorimetric analysis, luminescence decay time and anti-microbial properties of complexes were studied. The luminescence emission spectra of binary and ternary complexes displayed three characteristic peaks at 565, 603 and 650 nm in the powder form and four peaks at 563, 605, 646 and 703 nm in a solution phase due to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions respectively. The most intense transition in the solid phase (4G5/2 → 6H7/2) is accountable for orange color, and in the solution form, the highly luminescent peak (4G5/2 → 6H9/2) is responsible for reddish orange color of Sm3+ complexes. PXRD and SEM analyses suggested that the complexes possess a nanoparticle grain size with crystalline nature. The decent optoelectrical properties of title complexes in the orangish-red visible domain indicated possible applications in the manufacturing of display and optoelectronic devices.

Structure, mechanism, and toxicity in antibiotics metal complexation: Recent advances and perspectives

Antibiotic-metal complexes (AMCs) formed by antibiotics and metal ions have attracted considerable attentions in recent years. Although different removal methods for AMCs have been reported in the literature, very few investigations have focused on the mechanisms and toxic effects of antibiotic-metal coordination. This review briefly describes the structural characteristics of various commonly used antibiotics and the coordination mechanisms with metal ions. Considering the complexity of the real environment, various environmental factors affecting AMC formation are highlighted. The effects of AMCs on microbial community structure and the role of metal ions in influencing resistant genes from the molecular perspective are of interest within this work. The toxicities and mechanisms of AMCs on different species of biota are also discussed. These findings underline the need for more targeted detection and analysis methods and more suitable toxicity markers to verify the combination of antibiotics with metal ions and reveal environmental toxicities in future. This review presents an innovative idea that antibiotics combined with metal ions will change the toxicity and environmental behavior of antibiotics.

A Study on Repositioning Nalidixic Acid via Lanthanide Complexation: Synthesis, Characterization, Cytotoxicity and DNA/Protein Binding Studies

“Drug repositioning” is a modern strategy used to uncover new applications for out-of-date drugs. In this context, nalidixic acid, the first member of the quinolone class with limited use today, has been selected to obtain nine new metal complexes with lanthanide cations (La³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺); the experimental data suggest that the quinolone acts as a bidentate ligand, binding to the metal ion via the keto and carboxylate oxygen atoms, findings that are supported by DFT calculations. The cytotoxic activity of the complexes has been studied using the tumoral cell lines, MDA-MB-231 and LoVo, and a normal cell line, HUVEC. The most active compounds of the series display selective activity against LoVo. Their affinity for DNA and the manner of binding have been tested using UV–Vis spectroscopy and competitive binding studies; our results indicate that major and minor groove binding play a significant role in these interactions. The affinity towards serum proteins has also been evaluated, the complexes displaying higher affinity towards albumin than apotransferrin.

Bacterial Nosocomial Infections: Multidrug Resistance as a Trigger for the Development of Novel Antimicrobials

Nosocomial bacterial infections are associated with high morbidity and mortality, posing a huge burden to healthcare systems worldwide. The ongoing COVID-19 pandemic, with the raised hospitalization of patients and the increased use of antimicrobial agents, boosted the emergence of difficult-to-treat multidrug-resistant (MDR) bacteria in hospital settings. Therefore, current available antibiotic treatments often have limited or no efficacy against nosocomial bacterial infections, and novel therapeutic approaches need to be considered. In this review, we analyze current antibacterial alternatives under investigation, focusing on metal-based complexes, antimicrobial peptides, and antisense antimicrobial therapeutics. The association of new compounds with older, commercially available antibiotics and the repurposing of existing drugs are also revised in this work.

Synthesis, structural, spectral and antimicrobial activity studies of copper-nalidixic acid complex with 1,10-phenanthroline: DFT and molecular docking

The mix-ligand coordination compound, [Cu(Nal)(Phen)(H₂O)].(Phen).ClO₄.(H₂O)₂ (Nal= Monoanion of nalidixic acid and Phen = 1,10- Phenanthroline), was investigated by focusing on its supramolecular architecture. Structural properties of the complex were characterized by XRD, spectroscopic methods and elemental analysis. The complex has crystallized in the triclinic crystal system and P-1 space group. In the structure where the Cu (II) ion is in the center of symmetry, nalidixate anion and water molecule coordinated to Cu (II) metal through oxygen atoms while phen coordinated through nitrogen atoms. The monomer units are connected by hydrogen bonds to form supramolecular structures. The ground state molecular structure of the complex was optimized using DFT/B3LYP/LANL2DZ method, and compared with experimental X-ray geometry. The FT-IR study of the complex was carried out in the middle IR region focusing on the characteristic vibrations of the free ligands and the complex. Scaled calculated vibrational frequencies are compared with experimental values. The magnetic properties of the complex were investigated by electron paramagnetic resonance (EPR) spectroscopy. Further ultra-violet (UV)-visible spectral analysis was also performed to understand optical properties. The experimental UV-Vis data were associated with the calculated frontier molecular orbitals HOMO/LUMO and, molecular electrostatic potentials (MEP) are also investigated. Biological study of the complex against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Candida albicans showed very strong antibacterial activity with MIC values ranging from 128 μg/ml to 1 μg/ml concentration. The optimized complex is docked to the DNA Gyrase (3LPX) and gyrase tip IIA topoisomerase (3UC1).

Biological Activity of Au(III) Complexes

The earliest therapy use of gold compounds dated in 2500 AD. In 1960s gold compounds were used in the treatment of rheumatoid arthritis, discoid lupus erythematosus, etc. Although the compounds of Au(I) are well-known and used in the modern medicine, new complexes of Au(III) and ligands with different donor atoms are synthetized and examined for their biological (antitumor, antimicrobial) activity. So far conducted studies show that complexes with Au(III) as central metal ions have greater activity compared with free ligands. Future syntheses should be based on the increase of biological activity with complexes that have necessary stability under physiological conditions.

Structural and morphological aspects of (fluoro)quinolone delivery by layered double hydroxide nanoparticles

Synthesis conditions affect the composition and morphology of LDH-based delivery systems loaded with nalidixic acid and, consequently, their biopharmaceutical behavior.