Chemistry and properties of fluorescent pyrazole derivatives: an approach to bioimaging applications

Fluorescent bioimaging is a crucial technique for in vivo studies in real cell samples, providing vital information about the metabolism of ions or molecules of biological and pharmaceutical significance. This technique typically uses probes based on organic small-molecule fluorophores, with N-heteroaromatic scaffolds playing an essential role due to their exceptional electronic properties and biocompatibility. Among these, pyrazole derivatives stand out as particularly promising due to their high synthetic versatility and structural diversity. This review highlights prominent examples from the period 2020-2024, focusing on the chemistry, properties, and bioimaging applications of fluorescent pyrazole derivatives. By highlighting the latest advancements in this field, this manuscript aims to inspire and motivate researchers, emphasizing the potential impact of this work on the future of bioimaging.

DNA Interaction, Molecular Docking, Antimicrobial, Anticancer and Thermal Studies of Ternary Metal Complexes of N‐Methylbenzylamine and Ethylenediamine

N‐Methylbenzylamine and ethylenediamine were utilized as primary and auxiliary ligands, respectively, alongside metal salts to synthesize ternary metal complexes: [FeCl3(Nmba)(en)], [CoCl2(Nmba)(en)(H2O)] and [CuCl2(Nmba)(en)(H2O)]. These complexes were thoroughly characterized using spectral and analytical techniques, revealing an octahedral geometry for all. Coats–Redfern calculations indicated their non‐spontaneous nature yet highlighted their thermal stability. DNA binding studies unveiled a groove binding mode for the complexes, with intrinsic binding constants (Kb) and Stern–Volmer quenching constant (Ksq) supporting their strong binding capabilities. Nuclease activity against pBR322 was assessed through gel electrophoresis. Additionally, docking studies using AutoDock 4.2 software provided insights into their binding affinities. In terms of biological activities, the Cu complex demonstrated superior cytotoxicity and antibacterial and antifungal properties compared to the other ternary metal complexes. This suggests its potential for further exploration in biomedical applications.

Linkage of the Dinuclear Gold(I) Complex Luminescence and Origin of Endocyclic Amino Group of Cyclic P2N2-Bridging Ligands

Gold(I) complexes of LAu2Cl2 composition based on P2N2 ligands, namely 1,5-diaza-3,7-diphosphacyclooctanes, containing ethylpyridyl substituents at the phosphorus atoms and sp2- or sp3-hybridized endocyclic nitrogen atoms were synthesized. The SCXRD analysis indicated the strong impact of the geometry of the nitrogen atom on the structure and conformational flexibility of the complexes. The N-aryl substituted ligand with the planar endocyclic nitrogen atom provides higher flexibility of the complex and an ability to bind the solvent molecules in the "host-guest" mode, whereas that kind of behavior is forbidden for the complex with an N-alkyl substituted ligand with a pyramidal nitrogen atom. The substituents at nitrogen atoms also control the origin of the emission, which is phosphorescence for the N-aryl substituted complex and fluorescence for the N-alkylaryl substituted complex. The phosphorescent gold(I) complex displays high cytotoxicity without selectivity toward the m-HeLa and normal cells, but the core-shell nanoparticles formed on the base of the complex demonstrate reduced cytotoxicity. The luminescence of the NPs allows tracking the complexes in the cell samples.

Breast Cancer Treatment: The Case of Gold(I)-Based Compounds as a Promising Class of Bioactive Molecules

Breast cancers (BCs) may present dramatic diagnoses, both for ineffective therapies and for the limited outcomes in terms of lifespan. For these types of tumors, the search for new drugs is a primary necessity. It is widely recognized that gold compounds are highly active and extremely potent as anticancer agents against many cancer cell lines. The presence of the metal plays an essential role in the activation of the cytotoxicity of these coordination compounds, whose activity, if restricted to the ligands alone, would be non-existent. On the other hand, gold exhibits a complex biochemistry, substantially variable depending on the chemical environments around the central metal. In this review, the scientific findings of the last 6–7 years on two classes of gold(I) compounds, containing phosphane or carbene ligands, are reviewed. In addition to this class of Au(I) compounds, the recent developments in the application of Auranofin in regards to BCs are reported. Auranofin is a triethylphosphine-thiosugar compound that, being a drug approved by the FDA—therefore extensively studied—is an interesting lead gold compound and a good comparison to understand the activities of structurally related Au(I) compounds.

Antibacterial Activity of Co(III) Complexes with Diamine Chelate Ligands against a Broad Spectrum of Bacteria with a DNA Interaction Mechanism

Cobalt coordination complexes are very attractive compounds for their therapeutic uses as antiviral, antibacterial, antifungal, antiparasitic, or antitumor agents. Two Co(III) complexes with diamine chelate ligands ([CoCl₂(dap)₂]Cl (1) and [CoCl₂(en)₂]Cl (2)) (where dap = 1,3-diaminopropane, en = ethylenediamine) were synthesized and characterized by elemental analysis, an ATR technique, and a scan method and sequentially tested against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration results revealed that anaerobic and microaerophilic bacteria were found to be the most sensitive; the serial passages assay presented insignificant increases in bacterial resistance to both compounds after 20 passages. The synergy assay showed a significant reduction in the MIC values of nalidixic acid when combined with Compounds (1) or (2). The assessment of cell damage by the complexes was performed using scanning electron microscopy, transmission electron microscopy, and confocal microscopy, which indicated cell membrane permeability, deformation, and altered cell morphology. DNA interaction studies of the Co(III) complexes with plasmid pBR322 using spectrophotometric titration methods revealed that the interaction between Complex (1) or (2) and DNA suggested an electrostatic and intercalative mode of binding, respectively. Furthermore, the DNA cleavage ability of compounds by agarose gel electrophoresis showed nuclease activity for both complexes. The results suggest that the effect of the tested compounds against bacteria can be complex.

Impact of oppositely charged shell and cores on interaction of core-shell colloids with differently charged proteins as a route for tuning of the colloids cytotoxicity

The present work represents interactions between the core-shell nanoparticles and different proteins, exemplified by lysozyme (LSZ), pepsin, bovine serum albumin (BSA), thioredoxin (TRX) and yellow fluorescent protein (YFP). The core-shell morphology derives from the non-covalent deposition of polyethyleneimine (PEI) onto nanoprecipitated luminescent complex (AuCl)₂L (L is cyclic PNNP ligand). Analysis of the data obtained by DLS, CD spectroscopy, luminescence derived from both (AuCl)₂L and YFP reveal the electrostatically driven interaction of negatively charged proteins with the shell of PEI-(AuCl)₂L. The fluorescence of YFP enables to reveal the inclusion of the protein molecules into the shell. The lack of any luminescent response of PEI-(AuCl)₂L on TRX conforms its electrostatically driven interactions with the shell which, in turn, excludes a binding of the exposed thiol moieties with (AuCl)₂L. The negatively charged surface of pepsin provides the greatest recharging of the PEI-based shell versus the other proteins, which is followed by the enhanced luminescence of (AuCl)₂L. The significant effect of PEI-(AuCl)₂L on the CD spectra of LSZ followed by the decreased intensity of (AuCl)₂L-based luminescence points to specific interaction mode of PEI-(AuCl)₂L with LSZ. The flow cytometry and fluorescent microscopy measurements revealed efficient internalization of PEI-(AuCl)₂L into the Wi-38 cell samples resulting in the efficient staining of all cell organelles. The concentration dependent cytotoxicity of PEI-(AuCl)₂L is detectably enhanced by LSZ, which is correlated with its interaction mode with the nanoparticles.