Search Results (313)

A series of sulfur dissolving tetrathionate ionic liquids (ILs), featuring imidazolium and pyridinium cationic heads, have been prepared and characterized along with their chloride IL precursors. A novel synthetic approach for the preparation of the proposed tetrathionate ILs has been introduced and successfully tested in the current work, yielding the desired compounds in quantitative yield and high purity, offering a significant advancement over the traditional Volynskii–Smolyaninov reaction. The presented method addresses key challenges of the traditional approach, solving the issues deriving from the influence of the IL cation on the reaction outcome and the unpredictability of the formed polythionate species. The solubility of elemental sulfur in the considered tetrathionate ILs has been investigated at various temperatures, providing good preliminary evidence of the suitability of these ILs as convenient and effective sulfur solubilizing media readily available on the field in “sour” gas extraction plants. Furthermore, the use of ILs instead of traditional organic solvents in operative conditions represents a noteworthy safety improvement due to their lower flammability and volatility. Finally, interesting results were obtained studying binary mixtures of organic solvents and ILs, with cooperative effects or salting-out effects being observed in relation to the type of solvent used. Full article

We report the synthesis and characterization of the novel pyridinium salts from (E)-2-(pyridin-4-ylmethylene)hydrazine-1-carboximidamide. The pyridinium salts were obtained via the reaction of guanylhydrazone derived from pyridine-4-carbaldehyde with phenacyl bromides. Structural characterization was carried out using IR, ¹H, and ¹³C NMR spectroscopy and mass spectrometry. Full article

Background: Poor water solubility is a major limitation for the therapeutic use of many anticancer drugs. In this study, we report the design and development of two halloysite-based hybrid nanomaterials for the encapsulation and delivery of hydrophobic and positively charged drugs. Methods: A novel multicavity platform was obtained by covalently grafting calix[5]arene macrocycles onto the external surface of halloysite nanotubes (HNTs), combining lumen encapsulation with supramolecular host–guest recognition. PB4, a planar and hydrophobic pyridinium salt with significant antiproliferative activity, was selected as a model compound. Both PB4-loaded HNTs (HNTs/PB4) and calixarene-functionalized HNTs (HNTs-Calix/PB4) were incorporated into Laponite^®-based thixotropic hydrogels to obtain injectable and biocompatible systems. Results: The nanomaterials were thoroughly characterized, and their loading efficiency, release behavior, and aqueous dispersibility were evaluated. Antiproliferative tests on MCF-7 cells demonstrated that both hydrogels retained PB4 activity, with distinct release profiles: the pristine HNTs allowed faster drug availability, while calix[5]arene-functionalized systems promoted sustained release. Conclusions: This work introduces the first example of covalently calixarene-functionalized halloysite and presents a versatile drug delivery platform adaptable to different therapeutic contexts and combination strategies. Full article

Three new series of indolizines (5a–f, 6a–f and 7a–g), functionalized with bromine or ethyl ester substituents on the pyridine ring, were designed and synthesized as promising anticancer agents. The synthesis of indolizine derivatives was carried out using the 1,3-dipolar cycloaddition of pyridinium N-ylides to ethyl propiolate as a key step. Spectral characterization (using NMR, FT-IR, HRMS and X-ray diffraction) showed that two types of cycloadducts 5a–f and 6a–f were obtained when the ylides generated by the 3-bromopyridinium salts were used as 1,3-dipoles in Huisgen cycloaddition reactions to ethyl propiolate. The anticancer effect of selected compounds was in vitro assessed against the National Cancer Institute (NCI) panel of 60 human tumor cells, at 10 μM concentration, with three compounds (5c, 6c and 7g) showing promising inhibitory activity on the growth of several cell lines including lung, brain, renal cancer and melanoma, as well as a cytotoxic effect against HOP-62 non-small cell lung cells (34% for compound 5c and 15% for compound 7g) and SNB-75 glioblastoma cells (15% for compound 5c and 14% for derivative 7c). Molecular docking revealed favorable binding affinities for 5c, 6c and 7g (–9.22 to –9.88 kcal/mol) at the colchicine-binding site of tubulin with key interactions involving βASN-258, βALA-317, and βLYS-352 residues for 5c, βASN-258 in case of 6c, and αVAL-181 and βLYS-254 for derivative 7g. According to the in silico ADMET analysis, the active compounds are predicted to exhibit good oral bioavailability, promising drug-like qualities and low toxicity risks. Full article

Background/Objectives: The growing threat of antibiotic resistance necessitates the development of novel antimicrobial agents that effectively target pathogenic microorganisms while minimizing toxicity. Methods: Two series DABCO-based cationic homopolymers (D-subs 1kDa, D-subs 5kDa, D-subs 15kDa) and DABCO–pyridinium-based copolymers (PyH-subs 5kDa_Dsubs 5kDa, PyH-subs 7kDa_Dsubs 3kDa, PyH-subs 3kDa_Dsubs 7kDa) were synthesized to mimic to host-defense cationic peptides via ring-opening metathesis polymerization (ROMP). The antimicrobial activities of these polymers were determined by their minimum inhibitory concentrations (MICs) against E. coli (Gram-negative bacteria), P. aeruginosa (Gram-negative bacteria), S. aureus (Gram-positive bacteria), and C. albicans (fungus). In vitro cytotoxicity assays revealed selective toxicity towards bacterial cells, with high selectivity indices for several copolymers. To gain insight into the mechanism of action, morphological changes in S. aureus upon exposure to D-subs 1kDa were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: The D-subs 15kDa homopolymer demonstrated the highest overall antimicrobial activity, particularly against S. aureus (MIC: 8 µg/mL), with all polymers exhibiting minimal hemolytic activity (HC₅₀ ≥ 1024 µg/mL). SEM and TEM results revealed membrane disruption indicative of polymer–bacteria interactions. Additionally, stability studies confirmed polymer integrity under physiological conditions for at least 28 days. Conclusions: These results support the potential of DABCO-based cationic polymers as a promising platform for next-generation antimicrobial therapeutics. Full article

Because allopregnanolone and derivatives represent biologically active molecules, in this letter, we present the synthesis of a new bioconjugate steroid pyridinium salt derived from allopregnanolone in three steps. The key steps involve the formation of the hydrazone intermediate, followed by condensation with bromoacetyl bromide and subsequent coupling with pyridine to generate the pyridinium bromide salt. The new bioconjugate steroid pyridinium salt, 4, was fully characterized by proton and carbon nuclear magnetic resonance (¹H and ¹³C NMR) spectroscopy, mass spectrometry (MS), and Fourier transform infrared spectroscopy (FTIR). ¹H-NMR analysis revealed the presence of a dynamic rotameric mixture in a 7:3 ratio of Z/E amide conformers, which were identified by a 2D NOESY experiment. Full article

A wide range of water-soluble quaternary ammonium acylhydrazones based on catecholaldehyde were synthesized and characterized using NMR, IR spectroscopy, and elemental analysis. The total antioxidant capacity of the acylhydrazones discussed herein was estimated via coulometric titration with electrogenerated bromine. Pyridinium derivatives 11a–e exhibited the highest antioxidant capacity. Quaternary ammonium acylhydrazones demonstrated high antimicrobial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus strains. Furthermore, low hemo- and cytotoxicity and the absence of a negative effect on the hemostatic system were confirmed for the studied compounds. According to the results of a CV test, the antimicrobial effect of the most active acylhydrazones, namely, 9a, 10b, 10c, and 11a, is associated with the destruction of the bacterial cell wall. High or moderate activity against phytopathogens of bacterial origin was observed for all the acylhydrazones evaluated. Anti-aggregation activity was observed for compound 10b; the extent was 1.6-fold greater than that exhibited by acetylsalicylic acid. On the contrary, compound 9d exhibited a pro-aggregant effect (with a 6.3% increase in platelet aggregation and a >15% decrease in the latent period compared to the control). Thus, the data obtained can be considered the basis for further pharmaceutical development of these effective drugs with antithrombotic and hemostatic potential. Full article

Porphyrins play an extremely important role in both photodynamic (PDT) and sonodynamic therapy (SDT). These techniques, which have a lot in common, are largely based on the interaction between the sensitizer and light or ultrasounds (US), respectively, resulting in the formation of reactive oxygen species (ROS) that have the ability to destroy target cells. SDT requires the use of an appropriate frequency of US waves that are able to excite the chemical compound used. In this study, five porphyrin complexes were used: free-base meso-tetra(N-methyl-pyridinium-4-yl)porphyrin (TMPyP) and its transition metal complexes containing zinc(II), palladium(II), copper(II), and chloride-iron(II). The sonodynamic activity of these compounds was studied in vitro. The obtained results confirm the significant relationship between the chemical structure of the macrocycle and its stability and ability to generate ROS. The highest efficiency in ROS generation and high stability were demonstrated by non-metalated compound and its complex with zinc(II), while complex with copper(II), although less stable, were equally effective in terms of ROS production. Antibacterial activity tests showed the unique properties of the tested compounds, including a reduction in the number of both planktonic and biofilm antibiotic-resistant microorganisms above 5 log, which is rare among sonosensitizers. Full article

Wheat (Triticum aestivum L.) is a major cereal crop globally, but its production is increasingly threatened by fungal pathogens, particularly Fusarium culmorum (Wm. G. Sm.) Sacc., which causes seedling blight and root rot, leading to yield losses and mycotoxin contamination. Conventional control strategies, such as crop rotation and the use of fungicides, are often inadequate and contribute to the development of resistance, particularly with the overuse of similar modes of action. This study investigated quaternary pyridinium salts—nicotinamide and isonicotinamide derivatives—as potential sustainable antifungal agents. In vivo tests involved treating sterilized wheat seeds grown in sterile sand that had been inoculated with F. culmorum, using compounds previously confirmed to be active in vitro. Disease index, shoot and root length, and fresh and dry biomass were measured. Among the tested compounds, nicotinamide derivatives (2) and (3) showed the lowest disease index (0.9) at a concentration of 10 µg/mL. Most compounds promoted plant and root growth. Isonicotinamide derivatives (6) and (7) at 100 µg/mL increased root dry weight, while compound (6) at 10 µg/mL resulted in the most significant increase in plant length. These findings highlight the dual antifungal and growth-promoting potential of certain eco-friendly derivatives for managing F. culmorum and supporting wheat seedling development. Full article

Main-chain conjugated and non-conjugated polyelectrolytes are an important class of materials that have many technological applications ranging from fire-retardant materials to carbon-nanotube composites, nonlinear optical materials, electrochromic materials for smart windows, and optical sensors for biomolecules. Here, we describe a series of poly(pyridinium salt)s-fluorene containing 9,9-bis(4-aminophenyl)fluorene moieties with various organic counterions that were synthesized using ring-transmutation polymerization and metathesis reactions, which are non-conjugated polyelectrolytes. Their chemical structures were characterized by Fourier transform infrared (FTIR), proton (¹H) and fluorine 19 (¹⁹F) nuclear magnetic resonance (NMR) spectrometers, and elemental analysis. They exhibited polyelectrolytic behavior in dimethyl sulfoxide. Their lyotropic liquid-crystalline phases were examined by polarizing optical microscopy (POM) and small angle X-ray scattering (SAXS) studies. Their emission spectra exhibited a positive solvatochromism on changing the polarity of solvents. They emitted greenish-yellow lights in polar organic solvents. They formed aggregates in polar aprotic and protic solvents with the addition of water (v/v, 0–90%), whose λ_em peaks were blue shifted. Full article

Ionic liquids (ILs) can ideally reduce defects and improve the film stability of emissive metal halide perovskite films. In this work, we measure how the structure and emission of methylammonium lead tribromide (MAPbBr₃) perovskite films is modulated by long alkyl chain-containing pyridinium, imidazolium, or pyrrolidinium ILs. Two different film deposition methods are compared, with the resultant films characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. For the latter, the differences in PL intensity of the perovskite are quantified using photoluminescence quantum efficiency (PLQE) measurements. It is found that a spin coating method in conjunction with the use of an imidazolium-containing IL (for a given precursor concentration) produces the strongest emissive perovskite. This optimal enhancement is attributed to a function of accessible surface charges associated with the heterocyclic cation of a given IL and perovskite defect passivation by bromide, the latter elucidated with the help of density functional theory. Proof-of-concept device fabrication is demonstrated for the case of a light emitting diode (LED) with the IL present in the emissive perovskite layer. Full article

Carbon dioxide, the primary greenhouse gas responsible for global warming, represents today a critical environmental challenge for humans. Mitigating CO₂ emissions and other greenhouse gases is a pressing global concern. The primary goal of this study is to investigate the potential of particular ionic liquids (ILs) in capturing CO₂ for the sweetening of natural and other gases. The solubility of CO₂ was measured in three distinct ILs, which shared a common anion (triflate, TfO) but differed in their cations. The selected ionic liquids were {1-butyl-3-methylimidazolium triflate [BMIM][TfO], 1-butyl-1-methylpyrrolidinium triflate [BMP][TfO], and 1-butyl-4-methylpyridium triflate [MBPY][TfO]}. The solvents were screened based on results from a molecular computational study that predicted low CO₂ Henry’s Law constants. Solubility measurements were conducted at 303.15 K, 323.15 K, and 343.15 K and pressures up to 1.5 MPa using a gravimetric microbalance (IGA-003). The CO₂ experimental results were modeled using the Peng–Robinson Equation of state with three mixing rules: van der Waals one (vdWI), van der Waals two (vdWII), and the non-random two-liquid (NRTL) Wong–Sandler (WS) mixing rule. For the three ILs, the NRTL-WS mixing rule regressed the data with the lowest average deviation percentage of 1.24%. The three solvents had similar alkyl chains but slightly different polarities. [MBPY][TfO], with the largest size, exhibited the highest CO₂ solubility at all three temperatures. Calculation of its relative polarity descriptor (N) shows it was the least polar of the three ILs. Conversely, [BMP][TfO] showed the highest Henry’s Law constant (lowest solubility) across the studied temperature range. Comparing the results to published data, the study concludes that triflate-based ionic liquids with three fluorine atoms had lower capacity for CO₂ compared to bis(trifluoromethylsulfonyl) imide (Tf2N)-based ionic liquids with six fluorine atoms. Additionally, the study provided data on the enthalpy and entropy of absorption. A final comparison shows that the ILs had a lower CO₂ capacity than Selexol, a solvent widely used in commercial carbon capture operations. Compared to other ILs, the results confirm that the type of anion had a more significant impact on solubility than the cation. Full article

The treatment of trans-dihydroxo[5,10,15,20-tetrakis(3-pyridyl)porphyrinato]Sn(IV) or [Sn(OH)₂(TPyP)] with 1% nitric acid in a mixture of water and acetone resulted in the formation of an ionic complex 1 [Sn(OH)₂(TPy^HP)](NO₃)₄. Complex 1 was fully characterized by ¹H NMR spectroscopy, elemental analysis, UV-vis spectroscopy, powder X-ray diffraction, fluorescence spectroscopy, FT-IR spectroscopy, and single-crystal X-ray crystallography. X-ray crystallographic analysis confirmed that each peripheral pyridyl N atom is protonated to form tetra-cationic species {Sn(OH)₂(TPy^HP)}⁴⁺ stabilized by four NO₃⁻ counter anions. Intermolecular hydrogen bonding interaction between axial hydroxo ligands leads to the formation of a 1D porphyrin array. Nitrate anions also involve hydrogen bonding interactions with axial hydroxo ligands and the peripheral pyridinium groups. Full article

This article discloses the synthesis of four new positional isomeric zwitterionic ligands exhibiting semi-flexible and flexible characteristics—n-pyridinium-1,2,3-triazole-4-carboxy-5-Acetate (n-PTCA), and n-methylpyridinium-1,2,3-triazole-4-carboxy-5-Acetate (n-MPTCA; where n = 3, 4)—which were derived from an aqueous solution of the corresponding sodium salts in an acidic medium (HCl). These compounds are successfully synthesized and characterized with FT-IR and multinuclear NMR spectroscopy; likewise, proper single crystals are obtained for each compound. All compounds adopt zwitterionic forms in the solid state, which are stabilized via intermolecular proton transfer processes involving HCl and solvent molecules. A single-crystal X-ray analysis revealed how positional isomerism and molecular flexibility influence the supramolecular topology. Specifically, 3-PTCA and 4-PTCA exhibit isomorphic hydrogen bond networks, while 3-MPTCA and 4-MPTCA display distinct packing motifs, attributed to the presence of a methylene spacer between the pyridinium and triazole rings. The Hirshfeld surface analysis quantitatively confirmed the dominance of O···H/H···O and N···H/H···N interactions in the solid-state architecture. These strong hydrogen-bonding networks are indicative of the potential proton-conductive behavior in the crystalline state, positioning these compounds as promising candidates for applications in proton-conducting materials. The structural insights gained underscore the pivotal role of molecular topology in tailoring crystal packing, with implications for the rational design of zwitterionic ligands in functional materials, including MOFs and coordination polymers. The calculated HOMO-LUMO energy gaps reveal a significant electronic variability among the ligands, influenced primarily by the positional isomerism and structural flexibility introduced by the methylene spacer. Full article

Colonization of surfaces by bacteria followed by biofilm formation is a cause of wound infections associated with the use of medical devices as stents, catheters, implants, etc. For prevention of such infections, the preparation of surfaces with antifouling, anti-adhesive and antibacterial properties is of great interest. In this context, four zwitterionic (styrenic or methacrylic) monomers bearing a pyridinium, imidazolium or ammonium cationic group linked to a sulfonate anionic group were chosen and polymerized on ceramic for implant technology. Zwitterionic polymers were successfully grafted onto zirconia pellets through surface-initiated radical polymerization with blue-light photoactivation (“grafting from”). Wettability measurements showed the formation of hydrophilic surfaces with water contact angles in the range of 35–40°. Detailed X-ray photoelectron spectroscopy analysis revealed a surface where the zirconia pellets exhibited zwitterionic polymer brushes with high coverage. The core-level spectra of C1s, N1s and S2p were separated into many components, allowing their attribution to the different atoms in the monomer unit and confirming that zwitterionic polymers were successfully grafted from zirconia surfaces. Full article