Search Results (325)

This work focuses on the production of biodiesel from Nannochloropsis sp. microalgae. The study compares the effectiveness of conventional methods, such as Soxhlet extraction and the Bligh and Dyer method with a non-conventional method that uses an ionic liquid as solvent for lipid extraction. The Bligh and Dyer method demonstrated superior efficiency with a lipid yield of 8.19% compared to Soxhlet extraction. Sample parameters were optimized in a maximum lipid yield of 18.29% at a sample volume of 91.9 mL, a duration of 7 min, and a power rate of 0.62 W. We further investigated the use of ionic liquids for lipid extraction from microalgae. We synthesized ionic liquids, and 1-(4 sulphonic acid) butyl-3-Methyl imidazolium hydrogen sulphate and 1-(4 sulphonic acid) butyl pyridinium hydrogen sulphate were characterized using FTIR, NMR and TGA. This method showed lipid extraction efficiency values of 10.7% and 0.402%. Subsequent transesterification of algal oil using 1-(4 sulphonic acid) butyl-3-Methyl imidazolium hydrogen sulphate yielded 19.82% biodiesel. FTIR analysis confirmed the presence of lipids and esters in the biodiesel, and the produced biodiesel met ASTM specifications, indicating its suitability for use as biofuel. Full article

The synthesis of three novel, valuable bioconjugates obtained by coupling cholesterol bromoacetate with pyridine derivatives via an SN2 reaction was successfully carried out. Each of the products was fully characterized by magnetic nuclear resonance (¹H, ¹³C, APT, ¹H−¹H COSY, ¹H–¹³C HMBC, ¹H–¹³C HSQC), infrared spectroscopy (IR), and high-resolution mass spectrometry (HRMS). Full article

A diverse range of 4-dimethylaminopyridinium (DMAP) bis(trifluoromethylsulfonyl)-amide ionic liquids with specific functionalities (alkyl, alkoxy, hydroxyalkyl and benzyl) were designed, characterized and compared with their pyridinium analogs in terms of their physical and radiolytic properties. The influence of the dimethylamino group on ionic liquid structure was investigated by X-ray diffraction and molecular dynamics simulations. The influence of the electron-donating ability of the dimethylamino-substituted cation is evident in the differences in the electronic density of states between the DMAP and pyridinium ILs. This leads to substantial changes in the radical transients observed in pulse radiolysis of the neat ILs. It was found that the DMAP salts were higher melting, more viscous and less conducting than their pyridinium analogs. However, the DMAP salts exhibited higher thermal stabilities and could therefore be useful for high-temperature applications. Full article

A series of 6-azaindole pyridinium derivatives were synthesized, structurally characterized, and evaluated for their antimicrobial (against Staphylococcus aureus, Escherichia coli, and Candida albicans) and anticancer properties (against NCI 60 panel). Hemocompatibility was evaluated using the hemolytic index, while ADME properties were estimated using in silico methods. Structure–activity relationship analysis indicated that para-substitution of the phenyl ring, particularly with halogen or methoxy groups, influences antimicrobial activity, selectivity toward Gram-positive bacteria, and hemocompatibility. Compounds 2b and 2c showed the most notable antimicrobial effects, including inhibition of microbial adhesion at hemocompatible concentrations. Compound 2b exhibited growth inhibition against cancer cells, showing 57% percent growth inhibition (PGI) against the MDA-MB-468 breast cancer cell line at 10 mM. Overall, these results highlight 6-azaindole pyridinium salts as a promising class of compounds for further investigation. Full article

In this study, potential fungicides were prepared following the principles of green chemistry. The compounds were synthesized in deep eutectic solvents as an alternative medium and compared with syntheses in traditional solvents such as ethanol. The efficiency of the reaction was improved by ultrasonic synthesis in both eutectic solvents and ethanol, resulting in higher yields while reducing reaction energy and time. For the first time, deep eutectic solvents (DES) were used for quaternisation reactions, with choline chloride as a hydrogen bond acceptor and urea, glycerol, malic acid, malonic acid, and levulinic acid as donors. DES, composed of biodegradable, non-toxic, and renewable components, represented a greener alternative to conventional solvents. However, reactions in DES by the conventional method generally resulted in lower yields, probably due to solubility and viscosity limitations inherent in the eutectic medium. The combination of ultrasound and deep eutectic solvents proved to be a good alternative to organic solvents for the quaternisation reaction, as higher yields were achieved in a shorter time compared to conventional methods. The antifungal activity of all 18 synthesized compounds was tested. The compounds exhibited significant antifungal activity against all four pathogens, with varying levels of mycelial growth inhibition. B. cinerea was the most sensitive species (up to 70.7% inhibition), while F. culmorum was the least sensitive (≤32%). Full article

Background: The escalating spread of drug-resistant bacteria is intensifying the antibiotic resistance crisis, necessitating the urgent development of novel antimicrobial agents to address the resulting high global mortality rates and significant socioeconomic burden. Objectives: This study aimed to aminate the C-6 position of β-carboline and investigate the antibacterial activity and mechanism of action of the derivatives. Results: For the first time, 16 derivatives with various nitrogen-containing moieties, including aliphatic- and phenyl-amino, imidazolium, pyridinium, and quinolinium, were synthesized via amination at the C-6 position of β-carboline. These compounds exhibited moderate to good activity against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Bacillus subtilis, with minimum inhibitory concentration (MIC) values ranging from 1.56 to 100 μg/mL. The study reveals that elongating an alkyl chain, incorporating a cationic scaffold, and expanding a π-delocalized system can enhance antibacterial activity. The most potent derivative from each series was selected for further mechanistic investigation against MRSA. All studied compounds demonstrated low hemolytic activity and low cytotoxicity. Studies on the antibacterial mechanism indicated that the compounds exert their antibacterial effects by disrupting bacterial cell walls and membranes. Additionally, two of the compounds were found to potentially disrupt the secondary structure of DNA. All tested compounds exhibited antibiofilm activity. Conclusions: Our findings demonstrate that amination modification at the C-6 position of β-carboline can enhance antibacterial activity by disrupting the cell wall membranes and interacting with bacterial DNA. These results provide a basis for further optimization of antibacterial agents based on β-carboline. Full article

We report a straightforward and versatile synthetic route to pyridinium-fused 1,3-selenazoles via the electrophilic cyclization of 2-pyridylselenyl chloride with alkynes. The reaction proceeds efficiently under mild conditions with representative terminal and internal alkynes. While the cyclization exhibits high regioselectivity favoring the 3-substituted isomer for most substrates, reactions with 2-pyridyl- and 2-quinolylacetylenes yield regioisomeric mixtures. DFT calculations rationalize this divergence, revealing a competition between kinetic and thermodynamic control; the 3-isomer is kinetically favored, while the 2-isomer is thermodynamically stabilized by an ancillary chalcogen bond between the selenium atom and the pyridine nitrogen of the alkyne substituent. Molecular structures were confirmed by single-crystal X-ray diffraction, and the non-covalent interactions governing supramolecular assembly in the solid state were rigorously analyzed using MEP surfaces, the QTAIM, and NBO analysis. Antifungal evaluation identified several compounds with notable activity against phytopathogenic fungi, highlighting the potential of this novel heterocyclic scaffold in agrochemical applications. Full article

The relative position of the oxime group within pharmaceutically relevant pyridinium oximes is a pivotal factor that governs their intrinsic physicochemical properties and their biological reactivity. However, studies providing in-depth, molecular-level insight into these structure–reactivity relationships are still limited. In this work, we present an integrated experimental and computational study of N-methylpyridinium-2-aldoxime chloride (PAM2-Cl), N-methylpyridinium-3-aldoxime iodide (PAM3-I), and N-methylpyridinium-4-aldoxime iodide (PAM4-I), aimed at elucidating discrete differences in their ionization behavior, electronic structure, σ-donor properties, and nucleophilicity. The crystal structure of PAM3-I was determined by X-ray diffraction. Comparative structural and spectroscopic (UV–Vis, NMR, IR) analyses elucidated the structural and electronic effects arising from the position of the oxime group. Kinetic studies of substitution reactions with aquapentacyanoferrate(II) in aqueous solution enabled the determination of pentacyano(PAM)ferrate(II) formation and dissociation rate constants, coordination modes, pK_a values of the coordinated ligands, complex stability constants, and σ-donating capabilities. The DFT-based analysis of atomic charge distribution transcended experimental limitations, offering a new perspective on electronic structure-related properties. This study presents the first side-by-side, internally consistent structure–reactivity map across PAM2, PAM3, and PAM4 isomers that triangulates crystallography, UV–Vis-derived pK_a values, substitution kinetics, and DFT descriptors in a single framework. Full article

Heterocyclic organic compounds, namely 1,1′-methylenebis(pyridinium) bromide (Inhibitor I) and 1,1′-ethylenebis(pyridinium) bromide (Inhibitor II), were investigated as corrosion inhibitors for mild steel in acidic wastewater (0.5 M H₂SO₄). The inhibition performance was evaluated using gravimetric weight-loss measurements and electrochemical techniques. The results show that increasing inhibitor concentration significantly reduces the corrosion rate and enhances the inhibition efficiency, reaching maximum values of 90.42% for Inhibitor I and 87.85% for Inhibitor II at 7.5 × 10⁻³ M. This improvement is associated with a notable decrease in corrosion current density, indicating adsorption of inhibitor molecules at the steel/electrolyte interface. Adsorption studies reveal that both inhibitors follow the Langmuir adsorption isotherm, suggesting a mixed physisorption–chemisorption mechanism. Density functional theory (DFT) calculations and molecular dynamics simulations provide qualitative insight into the adsorption behavior, emphasizing the contribution of heteroatoms and π-electron systems to inhibitor–metal interactions. Overall, Inhibitor I exhibits superior inhibition performance, which can be attributed to its higher molecular reactivity, lower HOMO–LUMO energy gap, and higher dipole moment. The combined experimental and theoretical results demonstrate that the investigated compounds exhibit high corrosion inhibition efficiency under the studied conditions for mild steel in acidic wastewater environments. Full article

Managing bacterial infections and the spread of microbial resistance is one of the most critical and complex tasks of modern healthcare infrastructures. Antiseptics and disinfectants such as biocides play a significant role in controlling microbial resistance by reducing the microbial load on surfaces, skin, and environments, thereby limiting the opportunity for pathogens to proliferate and develop resistance. Herein, we tested the different interactions of quaternary ammonium compound (QAC)-based biocide compositions in pursuit of a better antimicrobial performance. An extensive microbiological analysis was conducted for 12 selected compositions of various combinations of mono-QACs, bis-QACs, and alcohols on 17 strains of bacteria of the ESKAPEE group and fungi, including 11 clinical highly resistant varieties, highlighting synergistic or additive dynamics. The evaluation showed noticeable improvements in activity, with up to 16-fold MBC and 32-fold MBEC reductions for alcohol-based compositions of lead QAC. Moreover, synergistic interactions were detected and confirmed via an optimized checkerboard assay for pyridinium QAC combinations against planktonic Gram-positive S. aureus with a fractional inhibitory concentration index (FICI) and fractional bactericidal concentration index (FBCI) of 0.39–0.5 and Gram-negative A. baumannii biofilms. The studied biocides demonstrated the long-term preservation of antimicrobial efficiency without resistance development during a 40-day period and do not induce QAC-associated cross-resistance for four commercially available antibiotics with similar mechanisms of action. Full article

Pyridinium ylides, along with related azaheterocyclic ylides, are widely used in synthetic organic chemistry. However, reactions that yield stable zwitterionic adducts from these ylides remain underexplored. In this work, we demonstrate that the reaction of pyrrole-2,3-diones with in situ-generated pyridine-based azomethine ylides affords stable zwitterionic adducts, which are typically transient species in analogous processes. These betaines are used as key intermediates for the synthesis of cyclopropane-fused pyrroles or pyridine-2,3-diones via thermolysis in chlorobenzene. Full article

This study investigates the interfacial behavior of four phosphate ester ionic liquids (ILs) with contrasting cation hydrophobicity under humid environments. Through tribological tests, surface analysis, and molecular dynamics simulations, we reveal how moisture absorption governs lubricant film organization at metal interfaces. Aromatic ILs (imidazolium/pyridinium cations) exhibit significant degradation in lubrication after moisture exposure, with friction coefficients increasing by 0.03–0.05 and wear volumes scaling with humidity. This deterioration arises from competitive water–cation adsorption, where hydrogen bonding disrupts Fe-cation coordination bonds and destabilizes the protective film. In contrast, aliphatic ILs (tetraalkylammonium/phosphonium cations) maintain robust tribological performance. Their alkyl chains spatially confine water to outer adsorption layers (>17 Å from the surface), preserving a stable core lubricating film (~14 Å thick). Molecular dynamics simulations confirm that water co-adsorbs with aromatic cations (RDF peak: 2.5 Å), weakening interfacial interactions, while aliphatic ILs minimize cation–water affinity (RDF peak: 4 Å). These findings establish cation hydrophobicity as a critical design parameter for humidity-resistant lubricants, providing fundamental insights into water-mediated interfacial phenomena in complex fluid systems. Full article

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