Search Results (863)

Salophen-type Schiff base ligands derived from salicylaldehyde and naphthalene aldehydes were synthesized and coordinated to Ni(II) to obtain three nickel complexes (NiL1–NiL3), which were evaluated as heterogeneous electrocatalysts for the methanol electro-oxidation reaction (MOR) in alkaline media. The ligands and complexes were fully characterized by FT-IR, ¹H NMR, EPR, DART-MS, and elemental analysis, confirming tetradentate coordination through imine nitrogen and phenoxide oxygen donors. Electrochemical studies were carried out using carbon paste electrodes modified with 15 wt % of each complex. Cyclic voltammetry revealed that the electrocatalytic activity is mediated by the Ni(II)/Ni(III) redox couple, with Ni(III) oxohydroxide species acting as the active sites for methanol oxidation. Among the evaluated systems, NiL1@CPE showed superior performance at low methanol concentrations, while NiL2@CPE and NiL3@CPE exhibited higher current densities at elevated methanol concentrations. Scan-rate studies indicated that the oxidation process is diffusion-controlled, and a linear response to methanol concentration was observed over a wide concentration range. The results demonstrate that ligand structure and coordination geometry play a crucial role in modulating the electrocatalytic behavior of Ni(II) Schiff base complexes, highlighting their potential as cost-effective molecular catalysts for alkaline methanol oxidation. Full article

N,N-Dimethyl-1,3-propanediamine (DMAPA) is an important aliphatic diamine widely used in fine chemical manufacturing. Its industrial production traditionally relies on Raney nickel catalysts, which suffer from pyrophoric hazards and limited selectivity due to imine condensation side reactions. To address these challenges, we report an Al₂O₃-supported Ni-Cu alloy catalyst as an efficient alternative for the selective hydrogenation of N,N-dimethylaminopropionitrile (DMAPN). The optimized Ni₃₀Cu₅/Al₂O₃ catalyst achieves complete DMAPN conversion and over 90% DMAPA selectivity under industrially relevant conditions (120 °C, 2.5 MPa H₂). X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses confirm the formation of substitutional Ni-Cu alloy nanoparticles, where Cu incorporation induces both geometric isolation of Ni ensembles and electronic modulation of surface active sites, thereby suppressing condensation-derived by-products. In addition, an NH₃/ethanol-assisted process further improves selectivity while reducing autogenous operating pressure. Overall, this work demonstrates a safe and highly selective catalytic system for primary diamine synthesis, providing a practical alternative to conventional Raney Ni-based processes. Full article

Organometallic and metal–organic compounds are widely used in different fields of chemistry and allied disciplines, including bioinorganic and medicinal chemistry. Of particular interest is the development of novel potential anticancer agents based on palladium(II) complexes of the so-called pincer-type ligands, featuring a specific monoanionic tridentate framework. In this work, hybrid imine–thiocarbamate ligands are shown to readily undergo direct cyclopalladation in solution and under solvent-free conditions, in particular upon mechanochemical activation, yielding a series of Pd(II) pincer complexes. The latter exhibit promising cytotoxic activity against several solid and hematopoietic cancer cell lines. Full article

1,3-Dipolar cycloaddition reactions of nitrile imines are a powerful tool for the construction of spirocyclic frameworks, yet controlling chemoselectivity remains challenging when dipolarophiles contain multiple reactive sites. In this study, we investigated the cycloaddition of nitrile imines with 5-arylmethylene-2-methylthiohydantoins, which possess both exocyclic C=C and endocyclic C=N bonds. Nitrile imines were generated from hydrazonoyl chlorides under basic conditions and reacted with the thiohydantoin substrates under optimized reaction conditions. The cycloaddition proceeded smoothly, affording spiro-fused thiohydantoin–pyrazoline derivatives. In all cases, the reaction occurred selectively at the exocyclic C=C bond, while the C=N bond remained unreactive even in the presence of excess dipole. This chemoselectivity is attributed to the greater steric accessibility of the exocyclic double bond. These results clarify key factors governing nitrile imine chemoselectivity and provide a reliable approach to structurally complex spirocyclic thiohydantoin derivatives. Full article

Δ¹-Pyrroline-5-carboxylate reductase (EC 1.5.1.2; called ProC in most bacteria) is an enzyme of central metabolism that catalyzes the last step of the proline biosynthetic pathways, namely the NADPH-dependent reduction of pyrroline-5-carboxylate (P5C) to L-proline (L-Pro). The enzyme, however, is also active towards other substrates, and these reactions might have physiological relevance. Herein, the substrate versatility of ProC from Escherichia coli was explored as follows. We initially characterized the reverse reaction carried out by ProC, i.e., the formation of P5C from L-Pro. This reaction was easily measurable at pH 10, allowing the determination of the kinetic parameters. Under the same conditions, we then tested the ability of ProC to oxidize a number of L-Pro analogs, confirming that ProC reacts most effectively with analogs containing a simple five-membered ring such as L-thioproline (THP) and 3,4-dehydro-L-proline (DHP). Larger substrates such as L-pipecolate (PIP) reacted with lower efficiency, and the four-membered ring analog, L-azetidine-2-carboxylate (A2C) showed no detectable reactivity and behaved as a weak inhibitor of the ProC reaction. To interpret these results, we built a structural model of ProC and employed this model for a docking analysis of L-Pro and of its analogs. This approach highlighted the presence of a peculiar “three-point interaction”, in which the L-Pro carboxylate and amino groups form hydrogen bonds with conserved residues in the binding site, while the substrate ring stacks with the nicotinamide ring of NADP⁺. The L-Pro analogs tried to preserve as much as possible these critical interactions for a correct positioning and a favorable binding. The possibility of an inherent multifunctionality of ProC was further explored by examining the genomic context of the proC gene in a large number of bacterial species. Full article

The rate constant k_OH for the reaction of 1,1,1,3,3,3-hexafluoroprop-2-imine with OH radicals was measured relative to two reference compounds, CH₃F and CH₃CHF₂, to be k_OH = (4.2 ± 1.1) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ at 295 K. This implies an atmospheric lifetime with respect to consumption by OH of 0.75 years. Reaction with Cl atoms yielded k_Cl = (7.9 ± 1.7) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ at 295 K, and reaction with O₃ has an upper limit of k_O3 < 4 × 10⁻²³ cm³ molecule⁻¹ s⁻¹, so that the atmospheric consumption by Cl and O₃ is negligibly slow. Absolute infrared cross sections of the imine yield a radiative efficiency of 0.34 W m⁻² ppb⁻¹, which is corrected to 0.23 W m⁻² ppb⁻¹ for the effects of atmospheric lifetime. The imine’s corresponding 100-year global warming potential is 64 ± 19. This value is an upper limit, given that heterogenous atmospheric removal paths, such as hydrolysis in water droplets, are not included. Full article

A well-defined heterojunction and tailored interface of the photocathode are desired to facilitate the efficient separation and transfer of photogenerated charge carriers for photoelectrochemical (PEC) hydrogen generation. Herein, optimized Z-scheme heterojunction (denoted as F-COF/TiO₂) photoelectrodes were designed and fabricated by solvothermally growing a F-substituted imine-linked covalent organic framework (F-COF) from 1,3,5-tris(3-fluoro-4-formylphenyl)benzene and 1,4-diaminobenzene on the surface of anodized TiO₂ nanotubes for enhanced PEC hydrogen evolution. The F-COF/TiO₂ heterojunction with photo-deposited Pt species as cocatalysts (Pt@F-COF/TiO₂) revealed higher cathodic photocurrent density, decreased interfacial resistance, and improved onset potential due to the improved charge separation and transfer efficiency at the interface. Both the internal electric field between F-COF and TiO₂, as well as the enhanced photophysical nature of F-COF films, contributed to the efficient interfacial charge separation and transfer. The photo-deposited Pt species and applied bias voltage also demonstrated a synergetic effect on facilitating charge separation and transfer for hydrogen production. The Pt@F-COF/TiO₂ photoelectrode featured an improved PEC hydrogen evolution rate under AM 1.5G simulated sunlight irradiation and a durable PEC hydrogen evolution performance. This study provides valuable insights into the design of heterojunction-based photoelectrodes for efficient solar-driven hydrogen production for sustainable energy applications. Full article

A new series of promising and easily accessible antiproliferative agents based on cycloruthenated imines of benzene and thiophene carbaldehydes has been developed and fully characterized using UV-Vis spectroscopy, X-ray diffraction, NMR, HRMS, and cyclic voltammetry. The biological activity of these compounds was tested against A2780, cisplatin-resistant A2780, and HEK293 cell lines, and they exhibited nanomolar IC₅₀ values. They also showed a selectivity index of up to 2.5, indicating their potential as promising antiproliferative compounds. Full article

Schiff bases are bioactive compounds that have been synthesized by many researchers in recent years. They may also exhibit strong antimicrobial activities against various pathogenic microorganisms in both medicine and veterinary applications. The synthesis of new Schiff base-derived compounds remains of interest due to the increasing problem of antibiotic-resistance in clinical practice. Seven new Schiff base derivatives were synthesized, and their chemical structures were characterized using FT-IR, ¹H/¹³C NMR, and LCMS-MS analyses. The antimicrobial activities of thesyntesized compounds against various pathogenic bacteria, yeasts, and fungi were evaluated using the disk-diffusion method, and their MIC values were also determined. In addition, one representative microorganisms from each class were selected for molecular docking studies. IFD analyses were performed for the 4f and 4g ligands using the dihydrofolate reductase enzyme. Spectroscopic analyses confirmed the structures of the synthesized compounds, revealing the presence of characteristic imine functionalities and validating the integrity of the molecular frameworks. Antimicrobial assays demonstrated that several derivatives exhibited measurable activity, with compounds 4f and 4g showing the most potent effects, displaying MIC values of 32 µg/mL against B. cereus and E. faecalis, respectively. Molecular docking studies further indicated that both 4f and 4g bind efficiently to the DHFR active site. These findings indicate that among the synthesized Schiff base derivatives, compounds 4f and 4g exhibit particularly promising antimicrobial activity, warranting further pharmacological evaluation and medicinal chemistry optimization. Full article

The current study aims to model the potential energy surface (PES) of three much less investigated hydroxyaryl(hetaryl)idene azomethine imine derivatives, possessing the same proton crane unit—namely the azomethine imine moiety—but slightly differing in the structure of the proton transfer platform (stator), by applying the tools of computational chemistry. The obtained calculational results are compared with already reported experimental structural, ¹H NMR, and UV absorption spectra in an attempt to shed light on the observed data, mainly with regard to the efficiency of the excited state intramolecular proton transfer. Full article

Heterocyclic sulfur and nitrogen containing compounds capable of forming an equilibrium: thiol/imine = thione/amine (N=C-S-H ⇌ H-N-C=S) were reacted with levoglucosenone (LG) in the presence of triethylamine. Unexpectedly, the only isolated products were the result of the aza-Michael addition. No S-adducts were detected. All products were crystalline with good to excellent yields. The structure of products was determined using NMR, MS, and single-crystal X-ray analysis. Full article

Schiff bases are widely studied for their biological activities, yet structure–activity relationships governing their anticancer potential remain insufficiently understood. In this work, eight structurally diverse imine derivatives (A–H) were evaluated for their cytotoxic, biochemical, and biomolecular interactions in human cancer cells. Their antiproliferative effects were assessed in HeLa, A549, and LS174T cell lines, with MRC-5 fibroblasts used as a non-malignant control. Cytotoxicity screening identified three compounds (A, B, and F) with the highest potency, prompting further mechanistic investigation. Cell cycle analysis revealed G1 arrest and accumulation of sub-G1 populations for all three derivatives, with compound B additionally increasing S-phase content and compound F inducing G2/M arrest. All compounds reduced intracellular ROS levels and caused significant DNA damage at subtoxic concentrations. Western blot analysis demonstrated downregulation of HIF-1α and PDK3, suggesting disruption of hypoxia-associated metabolic signaling. Fluorescence quenching experiments showed strong binding of the active compounds to bovine serum albumin (K_a ≈ 10⁶ M⁻¹), and molecular docking supported stable interactions near tryptophan-adjacent binding regions. Collectively, these findings indicate that selected Schiff bases exert multi-target anticancer activity by modulating oxidative stress, DNA integrity, cell-cycle progression, and metabolic adaptation pathways, warranting further investigation of their therapeutic potential. Full article

The accurate determination of trace metals in aqueous matrices necessitates robust sample preparation techniques that enable selective preconcentration of analytes while ensuring compatibility with subsequent instrumental analysis. Dispersive solid-phase extraction (d-SPE), a suspension-based variant of conventional solid-phase extraction (SPE), facilitates rapid sorbent–analyte interactions and enhances mass transfer efficiency through direct dispersion of the sorbent in the sample solution. This approach offers significant advantages over traditional column-based SPE, including faster extraction kinetics and greater operational simplicity. When supported by appropriately engineered sorbents, d-SPE exhibits considerable potential for the selective enrichment of trace metal analytes from complex aqueous matrices. In this work, a fibrous silica-based chelating material, DSA-KCC-1, was synthesized by grafting 3,5-Di-tert-butylsalicylaldehyde (DSA) onto aminopropyl-modified KCC-1. The dendritic KCC-1 scaffold enables fast dispersion and short diffusion pathways, while the immobilized phenolate–imine ligand introduces defined binding sites for transition-metal uptake. Characterization by FTIR, TGA, BET, FESEM/TEM, XRD, and elemental analysis confirmed the successfulness of functionalization and preservation of the fibrous mesostructured. Adsorption studies demonstrated chemisorption-driven interactions for Pb(II) and Co(II) from water, with Langmuir-type monolayer uptake and pseudo-second-order kinetic behavior. The nano-adsorbent exhibited a markedly higher affinity for Pb(II) than for Co(II), with maximum adsorption capacities of 99.73 and 66.26 mg g⁻¹, respectively. Integration of the DSA-KCC-1 nanosorbent into a d-SPE–ICP-OES workflow enabled the reliable determination of trace levels of the target ions, delivering low limits of detection, wide linear calibration ranges, and stable performance over repeated extraction cycles. Analysis of NIST CRM 1643d yielded results in good agreement with the certified values, while the method demonstrated high tolerance toward common coexisting ions. The combined structural features of the KCC-1 support and the Schiff-base ligand indicate the suitability of DSA-KCC-1 for d-SPE workflows and demonstrate the potential of this SPE format for selective preconcentration of trace metal ions in aqueous matrices. Full article

Reusable enzyme carriers are valuable for proteomic workflows, yet many supports are expensive or lack robustness. This study describes the covalent immobilization of recombinant trypsin on micrometer-sized corundum particles and assesses their performance in protein digestion and antibody analysis. The corundum surface was cleaned with potassium hydroxide, silanized with 3-aminopropyltriethoxysilane and activated with glutaraldehyde. Recombinant trypsin was then attached, and the resulting imines were reduced with sodium cyanoborohydride. Aromatic amino acid analysis (AAAA) estimated an enzyme loading of approximately 1 µg/mg. Non-specific adsorption of human plasma proteins was suppressed by blocking residual aldehydes with a Tris-glycine-lysine buffer. Compared with free trypsin, immobilization shifted the temperature optimum from 50 to 60 °C and greatly improved stability in 1 M guanidinium hydrochloride. Activity remained above 80% across several reuse cycles, and storage at 4 °C preserved functionality for weeks. When applied to digesting the NISTmAb, immobilized trypsin provided peptide yields and sequence coverage comparable to soluble enzyme and outperformed it at elevated temperatures. MALDI-TOF MS analysis of Herceptin digests yielded fingerprint spectra that correctly identified the antibody and achieved >60% sequence coverage. The combination of low cost, robustness and analytical performance makes corundum-immobilized trypsin an attractive option for research and routine proteomic workflows. Full article