Search Results (173)

The efficient recovery of rhenium (Re), a critical metal in high-tech industries, is essential to address its growing demand and reduce reliance on primary mining. In this study, we developed novel anion-exchange resins for the selective adsorption and recovery of Re(VII) ions from acidic solutions, simulating industrial by-products. The resins were synthesized from a vinylbenzyl chloride-co-divinylbenzene copolymer modified with aliphatic, heterocyclic, and aromatic weakly basic amines, selected from among bis(3-aminopropyl)amine (BAPA), 1-(2-pyrimidinyl)piperazine (PIP), thiosemicarbazide (TSC), 2-amino-3-hydroxypyridine (AHP), 1-(2-hydroxyethyl)piperazine (HEP), 4-amino-2,6-dihydroxypyrimidine (AHPI), and 2-thiazolamine (TA). The adsorption of Re on BAPA, PIP, and HEP resins obeyed the Langmuir model, and the resins exhibited high adsorption capacities, with maximum values reaching 435.4 mg Re g⁻¹ at pH 6. Furthermore, strong selectivity for ReO₄⁻ ions over competing species, including Mo, Cu, and V, was noted in solutions simulating the leachates of the by-products of Cu-Mo ores. Additionally, complete elution of Re was possible. The developed resins turned out to be highly suitable for the continuous-flow-mode adsorption of ReO₄⁻, revealing outstanding adsorption capacities before reaching column breakthrough. In this context, the novel anion-exchange resins developed offer a reference for further Re recovery strategies. Full article

A series of porphyrinoids fused to highly electron-withdrawing bis(thiadiazolo)benzene units have been prepared and spectroscopically characterized. These structures have modified chromophores and exhibit large bathochromic shifts. The nickel(II), copper(II) and zinc complexes of a bis(thiadiazolo)benzoporphyrin were prepared, and these showed strong absorptions above 600 nm that shifted to longer wavelengths with increasing atomic number for the coordinated metal cations. Although the investigated porphyrinoids were poorly soluble, proton NMR data could be obtained, and these demonstrated that the structures possess global aromatic character. This was confirmed with nucleus-independent chemical shift (NICS) calculations and anisotropy of induced current density (AICD) plots. The AICD plots also demonstrate that the fused heterocyclic unit is disconnected from the porphyrinoid π-system, and in this respect, it differs from phenanthroline-fused porphyrinoids as it shows the presence of extended conjugation pathways. Full article

Background: Carbazoles represent one of the most important classes of nitrogen-based tricyclic aromatic heterocycles and are present in natural sources and chemically obtained drugs. Recently, several research groups disclosed their large biological and chemical applications in different fields, leading to an increased interest towards this class of molecules. Some of the obtained derivatives have been successfully employed in the clinical treatment of different tumor types, but the onset of heavy side effects impaired their efficacy and discouraged their use. Pursuing the aim of obtaining carbazoles with less negative features, a lot of chemically modified compounds have been produced and evaluated. Objectives/Methods: In this paper, we describe the in vitro and in vivo evaluation of a bis-carbazole derivative with strong anticancer properties against two breast cancer cell lines. Results: This compound has been found to impact the cell cytoskeleton dynamics, triggering the activation of some key proteins playing a role in the intrinsic and extrinsic apoptotic pathways. Equally important, this derivative has been found to be selective for cancer cells and has shown a safe profile in Balb/c-treated mice. Conclusions: Overall, the disclosed outcomes represent an important landmark for encouraging further studies directed toward the potentiation of this lead to be potentially exploited in both preclinical and clinical applications. Full article

The innovation of energy storage technology and its solutions for energetic materials is an important direction in the current energy technology field. Hence, series of tetrazole-based ultra-high-energy-density high-nitrogen heterocyclic power compounds were designed and their energy characteristics and safety performances were evaluated by density functional theory (DFT). The results indicate that the type, number, and position of substituents have a significant effect on the comprehensive performance of these compounds. Research on electronic features shows that mono-substituents on the N atom connecting two tetrazole rings, substituents with more H atoms on the tetrazole ring, and less energetic substituents are beneficial for the stability of compounds. The discussion on energy characteristics and safety performance indicates that compounds B1(N-(1-nitro-1H-tetrazol-5-yl)-N-(1H-tetrazol-5-yl)nitramide), B7(N’-(1-nitro-1H-tetrazol-5-yl)-N’-(1H-tetrazol-5-yl)nitric hydrazide), B8(N-(1-(nitroamino)-1H-tetrazol-5-yl)-N-(1H-tetrazol-5-yl)nitramide), C1(5,5′-(hydrazine-1,1-diyl)bis(1-nitro-1H-tetrazole)), C4(N,N-bis(1-nitro-1H-tetrazol-5-yl)nitramide), and C6(N-(1-amino-1H-tetrazol-5-yl)-N-(1-nitro-1H-tetrazol-5-yl)nitramide) possess outstanding comprehensive performance concerning density, heat of formation, detonation heat, detonation velocity and pressure, oxygen balance, and impact sensitivity, and can be screened as candidates for high-energy-density compounds. The results are expected to provide new solutions for the innovation and progress of energy storage technologies in the energetic materials field. Full article

The benzimidazole core (BI) plays a central role in biologically active molecules. The BI nucleus is widely used as a building block to generate a variety of bioactive heterocyclic compounds to be used as antihelmintics, antiprotozoal, antimalarials, anti-inflammatories, antivirals, antimicrobials, antiparasitics, and antimycobacterials. A versatile BI derivative is the 2-guanidinobenzimidazole (2GBI), which, together with its derivatives, is a very interesting poly-functional planar molecule having a delocalised 10 π electrons system conjugated with the guanidine group. The 2GBI molecule has five nitrogen atoms containing five labile N–H bonds, which interact with the out-ward-facing channel entrance, forming a labile complex with the biological receptor sites. In this work, 2GBI and their derivatives were analyzed as ligands to form host–guest, coordination and organometallic complexes. Synthesis methodology, metal geometries, hydrogen bonding (HB) interactions, and the biological activities of the complexes were discussed. Full article

Silver drugs have played a vital role in human healthcare for the treatment of infections for many centuries. Currently, due to antibiotic resistance, a potential scenario or the application of silver complexes may arise as substitutes for conventional antibiotics. In this perspective, N-heterocyclic carbene (NHC) ligands have been selected as carrier molecules for silver ions. In this study, we selected two mono NHC-silver halide complexes: bromo[1,3-diethyl-4,5-bis(4-methoxyphenyl)imidazol-2-ylidene]silver(I) (Ag4MC) and chloro[2-pyridin- N-(2-ethylacetylamido)-2-yl-2H-imidazol-2-ylidene]silver(I) (Ag5MC), and two cationic bis NHC silver complexes: bis[1,3-diethyl-4,5-bis(4-methoxyphenyl)imidazol-2-ylidene]silver(I) (Ag4BC) and bis[2-pyridin-N-(2-ethylacetylamido)-2-yl-2H-imidazol-2-ylidene]silver(I) (Ag5BC). The inhibitory properties of the four complexes were evaluated for their antimicrobial potential against a set of Gram (+) and Gram (−) bacterial strains and the fungus C. albicans. In addition, further investigations were made using fluorescence and scanning electron microscopy (SEM) in order to gain more insights into the mechanism of action. Some preliminary information on the Ag target was obtained by analyzing the cytosol of E. coli treated with Ag5MC by size-exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Full article

Polyphenolic compounds are considered one as the most important plant-originated species with antioxidant properties. This paper focuses on exploring the structure and antiradical properties of supramolecular complexes derived from the selected polyphenolic (caffeic and protocatechuic) acids and isomers of pyridinecarboxamide. The chemical interactions between polyphenolic acids and carboxamides were analyzed using FT–IR spectroscopy. The thermal behavior of the solid phases was tested with the help of thermal analysis via thermogravimetry (TG) coupled with differential scanning calorimetry (DSC). The antiradical activity was determined by using the ABTS method (2,2′-azino-bis(3-ehylbenzothiazoline-6-sulfonic acid). The obtained results indicate that the solutions prepared by dissolving the solid materials exhibited better antiradical activity than the binary mixtures prepared by mixing the stock reagents’ solutions. These studies confirmed that supramolecular complexes derived from polyphenolic compounds and N-heterocyclic entities may constitute a quite interesting material for future research. Full article

Oximation of substituted ketofurfuryl alcohols in the presence of hydroxylamine hydrochloride and pyridine in ethanol as solvent led to a new class of spiro derivatives presenting a 7-methylene-1,6-dioxa-2-azaspiro [4.4] nona-2,8-diene skeleton along with, in some cases, the predictable oxime. The structures of such spiro compounds were determined by 2D NMR spectroscopy. The suggested formation of this skeleton involves an in situ oximation/dehydration/S_N’ cascade reaction. Full article

Herein, we report the structure-based selection via molecular docking of four N-heterocyclic bis-carbene gold(I) complexes, whose potential as ligands for the hTel23 G-quadruplex structure has been investigated using circular dichroism (CD) spectroscopy, CD melting, and polyacrylamide gel electrophoresis (PAGE). The complex containing a bis(1,2,3,4,6,7,8,9-octahydro-11H-11λ³-pyridazino[1,2-a]indazol-11-yl) scaffold induces a transition from the hybrid (3 + 1) topology to a prevalent parallel G-quadruplex conformation, whereas the complex featuring a bis(2-(2-acetamidoethyl)-3λ³-imidazo[1,5-a]pyridin-3(2H)-yl) moiety disrupted the original G-quadruplex structure. These results deserve particular attention in light of the recent findings on the pathological involvements of G-quadruplexes in neurodegenerative diseases. Full article

Bis-heterocyclic compounds containing imidazo[1,2-a]pyridines (IMPs) are privileged heterocyclic drug scaffolds due to their potential applications. The Groebke–Blackburn–Bienaymé reaction (GBBR) is a greener alternative to synthesizing IMPs. On the other hand, 1,2,3-triazole scaffolds are biososteres of the trans amide, and their incorporation in bioactive molecules provides advantages such as resistance to cleavage mediated by proteases and improved stability. In this context, the CuAAC reaction is the most efficient approach to synthesizing 1,4-disustituted-1,2,3-triazoles. Herein, we describe a novel one-pot synthesis of IMPs by the GBBR-CuAAC strategy assisted by microwave irradiation. Full article

The six-membered N,S-heterocyclic 1,3-thiazines and their derivatives are widely acknowledged as pharmaceutical molecules with a wide range of biological activities. In this study, we developed a unique thiol-involved cascade reaction that enables the efficient construction of the 5,6-dihydro-4H-1,3-thiazine scaffold through consecutive intermolecular thiol-isothiocyanate and intramolecular thiol-halogen click reactions. Structurally diverse 2-mercapto dihydrothiazines including three antitumour candidates of bis-dihydrothiazines were readily obtained in high yields from the readily available thiols and 3-chloroisothiocyanate in the green solvent EtOH/H₂O (1:1) using K₂CO₃ (0.6 equiv.) as the base. Between the two synthesis procedures investigated, the microwave-assisted reaction generally behaved more efficiently than that under routine heating conditions. Furthermore, DFT calculation confirmed the sequential addition–substitution mechanism. This cascade C–S coupling reaction methodology offers several advantages, including rapid completion, high reliability, easy purification, and benign conditions. Full article

Tetronic acid, a five-membered heterocyclic moiety present in various natural products, has emerged as a significant building block for many pharmaceutically active compounds. In this study, a novel protocol for the synthesis of the bis-tetronic acid 3,3′-((4-methoxyphenyl)methylene)bis(4-hydroxyfuran-2(5H)-one) (3) via a domino Knoevenagel–Michael reaction is presented. The natural deep eutectic solvent L-proline/glycerol 1:2 molar ratio was utilized as a solvent and catalyst, while the reaction was further promoted via microwave irradiation, providing the desired product in high yield (83%). The solvent was successfully recycled and reused up to three times. Full article

In the present study, a series of isatin bis-imidathiazole hybrids was designed and synthesized to develop a new class of heterocyclic compounds with improved antimicrobial activity against pathogens responsible for hospital- and community-acquired infections. A remarkable inhibitory activity against Staphylococcus aureus was demonstrated for a subset of compounds (range: 13.8–90.1 µM) in the absence of toxicity towards epithelial cells and human red blood cells. The best performing derivative was further investigated to measure its anti-biofilm potential and its effectiveness against methicillin-resistant Staphylococcus aureus strains. A structure–activity relationship study of the synthesized molecules led to the recognition of some important structural requirements for the observed antibacterial activity. Molecular docking followed by molecular dynamics (MD) simulations identified the binding site of the active compound FtsZ, a key protein in bacterial cell division, and the mechanism of action, i.e., the inhibition of its polymerization. The overall results may pave the way for a further rational development of isatin hybrids as FtsZ inhibitors, with a broader spectrum of activity against human pathogens and higher potency. Full article

Bis-triazoles separated by a symmetrical linking group are joined at C4 of each triazole or at N1 of each triazole. Preparation of a series of bis-1H-1,2,3-triazoles derived from o-bis(azidomethyl)benzene and an alkyne is reported with use of copper N-heterocyclic carbene catalysis with microwave-assisted heating in an aqueous solvent. The products were symmetrical N1–N1′-bis-1H-1,2,3-triazoles. Additional syntheses utilized dialkynes and organic azides to prepare symmetrical C4–C4′-bis-1H-1,2,3-triazoles. Pure products were often obtained directly when water was used as the solvent with microwave-assisted heating. Results are given for experiments using conventional heating or no heating. Sonication results are given for a reaction where microwave-assisted heating was unsatisfactory. Full article

The antimicrobial properties of a series of anionic bis(carbene) silver complexes Na₃[Ag(NHC^R)₂] were investigated (2a–2g and 2c′, where NHC^R is a 2,2′-(imidazol-2-ylidene)dicarboxylate-type N-heterocyclic carbene). The complexes were synthesized by the interaction of imidazolium dicarboxylate compounds with silver oxide in the presence of aqueous sodium hydroxide. Complexes 2f,g were characterized analytically and spectroscopically, and the ligand precursor 1f and complexes 2c and 2g were structurally identified by X-ray diffraction methods. The anions of 2c and 2g, [Ag(NHC^R)₂]³⁻, showed a typical linear disposition of C_carbene-Ag-C_carbene atoms and an uncommonly eclipsed conformation of carbene ligands. The antimicrobial properties of complexes 2a–g, which contains chiral (2b–2e and 2c′) and non-chiral derivatives (2a,f,g), were evaluated against Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and a Gram-positive bacterium, Staphylococcus aureus. From the observed values of the minimal inhibitory concentration and minimal bactericidal concentration, complexes 2a and 2b showed the best antimicrobial activity against all strains. An interesting chirality–antimicrobial relationship was found, and eutomer 2c′ showed better activity than its enantiomer 2c against the three bacteria. Furthermore, these complexes were investigated experimentally and theoretically by ¹⁰⁹Ag nuclear magnetic resonance, and the electronic and steric characteristics of the dianionic carbene ligands were also examined. Full article