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Synthesis of heterocyclic compounds is fundamental for all the research area in chemistry, from drug synthesis to material science. In this framework, catalysed synthetic methods are of great interest to effective reach such important building blocks. In this review, we will report on some selected examples from the last five years, of the major improvement in the field, focusing on the most important conventional catalytic systems, such as transition metals, organocatalysts, to more sustainable ones such as photocatalysts, iodine‐catalysed reaction, electrochemical reactions and green innovative methods. [ABSTRACT FROM AUTHOR]

One of the main causes of mortality in humans continues to be infectious diseases. Scientists are searching for new alternatives due to the fast increase in resistance of some harmful bacteria to the frontline antibiotics. To effectively treat pathogenic infections, it is crucial to design antibiotics that can prevent the development of pathogenic resistance. For this purpose, a set of 39 quaternary pyridinium and bis-pyridinium salts with different lengths of side alkyl or fluorinated chains, heterocyclic spacers, and counter ions were tested on diverse reference bacterial ATCC (American Type Culture Collection) strains, such as S. aureus and E. coli. Subsequently, 6 out of the 39 pyridinium salts showing relevant MIC (Minimum Inhibitory Concentration) values were tested on clinically isolated, resistant strains of S. aureus, S. epidermids, S. haemolyticus, K. pneumoniae, A. baumannii, and P. aeruginosa. Additional tests have been performed to assess if the minimum concentration detected through MIC assay may limit the growth of biofilms. [ABSTRACT FROM AUTHOR]

Supramolecular eutectogels were obtained from the gelation of 1,3 : 2,4‐dibenzylidene‐D‐sorbitol (DBS) in cholinium chloride‐based deep eutectic solvents (DES), differing for the nature of the hydrogen bond donor. Ethylene glycol, diethylene glycol, triethylene glycol, glycerol and urea were tested. Soft materials were fully characterized, determining critical gelation concentration, gel‐sol transition temperatures and mechanical properties. Furthermore, to have information about the organization of the gelator in the tridimensional network, resonance light scattering, circular dichroism and microscopy investigations were performed. Eutectogels were used as organized "vessels" to perform the L‐proline catalyzed Michael addition reaction. The probe reaction was carried out in gel phase and in DES solution. Data collected shed light on the effect that gel microenvironment exerts on the outcome of the reaction. In general, gel phases allowed having comparable or even better results than the ones collected in DES solution, with better results obtained in soft materials with the highest organization, as accounted for by the presence of larger aggregates and the occurrence of stronger intermolecular interactions. In turn, this accounts also for the effect of substrates structure that indicates that better yields could be obtained in the presence of more flexible nucleophile and dienones, having more extended π‐surface. [ABSTRACT FROM AUTHOR]

With the aim to obtain targeted chemotherapeutic agents, imidazolium and ammonium-based folate salts were synthesized. Their photophysical behavior was investigated both in buffer and buffer/DMSO solution as well as in solid phase, performing UV-vis and fluorescence investigations. Properties of the aggregates were also analyzed by dynamic light scattering. Gelation ability of the salts was analyzed in biocompatible solvents, and gel phases obtained were characterized by determining critical gelation concentrations and gel-solution transition temperatures. Insights about gelator interactions in the tridimensional network were also gained performing ATR-FTIR investigation. Properties of soft materials were further analyzed performing rheology measurements, scanning electron microscopy, fluorescence and resonance light scattering investigations. Antiproliferative activity of organic salts was tested towards two breast cancer cell lines, expressing different levels of folate receptor, namely MDA-MB-231 and MCF-7, and a normal epithelial cell line, like h-TER T-RPE-1, by using MTT assay. Dichlodihydrofluorescein acetate test was performed to verify the role of oxidative stress in cell death. Finally, antiproliferative activity was also evaluated in gel phase, to verify if salts were able to retain biological activity also after the entrapment in the gelatinous network. Results collected evidence that folate based organic salts were able to behave as targeted chemotherapeutic agents both in solution and gel phase, showing uptake mechanism and selectivity indexes that depend on both cancer cell line nature and salt structure. [ABSTRACT FROM AUTHOR]

The inclusion of fluorine atoms or heterocyclic moiety into drug structures represents a recurrent motif in medicinal chemistry. The combination of these two features is constantly appearing in new molecular entities with various biological activities. This is demonstrated by the increasing number of newly synthesized fluorinated heterocyclic compounds among the Food and Drug Administration FDA-approved drugs. In this review, the biological activity, as well as the synthetic aspects, of 33 recently FDA-approved fluorinated heterocyclic drugs from 2016 to 2022 are highlighted. [ABSTRACT FROM AUTHOR]

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring. [ABSTRACT FROM AUTHOR]

Desulfurization of fuel that avoids the introduction in the atmosphere of toxic sulfur volatile compounds, usually formed during combustion, is a viable strategy to reduce pollution. To find new efficient and eco-sustainable adsorbent materials, bio-based polymers such as chitosan (CS), cellulose (CE) and cellulose acetate (CEOAc) were dissolved in ionic liquids (ILs) to form ionic liquid gels (ILGs). Gelling and swelling ability, porosity, morphology, rheology and mechanical response were studied as a function of the polymer and ionic liquid (IL) used. The best performing gels were tested for fuel desulfurization using a fuel mimicking solution of thiophene (T), benzothiophene (BT) and dibenzothiophene (DBT) in hexane. T was the sulfur compound that adsorbed the fastest on gels, and the effect of different parameters affecting the adsorption process, such as the total concentration of sulfur compounds, volume of fuel, and the contact surface area of the gel, under static or dynamic conditions, was analyzed. Bio-based polymer ILGs proved to be promising adsorbents for fuel desulfurization allowing 84% removal efficiency to be reached for T and 60% for DBT and BT in a multistage apparatus. In addition, gels could be reused up to four times without any leaching of IL or polymer in fuel, proving to be competitive with other adsorbent materials currently used. [ABSTRACT FROM AUTHOR]

Let A be an associative algebra with involution * over a field of characteristic zero. A central *-polynomial of A is a polynomial in non-commutative variables that takes central values in A. Here we prove the existence of two limits called the central *-exponent and the proper central *-exponent that give a measure of the growth of the central *-polynomials and proper central *-polynomials, respectively. Moreover, we compare them with the PI-*-exponent of the algebra. [ABSTRACT FROM AUTHOR]

Natural eutectogels were prepared by combining the properties of amino acids with the ones of deep eutectic solvents. The soft materials obtained were fully characterised by determining the gel–sol transition temperatures and analysing the mechanical and morphological features through rheological measurements and polarised optical microscopy. All eutectogels were tested as catalytic reaction media for the enantioselective aldol reaction and the best performing one was also used to carry out the Michael addition. In both cases, eutectogels proved to have great potential as sustainable reaction media, allowing them to perform processes under mild conditions, affording excellent yields and, in some cases, also good enantiomeric excess. Catalytic soft materials can be reused up to five cycles keeping the stereochemical control of the reaction and using a recommended solvent by recent sustainable solvent guidelines. [ABSTRACT FROM AUTHOR]

Supramolecular gels are a fascinating class of materials, originated by the self‐assembly of low molecular weight molecules. Underpinned by non‐covalent interactions, they find application in a diverse range of fields. Among these, supramolecular gels can be considered as organized, non‐conventional reaction media, able to influence reactivity in a radically different way, compared with what happens in solution. This short review will focus on this aspect, covering literature from 2010 onwards, addressing the application of supramolecular gels as reaction media. In particular, in the first section we explore organocatalytic reactions in gel phase, with wide synthetic relevance, such as aldol and Mannich reactions as well as Friedel Crafts or ester hydrolysis processes. Subsequently, focus is laid on metal‐catalysed reactions, among which relevance is given to widely used reactions like cross‐coupling and click reactions. Then, the final sections describe the use of supramolecular gels as reaction media for photo‐ and biocatalysed processes. [ABSTRACT FROM AUTHOR]

Current concerns for sustainability and the environment make low‐impact materials desirable for environmental remediation and, in particular wastewater treatment. We obtained supramolecular gels of l‐amino acids in the deep eutectic solvent formed by choline chloride and phenylacetic acid. After gel characterization, and investigating gel–sol transition temperatures, gelation kinetics, rheological properties, and morphology, the gels were applied as sorbents to remove cationic dyes from aqueous solutions. The effects of the pH, dye nature, volume, and concentration of wastewater were analyzed, and the best result was obtained with a l‐phenylalanine‐based eutectogel. It can be reused for at least 9 times without losing efficiency, also with dye mixtures. Interestingly, this gel can be loaded onto columns to decolorize flowing solutions, achieving 85 % of removal efficiency in only 10 minutes and allowing its reuse for at least 4 cycles. In terms of adsorption capacity, this eutectogel is competitive with efficient gel‐based dye sorbent systems, with a value 1930 mg/g reached at a high concentration of rhodamine B 479 mg/L. [ABSTRACT FROM AUTHOR]

The cathodic reduction of dicationic imidazolium bromides, whose spacer is either an aliphatic chain or a xylyl group, leads to the formation of the corresponding N‐heterocyclic carbenes (NHCs), which were isolated as the corresponding thiones, after reaction with elemental sulfur. The behaviour of the dications was compared with the corresponding monocations. The behaviour of dicarbenes depends on the nature of the spacer. This study evidenced that dicarbenes deriving from xylyl dications are less stable than the corresponding aliphatic ones (giving lower yields in thiones), due to a debenzylation reaction. On the other hand, the yields in thiones starting from aliphatic dications are higher than the corresponding monocations, suggesting a cooperative reduction at the electrode of the two imidazolium moieties. The cathodic process was confirmed using the co‐electrogenerated hydrogen to reduce 2,2,2‐trifluoroacetophenone to the corresponding alcohol. [ABSTRACT FROM AUTHOR]

Diimidazolium-based organic salts, bearing peptides or amino acids as anions have been synthesised and tested for their gelling ability in biocompatible solvents. These low molecular weight salts were successfully used as gelators in phosphate buffered saline (PBS) solution and ionic liquids. Then, the properties of the obtained soft materials were analysed in terms of melting temperature and gel strength as accounted for by rheological investigations. The gel-phase formation was studied by using UV/Vis and resonance light scattering measurements, whereas the morphology of the soft materials was analysed by using polarised optical microscopy and scanning electron microscopy. To get information about the organisation of the gelator in the gelatinous matrix, X-ray diffraction measurements were performed both on the neat gelators and their gels. The results collected show that the properties of the gel phases, like the thermal stability, the self-repairing ability, the resistance to flow as well as the morphology, are dependent on the nature of the anion. Furthermore, bioassays revealed that the obtained diimidazolium organic salts possessed antimicrobial activity, against gram-negative and gram-positive tester strains. In particular and noteworthy, the diimidazolium organic salts exert a bactericidal capability, which was retained even if they are included in the gel phase. Thus, a novel kind of bioactive soft material was obtained that could be fruitfully employed as a non-covalent coating exerting antibacterial capability. [ABSTRACT FROM AUTHOR]

To gain more insights into the factors acting on the stability of complexes formed by pillar[5]arenes, we investigated the interaction of dimethoxypillar[5]arene with some 1-(n-alkyl)-3-(9-anthracenylmethyl)-imidazolium based organic salts. In particular, we used salts differing in not only the anion nature ([Cl−], [BF4−], [NTf2−] and [SbF6−]) and alkyl chain length (butyl, octyl and dodecylimidazolium derivatives), but also the presence of a hydrogenated or fluorinated tail (octyl and perfluorooctylimidazolium derivatives). Host–guest systems were analysed in solution, solid state and gas phase, using a combined approach of different techniques like fluorescence, 1H NMR, ESI-MS, DSC and DFT calculations. Data collected show that the complex stability is heavily affected by solvent nature. Furthermore, solvent being the same, it increases with the decrease of the alkyl chain length and the anion coordination ability. The joint information obtained from 1H NMR and DFT calculations allows drawing a picture of the complex geometry. On the other hand, fluorescence investigation on the solid state evidences the occurrence of an aggregation enhanced emission process for these systems. [ABSTRACT FROM AUTHOR]

Insights are provided into the properties of molecular gels formed by diimidazolium salts both in 'normal' solvents and ionic liquids. These materials can be interesting for applications in green and sustainable chemistry in which ionic liquids play a significant role, like catalysis and energy. In particular, two positional isomers of a diimidazolium cation have been examined with a wide range of anions for their ability to form gel phases. In particular, di-, tri-, and tetravalent anions bearing aliphatic or aromatic spacers were paired with the divalent cations. The properties of the organo- and ionogels formed have been analyzed by means of several different techniques, including calorimetry, rheology, resonance light scattering, UV/Vis absorption, polarizing optical microscopy, and powder X-ray diffraction measurements. The investigations performed enabled us to obtain a wide range of conductive materials characterized by a high thermal stability and a low corrosiveness of the gelator (organogels) or of both gelator and solvent (ionogels). The information gained should be useful in the broader quest to identify and promote their applications. [ABSTRACT FROM AUTHOR]

Phenylene ethynylene based diimidazolium salts differing in the alkyl chain length borne on the imidazolium ion and anion nature were synthesized. Their properties were studied both in solution and in the solid state. Salts obtained were able to aggregate in organic solvent solution. Aggregate formation was studied by performing concentration dependent measurements using UV-vis, fluorescence and Resonance Light Scattering. Furthermore, features of the aggregates were also investigated in the solid state by means of fluorescence and Scanning Electron Microscopy measurements. Finally, Density Functional Theory calculations were performed to obtain insights into the interaction geometry in the salts investigated. Data collected evidence that aggregation processes are affected by a combined action of different factors derived from the nature of the salt and solvent. The above features also influence the morphology of the aggregates as well as the ability of their thin films to give blue emission. On the whole, information gained could represent a useful starting point for applications of these salts in the optoelectronic field among others. [ABSTRACT FROM AUTHOR]

Nine functionalized dicationic ionic liquids were used to study the base catalyzed mononuclear rearrangement of (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the corresponding triazole at 363 K. Ionic liquids were characterized by the presence of 1-(1-imidazolylmethyl)-3,5-di[1-(3'-octylimidazolylmethyl)]benzene cation, bearing on the structure a neutral imidazole unit as basic functionality. Besides anions generally used for monocationic ionic liquids, such as [Br-], [BF4-], and [NTf2-], also dianions having a rigid aromatic spacer such as 1,4-benzenedicarboxylate, 2,6-naphthalenedicarboxylate, and 1,5- and 2,6-naphthalenedisulfonate were taken into account. Furthermore, to have information about the effect deriving from the spacer rigidity also dianions such as 1,4-butanedicarboxylate and 1,6-hexanedicarboxylate were used. The basic strength of dicationic ionic liquids was determined using the Hammett indicator method. Data collected gave evidence that the outcome of the target reaction was affected by the nature of interactions operating between cation and anion of the ionic liquid used. Quite interestingly, solvent systems used had a good recyclability. Indeed, in some cases, they were reused for four cycles without significant loss in yield. [ABSTRACT FROM AUTHOR]

Supramolecular hydrogels, obtained from small organic molecules, may be advantageous over polymeric ones for several applications, because these materials have some peculiar properties that differentiate them from the traditional polymeric hydrogels, such as elasticity, thixotropy, self-healing propensity, and biocompatibility. We report here the preparation of strong supramolecular pseudopeptide-based hydrogels that owe their strength to the introduction of graphene in the gelling mixture. These materials proved to be strong, stable, thermoreversible and elastic. The concentration of the gelator, the degree of graphene doping, and the nature of the trigger are crucial to get hydrogels with the desired properties, where a high storage modulus coexists with a good thixotropic behavior. Finally, NIH-3T3 cells were used to evaluate the cell response to the presence of the most promising hydrogels. The hydrogels biocompatibility remains good, if a small degree of graphene doping is introduced. [ABSTRACT FROM AUTHOR]