Exploring the role of ionic liquids to tune the polymorphic outcome of organic compounds

Alkyl-templated cocrystallization of long-chain 1-bromoalkanes by lipid-like ionic liquids

The serendipitous discovery of an unorthodox ionic cocrystallization system using 2-mercaptothiazolium-based ionic liquids as a crystallization milieu paves the way for the first report of crystal structures of long-chain 1-bromoalkanes. We used single crystal X-ray diffraction to determine the structures of 1-bromo-hexadecane and 1-octadecane with the aid of ionic liquids with alkyl side chains of equivalent length to the bromoalkane at room temperature. Long alkyl chains in combination with σ-hole interactions from strategically placed sulfur motifs synergistically function to crystallize the 1-bromoalkanes.

Bridging the crystal and solution structure of a series of lipid-inspired ionic liquids

A series of 1,2-dimethylimidazolium ionic liquids bearing a hexadecyl alkyl chain are thoroughly examined via X-ray crystallography. The crystal structures reveal several key variations in the non-covalent interactions in the lipid-like salts. Specifically, distinct cation-cation π interactions are observed when comparing the bromide and iodide structures. Changing the anion to bis(trifluoromethane)sulfonimide (Tf₂N^-) changes these cation-cation π interactions with anion⋯π interactions. Additionally, several well-defined geometries of the cations are noted based on torsion and core-plane angles of the alkyl chains. Hirshfeld surface analysis is used to distinguish the interactions and geometries in the solid state, helping to reveal characteristic structural fingerprints for the compounds. The solid-state structures of the ionic liquids are correlated with the solution-state structures through UV-vis spectroscopic studies, further emphasizing the importance of the π interactions in the formation of aggregates. Finally, we investigated the thermal properties of the ionic liquids, revealing complex phase transitions for the iodide-containing species. These phase transitions are further rationalized via the analysis of the data gathered from the structures of the other crystallized salts.

Synthesis and Biological Evaluation of Amphotericin B Formulations Based on Organic Salts and Ionic Liquids against Leishmania infantum

Nowadays, organic salts and ionic liquids (OSILs) containing active pharmaceutical ingredients (APIs) are being explored as drug delivery systems in modern therapies (OSILs-API). In that sense, this work is focused on the development of novel OSILs-API based on amphotericin B through an innovative procedure and the evaluation of the respective biological activity against Leishmania infantum. Several ammonium, methylimidazolium, pyridinium and phosphonium organic cations combined with amphotericin B as anion were synthesized in moderate to high yields and high purities by the water-reduced buffer neutralization method. All prepared compounds were characterized to confirm the desired chemical structure and the specific optical rotation ([α]_D²⁵) was also determined. The biological assays performed on L. infantum promastigotes showed increased activity against this parasitic disease when compared with the starting chloride forms and amphotericin B alone, highlighting [P_6,6,6,14][AmB] as the most promising formulation. Possible synergism in the antiprotozoal activity was also evaluated for [P_6,6,6,14][AmB], since it was proven to be the compound with the highest toxicity. This work reported a simple synthetic method, which can be applied to prepare other organic salts based on molecules containing fragile chemical groups, demonstrating the potential of these OSILs-AmB as possible agents against leishmaniasis.

Polymorph control by designed ultrasound application strategy: The role of molecular self-assembly

Molecular self-assembly plays a vital role in the nucleation process and sometimes determines the nucleation outcomes. In this study, ultrasound technology was applied to control polymorph nucleation. For the first time, different ultrasonic application methods based on the nucleation mechanisms have been proposed. For PZA-water and DHB-toluene systems that the molecular self-assembly in solution resembles the synthon in crystal structure, ultrasound pretreatment strategy was conducted to break the original molecular interactions to alter the nucleated form. When the solute molecular self-associates can't give sufficient information to predict the nucleated polymorph like INA-ethanol system, the method of introducing continuous ultrasonic irradiation in the nucleation stage was applied. The induction of ultrasound during nucleation process can break the original interactions firstly by shear forces and accelerate the occurrence of nucleation to avoid the reorientation and rearrangement of solute molecules. These strategies were proved to be effective in polymorph control and have a degree of applicability.

Polymorphs and Isostructural Cocrystals of Dexamethasone: Towards the improvement of aqueous solubility

Dexamethasone (DEX) is a corticosteroid drug used to treat arthritis, asthma, and considered as a promising drug for the treatment of Covid-19. The major drawback of DEX is its poor...

Use of additives to regulate solute aggregation and direct conformational polymorph nucleation of pimelic acid

Understanding the nucleation pathway and achieving regulation to produce the desired crystals are mutually beneficial. The authors previously proposed a nucleation pathway of conformational polymorphs in which solvation and solute self-assembly could affect the result of the conformational rearrangement and further nucleation outcomes. Based on this, herein α,ω-alkanedi-carb-oxy-lic acids (DAn, where n represents the number of carbon atoms in the molecule, n = 2-6, 8-11) were designed as homologous additives to interfere with the self-assembly of pimelic acid (DA7) to further induce the form II compound, which differs from form I only in conformation. Interestingly, longer-chain additives (DA6-11) have a stronger form II-inducing ability than short-chain ones (DA2-4). In addition, an apparent gradient of the degree of interference with solute self-assembly, consistent with form II-inducing ability, was detected by infrared and nuclear magnetic resonance spectroscopy. The calculated molecular electrostatic potential charges also clearly indicate that additive-solute electrostatic interactions gradually increase with increasing carbon chain length of the additives, reaching a maximum value with DA6-11. This novel use of additives demonstrates a direct link between solute aggregation and conformational polymorph nucleation.

Recycling Old Antibiotics with Ionic Liquids

Antibiotics are considered one of the great "miracles" of the 20th century. Now in the 21st century in the post-antibiotic era, the miracle is turning into a nightmare, due to the growing problem of the resistance of microorganisms to classic antimicrobials and the non-investment by the pharmaceutical industry in new antimicrobial agents. Unfortunately, the current COVID-19 pandemic has demonstrated the global risks associated with uncontrolled infections and the various forms of impact that such a pandemic may have on the economy and on social habits besides the associated morbidity and mortality. Therefore, there is an urgent need to recycle classic antibiotics, as is the case in the use of ionic liquids (ILs) based on antibiotics. Thus, the aim of the present review is to summarize the data on ILs, mainly those with antimicrobial action and especially against resistant strains. The main conclusions of this article are that ILs are flexible due to their ability to modulate cations and anions as a salt, making it possible to combine the properties of both and multiplying the activity of separate cations and anions. Also, these compounds have low cost methods of production, which makes it highly attractive to explore them, especially as antimicrobial agents and against resistant strains. ILs may further be combined with other therapeutic strategies, such as phage or lysine therapy, enhancing the therapeutic arsenal needed to fight this worldwide problem of antibacterial resistance. Thus, the use of ILs as antibiotics by themselves or together with phage therapy and lysine therapy are promising alternatives against pathogenic microorganisms, and may have the possibility to be used in new ways in order to restrain uncontrolled infections.

Probing the structural pathway of conformational polymorph nucleation by comparing a series of α,ω-alkanedicarboxylic acids

Herein the nucleation pathway of conformational polymorphs was revealed by studying the relationships and distinctions among a series of α,ω-alkanedicarboxylic acids [HOOC-(CH2) n-2-COOH, named DAn, where n = 5, 7, 9, 11, 13, 15] in the solid state and in solution. Their polymorphic outcomes, with the exception of DA5, show solvent dependence: form I with conformation I crystallizes from solvents with hydrogen-bond donating (HBD) ability, whereas form II with conformation II crystallizes preferentially from solvents with no HBD ability. In contrast, form II of DA5 does not crystallize in any of the solvents used. Quantum mechanical computation showed that there is no direct conformational link between the solvents and the resultant polymorphic outcomes. Surprisingly, solute aggregates were found in no-HBD solvents by Fourier transform infrared spectroscopy, and only monomers could be detected in HBD solvents, suggesting stronger solvation. Furthermore, it was found that all six compounds including DA5 followed the same pattern in solution. Moreover, crystal-packing efficiency calculations and stability tests stated that dimorphs of DA5 bear a greater stability difference than others. These suggest that the rearrangement from conformation II to I could not be limited by hard desolvation in HBD solvents, where form I was also obtained. In other systems, metastable II was produced in the same solvents, probably as a result of the rearrangement being limited by hard desolvation. In this work, a comparative study uncovers the proposed nucleation pathway: difficulty in desolvation has a remarkable effect on the result of rearrangement and nucleation outcome.

Solubility Studies of Cyclosporine Using Ionic Liquids

Six ionic liquids (ILs) were selected based on their chemical and physical properties to study the solubility of cyclosporine A. Of these, cyclosporine exhibited higher room temperature solubility in 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) than in acetone, an effective molecular solvent used to solubilize and purify cyclosporine. The solubility of cyclosporine in the ILs dramatically increased at higher temperatures, a critical factor that cannot be varied in a wide range with low boiling molecular solvents. The differences in solubility were explored for cyclosporine purification. Cyclosporine was purified up to ∼93% with n-butylammonium acetate ([C₄NH₃][OAc]) and could be further purified to 95% using an IL/organic solvent biphasic system. After purification, cyclosporine was recovered as an amorphous solid using the ILs.

A mononuclear tantalum catalyst with a peroxocarbonate ligand for olefin epoxidation in compressed CO2

A mononuclear tantalum complex bonded to a peroxocarbonate ligand has been proved to be particularly important in the epoxidation reactions.

Cocrystal formation by ionic liquid-assisted grinding: case study with cocrystals of caffeine

Liquid assisted grinding using imidazolium-based ionic liquids (IL-AG) was found to be effective in isolation of cocrystals and cocrystal polymorphs.