Systematic Synthesis and Properties Evaluation of Dicationic Ionic Liquids, and a Glance Into a Potential New Field

A Combined Experimental/Computational Study of Dicationic Ionic Liquids with Bromide and Tungstate Anions

A panel of dicationic ionic liquids (DILs) with different rigid xylyl (ortho, meta, para) spacers and different anions (bromide and tungstate) has been synthetised and characterised through different experimental and computational techniques. Differences and analogies between the systems are analysed using information derived from their DFT structures, semiempirical dynamics, thermal behaviour, and catalytic properties versus the well-known reaction of CO2 added to epichlorohydrin. A comparison between the proposed systems and some analogues that present non-rigid spacers shows the key effect displayed by structure rigidity on their characteristics. The results show an interesting correlation between structure, flexibility, properties, and catalytic activity.

Crystal structure of 3,3′-(1,4-phenylenebis(methylene))bis(1-allyl-1H-imidazol-3-ium) bis(hexafluoro phosphate)(V), C10H12F6N2P

[C10H11N2 +, PF6 −], triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 8.9854(3) Å, b = 9.1004(3) Å, c = 9.2312(3) Å, α = 66.667(3)°, β = 74.875(3)°, γ = 74.024(3)°, V = 656.40(4) Å3, Z = 2, Rgt (F) = 0.0513, wRref (F 2) = 0.1515, T = 296(2) K.

Physico-Chemical Properties of Magnetic Dicationic Ionic Liquids with Tetrahaloferrate Anions

A series of imidazolium-based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl3 Br]- as counter ion have been synthesized. The synthesized DcILs are characterized by using FTIR and Raman spectroscopy as well as mass spectrometry, along with single-crystal XRD analysis. Physicochemical properties such as solubility, thermal stability and magnetic susceptibility are also measured. These compounds show low melting points, good solubility in water and organic solvents, thermal stability, and paramagnetism. The products of molar susceptibility and temperature (χmol ⋅T) for the synthesized DcILs have been found between 4.05 to 4.79 emu mol-1  K Oe-1 and effective magnetic moment values have also been determined to be compared to that expected from the spin-only approximation.

Assessing the Suitability of a Dicationic Ionic Liquid as a Stabilizing Material for the Storage of DNA in Aqueous Medium

The present study has been undertaken with an objective to find out a suitable medium for the long-term stability and storage of the ct-DNA structure in aqueous solution. For this purpose, the potential of a pyrrolidinium-based dicationic ionic liquid (DIL) in stabilizing ct-DNA structure has been investigated by following the DNA-DIL interaction. Additionally, in order to understand the fundamental aspects regarding the DNA-DIL interaction in a comprehensive manner, studies are also done by employing structurally similar monocationic ionic liquids (MILs). The investigations have been carried out both at ensemble-average and single molecular level by using various spectroscopic techniques. The molecular docking study has also been performed to throw more light into the experimental observations. The combined steady-state and time-resolved fluorescence, fluorescence correlation spectroscopy, and circular dichroism measurements have demonstrated that DILs can effectively be used as better storage media for ct-DNA as compared to MILs. Investigations have also shown that the extra electrostatic interaction between the cationic head group of DIL and the phosphate backbone of DNA is primarily responsible for providing better stabilization to ct-DNA, retaining its native structure in aqueous medium. The outcomes of the present study are also expected to provide valuable insights in designing new polycationic IL systems that can be used in nucleic acid-based applications.

The Structure-Property Relationship of Pyrrolidinium and Piperidinium-Based Bromide Organic Materials

Two couples of dicationic ionic liquids, featuring pyrrolidinium and piperidinium cations and different linker chains, were prepared and characterized. 1,1'-(propane-1,3-diyl)bis(1-methylpyrrolidinium) bromide, 1,1'-(octane-1,8-diyl)bis(1-methylpyrrolidinium) bromide, 1,1'-(propane-1,3-diyl)bis(1-methylpiperidinium) bromide, and 1,1'-(octane-1,8-diyl)bis(1-methylpiperidinium) bromide were synthesized in quantitative yields and high purity and thermally characterized through TGA and DSC analysis. In this study, we propose a preliminary comparative evaluation of the effect of the linker chain length and of the size of the aliphatic ammonium ring on the thermal and solubility properties of bromide dicationic ionic liquids.

Scalable and Room-Temperature Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Active Lithium Tetramethylene-Tethered Bis[N-(N'-butylimidazol-2-ylidene)] N-Heterocyclic Carbene as a Lewis Acid Organocatalyst

The Lewis acid organocatalytic system of lithium tetramethylene-tethered bis[N-(N'-butylimidazol-2-ylidene)] N-heterocyclic carbene (1,4-bisNHC) including lithium benzyloxide and benzyl alcohol has been successfully utilized in the ring-opening polymerization (ROP) of ε-caprolactone (CL) for the first time. The catalytic performance of this organic catalyst in the synthesis of high-molecular-weight polymers was investigated via bulk polymerization using different combinations of tetramethylene-tethered bis[N-(N'-butylimidazolium)] hexafluorophosphate (1,4-bis[Bim][PF₆]), benzyl alcohol (BnOH), and n-butyl lithium (nBuLi) ([1,4-bis[Bim][PF₆]]/[BnOH]/[nBuLi]) with the molar ratios of 0:2:2, 1:1:3, 1:2:3, and 1:2:4. The results showed that the molar ratio of 1:2:3 efficiently and rapidly initiated the bulk ROP of CL at room temperature with a high molar ratio of CL to 1,4-bis[Bim][PF₆] of 3000/1 and produced the highest number of average-molecular-weight (M_n) poly(ε-caprolactone) (103,057 g mol^-1) with the dispersity (D̵) and %conversion of 1.73 and 98% in a short period of time (152 s). From comparative studies, the relative polymerization rates of the bulk ROP of CL with different [1,4-bis[Bim][PF₆]]/[BnOH]/[nBuLi] molar ratios was determined in the following order: 1:2:4 > 1:1:3 > 1:2:3 > 0:2:2. For mechanistic investigation, the bulk ROP mechanism of CL with our organic catalyst was proposed through the intramolecular bis-lithium-carbene interaction pathway for 1,4-bisNHC_1,1,3, 1,4-bisNHC_1,2,3, and 1,4-bisNHC_1,2,4 systems.

Enhanced In Vitro Antiviral Activity of Hydroxychloroquine Ionic Liquids against SARS-CoV-2

The development of effective antiviral drugs against SARS-CoV-2 is urgently needed and a global health priority. In light of the initial data regarding the repurposing of hydroxychloroquine (HCQ) to tackle this coronavirus, herein we present a quantitative synthesis and spectroscopic and thermal characterization of seven HCQ room temperature ionic liquids (HCQ-ILs) obtained by direct protonation of the base with two equivalents of organic sulfonic, sulfuric and carboxylic acids of different polarities. Two non-toxic and hydrophilic HCQ-ILs, in particular, [HCQH2][C1SO3]2 and [HCQH2][GlcCOO]2, decreased the virus-induced cytopathic effect by two-fold in comparison with the original drug, [HCQH2][SO4]. Despite there being no significant differences in viral RNA production between the three compounds, progeny virus production was significantly affected (p < 0.05) by [HCQH2][GlcCOO]2. Overall, the data suggest that the in vitro antiviral activities of the HCQ-ILs are most likely the result of specific intra- and intermolecular interactions and not so much related with their hydrophilic or lipophilic character. This work paves the way for the development of future novel ionic formulations of hydroxychloroquine with enhanced physicochemical properties.

Thermal Kinetics of Monocationic and Dicationic Pyrrolidinium-Based Ionic Liquids

This work presents an in-depth kinetic thermal degradation comparison between traditional monocationic and the newly developed dicationic ionic liquid (IL), both coupled with a bromide (Br⁻) anion by using non-isothermal thermogravimetric analysis. Thermal analyses of 1-butyl-1-methylpyrrolidinium bromide [C₄MPyr][Br] and 1,4-bis(1-methylpyrrolidinium-1-yl)butane dibromide [BisC₄MPyr][Br₂] were conducted at a temperature range of 50–650 °C and subjected to various heating rates, which are 5, 10, 15, 20 and 25 °C/min. Thermogravimetric analysis revealed that dicationic IL, [BisC₄MPyr][Br₂] is less thermally stable compared to monocationic [C₄MPyr][Br]. A detailed analysis of kinetic parameters, which are the activation energy (E_a) and pre-exponential factor (log A), was calculated by using Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Starink. This study revealed that the average E_a and log A of [BisC₄MPyr][Br₂] are lower than [C₄MPyr][Br], which may be contributed to by its low thermal stability. Conclusively, it proved that the E_a and log A of ILs are strongly related to the thermal stability of ILs.

Recent Advances in Imidazolium-Based Dicationic Ionic Liquids as Organocatalysts: A Mini-Review

Imidazolium-based dicationic ionic liquids (DILs) are gaining considerable space in the field of organocatalysis mainly due to the opportunities in offering new possible applicable structural variations. In addition to the well-known variables which made the ionic liquids (ILs) famous as the type of cation and anion used, the nature of the molecular spacer moiety turns out a further possibility to improve some physicochemical properties, for example, solubility, acidity, electrochemical behavior, and so on. For this reason, this class of ionic liquids has been considered as possible competitors to their corresponding monocationic salts in replacing common catalysts in organic synthesis, particularly in cases in which their bidentate nature could positively affect the catalytic activity. This mini-review is intended to highlight the progress carried out in the last six years in the field of organocatalysis, including DILs as such and as hybrids with polymers, nanomaterials, and composites.

Improved carbon dioxide absorption in double-charged ionic liquids

Four divalent ionic liquids based on imidazolium cations with alkyl or ether functionalized side-chains were synthesised and characterized: 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)bromide, [tetraEG(mim)₂][Br]₂, 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)acetate, [tetraEG(mim)₂][OAc]₂, 1-butyl-3-methylimidazolium malonate, [C₄mim]₂[Mal], and 3-butyl-1-methylimidazolium glutarate, [C₄mim]₂[Glut]. Their densities vary between 1.1 and 1.5 g cm^-3 and their viscosities between 0.2 and 4 Pa s at 353 K. We found that the molar volumes are not additive, especially in the case of the divalent ionic liquids based on the double-charged imidazolium cations, meaning that they cannot be predicted using common group contribution methods. The reason for this behaviour could be explained by the structure of the cations, which is dominated by intramolecular hydrogen bonding. The carboxylate-based divalent ionic liquids absorb reversibly large quantities of carbon dioxide following a chemical mechanism described before. An improved 1 : 1 stoichiometry is achieved both in a double-charged imidazolium acetate ionic liquid and in imidazolium carboxylate salts with double charged anions. This behaviour places these ionic liquids amongst the best performing for carbon dioxide absorption.

Expanding the Chemical Space of Benzimidazole Dicationic Ionic Liquids

Benzimidazole dicationic ionic liquids (BDILs) have not yet been widely explored in spite of their potential. Therefore, two structurally related families of BDILs, paired with either bromide or bistriflimide anions and bearing alkyl spacers ranging from C3 to C6, have been prepared. Their thermal properties have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), while their electrical properties have been assessed by cyclic voltammetry (CV). TG analysis confirmed the higher stability of the bistriflimide BDILs over the bromide BDILs, with minor variation within the two families. Conversely, DSC and CV allowed for ascertaining the role played by the spacer length. In particular, the thermal behavior changed dramatically among the members of the bistriflimide family, and all three possible thermal behavior types of ILs were observed. Furthermore, cyclic voltammetry showed different electrochemical window (C3(C1BenzIm)2/2Tf2N < C4(C1BenzIm)2/2Tf2N, C5(C1BenzIm)2/2Tf2N < C6(C1BenzIm)2/2Tf2N) as well as a reduction peak potential, shape, and intensity as a function of the spacer length. The results obtained highlight the benefit of accessing a more structurally diverse pool of compounds offered by dicationic ILs when compared to the parent monocationic ILs. In particular, gains are to be found in the ease of fine-tuning their properties, which translates in facilitating further investigations toward BDILs as designer solvents and catalysts.

Fe-functionalized paramagnetic sporopollenin from pollen grains: one-pot synthesis using ionic liquids

The preparation of Fe-decorated sporopollenins was achieved using pollen grains and an ionic liquid as solvent and functionalizing agent. The integrity of the organic capsules was ascertained through scanning electron microscopy studies. The presence of Fe in the capsule was investigated using FT-IR, X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Electron paramagnetic resonance and magnetization measurements allowed us to demonstrate the paramagnetic behavior of our Fe-functionalized sporopollenin. A few potential applications of pollen-based systems functionalized with magnetic metal ions via ionic liquids are discussed.

1, 1'-Sulfinyldiethylammonium Bis (Hydrogen Sulfate) as a Recyclable Dicationic Ionic Liquid Catalyst for the Efficient Solvent-free Synthesis of 3, 4-Dihydropyrimidin-2(1H)-ones via Biginelli Reaction

OBJECTIVE

A facile and efficient method for synthesis of 3, 4-dihydropyrimidin-2(1H)-ones via Biginelli reaction catalyzed by a novel dicationic Brönsted acidic ionic liquid, [(EtNH2)2SO][HSO4]2, has been successfully developed.

MATERIALS AND METHODS

3, 4-Dihydropyrimidin-2(1H)-ones were synthesized through one-pot condensation of aromatic aldehydes, ethyl acetoacetate, and urea under solvent-free conditions using [(EtNH2)2SO][HSO4]2 as a novel catalyst. The progress of the reaction was monitored by thin-layer chromatography (ethyl acetate / n-hexane = 1 / 5). The products have been characterized by IR, 1H NMR, 13C NMR, and also by their melting points.

RESULTS

In this research, a library of dihydropyrimidinone derivatives was synthesized via Biginelli reaction under solvent-free conditions at 120oC using [(EtNH2)2SO][HSO4]2 as a catalyst. Various aromatic aldehydes, as well as heteroaromatic aldehydes, were employed, affording good to high yields of the corresponding products and illustrating the substrate generality of the present method. In addition, the prepared dicationic Brönsted acidic ionic liquid can be easily recovered and reused.

CONCLUSION

1, 1'-Sulfinyldiethylammonium bis (hydrogen sulfate), as a novel dicationic ionic liquid, can act as a highly efficient catalyst for the synthesis of 3, 4-dihydropyrimidin-2(1H)-ones under solvent-free conditions.

Exploiting pollen and sporopollenin for the sustainable production of microstructures

Pollen grains can be easily processed in order to obtain versatile and sustainable microcapsules.

1-Octyl-3-(3-(1-methylpyrrolidiniumyl)propyl)imidazolium Bis(trifluoromethane)sulfonimide

The title compound 1-octyl-3-(3-(1-methylpyrrolidiniumyl)propyl)imidazolium bis(trifluoromethane)sulfonimide was prepared in three steps. This asymmetrical dicationic ionic liquid (ADIL) is composed of two different positively charged head groups (1-octylimidazolium and methylpyrrolidinium cations), which are linked through a propyl alkyl chain and by two bis(trifluoromethane)sulfonimide anions. The final ADIL was obtained by a simple metathesis reaction of the corresponding dibromide ionic liquid, in turn prepared by alkylation of 3-(3-bromopropyl)-1-propylimidazolium bromide. The ADIL structure and those of its precursors were confirmed through NMR and infrared spectroscopy, and the thermal properties of all compounds were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Density, solubility, and viscosity were measured for the prepared compounds.

pH-Responsive Carboxymethylcellulose Nanoparticles for 68Ga-WBC Labeling in PET Imaging

Carboxymethylcellulose (CMC) is a well-known pharmaceutical polymer, recently gaining attention in the field of nanomedicine, especially as a polyelectrolyte agent for the formation of complexes with oppositely charged macromolecules. Here, we report on the application of pH-sensitive pharmaceutical grade CMC-based nanoparticles (NP) for white blood cells (WBC) PET imaging. In this context and as an alternative to ^99mTc-HMPAO SPECT labeling, the use of ⁶⁸Ga³⁺ as PET radionuclide was investigated since, at early time points, it could provide the greater spatial resolution and patient convenience of PET tomography over SPECT clinical practices. Two operator-friendly kit-type formulations were compared, with the intention of radiolabeling within a short time (10 min), under mild conditions (physiological pH, room temperature) and in agreement with the actual clinically applied guidelines. NP were labeled by directly using ⁶⁸Ga³⁺ eluted in HCL 0.05 N, from hospital suited ⁶⁸Ge/⁶⁸Ga generator and in absence of chelator. The first kit type approach involved the application of ⁶⁸Ga³⁺ as an ionotropic gelation agent for in-situ forming NP. The second kit type approach concerned the re-hydration of a proper freeze-dried injectable NP powder. pH-sensitive NP with 250 nm average diameter and 80% labeling efficacy were obtained. The NP dispersant medium, including a cryoprotective agent, was modulated in order to optimize the Zeta potential value (−18 mV), minimize the NP interaction with serum proteins and guarantee a physiological environment for WBC during NP incubation. Time-dependent WBC radiolabeling was correlated to NP uptake by using both confocal and FT-IR microscopies. The ready to use lyophilized NP formulation approach appears promising as a straightforward ⁶⁸Ga-WBC labeling tool for PET imaging applications.

Unexpected Intrinsic Lability of Thiol-Functionalized Carboxylate Imidazolium Ionic Liquids

New thiol-functionalized carboxylate ionic liquids (ILs), varying both for the cation and for the anion structures, have been prepared as new potential redox switching systems by reacting either 3-mercapto propionic acid (3-MPA) or N-acetyl-cysteine (NAC) with commercially available methyl carbonate ILs. Different ratios of thiol/disulfide ILs were obtained depending both on the acid employed in the neutralization reaction and on the reaction conditions used. Surprisingly, the imidazolium ILs displayed limited thermal stability which resulted in the formation of an imidazole 2-thione and a new sulfide ionic liquid. Conversely, the formation of the imidazole 2-thione was not observed when phosphonium disulfide ILs were heated, thus confirming the involvement of the imidazolium ring in an unexpected side reaction. An insight into the mechanism of the decomposition has been provided by means of DFT calculations.

Remarkable Effect of [Li(G4)]TFSI Solvate Ionic Liquid (SIL) on the Regio- and Stereoselective Ring Opening of α-Gluco Carbasugar 1,2-Epoxides

Carba analogues of biologically relevant natural carbohydrates are promising structures for the development of future drugs endowed with enhanced hydrolytic stability. An open synthetic challenge in this field is the optimization of new methodologies for the stereo- and regioselective opening of α-gluco carbasugar 1,2-epoxides that allow for the preparation of pseudo mono- and disaccharides of great interest. Therefore, we investigated the effect of Lewis acids and solvate ionic liquids (SILs) on the epoxide ring opening of a model substrate. Of particular interest was the complete stereo- and regioselectivity, albeit limited to simple nucleophiles, toward the desired C(1) isomer that was observed using LiClO4. The results obtained with SILs were also remarkable. In particular, Li[NTf2]/tetraglyme ([Li(G4)]TFSI) was able to function as a Lewis acid and to direct the attack of the nucleophile preferentially at the pseudo anomeric position, even with a more complex and synthetically interesting nucleophile. The regioselectivity observed for LiClO4 and [Li(G4)]TFSI was tentatively ascribed to the formation of a bidentate chelating system, which changed the conformational equilibrium and ultimately permitted a trans-diaxial attack on C(1). To the best of our knowledge, we report here the first case in which SILs were successfully employed in a ring-opening process of epoxides.

Insights into the levulinate-based ionic liquid class: synthesis, cellulose dissolution evaluation and ecotoxicity assessment

New levulinate ionic liquids (ILs) were able to dissolve cellulose in high amounts. The ecotoxicity profiles of these new ILs were also assessed.

Levulinate amidinium protic ionic liquids (PILs) as suitable media for the dissolution and levulination of cellulose

Levulinate protic ionic liquids allow for the dissolution and the levulination of their parent polysaccharide.

An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations

Dicationic ionic liquids (DILs) are a subclass of the ionic liquid (IL) family and are characterized by two cationic head groups linked by means of a spacer. While DILs are increasingly attracting interest due to their peculiar physico-chemical properties, there is still a lack of understanding of their intermolecular interactions. Herein, we report our investigations on the intermolecular vibrational modes of two bromide DILs and of a bistriflimide DIL. The minimal possible neutral cluster of ions was studied as a simplified model of these systems and was optimized at the DFT level. Normal modes of two sandwich-like conformers were then calculated using the harmonic approximation with analytical computation of the second derivatives of molecular energy with respect to the atomic coordinates. The calculated spectra were compared to far-infrared experimental spectra and two groups of peaks over three, for the two bromide DILs, and three over five, for the Tf₂N⁻ DIL, were described by the proposed neutral cluster model. Therefore, this model represents a reliable and computationally affordable model for the exploration of the intermolecular interactions of this kind of system.

The minimal cluster of ions represents a reliable and computationally affordable model for the exploration of the intermolecular interactions of dicationic ionic liquids.