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The molar heat capacity of 1,4-bis(3-methylimidazolium-1-yl)butane bis(trifluoromethylsulfonyl)imide dicationic ionic compound ([C4(MIm)2][NTf2]2) has been studied over the temperature range from 6 to 350 K by adiabatic calorimetry. In the above temperature interval, this compound has been found to form crystal, liquid, and supercooled liquid. For [C4(MIm)2][NTf2]2, the temperature of fusion T°fus = (337.88 ± 0.01) K has been determined by the fractional melting experiments, the enthalpy of fusion ΔfusH° = (52.79 ± 0.28) kJ mol−1 has been measured using the calorimetric method of continuous energy input, and the entropy of fusion ΔfusS° = (156.2 ± 1.7) J K−1 mol−1 has also been evaluated. The standard thermodynamic functions of the studied dicationic ionic compound, namely, the heat capacity Cp°(T), the enthalpy [H°(T) − H°(0)], the entropy S°(T) and the Gibbs free energy [G°(T) − H°(0)] have been calculated on the basis of the experimental data for the temperature range up to 350 K. The results have been discussed and compared with those available in the literature and in the NIST Ionic Liquids Database (ILThermo) for monocationic ionic compounds. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

The present work centered attention on novel ionic liquid (IL) based on dicationic benzimidazolium ion containing amide group (DBimIL) synthesized using dialkylation of N-ethyl benzimidazole to followed with anion exchange reaction. To explore the potential application of ILs, there is a great need to grasp their structural and physical properties. We have developed three different set of DBimIL based ionic liquids with chloride, hexafluorophosphate and perchlorate anions in aqueous media, respectively. Their structural features were studied using 1H, 13C-NMR, FTIR, and HRMS spectroscopy, respectively. The temperature-dependent dielectric characteristics of ILs were closely examined angular frequency in the range of 0.6–125 rad/s from 30 to 150 °C. The relationship between the structural and dielectric properties of ILs established. The dielectric parameters like dielectric constant, dissipation factor and the real part of ac conductivity were found to be affected significantly with the tuning of anionic moieties of ionic liquids. The ability of materials to store a charge in electromagnetic field was measured. From dielectric and electrical studies, to bring to an end, especially in particular way that the present IL systems have an enormous potential for the designing of modern-day energy storage devices. [ABSTRACT FROM AUTHOR]

The molar heat capacity of 1,4-bis(3-methylimidazolium-1-yl)butane bis(trifluoromethylsulfonyl)imide dicationic ionic compound ([C4(MIm)2][NTf2]2) has been studied over the temperature range from 6 to 350 K by adiabatic calorimetry. In the above temperature interval, this compound has been found to form crystal, liquid, and supercooled liquid. For [C4(MIm)2][NTf2]2, the temperature of fusion T°fus = (337.88 ± 0.01) K has been determined by the fractional melting experiments, the enthalpy of fusion ΔfusH° = (52.79 ± 0.28) kJ mol−1 has been measured using the calorimetric method of continuous energy input, and the entropy of fusion ΔfusS° = (156.2 ± 1.7) J K−1 mol−1 has also been evaluated. The standard thermodynamic functions of the studied dicationic ionic compound, namely, the heat capacity Cp°(T), the enthalpy [H°(T) − H°(0)], the entropy S°(T) and the Gibbs free energy [G°(T) − H°(0)] have been calculated on the basis of the experimental data for the temperature range up to 350 K. The results have been discussed and compared with those available in the literature and in the NIST Ionic Liquids Database (ILThermo) for monocationic ionic compounds.

Benzene (BEN) and cyclohexane (CYH), which have very close boiling points and a binary azeotrope, are the most difficult binary components in the separation of aromatic and non-aromatic hydrocarbons. This study further explored the separation mechanism and industrial application prospects of BEN ​+ ​CYH mixtures separated by a dicationic ionic liquid (DIL) [C5(MIM)2][NTf2]2 based on experimental research. The calculation results of the Conductor-like Screening model Segment Activity Coefficient (COSMO-SAC) model show that selectivity and solvent capacity of the DIL are significantly improved. The effects of different anions and cations on the microstructure distribution and diffusion behavior of BEN ​+ ​CYH system were investigated by quantum chemistry (QC) calculations and molecular dynamics (MD) simulations. The results indicate that the anion [NTf2]− has low polarity, uniform charge distribution, and a dual role of hydrogen bonding and π-π bonding, and the cation [C5(MIM)2]2+ has stronger interaction with BEN and higher selectivity than conventional cations. The liquid-liquid extraction and extractive distillation (LLE-ED) process using an optimized 65 mol/mol DIL ​+ ​35 mol/mol H2O mixed solution as the extractant was proposed, which solved the problem of low product purity in the LLE process and high energy consumption in the ED process. Under the best operating conditions, the purity of CYH product was 99.9%, the purity of BEN product was 99.6%, the recovery rate of BEN reached 99.9%, and the recovery rate of DIL reached 99.9%. The heat-integrated LLE-ED process reduced total annual cost by 21.6%, and reduced CO2 emissions by 48.0%, which has broad industrial application prospects.

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.

Bis(trifluoromethylsulfonyl)imide dicationic ionic liquids with an ethereal linker between imidazolium cations have been synthesized. Their thermal stability has been studied, melting points, viscosity, and volatility in vacuum have been measured. The properties of the synthesized ionic liquids with ethereal linkers have been compared with the properties of ionic liquids of a similar structure, but with polymethylene linkers. [ABSTRACT FROM AUTHOR]

Airborne transmission is one of the most unpredictable routes of infection. Nowadays, airborne diseases increase ever than before because of the complex living air environment. Apart from the inorganic particles, active microorganisms including bacteria, viruses, and fungi are incorporated in the pathogens acting as threaten to public health, which can hardly be treated by the traditional air purification methods based on adsorption. Therefore, effective filtration material with antimicrobial activity is demanded to solve the problem. Ionic liquids (ILs) are a category of salts that remain liquid at room temperature. The stable physico-chemical properties and extremely low vapor pressure make them suitable for a wide range of applications. Thanks to the numerous combinations of cations and anions, as well as the ability of inheriting properties from the parent ions, Ils are believed to be a promising industrial material. In recent decades, several Ils, such as imidazolium, pyridinium, pyrrolidinium, phosphonium, and choline, have been found to have antimicrobial activity in their monomeric or polymeric forms. This work focuses on the antimicrobial activity and safety of the latest types of ionic liquids, discussing the synthesis or manufacturing methods of Ils for air purification and filtration. Furthermore, possible applications of Ils antimicrobial materials in medical instruments and indoor environments are mentioned to encourage the scientific community to further explore the potential applications of Ils. [ABSTRACT FROM AUTHOR]

New dicationic ionic liquids (DcILs) based on carboxylic acid-derived, N-acetyl amino acid-derived or bromide anions, and ammonium cations were synthesized and characterized. DcILs were employed as co-solvents to improve the solubility of ibuprofen and ketoprofen belonging to BCS class II. These DcILs demonstrated to be less cytotoxic towards fibroblasts L929 cells and contributed to an augment in the solubility of both drugs when compared with monocationic ionic liquids (McILs). The cytotoxic profile of some of these ILs was established, and when the linker between two ammonium cations was an ether group or a short alkyl chain an IC50 higher than 200 mM for fibroblasts L929 cells was achieved.The anion structure showed to be a key factor in the solubility of both drugs, being the family of carboxylic acid-derived, the one that presented the most significant effect, followed by N-acetyl amino acid-derived and finally bromide. The two dimensional 1H1H– NOESY NMR spectra showed the interaction between the IL and the two oral drugs, responsible for the improvement of their solubility. The lipophilicity (logP) of ibuprofen and ketoprofen reduced in the presence of these new DcILs.

Focused bis-pyridinium based-ionic liquids were successfully synthesized through the quaternization of the selected 1,2-di(pyridin-4-yl)ethane followed by metathetical anion exchange. The synthesized pyridinium derivatives were fully characterized using various NMR-spectroscopic techniques including 1H, 13C, 11B, 31P and 19F NMR. The synthesized compounds were tested for their potential effect against Toxoplasma gondii. It was revealed that compound 5 had higher antiparasitic activity compared to other compounds. Parasitic reduction percentage reached 38, 50, 77 and 79 for groups III, IV, V and VI respectively in the liver with noticed distortion and deformation in tachyzoites’ shape. Surprisingly there was no statistically significant difference between the synthesized compound 5 and the known anti-toxoplasmosis drug pyrimethamine. Histopathological study proved the effectiveness of the synthesized compound 5 on liver, spleen and brain tissues with observed better histological features compared to pyrimethamine treated group. The present investigation may pave the way to the possible use of compound 5 to replace the known drug pyrimethamine with better antiparasitic profile and fewer side effects.

The intermediate di-[EMIM]Cl was synthesized from methyl imidazole and 1,4-dichlorobutane and then reacted with cobalt chloride at 105 °C to prepare a bi-[EMIM]CoCl3 ionic liquid catalyst. The di-[EMIM]CoCl3 catalyst coupled with oxone to remove sulfur-containing organics in octane. The di-[EMIM]CoCl3 catalyst was characterized by HNMR, FTIR, TG, and SEM–EDS. The dibenzothiophene (DBT) was dissolved in octane to prepare a model oil with an initial sulfur content of 500 ppm. Six grams of the model oil was added. The results showed that the optimal dosages of di-[EMIM]CoCl3, oxone (20 wt%), and [BMIM]BF4 extractant were 1 g, 2 g, and 2 g, respectively. At the optimum temperature of 45 °C, 100% of sulfur was removed after 40 min. After di-[EMIM]CoCl3 was recycled five times, the sulfur removal percentage remained above 91%. The sulfur removal percentages for different sulfur-containing organics followed the order of dibenzothiophene (DBT) > benzothiophene (BT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT). The oxidation product was determined to be DBTO2 by GC–MS analysis, and the oxidation mechanism was discussed. The active oxygen atoms of oxone oxidized DBT to form DBTO, and then persulfate oxidized DBTO to DBTO2 via an identical oxidation mechanism. [ABSTRACT FROM AUTHOR]

A series of imidazolium‐based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl3Br]− 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. [ABSTRACT FROM AUTHOR]

This work reports the influence of the dicarboxylate anion (oxalate, malonate succinate, glutarate, adipate, pimelate) on the aggregation process of ionic liquids derived from 1,8-bis(3-methylimidazolium-1-yl)-octane [C 8 (MIM) 2 ] and 1,10-bis(3-methylimidazolium-1-yl)-decano [C 10 (MIM) 2 ] in water solution. The aggregation behavior was investigated using electrical conductivity, nuclear magnetic resonance, transmission electron microscopy, atomic force microscopy, and zeta potential. Results showed that the aggregates have a wormlike morphology. The CAC values for [C 10 (MIM) 2 ]2+ increase in the following order: [Oxa] < [Suc] < [Mal] < [Glu] < [Adi] < [Pim], which indicates a direct relationship with the increase in the number of methylene groups of the dianion spacer. In the case of [C 8 (MIM) 2 ]2+, there was no relationship between the CAC value and the anion's alkyl spacer chain length, which was attributed to the flexibility and complexity of the dynamic behavior of the aggregates. Anions on the nanorganized structures of micelles are oriented in the way that carboxylate groups are at the aggregate surface (forming hydrogen bonds with cationic heads and water), and apolar alkyl chains are in the hydrophobic (downshift) region of the micelles making an arrangement where they also adopt the bend conformation of alkyl chains. The aggregation of dicationic ILs with dicarboxylate anions is a very innovative topic of investigation in the literature, and more research on different structures, system conditions, and techniques could be done to gain a better understanding of these systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract A series of imidazolium‐based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl3Br]− 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.

Two series of DILs based on 1,4-bis(4-methyl-triazolium) phenyl ([p-C6H4(MTAZ)2]2+ = [PHTA]2+) and 1,4-bis (4-methyl-triazolium) 1,1'-perfluoro-phenyl ([p-C6F4(MTAZ)2]2+ = [PFTA]2+) dications and also [CH3CO2]−, [NO3]−, [CF3CO2]−, [BF4]−, [ClO4]− and [PF6]− anions were designed, investigated and compared using density functional theory at M06–2X–GD3-/AUG-cc-pVDZ level of theory. The roles of using different anions as well as fluorination of the linkage group on the possibility of forming hydrogen bonds and strength of the intermolecular interactions between dications and anions and also on the physicochemical properties of the formed DILs were examined. The potential electrostatic maps, values of interaction thermodynamic energies, structural parameters, topological properties of the atoms in molecules analysis, natural charge of atoms, charge transfer and charge transfer energy of acceptor–donor interactions of natural bond orbital calculations, reduced gradient density plots and electrochemical windows for designed DILs were evaluated. The results show that the strongest interaction in the gas phase belongs to DILs based on [CH3CO2]−, [NO3]− and [CF3CO2]− anions. The interaction strength of the DILs with [PFTA]2+ is more than [PHTA]2+. The energy level of HOMO and LUMO for dications and anions shows that both of the cathodic and anodic stability of the studied DILs in water solvent are controlled by corresponding dications. [ABSTRACT FROM AUTHOR]

Dicationic ionic liquids with a polymethylene (nC = 5, 9) linker between the imidazolium cations and the bis(trifluoromethylsulfonyl)imide anion have been synthesized. Their thermal stability was studied, and the melting points, viscosity, and volatility in vacuum were measured. The possibility of using the obtained ionic liquids as heat transfer fluids in vacuum was assessed. [ABSTRACT FROM AUTHOR]

A series of imidazolium and pyridinium-based bridged dicationic ionic liquids have been analysed using X-ray photoelectron spectroscopy. The different electronic environments of the dications have been investigated and a robust fitting model for the carbon C1s region has also been developed. The relative positions of different C1s components and N1s of dications have been determined and their complex C1s photoemission spectra produced from both aromatic and aliphatic carbon states giving photoemission peaks in the binding energy range of 289.0–283.9 eV. A contemporary fitting approach has been applied to a different set of environments which allowing comparison of the binding energies of cationic components of imidazolium and pyridinium-based dicationic ionic liquids. The experimental stoichiometry of all the carbons and nitrogens have also been calculated from XP spectra of the dicationic ionic liquids. [ABSTRACT FROM AUTHOR]

[Display omitted] New dicationic ionic liquids with pentasiloxane linker between two imidazolium moieties and bis(trifluoromethyl-sulfonyl)imide anions were synthesized; their melting points, glass transition temperatures and viscosities were measured, and thermal and hydrolytic stabilities were investigated. The dependence of the properties of these ionic liquids on the length of the siloxane linker in the cation part is revealed. [ABSTRACT FROM AUTHOR]

Ten novel hydrophobic dicationic ionic liquids (DILs) were synthesized and applied for the extraction of heavy metals in aqueous solutions. Their physicochemical properties were measured at ambient temperature, and the leaching behaviors of the as-prepared DILs in water were assessed by TOC analysis. Metal extraction experiments were carried out to evaluate the extraction performances of the DILs. It was found that the extraction rates of up to 0.45 and 0.53 mg·(g·min)−1 were achieved with 100 mg DILs for 5 mL of 5 mg/L Cd2+ and Pb2+ solutions. Besides, the extraction efficiencies of Cd2+ and Pb2+ were respectively up to 95.48% and 98.46%, when the volumes of the simulated wastewater were expanded by a factor of 20 at a constant extraction phase ratio (1000 mg DILs for 50 mL of 5 mg/L Cd2+ or Pb2+ solutions). The reusability of the novel DILs was successfully proved by the back-extraction experiments with 0.5 M HNO 3. Finally, taking Cd2+ extraction as an example, the extraction mechanism based on FTIR analysis and quantum chemical calculations showed that both S and O atoms in the anions of DILs had physical and quasi-chemical interactions with Cd2+, which were stronger than the electrostatic attraction. [Display omitted] • Two types of non-liquid hydrophobic novel dicationic ionic liquids for heavy metal extraction were synthesized. • As-Prepared ionic liquids demonstrated high efficiency on extracting Cd2+ and Pb2+ from the simulated wastewater. • [HxPrHx][BTB] 2 possessed extraction rates up to 0.45 and 0.53 mg/g·min−1 for Cd2+ and Pb2+ in the studied condition. • [HxPrHx][BTB] 2 exhibited excellent reversibility after five cycles of Cd2+ extraction/back-extraction process. [ABSTRACT FROM AUTHOR]

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.

Ionic liquids (ILs) are neoteric solvents characterized by unique physicochemical properties and considerable structural variability. The thermal behavior of 24 ILs, belonging to two structurally related families with either bromide or Tf2N as counteranion, was analyzed. For bromide mono- and dicationic ionic liquids (DILs), thermal gravimetric analysis showed similar decomposition events, with only small gain in stability for a few members of the latter class. Conversely, all Tf2N DILs displayed higher stabilities (up to 34 K) than the corresponding monocations, thus highlighting the different role played by the two counteranions. Mono- and dicationic ILs bearing a reactive group on the imidazolium substituent resulted instead the least stable ILs studied. Differential scanning calorimetry analyses of most of the (D)ILs only showed glass transition temperatures, a behavior in agreement with the broad liquid range of ILs. The impact of the cationic structure and/or of the type of anion on the above-mentioned transition temperatures has been studied. The apparent activation energy (Ea) and the fragility index (m) for some (D)ILs have also been obtained. Finally, a few bromide (D)ILs presented peculiar thermal events. [ABSTRACT FROM AUTHOR]

• Dicationic ionic liquids (DILs) were studied in the cycloaddition of CO 2 to epoxides. • Some of the bromide DILs were partially soluble in model epichlorohydrin. • Solubility issues were overcome by adding 20 mol% of epichlorohydrin carbonate. • Bromide DILs displayed a pseudo-first order kinetic. The cycloaddition of CO 2 to epoxides has attracted a great deal of interest in recent years as an atom efficient way to employ this greenhouse gas as a useful C1 building block. While several ionic liquids have been tested as catalysts for the reaction, little attention has been devoted to dicationic ionic liquids (DILs). Herein, the catalytic activity of a panel of structurally-related DILs has been evaluated in the cycloaddition of CO 2 to epichlorohydrin, in order to study the influence of the DILs' structure on their activity. The solubilities of a series of bromide DILs in epichlorohydrin, featuring various linker lengths and imidazolium substituents, were investigated. The bromide C n (MIM) 2 series displayed a limited solubility in this medium, which particularly affected the performances of C 3 (MIM) 2 2Br. However, the addition of 20 mol% of reaction product to the reactants was found to be an effective way to overcome this issue. This way, it was possible to compare the catalytic activity of both soluble and only partially soluble systems in epichlorohydrin. C 6 (MIM) 2 2Br and C 5 (HIM) 2 2Br were found to be the best performing DILs and have been tested, together with monocation C 4 MIM Br, also on less reactive epoxides. Mono and dicarboxylate (D)ILs instead proved to be less active than the bromide DILs and, when considering their synthesis, thermal stability and moisture sensitivity, ultimately less attractive for the development of future catalysts. Finally, a convenient and operationally simple way of recovering and reusing the bromide DILs at the end of the reaction was also evaluated. [ABSTRACT FROM AUTHOR]

A focused library of new dicationic ionic liquids (DiILs) 6 – 41 appended pyridinium hydrazone and phenoxy side chain hybrids as counter cations were designed and synthesized, utilizing quaternization and metathesis reactions under both conventional and microwave irradiation. The novel DiILs 6 – 41 were fully characterized using different spectroscopic tools (1H, 13C, 19F, 11B, 31P NMR and mass spectra) and evaluated for their antimicrobial activity against diverse types of high resistant strains including two Gram-positive bacteria; methicillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile , two Gram-negative bacteria; two Escherichia coli isolates, and Neisseria gonorrhea, and fungal strain; Candida albicans. The antibacterial screening was carried out by broth microdilution method and MIC values were reported as indicator of growth inhibition. They mostly exhibited antibacterial effect against MRSA and EC strains. The effect of the synthesized ILs on Gram-positive bacteria showed the phenoxy linker chain increases, the MIC values increases with more lethal effect due to the hydrophobicity parameter. This behavior was confirmed by the molecular dynamic simulation through the interaction with surface membrane as general mechanism of ILs. The dicationic ionic liquids are considered promising motifs for further investigations with focusing on the terminal hydrophobic adjuster. Unlabelled Image • Novel dicationic ionic liquids tethering pyridinium hydrazone-phenoxy conjugates were designed and synthesized. • The novel DiILs were screened for their antimicrobial activity against diverse types of high resistant strains. • Molecular docking studies were carried out for SAR analyses. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the structures and energetics of 1,3-bis[3-methylimidazolium-yl] pentane ([bis-Mim]2+) dication and bis(mandelato) borate [BMB]− and bis(salicylato) borate [BScB]−anions in isolated forms, ion pairs (IPs) and dicationic ionic liquids (DILs) were studied by Density Functional Theory (DFT) at the M06-2X/6-31G(d,p) level of theory. According to the IUPAC criteria, the hydrogen bonds between anion and cation were characterized and classified in the optimized geometries of the isolated ions, IPs and DILs. Inspection of the optimized structures revealed that the interionic hydrogen binding has important effect on the ions structures. The interaction energies between a dication and anions have been described in terms of NBO charge distribution, the stabilization energy E(2) values, changes of vibrational frequencies and the reduced density gradient (RDG) analysis. Also, the reactivity and interactions between chemical species were interpreted in terms of global electronic properties. Electrostatic potential surfaces (ESP) have been applied for visualizing the charge related properties and characterization of the most energetic sites of isolated ions and ion complexes. Graphical Abstract The H-bonds in the [bis-Mim][BMB] 2 DIL between acidic hydrogen atoms of dication and oxygen atoms of the anions. Unlabelled Image Highlights • The geometry of halogen-free Boron based DILs containing [BMB]− and [BScB]− anions was analyzed and characterized. • The calculated ESP maps demonstrate the charge distributions to understand the active sites of isolated ions, IPs and DILs. • The various H-bonds of the IPs and DILs were found and analyzed. • NBO was performed to shed light on the charge transfer and orbital interactions in IPs and DILs. • Electronic properties of the complexes were determined. • For strength of interactions, the stabilization energy E (2) values were calculated. • RDG analysis of the DILs was used to classify the identified H-bonds. [ABSTRACT FROM AUTHOR]

Ionic liquids have developed and been applied in lubricant field since 2001. Nevertheless, it is little known about novel dicationic ionic liquids for tribology applications in the past several years. In this paper, a sequence of novel dicationic ionic liquids based on 1,4-diazabicyclo[2.2.2]octane cations (DABCO) and different anions have been designed and identified. The structures of ILs were confirmed by Fourier transform infrared (FTIR) spectra, multinuclear (1H, 13C, 11B, 31P and 19F) magnetic resonance and mass spectrometry. The effects of anion type on thermal properties, wettability, kinematic viscosity and tribological properties were studied. It is found that all of these dicationic ionic liquids as additives exhibit excellent anti-wear and friction-reducing properties in PEG synthetic base oil under boundary lubrication conditions for steel-to-steel contact, which offers great potential for the highly efficient lubricant additives. Simultaneously, novel 1,4-diazabicyclo[2.2.2]octane cation offers an exceptional chance for the research and development of dicationic ionic liquids in various applications. [ABSTRACT FROM AUTHOR]

A number of dicationic ionic liquids with a disiloxane linker between imidazolium cations and bis(trifluoromethylsulfonyl)imide anion were synthesized and characterized. Melting points, viscosity, and volatility in a vacuum were measured; the thermal and hydrolytic stability of ionic liquids were also studied. The dependence of the properties on the structure of substituents in the cation of the ionic liquid was demonstrated.

Dicationic ionic liquids (DILs), a subset of the ionic liquid (IL) family, have attracted growing interest in recent years, and the range of applications within which they are investigated is constantly expanding. However, data which allows structure to property correlation of a DIL is still limited, and thus selecting an appropriate salt to address a specific challenge can be problematic. In comparison to traditional ILs, DILs physico-chemical properties can be tuned by changing the length and type of spacer which connects the cationic heads as well as the type of cation. This in turn could give rise to symmetrical or asymmetrical DILs. In this work, a systematic study of a homogeneous class of 12 dibromide DILs and 12 di-carboxylate salts has been performed. The latter class of DILs were also compared to mono cation derivatives. The different traditional exchange methods to prepare carboxylate DILs have been evaluated and an insight into the drawbacks encountered is also presented. Prepared DILs were characterized (NMR, TGA, DSC) allowing the influence of the structure on their thermal stability to be understood. Most DILs were obtained as solid salts after careful drying. For some of these compounds, a new possible application was studied, namely their use as hydrogen bond acceptors (HBA) of deep eutectic mixtures, showing again some significant structural related effects.

A series of dicationic ionic liquids (ILs) including [C4(MIM)2][PF6]2, [C5(MIM)2][PF6]2, [C6(MIM)2][PF6]2 and [C4(PYR)2][PF6]2 were synthesized. Their thermal stability and melting points were analysed. It was found that dicationic ILs presented important implications in the design of homogeneous and heterogeneous system with water. A homogeneous system of dicationic ILs with water could be formed at a relatively high temperature and then a heterogeneous system was formed when the solution was cooled to a low temperature. The ILs recovered by altering the temperature were obtained in high percentage yields of [C4(MIM)2][PF6]2 (97.6%), [C5(MIM)2][PF6]2 (97.3%), [C6(MIM)2][PF6]2 (98.0%) and [C4(PYR)2][PF6]2 (94.2%). On the other hand, [C4(MIM)2][PF6]2 and [C5(MIM)2][PF6]2 exhibited good solubility in acetonitrile and acetone. A homogeneous system could be achieved with imidazolium-based ILs with a relatively low amount of water and acetonitrile at room temperature. All of the properties of dicationic ILs have a strong correlation with the nature of dications, the linkage chain and the symmetry of dications. Dicationic ILs may provide a new opportunity for some specific applications in order to enable the effective separation and isolation of products.

Yolk-shell metal-organic framework (YS-MOF) liquids are candidate materials in large-size species with high-efficiency separation, owing to their hierarchical porosity, faster mass transfer, better compatibility, and higher solution processability than MOF liquids with micropores. Nevertheless, facile synthesis strategies of yolk-shell porous ionic liquids (YSPILs) with regulations of size and morphology are an ongoing challenge. Herein, we propose a general strategy to construct YSPILs based on Z67@PDA with tunable core sizes and morphologies. Benefiting from the unique hierarchical yolk-shell structure, as-prepared YSPILs exhibit promise in C 3 H 6 /C 3 H 8 capture and separation with the increased sizes of core in yolk-shell ZIF-67@PDA. Advanced YS-MOF liquids have improved the adsorption properties and increased our ability to tailor chemical composition and pore architecture. Impressively, the adsorption capacity of C 3 H 6 and C 3 H 8 of YSPILs exhibits an approximately 3-fold enhancement compared with that of the neat ILs, confirming that the accessible porosities are retained. Effective C 3 H 6 /C 3 H 8 separation performance of YSPILs over PILs based on ZIF-67, revealing the hierarchical porosity of YS-Z67@PDA liquids, benefits larger-size gas separation. Therefore, we believe that this work can not only help us to rationally design novel hierarchically porous ionic liquids but also promote candidate applications in large-size species separation, catalysis, and nanoreactors.

Abstract Dicationic ionic liquids (DILs) are more and more accepted as a new class of high temperature and polar stationary phases for gas chromatography (GC). This study deals with the effect of seven different fluorosulfonyl derivatized anions associated with two dications: 1,3-di(3-methylimidazolium)-2-methylpropane [2mC 3 (mim) 2 ], and 1,3-di(3-methylimidazolium)-isobutene [i-eneC 4 (mim) 2 ]. Thermophysical properties of the 14 synthesized DILs were evaluated in terms of melting point, viscosity, and thermal stability. The optimal physicochemical properties of 13 DILs allowed preparing 13 GC capillary columns. Accordingly, the polarity and selectivity of the DILs were evaluated by determining the Rohrschneider-McReynolds constants and the equivalent chain lengths of C18 fatty acid methyl esters (FAMEs). The symmetrical fluoroalkylsulfonyl and the trifluorosulfonate anions seem to produce the most polar DILs. Compared to classical polyethyleneglycol phases, the DILs showed substantially decreased retention of apolar compounds and a much stronger retention of the polar ones. Unique selectivities were observed with unsaturated FAMEs, polyaromatic hydrocarbons, and bacterial specific FAMEs. The two applications presented included a biodiesel and bacterial FAME analyses. Graphical abstract Image 1 Highlights • 14 newly synthesized dicationic ionic liquids varying by the anion. • A McReynolds polarity passing 6000 or polarity number of 143. • Strong selectivity differences between polar and apolar solutes. • Anthracene eluting BEFORE phenanthrene showing unique shape selectivity. [ABSTRACT FROM AUTHOR]

Abstract Three classes of dicationic ionic liquids (DILs) were synthesized, in which the cationic species [ N ‑methyl pyrrolidinium (MPy), N ‑butyl imidazolium (BIm) or diethylsulfide (DES)] were separated with oligoether moieties. The counter anions are either dicyanamide (DCA) or bis(trifluoromethane sulfonyl)imide (TFSI). The molecular structures of these compounds were identified by FT-IR, 1H NMR and 13C NMR analysis. The DILs were investigated for their potential as electrolyte solvents. Thermal behaviors were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) showing excellent thermal stability up to 150 °C for all DILs. Their physicochemical properties were comprehensively characterized regarding their densities, melting points, viscosities, and miscibility with polar and nonpolar solvents. To compensate high viscosity limitation of DILs, two low viscosity ionic liquids (thinners), [MImEt] [DCA] and [MImEt] [TFSI] were used. To further improve the lithium ion conduction ability of the electrolyte systems, a lithium salt (LiTFSI) was added. Then several ternary electrolyte systems, LiTFSI in DILs/thinner (the weight ratio of DILs/thinner was fixed equal to 1/1) were developed, and their ionic conductivity and electrochemical stability were analyzed. Highlights • Three classes of new dicationic ionic liquids (DILs) have been synthesized and characterized. • The density, miscibility, viscosity, and neat ionic conductivity are reported for each. • Additionally, several electrolyte systems containing DILs and LiTFSI were tested for flammability and ionic conductivity. • All DILs exhibited thermal stability up to 150 °C and non-flammability. • These DIL-based electrolyte systems were determined to be electrochemically suitable for use in lithium-sulfur batteries. [ABSTRACT FROM AUTHOR]

Three phosphonium‐based dicationic ionic liquids were synthesized as bis(trifluoromethylsulfonyl) imide salts. The three dications had a nonyl spacer between two identical phosphonium‐substituted groups. The three phosphonium moieties were dipropyl(phenyl), diphenyl(propyl), and diphenyl(toluyl). The physicochemical properties of the dicationic ionic liquids were appropriate to prepare 30 m capillary columns that were tested in gas chromatography. A unique selectivity compared to different polysiloxane or polar cyanosiloxane commercial columns was observed for selected mixes of phthalates, polyaromatic hydrocarbons, polychlorobiphenyls, and dioxins. Only minor selectivity variations were observed with the three dicationic ionic liquids. The different number of aromatic rings on the positively charged phosphonium group did not influence the dicationic ionic liquid selectivity significantly. [ABSTRACT FROM AUTHOR]

Abstract: In this study, new quaternary bis(ammonium) salts with alkyl-1,X-bis(dimethyldecylammonium) cation and saccharinate, acesulfamate, lactate and pyroglutamate anions were synthesized and characterized by 1H and 13C NMR spectroscopy. Thermal gravimetric and differential scanning calorimetry analyses confirmed that all salts were thermally stable and the majority of them exhibited melting points below 100 °C. The physicochemical properties (viscosity, density, refractive index values, and solubility) of the obtained salts were determined for three compounds with lactate anions. All the tested salts have suitable properties which, in practical application, will reduce the losses caused by the most important storage insects. Most of the synthesized ionic liquids had comparable or better deterrent activity than azadirachtin—an alkaloid known as the most active antifeedant.Graphical abstract: [ABSTRACT FROM AUTHOR]

An array of dicationic pyridinium ionic liquids (DILs) based hydrazone linkage were designed and synthesized via the quaternization of the appropriate bispyridine hydrazone with different phenacyl halides and led to the formation of halogenated DILs, which undergo metathesis reaction to give the specific task dicationic pyridinium liquids carrying fluorinated counter anions (PF 6 − , BF 4 − , CF 3 COO − ). The newly synthesized DILs were well characterized using whole spectroscopic data. The Anticancer evaluation of DILs against breast and colon cancer cell lines revealed that compound 22 appears to be the most active compound in the series with IC 50 in the two-digit micromolar range. The in-vitro anticancer results were further supported by in-silico molecular docking studies revealing the highest potency of compound 22 . The docking analysis demonstrated good docking score and binding affinities of the synthesized compounds on the target protein PI3Kinase. [ABSTRACT FROM AUTHOR]

Halogen containing IL based lubricants are sensitive to the moistures and produce acidic corrosive products. So, there is a growing need towards the development and study of the halogen-free boron based ILs (hf-BILs).In this research, we used the Density Functional Theory (DFT) at the M06-2X/6-31G(d,p)level to study the interactions between 1,3-bis[3-methylimidazolium-yl] pentane dication ([C 5 (mim) 2 ] 2+ ) and bis(oxalato) borate [BOB] − and bis(malonato) borate [BMLB] − anions (halogen-free Boron based anions). The structures changes in the ion complexes have discussed. The interactions of a dication and anions in the ion pairs (IPs) and ion triplets (ITs) have characterized in terms of changes of vibrational frequencies, NBO charge distribution, reduced density gradient (RDG) analysis, and the stabilization energy E (2) values. The interaction energies, thermodynamic parameters and electronic properties of the isolated ions and their complexes were calculated. Electrostatic potential surface (ESP) studies have also been employed to understand the active sites of isolated ions, IPs and ITs. The results demonstrated that intermolecular hydrogen bonding and electrostatic interactions have a significant role in the stabilizing of the ion pairs and dicationic ionic liquids (DILs). The favorable sites for the cation–anion systems have been determined. The results of this research can shed light on the nature of bonding and interactions between ions to help the design of the new task-specific DILs with a lower impact on the environment. [ABSTRACT FROM AUTHOR]

Dicationic ionic liquids (DILs) typically have higher viscosities and thermal stabilities than most conventional monocationic ionic liquids. However, due to their coulombic interactions, they often demonstrate higher melting points than conventional ILs which limit their use in many applications. Utilizing branched alkyl spacer chains between two cationic terminal groups resulted in dicationic ILs with lower melting points and therefore extended liquid ranges. A systematic investigation was conducted to determine how the position and type of substituent groups may affect the physicochemical properties of branched DILs. When compared to their linear counterparts, an increase in the kinematic viscosities and lower densities were observed for branched DILs. Thermal stability was found to be highly dependent on the position of the alkyl substituent group along with the length of the spacer chain. While the substitution on the α‑carbon of a spacer chain resulted in a significant decline in the thermal stability of DILs, the effect of mid-chain substitution on their stability was negligible. The performance testing of branched DILs as gas chromatography (GC) stationary phase displayed excellent separation of geometrical isomers in BTEX mixture. [ABSTRACT FROM AUTHOR]

The conversion of cellulose to platform chemicals and renewable energies is the most promising and sustainable route to solve the crisis of fossil fuel resources. With this aim, the one-pot conversion of cellulose to industrial important levulinic acid (LA) using dicationic ionic liquids as a catalyst has been investigated. In the present research work, dicationic ionic liquids, containing 1,1-bis(3-methylimidazolium-1-yl) butylene ([C 4 (Mim) 2 ]) cation with counter anions hydrogensulfate, dihydrogensulfate, methanesulfonate, and trifluoromethanesulfonate has been synthesized and applied for one-pot conversion of cellulose to LA. The structures, thermal stability, and acidity of ILs were determined by 1 H NMR, CHNS values, thermogravimetric analyzer (TGA) and Hammet acidity function, respectively. Among the synthesized ionic liquids, [C 4 (Mim) 2 ][(2HSO 4 )(H 2 SO 4 ) 2 ] showed higher catalytic activity for conversion of cellulose to LA (55%) without using any additional catalyst or solvent at 100 °C for 3 h, which is the best result compared to previous reports. A mechanism to explain the reaction route toward LA formation is proposed. Moreover, the recycling of IL was easily achieved without structural changes or any impurities. This one-pot production of levulinic acid from untreated cellulose will open new opportunity for the conversion of sustainable biomass resources into valuable chemicals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of the reaction media on the properties of ZnO nanoparticles (ZnO NPs). • ZnO NPs synthesized by the conventional method (ZnO-S) and samples elaborated in an ionic liquid (IL) media (ZnO-IL). • XRD, FTIR, UV–VIS and TEM measurements. • The ionic liquid (IL) is a very advantageous reaction media for directing a chemical transformation. • Diluted media of ([M(CH 2) 3 IM2+][2Br-]) can be decisive concerning the sizes and the morphologies of the obtained ZnO NPs. In this work, we make a comparative study between ZnO nanoparticles samples (NPs) synthesized by the conventional method (ZnO-S) and samples elaborated in an ionic liquid (IL) media (ZnO-IL) to see the effect of the latter on the structural, optical and morphological properties of these NPs. The results of this study are obtained using the following characterization methods: X-ray diffraction for the study of the structural properties of the different ZnO NPs samples, infrared spectroscopy (FTIR) to determine the nature of the different bonds present in our samples, UV–Visible spectrometry to determine the gap energy of zinc oxide. The results of Transmission Electron Microscopy have also been reported to show the effect of ionic liquid on the morphology of ZnO NPs. The XRD allowed us to see the effect of ionic liquid on the size of the crystallites manifested by a noticeable decrease. The curves of the UV–Vis show that the value of the gap energy is not the same for the two samples of ZnO-S and ZnO-IL, which implies that the latter has been influenced by the change in the reaction media. Transmission electron microscopy shows that the ionic liquid influences the size of the nanoparticles, there are two populations of nanoparticles, the first between (50 and 100 nm) as for ZnO-S NPs and a second in the order of 20 nm, which implies that the presence of the ionic liquid reduced the size of the NPs. We conclude that ionic liquid can be very useful to control the size of ZnO NPs and the appearance of novel properties. [ABSTRACT FROM AUTHOR]

In this work, binary mixtures of a non-ionic surfactant (Triton X-100) and water were studied with concentrations of 30%wt H2O, showing, lamellar mesophase at temperatures below 10oC. Different dicationic ionic liquids were used for doping these mesophases: 1,n-bis(3-methylimidazolium-1-yl)alkane, 1,n-bis(1-methylpyrrolidinium-1-yl)alkane and 1,n-bis(pyridinium-N-yl)alkane dibromide, where n = 6 and 8. Polarized Optical Microscopy and Small-Angle X-ray Scattering were used for identifying the mesophases and the influence of different dicationic ionic liquids on the lyotropic liquid crystals phase transitions. The addition of dicationic ionic liquids to the lyotropic liquid crystals samples led to changes in transition temperature and in mesophase structure itself (such as characteristic distances). [ABSTRACT FROM PUBLISHER]

This research investigates the influence of the subsituent's relative positions (ortho, meta, or para) of dicationic ionic liquids (ILs) on the catalytic production of 5-hydroxymethylfurfural (HMF). This research started with the facile synthesis of new dicationic ILs followed by its characterization using NMR, FT-IR, CHN, and UV–Vis. Then the acidity properties are measured using the Hammet method. The screening process revealed that the relative positions of substituents (ortho, meta and para) on the cationic site remarkably affect the overall catalytic performance. Highly efficient and selective dehydration of d -fructose to HMF was obtained using Brønsted ortho-IL with a fructose conversion of 95.7% and HMF yield of 90.5% after 60 min at 100 °C. The results revealed that the geometry of the isomer ILs influences the yield of HMF. The effects of reaction time, temperature, catalyst concentration and reusability of the dicationic ILs are studied in this work. [ABSTRACT FROM AUTHOR]

BACKGROUND Macroalgae has high potential as a bio-fuel feedstock due to its high carbohydrate content. Conventional aqueous systems require a huge amount of energy to catalyze depolymerization and hydrolysis of macroalgae. Recently various task-specific ionic liquids ( ILs) successfully depolymerized different biomasses, but were thermally unstable. A variety of dicationic acidic ILs ( DAILs) connected by oligo-ethylene glycol ( EG) chains bearing hydrogen sulfate ( HSO4−) anions were synthesized with better thermal stability and utilized in hydrolysis of macroalgal biomass, Gelidium amansii. RESULTS The structures of DAILs were confirmed by 1H and 13C NMR as well as FT-IR. EG-linker chain lengths and dicationic structure increased the thermal stability of DAILs and influenced their catalytic performance for G. amansii hydrolysis. DAILs linked with short oligo- EG chains afforded higher sugar yields and exhibited faster hydrolysis rates compared with those linked by long oligo- EG chains (i.e. PEG400 and PEG600). A maximum sugar yield of 67.45 wt% was recovered from G. amansii using [Tri- EG-( MIm)2] 2HSO4 DAIL, after 3 min at 120 °C. CONCLUSION The synthesized DAILs showed dual properties as catalyst and reaction medium for hydrolysis of macroalgae in solvent-less conditions. Shorter oligo- EG chain linked DAILs exhibited faster reaction rates with higher sugar yields. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

In the present work, four dicationic ionic liquids (DILs) having 1,1-Bis(3-methylimidazolium-1-yl) butylene ([C 4 (Mim) 2 ]) cation with counter anions namely hydrogensulfate, methanesulfonate, trifluoromethanesulfonate, and paratoluene sulfonate were synthesized and characterized. The structures of ILs were confirmed by 1 H NMR, 13 C and elemental analysis (CHNS). The effect of temperature and anion type on thermophysical properties such as refractive index, density and viscosity were studied. Density and viscosity values were measured within the temperature range of 293.15–273.15 K. Moreover, thermal expansion coefficient, molecular volume, molar volume, free volume, standard entropy, and lattice energy were derived from the density and viscosity values. Viscosity values were used for calculation of activation energy using the Arrhenius equation. Refractive index values were measured in the temperature range of 293.15–323.15 K and the values of refractive index were used further to estimate the electronic polarizability using Lorenz-Lorentz equation. Thermal properties of the synthesized DILs were determined using thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). [ABSTRACT FROM AUTHOR]

Airborne transmission is one of the most unpredictable routes of infection. Nowadays, airborne diseases increase ever than before because of the complex living air environment. Apart from the inorganic particles, active microorganisms including bacteria, viruses, and fungi are incorporated in the pathogens acting as threaten to public health, which can hardly be treated by the traditional air purification methods based on adsorption. Therefore, effective filtration material with antimicrobial activity is demanded to solve the problem. Ionic liquids (ILs) are a category of salts that remain liquid at room temperature. The stable physico-chemical properties and extremely low vapor pressure make them suitable for a wide range of applications. Thanks to the numerous combinations of cations and anions, as well as the ability of inheriting properties from the parent ions, Ils are believed to be a promising industrial material. In recent decades, several Ils, such as imidazolium, pyridinium, pyrrolidinium, phosphonium, and choline, have been found to have antimicrobial activity in their monomeric or polymeric forms. This work focuses on the antimicrobial activity and safety of the latest types of ionic liquids, discussing the synthesis or manufacturing methods of Ils for air purification and filtration. Furthermore, possible applications of Ils antimicrobial materials in medical instruments and indoor environments are mentioned to encourage the scientific community to further explore the potential applications of Ils., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Song, Tian and Liu.)

Focused bis-pyridinium based-ionic liquids were successfully synthesized through the quaternization of the selected 1,2-di(pyridin-4-yl)ethane followed by metathetical anion exchange. The synthesized pyridinium derivatives were fully characterized using various NMR-spectroscopic techniques including 1 H, 13 C, 11 B, 31 P and 19 F NMR. The synthesized compounds were tested for their potential effect against Toxoplasma gondii . It was revealed that compound 5 had higher antiparasitic activity compared to other compounds. Parasitic reduction percentage reached 38, 50, 77 and 79 for groups III, IV, V and VI respectively in the liver with noticed distortion and deformation in tachyzoites' shape. Surprisingly there was no statistically significant difference between the synthesized compound 5 and the known anti-toxoplasmosis drug pyrimethamine. Histopathological study proved the effectiveness of the synthesized compound 5 on liver, spleen and brain tissues with observed better histological features compared to pyrimethamine treated group. The present investigation may pave the way to the possible use of compound 5 to replace the known drug pyrimethamine with better antiparasitic profile and fewer side effects., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors. Published by Elsevier Ltd.)

Two new dicationic ionic liquids were synthesized: bis-methyl imidazolium methylidene hexafluorophosphate [M(CH)IM][2PF] and bis-methyl imidazolium propylidene hexafluorophosphate [M(CH)IM][2PF]. Their structures were identified by H, C, P, F NMR, FTIR/ATR, and FT-Raman spectroscopies in order to study the effect of cation alkyl chain length on vibration behaviors. Several changes were recorded, which were related to alkyl chain length. A frequency shift was observed in some modes while others remained insensitive. A greater number of peaks was found in the FTIR/ATR spectra and the FT-Raman spectra with increasing alkyl chain length, which indicated that chain length influences the N-C connection twisting. More peaks with strong intensity appeared for longer alkyl chain lengths. [ABSTRACT FROM AUTHOR]