Effect on aggregation behavior of long-chain spacers of dicationic imidazolium-based ionic liquids in aqueous solution

Surface-Active Ionic Liquids and Surface-Active Quaternary Ammonium Salts from Synthesis, Characterization to Antimicrobial Properties

The present work provides new evidence of the ongoing potential of surface-active ionic liquids (SAILs) and surface-active quaternary ammonium salts (surface-active QASs). To achieve this, a series of compounds were synthesized with a yield of ≥85%, and their thermal analyses were studied. Additionally, antimicrobial activity against both human pathogenic and soil microorganisms was investigated. Subsequently, their surface properties were explored with the aim of utilizing SAILs and surface-active QASs as alternatives to commercial amphiphilic compounds. Finally, we analyzed the wettability of the leaves' surface of plants occurring in agricultural fields at different temperatures (from 5 to 25 °C) and the model plant membrane of leaves. Our results show that the synthesized compounds exhibit higher activity than their commercial analogues such as, i.e., didecyldimethylammonium chloride (DDAC) and dodecyltrimethylammonium bromide (C12TAB), for which the CMC values are 2 mM and 15 mM. The effectiveness of the antimicrobial properties of synthesized compounds relies on their hydrophobic nature accompanied by a cut-off effect. Moreover, the best wettability of the leaves' surface was observed at 25 °C. Our research has yielded valuable insights into the potential effectiveness of SAILs and surface-active QASs as versatile compounds, offering a promising alternative to established antimicrobials and crop protection agents, all the while preserving substantial surface activity.

Synthesis and Micellization of Carbosilane Sulfonate Surfactants with Short Alkyl Chains

Carbosilane surfactants, consisting of carbosilane as a hydrophobic group linked to hydrophilic groups, are one kind of silicone surfactants. In this paper, a series of carbosilane sulfonate surfactants with short alkyl chains (Cn-Si2C-SO3Na (n = 1-6)), Me-Si2C-SO3Na, Et-Si2C-SO3Na, Pr-Si2C-SO3Na, Bu-Si2C-SO3Na, Pen-Si2C-SO3Na, and Hex-Si2C-SO3Na, were prepared and characterized by 29 Si NMR, 1H NMR, and FT-IR spectroscopies. The influence of the alkyl chain length on their micellization was studied using surface tension, dynamic light scattering, conductivity, and transmission electron microscopy. The CMC value decreases with increasing length of the short alkyl group. The γCMC value of Cn-Si2C-SO3Na (n = 1-6) increases as the alkyl chain increases from methyl to propyl, while the γCMC value gradually decreases as the alkyl chain increases from propyl to hexyl. The larger and rigid tetramethyldicarbosilane group functioned synergistically with a short alkyl chain, resulting in carbosilane sulfonate surfactants adsorbing at the air/water interface with a rugby ball shape; accordingly, the Amin values of the investigated carbosilane sulfonate surfactants increase with increasing length of the alkyl chain. The micellization process of carbosilane sulfonate surfactants is enthalpy-driven at lower temperatures and entropy-driven at high temperatures. The ΔHm0 values became more negative and ΔSm0 values more positive as the alkyl chain length increased. Aggregates in the range of 10-800 nm were observed for Cn-Si2C-SO3Na (n = 1-6) in an aqueous solution, and the hydrodynamic diameter (Dh) decreased with increasing length of the short alkyl group.

Predicting the aggregation number of cationic surfactants based on ANN-QSAR modeling approaches: understanding the impact of molecular descriptors on aggregation numbers

In this work, a quantitative structure-activity relationship (QSAR) study is performed on some cationic surfactants to evaluate the relationship between the molecular structures of the compounds with their aggregation numbers (AGGNs) in aqueous solution at 25 °C. An artificial neural network (ANN) model is combined with the QSAR study to predict the aggregation number of the surfactants. In the ANN analysis, four out of more than 3000 molecular descriptors were used as input variables, and the complete set of 41 cationic surfactants was randomly divided into a training set of 29, a test set of 6, and a validation set of 6 molecules. After that, a multiple linear regression (MLR) analysis was utilized to build a linear model using the same descriptors and the results were compared statistically with those of the ANN analysis. The square of the correlation coefficient (R ²) and root mean square error (RMSE) of the ANN and MLR models (for the whole data set) were 0.9392, 7.84, and 0.5010, 22.52, respectively. The results of the comparison revealed the efficiency of ANN in detecting a correlation between the molecular structure of surfactants and their AGGN values with a high predictive power due to the non-linearity in the studied data. Based on the ANN algorithm, the relative importance of the selected descriptors was computed and arranged in the following descending order: H-047 > ESpm12x > JGI6> Mor20p. Then, the QSAR data was interpreted and the impact of each descriptor on the AGGNs of the molecules were thoroughly discussed. The results showed there is a correlation between each selected descriptor and the AGGN values of the surfactants.

Upgrading the Properties of the Crude Oil-Water System for EOR with Simultaneous Effects of a Homologous Series of NanoGemini Surface-Active Ionic Liquids, Electrolytes, and pH

This study investigated the simultaneous effects of electrolytes, NaCl and MgCl₂ electrolytes, individually and as a mixture, and pH on a homologous series of imidazolium nano-Gemini surface-active ionic liquids (GSAILs), [C₄im-C _m -imC₄][Br₂], where m = 2, 4, and 6. These can improve the properties of the crude oil-water system and consequently enhance the oil recovery. The results precisely revealed that interfacial tension (IFT) and critical micelle concentration were initially decreased with electrolyte concentration up to 55.7 and 58.6%, respectively, in comparison to the salt-free condition, followed by a slight increase. Moreover, adjusting the pH can provide a further improvement so that 79.2% IFT reduction is attained at pH 9.5 compared to that at the natural pH and that GSAILs show high stability in the pH range of 2.5-9.5. Meanwhile, aqueous solutions of crude oil and electrolyte presented 1 day emulsification indices within 43-53%, followed by minor changes after 1 week. Interestingly, the emulsification index of 77.1% was attained at pH 9.5. Surface wettability was also favorably altered from oil-wet to water-wet with the nanoGSAILs. The findings of this study help gain a better understanding of the effects of nanosurface active materials to improve oil extraction under reservoir conditions.

Safe and selective anticancer agents from tetrafluorinated azobenzene-imidazolium ionic liquids: Synthesis, characterization, and cytotoxic effects

A new series of tetrafluorinated azobenzene-imidazolium salts is reported. The azobenzene and imidazolium moieties were functionalized with long alkyl chains and connected via a methylene spacer of varying lengths (n = 3-12). They were characterized using FTIR and NMR spectroscopy, and elemental microanalysis. The cytotoxic potential of these ionic dimers against neuroblastoma (SHSY-5Y), estrogen-positive breast cancer cells (MCF-7), triple-negative breast cancer cells (MDA-MB-231), cervical cancer cells (HeLa), and human skin fibroblasts (Hs27) was evaluated using the MTT assay. The cytotoxicity of these ionic liquids (ILs) was dependent on the spacer length. A cut-off effect was observed, wherein the cytotoxicity of the ILs was enhanced by increasing the nonpolar, hydrophobic spacer length up to a threshold and the potency was leveled off upon chain elongation. All ILs exhibited selective and remarkable inhibition potentials against HeLa cells in a dose-dependent manner, which was 2-22 times stronger than that of etoposide, a clinical anticancer drug. These ILs were less toxic toward skin fibroblasts as implied by much higher IC₅₀ values. The long-spacer ILs (n = 7-10) were very selective toward HeLa cells. They had a broad safety window with selectivity indices ranging between 5.6 and 11.0. The selectivity of these compounds toward HeLa cells may serve as a new strategy for the design and development of safe and effective chemotherapeutics.

Review on Amphiphilic Ionic Liquids as New Surfactants: From Fundamentals to Applications

The demand for lowering interfacial tension (IFT) in different processes has persuaded researchers to use stable and resistant surfactants with low environmental impact. For this purpose, surface-active ionic liquids (SAILs) have attracted much attention owing to their good amphiphilic nature and prominent properties like recyclability and high performance under harsh conditions. This review initially explains how the IFT and critical micelle concentration of different systems vary in the presence of different SAILs with a variety of alkyl chain lengths, head groups, and counter anions. Towards this aim, some physicochemical properties of SAILs as well as the corresponding theoretical aspects of adsorption are considered. Then, recent advances in utilizing SAILs for reducing IFT of different chemical systems are surveyed. Relevantly, the role of important operating parameters of temperature, pH, presence of electrolytes, and the chemical nature of involved phases are adequately discussed. Further, an overview of different SAILs applications in stabilization, separation, and in petroleum industries is scrutinized. To allow better judgment, precise comparisons between different types of SAILs and conventional surfactants are provided. Finally, challenges and possible directions of future research on SAILs are highlighted.

Antimicrobial and Toxicity Evaluation of Imidazolium-Based Dicationic Ionic Liquids with Dicarboxylate Anions

Imidazolium-based dicationic ILs (DILs) presenting antimicrobial activity and relatively low toxicity are highly desirable and are envisioned for use in live tissue to prevent bacterial or fungal infections. In this context, we present here DILs with dicarboxylate anions [C_n(MIM)₂[C_n(MIM)₂][CO₂-(CH₂)_mCO₂], in which n = 4, 6, 8, and 10, and m = 0, 1, 2, 3, 4, and 5. The results showed that DILs with an alkyl chain spacer of ten carbons were active against yeasts and the bacterial strains tested. However, most of the DILs were cytotoxic and toxic at 1 mM. By contrast, DILs with alkyl chains possessing less than ten carbons were active against some specific Candidas and bacteria (mainly S. aureus), and they showed moderate cytotoxicity. The best activity against Gram-positive bacteria was observed for [C₄(MIM)₂][Pim] toward MRSA. For the DILs described herein, their level of toxicity against C. elegans was lower than that of most of the mono- and dicationic IL analogs with other anions. Our results showed that the presence of carboxylate anions reduces the toxicity of DILs compared to DILs containing halide anions, which is particularly significant to the means of designing biologically active compounds in antimicrobial formulations.

Ammonium Gemini Surfactants Form Complexes with Model Oligomers of siRNA and dsDNA

Dimeric cationic surfactants (gemini-type) are a group of amphiphilic compounds with potential use in gene therapy as effective carriers for nucleic acid transfection (i.e., siRNA, DNA, and plasmid DNA). Our studies have shown the formation of lipoplexes composed of alkanediyl-α,ω-bis[(oxymethyl)dimethyldodecylammonium] chlorides and selected 21-base-pair nucleic acid (dsDNA and siRNA) oligomers. To examine the structure and physicochemical properties of these systems, optical microscopy, circular dichroism spectroscopy (CD), small-angle X-ray scattering of synchrotron radiation (SR-SAXS), and agarose gel electrophoresis (AGE) were used. The lengths of spacer groups of the studied surfactants had a significant influence on the surfactants’ complexing properties. The lowest charge ratio (p/n) at which stable lipoplexes were observed was 1.5 and the most frequently occurring microstructure of these lipoplexes were cubic and micellar phases for dsDNA and siRNA, respectively. The cytotoxicity tests on HeLa cells indicated the non-toxic concentration of surfactants to be at approximately 10 µM. The dicationic gemini surfactants studied form complexes with siRNA and dsDNA oligomers; however, the complexation process is more effective towards siRNA. Therefore these systems could be applied as transfection systems for therapeutic nucleic acids.

Heteroassembly Ability of Dicationic Ionic Liquids and Neutral Active Pharmaceutical Ingredients

Extensive investigation of interactions and aggregation properties of IL + API systems is necessary to apply ionic liquids (ILs) with different hydrophobic characteristics to drug delivery or in active pharmaceutical ingredient (API) formulations. Therefore, this study aims to investigate the heteroassembly between dicationic ILs ([BisOct(MIM)₂][2X], in which X is Br or BF₄, and [BisOct(BnIM)₂][2Br]), both in the absence and the presence of neutral APIs (salicylic acid, ibuprofen, and paracetamol) with different functional groups. Isothermal titration calorimetry results demonstrate that IL-API associations occur at very low concentrations of IL. These results were reinforced by electrospray ionization mass spectrometry with variable collision-induced dissociation, in which the IL dication interactions with APIs were detected. The strength of the dication-API interaction was determined from E _cm,1/2 data. The aggregation parameters (cac, ΔG _agg ^°, and K) between ILs and APIs were evaluated by conductivity. The ¹H NMR data showed that differences in chemical shifts provided relevant insights about interaction sites in both components.

Impact of Anions on the Partition Constant, Self-Diffusion, Thermal Stability, and Toxicity of Dicationic Ionic Liquids

Partition constants (K_D^°), molecular dynamics (T₁, T₂, and DOSY measurements), thermal stability, and toxicity of dicationic ionic liquids (ILs) were determined. The dicationic ILs derived from 1,n-bis(3-methylimidazolim-1-yl)octane, [BisOct(MIM)₂][2X] (in which X = Cl, Br, NO₃, SCN, BF₄, and NTf₂), were evaluated to verify the influence of anion structure on the IL properties. A monocationic IL [Oct(MIM)][Br] was also monitored for comparison. In general, the solubility of the ILs followed the anion free energy of hydration (ΔG°_hyd). The thermokinetic and thermodynamic functions of activation of the ILs were determined via thermogravimetric data, and it was observed that polyatomic anions influence the decomposition mechanism of these IL structures. Furthermore, [Oct(MIM)][Br] had a decomposition rate greater than that of the dicationic analogue, and the thermodynamic parameters of activation data corroborate these results. Finally, the dicationic ILs did not indicate toxic effects (LD₅₀ > 40 mM).

Self-assembly of a short-chain ionic liquid within deep eutectic solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) are receiving increased attention from both academic and industrial research due to their immense application potential. These designer solvents are environmentally friendly in nature with tunable physicochemical properties. In the present investigation, we have studied the aggregation behavior of a short-chain IL 1-butyl-3-methylimidazolium octylsulphate [Bmim][OS] within aqueous DESs using fluorescence, UV-vis, dynamic light scattering (DLS) and FT-IR spectroscopic techniques. We have prepared two DESs, ChCl–urea and ChCl–Gly, which are obtained by heating a mixture of an ammonium salt choline chloride with hydrogen bond donor urea or glycerol, respectively, in 1 : 2 molar ratios. The local microenvironment and size of the aggregates are obtained from steady state fluorescence (using pyrene and pyrene-1-carboxaldehyde as polarity probes) and DLS measurements, respectively. DLS results shows that IL [Bmim][OS] forms relatively larger micelles within the aqueous solution of DES ChCl–urea (avg. hydrodynamic radii = 209 nm) than compared to ChCl–Gly (avg. hydrodynamic radii = 135 nm). A significant decrease in the critical micelle concentration and increase in the aggregation number (N_agg) are observed within DES solutions as compared to that in water, thus indicating that the micellization process of the IL [Bmim][OS] is much favored in the DES solutions. Molecular interactions of [Bmim][OS] in DESs are revealed from FT-IR spectroscopic investigation. Furthermore, these systems were applied to study the IL-drug binding of the antidepressant drug promazine hydrochloride (PH).

Self-assembly of short-chain imidazolium-based ILs within DESs have been investigated by fluorescence, UV-Vis, DLS and FT-IR spectroscopy. Further, these micellar systems [Bmim][OS]-DESs are utilized to study the IL-drug binding of an antidepressant drug (PH).

Self-assembly of a short-chain ionic liquid within deep eutectic solvents

Self-assembly of short-chain imidazolium-based ILs within DESs have been investigated by fluorescence, UV-Vis, DLS and FT-IR spectroscopy. Further, these micellar systems [Bmim][OS]-DESs are utilized to study the IL-drug binding of an antidepressant drug (PH).

Thermodynamic Insights into the Binding of Mono- and Dicationic Imidazolium Surfactant Ionic Liquids with Methylcellulose in the Diluted Regime

Alkylimidazolium salts are an important class of ionic liquids (ILs) due to their self-assembly capacity when in solution and due to their potential applications in chemistry and materials science. Therefore, detailed knowledge of the physicochemical properties of this class of ILs and their mixtures with natural polymers is highly desired. This work describes the interactions between a homologous series of mono- (C_nMIMBr) and dicationic imidazolium (C_n(MIM)₂Br₂) ILs with cellulose ethers in aqueous medium. The effects of the alkyl chain length (n = 10, 12, 14, and 16), type, and concentration range of ILs (below and above their cmc) on the binding to methylcellulose (MC) were evaluated. The thermodynamic parameters showed that the interactions are favored by the increase of the IL hydrocarbon chain length, and that the binding of monocationic ILs to MC is driven by entropy. The monocationic ILs bind more effectively on the methoxyl group of MC when compared to dicationic ILs, and this outcome may be rationalized by considering the structural difference between the conventional (C_nMIMBr) and the bolaform (C_n(MIM)₂Br₂) surfactant ILs. The C₁₆MIMBr interacts more strongly with hydroxypropylcellulose when compared to methylcellulose, indicating that the strength of the interaction also depends on the hydrophobicity of the cellulose ethers. Our findings highlight that several parameters should be taken into account when designing new complex formulations.

Synthesis, self-assembly, and in vitro toxicity of fatty acids-modified Bletilla striata polysaccharide

Hydrophobic modification of Bletilla striata polysaccharide (BSP) was performed by grafting fatty acids to BSP backbone and then characterized on their physicochemical properties. All neutral derivatives were able to self-assemble into spherical particles within the size range of 250-400 nm, their size and critical micelle concentration decreased with increasing hydrophobicity and substitution degree of the fatty acids. Also, the BSP-stearic acid conjugates showed a preferable performance on hemolysis test and cytotoxicity analysis on HepG2 cells, which suggested their potential application as a drug delivery vector.

Aggregation behavior of N-alkyl imidazolium-based poly(ionic liquid)s in an organic solvent

PILs with long alkyl chains in an organic solvent display onion-like multilamellar structures and their aggregation is an entropy-driven spontaneous process.

Use of dicationic ionic liquids as a novel liquid platform for dielectrophoretic cell manipulation

Separation, characterization and analysis of target cells demonstrate critical cues for diagnosis and monitoring of chronic diseases.

Improvement of tribological and anti-corrosive performance of titanium surfaces coated with dicationic imidazolium-based ionic liquids

In this work, dicationic imidazolium-based ionic liquids (ILs) with amino acid anionic moieties were employed as coatings for commercially pure titanium (Ti) surfaces.

Ionic Liquid Coatings for Titanium Surfaces: Effect of IL Structure on Coating Profile

Dicationic imidazolium-based ionic liquids (ILs) having bis(trifluoromethylsulfonyl)imide (NTf2) and amino acid-based (methionine and phenylalanine) anionic moieties were synthesized and used to coat titanium surfaces using a dip-coating technique. Dicationic moieties with varying alkyl chains (8 and 10 carbons) and anions with distinct characteristics were selected to understand the influence of IL structural features on deposition profile. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used in this study to help elucidate intermolecular interactions within ILs as well as between ILs and TiO2 surfaces and to investigate IL coating morphology. Charge concentration on IL moieties, as well as the presence of functional groups that can interact via hydrogen bond, such as carboxylate and amino groups, were observed to influence the deposition profile. ILs containing amino acids as the anionic moiety were observed to interact strongly with TiO2, which resulted in more pronounced changes in Ti 2p binding energy. The higher hydrophobicity of the IL having NTf2 as the anionic moiety resulted in higher adhesion strength between the IL coating and TiO2.