Imidazolium Surfactants Research Articles

Self-assembly of an imidazolium surfactant in aprotic ionic liquids. 2. More than solvents.

As tailorable solvents, the physiochemical properties of ionic liquids can be tuned by the structure of ions. Herein, we investigate the structural effects of ILs on the self-assembly of surfactants. It has been confirmed that the cationic surfactant 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) can self-assemble into micellar and lamellar lyotropic liquid crystal phases in the aprotic ionic liquid (AIL) 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4). In this work, we explore the aggregation behaviours in AILs with different alkyl chains on the imidazolium group, i.e., 1-propyl-3-methylimidazolium tetrafluoroborate ([Pmim]BF4), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim]BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4). With the increase of the cation chain length, AILs have better solubility of the solvophobic part of the surfactants and hence a weaker driving force for self-assembly. Therefore, the critical micellization concentration of C16mimBr in AILs increases as confirmed by the surface tension and small angle X-ray scattering characterizations. More interesting things happen to the phase behaviours. Besides the micellar and lamellar lyotropic liquid crystal phases, a hexagonal lyotropic liquid crystal phase is formed in [Pmim]BF4 while hexagonal and bicontinuous cubic lyotropic liquid crystal phases are formed in [Bmim]BF4, [Hmim]BF4 and [Omim]BF4. It is surprising to observe richer phase behaviours in solvents of lower cohesive energy. The detailed structural information of various aggregates has been obtained by small-angle X-ray scattering. It is demonstrated that AILs work as not only solvents but also co-surfactants.

The structure – Activity correlation in the family of dicationic imidazolium surfactants: Antimicrobial properties and cytotoxic effect

BackgroundThe development of new effective microbicide surfactants and the search for the structure–biological activity relationship is an important and promising problem. Surfactants containing imidazolium fragment attract attention of researchers in the field of chemotherapy, because these compounds often exhibit high antimicrobial activity. The aim of this work is to identify the newly synthesized surfactants from the viewpoint of their potential usefulness in pharmacology and medicine. For this purpose, a detailed study of antimicrobial, hemolytic and cytotoxic activity of dicationic alkylimidazolium surfactants of the m-s-m (Im) series with a variable length of a hydrocarbon tail (m = 10, 12) and a spacer fragment (s = 2, 3, 4) was carried out. MethodsAggregation of surfactants in solutions was estimated by tensiometry and conductivity. Antimicrobial activity was determined by the serial dilution technique. Cytotoxic effects of the test compounds on human cancer and normal cells were estimated by means of the multifunctional Cytell Cell Imaging system. Cell Apoptosis Analysis was made by flow cytometry. ResultsThe test compounds show high antimicrobial activity against a wide range of test microorganisms and do not possess high hemolytic activity. Importantly, some of them display a bactericidal activity comparable to ciprofloxacin fluoroquinolone antibiotic against Gram-positive bacteria, including methicillin-resistant strains of S. aureus (MRSA). The cytotoxicity of the compounds against normal and tumor human cell lines has been tested as well, with cytotoxic effect and selectivity strongly controlled by structural factor and kind of cell line. Superior results were revealed for compound 10–4-10 (Im) in the case of HuTu 80 cell line (duodenal adenocarcinoma), for which IC50 value at the level of doxorubicin and a markedly higher selectivity index (SI 7.5) were demonstrated. Flow cytometry assay shows apoptosis-inducing effect of this compound on HuTu 80 cells, through significant changes in the potential of mitochondrial membrane. Major conclusionsAntibacterial properties are shown to be controlled by alkyl chain length, with the highest activity demonstrated by surfactants with decyl tail, with the length of the spacer fragment showing practically no effect. The results indicate that the mechanism of cytotoxic effect of the compounds can be associated with the induction of apoptosis via the mitochondrial pathway. General significanceSelectivity against pathogenic microorganisms and low toxicity against eukaryotic cells allow considering dicationic imidazolium surfactants as new effective antimicrobial agents. At the same time, high selectivity against some cancer cell lines indicates the prospect of their using as components of new anticancer drugs.

Adsorption of bisphenol A in aqueous solution by composite bentonite with organic moity

Bisphenol A (BPA) is a pollutant in the sewage of petroleum and petrochemical field, which is difficult to be treated efficiently. In this work, the composite modified Bentonite (CPAB/EGIS/B) was prepared by using ester-containing gemini imidazolium surfactant (EGIS) and cationic polyacrylamide (CPAB) as modifiers, CPAB/B and EGIS/B were also prepared. The samples were characterized by XRD, EA, FT-IR, SEM, and N 2 Physical adsorption and desorption, the changes of composition and structure of modified bentonite were studied. The adsorption performance of samples was tested by BPA, which shows that CPAB/EGIS/B has the strongest adsorption capacity for BPA solution. Under the conditions of initial pH, at 30 °C, the best adsorption effect was obtained when the dosage of the composite was 2.5 g/L for 180 min, the theoretical maximum adsorption capacity was 119.88 mg/g. CPAB and EGIS formed a more affinity organic micro-environment between bentonite layers and establish a nice structure-activity relationship with BPA. The adsorption of BPA onto CPAB/EGIS/B matched well with the pseudo-second-order model. The obtained isotherms data were described well by the Langmuir model and the adsorption is a spontaneous exothermic process. • Composite bentonite with ester imidazolium surfactant and cationic polyacrylamide. • A novel organic moity micro-environment between bentonite layers formed. • Composite bentonite shows high adsorption capacity to bisphenol A in aqueous solution. • The adsorption mechanism, kinetics, isotherms, and thermodynamics were studied. • Structure-activity relationship was established between composite bentonite and bisphenol A.

Micellization and Solvation Properties of Newly Synthesized Imidazolium- and Aminium-Based Surfactants

This work aimed to study the solvation properties of newly synthesized cationic surfactants: 1-hexyl-1-methyl-1H-imidazol-1-ium bromide (R6Im), 1-dodecyl-1-methyl-1H-imidazol-1-ium bromide (R12Im), N,N,N-tributylhexan-1-aminium bromide (R6N4), and N,N,N-tributyldodecan-1-aminium bromide (R12N4) in water and ethanol–water solvents with a 0.237 mole fraction of ethanol at 298.15 K using conductivity, refractive index, surface tension, and density measurements. Critical micelle concentration (CMC) for the synthesized surfactants was determined and discussed. Thermodynamic parameters including association constant, molal volume, and polarizability were calculated and discussed. Some surface properties of surfactants including excess surface concentration and minimum area per molecule were also calculated and discussed. A good agreement was found between the CMC values obtained from different techniques, such as conductivity, refractive index, and surface tension. Imidazolium surfactants had been proved to decrease the CMC and increase the association constant with the increase of ethanol mole fraction, while tributylamine had been proved to increase the CMC and decrease the association constant with the increase of ethanol mole fraction. Also, imidazolium surfactants had been proved to have higher CMC than tributylamine, which may be related to higher solvation of imidazolium surfactants than that of tributylamine. Both surfactants (R12Im) and (R12N4) were proved to have lesser CMC.

Application of Quantitative Structure-Property Relationship (QSPR) Models for the Predictions of Critical Micelle Concentration of Gemini Imidazolium Surfactants

The critical micelle concentration (cmc) is important indexes to determine the performance of surfactants quantitatively. In this study, based on the molecular descriptors, which calculated, by Dragon software, were proposed a quantitative structure-property relationship analysis for prediction of cmc of gemini imidazolium surfactants. In the present study, the associative neural networks (ASNN) and multiple linear regression analysis (MLRA) technique were used to interpret the chemical structural functionality (molecular descriptors) against the cmc of gemini imidazolium surfactants. The models were validated rigorously through 5-fold cross-validation. The ASNN method showed to be better than the MLRA method in terms of the internal and the external prediction accuracy with high statistical quality r2 = 0.96, q2 = 0.95, RMSE = 0.08 and MAE = 0.04 respectively. The developed QSPR models are publicly available on the web site at https://ochem.eu/model/11583111 for ASNN model and https://ochem.eu/model/43858671 for MLRA model. These models can be applied to predict the cmc of new gemini imidazolium surfactants.

The self-assembly of an imidazolium surfactant in an aprotic ionic liquid. 1. Comparison in aprotic and protic ionic liquids.

The aggregation behaviour of a cationic surfactant in an aprotic ionic liquid has been explored. Prolate micelles are formed at low surfactant concentrations, while a lamellar lyotropic liquid crystal phase is formed at high surfactant concentrations.

Light-responsive vesicles based on azobenzene containing imidazolium surfactants and sodium oleate

In this work, three light responsive imidazolium surfactants containing azobenzene moiety (CmAZOCnIMB, m = 0, 2, 4 and m + n = 6), namely, 1-[2-(4-phenylazo-phenoxy)-ethyl]-7-methylimidazolium bromide (C0AZOC6IMB), 3-[2-(4-phenylazo-phenoxy)-ethyl]-7-methylimidazolium bromide (C2AZOC4IMB), and 5-[2-(4-phenylazo-phenoxy)-ethyl]-7-methylimidazolium bromide (C4AZOC2IMB), were developed. These surfactants showed strong micellization tendency in the aqueous solution with their critical micelle concentrations (cmc) highly depending on the location of azobenzene moiety. Moreover, they also showed innate light response with excellent reversibility attributing to the trans-and cis-isomerization of azobenzene moiety under UV- and visible-light irradiation, respectively. Phase behavior showed that the addition of CmAZOCnIMB in the sodium oleate (NaOA) aqueous solution could induce the apparent growth of aggregates from spherical micelles to vesicles via wormlike micelles. Moreover, the presence of CmAZOCnIMB also endowed the catanionic systems with excellent light response, i.e., the typically reversible vesicle to multi-connected wormlike micelle network transitions. Static light scattering and dynamic rheological measurements were employed to characterize the turbidity and viscosity variation during the transitions. The morphological changes between vesicles and wormlike micelles were demonstrated by cryogen transmission electron microscopy (cryo-TEM) observation. Moreover, the transition mechanism was illustrated by 1H NMR and 2D Noesy spectra.

Co-assembly of gold nanocluster with imidazolium surfactant into ordered luminescent fibers based on aggregation induced emission strategy

Metal nanoclusters (NCs) with outstanding luminescent nature have been engineered as an emerging material, while the application of NCs in aqueous solution is subjected to major limitations because of their luminescence quenching in water. Herein, imidazolium surfactant 1-hexadecyl-3-methylimidazoliumbromide (C16mimBr) with opposite charge was used to overcome this issue based on aggregation induced emission (AIE) strategy through mild co-assembly of Au-NCs with C16mimBr. Of interest is that not only the luminescence of Au-NCs was enhanced but also fibers with strikingly regular layer-like periodic structures were obtained which is rarely prepared at room temperature. The underlying mechanism for the formation of ordered fibers was systematically investigated by a series of experiments. Firstly, the electrostatic interaction between Au-NCs and C16mimBr induces the aggregation of Au-NCs while the directional H-bonding facilitates the elongation of aggregates into 1D ordered structures. Besides, the hydrophobic interaction of alkyl chains is also crucial for the formation of fibers. Importantly, the emission of fibers exhibited reversible pH-responsiveness, i.e. when adding H+, the emission turns off meaning that the aggregates disintegrate along with fluorescence quenching. While with the addition of equal OH−, it turns on again. Such a type of optical materials with ordered structure will have potential applications in pH sensors and photoelectronic devices. It can be expected that this work will serve as a simple and low-cost platform for the preparation of ordered luminescent materials based on metal NCs.

Comparative study of three novel organo-clays modified with imidazolium-based gemini surfactant on adsorption for bromophenol blue

In this paper, an imidazolium-based gemini surfactant [C14-4-C14im]Br2 was fabricated as modifiers of vermiculite, silica nanosheets (from acid treating vermiculite) and montmorillonite. The modified clays were characterized with FT-IR, XRD, TG, EA, SEM and Washburn capillary rise method and investigated regarding the adsorption capacity for bromophenol blue (BPB). These organo-clays under similar availability of modifier show efficient removal for BPB with the order: C14-4-C14im-Vt > C14-4-C14im-SiNSs > C14-4-C14im-Mt. The adsorption processes are discovered fitting pseudo-second-order kinetics and Langmuir isotherm models. The qmax of organo-Vt, organo-SiNSs and organo-Mt calculated with Langmuir isotherm model are 400.19, 230.77 and 220.27 mg g−1, respectively, which prove organo-clays with imidazolium surfactants acquiring superior adsorbability to other known adsorbents. The adsorption capacity get higher with lower pH value and perform a positive correlation with the wettability. It can be concluded that electrostatic and hydrophobic interactions paly critical roles during the process. C14-4-C14im-SiNSs possesses higher adsorption efficiency (R = 99.53% at pH = 2, C0 = 200 mg L−1) noticeably. These provide some ideas for the use of imidazole-containing surfactants in modifying clays for contaminant treatment.

Tensiometric and Rheological Properties of Functionalized Imidazolium Surfactants at a Liquid–Gas Interface

The Du Nouy ring detachment, pendant drop, and maximum bubble pressure methods have been employed to study the tensiometric (surface tension) and rheological (viscoelasticity modulus and phase angle) characteristics of solutions of dicationic and monocationic imidazolium oximes at a liquid–gas interface. It has been revealed that dicationic oxime (1,3-bis(3'-cetylimidazolium-1'-yl)-2-oxyminopropane dichloride) has high surface activity and viscoelasticity modulus values. The experimental dependences of the dynamic surface (interfacial) tension and the rheological parameters of the surface layers of imidazolium oximes are adequately described in terms of the reorientational model. Ideas have been suggested on a possible reason for the high values of the viscoelasticity modulus of cetyl-substituted dicationic oxime at the liquid–gas interface.

Changes in Secondary Structure of Human Prion Protein Peptide 30-90 under the Influence of Selected Dicationic and Anionic Surfactants

The peptide (PrP30-90), which was used in this study, was designed on the basis of amino acid sequence of the unstructured N-terminal domain of human prion protein. Flexibility of this moiety and physicochemical properties of PrP N-terminal domain are related to the ability of prion protein to bind metal cations and are probably linked with the pathological conformational changes and formation insoluble deposits of this protein in the brain, which were observed in transmissible spongiform encephalopathies (e.g. Creutzfeldt-Jakob disease, CJD) [1]. This peptide, as well as N-terminal domain of PrP, possesses octarepeat sequences containing four histidine residues which overlap with binding sites of metal ions (copper, zinc etc). Interactions with surfactants probably could influence secondary structure of N-terminal domain or even full human prion protein. The present study was aimed at determination of the effects of cationic gemini imidazolium surfactant and anionic surfactant with different spacer groups on secondary structure of human prion protein at different pH values. The studies were carried out in MES buffer (pH 5.5) and phosphate buffer (pH 7,4) using circular dichroism (CD, Fourier transform infrared spectroscopy (FTIR) spectroscopy, NMR diffusometry and transmission electron microscopy (TEM). This work was supported by the funds from the National Science Centre (Poland) granted on the basis of decision no. 2016/23/N/ST5/02013. [1] Cobb N.J., Surewicz W.K. (2009) Biochemistry. 48(12), 2574-2585.

Association of imidazolium surfactants with poly(N-isopropylacrylamide)

Most investigations about polymer and surfactant interactions are related to standard surfactants, while the scope of literature using imidazolium surfactants is limited. In this work, conductometric and calorimetric techniques have been combined to determine the interaction of poly(N-isopropylacrylamide) with two surfactants: 1-tetradecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methylimidazolium chloride. The critical aggregation concentration and the polymer saturation point have been determined as a function of the polymer concentration. To explain the conductivity results, a new model has been proposed that considers the possibility of formation of free micelles before the polymer saturation. This model allows estimating the fraction of surfactant molecules aggregated to the polymer and the ionization degree of them, as well as the fraction of surfactant in the form of free micelles. Isothermal titration calorimetry results reveal that the interaction between the polymer and both surfactants is driven by entropic processes and that the aggregation process is non-cooperative at the initial stages.

Systematic investigation of ionic liquid-type gemini surfactants and their abnormal salt effects on the interfacial tension of a water/model oil system

Ionic liquid-type gemini surfactants have the advantages of both a gemini surfactant and a surface active ionic liquid and have been widely applied in multiple fields. A series of ionic liquid-type gemini imidazolium surfactants with a four-methylene spacer group (CnD, n=8, 10, 12) was introduced for chemical enhanced oil recovery. The CnD had great effects on the interfacial tension (IFT) between water and a model oil (toluene and n-decane, v:v=1:1), which appears to be closely related to the hydrocarbon chain length. Interestingly, the addition of NaCl caused abnormal variations in the IFT values. Based on the phase behaviour of the surfactants in solution, we proposed a mechanism to explain the relationship between the salt effects and the surfactant concentration, which was verified by measuring the IFT values between the surfactant solutions and a homologous series of alkanes with different alkane carbon numbers. The temperature effects were also evaluated to further explore the effects of the CnD molecular structures on the IFT.

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- (CnMIMBr) and dicationic imidazolium (Cn(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 (CnMIMBr) and the bolaform (Cn(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.

Reactivity of co-micellar systems based on dimeric functionalized tetraalkylammonium surfactant in phosphoryl and sulfonyl group transfer processes

The reactivity of co-micellar systems based on dimeric functionalized tetraalkylammonium surfactant in phosphoryl and sulfonyl group transfer processes is lower than the reactivity of systems based on analogous imidazolium surfactant. The observed difference in the kinetics of acyl group transfer promoted by dimeric surfactants differing by the nature of the cationic center is likely to be general, and it results from both different nucleophilicities of their oximate fragments and different modes of solubilization of hydrophobic substrates. The most probable reasons for the latter are differences in intramolecular Coulomb interactions and packing of surfactant molecules in co-micelles.

Surface Rheological Properties of Hydrophobically Modified Polyacrylamide and Imidazolium Surfactant Systems

AbstractThe dilational rheological properties of hydrophobically modified polyacrylamide (HMPAM) or hydrolyzed polyacrylamide (HPAM) solutions without and with imidazolium surfactants ([C14‐4‐C14im]Br2 and [C14mim]Br) at the air/water surface were investigated using oscillating bubble measurements. The results obtained suggest that imidazolium surfactants interact with the polymer on the surface, enhancing the dilational viscoelasticity of surface film. The dilational modulus value of [C14‐4‐C14im]Br2/HMPAM is higher than that of the [C14mim]Br/HMPAM system at low polymer concentration, confirming that [C14‐4‐C14im]Br2 with two head groups and two hydrophobic chains can combine with a polymer to form a strong film on the surface. Moreover, imidazolium surfactants have stronger hydrophobic interaction with HMPAM chains than those of HPAM, thus enhancing the surface film strength for a surfactant/HMPAM system. The surface interaction mechanism between polyacrylamide and imidazolium surfactant is proposed to result from the electrostatic interactions and the hydrophobic effect.

Manipulation of lyotropic liquid crystal behavior of ionic liquid-type imidazolium surfactant by amino acids

The effects of alkaline amino acids l-Lysine (l-Lys) and l-Arginine (l-Arg) on the lyotropic liquid crystal (LLC) behavior of ionic liquid-type imidazolium surfactant (1-tetradecyl-3-methylimidazolium bromide, C14mimBr) were investigated systematically. The corresponding properties were investigated by polarized optical microscopy (POM), small angle X-ray scattering (SAXS), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and rheological measurements. The results indicated that with the introduction of l-Lys, LLC phase of C14mimBr gradually undergoes the transition to an isotropic homogeneous phase, which demonstrated to be worm-like micelles (WLMs). While for C14mimBr/l-Arg system, it remained the hexagonal phases and merely induced the variation of the mechanical strength of C14mimBr LLCs. It can be speculated that the balance between electrostatic interaction, H-bond interaction, and hydrophobic interaction plays an important role in the phase transition of C14mimBr/amino acids. Our work can contribute to a better understanding of the effect of the additions especially amino acids on the influence of the surfactant aggregates and their macroscopic properties, which maybe open the door for wide applications in the biological system.

Properties of Polystyrene Clay Nanocomposites Prepared Using Two New Imidazolium Surfactants

Montmorillonite/polystyrene nanocomposites were prepared by in situ photopolymerization of styrene in the presence of 2% by weight of clay organomodified by two new imidazolium surfactants having in their structure an alkyl chain with 20 or 22 carbon atoms, respectively. Thermogravimetry showed that the new surfactants are more thermally stable than conventional alkylammonium surfactants. The properties of the obtained nanocomposites were compared with those of pristine polystyrene, with those of a microcomposite obtained by in situ polymerization of styrene in the presence of unmodified clay, and with those of a nanocomposite obtained starting from an organomodified clay with a short alkyl chain (12 carbon atoms) imidazolium surfactant. XRD, TEM, and rheological analysis showed that the clay/PS nanocomposites have a mixture of intercalated and partially exfoliated structure layers, where the higher the surfactant alkyl chain length, the higher the exfoliation degree. Kinetics curve of accelerated UV aging, obtained by following through infrared spectroscopy the increase of carbonyl functions during aging, showed that the rate of photooxidation of clay containing samples is higher than neat polystyrene. The rate is higher as a function of the degree of dispersion of the filler in the polymer matrix.

Equilibrium, kinetics, and thermodynamics studies of Cr(VI) adsorption from aqueous solutions on organoclay using ionic liquid-type imidazolium surfactants

Equilibrium, kinetics, and thermodynamics studies of Cr(VI) adsorption from aqueous solutions on organoclay using ionic liquid-type imidazolium surfactants

Sustainable oleic and stearic acid based biodegradable surfactants

Renewable ester functionalized fatty acid based imidazolium surfactant.