A Step toward the Development of High-Temperature Stable Ionic Liquid-in-Oil Microemulsions Containing Double-Chain Anionic Surface Active Ionic Liquid

Dielectric Depiction of 1-Butyl-3-methylimidazolium Tetrafluoroborate/1-Butyl-3-methylimidazolium 1,4-Bis(2-ethylhexyl) Sulfosuccinate/Benzene Microemulsions: Percolation, Interface Polarization, and Electrical Parameters

Two dielectric relaxations located at approximately 10 and 300 MHz were analyzed in the microemulsion composed of the polar ionic liquid (PIL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), the surface-active ionic liquid (SAIL) 1-butyl-3-methylimidazolium 1,4-bis(2-ethylhexyl) sulfosuccinate ([bmim][AOT]), and benzene. The curve of the dc conductivity vs PIL weight fraction shows two inflection points, namely, 16.69 and 27.90 wt %, which are used to divide the PIL/O, bicontinuous (B.C.), and O/PIL subregions. The critical exponents of percolation u = 0.75, 0.79, and 0.80 are suggested from the scaling dependence of dc conductivity on the PIL weight fraction, together with frequency dependences of both permittivity and loss angle, which all infer that static percolation occurs in the microemulsion. Only one dielectric relaxation at high frequency was observed in the PIL/O subregion, when the concentration increased to the boundary between the PIL/O and B.C. subregions; the second dielectric relaxation appeared at low frequency. The high-frequency relaxation is caused by interfacial polarization. The low-frequency relaxation is attributed to the dipole-oriented polarization of AOT-. When the oil content of the system was reduced, the interface became softer to allow more AOT- to rotate, and the cation shifted from moving around its long axis to rotating along its short axis. The static dielectric constant of [bmim][AOT] was given. The dielectric constants and conductivity of the dispersed and continuous phases in the PIL/O and O/PIL subregions were calculated from the dielectric parameters of high-frequency relaxation.

Ionic Liquids in Pharmaceutical and Biomedical Applications: A Review

The unique properties of ionic liquids (ILs), such as structural tunability, good solubility, chemical/thermal stability, favorable biocompatibility, and simplicity of preparation, have led to a wide range of applications in the pharmaceutical and biomedical fields. ILs can not only speed up the chemical reaction process, improve the yield, and reduce environmental pollution but also improve many problems in the field of medicine, such as the poor drug solubility, product crystal instability, poor biological activity, and low drug delivery efficiency. This paper presents a systematic and concise analysis of the recent advancements and further applications of ILs in the pharmaceutical field from the aspects of drug synthesis, drug analysis, drug solubilization, and drug crystal engineering. Additionally, it explores the biomedical field, covering aspects such as drug carriers, stabilization of proteins, antimicrobials, and bioactive ionic liquids.

Water-pluronic-ionic liquid based microemulsions: Preparation, characterization and application as micro-reactor for enhanced catalytic activity of Cytochrome-c

Microemulsions (µEs), comprising water as polar component, pluronic (normal, L35 and reverse, 10R5) as surfactant and a hydrophobic ionic liquid (HIL) as non-polar component have been prepared and characterized. Owing to higher surface activity, pluronics have promoted the formation of µEs without the use of co-surfactant. Thus prepared µEs have been utilized as nano-reactors for the oxidation of guaiacol in the presence of Cytochrome-c (Cyt-c) at 15, 20, and 25 °C. A 3.2- and 1.3-fold increase in the rate of formation of product of enzymatic catalysis in direct µE (HIL-in-water) with reverse pluronic (10R5) is observed at 15 and 20 °C as compared to that in buffer. However, negligible enzymatic activity is observed in the direct µE formed by normal pluronic (L35). The catalytic activity of Cyt-c decreases in reverse µEs (water-in-HIL) as compared to direct µEs irrespective of the nature of pluronic used. The contrasting nature of nano-interfaces formed by pluronics in µEs and the extent of hydration of these nano-interfaces controlled by temperature exerts varying influence on the catalytic activity of Cyt-c. It is expected that the present work would result in providing a versatile platform for the creation of new IL and pluronic-based µEs for bio-catalytic applications, which have never been reported.

Deciphering Solvation Effects in Aqueous Binary Mixtures by Fluorescence Behavior of 4-Aminophthalimide: The Comparison Between Ionic Liquids and Alcohols as Cosolvents

Ionic liquids (ILs) have received attention for many years due to them being very promising as green solvent substitutes, but they are not fully understood, especially their behavior dissolved in other solvents, for example, water. Thus, the goal of this contribution is to show insight into the different IL-water mixtures interaction. In this way, two protic ILs (PILs), ethylammonium nitrate (EAN) and 1-methylimidazolium acetate (MIA), mixed with water were investigated. To study the PILs-water interaction, the unique spectroscopical behavior in water of the molecular probe 4-aminophthalimide (4-AP) was used. 4-AP emission spectra show hypsochromic shifting by changing the excitation wavelength and, using time-resolved spectroscopy, can be detected by a blue shifting with time. Also, the water mixture of an aprotic IL, 1-methyl-3-butylimidazolium tetrafluoroborate (bmimBF₄), and three alcohols, methanol (MeOH), 2-propanol (2-PrOH), and t-butanol (t-BOH), were investigated for comparison. Our results show that the water-ILs interaction is dominated by the size of the IL components, in particular, the cation size. Thus, in MIA-water and bmimBF₄-water mixtures, 4-AP is mostly solvated by the IL, even at a low IL molar fraction, as in the t-BOH-water mixture. This finding is especially interesting when ILs-water mixtures are used as a solvent in an organic reaction, where it may call attention to water probably not being the solvent that is interacting with the reactants.

Advances Brought by Hydrophilic Ionic Liquids in Fields Involving Pharmaceuticals

The negligible volatility and high tunable nature of ionic liquids (ILs) have been the main drivers of their investigation in a wide diversity of fields, among which is their application in areas involving pharmaceuticals. Although most literature dealing with ILs is still majorly devoted to hydrophobic ILs, evidence on the potential of hydrophilic ILs have been increasingly provided in the past decade, viz., ILs with improved therapeutic efficiency and bioavailability, ILs with the ability to increase drugs' aqueous solubility, ILs with enhanced extraction performance for pharmaceuticals when employed in biphasic systems and other techniques, and ILs displaying low eco/cyto/toxicity and beneficial biological activities. Given their relevance, it is here overviewed the applications of hydrophilic ILs in fields involving pharmaceuticals, particularly focusing on achievements and advances witnessed during the last decade. The application of hydrophilic ILs within fields involving pharmaceuticals is here critically discussed according to four categories: (i) to improve pharmaceuticals solubility, envisioning improved bioavailability; (ii) as IL-based drug delivery systems; (iii) as pretreatment techniques to improve analytical methods performance dealing with pharmaceuticals, and (iv) in the recovery and purification of pharmaceuticals using IL-based systems. Key factors in the selection of appropriate ILs are identified. Insights and perspectives to bring renewed and effective solutions involving ILs able to compete with current commercial technologies are finally provided.

Photoresponsive supramolecular strategy for controlled assembly in light-inert double-chain surfactant system

HYPOTHESIS

One of the main advances in double-chain surfactant systems has been their progress from the construction of assemblies to the transformation application in medicine and material science, especially to the drug delivery systems. Thus, it is critical to develop stimuli-responsive assemblies based on double-chain surfactants. We predicted that reversible assembly switching can be achieved by manipulation of the ternary host-guest competitive complexation among β-cyclodextrin (β-CD), surfactants, and designed azobenzene (Azo).

EXPERIMENTS

In this work, Azo was introduced into vesicles using supramolecular assembly strategy. Vesicles are formed only when Azo moieties are in trans-form. UV switching of Azo groups led to fast disruption of the Azo@β-CD complexes and relatively slow disintegration of the vesicles. With the alterative irradiation of UV and Vis light, the photoisomerization of azo group provokes the reversible disassembly and reassembly of vesicles.

FINDINGS

This photo-responsive supramolecular strategy offered a controllable way to prepare responsive vesicles assembled from complex double-chain surfactants, such as phospholipids, which could be further used in drug delivery systems. This new perspective is instructive for the design and functional use of complex surfactants assembly. Importantly, the study results paved the way for the development of novel light-responsive assembly materials operating in aqueous media and biological field.

Biocompatible Ionic Liquid-Mediated Micelles for Enhanced Transdermal Delivery of Paclitaxel

Chemotherapeutic cytotoxic agents such as paclitaxel (PTX) are considered essential for the treatment of various cancers. However, PTX injection is associated with severe systemic side effects and high rates of patient noncompliance. Micelle formulations (MFs) are nano-drug delivery systems that offer a solution to these problems. Herein, we report an advantageous carrier for the transdermal delivery of PTX comprising a new MF that consists of two biocompatible surfactants: cholinium oleate ([Cho][Ole]), which is a surface-active ionic liquid (SAIL), and sorbitan monolaurate (Span-20). A solubility assessment confirmed that PTX was readily solubilized in the SAIL-based micelles via multipoint hydrogen bonding and cation-π and π-π interactions between PTX and SAIL[Cho][Ole]. Dynamic light scattering (DLS) and transmission electron microscopy revealed that in the presence of PTX, the MF formed spherical PTX-loaded micelles that were well-distributed in the range 8.7-25.3 nm. According to DLS, the sizes and size distributions of the micelle droplets did not change significantly over the entire storage period, attesting to their physical stability. In vitro transdermal assessments using a Franz diffusion cell revealed that the MF absorbed PTX 4 times more effectively than a Tween 80-based formulation and 6 times more effectively than an ethanol-based formulation. In vitro and in vivo skin irritation tests revealed that the new carrier had a negligible toxicity profile compared with a conventional ionic liquid-based carrier. Based on these findings, we believe that the SAIL[Cho][Ole]-based MF has potential as a biocompatible nanocarrier for the effective transdermal delivery of poorly soluble chemotherapeutics such as PTX.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Ionic Liquid Green Assembly-Mediated Migration of Piperine from Calf-Thymus DNA: A New Possibility of the Tunable Drug Delivery System

Biocompatible surface-active ionic liquid (SAIL) was used first to study the deintercalation process of a well-known natural compound piperine (PIP) as an anticancer drug, obtained from PIP-calf thymus DNA (ctDNA) complex under controlled experimental conditions. In this study, we have been exploring the interaction of PIP in SAIL (1-butyl-3-methylimidazolium octyl sulfate ionic liquid ([C₄mim][C₈OSO₃])), ctDNA, and deintercalation of PIP from the PIP-ctDNA complex through SAIL micelle using various spectroscopic techniques. Absorption, emission, and lifetime decay measurements provide strong evidence of the relocation of PIP molecules from ctDNA to SAIL micelle. Fluorescence quenching and steady-state fluorescence anisotropy were employed to examine the exact location of PIP in different media. Moreover, the surface tension technique was also employed to confirm the release of PIP molecules from the PIP-ctDNA complex in the presence of SAIL. Circular dichroism analysis suggested that SAIL micelle does not perturb the ctDNA structure, which supported the fact that SAIL micelle can be used as a safe vehicle for PIP. Overall, the study highlighted a novel strategy for deintercalation of drug using SAIL because the release of the drug can be controlled over a period by varying the concentration and composition of the SAIL.

Ionic liquid associated with ultrasonic-assisted extraction: A new approach to obtain carotenoids from orange peel

The aim of this study was to develop a new method for carotenoid extraction from orange peel, using ionic liquid (IL) to replace conventional organic solvents, assisted by ultrasound. Four different IL were tested: 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]), 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]), and 1-hexyl-3-methylimidazolium chloride ([HMIM][Cl]). Response surface methodology was applied in order to optimize the carotenoid extraction conditions, and Amberlite XAD-7HP resin was used to separate the carotenoids from the IL, allowing their recovery. Determination of carotenoids was carried out by high-performance liquid chromatography coupled to photodiode array and mass spectrometry detectors (HPLC-DAD-MSⁿ). Thermal stability at different temperatures (60 °C and 90 °C) and peroxyl radical scavenging activity of the carotenoid extracts obtained with acetone and IL were evaluated. [BMIM][Cl] was the most effective IL, leading to a total carotenoid content of 32.08 ± 2.05 μg/g, while 7.88 ± 0.59 μg/g of dry matter was obtained by acetone extraction. IL and carotenoid recoveries using XAD-7HP resin were in the range of 59.5-63.8% and 52.2-58.7%, respectively. A carotenoid extract was successfully obtained with IL, finally isolated just by using ethanol, besides being more stable and presenting higher antioxidant activity than that obtained with acetone.

Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

Nanoreactors stable up to 200 °C: a class of high temperature microemulsions composed solely of ionic liquids

A class of microemulsions solely consisting of ionic liquids was shown to maintain nanoscale droplets up to about 200 °C, and this unique property was used to prepare porous Pt where the microemulsions played the roles of a solvent, a template and a reductant.

Broadband dielectric spectroscopy of micelles and microemulsions formed in a hydrophilic ionic liquid: the relaxation mechanism and interior parameters

Permittivity, conductivity and volume fraction of continuous and dispersed phases of micelles and non-aqueous microemulsions formed in ionic liquid.

Cholesterol Based Surface Active Ionic Liquid That Can Form Microemulsions and Spontaneous Vesicles

In this article, we have reported the synthesis and physicochemical characterization of a novel l-glycine amino acid derived cholesterol based surface active ionic liquid (SAIL). This SAIL has been explored for the preparation of ionic liquid (IL)-in-oil microemulsions and vesicles. The formation of IL-in-oil microemulsion is characterized by construction of a ternary phase diagram, dynamic light scattering (DLS) measurement, proton nuclear magnetic resonance (¹H NMR) study, fluorescence measurement using coumarin 480 (C-480) as a molecular probe, and also by recording the diffusion behavior of the molecular probe rhodamine 6G (R6G) in microemulsion droplets through the fluorescence correlation spectroscopy (FCS) technique. Similarly, the spontaneous vesicle formation from the SAIL in water has been established using DLS, transmission electron microscopy (TEM), cryogenic-transmission electron microscopy (cryo-TEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), FCS, and fluorescence lifetime imaging microscopy (FLIM) measurements. These aggregates may potentially serve as good biomimicking models and possible drug carriers.

Surfactant-free microemulsions of 1-butyl-3-methylimidazolium hexafluorophosphate, propylamine nitrate, and water

Generally, surfactants (or amphiphiles) are believed to be necessary components of microemulsions. However, it has been demonstrated that, in the absence of traditional surfactants, microemulsions can also form from a ternary system of two immiscible fluids (i.e., oil and water phases) and an amphi-solvent, but the current understanding of such surfactant-free microemulsions (SFMEs) is very limited. Herein, we report an SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), the protic IL propylamine nitrate (PAN), and water, in which bmimPF₆ and PAN are used as the oil phase and the amphi-solvent, respectively. The microstructures and structural transitions of the SFME were investigated using cyclic voltammetry, fluorescence spectroscopy, and ultraviolet-visible spectroscopy. The SFME exhibited water-in-bmimPF₆ (W/IL), bicontinuous (BC), and bmimPF₆-in-water (IL/W) microstructures, depending on the composition of the ternary system, similar to the case of traditional surfactant-based microemulsions (SBMEs). The three kinds of microstructures were confirmed by cryogenic transmission electron microscopy (cryo-TEM) observations. To the best of our knowledge, this is the first report on SFMEs composed of two ILs as components, especially where one is used as the amphi-solvent.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

Enhanced stability and water solubilizing capacity of water-in-oil microemulsions based on protic ionic liquids

In view of this limited research on pILs in microemulsions, here we study the formation and characterization of a series of pIL–water/oil microemulsions with specific questions on the effect of pILs on water uptake capacity and thermal stability of W/O microemulsions.

N,N-Dimethylpyridin-4-amine (DMAP) based ionic liquids: evaluation of physical properties via molecular dynamics simulations and application as a catalyst for Fisher indole and 1H-tetrazole synthesis

N,N-dimethylpyridin-4-amine (DMAP) based ionic liquids (ILs) as new and efficient catalysts for the facile synthesis of indoles (via Fischer indole synthesis), and 1H-tetrazoles (via click chemistry).

How the cation 1-butyl-3-methylimidazolium impacts the interaction between the entrapped water and the reverse micelle interface created with an ionic liquid-like surfactant

The behavior of the interfacial water entrapped in reverse micelles (RMs) formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) dissolved in benzene (or chlorobenzene) was investigated using noninvasive techniques such as dynamic light scattering (DLS), static light scattering (SLS), FT-IR and (1)H NMR. The DLS and SLS results reveal the formation of discrete spherical and non-interacting water droplets stabilized by the bmim-AOT surfactant. Moreover, since the droplet size increases as the W0 (W0 = [water]/[surfactant]) value increases, water interacts with the RM interface. From FT-IR and (1)H NMR data, a weaker water-surfactant interaction in bmim-AOT RMs in comparison with the RMs created by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) is detected. Consequently, there are less water molecules interacting with the interface in bmim-AOT RMs, and their hydrogen bond network is not completely disrupted as they are in Na-AOT RMs. The results show how the nature of the new cation impacts the interaction between the entrapped water and the RM interface, modifying the interfacial water structure in comparison with the results known for Na-AOT.

Solvation, rotational relaxation and fluorescence correlation spectroscopic study on ionic liquid-in-oil microemulsions containing triple-chain surface active ionic liquids (SAILs)

In this article, solvation dynamics and rotational relaxation approaches have been applied to explore the microheterogeneity of surface active ionic liquid (SAIL) containing microemulsions, i.e. [P₁₃][Tf₂N] or [N₃₁₁₁][Tf₂N]/[BHD][AOT]/[IPM].

Aggregation Behaviours of Surface-Active Ionic Liquids 1-Alkyl-3-methylimidazolium Bis(2-ethylhexyl)sulfosuccinate

The systematic investigation of the aggregation behaviours of newly synthesised surface-active ionic liquids 1-alkyl-3-methylimidazolium bis(2-ethylhexyl)sulfosuccinate ([Cnmim][AOT], n = 2, 3, 5, 6, 7) by various techniques is reported. The critical aggregation concentrations (CACs) and the standard Gibbs free energies of aggregation () were determined from measurements on conductivity, fluorescence, and surface tension, which suggested a stronger self-assembly ability in the bulk solution for [Cnmim][AOT] surfactants with longer alkyl chain cations. An interesting structure transition driven by the penetration of the imidazolium cation into the aggregate when n > 4 was found by analysis of the variations of the values of CAC, , the degree of counter ion binding (β), and the micropolarity (I1/I3) immediately after the CAC with changing alkyl chain length of the imidazolium cation, which was further confirmed by 1H NMR measurements.

Non-Faradaic Energy Storage by Room Temperature Ionic Liquids in Nanoporous Electrodes

The enhancement of non-Faradaic charge and energy density stored by ionic electrolytes in nanostructured electrodes is an intriguing issue of great practical importance for energy storage in electric double layer capacitors. On the basis of extensive molecular dynamics simulations of various carbon-based nanoporous electrodes and room temperature ionic liquid (RTIL) electrolytes, we identify atomistic mechanisms and correlations between electrode/electrolyte structures that lead to capacitance enhancement. In the symmetric electrode setup with nanopores having atomically smooth walls, most RTILs showed up to 50% capacitance increase compared to infinitely wide pore. Extensive simulations using asymmetric electrodes and pores with atomically rough surfaces demonstrated that tuning of electrode nanostructure could lead to further substantial capacitance enhancement. Therefore, the capacitance in nanoporous electrodes can be increased due to a combination of two effects: (i) the screening of ionic interactions by nanopore walls upon electrolyte nanoconfinement, and (ii) the optimization of nanopore structure (volume, surface roughness) to take into account the asymmetry between cation and anion chemical structures.

Light induced micelle to vesicle transition in an aqueous solution of a surface active ionic liquid

A new simple surface active ionic liquid displayed reversible micelle–vesicle transition under alternative UV/vis irradiation without additives.

CO₂-responsive microemulsions based on reactive ionic liquids

We demonstrate that the nanodomains within a ternary system consisting of oil, surfactant, and a new reactive ionic liquid can be tuned reversibly upon exposure to and removal of CO2 under mild conditions of temperature and pressure. The equilibrium microstructures of these domains have been characterized by small-angle neutron scattering and demonstrate that control over emulsion morphology (and therefore physicochemical properties such as viscosity) and the breaking of emulsions can be achieved without the need for irreversible changes in system composition or significant energy input.

Fluorescence resonance energy transfer in microemulsions composed of tripled-chain surface active ionic liquids, RTILs, and biological solvent: an excitation wavelength dependence study

In this article we have reported the fluorescence resonance energy transfer (FRET) study in our earlier characterized surface active ionic liquids (SAILs)-containing microemulsion, i.e., N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([P13][Tf2N])/[CTA][AOT]/isopropyl myristate ([IPM]) and N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide ([N3111][Tf2N])/[CTA][AOT]/[IPM] microemulsions (Banerjee, C.; Mandal, S.; Ghosh, S.; Kuchlyan, J.; Kundu, N.; Sarkar, N. J. Phys. Chem. B 2013, 117, 3927-3934). The occurrence of effective FRET from the donor, coumarin-153 (C-153) to the acceptor rhodamine 6G (R6G) is evident from the decrease in the steady state fluorescence intensity of the donor with addition of acceptor and subsequent increase in the fluorescence intensity of the acceptor in the presence of donor. The excitation wavelength dependent FRET from C-153 to R6G has also been performed to assess the dynamic heterogeneity of these confined systems. In time-resolved experiments, the significant rise time of the acceptor in the presence of the donor further confirms the occurrence of FRET. The multiple donor-acceptor (D-A) distances, for various microemulsions, obtained from the rise times of the acceptor emission in the presence of a donor can be rationalized from the varying distribution of the donor, C-153, in the different regions of the microemulsion. Time-resolved measurement reveals that with increasing excitation wavelength from 408 to 440 nm, the contribution of the faster rise component of FRET increases significantly due to the close proximity of the C-153 and R6G in the polar region of the microemulsion where occurrence of FRET is very high. Moreover, we have also studied the FRET with variation of R (R = [room temperature ionic liquids (RTILs)]/[surfactant]) and shown that the effect of excitation wavelength on FRET is similar irrespective of R values.