A Novel Ionic Liquid-in-Oil Microemulsion Composed of Biologically Acceptable Components: An Excitation Wavelength Dependent Fluorescence Resonance Energy Transfer Study

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.

Mimic Nature Using Chemotaxis of Ionic Liquid Microdroplets for Drug Delivery Purposes

Due to the growing prevalence of incurable diseases, such as cancer, worldwide, nowadays, the development of smart drug delivery systems is an inevitable necessity. Chemotaxis-driven movement of ionic liquid microdroplets containing therapeutic compounds is a well-known example of a smart drug delivery system. This review aims to classify, summarize, and compare ionic liquid-based chemotaxis systems in an easily understandable article. Chemotaxis is the basis of the movement of cells and microorganisms in biological environments, which is the cause of many vital biochemical and biological processes. This review attempts to summarize the available literature on single-component biomimetic and self-propelling microdroplet systems based on ionic liquids, which exhibit chemotaxis and spontaneously move in a determined direction by an external gradient, particularly a chemical change. It also aims to review artificial ionic liquid-based chemotaxis systems that can be used as drug carriers for medical purposes. The various ionic liquids used for this purpose are discussed, and different forms of chemical gradients and mechanisms that cause movement in microfluidic channels will be reviewed.

In Situ Generated Silver Nanodot Förster Resonance Energy Transfer Pair Reveals Nanocage Sizes

Characterizing nanocages in macromolecules is one of the keys to understanding various biological activities and further utilizing nanocages for novel materials synthesis. However, fast and straightforward detection of the nanocage size remains challenging. Here, we present a new approach to detect the diameter of a nanocage by Förster resonance energy transfer (FRET) of luminescent silver nanodot pairs with reverse micelles as a model. Silver nanodot FRET pairs can be generated in situ from a single silver nanodot species with critical energy transfer distances, R₀, of 4.8-6.5 nm. We have applied this approach to clarify the size variation of the water nanocage in nonionic surfactant Triton X-100-based reverse micelles. FRET efficiency decreases as more water is added, indicating that the size of the reverse micelles continuously expands with water content. The silver element in the nanocage also enhances the visualization of the nanocage under cryo-TEM imaging. The diameter of the water nanocage measured with the above approach is consistent with that obtained by cryo-TEM, demonstrating that the FRET measurement of silver nanodots can be a fast and accurate tool to detect nanocage dimensions. The above demonstration allows us to apply our strategy to other protein-based nanocages.

Study of Ionic Liquid Microemulsions: Ethylammonium Nitrate/TritonX-100/Cyclohexane

In this study, ionic liquid (IL), specifically ethylammonium nitrate (EAN), was used instead of water to form nonaqueous microemulsions with cyclohexane and the nonionic surfactant Triton X-100 (TX-100). The phase behavior of the ternary system was investigated, and the microemulsions of ionic liquid-in-oil (IL/O) and oil-in-ionic liquid (O/IL) and the bicontinuous microregion were identified through traditional electrical conductivity measurement. The micropolarities of the IL/O microemulsions were determined via UV–Vis spectroscopy with methyl orange as an absorption probe. Results indicated that the polarity of the reverse micelles remained constant but that of the IL/O microemulsions increased when IL pools were formed. Fourier transform infrared spectroscopy was used to study the interaction mechanism between TX-100 and EAN molecules in IL/O microemulsions. We demonstrated that IL/O microemulsions may be promising for application due to the unique features of ILs and microemulsions.

Dielectric relaxation of nonaqueous ionic liquid microemulsions: polarization, microstructure, and phase transition

Two nonaqueous ionic liquid (IL) microemulsions (toluene/TX-100/[bmim][PF₆] and [bmim][BF₄]/TX-100/benzene) were studied by dielectric spectroscopy covering a wide frequency range (40 Hz to 110 MHz).

High internal ionic liquid phase emulsion stabilized by metal-organic frameworks

The emulsification of metal-organic frameworks (MOFs) for the two immiscible phases of water and ionic liquid (IL) was investigated for the first time. It was found that Ni-BDC (BDC = 1,4-dicarboxybenzene) can emulsify water and ILs and favor the formation of high internal phase emulsions (HIPEs) under certain experimental conditions. The microstructures of the HIPEs were characterized by confocal laser scanning microscopy using a fluorescent dye Rhodamine B, which proves that the HIPEs are the IL-in-water type. Further results reveal that the HIPE forms during the IL-in-water to water-in-IL emulsion inversion. The possibilities of the HIPE formation by other MOFs (Cu-BDC and Zn-BDC) were explored and the mechanism for HIPE formation was discussed. The MOF-stabilized HIPE was applied to the in situ synthesis of a MOF/polymer composite by HIPE polymerization. The macroporous MOF/polyacrylamide network and MOF/polystyrene microspheres were obtained from the HIPEs, respectively.

Amphiphile self-assemblies in supercritical CO2 and ionic liquids

Supercritical (sc) CO2 and ionic liquids (ILs) are very attractive green solvents with tunable properties. Using scCO2 and ILs as alternatives of conventional solvents (water and oil) for forming amphiphile self-assemblies has many advantages. For example, the properties and structures of the amphiphile self-assemblies in these solvents can be easily modulated by tuning the properties of solvents; scCO2 has excellent solvation power and mass-transfer characteristics; ILs can dissolve both organic and inorganic substances and their properties are designable to satisfy the requirements of various applications. Therefore, the amphiphile self-assemblies in scCO2 and ILs have attracted considerable attention in recent years. This review describes the advances of using scCO2 or/and ILs as amphiphile self-assembly media in the last decade. The amphiphile self-assemblies in scCO2 and ILs are first reviewed, followed by the discussion on combination of scCO2 and ILs in creating microemulsions or emulsions. Some future directions on the amphiphile self-assemblies in scCO2 and ILs are highlighted.

Development of novel ionic liquid-based microemulsion formulation for dermal delivery of 5-Fluorouracil

The present study was aimed at synthesizing an imidazole-based ionic liquid 1-butyl-3-methylimidazolium bromide (BMIMBr) and subsequent development of a novel ionic liquid-in-oil (IL/o) microemulsion (ME) system for dermal delivery of a poorly permeating drug 5-fluorouracil (5-FU). A significant enhancement in the solubility of 5-FU was observed in BMIMBr. IL/o MEs of 5-FU were prepared using isopropyl myristate, Tween 80/Span 20, and BMIMBr. Results of ex vivo skin permeation studies through mice skin indicated that the selected IL/o ME exhibited 4-fold enhancement in percent drug permeation as compared to aqueous solution, 2.3-fold as compared to hydrophilic ointment, and 1.6-fold greater permeation than water in oil (w/o) ME. The results of in vivo studies against dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mice skin carcinogenesis demonstrated that the IL/o ME could effectively treat skin cancer in 4 weeks. In addition, the side effects such as erythema and irritation associated with the conventional formulations were not observed. Histopathological studies showed that the use of IL/o ME caused no anatomic and pathological changes in the skin structure of mice. These studies suggest that the use of IL-based ME system can efficiently enhance the solubility and permeability of 5-FU and hence its therapeutic efficacy.

Shape and size controlled synthesis of MOF nanocrystals with the assistance of ionic liquid mircoemulsions

In this work, the La-metal-organic frameworks (La-MOFs) were synthesized using lanthanum(III) nitrate and 1,3,5-benzenetricarboxylic acid (BTC) in H2O-in-1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), bmimPF6-in-water, and the bicontinuous microemulsions stabilized by surfactant TX-100. The MOFs prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and FT-IR methods, and the microstructures of the microemulsions in the H2O/bmimPF6/TX-100 system were studied by small-angle X-ray scattering (SXAS) technique. It was shown that the dispersed droplets in the water-in-bmimPF6, bicontinuous and bmimPF6-in-water microemulsions were spherical, lamellar, and cylindrical, respectively. The shapes of the La-MOFs synthesized were similar to that of the droplets in the corresponding microemulsions. This indicated that the morphology of MOFs could be controlled by the microstructures of the microemulsions. On the basis of the systematic experimental results, the mechanism for controlling the morphology of the MOFs was proposed.

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.