Formation, characterization and enzyme activity in water-in-hydrophobic ionic liquid microemulsion stabilized by mixed cationic/nonionic surfactants

A study on the preparation conditions of lidocaine microemulsion based on multi-objective genetic algorithm

Background: Topical lidocaine microemulsion preparations with low toxicity, low irritation, strong transdermal capability and convenient administration are urgently needed. Methods: Box-Behnken design was performed for three preparation conditions of 5% lidocaine microemulsions: mass ratio of the mass ratio of surfactant/(oil phase + surfactant) (X1), the mass ratio of olive oil/(α-linolenic acid + linoleic acid) (X2) and the water content W% (X3). Then, five multi-objective genetic algorithms were used to optimize the three evaluation indices to optimize the effects of lidocaine microemulsion preparations. Finally, the ideal optimization scheme was experimentally verified. Results: Non-dominated Sorting Genetic Algorithm-II was used for 30 random searches. Among these, Scheme 2: X1 = 0.75, X2 = 0.35, X3 = 75%, which resulted in Y1 = 0.17 μg/(cm2·s) and Y2 = 0.74 mg/cm2; and the Scheme 19: X1 = 0.68, X2 = 1.42, X3 = 75% which resulted in Y1 = 0.14 μg/(cm2·s) and Y2 = 0.80 mg/cm2, provided the best matches for the objective function requirements. The maximum and average fitness of the method have reached stability after 3 generations of evolution. Experimental verification of the above two schemes showed that there were no statistically significant differences between the measured values of Y1 and Y2 and the predicted values obtained by optimization (p > 0.05) and are close to the target value. Conclusion: Two lidocaine microemulsion preparation protocols were proposed in this study. These preparations resulted in good transdermal performance or long anesthesia duration, respectively.

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.

Mixed micelles and bicontinuous microemulsions: Promising media for enzymatic reactions

Enzymes, the natural catalysts, replace catalysts of chemical origin in a wide spectrum of reactions and generally work under environment friendly conditions. Various strategies are adopted to modify catalytic activities of enzymes further, of which one is application of novel reaction medium. This work reviews applicability of novel media like mixed micelles and bicontinuous microemulsions in enzymatic reactions and points out their capability to play bigger roles in enzyme catalysis. Ionic reverse micelles reduced catalytic activities of enzymes through denaturation. Addition of nonionic surfactant to these reverse micelles led to corresponding mixed micelles and thus restored or sometimes enhanced catalytic abilities of enzymes. Mixed micelles comprising of two nonionic surfactants, bicontinuous microemulsion containing two anionic surfactants also acted as efficient reaction media for enzymes. Even a cationic/anionic/nonionic mixed micelle was found to increase activity of enzyme. Mixed micelles and bicontinuous microemulsions comprising of anionic and zwitterionic surfactants augmented enzyme catalysis. Mixed micelles and bicontinuous microemulsions containing ionic liquid and surfactant also had critical impact on enzyme catalysis. Catalytic abilities of enzymes altered significantly in substrate/surfactant and bile salt/surfactant mixed micelles. Concentrations of individual surfactant, molar ratio of surfactants, and molar ratio of water to total surfactants had notable impacts on enzyme catalysis in those media.

Design, optimization and evaluation of co-surfactant free microemulsion-based hydrogel with low surfactant for enhanced transdermal delivery of lidocaine

Microemulsion is the preferred vehicle for local anesthetics; however, the toxicity and irritation associated with a quantity use of surfactants (S) and co-surfactants (CS), i.e., medium- or short-chain alcohols, restrict its commercial application. In this study, efforts have been made to enlarge the CS-free microemulsion area by mixing olive oil (OL) with α-linolenic acid (ALA) and linoleic acid (LA), and by using vitamin E succinate (VES) as an auxiliary oil. Through Box-Behnken design and the optimization of nondominated sorting genetic algorithm II, the optimal microemulsion formulation (M_E0) with a large steady-state simultaneous permeation rate (J_s) and skin retention was screened as 3.23% OL, 0.45% ALA, 1.81% LA, 0.91% VES, 13.60% S, 5% lidocaine and water. Three percent ethanol was screened as a permeability enhancer for the hydrogel of M_E0, which showed a statistical increase in J_s and skin retention through the abdominal skin of guinea pigs. The optimized formulation had desirable characterization, good stability and negligible irritation. The large J_s and skin retention were well reflected in the pinprick test, wherein intensity of anesthetic effect and duration of action were increased significantly over the commercial cream. The developed CS-free microemulsion hydrogel with low S could be a promising strategy for the topical delivery of lidocaine.

Nonaqueous Microemulsion in the Bmim Tf2N/Brij 30/ n-Nonane System: Structural Investigation and Application as Gold Nanoparticle Microreactor

Microemulsions based on ionic liquids (ILs) are being increasingly studied in many different areas of physical chemistry because of the attractive properties of ILs. In particular, waterless microemulsions where the IL represents the polar phase can be of interest for those applications that demand the nanosegregation of polar substances, but in which the absence of water is a strict requirement. In this work, we prepared a reverse, nonaqueous microemulsion based on the low-viscosity room-temperature IL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide , the surfactant Brij 30, and n-nonane. The systems were characterized by dynamic light scattering and small-angle X-ray scattering; the IL/oil microemulsion was further employed as a templating system for the synthesis of gold nanoparticles from hydrogen tetrachloroaurate(III), HAuCl₄, by UV-photoreduction technique.

"Solvent-in-salt" systems for design of new materials in chemistry, biology and energy research

Inorganic and organic "solvent-in-salt" (SIS) systems have been known for decades but have attracted significant attention only recently. Molten salt hydrates/solvates have been successfully employed as non-flammable, benign electrolytes in rechargeable lithium-ion batteries leading to a revolution in battery development and design. SIS with organic components (for example, ionic liquids containing small amounts of water) demonstrate remarkable thermal stability and tunability, and present a class of admittedly safer electrolytes, in comparison with traditional organic solvents. Water molecules tend to form nano- and microstructures (droplets and channel networks) in ionic media impacting their heterogeneity. Such microscale domains can be employed as microreactors for chemical and enzymatic synthesis. In this review, we address known SIS systems and discuss their composition, structure, properties and dynamics. Special attention is paid to the current and potential applications of inorganic and organic SIS systems in energy research, chemistry and biochemistry. A separate section of this review is dedicated to experimental methods of SIS investigation, which is crucial for the development of this field.

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.

Colloidal lattices of environmentally responsive microgel particles at ionic liquid-water interfaces

This work reports new evidence of the versatility of soft and environmentally responsive micron-sized colloidal gel particles as stabilizers at ionic liquid-water droplet interfaces. These particles display a duality with properties ascribed typically to both polymeric and colloidal systems. The utilization of fluorescently labeled composite microgel particles allows in-situ and facile visualization without the necessity of invasive sample preparation. When the prepared particles form monolayers equilibrated at the ionic liquid-water interface on fully covered droplets, the colloidal lattice re-orders itself depending on the surface charge of these particles. Finally, we demonstrate that the spontaneously formed and densely packed layer of microgel particles can be employed for extraction applications, as the interface remains permeable to small active species.

Water Soluble Chitosan Mediated Voriconazole Microemulsion as Sustained Carrier for Ophthalmic Application: In vitro/Ex vivo/In vivo Evaluations

Background:

Voriconazole (VCZ) is a lipophilic candidate, effective against fungal infections like ocular keratitis and endopthalmitis.

Objective:

The purpose to develop, optimize and characterize voriconazole microemulsion as sustained medication for ophthalmic application.

Methods:

The pseudo-ternary phase diagrams were developed using oleic acid, isopropyl myristate and isopropyl palmitate (oil phases), tween 80 (surfactant), propylene glycol (co-surfactant), distilled water (aqueous phase) and modified chitosan (Mod.CH) as mucoadhesive polymer. The optimum composition of oil, Smix and water was selected on the basis of phase diagrams and as mucoadhesive polymer Mod.CH was used in the formulations. All the formulations were evaluated for thermodynamic stability/dispersibility, physicochemical parameters (droplet size, polydispersity index, zeta potential, drug content, viscosity, pH and conductivity), in vitro, ex vivo and in vivo studies.

Results:

All formulations showed droplet size below 250 nm, positive zeta potential and polydispersity index below 0.5. The in vitro drug release study performed on selected formulations showed maximum sustained release than marketed formulation. The in vitro transcorneal permeation experiment of formulations suggests that optimized formulations showed better permeation. The selected formulation of voriconazole microemulsion was able to produce maximum antifungal activity against Candida albicans when compared to marketed formulation. In vivo study performed on rabbit eyes, found more drug concentration in aqueous humor of optimized formulation; the AUC0→t of IPMVM-11 was approximately 6.84-fold higher than VOZOLE and efficiently enhanced the corneal bioavailability.

Conclusion:

The modified chitosan based on voriconazole loaded microemulsion was promising novel carrier for sustained action in ophthalmic medication.

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.

About the nanostructure of the ternary system water - [BMIm]PF6 - TX-100

HYPOTHESIS

Many efforts have been made to formulate water-IL microemulsions. One of the most intensely studied systems is H₂O - 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF₆) - 4-octylphenol polyethoxylate (TX-100) and it is not questioned that this system forms microemulsions. The nanostructures observed for traditional microemulsions are postulated with the surfactant being adsorbed at the interface such that the hydrophilic EO sides intrude into the water domains, while the hydrophobic hydrocarbon chains are immersed into [BMIm]PF₆. However, the high polarity of [BMIm]PF₆ and the observation that [BMIm]PF₆ mixes well with oligoethylene oxides but hardly with non-polar solvents like toluene or alkanes are not in line with this picture.

EXPERIMENTS

We re-studied the ternary system H₂O - [BMIm]PF₆ - TX-100 by measuring phase diagrams, determining tie-lines, and carrying out ROESY NMR and PFG NMR measurements.

FINDINGS

We found that the hydrophobic part of the surfactant interacts neither with water nor with [BMIm]PF₆, while both solvents interact with the hydrophilic part of the surfactant. We suggest that the surfactant is not adsorbed at the interface between water and the IL, but forms normal spherical or elongated micelles or even continuous aggregates with the hydrocarbon chains forming the interior of the aggregates.

Linear Polyethers as Additives for AOT-Based Microemulsions: Prediction of Percolation Temperature Changes Using Artificial Neural Networks

Predictive models based on artificial neural networks have been developed for the percolation threshold of AOT based microemulsions with addition of either glymes or polyethylene glycols. Models have been built according to the multilayer perceptron architecture, with five input variables (concentration, molecular mass, log P, number of C and O of the additive). Best model for glymes has a topology of five input neurons, five neurons in a single hidden layer and one output neuron. Polyethylene glycol model's architecture consists in five input neurons, three hidden layers with eight neurons in both first two and five in the last, and a neuron in the last output layer. All of them have a good predictive power according to several quality parameters.