Thermodynamics of Formation of Biological Microemulsion (with Cinnamic Alcohol, Aerosol OT, Tween 20, and Water) and Kinetics of Alkaline Fading of Crystal Violet in Them

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.

Investigation on the structure of water/AOT/IPM/alcohols reverse micelles by conductivity, dynamic light scattering, and small angle X-ray scattering

We have systematically investigated the effect of alcohols (ethanol, propanol, butanol, and pentanol) on the structure of the water/AOT/IPM system using conductivity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. The results show that no percolation phenomenon is observed in the water/AOT/IPM system, whereas the addition of ethanol (propanol and butanol) induces apparently percolation. The threshold water content (W(p)) depends closely on the alcohol type and concentration. The effect of alcohols on the conductance behavior is discussed from the physical properties of alcohols, the interfacial flexibility, and the attractive interactions between droplets. The hydrodynamic diameter of droplets (d(H)) obtained from DLS increases markedly with the increase in water content (W(0)); however, it decreases gradually with increasing alcohol chain length and concentration. SAXS measurements display distinctly the shoulder, the low hump peaks, and the heavy tail phenomenon in the pair distance distribution function p(r) profile, which rely strongly on the alcohol species and its concentration. The gyration radius (R(g)) increases with increasing W(0), and decreases with the increase of alcohol chain length and concentration. Schematic diagram of the conductance mechanism of water/AOT/IPM/alcohol systems is primarily depicted. Three different phases of the discrete droplets, the oligomers, and the isolated ellipsoidal droplets existed in the different W(0) ranges correspond to three different stages in the conductivity-W(0) curve. Coupling the structure characteristics of reverse micelles obtained from DLS and SAXS techniques with conductivity could be greatly helpful to deeply understand the percolation mechanism of water/AOT/IPM/alcohols systems.

Alkaline Fading of Triarylmethyl Carbocations in Self-Assembly Microheterogeneous Media

This review reports on the alkaline fading of crystal violet and other related carbocations in the presence of different microheterogeneous media (micelles, microemulsions and vesicles).

Designing and Testing of an Effective Oil-in-Water Microemulsion Drug Delivery System forIn VivoApplication

The phase behavior of a new psedoternary system of clove oil/Tween 20 has been studied. Several compositions from the single-phase region were selected and their stability toward time, temperature, and electrolytes has been examined. A particular composition(clove oil/Tween 20/water as 5/30/65) was chosen as the drug delivery system from the clear oil-in-water zone of the pseudoternary system. The droplet dimension and the polydispersity state of the particular composition was determined by dynamic light scattering. A bioactive compound quarcetin was encapsulated in the vehicle. The efficacy of the drug in the vehicle was examined against leishmaniasis in hamster models. The hepatotoxicity of the vehicle (o/w microemulsion) with and without the drug quarcetin was examined by estimating serum alkaline phosphatase, glutamate pyruvate transaminase, urea, and creatinine.

Biocompatible microemulsions and their prospective uses in drug delivery

Efficacy of lipophilic drugs is often hindered due to their poor aqueous solubility leading to low absorption after in vivo administration. A part of the administered dose is absorbed and reaches the pharmacological site of action and the remainder causes toxicity and undesirable side effects due to unwanted biodistribution. Enhancement in drug efficacy and lowering of drug toxicity could be achieved through encapsulation and delivery of the lipophilic drugs in aqueous based delivery systems. Microemulsions are macroscopically homogeneous pseudoternary and ternary colloidal assemblies having polar and nonpolar micro domains. Their dispersed phases in nanodimension have good shelf-life (due to thermodynamic stability), large surface area, low viscosity (in some compositions), and ultraslow surface tension. These properties qualify them to be prospective drug delivery systems provided they are composed of biocompatible excipients. Due to the existence of polar, nonpolar, and interfacial microdomains, encapsulation of different kinds of drugs is possible. The review entails reports on development and characterization of biocompatible microemulsion systems and their evaluation as probable vehicles for encapsulation, stabilization, and delivery of bioactive natural products and prescription drugs.

Physicochemical investigations of microemulsification of eucalyptus oil and water using mixed surfactants (AOT+Brij-35) and butanol

Microemulsification of a vegetable oil (eucalyptus) with single and mixed surfactants (AOT and Brij-35), cosurfactant of different lipophilicities (isomers of butanol), and water were studied at different surfactant and cosurfactant mixing ratios. The phase diagrams of the quaternary systems were constructed using unfolded and folded tetrahedron, wherein the phase characteristics of different ternary systems can be underlined. The microemulsion zone was found to be dependent upon the mixing ratios of surfactant and cosurfactant; the largest microemulsion zone was formed with 1:1 (w/w) S:CS. The effects of temperature and additives (NaCl, urea, glucose, and bile salts of different concentrations) on the phase behavior were examined. The mixed microemulsion system showed temperature insensitivity, whereas the Brij-35 (single) stabilized system exhibited a smaller microemulsion zone at elevated temperature. NaCl and glucose increased the microemulsion zone up to a certain concentration, beyond which the microemulsion zones were decreased. These additives decreased the microemulsion zones as temperature was increased. The effect of urea on microemulsion zone was found to be insignificant even at the concentration 3.0 mol dm(-3). Little effect on microemulsion zone was shown by NaC (sodium cholate) at 0.25 and 0.5 mol dm(-3) at different temperatures. The conductance of the single (AOT) and mixed microemulsion system (AOT+Brij-35) depends upon the water content and mixing ratios of the surfactants, and a steep rise in conductance was observed at equal weight percentages of oil and water. Viscosities for both single (AOT) and mixed (AOT+Brij-35) surfactant systems passed through maxima at equal oil and water regions showing structural transition. The viscosities for microemulsion systems increased with increasing Brij-35 content in the AOT+Brij-35 blend. Conductances and viscosities of different monophasic compositions in the absence and presence of additives (NaCl and NaC) were measured at different temperatures. The activation energy of conduction (DeltaE(cond)( *)) and the activation enthalpy for viscous flow (DeltaH(vis)( *)) were evaluated. It was found that both DeltaE(cond)( *) and DeltaH(vis)( *) were a function of the nature of the dispersion medium. Considering the phase separation point of maximum solubility, the free energy of dissolution of water or oil (DeltaG(s)(0)) at the microdispersed state in amphiphile medium was estimated and found to be a function of surfactant composition.

Physicochemical Investigations of Microemulsification of Coconut Oil and Water Using Polyoxyethylene 2-Cetyl Ether (Brij 52) and Isopropanol or Ethanol

The microemulsification of coconut oil/polyoxyethylene 2-cetyl ether/2-propanol or ethanol/water was investigated. The phase behaviors of the mixed system were examined. The shear viscosity at different temperatures was measured to derive activation parameters for the viscous flow. The diffusion coefficient of the microemulsions at different compositions was determined by the DLS method. The energetics of solubilization of water into oil + Brij + alkanol as well as of oil into water + Brij + alkanol forming w/o and o/w microemulsions, respectively, were calorimetrically determined.

Physicochemical investigations on microemulsification of eucalyptol and water in presence of polyoxyethylene (4) lauryl ether (Brij-30) and ethanol

The microemulsification of eucalyptol/polyoxyethylene(4)lauryl ether (Brij-30)/ethanol/water has been investigated. The phase behaviours of the mixed system in pseudoternary and tetrahedral representations have been examined to understand the topological nature of the multicomponent mixtures. Phase volumes of the heterogeneous combinations have been estimated to understand the mixing efficacy of the combinations. Shear viscosities of different monophasic compositions have been measured at different shear rates and temperatures, and the activation parameters for the viscous flow have been evaluated. The dimensions of the nanodispersions of w/o and o/w types, their diffusion coefficients and the polydispersity have been determined by the DLS method. The energetics of solubilisation (dissolution) of water in oil+Brij-30+ethanol as well as oil in water+Brij-30+ethanol forming w/o and o/w microemulsions, respectively, have been calorimetrically determined. Considering the phase separation point to be the point of maximum solubility, the energetic parameters (enthalpy, free energy and entropy) of the microemulsification process have been estimated.