Structural and Dynamic Properties of Lecithin-Alcohol Based w/o Microemulsions: A Luminescence Quenching Study

Development and Evaluation of a Water-in-oil Microemulsion Formulation for the Transdermal Drug Delivery of Teriflunomide (A771726)

Teriflunomide (TEF, A771726) is the active metabolite of leflunomide (LEF), a disease-modifying anti-rheumatic drug. The main purpose of this study was to develop and evaluate water-in-oil (W/O) microemulsion formulation of TEF. The W/O microemulsion was optimized formula is the physical and chemical stability of lecithin, ethanol, isopropyl myristate (IPM) and water (20.65/20.78/41.52/17.05 w/w) by using the pseudo-ternary phase diagram and the average droplet size is about 40 nm. The permeability of TEF microemulsion is about 6 times higher than control group in vitro penetration test. The results of anti-inflammatory effect showed that compared with the control group, the external TEF microemulsion group could significantly inhibit swelling of paw in rats, and no significant difference compared with oral LEF group. The results of hepatotoxicity test show that there were normal content of alanine aminotransferase (ALT)/aspartate aminotransferase (AST) and no obvious inflammatory infiltration of TEF microemulsion group compared with LEF group. The plasma concentration curve showed that compared with LEF group, the peak concentration of TEF microemulsion group was decreased, the half-life (t_1/2) was prolonged, and the relative bioavailability of TEF microemulsion was 75.35%. These results suggest that TEF W/O microemulsion can be used as a promising preparation to play an anti-inflammatory role while significantly reducing hepatotoxicity.

Influence of nanoreactor environment and substrate location on the activity of horseradish peroxidase in olive oil based water-in-oil microemulsions

Oxidative enzymatic reactions using horseradish peroxidase (HRP) were carried out in water-in-oil (w/o) microemulsions composed of olive oil/lecithin/1-propanol/water, a model biomimetic system. The substrates used (gallic acid, octyl gallate and 2,2'-azino-bis[3-ethylbenzo-thiazoline-6-sulfonic acid] (ABTS)) have different hydrophobicities and possible locations in the microemulsion system. HRP reactivity with reference to substrate hydrophobicity and structural characteristics of the microemulsions is discussed. The nature of the enzyme microenvironments was examined using dynamic light scattering (DLS), differential scanning calorimetry (DSC) and diffusion NMR (DOSY) methodologies while the location of various enzymatic substrates in the microemulsion phase was assessed by solubility measurements and by taking pressure-area isotherms of mixed monolayers of the substrates with dipalmitoyl-phosphatidylcholine (DPPC), which is a major constituent of lecithin. In contrast to the bulk aqueous phase, in the severely restricted environment of the polar domains of the microemulsion HRP reacted faster with octyl gallate, a substrate that is solubilized at the lipid interfaces. HRP was deactivated in the olive oil microemulsions within a few hours, a phenomenon that has also been observed in other microemulsion systems.

Effect of compressed CO2 on the properties of lecithin reverse micelles

Lecithin is a very useful biosurfactant. In this work, the effects of compressed CO 2 on the critical micelle concentration (cmc) of lecithin in cyclohexane and solubilization of water, lysozyme, and PdCl 2 in the lecithin reverse micelles were studied. The micropolarity and pH value of the polar cores of the reverse micelles with and without CO 2 were also investigated. It was found that CO 2 could reduce the cmc of the micellar solution and enhance the capacity of the reverse micelles to solubilize water, the biomolecule, and the inorganic salt significantly. Moreover, the water pools could not be formed in the reverse micelles in the absence of CO 2 because of the limited amount of water solubilized. However, the water pools could be formed in the presence of CO 2 because large amounts of water could be solubilized. All of these provide more opportunity for effective utilization of this green surfactant. The possible mechanism for tuning the properties of the reverse micelles by CO 2 is discussed.

Lecithin organogels used as bioactive compounds carriers. A microdomain properties investigation

Organogels were obtained by adding small amounts of water to a solution of lecithin in organic solvents. Either isooctane or isopropyl palmitate and isopropyl myristate were used as the continuous organic phase of the gels. EPR spectroscopy using both DSA membrane-sensitive and lipophilic spin probes was applied to define the dynamic structure of the surfactant monolayer and the continuous oil phase of lecithin organogels. It was found that by increasing the water quantity, an increase of the polar head area per lecithin molecule was induced, and as a consequence the total interface expanded. It was found that the use of esters as organic solvents induced a decrease of the size of the dispersed structures. The interconnection of the aqueous microdomains and their dynamics were monitored by both static and time-resolved fluorescence quenching spectroscopy using Ru(bipy)32+ as fluorophore and Fe(CN)63- as quencher. It was found that the rates of inter- and/or intra-micellar exchange of water molecules were very slow because they appeared quite immobilized close to the lecithin polar heads. According to the results of the dynamic studies, appropriate organogels were formulated and used to incorporate model bioactive compounds with medicinal or cosmetic interest such as caffeine and theophylline. When these systems were tested for trans-membrane diffusion, they showed a 24 h permeation of 20% and 35%, respectively.

Microemulsions: a potential delivery system for bioactives in food

Microemulsions are thermodynamically stable, transparent, low viscosity, and isotropic dispersions consisting of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. Microemulsions (so-called due to their small particle size; 5-100 nm) have found application in a wide variety of systems, such as pharmaceutical and oil recovery, but their application in food systems has been hindered by the types of surfactant permissible for use in food. The objective of this review is to provide an overview of the structures and phase behavior of microemulsions, methods of microemulsion formation, and techniques which may be used for characterization. A comprehensive review of previous work on both food-grade microemulsion systems, and non-food-grade systems of specific food interest is included. The application of microemulsions as reaction media, their ability to solubilize proteins and hence their use as a separation technique is also documented. In addition, attention is focused on the application of microemulsions as delivery systems for delivery of bioactive compounds, and the links between microemulsions and increased bioavailability. Future research, both applied and fundamental, should focus on surfactants which are not restricted for use in foods.

Controllable synthesis, characterization and catalytic properties of WO(3)/ZrO(2) mixed oxides nanoparticles

Tungsten-promoted zirconia (WO(3)/ZrO(2)) nanoparticles were synthesized in reverse micelles of water/sodium bis(2-ethylexyl) sulfosuccinate/isooctane, which were compared with WO(3)/ZrO(2) prepared by incipient wetness impregnation and sol-gel method. The control of particle size was achieved by varying the process variables, such as water-to-surfactant molar ratio and reagent concentration. Their sizes, appearances, crystal structures, and thermochemical behavior were characterized by UV-vis, TEM, XRD and TG-DTA. NH(3)-TPD and Hammett indicator measurement were also employed to study the acidity of samples. The results revealed that samples prepared in reverse micelles had higher percentages of T-ZrO(2) and greater acid strength than those of other samples. The alkylation of butene with isobutane on WO(3)/ZrO(2) was carried out in a fixed-bed reactor. Samples synthesized in reverse micelles had better reaction performance than others. A parallel relationship could be drawn between the catalytic activity and the acid amounts as well as the acid strength of the catalysis.

Formation and Characterization of Reversed Micelles Composed of Phospholipids and Fatty Acids

The formation of reversed micellar systems composed of phosphatidylcholine (PC) and fatty acid was newly demonstrated by a significant increase in water content in the organic ethyl oleate phase when the micelles were prepared by the contact method. The solubilized water concentration in the reversed micellar organic phase reached 3 wt%. The new systems are expected to be used as highly biocompatible reversed micellar systems. The structure of the reversed micelles composed of PC and oleic acid was characterized by determining the water concentration and by small-angle X-ray scattering analysis. The reversed micelles composed of PC and oleic acid formed in ethyl oleate were spherical. The radius of gyration was between 30 and 50 Å. The size of the reversed micelles decreased with an increase in the oleic acid concentration and was independent of the PC concentration. Experimental results indicated that the structure of the reversed micellar system was determined by the oleic acid concentration. An increase in the PC concentration caused an increase in the number of reversed micelles of the same size. These reversed micellar systems are expected to be used as solubilization media in pharmaceutical and food industries because they are not toxic. Copyright 2001 Academic Press.