Microemulsion-based Organogels Research Articles

Self-assembled organogelators as artificial stratum corneum models: Key-role parameters for skin permeation prediction

Self-assembled organogelators were explored as artificial stratum corneum (SC) models for the in vitro skin permeation assessment. Four SC models consisting of binary (organogels) or ternary (microemulsion-based organogels) mixtures were developed using stearic acid, tristearin, or sorbitan tristearate, at two different concentrations, gelled in squalene. The permeation of lipophilic butyl-methoxydibenzoylmethane and hydrophilic methylene blue as the permeant compounds across the SC models was compared with ex vivo experiments using excised porcine ear skin. A multi-analytical approach was adopted to provide detailed understanding about organogelator organization within the SC models and find possible parameters playing key-roles in SC permeation prediction. The SC models were investigated for gelling properties and microstructure. Parameters such as gel occurrence, organogelator concentration, and rheological properties appeared as negligible conditions for skin permeation prediction. Conversely, arrangement packing, interactions, and crystallinity extent of the self-assembled organogelator were found to play a fundamental role in the simulation of SC barrier function according to the permeant feature.

Increasing esterification efficiency by double immobilization of lipase-ZnO bioconjugate into sodium bis (2-ethylhexyl) sulfosuccinate (AOT)- reverse micelles and microemulsion based organogels

In the present study, we developed double immobilization system for entrapment of lipase to increase overall esterification efficiency. Lipase has been attached on functionalized ZnO (zinc oxide) particles. Fabricated lipase-ZnO conjugates were entrapped into sodium bis (2-ethylhexyl) sulfosuccinate (AOT)-reverse micelles. AOT-reverse micelles containing lipase-ZnO conjugate were further entrapped into microemulsion based organogels (MBGs), prepared from polyvinyl alcohol. These immobilization systems were characterized by fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Double immobilized lipase (i.e. organogels) showed highest stability and esterification activity. Organogel immobilized lipase was therefore further applied for the synthesis of pentyl valerate and ethyl valerate esters in n-hexane. Successfully, 90% of ethyl valerate and 86% of pentyl valerate were synthesized using prepared double immobilization enzyme. Furthermore, the immobilized biocatalyst shows reusability for 10 cycles with meager loss of activity. The present study revealed a promising perspective to overcome the well-known drawbacks of the chemical-catalyzed route.

Improved activity of lipase immobilized in microemulsion-based organogels for (R, S)-ketoprofen ester resolution: Long-term stability and reusability

Microemulsion-based organogels (MBGs) were effectively employed for the immobilization of four commonly used lipases. During the asymmetric hydrolysis of ketoprofen vinyl ester at 30°C for 24h, lipase from Rhizomucor miehei and Mucor javanicus immobilized in microemulsion-based organogels (RML MBGs and MJL MBGs) maintained good enantioselectivities (eep were 86.2% and 99.2%, respectively), and their activities increased 12.8-fold and 7.8-fold, respectively, compared with their free forms. They gave higher yields compared with other lipase MBGs and exhibited better enantioselectivity than commercial immobilized lipases. Immobilization considerably increased the tolerance to organic solvents and high temperature. Both MJL MBGs and RML MBGs showed excellent reusability during 30 cycles of repeated 24h reactions at 30°C (over 40 days). The system maintained yields of greater than 50%, while the ees values of RML MBGs and MJL MBGs remained nearly constant at 95% and 88%, respectively.

Lipase immobilized in microemulsion based organogels (MBGs) as an efficient catalyst for continuous-flow esterification of protected fructose

Sugar-based surfactants are important esters for the cosmetic, food and pharmaceutical industries due to their intrinsic properties.

Microemulsion-Based Organogels as an Efficient Support for Lipase-Catalyzed Reactions under Continuous-Flow Conditions

In this work, microemulsion-based organogels (MBGs) containing lipase are reported as an efficient catalytic system for monoacylglyceride (MAG) synthesis. More specifically, Candida antarctica lipase B (CaLB) was immobilized on an MBG matrix (MBGCaLB) formed with (hydroxypropyl)methyl cellulose as a gelling agent, and this catalyst revealed high conversion yields (expressed in grams of ester per hour per gram of enzyme) under both batch and continuous-flow conditions. Under flow conditions, 1:1 stearic acid/solketal (100 mM in n-heptane) could be converted to protected MAG (>99%) in a residence time of 11 min at 45 °C. A recycle study showed that the MBGCaLB system can be recycled 15 times without activity loss, a number 2 times higher than under batch conditions catalyzed by immobilized lipase, in agreement with green chemistry protocols.

Chemo-enzymatic epoxidation catalyzed by C. antarctica lipase immobilized in microemulsion-based organogels

The use of Candida antarctica lipase B immobilized in hydroxyl-propyl-methyl cellulose microemulsion-based organogels as media for the catalysis of oleic acid epoxidation with H2O2, has been tested. The optimization of several reaction conditions such as temperature, concentration of substrates and the enzyme content in the organogel has been examined. For this purpose an experimental design (central composite rotatable design) was applied. The results showed that the highest conversion yields are observed for the lower temperatures, while the enzyme and oleic acid concentrations do not affect significantly the reaction yield. Moreover, the reusability of the catalyst has been verified. The epoxidation of linoleic acid was tested as well and it was observed that the main products were the mono-epoxides and not the di-epoxide.

Effects of Additives on Lipase Immobilization in Microemulsion-Based Organogels

An inexpensive, facile, and environmentally benign method was developed to improve the activity and stability of Candida rugosa lipase (triacylglycerol acylhydrolase) immobilized on microemulsion-based organogels (CRL MBGs) via the addition of additives during immobilization. The additives used were polyethylene glycol (PEG) or polysaccharides. This study is the first report on the effect of additives in CRL MBGs. Among the tested additives, PEG produced the most improvement in the immobilized CRL, enhancing its stability in organic solvents (specifically polar solvents). The results of circular dichroism and fluorescence spectra experiments indicated that exposure of the acidic CRL to electronegative additives in the buffer, such as polyethylenimine and the electropositive surfactant cetyltrimethylammonium bromide, may change the lipase secondary structure, ultimately causing enzyme inactivation. However, sodium bis(2-ethylhexyl)sulfosuccinate and PEG 2000 had minimal effects on the secondary structure of CRL. The CRL MBGs containing PEG 2000 demonstrated remarkable retention of their catalytic activity during the recycling test. No significant changes in enzymatic activity were observed, even after nine runs, and 90% of the original yield was maintained after 15 cycles.

Biocatalytic synthesis of flavor ester "pentyl valerate" using Candida rugosa lipase immobilized in microemulsion based organogels: effect of parameters and reusability.

Pentyl valerate was synthesized biocatalytically using Candida rugosa lipase (CRL) immobilized in microemulsion based organogels (MBGs). The optimum conditions were found to be pH 7.0, temperature of 37°C, ratio of concentration of water to surfactant (Wo) of 60, and the surfactant sodium bis-2-(ethylhexyl)sulfosuccinate (AOT) for MBG preparation. Although kinetic studies revealed that the enzyme in free form had high affinity towards substrates (K m = 23.2 mM for pentanol and 76.92 mM for valeric acid) whereas, after immobilization, the K m values increased considerably (74.07 mM for pentanol and 83.3 mM for valeric acid) resulting in a slower reaction rate, the maximum conversion was much higher in case of immobilized enzyme (~99%) as compared to free enzyme (~19%). Simultaneous effects of important parameters were studied using response surface methodology (RSM) conjugated with Box-Behnken design (BBD) with five variables (process parameters), namely, enzyme concentration, initial water content (Wo), solvent used for MBG preparation, substrate ratio and time, and response as the final product formation, that is, pentyl valerate (%). The MBGs were reused for 10 consecutive cycles for ester synthesis. Efficacy of AOT/isooctane as dehydrating agent for extracting excess water from MBGs was found to exert a positive effect on the esterification reaction.

Enhancement of activity and stability of lipase by microemulsion-based organogels (MBGs) immobilization and application for synthesis of arylethyl acetate

► Lipase from Candida rugosa was coated with surfactants and immobilized in microemulsion-based organogels using AOT and its catalysis in organic solvents was explored. ► Immobilization increased the tolerance to organic solvent and high temperature. ► The reuse of CRL MBGs was up to 16 cycles of reaction at 50 °C. ► The low catalyst loading, mild reaction conditions, indicates the possibility of application in industrial chemical synthesis and other bulk applications. Lipase from Candida rugosa (CRL) was immobilized in microemulsion-based organogels (MBGs) and subsequently applied in large scale synthesis of arylethyl acetate in organic solvents as a more stable and efficient catalyst. Various reaction parameters (solvent, temperature, substrate concentration) were investigated for enhancement of ester production. Thermal and operational stabilities were improved compared with free CRL showing its potential for continuous applications. They were more stable at 50–60 °C and showed good recovery activity, which retained 70% of their initial activity after 16 recycles in organic media and remained constant at that level thereafter. Moreover, the immobilized lipase can maintain high catalytic activity in a variety of organic solvents, while free lipase was easily inactivated in polar solvent. A series of alcohols with different substitution groups were successfully applied in CRL MBGs-catalyzed transesterification, affording higher conversions than those with the free enzyme.

Microemulsion-based organogels: A novel matrix for transdermal drug delivery

Microemulsion-based organogels: A novel matrix for transdermal drug delivery

Water‐in‐ionic liquid microemulsion‐based organogels as novel matrices for enzyme immobilization

The use of water-in-ionic liquid microemulsion-based organogels (w/IL MBGs) as novel supports for the immobilization of lipase B from Candida antarctica and lipase from Chromobacterium viscosum was investigated. These novel lipase-containing w/IL MBGs can be effectively used as solid phase biocatalysts in various polar and non-polar organic solvents or ILs, exhibiting up to 4.4-fold higher esterification activity compared to water-in-oil microemulsion-based organogels. The immobilized lipases retain their activity for several hours at 70 degrees C, while their half life time is up to 25-fold higher compared to that observed in w/IL microemulsions. Fourier-transform infrared spectroscopy data indicate that immobilized lipases adopt a more rigid structure, referring to the structure in aqueous solution, which is in correlation with their enhanced catalytic behavior observed.

In this issue: Biotechnology Journal 8/2010

AbstractBiocatalyst microemulsionsPavlidis et al., Biotechnol. J. 2010, 5, 805–812Enzymes maintain their catalytic activity when hosted in aqueous nanodroplets like reverse micelles. Researchers from Ioannina, Greece, propose the use of water‐in‐ionic liquid microemulsionbased organogels (w/IL MBGs) as novel supports for the immobilization of lipase B from Candida antarctica and lipase from Chromobacterium viscosum. These novel lipase‐containing w/IL MBGs can be effectively used as solid phase biocatalysts in various polar and non‐polar organic solvents or ILs, exhibiting up to 4.4‐fold higher esterification activity compared to water‐in‐oil microemulsion‐based organogels. The immobilized lipases retain their activity for several hours at 70°C, while their half life time is up to 25‐fold higher compared to that observed in w/IL microemulsionsBiocatalyst cryogelationBieler et al., Biotechnol. J. 2010, 5, 881–885Entrapment of biocatalysts in hydrogel beads allows stable operation in otherwise deteriorating solvents. Doing this by cryogelation is a gentle method to extend the scope of biocatalysis. To foster the use of this versatile method, researchers from Aachen, Germany, devised an automated injector for the production of PVA/PEG‐enzyme immobilisates. The device consists of a thermostated reservoir connected to a programmable injector nozzle and an agitated receiving bath for the droplets. This lab‐scale production unit yields up to 1500 beads with immobilized enzyme per minute with a narrow size distribution and good roundness.Biocatalyst membrane reactorLyagin et al., Biotechnol. J. 2010, 5, 813–821Screening of biocatalysts, substrates or conditions in the early stages of bioprocess development requires an enormous number of experiments and is a tedious, expensive and time‐consuming task. Currently available screening systems can only be operated in batch or fed‐batch mode, which can lead to severe misinterpretations of screening results. Researchers from Berlin, Germany, now developed a novel screening system that enables continuous feeding of substrates and continuous removal of products. A prototype based on the membrane reactor concept was designed and operated for a model reaction, the hydrolysis of cellulose.

Microemulsion-based organogels containing inorganic nanoparticles

Under certain conditions thermo-reversible transparent gels can be formed by addition of gelatin to water-in-oil (w/o) microemulsions stabilized by the anionic surfactant AOT. Here it is shown that a variety of different surfactant-coated nanosized inorganic particles can be immobilized in MBGs, thus combining beneficial nanoparticle and organogel properties to form unique inorganic–organic hybrid materials with potential applications. UV-visible absorption suggests there to be little particle aggregation in these gel matrices, whilst small-angle neutron scattering (SANS) indicates only minimal changes to the organogel structure after particle inclusion. Furthermore, UV-visible spectra show no leaching of the nanoparticle components when the organogels are pelleted and stirred in apolar solvents.

Synthesis of the ‘green apple ester’ ethyl valerate in organic solvents by Candida rugosa lipase immobilized in MBGs in organic solvents: Effects of immobilization and reaction parameters

Ethyl valerate, also known as the green apple flavor is well known for its wide applications in the areas of food, pharmaceuticals and cosmetics industries. Candida rugosa lipase was immobilized in microemulsion based organogels (MBGs) and used for ethyl valerate synthesis in organic solvents. Various immobilization and reaction parameters were scrutinized for enhancement of ester production. Among the immobilization parameters, sodium bis-2-(ethylhexyl) sulfosuccinate (AOT), n-heptane and gelatin were found to be the highest yielding combination. Cyclohexane was found to be the solvent of choice as the reaction medium while pH 7, 40 °C and 1:1.6 ratio of valeric acid to ethanol were the reaction parameters exhibiting highest ester formation. The organogels were highly stable in the solvents and were reused for nine cycles with meager loss of activity. Also, immobilized enzyme was thermostable at 50–70 °C for ten hours. Hence, MBGs verify to be a promising enzyme immobilization system for ester synthesis in organic solvents.

Resolution of (R,S)-(±)-glycidyl butyrate with immobilized Y-11 Trichosporon capitatum lipase in gelatin-containing microemulsion-based organogels

Resolution of (R,S)-(±)-glycidyl butyrate with immobilized Y-11 Trichosporon capitatum lipase in gelatin-containing microemulsion-based organogels

Resolution of ( R, S)-(±)-glycidyl butyrate with immobilized Y-11 Trichosporon capitatum lipase in gelatin-containing microemulsion-based organogels

An extracellular lipase produced by the strain of Y-11 Trichosporon capitatum was purified to homogeneity by ammonium sulfate precipitation and four chromatographic steps. The purified lipase showed enhanced activity when it was immobilized in gelatin-containing microemulsion-based organogels. Furthermore, the resolution of ( R, S)-(±)-glycidyl butyrate by this immobilized lipase gave a product of ( S)-(−)-glycidol with ∼98% ee ( E = 96). By using chiral HPLC separation, ( S)-(−)-glycidol was obtained in enantiopure form. Scaled-up reaction in 2 l shake flask was also performed and the repeated use of 15 times of immobilized Y-11 T. capitatum lipase resulted in little loss in its activity (4.8%).

Gelatin‐stabilised microemulsion‐based organogels facilitates percutaneous penetration of Cyclosporin A In Vitro and dermal pharmacokinetics In Vivo

Gelatin-stabilised microemulsion-based organogels (MBGs) are very useful in transdermal and topical delivery of hydrophobic drugs because of their lipophilic nature. MBGs systems possessing a potentially improved skin bioavailability of Cyclosporin A were designed and explored for some characteristics. The release characteristics of drug from MBGs were studied according to drug concentration. As the concentration of drug increased, the release of drug from gel increased, showing concentration dependency. Percutaneous penetration studies using rat skin in vitro showed that the deposition of Cyclosporin A was significantly improved by MBGs compared to the control. We also evaluated the therapeutic advantage of dermal administration of Cyclosporin A in rat model. Local (subcutaneous and skin), systemic concentrations and organ distribution (liver and kidney) were evaluated serially following topical and oral application of the drug. In rat dermal applied with the MBGs containing Cyclosporin A, the deposition of the drug into skin and subcutaneous fat was, respectively, almost 55- and 3-fold higher than the concentrations compared with oral administration. Systemic distribution in blood, liver and kidney was much lower following topical than following oral administration. With high local concentrations and minimal distribution to other organs via the circulation, topical applied MBGs loaded with Cyclosporin A might deliver maximal therapeutic effect to local tissue while avoiding the side effects seen with systemic therapy. The histopathological findings revealed that the new MBGs vehicle was a safe vehicle for topical drug delivery systems.

Candida rugosa lipase immobilized in Triton-X100 microemulsion based organogels (MBGs) for ester synthesis

The esterification ability of the lipase VII from Candida rugosa was studied in the quaternary water-in-oil microemulsion Triton-X100/water/1-hexanol/ n-hexane based organogels. The gelatin concentration exerted a high influence on both the MBG formation and the esterification rate exhibiting highest esterification at 6% (w/v). Nature of cosurfactants and oil exploited in making of the MBGs also affected the lipase-catalyzed esterification, showing highest esterification using formulations derived from 1-hexanol and n-hexane. Ethyl butyrate formation by C. rugosa lipase increased while increasing mole ratio of water/surfactant ( W 0) at a particular mole ratio of cosurfactant/surfactant ( P 0). Recycling the immobilized enzyme was shown to be feasible, demonstrating that lipase retains its activity for several cycles. Immobilization did not change the optimum temperature for both free and immobilized lipase (37 °C), however, the half-life of the enzyme increased from 14.9 to 69.9 h. The thermal stability increased five times upon immobilization.

Reactivity of Candida rugosa lipase in cetyltrimethylammonium bromide microemulsion–gelatin complex organogels

Esterification activity of Candida rugosa lipase in cetyltrimethylammonium bromide (CTAB) microemulsion-based organogels (MBGs) containing gelatin as natural resource polymer was investigated. The lipase activity reached maximum at a water content of 48–50% (v/v) and at a CTAB concentration of 60 mM. During batch repeated reactions, the lipase activity gradually decreased and the MBGs were swollen in appearance.

Novel approach for the synthesis of ethyl isovalerate using surfactant coated Candida rugosa lipase immobilized in microemulsion based organogels

In our study Candida rugosa lipase coated with various surfactants viz. AOT, CTAB, and Tween 80 was immobilized in microemulsion based organogels (MBGs) and investigated for the production of ethyl isovalerate, a fruity flavor ester. Combinations of different surfactant coated lipase and the surfactant used for preparation of MBG were tried for esterification activity. Amongst various combinations used, CTAB coated lipase immobilized in AOT based MBGs exhibited maximum ethyl isovalerate synthesis (0.082 mol/L) in 9 days. The CTAB coated lipase immobilized in AOT based organogel showed eight-fold increase in the esterification activity as compared to the native lipase. We also found that, increase in the concentration of the CTAB led to the decrease in the catalytic activity of lipase immobilized in AOT based organogels. The AOT based organogels containing CTAB coated lipase could be reused five times, without significant loss in esterification activity. However, after fifth cycle the esterification activity decreased to 40% of the initial activity. The activation energy for catalytic activity of the untreated and surfactant coated lipase was found to be 29.8 and 9.15 kJ, respectively, which depicts some structural change in surfactant coated lipase. Thus, the surfactant coated lipase immobilized in MBGs exhibited significantly higher stability and activity in comparison to uncoated lipase immobilized in MBGs. This strategy seems to hold a good promise for the synthetic flavor industry.