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(Hydroxypropyl)methyl cellulose (HPMC) can be used to form gels integrating a w/o microemulsion. The formulation in which a microemulsion is mixed with a hydrated HPMC matrix has been successfully used as a carrier of biocompatible ingredients. However, little is known about the structure of these systems. To elucidate this, scanning electron microscopy was used to examine the morphology and the bulk of the microemulsion-based gels (MBGs) and small-angle X-ray scattering to clarify the structure and detect any residual reverse micelles after microemulsion incorporation in the gel. Electron paramagnetic resonance spectroscopy was applied using spin probes to investigate the polar and non-polar areas of the gel. Furthermore, the enzyme-labelling technique was followed to investigate the location of an enzyme in the matrix. A structural model for HPMC matrix is proposed according to which, although a w/o microemulsion is essential to form the final gel, no microemulsion droplets can be detected after incorporation in the gel. Channels are formed by the organic solvent (oil), which are coated by surfactant molecules and a water layer in which the enzyme can be hosted.

The synthesis, as well as the spectroscopic and structural characterization of three analogous palladium(II) complexes, [Pd{(Ph2P)2N(tBu)-κ2P,P´}X2], X = Cl, Br, I, is presented. X-ray crystallography studies revealed a similar square planar PdP2X2 first coordination sphere among the three complexes. The catalytic reactivity of these complexes was tested in the Suzuki-Miyaura coupling reaction, showing that the X = Cl, Br, complexes are more active than the X = I analogue. The differences in the catalytic reactivity within this series of complexes, as well as comparisons with similar palladium(II) catalysts reported in the literature, are discussed with respect to the different electronegativity of the three halogens and the strong +I inductive effect of the ligand's tBu group.

Lipase from Mucor miehei was immobilized on chitosan hydrogels without using any activation agent. These low-cost and easy to prepare lipase-containing hydrogels could be considered as novel solid-phase biocatalysts for use in organic media. When they were applied as biocatalysts towards the model esterification reaction of propyl laurate synthesis they showed an optimum operation temperature at 30 °C and maintained a high catalytic activity in various non-polar organic solvents. The higher initial esterification rates were obtained when biocatalysis took place in branched hydrocarbons where the initial rates recorded were twice the ones observed for straight hydrocarbons, being 0.22 mM/min in isooctane and 0.11 mM/min in hexane, respectively. The novel catalyst presented excellent reusability, with only 10% loss of activity after 12 uses, which is even higher than the one obtained by lipase-containing chitosan beads prepared with a cross-linker. Moreover, enzyme superactivity was evident for several runs.

Two commercially available and widely used enzymes, the parent Thermomyces lanuginosus lipase (TLL) and the shuffled phospholipase A1 Lecitase (Lecitase Ultra), were encapsulated in AOT/isooctane reverse micelles and evaluated regarding their structure and activity. Preparations were also tested as effective biocatalysts. Small-angle X-ray scattering (SAXS), electronic paramagnetic resonance (EPR), and fluorescence spectroscopy were the techniques applied to assess the effects of enzyme incorporation to a reverse micellar nanostructure. SAXS analysis showed that the radius of gyration (Rg) changed from 16 to 38 Å, as the water content (w0) increased. Elongated shapes were more commonly observed than spherical shapes after enzyme encapsulation. EPR studies indicated that enzymes do not participate in the interface, being located in the aqueous center. Fluorescence energy transfer showed that TLL is located in the water core, whereas Lecitase Ultra is closer to the interface. Enzymatic activity toward a standard esterification reaction endured after the enzyme was incorporated into the micelles. The activity of TLL for systems with w0 15 showed the highest conversion yield, 38% in 2 h, while the system with w0 10 showed the highest initial velocity, 0.43 μM/min. This last system had a Rg of 19.3 Å, similar to that of the TLL monomer. Lecitase Ultra showed the highest conversion yields in systems with w0 10, 55% in 2 h. However, the initial rate was much lower than that of TLL, suggesting less affinity for the substrates, which is expected since Lecitase Ultra is a phospholipase. In summary, we here used several spectroscopic and scattering techniques to reveal the shape and stability of TTL and Lecitase Ultra encapsulated systems, which allowed the selection of w0 values to provide optimized enzymatic activity.

Weak self-assembly systems consisted by a nonpolar hydrocarbon, an alcohol and water can form macroscopically homogeneous liquid media with distinct microenvironments of varying polarity. These ternary systems are very similar to classic water in oil microemulsions although they don't have any amphiphilic surfactant. They were thus, initially called “surfactantless” or “detergentless” microemulsions. One of the main application fields that these systems cover is the one of biocatalysis in non-conventional media, a pillar of industrial biotechnology. The present article reviews the use of surfactantless microemulsions as effective non-conventional media for enzymatic biotransformations with a focus on oxidases, lipases and their relation to the system's structure.

A novel water-in-oil (W/O) microemulsion based on natural oils, namely extra virgin olive oil (EVOO) and sunflower oil (SO), in the presence of non-ionic surfactants was successfully formulated. The novel microemulsion was used as a carrier for gallic acid (GA) to assure its protection and efficacy upon nasal administration. The work presents evidence that this microemulsion can be used as a nasal formulation for the delivery of polar antioxidants, especially, after incorporation of chitosan (CH) in its aqueous phase. The structure of the system was studied by Small Angle X-ray Scattering (SAXS), Dynamic Light Scattering (DLS) and Electron Paramagnetic Resonance (EPR) spectroscopy techniques. By the addition of CH, the diameter of the microemulsion remained unaltered at 47 nm whereas after the incorporation of GA, micelles with 51 nm diameter were detected. The dynamic properties of the surfactant monolayer were affected by both the incorporation of CH and GA. Moreover, the antioxidant activity of the latter remained unaltered (99 %). RPMI 2650 cell line was used as the in vitro model for cell viability and for GA nasal epithelial transport studies after microemulsion administration. The results suggested that the nasal epithelial permeation of GA was enhanced, 3 h post administration, by the presence of 0.2 % v/v microemulsion in the culture medium. However, the concentration of the transported antioxidant in the presence of CH was higher indicating the polymer’s effect on the transport of the GA. The study revealed that nasal administration of hydrophilic antioxidants could be used as an alternative route besides oral administration.

A novel biocompatible water-in-oil microemulsion was developed using nonionic surfactants and was investigated as a potential enzyme delivery system for pharmaceutical applications. The system was composed of isopropyl myristate/polysorbate 80 (Tween 80)/distilled monoglycerides/water/propylene glycol (PG), had a low total surfactant concentration (8.3% w/w), and was able to incorporate approximately 3% w/w aqueous phase containing horseradish peroxidase (HRP). Structural and activity aspects of the system were studied using a variety of techniques such as dynamic light scattering (DLS), electron paramagnetic resonance (EPR), and dynamic interfacial tension. The apparent hydrodynamic diameter of the empty droplets was calculated at about 37 nm. Different enzyme concentrations, ranging from 0.01 to 1.39 μM, were used for both DLS and EPR studies to effectively determine the localization of the macromolecule in the microemulsion. According to the results, for high enzyme concentrations, a participation of HRP in the surfactant monolayer of the microemulsion is evident. The number of reverse micelles in the microemulsion was defined by a theoretical model and was used to clarify how the enzyme concentration affects the number of empty and loaded reverse micelles. To assure that the system allows the enzyme to retain its catalytic activity, an oxidative reaction catalyzed by HRP was successfully carried out with the use of the model substrate 2,2'-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid]. The influence of several parameters such as temperature, pH, and PG concentration was examined to optimize the reaction conditions, and a kinetic study was conducted revealing an ordered-Bi-Bi mechanism. Values of all kinetic parameters were determined. The release of the encapsulated enzyme was studied using an adequate receiver phase, revealing the effectiveness of the proposed microemulsion not only as a microreactor but also as a carrier for therapeutic biomolecules.

The ability of two biocompatible amphiphilic block copolymers consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(ε-caprolactone) with different hydrophilic/hydrophobic block ratio to act as stabilizers of water-in-oil (w/o) microemulsions and enzyme encapsulation therein has been tested. Phase diagrams of the two block copolymers in mixtures of chloroform/isopropanol/water were constructed, revealing that the systems can incorporate important amounts of aqueous phase. The w/o microemulsions were then used to encapsulate R. miehei lipase. Empty as well as lipase-loaded systems were characterized by DLS as well as EPR spectroscopy. It was found that the incorporated lipase was preferably localized in the interior of the droplets. The apparent hydrodynamic radii of the droplets were found to vary from 86 to 3000 nm and from 66 to 2140 nm for empty PEO-PCL 30 and PEO-PCL 53 stabilized systems, respectively. In the presence of the lipase, the hydrodynamic radii were considerably decreased. The catalytic activity of the encapsulated lipase was successfully tested via a model esterification reaction. The effect of temperature on the catalytic behavior of the encapsulated R. miehei lipase was investigated, revealing that the initial rate of the esterification reaction depended on the type of the block copolymer used.

Monoacylglycerols are increasingly used in several industrial applications as effective and cheap emulsifiers. In the present work monostearin synthesis has been studied, using lipase as a biocatalyst of the esterification reaction of stearic acid with (R,S)-1,2-O-iso-propylidene glycerol (solketal). The lipase from Candida antarctica (CaL B) was immobilized in AOT/isooctane water in oil microemulsions. Optimization of the reaction conditions have shown that the highest production (80% in 30 min) could be achieved at 40 °C, in microemulsions with relatively low water content (wo = 8). Kinetic studies have shown that the esterification reaction of stearic acid with solketal catalyzed by CaL B occurs via the ordered bi–bi mechanism, in which inhibition by the acid was identified. Moreover, at high fixed solketal concentrations a negative cooperativity is pronounced, which means that binding of the alcohol lowers the affinity of the enzyme for binding of the acid. Values of all kinetic parameters have been determined.

Lipases from Rhizomucor miehei and Candida antarctica B were immobilized in hydroxypropylmethyl cellulose organogels based on surfactant-free microemulsions consisting of n-hexane, 1-propanol and water. Both lipases kept their catalytic activity, catalyzing the esterification reactions of various phenolic acids including cinnamic acid derivatives. High reaction rates and yields (up to 94%) were obtained when lipase from C. antarctica was used. Kinetic studies have been performed and apparent kinetic constants were determined showing that ester synthesis catalyzed by immobilized lipases occurs via the Michaelis-Menten mechanism. Biotechnology Letters

Lipases from Rhizomucor miehei (RmL) and Candida antartica (CaL-B) entrapped in surfactant free microemulsion-like ternary systems consisting of n-hexane, short chain alcohols (1-propanol or 2-methyl-2-propanol) and water, keep their catalytic activity at 30 degrees C, catalyzing efficiently the esterification of fatty acids or natural phenolic acids including cinnamic acid derivatives. High conversions (up to 95%) were obtained with both lipases entrapped in various ternary systems. Lipases catalytic efficiency and stability was influenced by the composition of the ternary systems used. Hydroxypropylmethyl cellulose (HPMC) microemulsions-based organogels (MBGs) formulated with various surfactant free microemulsion-like systems were used as a matrix for enzyme immobilization. These lipase-containing MBGs prove to be a novel solid-phase catalyst for use, under mild conditions, in non-polar solvents as well as in solvent free systems. CaL-B immobilized in surfactant free MBGs keep its catalytic activity for a storage period of 8 months, while the corresponding residual activity of immobilized RmL was decreased by 50%. The stability of enzymes in such surfactant free MBGs is higher than that observed in MBGs formulated with surfactant based w/o microemulsions. Lipases-containing surfactant free MBGs were used in seven consecutive batch syntheses of fatty esters with only 10-15% loss of activity. (c) 2005 Elsevier Inc. All rights reserved. Enzyme and Microbial Technology

A series of water-in-oil microemulsion systems formulated without surfactant were used to solubilize lipases from Rhizomucor miehei and Candida antarctica B. The effect of the system's composition on the velocity of enzymic reactions was investigated following a model esterification reaction. The interaction between enzymes and the microemulsion environment was studied by steady state fluorescence spectroscopy. The site of localization of the enzyme within the different microdomains of the dispersed phase was investigated by applying the fluorescence energy transfer technique. To determine the properties of the interface between water and organic solvent of the surfactantless microemulsion systems the Electron Paramagnetic Resonance (EPR) spectroscopic technique was applied. The results indicated that even at low water content, water-rich structures are formed. This was confirmed by conductivity measurements. By the addition of enzyme it was observed that when the aqueous phase of the surfactantless microemulsion systems exceeds 2% (v/v) the enzyme retains its catalytic activity, as it is located within the water pools that protect it from the organic solvent. These confined water phases show a propanol rich interface with hexane and their structure depends on the system's composition. Colloids and Surfaces B: Biointerfaces

Organogels based on water-in-oil microemulsions can be formed using various natural polymers such as gelatin, agar or cellulose derivatives. Enzymes entrapped in the water core of the microemulsion can keep their activity and enhance their stability within the gel matrix. The importance of the microemulsion based organogels (MBGs) leans on their numerous potential biotechnological applications. An important example is the use of various lipase microemulsion systems for hydrolytic or synthetic reactions. In this review, several MBGs are being evaluated as immobilization matrices for various enzymes. The main subject focuses on the parameters that affect the use of MBGs as media for bioorganic reactions using lipases as catalysts. (C) 2010 Elsevier Inc. All rights reserved. Biotechnology Advances

We report the immobilization of Rhizomucor miehei lipase (RmL) onto mesoporous silica materials, in particular the investigations concerning the effects of the level of silica condensation and of the pore size on the enzyme activity. The efficiency of the immobilization was revealed by FTIR spectroscopy. Infrared was also used to determine the quantity of adsorbed enzyme. Immobilization efficiency increased when the RmL concentration in the buffer solution was changed from 2 to 10 mg/mL. Nevertheless, while upon enzyme immobilization the mesopore ordering was sustained for the support recovered after hydrothermal treatment at 100 °C, a structure collapse occurred for the one prepared at 80 °C. The difference in behavior is attributed to the lower hydrothermal stability of this material, which reflects the lower level of silica condensation. The enzyme-containing mesostructured silica was effectively used to catalyze the model esterification reaction of lauric acid with 1-propanol, as the immobilized lipase retained its catalytic activity. A linear relationship was observed between the reaction rate and the amount of catalyst. RmL immobilized on mesoporous materials presented a satisfactory reusability, while the remaining activity of RmL after 4 months of storage was 47% of the initial one.

The preparation of biocompatible (w/o) microemulsions based on R-(+)-limonene, water, and a mixture of lecithin and either 1-propanol or 1,2-propanediol as emulsifiers was considered. The choice of the compositions of the microemulsions used was based on the pseudo-ternary phase diagrams of the four-component system determined at 30 degrees C for different weight ratios of the components. When 1-propanol was considered as co-surfactant, the area of the microemulsion zone was remarkably increased. Interfacial properties and the dynamic structure of the emulsifier's monolayer were studied by electron paramagnetic resonance (EPR) spectroscopy using the spin-labeling technique. The rigidity and polarity of the interface were affected by the nature of the alcohol used as co-surfactant. When 1-propanol was used, the emulsifier's interface was much more flexible, indicating a less tight packing of lecithin molecules than in the case of 1,2-propanediol. In addition, the membrane's polarity was decreased when the diol was added as co-surfactant in the microemulsion system. To evaluate the size of the dispersed aqueous domains as a function of water content and other additives concentration, dynamic light scattering (DLS) measurements were carried out. Radii in the range from 60 to 180 nm were observed when 1-propanol was used as co-surfactant, and the water content varied from 0 to 12% w/w. Electrical conductivity measurements of R-(+)-limonene/lecithin/1-propanol/water microemulsions with increasing weight fractions of water indicated the appearance of a percolation threshold at water content above 4% w/w. Lipase from Rhizomucor miehei was solubilized in the aqueous domains of the biocompatible microemulsions, and the esterification of octanoic, dodecanoic, and hexadecanoic acids with the short-chained alcohols used as co-surfactants for the formulation of microemulsions was studied. The enzyme efficiency was affected by the chain length of the carboxylic acids and the nature of the alcohol. In the case of 1-propanol, a preference for the long-chain carboxylic acids was observed. On the contrary, when 1,2-propanediol was used formulation of the corresponding esters was not observed. This behavior could be possibly attributed to either the specificity of the lipase toward the alcohol employed for the esterification of the acids or the structural changes induced in the system when 1-propanol was replaced by 1,2-propanediol.

Rhizomucor miehei lipase was immobilized in hydroxy(propylmethyl) cellulose or agar gels containing lecithin or AOT microemulsions. The effect of the diffusion of substrates and products to this catalyst was studied, as well as the effect of temperature on the initial rate of ester synthesis. The composition of the gel affects the reaction rate due to mass transport phenomena. The apparent activation energies were higher for the systems based on agar, independently of the microemulsion used, and lower for the systems based on AOT microemulsions, independently of the polymer used. Biotechnology Letters

Lipases from Candida antarctica and Mucor miehei were encapsulated in lecithin water-in-oil (w/o) microemulsion-based organogels (MBG). These gels were formulated with either hydroxypropylmethyl cellulose (HPMC) or gelatin. The esterification of lauric acid and 1-propanol catalyzed by these MBGs was examined in supercritical carbon dioxide (scCO2; 35 ° C, 110 bar) as solvent for the substrates. The results were compared to those obtained with the reference substrate solvent isooctane. It turned out that the initial rates of this model reaction in scCO2 were higher than those observed in the reference system. Various parameters affecting the biocatalysis such as pressure, alcohol and acid chain length, and gel composition were investigated. Kinetic studies showed that the ester synthesis catalyzed by the immobilized C. antarctica lipase occurs via a Ping Pong Bi Bi mechanism in which only inhibition by excess of alcohol was identified. Values of all kinetic parameters were determined. In addition, experiments on the reusability of these gels in scCO2 were carried out and the state of water within the organogel was examined with the help of differential scanning calorimetry. The present study shows that biocatalysis using MBGs in scCO2 is a promising alternative to other bioconversion processes.

Lipase from Mucor miehei was immobilized in bis-(2-ethylhexyl)sulfosuccinate sodium salt MOT) as well as lecithin water-in-oil (w/o) microemulsion-based organogels (MBGs) formulated with biopolymers such as agar and hydroxypropylmethyl cellulose (HPMC), respectively. These lipase-containing MBGs prove to be novel solid-phase catalysts for use in organic media. Using these organogels at 25degreesC, various esterification reactions in non-polar solvents as well as in solvent free systems were possible. Apparent lipase activity was influenced to some extent by the nature and the concentration of biopolymers used. Lipase stability in such MBGs is much higher than that observed in w/o microemulsions. MBGs containing lipase functioned effectively in repeated batch syntheses of fatty esters. Kinetic studies have shown that ester synthesis catalyzed by immobilized lipase occurs via the Ping-Pong bi-bi mechanism in which only inhibition by excess of alcohol has been identified. Values of all kinetic parameters were determined. Biocatalysis and Biotransformation