Sol-gel entrapment of lipase using a mixture of tetramethoxysilane and methyltrimethoxysilane as the alkoxide precursor: Esterification activity in organic media

Summary The sol-gel method, using a mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTrMOS) as the silicon alkoxide precursor, has been applied to entrapment of lipase catalyzing esterification reactions in organic media. Increasing molar ratio of MTrMOS to TMOS led to formation of opaque and non-shrinkable gels and resulted in an increase in the esterification activity of lipase. The hybrid gel-entrapped lipase based on [MTrMOS]/[TMOS] ratio of 4 exhibited almost equal activity with those of the deposited lipase on different supports at 35°C, and retained ca. ten times higher activity than the deposited counterparts at 65 °C.     

Application of a Burkholderia cepacia lipase-immobilized silica monolith to batch and continuous biodiesel production with a stoichiometric mixture of methanol and crude Jatropha oil

Background

The enzymatic production of biodiesel through alcoholysis of triglycerides has become more attractive because it shows potential in overcoming the drawbacks of chemical processes. In this study, we investigate the production of biodiesel from crude, non-edible Jatropha oil and methanol to characterize Burkholderia cepacia lipase immobilized in an n-butyl-substituted hydrophobic silica monolith. We also evaluate the performance of a lipase-immobilized silica monolith bioreactor in the continuous production of biodiesel.

Results

The Jatropha oil used contained 18% free fatty acids, which is problematic in a base-catalyzed process. In the lipase-catalyzed reaction, the presence of free fatty acids made the reaction mixture homogeneous and allowed bioconversion to proceed to 90% biodiesel yield after a 12 hour reaction time. The optimal molar ratio of methanol to oil was 3.3 to 3.5 parts methanol to one part oil, with water content of 0.6% (w/w). Further experiments revealed that B. cepacia lipase immobilized in hydrophobic silicates was sufficiently tolerant to methanol, and glycerol adsorbed on the support disturbed the reaction to some extent in the present reaction system. The continuous production of biodiesel was performed at steady state using a lipase-immobilized silica monolith bioreactor loaded with 1.67 g of lipase. The yield of 95% was reached at a flow rate of 0.6 mL/h, although the performance of the continuous bioreactor was somewhat below that predicted from the batch reactor. The bioreactor was operated successfully for almost 50 days with 80% retention of the initial yield.

Conclusions

The presence of free fatty acids originally contained in Jatropha oil improved the reaction efficiency of the biodiesel production. A combination of B. cepacia lipase and its immobilization support, n-butyl-substituted silica monolith, was effective in the production of biodiesel. This procedure is easily applicable to the design of a continuous flow-through bioreactor system.     

Sol-gel powders and supported sol-gel polymers for immobilization of lipase in ester synthesis

Candida rugosa lipase was entrapped in hybrid organic–inorganic sol-gel powder prepared by acid-catalyzed polymerization of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes, and used in catalyzing esterification reactions between ethanol and butyric acid in hexane. Optimum preparation conditions were studied, which are gels made from propyltrimethoxysilane (PTMS)/TMOS molar ratio=4:1, hydrolysis time of silane precursor=30 min, water/silane molar ratio=24, enzyme loading=6.25% (w/w) of gel, and 1 mg PVA/mg lipase. The percentage of protein immobilization was 95% and the resulting lipase specific activity was 59 times higher than that of a non-immobilized lyophilized lipase. To prepare magnetic lipase-immobilized sol-gel powder (MLSP) for easier recovery of the biocatalyst, Fe₃O₄ nanoparticles were prepared and co-entrapped with lipase during gel formation. This procedure induced surface morphological change of the sol-gel powder and showed adverse effect on enzyme activity. Hence, although only 9% decrease in protein immobilization efficiency was observed, the corresponding reduction in enzyme activity could be up to 45% when sol-gel powder was doped with 25% (v/v) Fe₃O₄ magnetic nanoparticles solution. Lipase-immobilized sol-gel polymer was also formed within the pores of different porous supports to improve its mechanical stability. Non-woven fabric, with a medium pore size of all the supports tested, was found to be the best support for this purpose. The thermal stability of lipase increased 55-fold upon entrapment in sol-gel materials. The half-lives of all forms of sol-gel-immobilized lipase were 4 months at 40 °C in hexane.     

Biosynthesis of glycerol carbonate from glycerol by lipase in dimethyl carbonate as the solvent

Glycerol carbonate was synthesized from renewable glycerol and dimethyl carbonate using lipase in solvent-free reaction system in which excess dimethyl carbonate played as the reaction medium. A variety of lipases have been tested for their abilities to catalyze transesterification reaction, and Candida antartica lipase B and Novozyme 435 exhibited higher catalytic activities. The silica-coated glycerol with a 1:1 ratio was supplied to prevent two-phase formation between hydrophobic dimethyl carbonate and hydrophilic glycerol. Glycerol carbonate was successfully synthesized with more than 90% conversion from dimethyl carbonate and glycerol with a molar ratio of 10 using Novozyme 435-catalyzed transesterification at 70 °C. The Novozyme 435 [5% (w/w) and 20% (w/w)] and silica gel were more than four times recycled with good stability in a repeated batch operation for the solvent-free synthesis of glycerol carbonate.     

Application of a Burkholderia cepacia lipase-immobilized silica monolith micro-bioreactor to continuous-flow kinetic resolution for transesterification of (R, S)-1-phenylethanol

Burkholderia cepacia lipase was immobilized in silicates forming from n-butyl-substituted precursors within a silica monolith from methyl-substituted precursors. The resultant preparation gave about 12 times higher rates of transesterification of (R, S)-1-phenylethanol with vinyl acetate and an approximately two-fold increase in the enantioselectivity toward (R)-1-phenylethanol, as compared to a non-immobilized counterpart. The highest enzymatic activity and enantioselectivity (reaching 250) were found at a low water activity of 0.11. The continuous-flow kinetic resolution of (R, S)-1-phenylethanol was successfully conducted using lipase-immobilized silica monolith micro-bioreactors with various inside diameters ranging from 0.25 to 1.6 mm. The reactor performance during continuous operation was consistent with the prediction from the batch reactor. A steady state conversion of 40% and enantiomeric excess more than 98% were maintained over a time period of 15 days.     

溶胶凝胶法固定化黑曲霉脂肪酶的性质研究

近年来溶胶-凝胶法固定脂肪酶已成为研究热点。选用TMOS、MTMS、ETMS和PTMS 4种硅烷试剂对黑曲霉脂肪酶进行了固定化研究。固定化的最佳配方为ETMS/TMOS=5：1、水与硅烷试剂分子比为8;固定化脂肪酶的固定率为80.2%、相对活性为136.3%;以乳化橄榄油作为底物,在50℃和pH4.0的条件下,固定化脂肪酶与游离脂肪酶K_m分别为1.899×10^-4M和2.789×10^-4M;最适反应pH均为pH4.0,固定化脂肪酶在pH4.0~pH5.5之间其活性能保持95%以上;固定化脂肪酶最适反应温度为60℃,较游离脂肪酶提高了10℃;固定化脂肪酶的酸碱稳定性和热稳定性较非固定化酶有显著的提高。固定化脂肪酶的使用寿命和保存稳定性良好,使用12次后仍能够保留71.7%活性,在室温避光条件下保存180天后仍可保留79.2%活性。     

Hyperactivation of Rhizomucor miehei lipase by hydrophobic xerogels

Although a variety of approaches exist for the immobilization of enzymes, the "science" of enzyme immobilization is still in its infancy. In recent years, considerable interest has developed regarding the use of xerogels for enzyme immobilization. There are several advantages to xerogels for enzyme immobilization, including the opportunity to produce them in defined shapes or thin films and the ability to manipulate their physical characteristics (e.g., porosity, hydrophobicity, and optical properties). In this study we examined the effect of xerogel hydrophobicity on the activity of lipase (EC 3.2.2.3) from Rhizomucor miehei. The hydrophobicity of the xerogels was manipulated by generating xerogels with various molar ratios of propyltrimethoxysilane (PTMS) to tetramethoxysilane (TMOS), from 1:1 to 10:1. The belief was that, by increasing the proportion of propyl groups, the hydrophobicity of the resulting xerogel would be increased. Differences in the hydrophobicity of the resulting xerogels were confirmed using water-affinity studies. Two approaches were taken for water-affinity determinations by examining the ability of the xerogels to remove water from air (controlled humidity) and from water-saturated isopropyl ether. Xerogels with higher propyl content showed a reduced affinity for water. A crude lipase preparation from Rhizomucor miehei was then contacted with sized xerogel particulates and the effect of the xerogel on lipase activity was determined. The presence of the xerogel resulted in hyperactivation of the lipase. Analysis of the protein adsorption revealed changes in the profile of proteins adsorbed to the xerogel based on the hydrophobicity of the xerogel. Based on estimations of the specific activity of the hyperactivated lipase, a minimum hyperactivation of 207% was observed. Part of the hyperactivation may be attributable to xerogel-lipase interactions, but also to the adsorption of a component from the crude lipase preparation that may complex with the lipase and the xerogel producing a stabilizing effect. Further improvements in hyperactivation and selectivity of the xerogels is likely possible by working at lower PTMS:TMOS ratios than those investigated in this study.     

Enantioselective resolution of 2-(1-hydroxy-3-butenyl)-5-methylfuran by immobilized lipase

An efficient and convenient strategy for synthesis of enantiomerically pure S-2-(1-hydroxy-3-butenyl)-5-methylfuran was for the first time described utilizing a lipase-mediated asymmetric acylation in organic solvents. Rhizopus arrhizus lipase was chosen as the biocatalyst, and different immobilization methods including sol–gel encapsulation and covalent attachment were adopted to improve its catalytic characteristics. Various influential factors of the reaction were also investigated. Finally, the results showed that the lipase covalently attached onto epoxy resin exhibited the highest enantioselectivity and operational stability. Under optimized reaction conditions, i.e., n-hexane as the solvent, 5/1 (mol/mol) of vinyl acetate to 2-(1-hydroxy-3-butenyl)-5-methylfuran and 30 °C, the ee value of S-1 reached up to above 98% at 52% conversion with an E value of 99.     

Production and purification of lipase by a mutant strain ofRhizopus arrhizus

Extracellular lipase production byRhizopus arrhizus was increased by mutant selection from 130 to 670 μmol FFA per mL per min using UV radiation and aziridine treatment. The produced lipase was purified 720-fold by ammonium sulfate fractionation and Sephadex G-100 gel filtration. The molar mass of the produced lipase was determined to be approximately 67 kDa which comigrated with bovine serum albumin in both a Sephadex G-100 column and SDS-PAGE.     

Ethyl isovalerate synthesis using Candida rugosa lipase immobilized on silica nanoparticles prepared in nonionic reverse micelles

Uniform and monodispersed silica nanoparticles were synthesized with a mean diameter of 100 ± 20 nm as analyzed by Transmission Electron Microscopy (TEM). Glutaraldehyde was used as a coupling agent for efficient binding of the lipase onto the silica nanoparticles. For the hydrolysis of pNPP at pH 7.2, the activation energy within 25–40 °C for free and immobilized lipase was 7.8 and 1.25 KJ/mol, respectively. The V_max and K_m of immobilized lipase at 25 °C for pNPP hydrolysis were found to be 212 μmol/min/mg and 0.3 mM, whereas those for free lipase were 26.17 μmol/min and 1.427 mM, respectively. The lower activation energy of immobilized lipase in comparison to free lipase suggests a change in conformation of the enzyme leading to a requirement for lower energy on the surface of the nanoparticles. A better yield (7 fold higher) of ethyl isovalerate was observed using lipase immobilized onto silica nanoparticles in comparison to free lipase.     

Enantioselective enzymatic hydrolysis of racemic drugs by encapsulation in sol–gel magnetic sporopollenin

Candida rugosa lipase was encapsulated within a sol–gel procedure and improved considerably by fluoride-catalyzed hydrolysis of mixtures of octyltriethoxysilane and tetraethoxysilane in the presence of magnetic sporopollenin. The catalytic properties of the immobilized lipases were evaluated into model reactions, i.e., the hydrolysis of p-nitrophenylpalmitate (p-NPP), and the enantioselective hydrolysis of racemic naproxen methyl ester, mandelic acid methyl ester or 2-phenoxypropionic acid methyl ester that were studied in aqueous buffer solution/isooctane reaction system. The encapsulated magnetic sporopollenin (Spo-M-E) was found to give 319 U/g of support with 342% activity yield. It has been observed that the percent activity yields and enantioselectivity of the magnetic sporopollenin encapsulated lipase were higher than that of the encapsulated lipase without support. The substrate specificity of the encapsulated lipase revealed more efficient hydrolysis of the racemic naproxen methyl ester and 2-phenoxypropionic acid methyl ester than racemic mandelic acid methyl ester. It was observed that excellent enantioselectivity (E > 400) was obtained for encapsulated lipase with magnetic sporopollenin with an ee value of S-Naproxen and R-2 phenoxypropionic acid about 98%.     

An innovative sol–gel naringinase bioencapsulation process for glycosides hydrolysis

In this work, a biocatalytic system was chosen to enable the deglycosylation of natural glycosides in order to improve their biological activity. Naringinase, which has both alpha-l-rhamnosidase and beta-d-glucosidase activities, was the enzyme used. Naringin, the glycoside substrate used in this bioconversion, and its aglycone product naringenin are compounds with interesting pharmacological activities such as anti-oxidant and anti-inflammatory; naringenin also acts as an anti-carcinogenic and neuroprotective agent, demonstrating a high potential for use by the pharmaceutical industry.Sol–gel, an innovative technique performed in aqueous media, was developed for naringinase immobilization in lens-shaped particles. Different sol–gel precursors, including tetramethoxysilane (TMOS), methyltrimethoxysilane (MTS), 3-aminopropyltrimethoxysilane (APS) and diglycerylsilane (DGS) with different aging times were tested in five consecutive trials. The best results were obtained with TMOS and TMOS/DGS after 4 h aging time and TMOS/glycerol and DGS at 14 h aging time. The characterization of these matrices was performed with respect to their diameter, volume, naringin and naringenin partition coefficients, and the optimum temperature and pH for naringinase activity. The operational stability of the bioencapsulated naringinase in the selected sol–gel matrices was studied through successive reutilizations. The naringinase sol–gel matrix (TMOS, DGS and TMOS/DGS) deactivation studies followed the Sadana model. The matrix TMOS/glycerol showed a constant 100% residual activity after 50 consecutive runs.     

Evaluation of a silica-coated magnetic nanoparticle for the immobilization of a His-tagged lipase

Magnetic particles of size 10 nm have been coated with silica to a mean diameter of 40 nm and charged with Cu²⁺ ions via a multidentate ligand, iminodiacetic acid (IDA), for the immobilization of His-tagged Bacillus stearothermopilus L1 lipase. Microporous (average pore diameter of 60 Å) silica gel with a mean particle diameter of 115 µm has been used as a comparative support material. The molar ratio of Cu²⁺ to IDA was found to be 1:1.14 and 1:1.99 in the silica gel and the silica-coated magnetic nanoparticles (SiMNs), respectively. The specific activity of the immobilized enzyme was found to conform to the following order: Cu²⁺-charged SiMN>SiMN>Cu²⁺-charged silica gel>silica gel. When it was immobilized on the Cu²⁺-charged SiMNs, over 70% of the initial activity of the lipase remained after it had been reused five times. However, only 20% of the initial activity remained after the enzyme immobilized on the Cu²⁺-charged silica gel had been reused five times. For the enzyme immobilized on supports without Cu²⁺ cations, all activity was lost after threefold reuse. The differences in the specific activities and the efficiencies of reuse of the enzymes immobilized on the various support materials are discussed in terms of immobilization mechanisms (physical adsorption vs. coordination bonding), mass transfer of a substrate and a product of the enzyme reaction, and the status of the Cu (Cu bound to the IDA on the silica layer vs. Cu directly adsorbed on the silica layer).     

Preparation of short chain esters by the lipase from mucor miehei using heptane and silica gel

Butyl acetate, isoamyl acetate and isoamyl valerate were prepared by Mucor miehei lipase catalyzed esterification of free acids and alcohols carried out in non-aqueous systems using heptane and silica gel which removes water formed in the reaction. For butyl and isoamyl acetate 1:3 and for isoamyl acetate 1:2 molar proportions of acid to alcohol were found to be optimal. Heptane(5 ml) and 0.01g silica gel per 0.1M acid were found to improve the yields. Under optimum conditions using 60°C, within 48 hours 40% butyl acetate, 53% isoamyl acetate and 61% isoamyl valerate conversions were observed.     

Improvement of catalytic properties of lipase from Arthrobacter sp. by encapsulation in hydrophobic sol–gel materials

In this work, lipase from Arthrobacter sp. was immobilized by sol–gel encapsulation to improve its catalytic properties. Various silanizing agents including vinyl-trimethoxy silane, octyl-trimethoxy silane, γ-(methacryloxypropyl)-trimethoxy silane (MAPTMS) and tetraethoxysilane (TEOS) were chosen as the precursors. Among them, MAPTMS was for the first time utilized to encapsulate lipases, and the prepared enzyme by copolymerization of MAPTMS and TEOS exhibited the highest activity in both the hydrolysis of p-nitrophenyl palmitate and the asymmetric acylation of 4-hydroxy-3-methyl-2-(2-propenyl)-2-cyclopenten-1-one. The effects of various immobilization parameters were investigated. Under the optimum conditions of MAPTMS/TEOS = 1/1 (mol/mol), water/silane molar ratio (R value) = 20 and lipase loading = 0.01 g/mL sol, the total activity of the immobilized enzyme reached up to 13.6-fold of the free form. Moreover, the encapsulated lipase exhibited higher thermal stability than the free form and retained 54% of the original activity after uses for 60 d. Enantioselectivity of enzyme was also improved with an E value of 150 after encapsulation from 85 for the free form.     

Investigations to optimize the catalytic performance of CPO encapsulated in PEG 200-doped silica matrices

A systematic investigation of the experimental conditions that affect the performance of chloroperoxidase (CPO) when encapsulated in organic/inorganic hybrid materials was carried out, aimed at optimizing the enzymatic catalytic efficiency. Sol–gel process was used to synthesize silica matrices and the incorporation of polyethylene glycols (PEGs) has allowed us to modify the properties of the matrices and the interactions between the silica network and the enzyme. Sol–gel process conditions, i.e. PEG/TMOS (tetramethylorthosilicate) molar ratio, aging and drying time, along with the H₂O₂ concentration in the reaction mixture were optimized to obtain a more efficient and reusable catalyst. A stable and easily recycled biocatalyst was obtained, even in the presence of high amounts of oxidizing agent. A stability of up to 3 complete cycles of reaction was obtained. CPO also exhibited an excellent thermostability even at 70 °C, being residual activity after 2 h of incubation greater than 90%, and it was a very favorable result, especially in view of synthetic applications of CPO.Moreover, it was found that the immobilized catalyst performance can be maintained unchanged over at least a month simply by storing the washed matrices at 4 °C. Further optimization of the experimental conditions will lead in the future to a larger-scale synthetic use of CPO.     

Optimal continuous biosynthesis of hexyl laurate by a packed bed bioreactor

Hexyl laurate, a medium-chain ester carried about fruity flavor, is primarily used in personal care formulations as an important emollient for cosmetic applications. On the basis of the hexyl laurate could be successfully synthesized by lipase within a batch system in our previous report. This study aimed to develop an optimal continuous procedure of lipase-catalyzed hexyl laurate synthesis in a packed-bed bioreactor to investigate the possibility of large-scale production further. The ability of lipase from Rhizomucor miehei (Lipozyme IM-77) to catalyze the direct-esterification of 1-hexanol and lauric acid in n-hexane was investigated. Response surface methodology (RSM) and 3-level-3-factor fractional factorial design were employed to evaluate the effects of synthesis parameters, such as reaction temperature (35–55 °C), mixture flow rate (1.5–4.5 mL/min) and substrate molar ratio 1-hexanol to lauric acid (1:1–1:3) on production rate (μmol/min) of hexyl laurate by direct-esterification. Based on the analysis of ridge max, the optimum synthesis conditions for hexyl laurate were as follows: 45 °C of reaction temperature, substrate molar ratio 1:2 and reaction flow rate 4.5 mL/min. The optimum predicted production rate was 435.6 ± 0.9 μmol/min and the actual value was 437.6 ± 0.4 μmol/min.     

Bioaugmentation of UASB reactors with immobilized <Emphasis Type="Italic">Sulfurospirillum barnesii</Emphasis> for simultaneous selenate and nitrate removal

Whole-cell immobilization of selenate-respiring Sulfurospirillum barnesii in polyacrylamide gels was investigated to allow the treatment of selenate contaminated (790 μg Se × L⁻¹) synthetic wastewater with a high molar excess of nitrate (1,500 times) and sulfate (200 times). Gel-immobilized S. barnesii cells were used to inoculate a mesophilic (30°C) bioreactor fed with lactate as electron donor at an organic loading rate of 5 g chemical oxygen demand (COD) × L⁻¹ day⁻¹. Selenate was reduced efficiently (>97%) in the nitrate and sulfate fed bioreactor, and a minimal effluent concentration of 39 μg Se × L⁻¹ was obtained. Scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis revealed spherical bioprecipitates of ≤2 μm diameter mostly on the gel surface, consisting of selenium with a minor contribution of sulfur. To validate the bioaugmentation success under microbial competition, gel cubes with immobilized S. barnesii cells were added to an Upflow Anaerobic Sludge Bed (UASB) reactor, resulting in earlier selenate (24 hydraulic retention times (HRTs)) and sulfate (44 HRTs) removal and higher nitrate/nitrite removal efficiencies compared to a non-bioaugmented control reactor. S. barnesii was efficiently immobilized inside the UASB bioreactors as the selenate-reducing activity was maintained during long-term operation (58 days), and molecular analysis showed that S. barnesii was present in both the sludge bed and the effluent. This demonstrates that gel immobilization of specialized bacterial strains can supersede wash-out and out-competition of newly introduced strains in continuous bioaugmented systems. Eventually, proliferation of a selenium-respiring specialist occurred in the non-bioaugmented control reactor, resulting in simultaneous nitrate and selenate removal during a later phase of operation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Immobilization of lipase within carbon nanotube–silica composites for non-aqueous reaction systems

The immobilization of lipases within sol–gel derived silica, using multi-walled carbon nanotubes (MWNTs) as additives in order to protect the inactivation of lipase during sol–gel process and to enhance the stability of lipase, was investigated. Three sol–gel immobilized lipases (Candida rugosa, Candida antarctica type B, Thermomyces lanuginosus) with 0.33% (w/w) MWNT showed much higher activities than lipase immobilized without MWNT. The influence of MWNT content and MWNT shortened by acid treatment in the sol–gel process on the activity and stability of immobilized C. rugosa lipase was also studied. In hydrolysis reaction, immobilized lipase containing 1.1% pristine MWNT showed 7 times higher activity than lipase immobilized without MWNT. The lipase coimmobilized with 2.7% shortened MWNT showed 10 times higher activity in esterification reaction, compared with lipase immobilized without MWNT. The lipase coimmobilized with 2.7% shortened MWNT retained 96% of initial activity after 5 times reuse, while the lipase immobilized without MWNT was fully inactivated under the same condition.     

Transgenic rice as bioreactor for production of the Candida antarctica lipase B

Candida antarctica lipase B (CALB) is a versatile biocatalyst used for a wide range of biotransformation. Methods for low cost production of this enzyme are highly desirable. Here, we report a mass production method of CALB using transgenic rice seeds as the bioreactor. The transgenic rice transformed with the CALB gene under the control of the promoter of the rice seed storage protein GT1 was found to have accumulated a large quantity of CALB in seeds. The transgenic line with the highest lipolytic activity reached to 85 units per gram of dry seeds. One unit is defined as the amount of lipase necessary to liberate 1 μmol p‐nitrophenol from p‐nitrophenyl butyrate in 1 min. The rice recombinant lipase (rOsCALB) from this line represents 40% of the total soluble proteins in the crude seed extracts. The enzyme purified from the rice seeds had an optimal temperature of 40 °C, and optimal pH of 8.5, similar to that of the fermentation products. Test of its conversion ability as a biocatalyst for biodiesel production suggested that rOsCALB is functionally identical to the fermentation products in its industrial application.