Solvent as a competitive inhibitor for Candida antarctica lipase B

Enzymatic synthesis of aromatic biobased polymers in green, low-boiling solvents

Given the urge to accelerate the substitution of petrol-derived solvents not only in more traditional fields like pharmaceuticals, personal care, or electronics but also in innovative research processes, this work focuses on the utilisation of four biobased solvents as media for the enzymatic synthesis of aliphatic-aromatic polyesters. As building blocks, the lignin-derived diethyl-2,4-pyridinedicarboxylate was selected as the potentially biobased, aromatic component while more classical diols such as 1,4-butanediol and 1,8-octanediol were used as the aliphatic portion. Results show that among the tested green solvents (cyclohexanone, phenetole, anisole and eucalyptol), the most suitable medium for lipase B from Candida antarctica-catalysed polycondensation reactions was eucalyptol that allowed reach monomer conversions >95 % and number average molecular weights up to 3500 g·mol-1. On the other hand, cyclohexanone led to the lowest monomer conversions (<80 %) and molecular weights (Mn<500 g·mol-1) confirming once again the unsuitability of ketone-containing solvents for enzymatic esterification and transesterification reactions. The lipase could be used up to three times, in eucalyptol as a solvent, without a significant decrease in monomer conversion or molecular weight.

Engineering diaryl alcohol dehydrogenase KpADH reveals importance of retaining hydration shell in organic solvent tolerance

Alcohol dehydrogenases (ADHs) are synthetically important biocatalysts for the asymmetric synthesis of chiral alcohols. The catalytic performance of ADHs in the presence of organic solvents is often important since most prochiral ketones are highly hydrophobic. Here, the organic solvent tolerance of KpADH from Kluyveromyces polyspora was semi-rationally evolved. Using tolerant variants obtained, meticulous experiments and computational studies were conducted to explore properties including stability, activity and kinetics in the presence of various organic solvents. Compared with WT, variant V231D exhibited 1.9-fold improvement in ethanol tolerance, while S237G showed a 6-fold increase in catalytic efficiency, a higherT 50 15 $$ {\mathrm{T}}_{50}^{15} $$ , as well as 15% higher tolerance in 7.5% (v/v) ethanol. Based on 3 × 100 ns MD simulations, the increased tolerance of V231D and S237G against ethanol may be ascribed to their enhanced ability in retaining water molecules and repelling ethanol molecules. Moreover, 6.3-fold decreased KM value of V231D toward hydrophilic ketone substrate confirmed its capability of retaining hydration shell. Our results suggest that retaining hydration shell surrounding KpADH is critical for its tolerance to organic solvents, as well as catalytic performance. This study provides useful guidance for engineering organic solvent tolerance of KpADH and other ADHs.

Evolving Robust and Interpretable Enzymes for the Bioethanol Industry

Obtaining a robust and applicable enzyme for bioethanol production is a dream for biorefinery engineers. Herein, we describe a general method to evolve an all-round and interpretable enzyme that can be directly employed in the bioethanol industry. By integrating the transferable protein evolution strategy InSiReP 2.0 (In Silico guided Recombination Process), enzymatic characterization for actual production, and computational molecular understanding, the model cellulase PvCel5A (endoglucanase II Cel5A from Penicillium verruculosum) was successfully evolved to overcome the remaining challenges of low ethanol and temperature tolerance, which primarily limited biomass transformation and bioethanol yield. Remarkably, application of the PvCel5A variants in both first- and second-generation bioethanol production processes (i. Conventional corn ethanol fermentation combined with the in situ pretreatment process; ii. cellulosic ethanol fermentation process) resulted in a 5.7-10.1 % increase in the ethanol yield, which was unlikely to be achieved by other optimization techniques.

Using Molecular Simulation to Guide Protein Engineering for Biocatalysis in Organic Solvents

Biocatalysis in organic solvents (OSs) is very appealing for the industry in producing bulk and/or fine chemicals, such as pharmaceuticals, biodiesel, and fragrances. The poor performance of enzymes in OSs (e.g., reduced activity, insufficient stability, and deactivation) negates OSs' excellent solvent properties. Molecular dynamics (MD) simulations provide a complementary method to study the relationship between enzymes dynamics and the stability in OSs. Here we describe computational procedure for MD simulation of enzymes in OSs with an example of Bacillus subtilis lipase A (BSLA) in dimethyl sulfoxide (DMSO) cosolvent with software GROMACS. We discuss main essential practical issues considered (such as choice of force field, parameterization, simulation setup, and trajectory analysis). The core part of this protocol (enzyme-OS system setup, analysis of structural-based and solvation-based observables) is transferable to other enzymes and any OS systems. Combining with experimental studies, the obtained molecular knowledge is most likely to guide researchers to access rational protein engineering approaches to tailor OS resistant enzymes and expand the scope of biocatalysis in OS media. Finally, we discuss potential solutions to overcome the remaining challenges of computational biocatalysis in OSs and briefly draw future directions for further improvement in this field.

Ethanol as additive enhance the performance of immobilized lipase LipA from Pseudomonas aeruginosa on polypropylene support

Immobilization is practical to upgrade enzymes, increasing their performance and expanding their applications. The recombinant, solvent tolerant lipase LipA PSA01 from Pseudomonas aeruginosa was immobilized on polypropylene Accurel® MP1004 to improve its performance. We investigated the effect of ethanol as an additive during the immobilization process at three concentrations (20%, 25%, and 30%) on the operational behavior of the enzyme. The immobilization efficiency was higher than 92%, and the immobilized enzymes showed hyperactivation and thermal resistance depending on the concentration of ethanol. For example, at 70 °C, the free enzyme lost the activity, while the prepared one with ethanol 25% conserved a residual activity of up to 73.3% (∆ T¹⁵ ₅₀ = 27.1 °C). LipA immobilized had an optimal pH value lower than that of the free enzyme, and the organic solvent tolerance of the immobilized enzymes depended on the ethanol used. Hence, the immobilized enzyme with ethanol 25% showed hyperactivation to more solvents than the soluble enzyme. Remarkable stability towards methanol (up to 8 folds) was evidenced in all the immobilized preparations. The immobilized enzyme changed their chemo preference, and it hydrolyzed oils preferentially with short-chain than those with long-chain. LipA had a notable shelf-life after one year, keeping its activity up to 87%. Ethanol facilitated the access of the enzyme to the hydrophobic support and increased its activity and stability according to the amount of ethanol added.

Less Unfavorable Salt Bridges on the Enzyme Surface Result in More Organic Cosolvent Resistance

Biocatalysis for the synthesis of fine chemicals is highly attractive but usually requires organic (co-)solvents (OSs). However, native enzymes often have low activity and resistance in OSs and at elevated temperatures. Herein, we report a smart salt bridge design strategy for simultaneously improving OS resistance and thermostability of the model enzyme, Bacillus subtilits Lipase A (BSLA). We combined comprehensive experimental studies of 3450 BSLA variants and molecular dynamics simulations of 36 systems. Iterative recombination of four beneficial substitutions yielded superior resistant variants with up to 7.6-fold (D64K/D144K) improved resistance toward three OSs while exhibiting significant thermostability (thermal resistance up to 137-fold, and half-life up to 3.3-fold). Molecular dynamics simulations revealed that locally refined flexibility and strengthened hydration jointly govern the highly increased resistance in OSs and at 50-100 °C. The salt bridge redesign provides protein engineers with a powerful and likely general approach to design OSs- and/or thermal-resistant lipases and other α/β-hydrolases.

Screening of solvents for favoring hydrolytic activity of Candida antarctica Lipase B

Lipases are a group of enzymes of considerable significance in organic synthesis, among which Candida antarctica lipase B (CALB) is one of the most widely studied enzymes. The activity of the biocatalyst has been intensively characterized in many organic media, but this paper aimed to compare the effect of 20 different solvents on the activity of CALB in the hydrolysis of p-nitrophenyl laurate. Nonpolar, polar aprotic, and polar protic solvents were used for enzyme pretreatment and then entered the composition of mixed solvents reaction medium. An impact of solvents on solvation processes affecting the catalysis steps, protein denaturation, and changes of its conformation was discussed. Moreover the hydrolytic activity of CALB with partition coefficient (logP) of the solvent used was correlated. It was emphasized that the substrate solubility plays an important role in solvent selection. In the presence of hydrophobic solvents, hydration layer becomes more hydrophobic facilitating the substrate access to the enzyme surface. In turn, polar compounds are good solvents for organic substrates facilitating the penetration of the aqueous layer that surrounds the surface of the enzyme. Two variants proved to be favorable for ester hydrolysis reaction: isooctane or polar solvent such as acetone, tert -butyl methyl ether, tert-butanol or acetonitrile.

Enzymatic Synthesis of a Diene Ester Monomer Derived from Renewable Resource

The total or partial substitution of fossil raw materials by biobased materials from renewable resources is one of the great challenges of our society. In this context, the reaction under mild condition as enzyme-catalyzed esterification was applied to investigate the esterification of the biobased 10-undecenoic acid with 2-hydroxyethyl methacrylate (HEMA) to obtain a new diene ester monomer. The environmentally friendly enzymatic reaction presented up to 100% of conversion; moreover, the production of possible by-products was minimized controlling reaction time and amount of enzyme. Furthermore, the presence of chloroform was evaluated during the enzymatic reactions and despite high conversions with higher enzyme concentration, the solvent-free system showed fast kinetics even with 1.13 U/g substrates. In addition, the commercial immobilized lipases Novozym 435 and NS 88011 could be applied for up to 10 cycles keeping conversions about 90%. The scale-up of the reaction was possible and a purification procedure was applied in order to isolate the diene ester monomer 2-(10-undecenoyloxy)ethyl methacrylate, preserving its double bonds, which could allow a potential use of this product in the synthesis of new renewable polymers through techniques as metathesis, thiol-ene, or free-radical polymerization.

Effects of cholinium-based ionic liquids on Aspergillus niger lipase: Stabilizers or inhibitors

Lipases are well-known biocatalysts used in several industrial processes/applications. Thus, as with other enzymes, changes in their surrounding environment and/or their thermodynamic parameters can induce structural changes that can increase, decrease, or even inhibit their catalytic activity. The use of ionic compounds as solvents or additives is a common approach for adjusting reaction conditions and, consequently, for controlling the biocatalytic activity of enzymes. Herein, to elucidate the effects of ionic compounds on the structure of lipase, the stability and enzymatic activity of lipase from Aspergillus niger in aqueous solutions (at 0.05, 0.10, 0.50, and 1.00 M) of six cholinium-based ionic liquids (cholinium chloride [Ch]Cl; cholinium acetate ([Ch][Ac]); cholinium propanoate ([Ch][Prop]); cholinium butanoate ([Ch][But]); cholinium pentanoate ([Ch][Pent]); and cholinium hexanoate ([Ch][Hex])) were evaluated over 24 hr. The enzymatic activity of lipase was maintained or enhanced in the lower concentrations of all the [Ch]⁺ -ILs (below 0.1 M). [Ch][Ac] maintained the biocatalytic behavior of lipase, independent of the IL concentration and incubation time. However, above 0.1 M, [Ch][Pent] and [Ch][Hex] caused complete inhibition of the catalytic activity of the enzyme, demonstrating that the increase in the anionic alkyl chain length strongly affected the conformation of the lipase. The hydrophobicity and concentration of the [Ch]⁺ -ILs play an important role in the enzyme activity, and these parameters can be controlled by adjusting the anionic alkyl chain length. The inhibitory effects of [Ch][Pent] and [Ch][Hex] may be of great interest to the pharmaceutical industry to induce pharmacological inhibition of gastric and pancreatic lipases.

High-level expression and molecular characterization of a recombinant prolidase from Escherichia coli NovaBlue

Long-term use of organophosphorus (OP) compounds has become an increasing global problem and a major threat to sustainability and human health. Prolidase is a proline-specific metallopeptidase that can offer an efficient option for the degradation of OP compounds. In this study, a full-length gene from Escherichia coli NovaBlue encoding a prolidase (EcPepQ) was amplified and cloned into the commercially-available vector pQE-30 to yield pQE-EcPepQ. The overexpressed enzyme was purified from the cell-free extract of isopropyl thio-β-D-galactoside IPTG-induced E. coli M15 (pQE-EcPepQ) cells by nickel-chelate chromatography. The molecular mass of EcPepQ was determined to be about 57 kDa by 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis and the result of size-exclusion chromatography demonstrated that the enzyme was mainly present in 25 mM Tris–HCl buffer (pH 8.0) as a dimeric form. The optimal conditions for EcPepQ activity were 60 °C, pH 8.0, and 0.1 mM Mn²⁺ ion. Kinetic analysis with Ala-Pro as the substrate showed that the K_m and k_cat values of EcPepQ were 8.8 mM and 926.5 ± 2.0 s⁻¹, respectively. The thermal unfolding of EcPepQ followed a two-state process with one well-defined unfolding transition of 64.2 °C. Analysis of guanidine hydrochloride (GdnHCl)-induced denaturation by tryptophan emission fluorescence spectroscopy revealed that the enzyme had a [GdnHCl]_0.5,N-U value of 1.98 M. The purified enzyme also exhibited some degree of tolerance to various water/organic co-solvents. Isopropanol and tetrahydrofuran were very detrimental to the enzymatic activity of EcPepQ; however, other more hydrophilic co-solvents, such as formamide, methanol, and ethylene glycol, were better tolerated. Eventually, the non-negative influence of some co-solvents on both catalytic activity and structural stability of EcPepQ allows to adjust the reaction conditions more suitable for EcPepQ-catalyzed bioprocess.

Lid opening and conformational stability of T1 Lipase is mediated by increasing chain length polar solvents

The dynamics and conformational landscape of proteins in organic solvents are events of potential interest in nonaqueous process catalysis. Conformational changes, folding transitions, and stability often correspond to structural rearrangements that alter contacts between solvent molecules and amino acid residues. However, in nonaqueous enzymology, organic solvents limit stability and further application of proteins. In the present study, molecular dynamics (MD) of a thermostable Geobacillus zalihae T1 lipase was performed in different chain length polar organic solvents (methanol, ethanol, propanol, butanol, and pentanol) and water mixture systems to a concentration of 50%. On the basis of the MD results, the structural deviations of the backbone atoms elucidated the dynamic effects of water/organic solvent mixtures on the equilibrium state of the protein simulations in decreasing solvent polarity. The results show that the solvent mixture gives rise to deviations in enzyme structure from the native one simulated in water. The drop in the flexibility in H₂O, MtOH, EtOH and PrOH simulation mixtures shows that greater motions of residues were influenced in BtOH and PtOH simulation mixtures. Comparing the root mean square fluctuations value with the accessible solvent area (SASA) for every residue showed an almost correspondingly high SASA value of residues to high flexibility and low SASA value to low flexibility. The study further revealed that the organic solvents influenced the formation of more hydrogen bonds in MtOH, EtOH and PrOH and thus, it is assumed that increased intraprotein hydrogen bonding is ultimately correlated to the stability of the protein. However, the solvent accessibility analysis showed that in all solvent systems, hydrophobic residues were exposed and polar residues tended to be buried away from the solvent. Distance variation of the tetrahedral intermediate packing of the active pocket was not conserved in organic solvent systems, which could lead to weaknesses in the catalytic H-bond network and most likely a drop in catalytic activity. The conformational variation of the lid domain caused by the solvent molecules influenced its gradual opening. Formation of additional hydrogen bonds and hydrophobic interactions indicates that the contribution of the cooperative network of interactions could retain the stability of the protein in some solvent systems. Time-correlated atomic motions were used to characterize the correlations between the motions of the atoms from atomic coordinates. The resulting cross-correlation map revealed that the organic solvent mixtures performed functional, concerted, correlated motions in regions of residues of the lid domain to other residues. These observations suggest that varying lengths of polar organic solvents play a significant role in introducing dynamic conformational diversity in proteins in a decreasing order of polarity.

Probing the emitter site of Renilla luciferase using small organic molecules; an attempt to understand the molecular architecture of the emitter site

Renilla luciferase is a sensitive enzyme and has wide applications in biotechnology such as drug screening. Previous studies have tried to show the catalytic residues, nevertheless, the accurate architecture and molecular behavior of its emitter site remains uncharacterized. In this study, the activity of Renilla luciferase, in the presence of two small organic molecules including dimethyl sulfoxide (DMSO) and isopropanol was considered and the structure was studied by circular dichroism (CD) and fluorescence spectroscopy. Moreover, the interaction of small organic molecules with the Renilla luciferase was studied using molecular dynamics simulations. Kinetics studies showed that at low concentration of DMSO (16.6-66mM) and isopropanol (19.3-76mM) the K_m changed and a competitive inhibition pattern was observed. Moreover, spectroscopy studies reveled that the changes of activity of Renilla luciferase in the presence of low concentrations of small organic molecules was not associated with structural collapse or severe changes in the enzyme conformation. Molecular dynamics simulations indicated that DMSO and isopropanol, as probing molecules, were both able to bind to the emitter site and remained with the residues of the emitter site. Based on the probing data, the architecture of the emitter site in the "non-binding" model was proposed.

Study on the enzyme's 1,3-positional specificity during lipozyme TL-mediated biodiesel production

Effect of organic solvent on lipase's 1,3-positional specificity from a kinetics study. Effect of water activity on lipase's 1,3-positional specificity from a kinetics study. Molecular dynamics simulation to reveal the mechanism.

Enantioselective synthesis of mosquito oviposition pheromone and its epimer from a naturally occurring fatty acid

Direct epoxidation of cis-5-hexadecenoic acid towards the synthesis of Mosquito Oviposition Pheromone (MOP) and evaluation of Dynamic Kinetic Asymmetric Transformation (DYKAT) for late-stage asymmetric induction are presented.

Enzymatic production of a solvent-free menthyl butyrate via response surface methodology catalyzed by a novel thermostable lipase from Geobacillus zalihae

Most substrate for esterification has the inherent problem of low miscibility which requires addition of solvents into the reaction media. In this contribution, we would like to present an alternative and feasible option for an efficient solvent-free synthesis of menthyl butyrate using a novel thermostable crude T1 lipase. We investigated the effects of incubation time, temperature, enzyme loading and substrate molar ratio and determined the optimum conditions. The high conversion of menthyl butyrate catalyzed by crude T1 lipase in a solvent-free system is greatly affected by temperature and time of the reaction media. The highest yield of menthyl butyrate was 99.3% under optimized conditions of 60 °C, incubation time of 13.15 h, 2.53 mg, 0.43% (w/w) enzyme to substrate ratio and at molar ratio of butyric anhydride/menthol 2.7:1. Hence, the investigation revealed that the thermostable crude T1 lipase successfully catalyzed the high-yield production of menthyl butyrate in a solvent-free system. The finding suggests that the crude T1 lipase was a promising alternative to overcome shortcomings associated with solvent-assisted enzymatic reactions.

Effects of methanol on lipases: molecular, kinetic and process issues in the production of biodiesel

The biotechnological production of biodiesel is based on transesterification/esterification reactions between a source of fatty acids and a short-chain alcohol, usually methanol, catalysed by enzymes belonging to the class known as lipases. Several lipases used in industrial processes, although stable in the presence of other organic solvents, are inactivated by methanol at or below the concentration optimal for biodiesel production, making it necessary to use stepwise methanol feeding or pre-treatment of the enzyme. In this review article we focus on what is currently know about methanol inactivation of lipases, a phenomenon which is not common to all lipase enzymes, with the goal of improving the biocatalytic process. We suggest that different mechanisms can lead to inactivation of different lipases, in particular substrate inhibition and protein unfolding. Attempts to improve the performances of methanol sensitive lipases by mutagenesis as well as process engineering approaches are also summarized.

Molecular mechanism of deactivation of C. antarctica lipase B by methanol

The catalytic activity of Candida antarctica lipase B upon alcoholysis of a constant concentration of 15.2% vinyl acetate (vol/vol) and varying concentrations of methanol (0.7-60%) in toluene was determined experimentally by measuring the initial reaction velocity. The molecular mechanism of the deactivation of the enzyme by methanol was investigated by fitting the experimental data to a kinetic model and by molecular dynamics simulations of C. antarctica lipase B in toluene-methanol-water mixtures. The highest catalytic activity (280 U/mg) was observed at methanol concentrations as low as 0.7% methanol (vol/vol), followed by a sharp decrease at higher methanol concentrations. For methanol concentrations above 10% (vol/vol), catalytic activity was at 30% of the maximum activity. A variation of water activity in the range 0.02-0.09 had only minor effects. These experimental observations are described by a simple kinetic model using three assumptions: (1) a ping-pong bi-bi mechanism of the enzyme, (2) competitive inhibition by the substrate methanol, and (3) by describing enzyme kinetics by the thermodynamic activities of the substrates rather than by their concentrations. Two equilibrium constants of methanol (KM,MeOH=0.05 and Ki,MeOH=0.23) were derived by modeling methanol binding to the substrate binding site of the lipase in molecular dynamics simulations of protein-solvent systems at atomic resolution. Thus, the sharp maximum of catalytic activity of C. antarctica lipase B at 0.7% methanol is a direct consequence of the fact that methanol-toluene mixtures are far from ideal. Understanding the thermodynamics of solvent mixtures is prerequisite to a quantitative model of enzymatic activity in organic solvents.

Immobilization and Biochemical Properties of the Enantioselective Recombinant NStcI Esterase of Aspergillus nidulans

The recombinant NStcI A. nidulans esterase was adsorbed on Accurel MP1000, where protein yield and immobilization efficiency were 42.48% and 81.94%, respectively. Storage stability test at 4°C and RT showed 100% of residual activity after 40 days at both temperatures. The biocatalyst retains more than 70% of its initial activity after 3 cycles of repeated use. Biochemical properties of this new biocatalyst were obtained. Maximum activity was achieved at pH 11 and 30°C, while the best stability was observed with the pH between 9 and 11 at 40°C. NStcI thermostability was increased after immobilization, as it retained 47.5% of its initial activity after 1 h at 60°C, while the free enzyme under the same conditions displayed no activity. NStcI preserved 70% of its initial activity in 100% hexane after 72 h. Enzymatic kinetic resolution of (R,S)-1-phenylethanol was chosen as model reaction, using vinyl acetate as acyl donor. After optimization of reaction parameters, the highest possible conversion (42%) was reached at 37°C, a_w of 0.07, and 120 h of bioconversion in hexane with an enantiomeric excess of 71.7%. NStcI has selectivity for (R)-enantiomer. The obtained E value (31.3) is in the range considered useful to resolve enantiomeric mixtures.

Organic co-solvents affect activity, stability and enantioselectivity of haloalkane dehalogenases

Haloalkane dehalogenases are microbial enzymes with a wide range of biotechnological applications, including biocatalysis. The use of organic co-solvents to solubilize their hydrophobic substrates is often necessary. In order to choose the most compatible co-solvent, the effects of 14 co-solvents on activity, stability and enantioselectivity of three model enzymes, DbjA, DhaA, and LinB, were evaluated. All co-solvents caused at high concentration loss of activity and conformational changes. The highest inactivation was induced by tetrahydrofuran, while more hydrophilic co-solvents, such as ethylene glycol and dimethyl sulfoxide, were better tolerated. The effects of co-solvents at low concentration were different for each enzyme-solvent pair. An increase in DbjA activity was induced by the majority of organic co-solvents tested, while activities of DhaA and LinB decreased at comparable concentrations of the same co-solvent. Moreover, a high increase of DbjA enantioselectivity was observed. Ethylene glycol and 1,4-dioxane were shown to have the most positive impact on the enantioselectivity. The favorable influence of these co-solvents on both activity and enantioselectivity makes DbjA suitable for biocatalytic applications. This study represents the first investigation of the effects of organic co-solvents on the biocatalytic performance of haloalkane dehalogenases and will pave the way for their broader use in industrial processes.

Combination of oxyanion Gln114 mutation and medium engineering to influence the enantioselectivity of thermophilic lipase from Geobacillus zalihae

The substitution of the oxyanion Q114 with Met and Leu was carried out to investigate the role of Q114 in imparting enantioselectivity on T1 lipase. The mutation improved enantioselectivity in Q114M over the wild-type, while enantioselectivity in Q114L was reduced. The enantioselectivity of the thermophilic lipases, T1, Q114L and Q114M correlated better with log p as compared to the dielectric constant and dipole moment of the solvents. Enzyme activity was good in solvents with log p < 3.5, with the exception of hexane which deviated substantially. Isooctane was found to be the best solvent for the esterification of (R,S)-ibuprofen with oleyl alcohol for lipases Q114M and Q114L, to afford E values of 53.7 and 12.2, respectively. Selectivity of T1 was highest in tetradecane with E value 49.2. Solvents with low log p reduced overall lipase activity and dimethyl sulfoxide (DMSO) completely inhibited the lipases. Ester conversions, however, were still low. Molecular sieves employed as desiccant were found to adversely affect catalysis in the lipase variants, particularly in Q114M. The higher desiccant loading also increased viscosity in the reaction and further reduced the efficiency of the lipase-catalyzed esterifications.

Biocatalytic synthesis of ascorbyl esters and their biotechnological applications

Ascorbyl fatty acid esters act both as antioxidants and surfactants. These esters are obtained by acylation of vitamin C using different acyl donors in presence of chemical catalysts or lipases. Lipases have been used for this reaction as they show high regioselectivity and can be used under mild reaction conditions. Insolubility of hydrophilic ascorbic acid in non-polar solvents is the major obstacle during ascorbic acid esters synthesis. Different strategies have been invoked to address this problem viz. use of polar organic solvents, ionic liquids, and solid-phase condensation. Furthermore, to improve the yield of ascorbyl fatty acid esters, reactions were performed by (1) controlling water content in the reaction medium, (2) using vacuum to remove formed volatile side product, and (3) employing activated acyl donors (methyl, ethyl or vinyl esters of fatty acids). This mini-review offers a brief overview on lipase-catalyzed syntheses of vitamin C esters and their biotechnological applications. Also, wherever possible, technical viability, scope, and limitations of different methods are discussed.