| 1. |
- Berglund, Per, et al.
(författare)
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Reversed enantiopreference of Candida rugosa lipase supports different modes of binding enantiomers of a chiral acyl donor
- 1998
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Ingår i: Journal of Molecular Catalysis - B Enzymatic. - 1381-1177 .- 1873-3158. ; 5:1-4, s. 283-287
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Tidskriftsartikel (refereegranskat)abstract
- Molecular modelling identifies two different productive modes of binding the enantiomers of a 2-methyldecanoic acid ester to the active site of Candida rugosa lipase (CRL). The fast reacting S-enantiomer occupies the previously identified acyl-binding tunnel of the enzyme, whereas the R- enantiomer leaves the tunnel empty. The modelling suggested that if both enantiomers were forced to bind to the active site leaving the tunnel empty, the enzyme would reverse its enantiopreference to become R-enantioselective. To test this hypothesis, we designed a structural analogue to 2- methyldecanoic acid, 2-methyl-6-(2-thienyl)hexanoic acid, which was expected to be too bulky to fit its acyl moiety into the acyl-binding tunnel. The CRL- catalysed hydrolysis of the ethyl ester of this substrate resulted in the preferential conversion of the R-enantiomer as predicted by molecular modelling. This represents the first kinetic evidence supporting the existence of two different modes of binding the enantiomers of a 2- methyldecanoic acid ester to the active site of CRL. We have shown that a rational 3D based approach in combination with substrate engineering can be used to predict and control the stereochemical outcome of a lipase catalysed reaction.
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| 2. |
- Hedenström, Erik, et al.
(författare)
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Stereoselective esterification of 2,6-dimethyl-1,7-heptanedioic acid, catalysed by Candida rugosa lipase
- 2003
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Ingår i: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 23:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- The immobilised Candida rugosa lipase (CRL) displayed S-preference for both stereogenic centres in this sequential esterification of 2,6-dimethyl-1,7-heptanedioic acid (1) (pure meso and meso: (+/-) mixture, 53/47) with n-butanol in cyclohexane at a(w) = 0.8. The reaction was faster when short-chain primary n-alcohols was used and very slow, or even none reactive, when a Ion-chain alcohol was used.
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| 3. |
- Kalogeris, E, et al.
(författare)
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Catalytic properties of the endoxylanase I from Thermoascus aurantiacus
- 2001
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Ingår i: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 11:4-6, s. 491-501
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Tidskriftsartikel (refereegranskat)abstract
- Endo-β-1,4-xylanase I previously purified from Thermoascus aurantiacus solid state culture was further characterized. The enzyme had a molecular weight of 33 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and 31 kDa by gel filtration. Thin layer chromatography (TLC) analysis showed that endoxylanase liberates aldotetrauronic acid MeGlcAα-1,2-Xylβ-1,4-Xylβ-1,4-Xyl as the shortest acidic fragment from glucuronoxylan and an isomeric xylotriose (Xyl3) of the structure Xylβ1-3Xylβ1-4Xyl from rhodymenan. The enzyme performed ideally on O-acetyl-4-O-methylglucuronoxylan, liberating large amounts of short acetylated and non-acetylated fragments. Also, the enzyme was capable to hydrolyse arabinoxylan to arabinose (Arab), xylose (Xyl) and xylobiose (Xyl2). The enzyme degraded pNPX (4-nitrophenyl β-D-xylopyranoside) by a complex reaction pathway that involved both hydrolysis and glycosyl transfer reactions. The enzyme tolerates the replacement of β-xylopyranosyl units in several artificial substrates by β-glucopyranosyl, α-L-arabinopyranosyl and α-L-arabinofuranosyl units and was active on pNPC (4-nitrophenyl β-D-cellobioside), pNP-Arap (4-nitrophenyl α-L-arabinopyranoside) and pNPAraf (4-nitrophenyl α-L-arabinofuranoside). The enzyme also hydrolysed the 4-methylumbelliferyl glycosides of β-D-xylobiose and β-D-xylotriose at the agluconic linkage. The results suggested that the xylanase I from T. aurantiacus has catalytic properties similar to those belonging to family 10. Copyright © 2001 Elsevier Science B.V.
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| 4. |
- Ottosson, Jenny, et al.
(författare)
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Influence of acyl chain length on the enantioselectivity of Candida antarctica lipase B and its thermodynamic components in kinetic resolution of sec-alcohols
- 2001
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Ingår i: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 11:4-6, s. 1025-1028
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Tidskriftsartikel (refereegranskat)abstract
- The enantioselectivity, E, of Candida antarctica lipase B (CALB) was found to be strongly influenced by the chain length of the achiral acyl donor employed in the transesterification of 3-methyl-2-butanol. Of the four studied acyl donors, the longest, vinyl octanoate, afforded the highest enantioselectivity. This was true over the temperature range studied, 6-70 degreesC. Measurements of the temperature dependence of E allows for separation of the enthalpic and entropic components of enantioselectivity. Changes in E with chain length were mainly caused by changes in the entropic component except for the reaction with vinyl propionate, which differed from the others also in the enthalpic component. Optimisation of acyl donor adds one more possibility to improve the yield of enantiopurity in the production of optically active compounds apart from optimisation of solvent, temperature, water activity, and choice of enzyme.
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| 5. |
- Stamatis, H., et al.
(författare)
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Studies on the synthesis of short-chain geranyl esters catalysed by Fusarium oxysporum esterase in organic solvents
- 1998
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Ingår i: Journal of Molecular Catalysis B. - 1381-1177 .- 1873-3158. ; 4:4, s. 229-236
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Tidskriftsartikel (refereegranskat)abstract
- A novel esterase isolated from Fusarium oxysporum was investigated for the synthesis of short-chain esters of geraniol by alcoholysis and direct esterification reactions in organic solvents. The enzyme was used as a dried powder (i.e., not immobilized). The reaction parameters affecting the enzyme behavior such as the nature of organic solvent and acyl donor, the concentration of substrates and the water activity of the system were studied. High yields (80–90%) were obtained by both approaches (alcoholysis and direct esterification) at low values of water activity (aw=0.11) in n-hexane. The enzyme retain its catalytic activity even after fifth reuse in n-hexane at aw=0.11, demonstrating its stability and efficiency under the conditions of this study.
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| 6. |
- Alberti, Jean-Christophe, et al.
(författare)
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A functional role identified for conserved charged residues at the active site entrance of lipoxygenase with double specificity
- 2016
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 123, s. 167-173
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Tidskriftsartikel (refereegranskat)abstract
- Plant lipoxygenases (LOXs) are a class of widespread dioxygenases catalyzing the hydroperoxidation of free polyunsaturated fatty acids, producing 9-hydroperoxides or 13-hydroperoxides from linoleic and alpha-linolenic acids, and are called 9-LOX or 13-LOX, respectively. Some LOXs produce both 9- and 13- hydroperoxides. The models proposed to explain the reaction mechanism specificity fail to explain the "double specificity" character of these LOXs. In this study, we used the olive LOX1 with double specificity to investigate the implication of the charged residues R265, R268, and K283 in the orientation of the substrate into the active site. These residues are present in a conserved pattern around the entrance of the active site. Our results show that these residues are involved in the penetration of the substrate into the active site: this positive patch could capture the carboxylate end of the substrate, and then guide it into the active site. Due to its position on alpha 2 helix, the residue K283 could have a more important role, its interaction with the substrate facilitating the motions of residues constituting the "cork of lipoxygenases" or the alpha 2 helix, by disrupting putative hydrogen and ionic bonds.
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| 7. |
- Bisagni, Serena, et al.
(författare)
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Cloning and expression of a Baeyer-Villiger monooxygenase oxidizing linear aliphatic ketones from Dietzia sp. D5
- 2014
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 109, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- A Baeyer-Villiger monooxygenase has been identified in the genome sequence of Dietzia sp. D5. Sequence similarity search revealed that the enzyme belongs to a group of BVMOs that are closely related to ethionamide monooxygenase from Mycobacterium tuberculosis (EthA). The BVMO was expressed in E. coli BL21-CodonPlus(DE3)-RP and the best expression was achieved when the E. coli cells were cultivated in terrific broth (TB) at 15 degrees C and induced with 0.1 mM of IPTG. Since the purified enzyme did not show any measurable activity, the substrate scope of the BVMO has been determined using whole-cell and crude cell extract systems. The enzyme was most active towards linear aliphatic substrates. However, it has shown a moderate degree of conversion for cyclobutanone, 2-methylcyclohexanone, bicyclo[3.2.0]hept-2-en-6-one, phenylacetone and thioanisole. There was no detectable conversion of ethionamide, cyclohexanone and acetophenone. (C) 2014 Elsevier B.V. All rights reserved.
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| 8. |
- Blikstad, Cecilia, et al.
(författare)
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Functional characterization of a stereospecific diol dehydrogenase, FucO, from Escherichia coli : substrate specificity, pH dependence, kinetic isotope effects and influence of solvent viscosity
- 2010
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 66:1-2, s. 148-155
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Tidskriftsartikel (refereegranskat)abstract
- FucO, (S)-1,2-propanediol oxidoreductase, from Escherichia coli is involved in the anaerobic catabolic metabolism of L-fucose and L-rhamnose, catalyzing the interconversion of lactaldehyde to propanediol. The enzyme is specific for the S-enantiomers of the diol and aldehyde suggesting stereospecificity in catalysis. We have studied the enzyme kinetics of FucO with a spectrum of putative alcohol and aldehyde substrates to map the substrate specificity space. Additionally, for a more detailed analysis of the kinetic mechanism, pH dependence of catalysis, stereochemistry in hydride transfer, deuterium kinetic isotope effect of hydride transfer and effect of increasing solvent viscosity were also analyzed. The outcome of this study can be summarized as follows: FucO is highly stereospecific with the highest E-value measured to be 320 for the S-enantiomer of 1,2-propanediol. The enzyme is strictly regiospecific for oxidation of primary alcohols. The enzyme prefers short-chained (2-4 carbons) substrates and does not act on bulkier compounds such as phenyl-substituted alcohols. FucO is an 'A-side' dehydrogenase transferring the pro-R-hydrogen of NADH to the aldehyde substrate. The deuterium KIEs of kcat and kcat/KM were 1.9 and 4.2, respectively, illustrating that hydride transfer is partially rate-limiting but also that other reaction steps contribute to rate limitation of catalysis. Combining the KIE results with the observed effects of increasing medium viscosity proposed a working model for the kinetic mechanism involving slow, rate-limiting, product release and on-pathway conformational changes in the enzyme-nucleotide complexes.
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| 9. |
- Bohlin, Christina, et al.
(författare)
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Differences in stereo-preference in the oxidative degradation of diastereomers of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol with enzymic and non-enzymic oxidants
- 2007
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Ingår i: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 45:1-2, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of equal amounts of the erythro and the threo forms of the β-O-4 lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized with different ligninolytic enzymes and non-enzymic oxidants. The oxidants included cerium(IV)ammonium nitrate (CAN), Fenton’s reagent, lead(IV) tetraacetate (LTA), laccase, laccase–mediator systems (based on the mediators ABTS, HBT,TEMPO, and VLA), and lignin peroxidase. The stereo-preference of the different oxidants was compared based on analyses of remaining substrateusing HPLC and UV-diode array detector or 1H NMR spectroscopy. Fenton’s reagent was the only oxidant tested that did not show preferentialdegradation of either the erythro or the threo form. CAN, LTA and lignin peroxidase preferentially oxidized the threo form. The stereo-preferenceof the laccase–mediator systems depended on the mediator. Oxidation mediated by HBT, TEMPO or VLA resulted in a preferential degradationof the threo form. Laccase/ABTS was the only system tested that showed preferential oxidation of the erythro form. The stereo-preference of theoxidants is discussed based on their redox potentials and their classification as outer-sphere and inner-sphere oxidants.
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| 10. |
- Bohlin, Christina, et al.
(författare)
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Product profiles in enzymic and non-enzymic oxidations of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol
- 2005
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Ingår i: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 35:4-6, s. 100-107
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Tidskriftsartikel (refereegranskat)abstract
- The erythro form of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) was oxidized with laccase/ABTS, lead(IV) tetraacetate (LTA), lignin peroxidase/H2O2, cerium(IV) ammonium nitrate (CAN) and Fenton's reagent. The product profiles obtained with the different oxidants were compared after separation, identification and quantification of the products using HPLC, UV-diode array detector and electrospray ionization mass spectrometry in positive ionization mode. The oxidants generated different product profiles that reflected their different properties. Oxidation with laccase/ABTS resulted almost exclusively in formation of 1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)-1-propanone (2). Oxidation with LTA resulted in more 3,4-dimethoxybenzaldehyde (3) than ketone 2. Lignin peroxidase and CAN gave similar product profiles and aldehyde 3 was the predominant product (only small amounts of ketone 2 were formed). Oxidation with Fenton's reagent resulted in the formation of more aldehyde 3 than ketone 2 but the yields were very low. CAN served as an excellent model for the lignin peroxidase-catalyzed oxidation, while the laccase-mediator system, LTA and Fenton's reagent provided distinctly different product profiles. Erythro-1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol was present among the products obtained on oxidation with LTA, lignin peroxidase, CAN and Fenton's reagent. The differences in redox potential between the oxidants afford an explanation of the diverse product patterns but other factors may also be of importance. The reactions leading to cleavage of the β-ether bond with formation of 1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol (veratrylglycerol) were found to proceed without affecting the configuration at the β-carbon atom.
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| 11. |
- Branneby, Cecilia, et al.
(författare)
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Aldol Additions with Mutant Lipase : Analysis by Experiments and Theoretical Calculations
- 2004
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 31:4-6, s. 123-128
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Tidskriftsartikel (refereegranskat)abstract
- A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol additions. Quantum chemical calculations predicted a reaction rate similar to that of natural enzymes, whereas experiments showed a much lower reaction rate. Molecular dynamics simulations, presented here, show that the low reaction rate is a consequence of the low frequencies of near attack complexes in the enzyme. Equilibrium was also considered as a reason for the slow product formation, but could be excluded by performing a sequential reaction to push the reaction towards product formation. In this paper, further experimental results are also presented, highlighting the importance of the entire active site for catalysis.
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| 12. |
- Carlquist, Magnus, et al.
(författare)
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Kinetic resolution of racemic 5,6-epoxy-bicyclo[2.2.1]heptane-2-one using genetically engineered Saccharomyces cerevisiae
- 2009
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 58:2, s. 98-102
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Tidskriftsartikel (refereegranskat)abstract
- (+)-5,6-Epoxy-bicyclo[2.2.1]heptane-2-one, (+)-1, and endo-(−)-5,6-epoxy-bicyclo[2.2.1]heptane-2-ol, endo-(−)-2, were obtained by kinetic resolution of rac-1 by asymmetric bioreduction catalyzed by whole cells of a genetically engineered Saccharomyces cerevisiae yeast strain. The strain, TMB4100, had 1% phosphoglucose isomerase (PGI) activity and overexpressed a specific short-chain dehydrogenase, encoded by the gene YMR226c. The whole cell biocatalystwas demonstrated to be significantly inactivated within 24 h, thus restricting the reaction to lowconcentration. Despite this, the resolution method could be used to produce optically pure (+)-1 and endo-(−)-2 from the racemic mixture at 5 g/L substrate. At optimal conditions, 1 g of rac-1 was kinetically resolved to give (+)-1 in 95% ee and 28% yield and endo-(−)-2 in 74% ee, 80% de and 45% yield.
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| 13. |
- Chávez, Georgina, et al.
(författare)
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Baeyer-Villiger oxidation with peracid generated in situ by CaLB-CLEA catalyzed perhydrolysis
- 2013
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 89, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- Candida antarctica lipase B, immobilized as cross linked enzyme aggregates (CLEAs) was used to mediate the Baeyer-Villiger oxidation of cyclohexanone to epsilon-caprolactone, and the reaction was compared with the one using Novozym (R) 435 as catalyst. The conversion was dependent on the initial concentration of cyclohexanone, and was about 90% after 48 h at concentrations of up to 0.25 M but was decreased at higher concentrations. Caprolactone concentrations up to 0.6 M had no effect on the reaction efficiency. Among the cyclic ketones tested, the highest degree of conversion was achieved for cyclopentanone (88%) and the lowest for cyclooctanone (about 2%). The effect of methyl substitution and position of substitution on the cycloketone was studied using methylcyclohexanone and it has shown to influence the conversion efficiency. Both hydrogen peroxide and the reaction by-product acetic acid had a deleterious effect on the stability of the biocatalyst. (C) 2012 Elsevier B.V. All rights reserved.
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| 14. |
- Chen, Shan, et al.
(författare)
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Stabilization of an amine transaminase for biocatalysis
- 2016
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier. - 1381-1177 .- 1873-3158. ; 124, s. 20-28
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Tidskriftsartikel (refereegranskat)abstract
- The amine transaminase from Chromobacterium violaceum (Cv-ATA) is a well-known enzyme to achievechiral amines of high enantiomeric excess in laboratory scales. However, the low operational stabilityof Cv-ATA limits the enzyme applicability on larger scales. In order to improve the operational stabilityof Cv-ATA, and thereby extending its applicability, factors (additives, co-solvents, organic solvents anddifferent temperatures) targeting enzyme stability and activity were explored in order to find out how tostore and apply the enzyme. The present investigation shows that the melting point of Cv-ATA is improvedby adding sucrose or glycerol, separately. Further, by storing the enzyme at higher concentrations and inco-solvents, such as; 50% glycerol, 20% methanol or 10% DMSO, the active dimeric structure of Cv-ATAis retained. Enzyme stored in 50% glycerol at −20◦C was e.g., still fully active after 6 months. Finally,the enzyme performance was improved 5-fold by a co-lyophilization with surfactants prior to usage inisooctane.
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| 15. |
- Gaber, Yasser, et al.
(författare)
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Rational mutagenesis of pig liver esterase (PLE-1) to resolve racemic clopidogrel
- 2015
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 122, s. 156-162
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Tidskriftsartikel (refereegranskat)abstract
- Clopidogrel is an important and widely used antiplatelet drug; only the (S)-isomer is the active biological enantiomer. The industrial production of the active enantiomer involves resolution of the racemic compound using stoichiometric amounts of L-camphor sulphonic acid and crystallization in a process using large amounts of solvent. In the present study, the possibility of enzyme catalysed kinetic resolution was investigated. Screening of a number of hydrolytic enzymes showed the crude pig liver esterase (PLE) to exhibit modest enantioselectivity in the hydrolysis of racemic clopidogrel. Molecular modeling simulations were applied on the homology model of PLE-1, the major isoenzyme in the crude PLE, and distinct sites of mutations were proposed and 'produced in the laboratory. The PLE-1 variants with one mutation i.e. PLE-1-F407L and PLE-1-F407I resolved the racemic substrate yielding the (R)-isomer with E value >100. Contrarily, the isoenzyme PLE-3 resolved the racemic substrate yielding (S)-clopidogrel with E value of 10. (C) 2015 Elsevier B.V. All rights reserved.
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| 16. |
- Gaffney, Darragh, et al.
(författare)
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Preparation and characterisation of a Ni2+/Co2+-cyclam modified mesoporous cellular foam for the specific immobilisation of His(6)-alanine racemase
- 2014
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 109, s. 154-160
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Tidskriftsartikel (refereegranskat)abstract
- Nickel and cobalt cyclam modified mesocellular foam (MCF) materials were prepared and characterised. The metal cyclam modified materials displayed reduced surface areas and pore diameters in comparison to MCF. The modified materials were used to specifically anchor a histidine tagged form of the enzyme, alanine racemase (HT-AlaR). Non-specific adsorption was predominantly hydrophobic//hydrophilic in nature and could be significantly reduced in the presence of 2% polyethylene glycol. The activity of HT-AlaR immobilised on Ni and Co-MCF was essentially the same as that of the free enzyme, demonstrating that enzymes can be specifically immobilised within the pores of mesoporous materials in a stable and catalytically active manner.
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| 17. |
- Hamnevik, Emil, et al.
(författare)
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Kinetic characterization of Rhodococcus ruber DSM 44541 alcohol dehydrogenase A
- 2014
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 99, s. 68-78
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Tidskriftsartikel (refereegranskat)abstract
- An increasing interest in biocatalysis and the use of stereoselective alcohol dehydrogenases in synthetic asymmetric catalysis motivates detailed studies of potentially useful enzymes such as alcohol dehydrogenase A (ADH-A) from Rhodococcus ruber. This enzyme is capable of catalyzing enantio-, and regioselective production of phenyl-substituted α-hydroxy ketones (acyloins) which are precursors for the synthesis of a range of biologically active compounds. In this study, we have determined the enzyme activity for a selection of phenyl-substituted vicinal diols and other aryl- or alkyl-substituted alcohols and ketones. In addition, the kinetic mechanism for the oxidation of (R)- and (S)-1-phenylethanol and the reduction of acetophenone has been identified as an Iso Theorell-Chance (hit and run) mechanism with conformational changes of the enzyme-coenzyme binary complexes as rate-determining for the oxidation of (S)-1-phenylethanol and the reduction of acetophenone. The underlying cause of the 270-fold enantiopreference for the (S)-enantiomer of 1-phenylethanol has been attributed to non-productive binding of the R-enantiomer. We have also shown that it is possible to tune the direction of the redox chemistry by adjusting pH with the oxidative reaction being favored at pH values above 7.
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| 18. |
- Hara, Piia, et al.
(författare)
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Supported ionic liquids in Burkholderia cepacia lipase-catalyzed asymmetric acylation
- 2010
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier. - 1381-1177 .- 1873-3158. ; 67:1-2, s. 129-134
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Tidskriftsartikel (refereegranskat)abstract
- Lipase PS from Burkholderia cepacia was successfully immobilized on Kynol™ ACC 507-15 active carbon cloth with and without ionic liquids as SILE catalysts. Activity, enantioselectivity and reuse of the catalysts were evaluated in the acylation of 1-phenylethanol with vinyl acetate in toluene and in hexane over the temperature range 25 - 60 °C. The presence of [EMIM][NTf2] clearly stabilized the enzyme against inactivation and preserved enantioselectivity in reuse in a process which is affected by the nature of the IL, solvent and substrate structure.
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| 19. |
- Hedfors, Cecilia, et al.
(författare)
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Lipase chemoselectivity towards alcohol and thiol acyl acceptors in a transacylation reaction
- 2010
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 66:1-2, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- The lipase chemoselectivity towards an alcohol and a thiol was investigated for the two lipases Candida antarctica lipase B (CalB) and Rhizomucor miehei lipase (Rml). Hexanol and hexanethiol were used as acyl acceptors in a transacylation reaction with ethyl octanoate in cyclohexane. CalB showed the highest chemoselectivity ratio (k(cat)/K-M)(OH)/(k(cat)/K-M)(SH), of 88,000 while the ratio for Rml was 1200. That could be compared with the ratio, k(OH)/k(SH), of 120 for the non-catalyzed reaction. Thus, the enzyme contribution to the chemoselectivity between hexanol and hexanethiol was 730 for CalB and 10 for Rml. High K-M values displayed towards hexanethiol (above 1.8 M) were the largest contribution to the selectivity. No saturation was achieved. The K-M values were more than two orders of magnitude higher than those of hexanol.
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| 20. |
- Henschel, Henning, et al.
(författare)
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Effect of the cross-linker on the general performance and temperature dependent behaviour of a molecularly imprinted polymer catalyst of a Diels-Alder reaction
- 2011
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 72:3-4, s. 199-205
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a series of molecularly imprinted polymers capable of catalysing the Diels-Alder reaction between benzyl 1,3-butadienylcarbamate (1) and N,N-dimethyl acrylamide (2). The polymer systems studied here demonstrated an unusual cross-linker and temperature dependent behaviour, namely that polymer catalysis of the Diels-Alder reaction was lower at elevated temperature, in contrast to the solution reaction. Furthermore, not only was the catalytic activity significantly influenced by the choice of cross-linker, but in a similar fashion also the extent of the temperature effect, indicating a close relationship between catalysis and the observed inhibition. Molecular dynamics simulations of both the polymer systems studied were used to provide insight into the molecular background of transition state stabilisation, and differences in properties of the systems based on different cross-linkers.
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| 21. |
- Ibrahim, Victor, et al.
(författare)
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Laccase catalysed modification of lignin subunits and coupling to p-aminobenzoic acid
- 2013
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 97, s. 45-53
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Tidskriftsartikel (refereegranskat)abstract
- Laccase catalysed oxidation of syringyl and guaiacyl subunits of lignin and their modification with an aromatic amine, p-aminobenzoic acid (PABA) were investigated. Laccase from Galerina sp. HC1 isolated earlier by us was used as the main catalyst, and Trametes versicolor laccase was used for comparison. Among the syringyl compounds, syringic acid and syringaldehyde were oxidised to 2,6-dimethoxy-1,4-benzoquinone, and in the presence of PABA yielded a cross-coupling imine product. The reaction with methyl syringol resulted in several products whose structures were determined. The possible oxidative coupling pathways were proposed for the formation of the identified products. Oxidation of syringol and the guaiacyl compounds resulted mainly in homooligomers by free radical mechanism, with a negligible tendency of reaction with the nucleophilic group of PABA. Similar treatment of Eucalyptus Kraft lignin, which is rich in syringyl moieties, showed the presence of identical products obtained with syringic acid and syringaldehyde. (C) 2013 Elsevier B.V. All rights reserved.
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| 22. |
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| 23. |
- Ivanova, Ekaterina V., et al.
(författare)
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Enantio selectivity of resolved Delta and Lambda orthoruthenated 2-phenylpyridine complexes Ru(o-C6H4-2-py)(LL)(2) PF6 (LL = bpy and phen) toward glucose oxidase
- 2006
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Ingår i: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 41:04-mar, s. 110-116
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Tidskriftsartikel (refereegranskat)abstract
- Cyclometalated 2-phenylpyridine complexes [Ru-II(o-C6H4-2-py)(LL)(2)]PF6, LL=2,2'-bipyridine (1) and 1,10-phenanthroline (2) were resolved into A and A enantiomers using column chromatography on SP Sephadex C-25 in the presence of (+)-2,3-dibenzoyl-D-tartrate. The absolute configuration of enantiomers was established using circular dichroism spectroscopy. The rate constants k(et) for the electron transfer from reduced glucose oxidase (GO from Aspergillus niger) and PQQ-dependent glucose dehydrogenase (GDH) at the generated Ru-III species were measured by cyclic voltammetry and UV-vis spectroscopy. The electron transfer shows enantioselectivity. In the case of GO, the bell-shaped pH profile for the ratio k(Lambda)/k(Delta) has a maximum at pH 7 (k(Lambda)/k(Delta) equals 3.4 and 3.9 for 1 and 2, respectively), but its inversion is observed at pH around 5 and 9. The k(Lambda)/k(Delta) ratio equals 2.0 for 2 and GDH at pH 7. The results of theoretical modeling of biological electron transfer for GO using functional docking Monte-Carlo simulations are presented and analyzed together with the experimental observations.
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| 24. |
- Johanson, Ted, et al.
(författare)
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Identification of a Candida sp reductase behind bicyclic exo-alcohol production
- 2009
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 59:4, s. 286-291
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Tidskriftsartikel (refereegranskat)abstract
- Stereoselective baker's yeast-catalysed bioreduction of bicyclo [2.2.2]octane-2.6-dione generates (1R, 4S, 6S)-6-hydroxy-bicyclo [2.2.2]octane-2-one (endo-alcohol) with high enantiomeric and diastereomeric excess. In contrast, whole cells and crude membrane fractions of Candida sp. have been reported to produce the unusual (I R, 4S, 6S)-diastereomer (exo-alcohol) as a major product. Previous in silica screening has identified seven membrane or membrane-bound reductases in C albicans as candidates for the exoactivity. In this work, purification of the corresponding exo-reductase(s) as well as the heterologous cloning of the seven candidate genes was attempted in C tropicalis. The overexpression of IPF4033 (AYR1) gene generated an increased exo-to-endo ratio and exo-alcohol production in whole cells and membranes of C tropicalis. In addition, a slight increased exo-to-endo ratio was observed when overexpressing IPF4033 in S. cerevisiae, although the reduction rate and exo-to-endo ratio were several fold lower compared to those obtained with C. tropicalis. (C) 2008 Elsevier B.V. All rights reserved.
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| 25. |
- Khan, Sami, et al.
(författare)
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Immobilization of thermostable beta-glucosidase variants on acrylic supports for biocatalytic processes in hot water
- 2012
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 80, s. 28-38
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Tidskriftsartikel (refereegranskat)abstract
- Two variants of the thermostable beta-glucosidase TnBgl1A (wt and N221S/P342L) from Thermotoga neapolitana were immobilized on acrylic supports (Eupergit (R) C, Eupergit (R) C250L, and cryogel) and evaluated at conditions close to the boiling point of water. Thermo-gravimetric analysis showed the supports to be stable <250 degrees C. Both wt and N221S/P342L were covalently bound to oxirane-groups respectively via glutaraldehyde spacers, and for coupling reactions 26 Lys and 20 Ser/Thr were surface-located. Immobilized enzymes were active on all supports in the temperature range 80-95 degrees C, but the observed specific activity was low (<= 19 U mg(-1)) using the cryogel. More than 91% of the initial activity was maintained after ten times recycling, and the same was recovered after 3 months storage at 4 degrees C for Eupergit (R) supports by simply incubating the preparation with bovine serum albumin. No storage loss was detectable on cryogels. The glutaraldehyde spacer improved activity on cryogels, but not on Eupergie supports. Immobilization on Eupergit (R) C250L yielded the highest observed specific activity (254 U mg(-1) for N221S/P342L) in a procedure including blocking of free oxirane-groups by BSA. This biocatalyst was used for on-line hydrolysis of quercetin-glucosides in a yellow onion extract at 80 degrees C, proving the immobilized biocatalyst to be promising in on-line systems for extraction and hydrolysis using hot pressurized water. (C) 2012 Elsevier B.V. All rights reserved.
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