| 1. |
- Bohlin, Christina, et al.
(author)
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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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In: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 45:1-2, s. 21-26
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Journal article (peer-reviewed)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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| 2. |
- Bohlin, Christina, et al.
(author)
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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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In: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 35:4-6, s. 100-107
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Journal article (peer-reviewed)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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| 3. |
- Carlquist, Magnus, et al.
(author)
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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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In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 58:2, s. 98-102
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Journal article (peer-reviewed)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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| 4. |
- Ivanova, Ekaterina V., et al.
(author)
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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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In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 41:04-mar, s. 110-116
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Journal article (peer-reviewed)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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| 5. |
- Johanson, Ted, et al.
(author)
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Identification of a Candida sp reductase behind bicyclic exo-alcohol production
- 2009
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In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 59:4, s. 286-291
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Journal article (peer-reviewed)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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| 6. |
- Kirsch, Nicole, et al.
(author)
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Molecularly imprinted polymer catalysis of a Diels-Alder reaction
- 2009
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In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 58:1-4, s. 110-117
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Journal article (peer-reviewed)abstract
- A series of synthetic polymers were designed and synthesized for enhancing the rate of the Diels-Alder cycloaddition reaction of 1,3-butadiene carbamic acid benzyl ester (11) and N,N-dimethyl acrylamide (2), to yield the corresponding endo- (3) and exo- (4) reaction products. Putative transition state analogues (TSAs) for the endo- (5) and exo- (6) reaction pathways were used as templates for the synthesis of molecularly imprinted methacrylic acid (MAA)-divinylbenzene (DVB) copolymers. The polymer system utilized was selected based upon a series of (1)H NMR studies of complex formation between template and a functional monomer analogue (K(d) (app) approximate to 70 mM, d(8)-toluene, 293 K). Batch binding studies revealed that the imprinted polymers were selective for the TSA corresponding to the template used in the polymer synthesis. Studies on the influence of the polymers on the catalysis of the reaction of 1 and 2 demonstrated a 20-fold enhancement of the rate of the reaction relative to the solution reaction. A surprising temperature dependence of the reaction of 1 and 2 in the presence of the polymers was observed, which provides support for the role of template-functional monomer complexes in the catalysis of the Diels-Alder reaction.
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| 7. |
- Leonard-Nevers, Valerie, et al.
(author)
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Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards secondary alcohols
- 2009
-
In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 59:1-3, s. 90-95
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Journal article (peer-reviewed)abstract
- The effect of water activity (a(w)) on Candida antarctica lipase B (CALB) activity and enantioselectivity towards secondary alcohols was assessed. Experimental results for the resolution of racemic pentan-2-ol, hexan-3-ol, butan-2-ol and octan-4-ol by immobilized CALB-catalyzed acylation with methyl propanoate were obtained by using a solid/gas reactor. Water and substrate adsorption mechanism on immobilized CALB were then studied using moisture sorption analyzer and inverse gas chromatography, and the effective hydration state of the biocatalyst when varying aw was defined. The data showed a pronounced aw effect on both activity and enantioselectivity. If secondary alcohol follows the steric rules for being efficiently resolved, water at very low aw increased enantioselectivity by acting predominantly as an enantioselective inhibitor, making the stereospecificity pocket smaller. When increasing aw, water decreased enantioselectivity, due to an unfavourable increase of the entropic term T Delta(R-S)Delta S-double dagger of the differential free energy of activation. The "turning point" at which water changed from one predominant role to another would correspond to aw allowing full coverage of polar groups of the immobilized biocatalyst by water molecules.
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| 8. |
- Orellana Coca Åkerman, Cecilia, et al.
(author)
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Lipase mediated simultaneous esterification and epoxidation of oleic acid for the production of alkylepoxystearates
- 2007
-
In: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 44:3-4, s. 133-137
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Journal article (peer-reviewed)abstract
- Epoxy alkylstearates were synthesized by lipase catalysed esterification and perhydrolysis followed by epoxidation of oleic acid in a one-pot process. Immobilized Candida antarctica lipase (Novozym 435) was used as the catalyst. The esterification reaction occurred relatively quickly and was followed by epoxidation of the alkyl ester and the remaining fatty acid. Higher degree of esterification was achieved with n-octanol, n-hexanol and n-butanol as compared to that with ethanol and iso-propanol. The rate and yield of epoxidation was enhanced with iso-propanol but was lowered with the other alcohols. The lipase suffered significant loss in activity during the reaction primarily due to hydrogen peroxide. The presence of alcohols, in particular ethanol. further contributed to the enzyme inactivation. The epoxidation reaction could be improved by step-wise addition of the lipase. (c) 2006 Elsevier B.V All rights reserved.
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| 9. |
- Sabbani, Sunil, et al.
(author)
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Control of water activity in lipase catalysed esterification of chiral alkanoic acids
- 2009
-
In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 58:1-4, s. 6-9
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Journal article (peer-reviewed)abstract
- Candida rugosa lipase (CRL) catalysed enantioselective esterification of racemic 2-methylhexanoic acid was performed with 1-decanol in organic solvent at constant water activity (aw). The aw was maintained either by a salt hydrate pair added in the reaction mixture or by performing the reaction in an air tight desiccator over an aqueous saturated salt solution. It was found that the enatiomeric ratio and average reaction rate profiles were similar when controlling the water activity for the esterification reaction with these two different methods. But, in some cases the average rate of the reaction and the enantioselectivity of CRL was affected when ions from the salt hydrate pairs were present in the reaction mixture.
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| 10. |
- Sabbani, Sunil, et al.
(author)
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The enantioselectivity of Candida rugosa lipase is influenced by the particle size of the immobilising support material Accurel
- 2006
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In: Journal of Molecular Catalysis B. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 42:1-2, s. 1-9
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Journal article (peer-reviewed)abstract
- When Candida rugosa lipase (CRL) was immobilised on the porous polypropylene carrier Accurel it was found that differences in the samples of the carrier influenced the enantiomeric ratio (E) when racemic 2-methylhexanoic acid was esterified with 1-decanol in organic solvent at a constant water activity (aw) of 0.76. CRL immobilised on Accurel with smaller particles and smaller pore diameters gave higher enantiomeric ratio in the esterification. The reaction rate was influenced by the different Accurel materials and also by the amount of CRL exposed to the carrier. Characterisation of the different Accurel grades, with and without adsorbed CRL, was performed by light scattering analysis, SEM and FT-IR.
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