| 1. |
- Alvarez, Maria Teresa, et al.
(författare)
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Lab-scale production of biogenic sulphide for metal precipitation in remote areas
- 2012
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Ingår i: International Journal of Environment and Waste Management. - 1478-9876. ; 9:3-4, s. 313-329
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Tidskriftsartikel (refereegranskat)abstract
- Batch cultures with wheat straw, biomass of Paja Brava (Festuca orthophylla), filter paper, newspaper and beech leaves (Fagus sylvatica) were established to produce sulphide. Sulphide production, sulphate reduction, concentration of Volatile Fatty Acids (VFAs), enzyme activities and Fluorescence in situ hybridisation were determined. Approximately 5 mM of sulphide was produced during anaerobic digestion of wheat straw, while the production with newspaper as carbon source was the lowest (ca.1 mM). The sulphide production (2-5 mM) in the semi-continuous culture of the consortium A10, using wheat straw supported Cu(II), Pb (II) and Zn (II) removal up to 90%.
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| 2. |
- 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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| 3. |
- Chávez, Georgina, et al.
(författare)
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Baeyer-Villiger Oxidation of Cyclohexanone in Aqueous Medium with In Situ Generation of Peracid Catalyzed by Perhydrolase CLEA
- 2014
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 57:5, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- A perhydrolase, immobilized as a cross linked enzyme aggregate (CLEA), was employed to catalyze the in situ formation of peracetic acid (PAA) from ethylene glycol diacetate (EGDA) and hydrogen peroxide. The produced PAA was used for the Baeyer-Villiger oxidation of cyclohexanone, which afforded caprolactone in 63 % yield. The effect of type and amount of acyl donor, solvent, pH, temperature and ratio of cyclohexanone to hydrogen peroxide on the production of caprolactone was studied. The highest caprolactone yield was obtained with 100 mM EGDA as the acyl donor at pH 6 and room temperature using a ratio of cyclohexanone to hydrogen peroxide ratio of 1:4. Interestingly, the perhydrolase CLEA exhibited the highest activity in aqueous medium in contrast to the well studied lipase B from Candida antarctica. The perhydrolase CLEA proved to be a very efficient catalyst; the K (m) and V-max values were 118 mM and 56.3 mu mol min(-1), respectively.
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| 4. |
- 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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| 5. |
- Chávez, Georgina
(författare)
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Oxidation of Ketones: A (Chemo-) Enzymatic Approach Using Oxygenases and Hydrolases
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oxidation reactions are important in organic chemistry as well as in nature. In industry, oxidations are commonly used for the synthesis of chemicals and pharmaceuticals, however such processes have a number of limitations, they use chlorinated solvents, stoichiometric oxidation reagents, and in some cases the reagents that have risks of explosion during transportation and storage. This has called for more environment-friendly alternative technologies for oxidation reactions. Baeyer-Villiger oxidation is a reaction in which a ketone is oxidized to an ester or a cyclic ketone to a lactone by treatment with peroxyacids. Lactones constitute an important group of chemicals used in flavors, fragrances, pharmaceutical intermediates and polymer building blocks. The work presented in this thesis concerns enzymes, including Baeyer-Villiger monooxygenases (BVMOs) that catalyse the Baeyer-Villiger oxidation using molecular oxygen as an oxidant, and perhydrolytic enzymes that can be used for in situ generation of peracid for oxidation of cyclic ketones. A simple colorimetric method was developed for detection of BVMO activity and was based on the formation of a purple colored product between an enolizable ketone and 3,5-dinitrobenzoic acid in an alkaline solution. The method was shown to have potential for screening of both wild type and recombinant microbial cells as well as for quantitative measurement of BVMO activity. Further, a recombinant BVMO from a strain of Dietzia was characterized. The sequence of the enzyme suggested that it is related to Ethionamide monooxygenases. The recombinant enzyme was active in whole cells and crude lysate but lost activity on purification. The enzyme was shown to have high activity towards several linear alkenes, and was also moderately active towards cyclobutanone, phenylacetone and thioanisole. Two perhydrolytic enzymes able to produce peracids from a carboxylic ester and hydrogen peroxide were studied for oxidation of cyclohexanone to caprolactone, a chemical of immense importance. The enzymes were immobilized as cross-linked enzyme aggregates (CLEAs). The well-studied lipase B from Candida antarctica (CaLB) gave a maximal caprolactone yield of 80% with ethyl acetate as acyl donor. The perhydrolase was able to produce peracids in an aqueous medium with ethylene glycol diacetate and hydrogen peroxide, and gave caprolactone yield of 70%. In both cases the formation as acetic acid as a coproduct showed to be an important factor for the deactivation of the enzyme. The use of monooxygenases, lipases and perhydrolases for the Baeyer-Villiger reaction constitutes a greener alternative to traditional chemical processes but the problem of enzyme stability remains to be solved.
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| 6. |
- Linares-Pastén, Javier, et al.
(författare)
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A method for rapid screening of ketone biotransformations: Detection of whole cell Baeyer-Villiger monooxygenase activity.
- 2012
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 50:2, s. 101-106
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Tidskriftsartikel (refereegranskat)abstract
- A method for screening of ketone biotransformations was developed and applied to the identification of Baeyer-Villiger monooxygenase (BVMO) activity. The method was based on the formation of a purple coloured product on reaction between an enolizable ketone and 3,5-dinitrobenzoic acid in an alkaline solution. Absorbance of the colour decreased with the size of the cycloketone ring. Stoichiometric ratio between cycloketone and 3,5-dinitrobenzoic acid was 1:1 at maximum absorbance. The method was applied for monitoring the consumption of cyclohexanone by bacteria under aerobic conditions, and was found to be potentially useful for both screening assays and quantitative measurements of BVMO activity. Compared to other existing methods, this method is faster, cheaper and amenable for whole cell assays.
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