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Fred van Rantwijk

Publications and source records attributed to Fred van Rantwijk.

10 recordsLinked to original sources
PubMed2005

Cross-linked aggregates of (R)-oxynitrilase: a stable, recyclable biocatalyst for enantioselective hydrocyanation.

[Reaction: see text] The (R)-oxynitrilase from almonds was immobilized as a cross-linked enzyme aggregate (CLEA) via precipitation with 1,2-dimethoxyethane and subsequent cross-linking using glutaraldehyde. The resulting preparation was a highly effective hydrocyanation catalyst under microaqueous conditions, which suppress the nonenzymatic background reaction. The beneficial effect of these latter conditions on the hydrocyanation of slow-reacting aldehydes is demonstrated. The oxynitrilase CLEA was recycled 10 times without loss of activity.

Aldehyde-Lyases↗
PubMed2004

A new, mild cross-linking methodology to prepare cross-linked enzyme aggregates.

Cross-linked enzyme aggregates (CLEAs) were prepared from several enzymes (penicillin G acylase, hydroxynitrile lyase, alcohol dehydrogenase, and two different nitrilases) by precipitation and subsequent cross-linking using dextran polyaldehyde. In most cases, higher immobilization yields were obtained using the latter cross-linker as compared with the commonly used glutaraldehyde. Active site titration of penicillin acylase CLEAs showed that the higher activity originated from a significantly lower loss in active sites using dextran polyaldehyde as a cross-linking agent. It is proposed that macromolecular cross-linkers are too large to penetrate the protein active site and react with catalytically essential amino acid residues.

Binding Sites↗
PubMed2003

Crude aminoacylase from aspergillus sp. is a mixture of hydrolases.

A range of cross-linked enzyme aggregates (CLEAs) was prepared from commercially available aminoacylase I. Results from three test reactions showed that aminoacylase does not possess aminolysis or alcoholysis activity, both previously ascribed to this enzyme. This result was confirmed using aminoacylase purified by chromatographic techniques, which leads us to conclude that the previously observed acylations of esters and amines is due to other enzymes present as impurities in the crude aminoacylase I.

Acylation↗
PubMed2003

Biocatalytic transformations in ionic liquids.

Room temperature ionic liquids are non-volatile, thermally stable and highly polar; they are also moderately hydrophilic solvents. Here, we discuss their use as reaction media for biocatalysis. Enzymes of widely diverging types are catalytically active in ionic liquids or aqueous biphasic ionic liquid systems. Lipases, in particular, maintain their activity in anhydrous ionic liquid media; the (enantio)selectivity and operational stability are often better than in traditional media. The unconventional solvent properties of ionic liquids have been exploited in biocatalyst recycling and product recovery schemes that are not feasible with traditional solvent systems.

Catalysis↗
PubMed2002

Glycosidation of fructose-containing disaccharides using MCM-41 material as the catalyst.

Glycosidation of saccharides combines the essential characteristics of two major renewable classes, viz. triglycerides and carbohydrates, leading to biofriendly surfactants and emulsifiers. The development of the alkylglycosides derived from reducing disaccharides has lagged, because no efficient synthesis was available. We have found that ordered mesoporous materials of the MCM-41 type are active and selective catalysts for the glycosidation of disaccharides containing fructose at the reducing end, i.e., isomaltulose, lactulose and leucrose. No alcoholysis or hydrolysis of the glycosidic bond was observed, demonstrating the mildness of the MCM-41 catalyst. Leucrose was found to be less reactive than the two other disaccharides, in accordance with the absence of furanose forms in leucrose.

Aluminum↗
PubMed2002

A two-step, one-pot enzymatic synthesis of cephalexin from D-phenylglycine nitrile.

A cascade of two enzymatic transformations is employed in a one-pot synthesis of cephalexin. The nitrile hydratase (from R. rhodochrous MAWE)-catalyzed hydration of D-phenylglycine nitrile to the corresponding amide was combined with the penicillin G acylase (penicillin amidohydrolase, E.C. 3.5.1.11)-catalyzed acylation of 7-ADCA with the in situ-formed amide to afford a two-step, one-pot synthesis of cephalexin. D-Phenylglycine nitrile appeared to have a remarkable selective inhibitory effect on the penicillin G acylase, resulting in a threefold increase in the synthesis/hydrolysis (S/H) ratio. 1,5-Dihydroxynaphthalene, when added to the reaction mixture, cocrystallized with cephalexin. The resulting low cephalexin concentration prevented its chemical as well as enzymatic degradation; cephalexin was obtained at 79% yield with an S/H ratio of 7.7.

Acetonitriles↗
PubMed2002

Active site titration as a tool for the evaluation of immobilization procedures of penicillin acylase.

Native and immobilized preparations of penicillin acylase from Escherichia coli and Alcaligenes faecalis were studied using an active site titration technique. Knowledge of the number of active sites allowed the calculation of the average turnover rate of the enzyme in the various preparations and allowed us to quantify the contribution of irreversible inactivation of the enzyme to the loss of catalytic activity during the immobilization procedure. In most cases a loss of active sites as well as a decrease of catalytic activity per active site (turnover rate) was observed upon immobilization. Immobilization techniques affected the enzymes differently. The effect of increased loading of penicillin acylase on the average turnover rate was determined by active site titration to assess diffusion limitations in the carrier.

Alcaligenes↗
PubMed2002

Penicillin acylase-catalyzed ampicillin synthesis using a pH gradient: a new approach to optimization.

The penicillin acylase-catalyzed synthesis of ampicillin by acyl transfer from D-(-)-phenylglycine amide (D-PGA) to 6-aminopenicillanic acid (6-APA) becomes more effective when a judiciously chosen pH gradient is applied in the course of the process. This reaction concept is based on two experimental observations: 1) The ratio of the initial synthesis and hydrolysis rates (V(S)/V(H)) is pH-dependent and exhibits a maximum at pH 6.5-7.0 for a saturated solution of 6-APA; 2) at a fixed 6-APA concentration below saturation, V(S)/V(H) increases with decreasing pH. Optimum synthetic efficiency could, therefore, be achieved by starting with a concentrated 6-APA solution at pH 7 and gradually decreasing the pH to 6.3 in the course of 6-APA consumption. A conversion of 96% of 6-APA and 71% of D-PGA into ampicillin was accomplished in an optimized procedure, which significantly exceeds the efficiency of enzymatic synthesis performed at a constant pH of either 7.0 or 6.3.

Ampicillin↗
PubMed2002

Evaluation of the performance of immobilized penicillin G acylase using active-site titration.

Penicillin G acylase from Escherichia coli was immobilized on Eupergit C with different enzyme loading. The activity of the immobilized preparations was assayed in the hydrolysis of penicillin G and was found to be much lower than would be expected on the basis of the residual enzyme activity in the immobilization supernatant. Active-site titration demonstrated that the immobilized enzyme molecules on average had turnover rates much lower than that of the dissolved enzyme. This was attributed to diffusion limitations of substrate and product inhibition. Indeed, when the immobilized preparations were crushed, the activity increased from 587 U g-1 to up to 974 U g-1. The immobilized preparations exhibited up to 15% lower turnover rates than the dissolved enzyme in cephalexin synthesis from 7-ADCA and D-(-)-phenylglycine amide. The synthesis over hydrolysis ratios of the immobilized preparations were also much lower than that of the dissolved enzyme. This was partly due to diffusion limitations but also to an intrinsic property of the immobilized enzyme because the synthesis over hydrolysis ratio of the crushed preparations was much lower than that of the dissolved enzyme.

Antigens, Neoplasm↗