Biomedical subjects

Adrie J J Straathof

Publications and source records attributed to Adrie J J Straathof.

10 recordsLinked to original sources

PubMed2006

In situ product recovery (ISPR) by crystallization: basic principles, design, and potential applications in whole-cell biocatalysis.

The removal of inhibiting or degrading product from a bioreactor as soon as the product is formed is an important issue in industrial bioprocess development. In this review, the potential of crystallization as an in situ product removal (ISPR) technique for the biocatalytic production of crystalline compounds is discussed. The emphasis of this review is on the current status of crystalline product formation by metabolically active cells for application in fine-chemicals production. Examples of relevant biocatalytic conversions are summarized, and some basic process options are discussed. Furthermore, a case study is presented in which two conceptual process designs are compared. In one process, product formation and crystallization are integrated by applying ISPR, whereas a second, nonintegrated process is based on a known conventional process equivalent for the production of 6R-dihydro-oxoisophorone. The comparison indicates that employing ISPR leads to significant advantages over the nonintegrated case in terms of increased productivity and yield with a corresponding decrease in the number of downstream processing steps, as well as in the quantity of waste streams. This leads to an economically more interesting process alternative. Finally, a general outlook on the various research aspects of ISPR by crystallization is given.

Biological Products↗

PubMed2005

Quantification of binary diffusion in protein crystals.

The use of confocal laser scanning microscopy for visualization and quantification of binary diffusion within anisotropic porous material is described here for the first time. The dynamics of adsorption profiles of dianionic fluorescein, zwitterionic rhodamine B, and their mixture in the cationic native orthorhombic lysozyme crystal were subsequently analyzed. All data could be described by a classical pore diffusion model. There was no change in the adsorption characteristics, but diffusion decreased with the introduction of a second solute in the solution. It was found that diffusion is determined by the combination of steric and electrostatic interactions,while adsorption is dependent on electrostatic and hydrophobic interactions. Thus, it was established that the outcome of binary transport depends on the solute, protein, and crystal characteristics.

Adsorption↗

PubMed2005

Feasibility of acrylic acid production by fermentation.

Acrylic acid might become an important target for fermentative production from sugars on bulk industrial scale, as an alternative to its current production from petrochemicals. Metabolic engineering approaches will be required to develop a host microorganism that may enable such a fermentation process. Hypothetical metabolic pathways for insertion into a host organism are discussed. The pathway should have plausible mass and redox balances, plausible biochemistry, and plausible energetics, while giving the theoretically maximum yield of acrylate on glucose without the use of aeration or added electron acceptors. Candidate metabolic pathways that might lead to the theoretically maximum yield proceed via beta-alanine, methylcitrate, or methylmalonate-CoA. The energetics and enzymology of these pathways, including product excretion, should be studied in more detail to confirm this. Expression of the selected pathway in a host organism will require extensive genetic engineering. A 100,000-tons/year fermentation process for acrylic acid production, including product recovery, was conceptually designed based on the supposition that an efficient host organism for acrylic acid production can indeed be developed. The designed process is economically competitive when compared to the current petrochemical process for acrylic acid. Although the designed process is highly speculative, it provides a clear incentive for development of the required microbial host, especially considering the environmental sustainability of the designed process.

Acrylates↗

PubMed2005

Adsorption of xanthene dyes by lysozyme crystals.

Adsorption characteristics of cross-linked lysozyme crystals of different morphologies (tetragonal, orthorhombic, triclinic and monoclinic) were examined using four anionic dyes (fluorescein, eosin, erythrosin, and rose bengal), one zwitterionic dye (rhodamine B), and one cationic dye (rhodamine 6G). The adsorption isotherms were of the Langmuir type for all examined systems with the exception of rhodamine B adsorption by monoclinic crystals. The weakest adsorption was observed for the cationic dye, rhodamine B, whereas dianionic dyes, eosin, rose bengal, and erythrosin were strongly adsorbed on the protein surface. The adsorption capacities of the crystals for the dyes were found to depend on both charge and hydrophobicity of the dye, reflecting the heterogeneous character of the lysozyme pore surface. The adsorption affinity of the crystals for the dyes was a function of the dyes' hydrophobicity. Furthermore, the crystal morphology was identified as an additional factor determining capacity and affinity for dye adsorption. Differences between crystals prepared in the presence of the same precipitant were lower than between morphologies prepared with different precipitants.

Adsorption↗

PubMed2005

Relation between pore sizes of protein crystals and anisotropic solute diffusivities.

The diffusion of a solute, fluorescein, into lysozyme protein crystals with different pore structures was investigated. To determine the diffusion coefficients, three-dimensional solute concentration fields acquired by confocal laser scanning microscopy (CLSM) during diffusion into the crystals were compared with the output of a time-dependent 3-D diffusion model. The diffusion process was found to be anisotropic, and the degree of anisotropy increased in the order: triclinic, tetragonal and orthorhombic crystal morphology. A linear correlation between the pore diffusion coefficients and the pore sizes was established. The maximum size of the solute, deduced from the established correlation of diffusion coefficients and pore size, was 0.73 +/- 0.06 nm, which was in the range of the average diameter of fluorescein (0.69 +/- 0.02 nm). This proves that size exclusion is the key mechanism for solute diffusion in protein crystals. Hence, the origin of solute diffusion anisotropy can be found in the packing of the protein molecules in the crystals, which determines the crystal pore organization.

Anisotropy↗

PubMed2004

In situ product removal using a crystallization loop in asymmetric reduction of 4-oxoisophorone by Saccharomyces cerevisiae.

In situ product crystallization was investigated for solid product crystals that were obtained during fermentation. The model reaction was the asymmetric reduction of 4-oxoisophorone (OIP) using baker's yeast (S. cerevisiae) as a biocatalyst. The target product was 6R-dihydro-oxoisophorone (DOIP), also known as levodione, a key intermediate in carotenoid synthesis. DOIP was degraded by baker's yeast mainly to (4S,6R)-actinol, an unwanted byproduct in the process. Actinol formation reached up to 12.5% of the initial amount of OIP in the reactor during a batch process. However, better results were obtained when the dissolved DOIP concentration was controlled using an integrated fermentation-crystallization process because: (a) actinol formation was reduced to 4%; and (b) DOIP crystal formation in the reactor was avoided. DOIP productivity was improved by 50% and its selectivity was raised from 87% to 96% relative to the batch process. In the integrated process, most of the product was recovered as pure crystals; this may already minimize, if not eliminate, the need for organic solvents in the final purification steps. An almost sixfold reduction in biocatalyst consumption per kilogram product was achieved, which also can contribute to the minimization of waste streams.

Biotransformation↗

PubMed2003

Enzymatic catalysis via liquid-liquid interfaces.

Enzymes acting in a biphasic liquid of water and organic solvent may show catalytic activity dependent on the amount of phase interface available. Such an effect may be caused by several mechanisms. For example, for hydroxynitrile lyase from Prunus amygdalus, substrate mass transfer limitation has been advocated, but also adsorption of the enzyme on the interface. In this commentary it is shown that often these two mechanisms will have qualitatively similar consequences. The reaction rate will be influenced by the organic substrate concentration, by the initial enzyme concentration, and by the volume-specific interfacial area, and these influences will be linear at low values but reach a saturation level at high values. To rule out any of the models, their quantitative mathematical descriptions should be compared, taking into account that both models may be valid simultaneously.

Adsorption↗

PubMed2003

Economically pertinent continuous amide formation by direct lipase-catalyzed amidation with ammonia.

An economically pertinent process for the lipase-catalyzed synthesis of amides was developed. A continuous plug flow reactor was used. The model reaction was the production of oleamide, a lubricant and anti-slip agent, via direct Candida antarctica lipase B-catalyzed amidation of oleic acid with ammonia. Of all solvents tested, 2-methyl-2-butanol was found to respond optimally to the demands formulated in our specifications. A continuous conversion of oleic acid into oleamide of 85% was obtained. A productivity of 4.5 tons oleamide per kg of enzyme per year was calculated, indicating a contribution of enzyme to the product price of only 4%. The volumetric productivity, 100 g. L(-1). h(-1), is 4 to 100 times higher than in literature procedures. A simple crystallization procedure leads to 99% purity.

Amides↗

PubMed2002

Development of a process model to describe the synthesis of (R)-mandelonitrile by Prunus amygdalus hydroxynitrile lyase in an aqueous-organic biphasic reactor.

A process model for the enzymatic synthesis of (R)-cyanohydrins in an aqueous-organic biphasic-stirred tank reactor was developed. The conversion of benzal-dehyde into (R)-mandelonitrile, catalyzed by Prunus amygdalus hydroxynitrile lyase at 5 degrees C and pH 5.5, was chosen as a model system with methyl tert-butyl ether as the organic phase. The process model consisted of a description of the reaction kinetics, mass transfer kinetics, and the mass balances for both the aqueous and the organic phase. Values for the enzyme kinetic parameters, according to ordered bi-uni kinetics, the lumped mass transfer coefficient for benzaldehyde, and the partition coefficients were determined separately. The process model is validated by using 11 experimental data sets of batch conversions in the aqueous-organic biphasic-stirred tank reactor. In these 11 experiments, different enzyme concentrations and phase volume ratios were used. The model was found to be valid with respect to both the conversion and the enantiomeric excess. To synthesize cyanohydrins with a high enantiomeric excess, the enzyme is required to work at mass transfer limited conditions. The developed process model will be used to investigate other process concepts and other substrates.

Acetonitriles↗

PubMed2002

The production of fine chemicals by biotransformations.

Today, biocatalysis is a standard technology for the production of chemicals. An analysis of 134 industrial biotransformations reveals that hydrolases (44%) and redox biocatalysts (30%) are the most prominent categories. Most products are chiral (89%) and are used as fine chemicals. In the chemical industry, successful product developments involve on average a yield of 78%, a volumetric productivity of 15.5 g/(L.h) and a final product concentration of 108 g/L. By contrast, the pharmaceutical industry focuses on time-to-market. The implications of this for future research and development on biocatalysis are discussed.

Biotechnology↗