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Dietmar C. Hempel - One of the best experts on this subject based on the ideXlab platform.
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Model-based prediction of Substrate Conversion and protein synthesis and excretion in recombinant Aspergillus niger biopellets
Chemical Engineering Science, 2005Co-Authors: Ursula Rinas, Dietmar C. Hempel, Hesham A. El-enshasy, M. Emmler, Andrea Hille, Harald HornAbstract:Aspergillus niger grown as biopellets in a submerged culture has been used as an expression system for glucose oxidase (GOD). With regard to mass transfer, Substrate utilization and the formation and excretion of the product GOD, the behavior of aggregated cells such as biopellets differed significantly from that of systems with suspended cells. A one-dimensional pellet model has been developed which is capable to describe the relevant processes in the pellet. Experimental results showed a phase with a highly dynamic pellet size distribution during the first 20 h of the cultivation. A stable number of pellets were usually found after this first period. In the model presented this initial process was described by assuming both suspended hyphae and a fixed number of pellets. The suspended hyphae were attached to the pellets and the Substrate Conversion and product formation was than described with the pellet model. The model predicted the production of GOD by A. niger in a bioreactor very well. The pellet density was identified as a key parameter which has to be provided as input parameter for the simulation runs. A sensitivity analysis with three different classes of pellet sizes showed that the influence of the final pellet size distribution on the simulation result was neglectable. On the other hand, it can be shown that the total pellet number, and thus the average pellet size was an important parameter. The pellet number influenced mainly the pellet surface area and, consequently, the turnover of Substrate and formation and excretion of the product.
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influence of growth conditions on biofilm development and mass transfer at the bulk biofilm interface
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
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Simulation of biofilm growth, Substrate Conversion and mass transfer under different hydrodynamic conditions.
Water Science and Technology, 2002Co-Authors: Harald Horn, Stefan Wäsche, Dietmar C. HempelAbstract:The hydrodynamic conditions and the Substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the Substrate Conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, Substrate Conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and Substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.
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Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface.
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
Stefan Wäsche - One of the best experts on this subject based on the ideXlab platform.
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influence of growth conditions on biofilm development and mass transfer at the bulk biofilm interface
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
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Simulation of biofilm growth, Substrate Conversion and mass transfer under different hydrodynamic conditions.
Water Science and Technology, 2002Co-Authors: Harald Horn, Stefan Wäsche, Dietmar C. HempelAbstract:The hydrodynamic conditions and the Substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the Substrate Conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, Substrate Conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and Substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.
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Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface.
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
Harald Horn - One of the best experts on this subject based on the ideXlab platform.
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Model-based prediction of Substrate Conversion and protein synthesis and excretion in recombinant Aspergillus niger biopellets
Chemical Engineering Science, 2005Co-Authors: Ursula Rinas, Dietmar C. Hempel, Hesham A. El-enshasy, M. Emmler, Andrea Hille, Harald HornAbstract:Aspergillus niger grown as biopellets in a submerged culture has been used as an expression system for glucose oxidase (GOD). With regard to mass transfer, Substrate utilization and the formation and excretion of the product GOD, the behavior of aggregated cells such as biopellets differed significantly from that of systems with suspended cells. A one-dimensional pellet model has been developed which is capable to describe the relevant processes in the pellet. Experimental results showed a phase with a highly dynamic pellet size distribution during the first 20 h of the cultivation. A stable number of pellets were usually found after this first period. In the model presented this initial process was described by assuming both suspended hyphae and a fixed number of pellets. The suspended hyphae were attached to the pellets and the Substrate Conversion and product formation was than described with the pellet model. The model predicted the production of GOD by A. niger in a bioreactor very well. The pellet density was identified as a key parameter which has to be provided as input parameter for the simulation runs. A sensitivity analysis with three different classes of pellet sizes showed that the influence of the final pellet size distribution on the simulation result was neglectable. On the other hand, it can be shown that the total pellet number, and thus the average pellet size was an important parameter. The pellet number influenced mainly the pellet surface area and, consequently, the turnover of Substrate and formation and excretion of the product.
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influence of growth conditions on biofilm development and mass transfer at the bulk biofilm interface
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
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Simulation of biofilm growth, Substrate Conversion and mass transfer under different hydrodynamic conditions.
Water Science and Technology, 2002Co-Authors: Harald Horn, Stefan Wäsche, Dietmar C. HempelAbstract:The hydrodynamic conditions and the Substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the Substrate Conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, Substrate Conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and Substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.
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Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface.
Water Research, 2002Co-Authors: Stefan Wäsche, Harald Horn, Dietmar C. HempelAbstract:In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and Substrate Conversion rates. Several biofilms were cultivated under different Substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the Substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured Substrate Conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.
Wen-yong Lou - One of the best experts on this subject based on the ideXlab platform.
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Novel and highly regioselective route for synthesis of 5-fluorouridine lipophilic ester derivatives by lipozyme TL IM
Journal of Biotechnology, 2007Co-Authors: Huai Wang, Min-hua Zong, Wen-yong LouAbstract:Abstract For the first time, lipozyme TL IM, an inexpensive lipase from Thermomyces lanuginosa, was successfully applied to the regioselective synthesis of lipophilic 5-fluorouridine ester derivatives. The ESI-MS and 13C NMR analysis confirmed that the end products of the acylation were 5′-O-acyl 5-fluorouridines, more powerful anti-tumor drugs than 5-fluorouridine itself. Notably, the chain length of acyl donors had an obvious effect on the initial rate and the maximum Substrate Conversion of the regioselective acylation. The acylation of 5-fluorouridine with vinyl laurate was used as a model to explore the influence of various factors on the reaction with respect to the initial rate, the maximum Substrate Conversion and the regioselectivity. The optimum water activity, the molar ratio of vinyl laurate to 5-fluorouridine, reaction temperature and shaking rate were 0.07, 15/1, 45 °C and 200 rpm, respectively, under which the maximum Substrate Conversion and the regioselectivity were as high as 98.4 and >99%, respectively, after a reaction time of around 6 h.
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Efficient regioselective acylation of 1-β-D-arabinofuranosylcytosine catalyzed by lipase in ionic liquid containing systems
Green Chem., 2006Co-Authors: Wen-yong Lou, Thomas J. Smith, Min-hua Zong, Ju-fang WangAbstract:Seven ionic liquids (ILs) were tested for use in the regioselective acylation of 1-β-D-arabinofuranosylcytosine (ara-C) by vinyl propionate, catalyzed by immobilized Candida antarctica lipase B. The results demonstrated that the nature of both the cations and the anions of ILs had a significant effect on the initial rate and the Substrate Conversion, but little effect on the regioselectivity of the reaction. The lipase displayed enhanced activity toward ara-C when the alkyl chain of CnMIm·BF4 increased in length (n = 4–8) and no acylation reaction occurred in C4MIm·Cl or C4MIm·Br. To further enhance the initial rate and Substrate Conversion, co-solvent mixtures of ILs and organic solvents were investigated. Among various IL-containing systems examined, 10% (v/v) C4MIm·PF6–tetrahydrofuran gave the highest initial rate and Substrate Conversion. In this reaction medium, the optimal water activity, vinyl propionate/ara-C molar ratio, temperature and shaking rate were 0.07, 15 ∶ 1 (mol/mol), 60 °C and 250 rpm, respectively. Under these conditions, the initial rate, Substrate Conversion and the regioselectivity were 94.0 mM h−1, 98.5% and 99%, respectively. An additional comparative study demonstrated that the enzymatic acylation proceeded with very similar initial rate, Substrate Conversion, regioselectivity and activation energy whether the reaction medium was 10% (v/v) C4MIm·PF6–tetrahydrofuran or 28% (v/v) hexane–pyridine (the best organic solvent mixture for the reaction). However, the lipase exhibited a much higher stability in the IL-containing system, which may also have environmental advantages. The product of the lipase-catalysed reaction was characterized by NMR, FT-IR spectroscopy and was shown to be the 5′-O-monoester of ara-C.
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Markedly improving Novozym 435-mediated regioselective acylation of 1-β-d-arabinofuranosylcytosine by using co-solvent mixtures as the reaction media
Journal of Biotechnology, 2006Co-Authors: Min-hua Zong, Wen-yong LouAbstract:Abstract A comparative study was made of Novozym 435-catalyzed regioselective acylation of 1-β- d -arabinofuranosylcytosine with vinyl propionate for the preparation of the 5′-O-monoester in eleven co-solvent mixtures and three pure polar solvents. Novozym 435 displayed low or no acylation activity toward 1-β- d -arabinofuranosylcytosine in pure polar solvents, although those solvents can dissolve the nucleosides well. When a hexane–pyridine co-solvent system was adopted, both the initial rate and the Substrate Conversion were enhanced markedly. The polarity of co-solvent mixtures had significant effect on the reaction. Among the solvent mixtures investigated, the higher the polarity of the solvent mixture, the lower the initial reaction rate and the Substrate Conversion. It was also found that the acylation was dependent on the hydrophobic solvent content, the water activity and the reaction temperature. The most suitable co-solvent, initial water activity, and reaction temperature were hexane–pyridine (28:72, v/v), 0.07, and 50 °C, respectively. Under these conditions, the initial rate, the Substrate Conversion and the regioselectivity were as high as 91.1 mM h−1, >97% and >98%, respectively, after a reaction time of 6 h. Among the reaction mediums examined, the lowest apparent activation energy was achieved with hexane–pyridine (28:72, v/v), in which Novozym 435 also exhibited good thermal stability.
Nobuya Itoh - One of the best experts on this subject based on the ideXlab platform.
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Engineering the phenylacetaldehyde reductase mutant for improved Substrate Conversion in the presence of concentrated 2-propanol.
Applied Microbiology and Biotechnology, 2007Co-Authors: Yoshihide Makino, Tohru Dairi, Nobuya ItohAbstract:Phenylacetaldehyde reductase (PAR) from Rhodococcus sp. ST-10 is useful for chiral alcohol production because of its broad Substrate specificity and high stereoselectivity. The Conversion of ketones into alcohols by PAR requires the coenzyme NADH. PAR can regenerate NADH by oxidizing additional alcohols, especially 2-propanol. However, Substrate Conversion by wild-type PAR is suppressed in concentrated 2-propanol. Previously, we developed the Sar268 mutant of PAR, which can convert several Substrates in the presence of concentrated 2-propanol. In this paper, further mutational engineering of Sar268 was performed to achieve higher process yield. Each of nine amino acid positions that had been examined for generating Sar268 was subjected to saturation mutagenesis. Two novel substitutions at the 42nd amino acid position increased m-chlorophenacyl chloride (m-CPC) Conversion. Moreover, several nucleotide substitutions identified from libraries of random mutations around the start codon also improved the PAR activity. E. coli cells harboring plasmid pHAR1, which has the integrated sequence of the top clones from the above selections, provided greater Conversion of m-CPC and ethyl 4-chloro-3-oxobutanoate than the Sar268 mutant, with very high optical purity of products. This mutant is a promising novel biocatalyst for efficient chiral alcohol production.
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Engineering of phenylacetaldehyde reductase for efficient Substrate Conversion in concentrated 2-propanol.
Applied and Environmental Microbiology, 2005Co-Authors: Yoshihide Makino, Tohru Dairi, Kousuke Inoue, Nobuya ItohAbstract:Phenylacetaldehyde reductase (PAR) is suitable for the Conversion of various aryl ketones and 2-alkanones to corresponding chiral alcohols. 2-Propanol acts as a Substrate solvent and hydrogen donor of coupled cofactor regeneration during the Conversion of Substrates catalyzed by PAR. To improve the Conversion efficiency in high concentrations of Substrate and 2-propanol, selection of a PAR mutant library and the subsequent rearrangement of mutations were attempted. With only a single selection round and following the manual combination of advantageous mutations, PAR was successfully adapted for the Conversion of high concentrations of Substrate with concentrated 2-propanol. This method will be widely applicable for the engineering of enzymes potentially valuable for industry.
