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Initial Reaction Rate (initial + reaction_rate)
Selected AbstractsFormulation and characterization of radio-opaque conjugated in situ gelling materials,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010Brandon Blakely Abstract X-ray visibility is an integral design component of in situ gelling embolization systems for neurovascular treatment. The goals of this project included the synthesis and characterization of a unique intrinsically radio-opaque in situ gelling material for neurovascular embolization. The gels formed using Michael-Type Addition between pentaerythritol tetrakis 3-mercaptopropionate (QT) thiols and poly(propylene glycol) diacrylate (PPODA) with the addition of the new material Iodobenzoyl poly(ethylene glycol) acrylate (IPEGA), a radio-opaque agent, synthesized successfully as confirmed with 1H NMR. The PPODA and IPEGA were mixed using a syringe coupler with QT and buffer at pH 11 for 90 seconds. Gel mixes were weighed to provide equal molar thiols and acrylate groups, changing the present acrylate-bearing compounds wt % ratios from 100 PPODA: 0 IPEGA, 90:10, 80:20, 70:30, 60:40, 50:50, and 0:100. Formulations with 10% and above of IPEGA were X-ray visible. Rheology showed that increasing the amount of IPEGA decreased the storage. Kinetic FT-IR studies indicate that the amphiphilic nature of the PEG backbone increased the reaction rate of the phase segregated reactants. Second order reaction constant modeling showed a change in initial reaction rate from 0.0029 to 0.0187 (M sec),1 from the 10% to 50% IPEGA formulations respectively. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Modeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor depositionAICHE JOURNAL, Issue 3 2009Sophie L. Pirard The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric, hydrodynamic, physical and physicochemical factors governing the process were analyzed in order to establish the reactor equations. While the study of the hydrodynamic factor suggests a co-current plug-flow approximation, the physical factor mainly deals with the phenomena of transport and the transfer of mass, which can be neglected. Concerning the physicochemical factor, the modeling is based on knowledge of the expression of the initial reaction rate, and takes into account catalytic deactivation as a function of time, according to a sigmoid decreasing law. The reactor modeling allows obtaining the evolution of partial pressure, carbon nanotube production and catalytic deactivation along the reactor for given initial operating conditions. The comparison between experimental and calculated production highlights a very good fit of data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effect of Polycarboxylate Blocks on the Amidase Activity of Trypsin through Complexation with PEG/Polycarboxylate Block IonomersMACROMOLECULAR BIOSCIENCE, Issue 3 2007Atsushi Harada Abstract The amidase reaction of trypsin, which is a member of the serine proteinase family, is accelerated by its complexation with block ionomers containing a polycarboxylate block, such as PEG-PAA, PEG-PGA, or PEG-PMA. PEG-PAA and PEG-PGA had similar effects, causing an increase in the kcat value and a shift in the pH profile to a lower pH region. On the other hand, PEG-PMA showed not only an increase in the kcat value, but also a decrease in the activation energy; however, there was no shift in the pH dependence of the initial reaction rate. Such differences might be induced by the difference in pKa values of the polycarboxylate block in block ionomers. [source] Microbial synthesis of ethyl (R)-4,4,4-trifluoro-3-hydroxybutanoate by asymmetric reduction of ethyl 4,4,4-trifluoroacetoacetate in an aqueous-organic solvent biphasic systemBIOTECHNOLOGY JOURNAL, Issue 2 2007Junyao He Abstract In this study, whole cells of Saccharomyces uvarum SW-58 were applied in an aqueous-organic solvent biphasic system for the asymmetric reduction of ethyl 4,4,4-trifluoroacetoacetate to ethyl (R)-4,4,4-trifluoro-3-hydroxybutanoate [(R)-2]. The results of reduction in different aqueous-organic solvent biphasic systems showed that dibutylphthalate provided the best compromise between the biocompatibility and the partition of substrate and product among the solvents tested. To optimize the reaction, several factors such as reaction pH, temperature, shaking speed, volume ratio of the aqueous phase to the organic phase and ratio of biomass/substrate were investigated. It was found that the change of these factors obviously influenced the conversion and initial reaction rate, and had a minor effect on the enatiomeric excess of the product. Under the optimal conditions, 85.0% of conversion and 85.2% of enatiomeric excess were achieved. The bioconversion in the biphasic system was more efficient compared with that in the monophasic aqueous system, and product concentration as high as 54.6 g/L was reached in the organic phase without addition of co-enzyme. [source] Design of a cytochrome P450BM3 reaction system linked by two-step cofactor regeneration catalyzed by a soluble transhydrogenase and glycerol dehydrogenaseBIOTECHNOLOGY PROGRESS, Issue 5 2009Tsuyoshi Mouri Abstract A cytochrome P450BM3-catalyzed reaction system linked by a two-step cofactor regeneration was investigated in a cell-free system. The two-step cofactor regeneration of redox cofactors, NADH and NADPH, was constructed by NAD+ -dependent bacterial glycerol dehydrogenase (GLD) and bacterial soluble transhydrogenase (STH) both from Escherichia coli. In the present system, the reduced cofactor (NADH) was regenerated by GLD from the oxidized cofactor (NAD+) using glycerol as a sacrificial cosubstrate. The reducing equivalents were subsequently transferred to NADP+ by STH as a cycling catalyst. The resultant regenerated NADPH was used for the substrate oxidation catalyzed by cytochrome P450BM3. The initial rate of the P450BM3-catalyzed reaction linked by the two-step cofactor regeneration showed a slight increase (approximately twice) when increasing the GLD units 10-fold under initial reaction conditions. In contrast, a 10-fold increase in STH units resulted in about a 9-fold increase in the initial reaction rate, implying that transhydrogenation catalyzed by STH was the rate-determining step. In the system lacking the two-step cofactor regeneration, 34% conversion of 50 ,M of a model substrate (p-nitrophenoxydecanoic acid) was attained using 50 ,M NADPH. In contrast, with the two-step cofactor regeneration, the same amount of substrate was completely converted using 5 ,M of oxidized cofactors (NAD+ and NADP+) within 1 h. Furthermore, a 10-fold dilution of the oxidized cofactors still led to approximately 20% conversion in 1 h. These results indicate the potential of the combination of GLD and STH for use in redox cofactor recycling with catalytic quantities of NAD+ and NADP+. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Promiscuous Zinc-Dependent Acylase-Mediated One-Pot Synthesis of Monosaccharide-Containing Pyrimidine Derivatives in Organic MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Qi Wu Abstract A facile one-pot synthesis route to monosaccharide-containing pyrimidine derivatives was developed by combining the two types of catalytic activities of one enzyme in an organic medium, i.e., the Michael addition/acylation activities of zinc-dependent D -aminoacylase (DA) from Escherichia coli. First, the stepwise approach was investigated. DA showed higher activity towards the Michael addition than acylation in this reaction system. The enzymatic Michael additions of pyrimidines to vinyl acrylate proceeded very rapidly and the initial reaction rates for the Michael addition of pyrimidines to vinyl acrylate were 7.2,16.5,mM,min,1. The catalytic specificity of aminoacylases toward Michael addition was demonstrated by the combination of different control experiments. Then, the two steps could be performed in one pot and a single aminoacylase catalyzed one-pot biotransformation was constructed. Using this strategy, a series of saccharide-pyrimidine complexes with potentially biological and pharmacological applications was prepared efficiently. This high Michael addition activity of zinc-dependent aminoacylases and the novel single aminoacylase-catalyzed one-pot synthesis combining two catalytic activities in vitro is of practical significance in expanding the application of enzymes and in the evolution of new biocatalysts. [source] Rate equations for the fischer-tropsch reaction on a promoted iron catalystTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001Montazer Rahmati Abstract Intrinsic rates for the Fischer-Tropsch synthesis reaction over a promoted iron catalyst fabricated at the Research Institute of the Petroleum Industry (RIPI) have been obtained in the temperature range of 290°C to 310°C, pressure range of 1500 to 2300 kPa, molar hydrogen to carbon monoxide ratio of 0.76 to 1.82, and a space velocity of 3300 h,1 under conditions of constant catalyst activity. To this end, the initial reaction rates have been measured at constant temperature (±1°C) in the absence of diffusion limitations, and power-law equations have been fitted in terms of the hydrogen and carbon monoxide partial pressures for the reaction rates. Des vitesses intrinsèques pour la réaction de synthèse de Fischer-Tropsch sur un catalyseur de fer activé fabriqué à l'Institut de recherche de l'industrie du pétrole (RIPI) ont été obtenues pour des températures entre 290°C et 310°C, des pressions entre 1500 et 2300 kPa, un rapport hydrogène molaire/oxyde de carbone entre 0.76 et 1.82 et une vitesse spatiale de 3300 h,1 avec une activité constante du catalyseur. À cette fin, les vitesses de réaction initiales ont été mesurées à température constante (±1°C) en l'absence de limitations par la diffusion, et des équations de loi de puissance ont été calées par rapport aux pressions partieiles de l'hydrogène et de l'oxyde de carbone pour les vitesses de réaction. [source] Mechanistic model for prediction of formate dehydrogenase kinetics under industrially relevant conditionsBIOTECHNOLOGY PROGRESS, Issue 1 2010T. Schmidt Abstract Formate dehydrogenase (FDH) from Candida boidinii is an important biocatalyst for the regeneration of the cofactor NADH in industrial enzyme-catalyzed reductions. The mathematical model that is currently applied to predict progress curves during (semi-)batch reactions has been derived from initial rate studies. Here, it is demonstrated that such extrapolation from initial reaction rates to performance during a complete batch leads to considerable prediction errors. This observation can be attributed to an invalid simplification during the development of the literature model. A novel mechanistic model that describes the course and performance of FDH-catalyzed NADH regeneration under industrially relevant process conditions is introduced and evaluated. Based on progress curve instead of initial reaction rate measurements, it was discriminated from a comprehensive set of mechanistic model candidates. For the prediction of reaction courses on long time horizons (>1 h), decomposition of NADH has to be considered. The model accurately describes the regeneration reaction under all conditions, even at high concentrations of the substrate formate and thus is clearly superior to the existing model. As a result, for the first time, course and performance of NADH regeneration in industrial enzyme-catalyzed reductions can be accurately predicted and used to optimize the cost efficiency of the respective processes. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||