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Substrate Conversion (substrate + conversion)
Selected AbstractsNumerical Simulation of Fluid Flow and Enzyme Catalysed Substrate Conversion in a Packed-bed Enzyme ReactorPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Ö. Özmutlu M. Sc. This numerical study evaluates the momentum and mass transfer in an immobilized enzyme reactor. The simulation gives detailed information of the local substrate and product concentrations with respect to external and internal transport limitations. The flow field characterization of the system makes it possible to understand fluid mechanical properties and its importance on transport processes. With the obtained data it is also possible to detect zones of high, low and latent enzymatic activity and to determine whether the conversion is limited due to mass transfer or reaction resistances. [source] Penicillin G splitting in a flow-through electro-membrane reactor with the membrane-bound enzymeASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Pavel Hasal Abstract Penicillin G (PenG) (0.05 mol dm,3 in phosphate buffer, pH = 8) was hydrolyzed in a continuous flow-through electro-membrane reactor (EMR) with the penicillin G acylase (PGA) (EC 3.5.1.11) immobilized in 10% (w/v) polyacrylamide membrane with an area of 900 mm2, thickness of 1 mm and enzyme activity of 100 U cm,3 and 160 U cm,3, respectively. The PenG was continuously fed to the substrate compartment adjacent to one membrane surface. Reaction products were washed from the membrane by a phosphate buffer solution fed to the product compartment adjacent to the other membrane surface. The mean residence time of both streams was varied from 11.3 min to 45 min. An electric field perpendicular to the membrane surface was imposed on the reactor and the electric current density was varied from 0 to 822 A m,2. Substrate conversion was determined as a function of the mean residence time, of the applied electric current density and of the enzyme activity of the membrane. The conversion increased with increasing residence time. The applied electric current increased substrate conversion by 200% at short residence times and at low enzyme activity of the membrane. Oscillatory reaction regime was evoked by step change of the mean residence time of reactant streams in the reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Enhancement of the NAD(P)(H) Pool in Escherichia coli for BiotransformationENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2007F. Heuser Abstract In pyridine nucleotide-dependent, reductive whole cell biotransformation with resting cells of Escherichia coli, the availability of intracellular NAD(P)(H) is a pivotal point for an efficient and highly productive substrate conversion. The question whether an increase of the intracellular NAD(P)(H) concentration could increase the productivity was discussed controversially in the past. This is the first report on an E. coli strain with an increased NAD(P)(H) pool which was tested in a reductive biotransformation system for an increased productivity. Biotransformation was performed with a strain overexpressing a gene encoding an (R)-specific alcohol dehydrogenase for the stereospecific, NADPH-dependent reduction of methyl acetoacetate (MAA) to (R)-methyl-3-hydroxybutanoate (MHB). Cofactor regeneration was implemented via glucose oxidation by coexpression of a gene encoding glucose dehydrogenase. The specific MHB productivity (mmol mg,1 cell dry weight,1h,1) enabled a comparison between the E. coli,BL21(DE3) wild-type and a genetically modified strain. The enhancement of the NAD(P)(H) pool was achieved by genetic manipulation of the NAD(H) biosynthetic pathways. After simultaneous overexpression of the pncB and nadE genes, encoding nicotinic acid phosphoribosyltransferase and NAD synthetase, measurements of the total NAD(P)(H) pool, sizes showed a 7-fold and 2-fold increased intracellular concentration of NAD(H) and NADP(H), respectively. However, the implementation of an E.,coli strain carrying a genomically integrated pncB gene with an upstream T7,promoter for biotransformation did not result in reproducible increased specific cell productivity. [source] In situ substrate conversion and assimilation by nitrifying bacteria in a model biofilmENVIRONMENTAL MICROBIOLOGY, Issue 9 2005Armin Gieseke Summary Local nitrification and carbon assimilation activities were studied in situ in a model biofilm to investigate carbon yields and contribution of distinct populations to these activities. Immobilized microcolonies (related to Nitrosomonas europaea/eutropha, Nitrosomonas oligotropha, Nitrospira sp., and to other Bacteria) were incubated with [14C]-bicarbonate under different experimental conditions. Nitrifying activity was measured concomitantly with microsensors (oxygen, ammonium, nitrite, nitrate). Biofilm thin sections were subjected to fluorescence in situ hybridization (FISH), microautoradiography (MAR), and local quantification of [14C]-bicarbonate uptake (beta microimaging). Nitrifying activity and tracer assimilation were restricted to a surface layer of different thickness in the various experiments (substrate or oxygen limitation). Excess oxygen uptake under all conditions revealed heterotrophic activity fuelled by decay or excretion products during active nitrification. Depth limits and intensity of tracer incorporation profiles were in agreement with ammonia-oxidation activity (measured with microsensors), and distribution of incorporated tracer (detected with MAR). Microautoradiography revealed a sharp individual response of distinct populations in terms of in-/activity depending on the (local) environmental conditions within the biofilm. Net in situ carbon yields on N, expressed as e, equivalent ratios, varied between 0.005 and 0.018, and, thus, were in the lower range of data reported for pure cultures of nitrifiers. [source] Kinetics of inhibition of acetylcholinesterase in the presence of acetonitrileFEBS JOURNAL, Issue 8 2009Markus Pietsch The hydrolysis of acetylthiocholine by acetylcholinesterase from Electrophorus electricus was investigated in the presence of the inhibitors tacrine, gallamine and compound 1. The interaction of the enzyme with the substrate and the inhibitors was characterized by the parameters KI, ,,, b or ,, Km and Vmax, which were determined directly and simultaneously from nonlinear Michaelis,Menten plots. Tacrine was shown to act as a mixed-type inhibitor with a strong noncompetitive component (,, , 1) and to completely block deacylation of the acyl-enzyme. In contrast, acetylcholinesterase inhibition by gallamine followed the ,steric blockade hypothesis', i.e. only substrate association to as well as substrate/product dissociation from the active site were reduced in the presence of the inhibitor. The relative efficiency of the acetylcholinesterase,gallamine complex for the catalysis of substrate conversion was determined to be 1.7,25% of that of the free enzyme. Substrate hydrolysis and the inhibition of acetylcholinesterase were also investigated in the presence of 6% acetonitrile, and a competitive pseudo-inhibition was observed for acetonitrile (KI = 0.25 m). The interaction of acetylcholinesterase with acetonitrile and tacrine or gallamine resulted in a seven- to 10-fold increase in the KI values, whereas the principal mode of inhibition was not affected by the organic solvent. The determination of the inhibitory parameters of compound 1 in the presence of acetonitrile revealed that the substance acts as a hyperbolic mixed-type inhibitor of acetylcholinesterase. The complex formed by the enzyme and the inhibitor still catalysed product formation with 8.7,9.6% relative efficiency. [source] Oxidation of phenols by laccase and laccase-mediator systemsFEBS JOURNAL, Issue 21 2002Solubility, steric issues To investigate how solubility and steric issues affect the laccase-catalysed oxidation of phenols, a series of oligomeric polyphenol compounds, having increasing size and decreasing solubility in water, was incubated with laccase. The extent of substrate conversion, and the nature of the products formed in buffered aqueous solutions, were compared to those obtained in the presence of an organic cosolvent, and also in the presence of two mediating species, i.e. N -hydroxyphthalimide (HPI) and 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO). This approach showed not only an obvious role of solubility, but also a significant role of the dimension of the substrate upon the enzymatic reactivity. In fact, reactivity decreases as substrate size increases even when solubility is enhanced by a cosolvent. This effect may be ascribed to limited accessibility of encumbered substrates to the enzyme active site, and can be compensated through the use of the appropriate mediator. While TEMPO was highly efficient at enhancing the reactivity of large, less soluble substrates, HPI proved less effective. In addition, whereas the laccase/HPI system afforded the same products as laccase alone, the use of TEMPO provided a different product with high specificity. These results offer the first evidence of the role of ,oxidation shuttles' that the mediators of laccase may have, but also suggest two promising routes towards an environmentally friendly process for kraft pulp bleaching: (a) the identification of mediators which, once oxidized by laccase, are able to target strategic functional groups present in lignin, and (b) the introduction of those strategic functional groups in an appropriate pretreatment. [source] Transgalactosylation by thermostable ,-glycosidases from Pyrococcus furiosus and Sulfolobus solfataricusFEBS JOURNAL, Issue 16 2000-glycosides during lactose conversion, Binding interactions of nucleophiles with the galactosylated enzyme intermediate make major contributions to the formation of new The hyperthermostable ,-glycosidases from the Archaea Sulfolobus solfataricus (Ss,Gly) and Pyrococcus furiosus (CelB) hydrolyse ,-glycosides of d -glucose or d -galactose with relaxed specificities pertaining to the nature of the leaving group and the glycosidic linkage. To determine how specificity is manifested under conditions of kinetically controlled transgalactosylation, the major transfer products formed during the hydrolysis of lactose by these enzymes have been identified, and their appearance and degradation have been determined in dependence of the degree of substrate conversion. CelB and Ss,Gly show a marked preference for making new ,(1,3) and ,(1,6) glycosidic bonds by intermolecular as well as intramolecular transfer reactions. The intramolecular galactosyl transfer of CelB, relative to glycosidic-bond cleavage and release of glucose, is about 2.2 times that of Ss,Gly and yields ,- d -Galp- (1,6)- d -Glc and ,- d -Galp- (1,3)- d -Glc in a molar ratio of ,,1 : 2. The partitioning of galactosylated Ss,Gly between reaction with sugars [kNu (m,1·s,1)] and reaction with water [kwater (s,1)] is about twice that of CelB. It gives a mixture of linear ,- d -glycosides, chiefly trisaccharides at early reaction times, in which the prevailing new glycosidic bonds are ,(1,6) and ,(1,3) for the reactions catalysed by Ss,Gly and CelB, respectively. The accumulation of ,- d -Galp- (1,6)- d -Glc at the end of lactose hydrolysis reflects a 3,10-fold specificity of both enzymes for the hydrolysis of ,(1,3) over ,(1,6) linked glucosides. Galactosyl transfer from Ss,Gly or CelB to d -glucose occurs with partitioning ratios, kNu/kwater, which are seven and >,170 times those for the reactions of the galactosylated enzymes with 1-propanol and 2-propanol, respectively. Therefore, the binding interactions with nucleophiles contribute chiefly to formation of new ,-glycosides during lactose conversion. Likewise, noncovalent interactions with the glucose leaving group govern the catalytic efficiencies for the hydrolysis of lactose by both enzymes. They are almost fully expressed in the rate-limiting first-order rate constant for the galactosyl transfer from the substrate to the enzyme and lead to a positive deviation by ,,2.5 log10 units from structure,reactivity correlations based on the pKa of the leaving group. [source] Selective Hydrogenation of 5-Ethoxymethylfurfural over Alumina-Supported Heterogeneous CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Erik-Jan Ras Abstract We report here the synthesis and testing of a set of 48 alumina-supported catalysts for hydrogenation of 5-ethoxymethylfurfural. This catalytic reaction is very important in the context of converting biomass to biofuels. The catalysts are composed of one main metal (gold, copper, iridium, nickel, palladium, platinum, rhodium, ruthenium) and one promoter metal (bismuth, chromium, iron, sodium, tin, tungsten). Using a 16-parallel trickle-flow reactor, we tested all 48 catalyst combinations under a variety of conditions. The results show that both substrate conversion and product selectivity are sensitive towards temperature changes and solvent effects. The best results of >99% yield to the desired product, 5-ethoxymethylfurfuryl alcohol, are obtained using an iridium/chromium (Ir/Cr) catalyst. The mechanistic implications of different possible reaction pathways in this complex hydrogenation system are discussed. [source] Palladium-Catalysed Telomerisation of Isoprene with Glycerol and Polyethylene Glycol: A Facile Route to New Terpene DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Alvaro Gordillo Abstract We present here the first example of the telomerisation of isoprene with glycerol and polyethylene glycol (PEG-200), opening a facile route to new terpene structures, based on a combination of renewable and petroleum-based feedstocks. The reaction is catalysed by a palladium-carbene complex. Significantly, this system gives >99% of linear monotelomer products. The factors that govern substrate conversion, dimerisation/telomerisation selectivity, and catalyst activity are studied and discussed. [source] Penicillin G splitting in a flow-through electro-membrane reactor with the membrane-bound enzymeASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Pavel Hasal Abstract Penicillin G (PenG) (0.05 mol dm,3 in phosphate buffer, pH = 8) was hydrolyzed in a continuous flow-through electro-membrane reactor (EMR) with the penicillin G acylase (PGA) (EC 3.5.1.11) immobilized in 10% (w/v) polyacrylamide membrane with an area of 900 mm2, thickness of 1 mm and enzyme activity of 100 U cm,3 and 160 U cm,3, respectively. The PenG was continuously fed to the substrate compartment adjacent to one membrane surface. Reaction products were washed from the membrane by a phosphate buffer solution fed to the product compartment adjacent to the other membrane surface. The mean residence time of both streams was varied from 11.3 min to 45 min. An electric field perpendicular to the membrane surface was imposed on the reactor and the electric current density was varied from 0 to 822 A m,2. Substrate conversion was determined as a function of the mean residence time, of the applied electric current density and of the enzyme activity of the membrane. The conversion increased with increasing residence time. The applied electric current increased substrate conversion by 200% at short residence times and at low enzyme activity of the membrane. Oscillatory reaction regime was evoked by step change of the mean residence time of reactant streams in the reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Recognition of acyl donors by lipase CAL-B in the acylation of 6-azauridineBIOTECHNOLOGY PROGRESS, Issue 3 2009Zhao-Yu Wang Abstract CAL-B-catalyzed synthesis of different 5,-O-monoester derivatives of 6-azauridine via a one-step highly regioselective enzymatic acylation route was successfully performed for the first time. The effects of some crucial factors on the enzymatic undec-10-enoylation of 6-azauridine were examined. The optimal reaction medium, molar ratio of 6-azauridine to vinyl undec-10-enoate and reaction temperature were found to be anhydrous acetone, 1:3 and 50°C, under which the reaction rate, the substrate conversion and the regioselectivity were 22.3 mM/h, 99.0% and 99.0%, respectively. In addition, the enzyme recognition of acyl donors was investigated. The results showed that the enzyme activity varied widely with different acyl donors owing to the specific structure of the lipase active site and the acyl donors. 5,-O-Monoesters of 6-azauridine were achieved exclusively with all the acyl donors tested. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Kinetic Study of the Conversion of Different Substrates to Lactic Acid Using Lactobacillus bulgaricusBIOTECHNOLOGY PROGRESS, Issue 3 2000Concepción N. Burgos-Rubio Lactic acid fermentation includes several reactions in association with the microorganism growth. A kinetic study was performed of the conversion of multiple substrates to lactic acid using Lactobacillusbulgaricus. Batch experiments were performed to study the effect of different substrates (lactose, glucose, and galactose) on the overall bioreaction rate. During the first hours of fermentation, glucose and galactose accumulated in the medium and the rate of hydrolysis of lactose to glucose and galactose was faster than the convesion of these substrates. Once the microorganism built the necessary enzymes for the substrate conversion to lactic acid, the conversion rate was higher for glucose than for galactose. The inoculum preparation was performed in such a way that healthy young cells were obtained. By using this inoculum, shorter fermentation times with very little lag phase were observed. The consumption patterns of the different substrates converted to lactic acid were studied to determine which substrate controls the overall reaction for lactic acid production. A mathematical model (unstructured Monod type) was developed to describe microorganism growth and lactic acid production. A good fit with a simple equation was obtained. It was found experimentally that the approximate ratio of cell to substrate was 1 to 10, the growth yield coefficient (YXS) was 0.10 g cell/g substrate, the product yield (YPS) was 0.90 g lactic acid/g substrate, and the , parameter in the Luedeking-Piret equation was 9. The Monod kinetic parameters were obtained. The saturation constant (KS) was 3.36 g/L, and the specific growth rate (,m ) was 1.14 l/h. [source] [(NHC)(NHCewg)RuCl2(CHPh)] Complexes with Modified NHCewg Ligands for Efficient Ring-Closing Metathesis Leading to Tetrasubstituted Olefins,CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2010Volodymyr Sashuk Abstract Imidazolium salts (NHCewg,HCl) with electronically variable substituents in the 4,5-position (H,H or Cl,Cl or H,NO2 or CN,CN) and sterically variable substituents in the 1,3-position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)ewg] complexes. The reactions of [(NHC)RuCl2(CHPh)(py)2] with the [AgI(NHCewg)] complexes provide the respective [(NHC)(NHCewg)RuCl2(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring-closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2,0.5,mol,% at 80,°C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHCewg group with 1,3-Me,iPr and 4,5-Cl,Cl substituents and can be synthesized in 95,% isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL-NHC)(NHCewg)RuCl2(CHPh)] and [(FL-NHCewg)(NHC)RuCl2(CHPh)], with a dansyl fluorophore (FL)-tagged electron-rich NHC ligand (FL-NHC) and an electron-deficient NHC ligand (FL-NHCewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore-tagged ligand. In this manner, it was shown for ring-opening metathesis ploymerization (ROMP) reactions at room temperature that the NHCewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium. [source] Comparative Experimental and EXAFS Studies in the Mizoroki,Heck Reaction with Heteroatom-Functionalised N-Heterocyclic Carbene Palladium CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2007Steven G. Fiddy Dr. Abstract A study on the Mizoroki,Heck coupling of selected aryl bromides with acrylates catalysed by a series of Pd complexes of bidentate pyridyl-, picolyl-, diphenylphosphinoethyl- and diphenylphosphinomethyl-functionalised N-heterocyclic carbene (NHC) is reported. The observed activity is dependent on the type of solvent and base used and the nature of the "classical" donors of the mixed-donor bidentate ligand and its bite angle. A mechanistic model is presented for the pyridine-functionalised NHC complexes based on an in situ EXAFS study under dilute catalyst conditions (2,mM Pd). The model involves pre-dissociation of the pyridine functionality and oxidative addition of ArBr in the early stages of the reaction, as well as formation of monomeric and dimeric Pd species at the time of substrate conversion. [source] Analysis of acetic acid productivity in a continuous two-stage bioreactor with cell recyclingJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005Akio Nishiwaki Abstract The performance of a two-stage system with cell recycling and fresh feed at each stage is studied numerically for continuous acetic acid production. In this system, both filtrate and bleed broth from the first stage are supplied to the second fermenter. At high substrate conversions, this configuration is found to provide higher acetic acid productivities than either a previous configuration where only the first-stage bleed broth is fed to the second stage or a single recycle chemostat at the same bleed ratios. Copyright © 2005 Society of Chemical Industry [source] Graphite-Supported Gold Nanoparticles as Efficient Catalyst for Aerobic Oxidation of Benzylic Amines to Imines and N -Substituted 1,2,3,4-Tetrahydroisoquinolines to Amides: Synthetic Applications and Mechanistic StudyCHEMISTRY - AN ASIAN JOURNAL, Issue 10 2009Man-Ho So Abstract Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite-supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate-to-excellent substrate conversions (43,100,%) and product yields (66,99,%) (19,examples). Oxidation of N -substituted 1,2,3,4-tetrahydroisoquinolines in the presence of aqueous NaHCO3 solution gave the corresponding amides in good yields (83,93,%) with high selectivity (up to amide/enamide=93:4) (6,examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o -phenylenediamines with benzaldehydes under aerobic conditions (8,examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N -benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol "AuNPs/C+O2" can be scaled to the gram scale, and 8.9,g (84,% isolated yield) of 3,4-dihydroisoquinoline can be obtained from the oxidation of 10,g 1,2,3,4-tetrahydroisoquinoline in a one-pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen-transfer reaction from amine to metal and oxidation of M-H is proposed. [source] Homogeneous [RuIII(Me3tacn)Cl3]-Catalyzed Alkene cis -Dihydroxylation with Aqueous Hydrogen PeroxideCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2008Wing-Ping Yip Dr. Abstract A simple and green method that uses [Ru(Me3tacn)Cl3] (1; Me3tacn=N,N,,N,,-trimethyl-1,4,7-triazacyclononane) as catalyst, aqueous H2O2 as the terminal oxidant, and Al2O3 and NaCl as additives is effective in the cis -dihydroxylation of alkenes in aqueous tert -butanol. Unfunctionalized alkenes, including cycloalkenes, aliphatic alkenes, and styrenes (14 examples) were selectively oxidized to their corresponding cis -diols in good to excellent yield (70,96,%) based on substrate conversions of up to 100,%. The preparation of cis -1,2-cycloheptanediol (119,g, 91,% yield) and cis -1,2-cyclooctanediol (128,g, 92,% yield) from cycloheptene and cyclooctene, respectively, on the 1-mol scale can be achieved by scaling up the reaction without modification. Results from Hammett correlation studies on the competitive oxidation of para -substituted styrenes (,=,0.97, R=0.988) and the detection of the cycloadduct [(Me3tacn)ClRuHO2(C8H14)]+ by ESI-MS for the 1 -catalyzed oxidation of cyclooctene to cis -1,2-cyclooctanediol are similar to those of the stoichiometric oxidation of alkenes by cis -[(Me3tacn)(CF3CO2)RuVIO2]+ through [3+2] cycloaddition (W.-P. Yip, W.-Y. Yu, N. Zhu, C.-M. Che, J. Am. Chem. Soc.2005, 127, 14239). [source] Base-free Pd/TOMPP-Catalyzed Telomerization of 1,3-Butadiene with Carbohydrates and Sugar AlcoholsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 9 2009Peter J. Sugar and alcohol,a superior combo: The telomerization activity of the Pd/TOMPP catalyst is screened using thirteen different biomass-derived carbohydrates and sugar alcohols. High substrate conversions are achieved by using low Pd loading and without the use of an added base. In terms of butadiene conversion, a clear structure,activity relationship is found, which is in line with the series: sugar,alcohols>sucrose>aldohexoses>aldopentoses>ketohexoses. [source] | |||||||||||||||||||||||||