bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microbial Reduction and in situ Product Crystallization Coupled with Biocatalyst Cultivation during the Synthesis of 6R‐Dihydrooxoisophorone
Authors: Buque‐Taboada Evelyn M. , Straathof Adrie J. J. , Heijnen Joseph J. , van der Wielen Luuk A. M. 
Published: June 2005

AbstractAn in situ product crystallization procedure was developed for a crystalline product formed during microbial reduction coupled with cell cultivation. The model reaction was the asymmetric reduction of 4‐oxoisophorone (OIP) by baker's yeast (Saccharomyces cerevisiae). Yeast cells were cultivated fed‐batch to reach a maximum concentration of 30 gdw⋅L−1. The desired product, 6R‐dihydrooxoisophorone (DOIP), may be further reduced by baker's yeast to an unwanted by‐product; thus, DOIP was removed immediately from the fermenter via an external crystallization loop in this procedure. The OIP reduction rate was five times higher (≅0.33 mmol⋅gdw−1⋅h−1) as compared to the reduction rate with resting cells. OIP reduction was started when the optimum cell concentration had already been reached in the reactor because the substrate (OIP) at ≥55 mM concentration inhibited cell growth. An appropriate supply of glucose as carbon and energy source was necessary to support the coupled reactions involving cell growth and maintenance and product formation while avoiding formation of metabolic by‐products. Final DOIP yield and selectivity were 85% and 99%, respectively, while over 100 g⋅L−1 of product was obtained in the crystallizer. The product crystals with favorable properties were readily recovered from the crystallizer. These results indicate that product crystallization is not impaired by the solutes present in the fermentation medium.
Study of the Chemoselectivity in the Aminolysis Reaction of Methyl Acrylate Catalysed by Lipase B from Candida antarctica
Authors: Torre Oliver , Gotor‐Fernández Vicente , Alfonso Ignacio , García‐Alles Luis Fernando , Gotor Vicente 
Published: June 2005

AbstractThe aminolysis reaction of methyl acrylate (MA) with N,N‐dimethyl‐1,3‐propanediamine (DMAPA) in organic solvents has been optimised using lipase B from Candida antarctica (CAL‐B) as biocatalyst. A kinetic study about the influence of the reactant concentrations, organic solvent, temperature and enzyme form has been developed focused on minimising the formation of the Michael addition products. The economic efficiency of this process has been finally investigated by reusing the enzyme in the best reaction conditions, thereby observing no significant loss of activity after three reaction cycles.
Asymmetric Synthesis of L‐α‐Methylcysteine with the Amidase from Xanthobacter flavus NR303
Authors: Inoue Atsushi , Komeda Hidenobu , Asano Yasuhisa 
Published: June 2005

AbstractAn amidase acting on d, l‐α‐methylcysteinamide was purified from Xanthobacter flavus NR303. The enzyme acted L‐stereoselectively on d,l‐α‐methylcysteinamide to yield L‐α‐methylcysteine. Based on the N‐terminal amino acid sequence of the amidase, the gene encoding the enzyme was cloned from the genomic DNA of X. flavus and sequenced. Analysis of 4840 bp of the genomic DNA revealed the presence of an open reading frame (mcaA) which encodes the amidase. This enzyme is composed of 355 amino acid residues (molecular mass, 38555 Da). The intact cells of the Escherichia coli transformant could be used for the L‐stereoselective hydrolysis of racemic α‐methylcysteinamide. It was activated in the presence of Mn2+, and had maximal activity at pH 7.0 and 55 °C. The E. coli transformant catalyzed the synthesis of L‐α‐methylcysteine from d, l‐α‐methylcysteinamide in a yield of 80% with high optical purity (>98% ee).
FADH2‐Dependence of Tryptophan 7‐Halogenase
Authors: Unversucht Susanne , Hollmann Frank , Schmid Andreas , van Pée Karl‐Heinz 
Published: June 2005

AbstractTryptophan 7‐halogenase (Trp 7‐hal) catalyses the regioselective chlorination and bromination of tryptophan. For halogenating activity, Trp 7‐hal requires FADH2 produced from FAD and NADH by a flavin reductase, halide ions (chloride or bromide), molecular oxygen and tryptophan as the organic substrate. Investigations of the flavin dependence showed that purified Trp 7‐hal itself does not contain flavin. Keeping the Trp 7‐hal separated from the flavin reductase during the reaction revealed that Trp 7‐hal can use diffusible FADH2 produced by a flavin reductase showing that direct contact between the halogenase and the flavin reductase is not absolutely necessary. Thus, the reaction also proceeds when chemically reduced flavin is used. For the catalytic regeneration of FADH2, the organometallic complex (pentamethylcyclopentadienyl)rhodium‐bipyridine {[Cp*Rh(bpy)(H2O)]2+} can be employed as the redox catalyst with formate as the electron donor. With this chemoenzymatic system about 85% yields of the product formed by the two‐component enzyme system consisting of Trp 7‐hal and a flavin reductase were obtained.
Peroxidase‐Catalyzed Coupling of Solid‐Supported ortho‐Methoxyphenols
Authors: Antoniotti Sylvain , Dordick Jonathan S. 
Published: June 2005

AbstractEnzyme‐catalyzed CC bond formation has been performed on solid‐supported phenols, thereby expanding the repertoire of enzymatic catalysis on resin‐bound substrates. In the presence of hydroquinone bound to various commercial resins, soybean peroxidase catalyzed the coupling of apocynin (acetovanillone) to give dimers, trimers, and oligomers with structures similar to what is obtained in solution‐phase reactions. In addition to phenolic coupling, peroxidase catalyzed a Fries rearrangement presumably due to rearrangement of the acyl phenolic radicals generated on the solid phase through peroxidase catalysis. This represents the first enzymatic Fries rearrangement reported to date. Together with the solid‐phase biocatalytic phenolic coupling, these results provide a route to the further expansion of enzymatic catalysis in combinatorial library synthesis.
A Fluorescence‐Based Assay for Baeyer–Villiger Monooxygenases, Hydroxylases and Lactonases
Authors: Sicard Renaud , Chen Lu S. , Marsaioli Anita J. , Reymond Jean‐Louis 
Published: June 2005

AbstractAlkylation of umbelliferone and nitrophenol with chloroacetone, 3‐chlorobutanone, 2‐chlorocyclopentanone and 2‐chlorocyclohexanone gave the corresponding 2‐coumaryloxy and 2‐nitrophenoxy ketones. The 2‐coumaryloxy ketones were used as fluorogenic substrates to detect Baeyer–Villiger monooxygenases activities of microbial cultures in high‐throughput using microtiter plates. The 2‐coumaryloxy ketones were oxidized by microorganisms producing Baeyer–Villiger monooxygenases (BVMO), releasing umbelliferone as a fluorescent signal. The substrates were also biotransformed by a microbial monooxygenase (Trichosporon cutaneum). Chemical Baeyer–Villiger oxidation of 2‐coumaryloxy ketones using meta‐chloroperbenzoic acid proceeded regioselectively to the corresponding acyloxyalkyl derivatives of umbelliferone and nitrophenol. These chiral lactones underwent a fluorogenic and chromogenic reaction upon hydrolysis by esterases, in particular pig liver esterase. Enantioselectivity of the ester hydrolysis reaction was determined by chiral‐phase analysis of the unreacted lactones.
Multienzyme Profiling of Thermophilic Microorganisms with a Substrate Cocktail Assay
Authors: Sicard Renaud , Goddard Jean‐Philippe , Mazel Magali , Audiffrin Carine , Fourage Laurent , Ravot Gilles , Wahler Denis , Lefèvre Fabrice , Reymond Jean‐Louis 
Published: June 2005

AbstractLabeled substrates for 16 different catalytic activities were combined into a cocktail reagent for multienzyme functional profiling, called PHENOZYMTM. The assay involves a single reaction followed by determination of substrate consumption by HPLC‐analysis. The method allows a rapid identification of multiple enzyme activities, and is compatible with a diversity of growth media and reaction conditions (pH, temperature). The PHENOZYMTM cocktail was used to analyze the activity of 16 enzyme activities in a series of microbial strains, including thermophilic microorganisms. The functional profiles were used for a functional classification of the different microbial strains tested by hierarchical cluster analysis. The resulting “phylo‐enzymatic” tree revealed associations consistent with the known phylogenetic classification of the strains. The influence of the culture medium on the enzyme activity profiles was also apparent.
Synthesis of Sialyl TN Glycopeptides – Enzymatic Sialylation by α2,6‐Sialyltransferase from Photobacterium damsela
Authors: Teo Chin‐Fen , Hwang Tzann‐Shun , Chen Pei‐Heng , Hung Chih‐Hung , Gao Heau‐Shan , Chang Lee‐Shang , Lin Chun‐Hung 
Published: June 2005

AbstractThe α2,6‐sialyltransferase from Photobacterium damsela was applied for the enzymatic sialylation of the TN glycopeptide (APGSTA) with GalNAc α‐linked to either the serine or threonine residue in the sequence. The enzyme preparation and reaction conditions were optimized prior to the application. In contrast to the mammalian sialyltransferases which recognize the moiety of GalNAcα(1,1)Thr only, this bacterial enzyme can accept GalNAcα(1,1)Thr as well as GalNAcα(1,1)Ser. Our study also introduced a 4‐dimethylaminoazobenzene‐4′‐sulfonyl (dabsyl) chromophore to the N‐terminus of the peptide backbone, which is suitable for glycoconjugate substrates without affecting the binding affinity
Current and Emerging Approaches for Natural Product Biosynthesis in Microbial Cells
Authors: Watts Kevin T. , Mijts Benjamin N. , Schmidt‐Dannert Claudia 
Published: June 2005

AbstractMicroorganisms and plants synthesize a tremendous diversity of chemical compounds. For centuries, these compounds have been used as medicines, foods and other useful materials. The still largely unexplored structural and chemical diversity of natural products is unmatched by synthetic methodology and continues to be the most successful source for the discovery of novel scaffolds with important biological activities. Thus, exploiting the selectivity and specificity of the biosynthetic machineries that make these complex compounds can provide ways of synthesizing diverse natural products or their core scaffolds for further synthetic modification. Microbial cells can be fitted with new biosynthetic abilities using metabolic and genetic engineering strategies to overproduce desired compounds. Efforts in genome sequencing give access to an incredible number of genes from microorganisms and, more recently, from plants that can be in silico screened for new biosynthetic functions allowing tapping into the synthetic potential of microorganisms, and especially plants. In addition, by exploiting natural biodiversity by using traditional screening methods or metagenomics approaches, novel biosynthetic pathways and genes can be discovered for the synthesis of additional structures in engineered microbial cells. In this review, we will describe some of the recent developments in natural product biosynthesis, and also describe some of the emerging approaches to harness the chemical diversity that lies hidden in nature.
Comparison of Alkyl Hydroperoxide Reductase (AhpR) and Water‐Forming NADH Oxidase from Lactococcus lactis ATCC 19435
Authors: Jiang Rongrong , Riebel Bettina R. , Bommarius Andreas S. 
Published: June 2005

AbstractWe have successfully applied the sequence comparison‐based approach to develop a peroxidase (gene AhpC) and a water‐forming NADH oxidase from Lactococcus lactis (L. lactis). We found a considerably lower maximum specific activity of nox‐1 (AhpF) (15 U/mg) from L. lactis compared to its nox‐2 counterpart (95 U/mg). Both nox‐1 and nox‐2 are turnover‐limited, as expected for enzymes with labile, redox‐active thiols in the active site. In the absence of exogenously added thiols, both nox‐1 and nox‐1/peroxidase are considerably more stable against overoxidation than nox‐2: the total turnover number TTN is 82,000 for nox‐1 and nox‐1/peroxidase vs. 39,000 for nox‐2. Addition of exogenous thiols, however, increases nox‐2 stability by a factor of two, up to the level of nox‐1. Kinetic and stability analysis does not reveal any clear advantage for oxygen scavenging via the nox‐1 or the nox‐2 routes in lactic acid bacteria. Expression levels in lactic acid bacteria upon exposure to oxidative stress rather than kinetic performance more likely account for the previously observed superiority of nox‐2 effectiveness over nox‐1.
Converting Phenylacetone Monooxygenase into Phenylcyclohexanone Monooxygenase by Rational Design: Towards Practical Baeyer–Villiger Monooxygenases
Authors: Bocola Marco , Schulz Frank , Leca François , Vogel Andreas , Fraaije Marco W. , Reetz Manfred T. 
Published: June 2005

AbstractA homology model of the most frequently used, but thermally somewhat labile, Baeyer–Villiger monooxygenase, cyclohexanone monooxygenase (CHMO) has been derived on the basis of the recently published crystal structure of the thermally stable phenylacetone monooxygenase (PAMO). This has led to the identification of a structural element crucial for substrate acceptance and stereoselectivity, namely an arginine‐interacting loop near the active site. A bulge in this loop occurring in PAMO (but not in CHMO) has been eliminated by mutation, enhancing the range of substrate acceptance and enantioselectivity of Baeyer–Villiger reactions while maintaining high thermal stability.
Regioselective Phosphorylation of Carbohydrates and Various Alcohols by Bacterial Acid Phosphatases; Probing the Substrate Specificity of the Enzyme from Shigella flexneri
Authors: van Herk Teunie , Hartog Aloysius F. , van der Burg Alida M. , Wever Ron 
Published: June 2005

AbstractBacterial non‐specific acid phosphatases normally catalyze the dephosphorylation of a variety of substrates. As shown previously the enzymes from Shigella flexneri and Salmonella enterica are also able to catalyze the phosphorylation of inosine to inosine monophosphate and D‐glucose to D‐glucose 6‐phosphate (D‐G6P) using cheap pyrophosphate as the phosphate donor. After optimization high yields (95%) are achieved in the latter reaction and we show here that it is possible to use these enzymes in a preparative manner. This prompted us to investigate by using 31P NMR and HPLC also the phosphorylation of a broad range of carbohydrates and alcohols. Many cyclic carbohydrates are phosphorylated in a regioselective manner. Non‐cyclic carbohydrates are phosphorylated as well. Phosphorylation of linear alcohols, cyclic and aromatic alcohols is also possible. In all cases the acid phosphatase from Shigella prefers a primary alcohol function above a secondary one. We conclude that these enzymes are an attractive alternative to existing chemical and enzymatic methods in the phosphorylation of a broad range of compounds.
Air pollution remediation in a fixed bed photocatalytic reactor coated with TiO2
Authors: Esterkin C. R. , Negro A. C. , Alfano O. M. , Cassano A. E. 
Published: June 2005

AbstractIn a previous article, the modeling and experimental verification of the radiation field inside a reactor made of several TiO2 coated, parallel, flat glass fiber meshes, bilaterally UV irradiated was accomplished. The degradation of trichloroethylene (TCE) in an air stream is studied using different values of the pollutant feed concentration, relative humidity and light intensity under operating conditions where kinetic control of the process is established. A kinetic model based on a reaction scheme that involves atomic chlorine as an active reaction intermediate is developed for describing concentration dependencies. It includes, explicitly, the effect of the absorbed light intensity on the rate. The interaction of the existing radiation field with the solid semiconductor to generate electrons, and holes in the reaction catalyst activation step is also modeled. All kinetic parameters are estimated from experiments. The obtained kinetic expression gives a first‐order dependence with respect to the TCE concentration and accounts for a competitive effect of water vapor and TCE for the catalyst active sites. An additional important feature of the derived expression is its ability to represent both limiting cases concerning the dependence of the reaction rate with the irradiation rate; that is, order 1 or order 0.5, as well as all possible intermediate values. In fact, the equivalent dependence obtained in this work was 0.6, a value closer to the second case. The results show good agreement between predictions derived from the proposed kinetic expression and TCE experimental concentration data at the reactor's exit. The proposed reactor design provides a practical device for the treatment of contaminated air; it permits a fairly uniform irradiation of the catalytic meshes and a good ratio of the irradiated surface area with respect to the volume of the gaseous reacting mixture. With these features, rather high TCE conversions can be obtained. © 2005 American Institute of Chemical Engineers AIChE J, 2005
Effect of ultrasound on the morphology and properties of polypropylene/inorganic filler composites
Authors: Chen Yingzi , Li Huilin 
Published: May 2005

AbstractThe effects of ultrasonic irradiation on the rheology, structure, and properties of PP/inorganic filler composites were studied. Scanning electron microscopy showed that ultrasound increased the orientation degrees of acicular fillers to the flow direction. WAXD indicated that ultrasound vibration induced sheet fillers orient with its surface perpendicular to the direction of the ultrasound vibration. The orderly rearrangements of fillers in the polymer melt induced by ultrasound vibration can reduce the steric hindrances in the flow field and increase the flowability of the PP/inorganic filler composites. The effect of ultrasound on reducing the apparent viscosities is very prominent, especially at lower shear rate. Ultrasound has an even more marked effect on reducing the apparent viscosities of composites containing fillers of larger size. With ultrasound vibration, the mechanical properties of the composites are also improved because of the orientation and uniform dispersion of fillers in the matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1553–1560, 2005
Rheological behavior of semi‐aromatic transparent polyamide
Authors: Chen Jinzhou , Qu Liangjun , Li Xinfa , Jiang Aiyun , Niu Mingjun , Wang Jingwu 
Published: May 2005

AbstractThe rheological behaviors of semi‐aromatic transparent polyamide (SATPA) melt are investigated using a capillary rheometer. The effects of shear rate, shear stress, and temperature on the apparent viscosity ηa of SATPA are discussed. A correlation of non‐Newtonian index with temperature is obtained. The results show the shear thinning of SATPA; meanwhile ηa decreases with increasing temperature and shear rate, and the viscous flow activation energy is further obtained from temperature dependence of the samples. It was concluded that the apparent viscosity ηa is sensitive to temperature at lower shear rate owing to the higher viscous flow activation energy; on the contrary, the influence of temperature effect on the apparent viscosity becomes minor at higher shear rate due to the lower viscous flow activation energy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1586–1589, 2005
Modification of an o‐cresol formaldehyde epoxy resin by the thermotropic liquid crystalline polymer
Authors: Huang Zeng Fang , Tan Song Ting , Wang Xia Yu 
Published: May 2005

AbstractTwo novel liquid crystalline polymers, polydiethyleneglycol bis(4‐hydroxybenzoate) terephthaloyl and block copolymer (PDBH), were synthesized by condensation reaction. The blends of the two liquid crystalline polymers and o‐cresol formaldehyde epoxy resin were prepared by linear phenol‐formaldehyde resin as curing reagent. Both mechanical and thermal properties of the blends containing liquid crystalline polymer were improved to a certain extent. By adding 5 wt % PDBH, the impact strength, bending strength, and the glass transition temperature were enhanced by 128%, 23.84%, and 28°C, respectively, compared with the unmodified version. The results of curing kinetics showed that the curing reaction active energy of the modified system by PDBH decreased from 79.70 to 70.26 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1626–1631, 2005
Continuous polymerization of ω‐lauryl lactam in an intermeshing corotating twin‐screw extruder
Authors: Kim In , White James L. 
Published: May 2005

AbstractThis article describes the synthesis of poly(ω‐lauryl lactam) by a reactive extrusion process. Anionic ring‐opening polymerization was performed in an intermeshing corotating twin‐screw extruder. We investigated the evolution of conversion of ω‐lauryl lactam as a function of reaction time, screw speeds, different feed rates, and different screw configurations along the screw axis in a twin‐screw extruder. For comparison with continuous polymerization in a twin‐screw extruder, we studied polymerization in an internal mixer, which was considered a batch reactor. We found the final conversion of ω‐lauryl lactam made in a twin‐screw extruder was higher than in an internal mixer. Higher molecular weights are found at lower screw speeds and feed rates. Melt viscosities and mechanical properties of the polymers were measured. Residence time, molecular weights, and shear mixing have the main effect on the mechanical properties of products. The twin‐screw extruder performance was interpreted in terms of commercial software. It was found that twin‐screw extruder reaction rate was higher than those in the batch reactor and increased locally with screw speed and feed rate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1605–1620, 2005
Isothermal and nonisothermal crystallization kinetics of novel even‐odd nylon 10 11
Authors: Cui Xiaowen , Yan Deyue , Wang Yanping 
Published: May 2005

AbstractIsothermal and nonisothermal crystallization kinetics of even‐odd nylon 10 11 were investigated by differential scanning calorimetry (DSC). Equilibrium melting point was determined to be 195.20°C. Avarmi equation was adopted to describe isothermal and nonisothermal crystallization. A new relation suggested by Mo was used to analyze nonisothermal crystallization and gave a good result. The crystallization activation energies have been obtained to be −583.75 and −270.06 KJ/mol for isothermal and nonisothermal crystallization, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1637–1643, 2005