bluuebunny/crossref_metadata_2025_split huggingface dataset:
Discussion of the Stray Light Rejection Efficiency of FT-IR Spectrometers: The Effects of Sample Emission on FT-IR Spectra
Authors: Tripp C. P. , McFarlane R. A. 
Published: May 2005

The effects of emitted radiation at the sample position in FT-IR spectrometers can produce spectral distortions and artifacts. Because of the high stray light rejection efficiency of FT-IR, these distortions are presumed to arise from the constant (dc) emission leading to nonlinearity in detector response or to a rise in temperature of the optical bench caused by the hot sample which leads to a drop-off in spectrometer performance. We show that the stray light advantage of FT-IR may not be valid for hot samples because some sample emission makes its way back to the interferometer, where it is modulated and can be passed back to the sample to produce distortions in peak shapes and relative intensities. Several approaches to eliminate these problems are provided. Although we have addressed only emission phenomena in this work, reflection from samples also leads to distortions, notably the presence of signal at n ( n = 2, 3, 4 …) times the frequency. As discussed by Hirschfeld,12,13 these effects can be eliminated by using a half-beam blocking aperture or by tilting the sample. From the above experiments, clearly these effects can also be eliminated by using the corner-cubed FT-IR.
Dielectric Elastomers in Actuator Technology
Authors: Löwe C. , Zhang X. , Kovacs G. 
Published: May 2005

AbstractElectroactive polymers (EAPs) are characterized by their ability to respond to external electric stimulation by displaying a significant shape or size displacement. Actuators, based on dielectric elastomers exhibiting low elastic stiffness and high dielectric constants, can produce high strain levels from 10 to 380 %. Typically, acrylic and silicone materials are used as dielectric layer in such actuators. Their potential to mimic the movement of animals, insects and even human body parts are increasingly of interest for researchers in the field of biomimetics, as well as more classical application fields like robotics. The control of the most important material properties, elastic moduli and dielectric constants of the dielectric elastomers and electrode materials, together with the control of fabrication parameters i.e. film thickness, electrode manufacturing as well as design of the actuator configuration allow the fabrication of tailor‐made actuators, which match the necessary requirements for a given application. Theoretical models contribute to a deeper understanding of EAP actuators and improve design and optimisation.
Enzymatic Baeyer–Villiger Oxidation of Benzaldehydes
Authors: Moonen Mariëlle J. H. , Westphal Adrie H. , Rietjens Ivonne M. C. M. , van Berkel Willem J. H. 
Published: June 2005

AbstractThe selectivity of the chemical Baeyer–Villiger oxidation of benzaldehydes depends on steric and electronic factors, the type of oxidizing agent and the reaction conditions. Here we report on the enzymatic Baeyer–Villiger oxidation of fluorobenzaldehydes as catalyzed by the flavoprotein 4‐hydroxyacetophenone monooxygenase (HAPMO). HAPMO was most active with 4‐amino‐ and 4‐hydroxybenzaldehydes. With these compounds significant substrate inhibition occurred. Monofluoro‐ and difluorobenzaldehydes were readily oxidized by HAPMO without substrate inhibition. 19F NMR analysis revealed that 4‐fluoro‐, 2,6‐difluoro‐, 3,4‐difluoro‐, 2‐fluoro‐4‐hydroxy‐ and 3‐fluoro‐4‐hydroxybenzaldehyde were quantitatively converted by HAPMO to the corresponding fluorophenyl formates. These products spontaneously hydrolyzed to fluorophenols. The HAPMO‐mediated conversion of 2‐fluoro‐, 3‐fluoro‐, 2,3‐difluoro‐ and 2,4‐difluorobenzaldehyde yielded, besides fluorophenols, also minor amounts of fluorobenzoic acids. The high preference of HAPMO for the production of fluorophenols is in disagreement with the rule derived from chemical studies that electron‐poor benzaldehydes form mainly benzoic acids. This suggests that interactions of the benzaldehyde substrates with amino acids and/or the flavin cofactor in the enzyme active site influence the selection of the migratory group in favor of the phenyl ring.
Enzymatic Baeyer–Villiger Oxidation of Bicyclic Diketones
Authors: Ottolina Gianluca , de Gonzalo Gonzalo , Carrea Giacomo , Danieli Bruno 
Published: June 2005

AbstractCyclohexanone monooxygenase from Acinetobacter calcoaceticus was employed for the Baeyer–Villiger oxidation of racemic bicyclic diketones such as the Wieland–Miescher and the Hajos–Parrish diketones and of some of their derivatives. The corresponding lactones were produced in a highly regio‐ and enantioselective manner. The reactions were carried out using a crude enzyme preparation in aqueous buffer, at room temperature, and the recycling of the expensive coenzyme NADPH was conducted with a second ancillary enzymatic system. The enzymatic process was simple and easy to handle, thus providing a very practical tool to access enantiopure lactones.
Optimisation of the Enantioselective Synthesis of Cyanohydrin Esters
Authors: Veum Lars , Kanerva Liisa T. , Halling Peter J. , Maschmeyer Thomas , Hanefeld Ulf 
Published: June 2005

AbstractThe base‐ and lipase‐catalysed enantioselective synthesis of cyanohydrin esters was investigated, and the problem of previously reported low yields due to residual water in the reaction mixture was addressed. When the lipase was immobilised on Celite R‐633 as a carrier, both the enantioselectivity and the reaction times for this dynamic kinetic resolution were improved, thus enabling a highly enantioselective synthesis of aromatic and heteroaromatic cyanohydrin acetates.
Biocatalytic Asymmetric Dihydroxylation of Conjugated Mono‐ and Poly‐alkenes to Yield Enantiopure Cyclic cis‐Diols
Authors: Boyd Derek R. , Sharma Narain D. , Bowers Nigel I. , Brannigan Ian N. , Groocock Melanie R. , Malone John F. , McConville Gareth , Allen Christopher C. R. 
Published: June 2005

AbstractDioxygenase‐catalysed asymmetric dihydroxylation, of a series of conjugated monoalkenes and polyenes, was found to yield the corresponding monols and 1,2‐dihydrodiols. The diol metabolites were obtained from monosubstituted, gem‐disubstituted, cis‐disubstituted, and trisubstituted alkene substrates, using whole cells of Pseudomonas putida strains containing toluene and naphthalene dioxygenases. Dioxygenase selection and alkene type were established as important factors, in the preference for dioxygenase‐catalysed 1,2‐dihydroxylation of conjugated alkene or arene groups, and monohydroxylation at benzylic or allylic centres. Competition from allylic hydroxylation of methyl groups was observed only when naphthalene dioxygenase was used as biocatalyst. The structures, enantiomeric excess values and absolute configurations of the bioproducts, were determined by a combination of stereochemical correlation, spectroscopy (NMR and CD) and X‐ray diffraction methods. cis‐1,2‐Diol metabolites from arenes, cyclic alkenes and dienes were generally observed to be enantiopure (>98% ee), while 1,2‐diols from acyclic alkenes had lower enantiomeric excess values (<88% ee). The enantiopure cis‐diol metabolite of a gem‐disubstituted fulvene was used as precursor in a new chemoenzymatic route to a novel C2‐symmetrical ketone.
Chemoenzymatic Route to Both Enantiomers of a 1‐Isopropyl‐3a‐methyloctahydroinden‐4‐one Derivative: A Synthetic Intermediate for Sesqui‐ and Diterpenoids
Authors: Fujieda Shigeo , Tomita Mina , Fuhshuku Ken‐ichi , Ohba Shigeru , Nishiyama Shigeru , Sugai Takeshi 
Published: June 2005

AbstractOn the way to a chemoenzymatic synthesis of a key intermediate for sesquiterpenoids and diterpenoids, 2‐methyl‐2‐(4‐methyl‐3‐oxopentyl)‐1,3‐cyclohexanedione was reduced with the whole cells of yeast biocatalysts. Torulaspora delbrueckii NBRC10921 reduced a cyclic ketone of three carbonyl groups in an enantiofacially selective manner (re‐face attack), but there was poor enantiotopic group selectivity between two carbonyl groups on the cyclohexane ring to yield a mixture of diastereomeric products. Candida floricola IAM13115 reduced mainly the pro‐(R) carbonyl group. In contrast, the reduction proceeded in an enantiofacially poorly selective manner to give another set of diastereomeric products. In both cases, another carbonyl group on the side chain worked as a ‘trapping arm’ of the resulting secondary alcohol. The diastereomeric products were effectively separated as the ‘syn’ or ‘cis’ isomer exclusively exist in the intramolecular hemiacetal structure, while ‘anti’ or ‘trans’ isomer being an equilibrated mixture of cyclic hemiacetal and open‐chain hydroxyketone (ca. 0.7 : 1). Starting separately from the enantiomerically enriched products as above, both enantiomers of the target compound, a key intermediate for terpenoids, were efficiently prepared via stereoselective ring closure under pinacol coupling reaction conditions. Furthermore, a daucane sesquiterpene intermediate, a hydroazulene derivative, was provided after one‐carbon homologation of the six‐membered ring.
Penicillin G Amidase‐Catalysed Hydrolysis of Phenylacetic Hydrazides on a Solid Phase: A New Route to Enzyme‐Cleavable Linkers
Authors: Basso Alessandra , Ebert Cynthia , Gardossi Lucia , Linda Paolo , Tran Phuong Thao , Zhu Mingzhao , Wessjohann Ludger 
Published: June 2005

AbstractA novel catalytic property of penicillin G amidase (PGA) is described. Unexpectedly, the enzyme can hydrolyse hydrazide bonds with good efficiency, and in solution the enzyme shows a selectivity that is similar to phenylacetamides. The hydrolysis of phenylacetic hydrazides releases hydrazine, but no inhibition due to the formation of such reactive compounds was observed. This novel catalytic property was assayed also on a solid phase as a pioneering route for the design of enzyme‐cleavable linkers and masked scavengers for ketones. On a solid phase a phenylacetic hydrazide compound was chemically synthesised on PEGA1900 and PEGA+ (two co‐polymers of acrylamide and ethylene glycol) and the efficiency of PGA in the release of phenylacetic acid depended on the diffusion of the protein inside the polymer. On PEGA+ the enzyme, as previously described, shows a good diffusion due to an improved electrostatic interaction with PGA thus achieving good hydrolytic conversions.
Production of Acrylamide using Alginate‐Immobilized E. coli Expressing Comamonas testosteroni 5‐MGAM‐4D Nitrile Hydratase
Authors: Mersinger Lawrence J. , Hann Eugenia C. , Cooling Frederick B. , Gavagan John E. , Ben‐Bassat Arie , Wu Shijun , Petrillo Kelly L. , Payne Mark S. , DiCosimo Robert 
Published: June 2005

AbstractA thermally‐stable nitrile hydratase produced by Comamonas testosteroni 5‐MGAM‐4D has been expressed in Escherichia coli, and the alginate‐immobilized transformant evaluated as catalyst for the conversion of acrylonitrile to acrylamide. In batch reactions with catalyst recycle, the catalyst productivity decreased with increasing acrylonitrile concentration or reaction temperature, but was relatively insensitive to acrylamide concentration. A total of 206 consecutive batch reactions with catalyst recycle were run at 5 °C and produced 1035 g acrylamide/g dry cell weight and 95 g acrylamide/L; the initial and final volumetric productivities of this series of recycle reactions were 197 and 96 g acrylamide/L/h, respectively. A packed column reactor yielded lower catalyst productivity than consecutive batch recycle reactions, presumably due to contact of the fixed‐bed catalyst with a constant high concentration of acrylonitrile.
Combined Application of Galactose Oxidase and β‐N‐Acetylhexosaminidase in the Synthesis of Complex Immunoactive N‐Acetyl‐D‐galactosaminides
Authors: Fialová Pavla , Namdjou Darius‐Jean , Ettrich Rüdiger , Přikrylová Věra , Rauvolfová Jana , Křenek Karel , Kuzma Marek , Elling Lothar , Bezouška Karel , Křen Vladimír 
Published: June 2005

AbstractA high‐yield preparatory procedure for the synthesis of p‐nitrophenyl 2‐acetamido‐2‐deoxy‐β‐D‐galacto‐hexodialdo‐1,5‐pyranoside (2) using the galactose oxidase from Dactylium dendroides in a batch reactor was developed. Enzymatic recognition of this aldehyde and the respective uronic acid 3 obtained by NaClO2 oxidation was studied using a set of 36 fungal β‐N‐acetylhexosaminidases from Acremonium, Aspergillus, Penicillium and Talaromyces genera. The aldehyde 2 was readily hydrolysed by all tested β‐N‐acetylhexosaminidases but neither the uronic acid 3 nor its methyl ester 4 were accepted. Molecular modelling with docking into the active centre of the β‐N‐acetylhexosaminidase from Aspergillus oryzae revealed that the aldehyde 2 is processed as a C‐6 geminal diol by the enzyme. The aldehyde 2 was tested for transglycosylation reactions using GlcNAc as an acceptor. The β‐N‐acetylhexosaminidase from Talaromyces flavus gave the best yields (37%) of the transglycosylation product 2‐acetamido‐2‐deoxy‐β‐D‐ galacto‐hexodialdo‐1,5‐pyranosyl‐(1→4)‐2‐acetamido‐ 2‐deoxy‐D‐glucopyranose, which was oxidised in situ to yield the final product 2‐acetamido‐2‐deoxy‐β‐D‐galactopyranosyluronic acid‐(1→4)‐2‐acetamido‐2‐deoxy‐D‐glucopyranose (6). Compounds 3 and 6 were shown to be high‐affinity ligands for two natural killer cell activation receptors, NKR‐P1A and CD69. For the latter receptor they turned out to be among the best ligands described so far. This increase was obviously due to the presence of a carboxy moiety.
Immobilization of Penicillin G Acylase: The Key to Optimum Performance
Authors: Kallenberg Agnes I. , van Rantwijk Fred , Sheldon Roger A. 
Published: June 2005

AbstractPenicillin G acylase is a major industrial biocatalyst that is used in the enzymatic production of 20,000 t a−1 of 6‐aminopenicillanic acid, the industrial β‐lactam intermediate, as well as in the enzymatic production of semi‐synthetic β‐lactam antibiotics. Because efficient recovery and reuse of the biocatalyst is a prerequisite for a viable process, much attention has been focused on the immobilization of penicillin G acylase. Methods that have been studied and will be discussed in this review include covalent attachment to porous organic and inorganic carriers, inclusion in and attachment to biopolymer gels and carrier‐free immobilization techniques. Highly active and stable preparations have been developed; mass transfer limitations in the carrier are now a major barrier to further improvement of the biocatalyst performance.
Significant and Unexpected Solvent Influence on the Selectivity of Laccase‐Catalyzed Coupling of Tetrahydro‐2‐naphthol Derivatives
Authors: Intra Annalisa , Nicotra Silvia , Riva Sergio , Danieli Bruno 
Published: June 2005

AbstractThe relative ratio of the dimers obtained by laccase‐catalyzed oxidation of tetrahydronaphthyl derivatives was profoundly influenced by the nature of the organic solvent used. For instance, in the oxidation of 5,6,7,8‐tetrahydronaphtalen‐2‐ol (1), the formation of the symmetrical 1,1′ product 1a with respect to the 1,3′ dimer 1b was highly favored in the aromatic solvents benzene and toluene.
Catalytic Hydroxylation in Biphasic Systems using CYP102A1 Mutants
Authors: Maurer Steffen C. , Kühnel Katja , Kaysser Leonard A. , Eiben Sabine , Schmid Rolf D. , Urlacher Vlada B. 
Published: June 2005

AbstractCytochrome P450 monooxygenases are biocatalysts that hydroxylate or epoxidise a wide range of hydrophobic organic substrates. Their technical application is, however, limited to a small number of whole‐cell processes. The use of the isolated P450 enzymes is believed to be impractical due to their low stability, stoichiometric need of the expensive cofactor NAD(P)H and low solubility of most substrates in aqueous media. We investigated the behaviour of an isolated bacterial monooxygenase (mutants of CYP102A1) in a biphasic reaction system supported by cofactor recycling with the NADP+‐dependent formate dehydrogenase from Pseudomonas sp 101. Using this experimental set‐up cyclohexane, octane and myristic acid were hydroxylated. To reduce the process costs a novel NADH‐dependent mutant of CYP102A1 was designed. For recycling of NADH an NAD+‐dependent FDH was used. The stability of the monooxygenase mutants under the reaction conditions in the biphasic system was quite high as revealed by total turnover numbers of up to 12,850 in the NADPH‐dependent cyclohexane hydroxylation and up to 30,000 in the NADH‐dependent myristic acid oxidation.
Purification and Cloning of a Ketoreductase used for the Preparation of Chiral Alcohols
Authors: Hanson Ronald L. , Goldberg Steven , Goswami Animesh , Tully Thomas P. , Patel Ramesh N. 
Published: June 2005

AbstractThe synthesis of the leading candidate compound in an anticancer program required (S)‐2‐chloro‐1‐(3‐chlorophenyl)‐ethanol as an intermediate. Other possible candidate compounds used analogues of the S‐alcohol. Of 119 microbial cultures screened for reduction of the corresponding ketone to the S‐alcohol, Hansenula polymorpha ATCC 58401 (73.8% ee) and Rhodococcus globerulus ATCC 21505 (71.8% ee) had the highest enantioselectivity for producing the desired alcohol. A ketoreductase from Hansenula polymorpha, after purification to homogeneity, gave the S‐alcohol with 100% ee. Amino acid sequences from the purified enzyme were used to design PCR primers for cloning the ketoreductase. The cloned ketoreductase required NADP(H), had a subunit molecular weight of 29,220 and a native molecular weight of 88,000. The cloned ketoreductase was expressed in E. coli together with a cloned glucose 6‐phosphate dehydrogenase from Saccharomyces cerevisiae to allow regeneration of the NADPH required by the ketoreductase. An extract of E. coli containing the two recombinant enzymes was used to reduce 2‐chloro‐1‐(3‐chloro‐4‐fluorophenyl)‐ethanone and two related ketones to the corresponding S‐alcohols. Intact E. coli cells provided with glucose were used to prepare (S)‐2‐chloro‐1‐(3‐chloro‐4‐fluorophenyl)‐ethanol in 89% yield with 100% ee.
Biocatalyzed Generation of Molecular Diversity: Selective Modification of the Saponin Asiaticoside
Authors: Monti Daniela , Candido Andrea , Cruz Silva M. Manuel , Křen Vladimir , Riva Sergio , Danieli Bruno 
Published: June 2005

AbstractAn array of different derivatives of the complex ursane‐type triterpene glycoside asiaticoside (1), a saponin component isolated from the perennial herb Centella asiatica, was generated by exploiting the stereo‐, regio‐ and site‐selectivity of four groups of enzymes (glycosidases, glycosyltransferases, lipases and laccases). A library of extracellular α‐L‐rhamnosidases (31 different items) was obtained by screening 16 different fungal strains under different cultivation conditions, and several of these preparations catalyzed the derhamnosylation of asiaticoside. Specifically, the enzymes produced by Fusarium oxysporum were selected for the synthesis of derhamno‐degluco‐asiaticoside (2) and also of derhamno‐asiaticoside (3), by in situ glucose‐inhibition of contaminating β‐D‐glucosidases. β‐1,4‐Galactosyltransferase from bovine milk was subsequently used for the galactosylation of the two asiaticoside derivatives 2 and 3, using 20% v/v DMSO as a cosolvent in order to increase substrate solubility. Finally, new acylated and oxidized derivatives of asiaticoside were also prepared by exploiting the lipase from Candida antarctica (Novozym 435) and the laccase from Trametes pubescens, respectively.
Microbiological Transformations 60. Enantioconvergent Baeyer–Villiger Oxidation via a Combined Whole Cells and Ionic Exchange Resin‐Catalysed Dynamic Kinetic Resolution Process
Authors: Gutiérrez Maria‐Concepción , Furstoss Roland , Alphand Véronique 
Published: June 2005

AbstractA dynamic kinetic resolution process was applied to an enantioconvergent microbial Baeyer–Villiger oxidation of benzyloxycyclopentanone, rac‐1. This was achieved by combining a whole cell‐based kinetic resolution and an anion exchange resin‐catalysed in situ racemisation. Several resins were screened according to their capacity to catalyse the racemisation of 1. As compared to our previous results, the presence of weakly basic Lewatit MP62 in biotransformations of 1 allowed a three‐fold improvement of usable substrate concentration and afforded nearly enantiopure lactone (R)‐2 (97% ee) in preparative (isolated) yields higher than 84%. Noyori's model was applied to this reaction and allowed kinetic constants determination.
Room Temperature Ionic Liquids in the Kinetic Resolution of Adrenaline‐Type Aminoethanols by Burkholderia cepacia Lipase under Normal and Microwave Conditions
Authors: Lundell Katri , Kurki Toni , Lindroos Maria , Kanerva Liisa T. 
Published: June 2005

AbstractThe lipase PS‐C II (lipase from Burkholderia cepacia immobilized on ceramic particles)‐catalyzed acylations of N‐acylated 2‐amino‐1‐phenylethanol (rac‐1) and N‐acylated norphenylephrine (rac‐2) have been studied in imidazolium‐ and pyridinium‐based ionic liquids, in tert‐butyl methyl ether (TBME) and in their mixtures. Enzymatic chemo‐ and enantioselectivities in the presence of hydrophobic EMIM⋅NTf2 and hydrophilic EMIM⋅BF4 have been studied in more detail using high substrate concentrations. The preparative‐scale kinetic resolution of rac‐1 and rac‐2 (both 0.45 M) with vinyl butanoate in the mixture of EMIM⋅NTf2 with TBME (2 : 1) took 9 and 27 hours, respectively. Microwave‐assisted acylation of rac‐1 and rac‐2 in the presence of EMIM⋅NTf2 proceeded similarly to the reactions under normal conditions.
Rational Strategies for Directed Evolution of Biocatalysts –Application to Candida antarctica lipase B (CALB)
Authors: Chodorge Matthieu , Fourage Laurent , Ullmann Christophe , Duvivier Vincent , Masson Jean‐Michel , Lefèvre Fabrice 
Published: June 2005

AbstractProvided that the industrial constraints have been properly defined, the directed evolution technologies available today enable one to design tailor‐made enzymes and biocatalytic routes for chemical processes. Family shuffling has proved to be a successful strategy using traditional recombination protocols. However, when starting from a single gene, the first step is to create the appropriate population of parental genes to ensure an efficient recombination during gene shuffling. Our recent work focused on the determination of rational directed evolution strategies that can be applied for the creation of an improved biocatalyst within the requested industrial timelines. For this purpose, we have developed a rational approach that first explores the “protein plasticity” (ability of the protein to accept mutations with a limited loss of activity) of the enzyme, which enables us to estimate (i) the “optimal mutation load” (number of mutations introduced per gene that gives the highest frequency of improved variants) and (ii) the “ad minima size sample” (minimal number of clones to be screened) that can be used to rapidly improve this enzyme. We have then applied this approach to create in a few weeks variants of the well known lipase B with a seven fold improvement in thermostability.
Recent Advances in the Oligosaccharide Synthesis Promoted by Catalytically Engineered Glycosidases
Authors: Perugino Giuseppe , Cobucci‐Ponzano Beatrice , Rossi Mosè , Moracci Marco 
Published: June 2005

AbstractIn oligosaccharide synthesis the chemo‐enzymatic approach is often chosen to obtain the desired glycosidic bond by exploiting the exquisite substrate specificity and stereoselectivity of glycosidases and glycosyltransferases. In recent years the invention of new enzymatic activities, named glycosynthases, created a third route for the enzymatic synthesis of oligosaccharides. Glycosynthases are mutant glycosidases, devoid of hydrolytic activity, that produce oligosaccharides with yields >80%. The glycosynthase technology is now well established and was greatly improved recently. Several groups experimentally proved that this methodology can be applied to several glycosidases and that the activity of existing glycosynthases can be significantly enhanced. In this review we briefly describe the characteristics of these synthetic tools and show a survey of the most recent findings. Methods for the prediction of the glycosynthetic potential of known glycosidases are also discussed.