bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and thermal degradation of poly(n‐butylisocyanate) modified by 1,3‐propanesultone
Authors: Dereszewska Alina , Olayo Roberto , Cardoso Judith 
Published: October 2003

AbstractPoly(n‐butylisocyanates) were synthesized by anionic homopolymerization with the addition of sulfonate groups in the termination stage. Two types of functional polymers were obtained from different quantities of added 1,3‐propanesultone (PrS). When a stoichiometric proportion of sultone is added, the reaction with poly(n‐butylisocyanate) renders a mix of a nonfunctionalized (PBIC) and a telechelic polymer (PBICT). In the presence of an excess of PrS, the proportion of end‐functionalized chains was higher, and a significant change in their thermal properties was observed. Polymers were characterized by FTIR and NMR, and measurements of intrinsic viscosity were made. Thermal degradation of the polymers was studied under nitrogen atmosphere for various heating rates. The kinetic parameters such as the activation energy and the reaction order were determined by using Ozawa's method. Thermal degradation analyses showed that the degradation processes depend strongly on the concentration of functional groups. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3594–3601, 2003
Study of self‐crosslinking acrylate latex containing fluorine
Authors: Chen Yanjun , Zhang Chaocan , Wang Yifeng , Cheng Shiyuan , Chen Peizhi 
Published: October 2003

AbstractSelf‐crosslinking acrylate latices containing fluorine were prepared by the batch method, with N‐hydroxymethyl acrylamide (NMA) as a crosslinking agent. The structure and component of latex polymers were studied by FTIR, ion‐selective electrode analysis, and DSC. The stabilities of latices, such as storage stability, centrifugal stability, and electrolyte‐resistant stability, were examined. The morphology of the latex particles was characterized by TEM and the surface properties were determined by the Wilhelmy method. The effects of NMA on Tg of the latex polymers, the average particle size of the latices, and the surface properties of the latex films were discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3609–3616, 2003
High‐resolution thermogravimetry of polyethersulfone chips in four atmospheres
Authors: Li Xin‐Gui , Shao Hong‐Tao , Bai He , Huang Mei‐Rong , Zhang Wei 
Published: October 2003

AbstractThermal degradation and kinetics of polyethersulfone (PES) chips were studied in air, nitrogen, helium, and argon from room temperature to 790°C by high‐resolution thermogravimetry (TG) at a variable heating rate in response to changes in the sample's degradation rate. In the four atmospheres, a two‐step degradation process in air, argon, and helium or a three‐step degradation process in nitrogen of the PES were found in this investigation. In particular, the three‐step degradation process in nitrogen of the PES revealed by the high‐resolution TG was hardly ever observed by a traditional TG. The initial thermal degradation temperature of the PES increases with the testing atmosphere in the following order: air < argon < helium < nitrogen but the activation energy of the first major degradation of PES increases in a different order: argon < nitrogen < helium < air. The degradation temperature, the temperature at the maximum weight‐loss rate, the maximum weight‐loss rate [(dα/dT)m1 and (dα/dT)m2], char yield at 790°C, and activation energy of the first major degradation process obtained by the high‐resolution TG were compared with those by traditional TG. The PES exhibits the largest (dα/dT)m1 and the greatest char yield at 790°C in helium but the largest (dα/dT)m2 and smallest char yield in air. A significant dependency of the thermal decomposition of the polymers on the physicochemical properties (density, thermal conductivity, and oxidative ability) of the testing atmospheres is elaborated for the first time. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3631–3637, 2003
Tensile fracture and failure behavior of technical flax fibers
Authors: Romhány G. , Karger‐Kocsis J. , Czigány T. 
Published: October 2003

AbstractThe apparent tensile strength of technical flax fibers was determined in single‐fiber tests at various clamping lengths (20, 40, and 80 mm) and the outcome was compared with literature data. It was demonstrated that the strength of flax at each clamping length obeyed the two‐parameter Weibull model. The failure mode and sequence were studied in situ (i.e., during loading) by SEM and acoustic emission (AE). The failure sequence (axial splitting of the technical fiber along its elementary constituents, radial cracking of the elementary fibers, multiple fracture of the elementary fibers) concluded reflected the hierarchical build‐up of the flax bast fibers. To the above failure events AE amplitude ranges were assigned. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3638–3645, 2003
Human severe combined immune deficiency and DNA repair
Authors: Schwarz Klaus , Ma Yunmei , Pannicke Ulrich , Lieber Michael R. 
Published: October 2003

AbstractHuman severe combined immune deficiency (SCID) is the most serious inherited immunological deficit. Recent work has revealed defects in the predominant pathway for double‐strand break repair called nonhomologous DNA end joining, or NHEJ. Progress in the biochemistry and genetics of NHEJ and of human SCID has proven to be synergistic between these two fields in a manner that covers the range from biochemical etiology to considerations about possible gene therapy for the B− SCID patients. BioEssays 25:1061–1070, 2003. © 2003 Wiley Periodicals, Inc.
Growing and shaping the vascular tree: multiple roles for VEGF
Authors: Ruhrberg Christiana 
Published: October 2003

AbstractVascular Endothelial Growth Factor (VEGF) is the most potent and ubiquitous vascular growth factor known to date. Yet, prior to its description as a secreted mitogen for endothelial cells, it was identified as a vascular permeability factor. These seemingly disparate avenues of discovery highlight VEGF's ability to control many distinct aspects of endothelial cell behaviour, including proliferation, migration, specialisation and survival. The versatility of VEGF as a patterning molecule is likely linked to its association with various signalling receptor complexes, but also its expression in several isoforms with a differential affinity for heparan sulfate proteoglycans in the extracellular matrix. In contrast to the absolute requirement for all known VEGF receptors, the presence of only a single VEGF isoform is sufficient for vascular development. However, the isoforms serve as exquisite tools for the fine patterning of growing vessel networks during embryogenesis and in postnatal life. BioEssays 25:1052–1060, 2003. © 2003 Wiley Periodicals, Inc.
Chronic activation of ERK and neurodegenerative diseases
Authors: Colucci‐D'Amato Luca , Perrone‐Capano Carla , di Porzio Umberto 
Published: October 2003

AbstractThe extracellular‐signal regulated kinases 1/2 (ERK or ERKs) are involved in the regulation of important neuronal functions, including neuronal plasticity in normal and pathological conditions. We present findings that support the notion that the kinetics and localization of ERK are intrinsically linked, in that the duration of ERK activation dictates its subcellular compartmentalization and/or trafficking. The latter, in turn, dictates whether ERK‐expressing cells would enter a program of cell death, survival or differentiation. We summarize experimental data showing that chronic activation of ERK plays a role in the mechanisms that trigger neurodegeneration. We also discuss how MKPs, members of the subclass of dual specificity phosphatases, might be the link between ERK kinetics and its subcellular localization. BioEssays 25:1085–1095, 2003. © 2003 Wiley Periodicals, Inc.
Crystal structure of achiral nonapeptide Boc–(Aib–ΔzPhe)4–Aib–OMe at atomic resolution: Evidence for a 310‐helix
Authors: Inai Yoshihito , Oshikawa Tatsuo , Yamashita Mitsuji , Tagawa Kenichi , Hirabayashi Tadamichi 
Published: October 2003

AbstractAn x‐ray crystallographic analysis was carried out for Boc–(Aib–ΔZPhe)4–Aib–OMe (1: Boc = t‐butoxycarbonyl; Aib = α‐aminoisobutyric acid; ΔZPhe = Z‐α,β‐didehydrophenylalanine) to provide the precise conformational parameters of the octapeptide segment –(Aib–ΔZPhe)4–. Peptide 1 adopted a typical 310‐helical conformation characterized by 〈ϕ〉 = ±55.8° (50°–65°), 〈ψ〉 = ±26.7° (15°–45°), and 〈ω〉 = ±179.5° (168°–188°) for the average values of the –(Aib–ΔZPhe)4– segment (the range of the eight values). The 310‐helix contains 3.1 residues per turn, being close to the “perfect 310‐helix” characterized by 3.0 residues per turn. NMR and Fourier transform infrared (FTIR) spectroscopy revealed that the 310‐helical conformation at the atomic resolution is essentially maintained in solution. Energy minimization of peptide 1 by semiempirical molecular orbital calculation converged to a 310‐helical conformation similar to the x‐ray crystallographic 310‐helix. The preference for a 310‐helix in the –(Aib–ΔZPhe)4– segment is ascribed to strong inducers of the 310‐helix inherent in Aib and ΔZPhe residues—in particular, the Aib residues tend to stabilize a 310‐helix more effectively. Therefore, the –(Aib–ΔZPhe)4– segment is useful to rationally design an optically inactive 310‐helical backbone, which will be of great importance to provide novel insights into noncovalent and covalent chiral interactions of a helical peptide with a chiral molecule. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 310–322, 2003
Structural transitions involved in a novel amyloid‐like β‐sheet assemblage of tripeptide derivatives
Authors: Ganesh S. , Jayakumar R. 
Published: October 2003

AbstractSelf‐assembly of two tripeptide derivatives containing three nonpolar isoleucine moieties and polar oxyethylene groups are studied in methanol. Peptide A [CH3(OCH2CH2)3OCH2CO(Ile)3OCH3] and peptide B [CH3(OCH2CH2)3OCH2CO(Ile)3NH (CH2CH2O)3CH3] take a mixture of unordered and helical conformation at low concentration (8.5×10−4M). However, at high concentration (2×10−3M), both the peptide showed significant increase in the helical conformation. An interesting conformational transition of peptides A and B at various methanol contents was observed in the solvated films of these compounds by spectroscopic methods like the far‐uv circular dichroism and Fourier transform infrared (FT‐IR) techniques. Peptide B, which contains more polar oxyethylene groups than A, showed a highly cooperative conformational transition when the methanol content was decreased. This transition was characterized by a large increase of β‐sheet, retaining a α‐helical contribution. Peptide A showed a conformational transition resulting in a β‐sheet in the aggregated state. From the CD spectra, the ratio in the ellipticity indicates that peptide B forms twisted antiparallel β‐sheet conformation, whereas peptide A takes a parallel β‐sheet conformation. The results obtained in this work indicates the role of polar derivatization on the conformational preference of peptides having similar sequence. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 336–345, 2003
Adsorption of actin at the air‐water interface: A monolayer study
Authors: Gicquaud C. , Chauvet J.‐P. , Grenier G. , Tancrède P. , Coulombe G. 
Published: October 2003

AbstractThe intrinsic surface activity of the contractile protein actin has been determined from surface tension measurements using the Wilhelmy hanging‐plate method. Actin, a very soluble protein, moves from the subphase to the air‐water interface to make a film. In the absence of magnesium, actin is monomeric and is known as G‐actin. During the compression the monomers change their conformation or orientation at the interface and they are then pushed reversibly into the subphase upon further compression. No collapse occurs. Actin monomers in the presence of magnesium become activated; at concentrations greater than some critical value, actin polymerizes to form filaments of F‐actin. The actin filaments have a higher surface activity than the actin monomers either because they are more hydrophobic or because F‐actin, a rigid polymer, is much more efficient at creating excluded volume. The actin filaments then form a rigid film at the interface that collapses when the surface area is decreased. At less than the critical concentration, the actin monomers are present in the subphase in their activated form. However, their concentration increases at the interface during film compression until the critical concentration is reached. The surface pressure isotherm in this case has the characteristics of a G‐actin film at the beginning of the compression and of an F‐actin film at the end of the compression process. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 289–296, 2003
Small‐angle X‐ray scattering studies of metastable intermediates of β‐lactoglobulin isolated after heat‐induced aggregation
Authors: Carrotta Rita , Arleth Lise , Pedersen Jan Skov , Bauer Rogert 
Published: October 2003

AbstractSmall‐angle x‐ray scattering was used for studying intermediate species, isolated after heat‐induced aggregation of the A variant of bovine β‐lactoglobulin. The intermediates were separated in two fractions, the heated metastable dimer and heated metastable oligomers larger than the dimer. The pair distance distribution functions for the two intermediate fractions as well as for the native protein have been obtained by indirect Fourier transformation. In addition, the scattering intensity data for samples of the native protein at different concentrations were fitted using a combination of monomer and dimer form factors, which provides an estimate of the amount of monomer in solutions. By subtracting the contribution from the monomer, the scattering intensity from the dimer of the native protein can be determined and compared with the results for the metastable dimer. An ellipsoidal model was used to fit the data for the metastable dimer, and for comparison the same analysis was performed on the dimer of the native protein. The results show that the metastable dimer is more elongated than the dimer of the native protein and it occupies a volume 1.4‐fold larger, in agreement with a more loose, partially unfolded conformation. The same ellipsoidal model was used to analyze the data for the fraction of larger metastable oligomers. In this case, an even more elongated ellipsoid was obtained, suggesting a linear association of monomers in the oligomers. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 377–390, 2003
Brownian dynamics simulations of ion atmospheres around polyalanine and B‐DNA: Effects of biomolecular dielectric
Authors: Cerutti David S. , Wong Chung F. , McCammon J. Andrew 
Published: October 2003

AbstractWe have extended an earlier Brownian dynamics simulation algorithm for simulating the structural dynamics of ions around biomolecules to accommodate dielectric inhomogeneity. The electrostatic environment of a biomolecule immersed in water was obtained by numerically solving the Poisson equation with the biomolecule treated as a low dielectric region and the solvent treated as a high dielectric region. Instead of using the mean‐field type approximations of ion interactions as in the Poisson–Boltzmann model, the ions were treated explicitly by allowing them to evolve dynamically under the electrostatic field of the biomolecule. This model thus accounts for ion–ion correlations and the finite‐size effects of the ions. For a 13‐residue α‐helical polyalanine and a 12‐base‐pair bp B‐form DNA, we found that the choice of the dielectric constant of the biomolecule has much larger effects on the mean ionic structure around the biomolecule than on the fluctuational and dynamical properties of the ions surrounding the biomolecule. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 391–402, 2003
Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobility
Authors: Jia Hongfei , Zhu Guangyu , Wang Ping 
Published: October 2003

AbstractNanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes‐Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility‐activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110–1000 nm were prepared. A model enzyme, α‐chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle‐attached enzyme. Compared to KM, kcat appeared to be less sensitive to particle size and viscosity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 406–414, 2003.
Measuring local flow velocities and biofilm structure in biofilm systems with Magnetic Resonance Imaging (MRI)
Authors: Manz Bertram , Volke Frank , Goll Danile , Horn Harald 
Published: October 2003

AbstractThe characterization of substrate transport in the bulk phase and in the biofilm matrix is one of the problems which has to be solved for the verification of biofilm models. Additionally, the surface structure of biofilms has to be described with appropriate parameters. Magnetic resonance imaging (MRI) is one of the promising methods for the investigation of transport phenomena and structure in biofilm systems. The MRI technique allows the noninvasive determination of flow velocities and biofilm structures with a high resolution on the sub‐millimeter scale. The presented investigations were carried out for defined heterotrophic biofilms which were cultivated in a tube reactor at a Reynolds number of 2000 and 8000 and a substrate load of 6 and 4 g/m2d glucose. Magnetic resonance imaging provides both structure data of the biofilm surface and flow velocities in the bulk phase and at the bulk/biofilm interface. It is shown that the surface roughness of the biofilms can be determined in one experiment for the complete cross section of the test tubes both under flow and stagnant conditions. Furthermore, the local shear stress was calculated from the measured velocity profiles. In the investigated biofilm systems the local shear stress at the biofilm surface was up to 3 times higher compared to the mean wall shear stress calculated on the base of the mean flow velocity. © 2003, Wiley Periodicals, Inc. Biotechnol Bioeng 84: 424–432, 2003.
Enzymatic activity and stability of d‐fructose dehydrogenase and sarcosine dehydrogenase immobilizd onto giant vesicles
Authors: Kato Keiichi , Walde Peter , Mitsui Hirokazu , Higashi Nobuyasu 
Published: October 2003

AbstractStable vesicles with diameters between about 1 and 10 μm were prepared by a particular emulsification technology that involved the use of the surfactants Span 80 and Tween 80 and the phospholipid lecithin (phosphatidylcholine from soybeans). Two membrane enzymes, d‐fructose dehydrogenase from Gluconobacter sp. (FDH) and sarcosine dehydrogenase from Pseudomonas putida (SDH), were for the first time immobilized onto the bilayer membranes of these type of vesicles; and the catalytic activity and enzymatic stability were measured and compared with the enzymes in a vesicle‐free solution. The enzyme activity as well as stability considerably increased upon immobilization. In particular, immobilized FDH at 25°C was stable for at least 20 days, while the activity of the free enzyme dropped to about 20% of its initial value during the same period of time.In contrast to FDH and SDH, immobilization of sorbitol dehydrogenase from Gluconobacter suboxydans (SODH) was not successful, as no improved activity or stability could be obtained. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 415–423, 2003.
One‐pot enzymatic production of dTDP‐4‐Keto‐6‐Deoxy‐d‐glucose from dTMP and glucose‐1‐phosphate
Authors: Oh Jongmin , Lee Sun‐Gu , Kim Byung‐Gee , Sohng Jae Kyung , Liou Kwangkyoung , Lee Hei Chan 
Published: October 2003

AbstractAn enzymatic production method for dTDP‐4‐keto‐6‐deoxy‐d‐glucose, a key intermediate of various deoxysugars in antibiotics, was developed starting from dTMP, acetyl phosphate, and glucose‐1‐phosphate. Four enzymes, i.e., TMP kinase, acetate kinase, dTDP‐glucose synthase, and dTDP‐d‐glucose 4,6‐dehydratase' were overexpressed using T7 promoter system in the E. coli BL21 strain, and the dTDP‐4‐keto‐6‐deoxy‐d‐glucose was synthesized by using the enzyme extracts in one‐pot batch system. When 20 mM dTMP of initial concentration was used, Mg2+ ion, acetyl phosphate, and glucose‐1‐phosphate concentrations were optimized. About 95% conversion yield of dTDP‐4‐keto‐6‐deoxy‐d‐glucose was obtained based on initial dTMP concentration at 20 mM dTMP, 1 mM ATP, 60 mM acetyl phosphate, 80 mM glucose‐1‐phosphate, and 20 mM MgCl2. The rate‐limiting step in this multiple enzyme reaction system was the dTDP‐glucose synthase reaction. Using the reaction scheme, about 1 gram of purified dTDP‐4‐keto‐6‐deoxy‐d‐glucose was obtained in an overall yield of 81% after two‐step purification, i.e., anion exchange chromatography and gel filtration. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 452–458, 2003.
High‐level expression of full‐length antibodies using trans‐complementing expression vectors
Authors: Bianchi Allison A. , McGrew Jeffrey T. 
Published: October 2003

AbstractRecombinant antibodies are increasingly used as therapeutics for a wide variety of diseases. Generation of cell lines expressing high levels of recombinant antibody typically requires labor‐intensive cloning and screening steps. We describe a mammalian expression system for the high‐level production of full‐length antibody molecules. It has been shown that the dihydrofolate reductase (DHFR) selectable marker can be divided into two fragments that, with the aid of a leucine zipper, can re‐associate to form an active molecule. Using bicistronic vectors, we linked the expression of each antibody chain to the expression of a DHFR fragment. Survival in selective media requires expression of both DHFR fragments that, by virtue of these vectors, also selects for the expression of both antibody chains. Initial pools produced 5 µg of Ab/106 cells/d (qP = µg/106 cells/d). Expression of each antibody chain in conjunction with a portion of DHFR also leads to concurrent amplification of both antibody chains in the presence of methotrexate, a DHFR inhibitor, and results in a two‐ to fivefold increase in antibody production with basal qPs ranging from 10–25 ug/106 cells/d. Shake‐flask cultures of amplified pools produced up to 600 mg/L of antibody in 7 days. This system allows for rapid generation of antibodies without cloning and greatly simplifies selection of cell lines for the production of potential antibody therapeutics. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 439–444, 2003.