bluuebunny/crossref_metadata_2025_split huggingface dataset:
Poly[(diphenylsilanediyl)ethynediyl]: Structure and optical and electroluminescent properties
Authors: Nešpůrek Stanislav , Toman Petr , Fujii Akihiko , Yoshino Katsumi 
Published: April 2007

AbstractPoly[(diphenylsilanediyl)ethynediyl] with a band‐gap energy of 5.2 eV is a wide‐band‐gap material with a photoluminescence maximum at a wavelength of 354 nm. It is suitable for the fabrication of ultraviolet electroluminescence diodes. The electroluminescence spectrum consists of a strong peak at 361 nm and a tail up to 570 nm. The external quantum emission efficiency at the main maximum, calculated in terms of emitted photons per transported electronic charge, is 0.01% (no sample optimization has been carried out). The electric characteristics are controlled by contact‐limited currents and double injection. The geometry of the neutral oligo[(diphenylsilanediyl)ethynediyl] molecule and its infrared spectra and the changes in the geometries and charge distributions during the formation of the positive and negative ions have been calculated by quantum chemical methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 208–214, 2007
Features of fluorescence spectra of polyethylene 2,6‐naphthalate films
Authors: Ouchi I. , Nakai I. , Ono M. , Kimura S. 
Published: April 2007

AbstractThe characteristics of the fluorescence spectra of polyethylene 2,6‐naphthalate (PEN) films were compared with those of poly(ethylene terephthalate) (PET). The fluorescence spectra of PEN films were found, by photoselection, to consist of two components, one peaking at 425 nm and the other at 445 nm, with their emission transition moments perpendicular to each other. The integrated excitation spectra of the PEN films were much more intense than those of PET. After the resolution of the integrated excitation spectra of PEN, most, but not all, of their component peaks corresponded to those of the absorption spectra. On the basis of this fact together with previous data on photodegradation, the spectral component peaking at 445 nm originated, at least partly, from traces of photochemical products generated by exposure during the measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 114–121, 2007
Synthesis and properties of self‐crosslinkable thermoplastic polyurethanes
Authors: Lapprand A. , Méchin F. , Pascault J.‐P. 
Published: April 2007

AbstractThe chemical modification of a thermoplastic polyurethane (TPU) has been realized by the grafting of polyisocyanates onto urethane groups through allophanate bonds to prepare self‐crosslinkable but still thermoplastic materials. Because of the lateral isocyanate groups, the resulting polymer can be easily crosslinked by the ambient moisture. However, because of the highly viscous character of the TPU even at a high temperature, this chemical reaction must be performed with a twin‐screw extruder above 190°C. The ability of linear, segmented TPUs to undergo physical (micro)structuration that strongly depends on their thermal history has been widely described in the literature, and these transformations usually occur in the same temperature range as that used for performing our chemical reactions. Moreover, the thermally reversible character of urethane and allophanate bonds above ∼ 170°C is also well‐known. Therefore, the precise characterization of the thermomechanical properties of the initial and modified materials is quite delicate because microstructural phenomena and chemical rearrangements can compete and always have to be considered simultaneously. Considering these restrictions, we have nevertheless demonstrated that the structural transformation is faster than crosslinking for a partially crosslinked TPU, but microphase separation is no longer possible for a TPU with a gel fraction higher than 50%. The chemical crosslinks of the modified TPU are reversible, but they still allow an important increase in the thermomechanical properties at a high temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 99–113, 2007
Composites of poly(L‐lactide) with hemp fibers: Morphology and thermal and mechanical properties
Authors: Masirek Robert , Kulinski Zbigniew , Chionna Donatella , Piorkowska Ewa , Pracella Mariano 
Published: April 2007

AbstractComposites of poly(L‐lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight‐average molecular weight = 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide‐angle X‐ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA–PEG/hemp composites were analyzed as a function of the fiber amount. The cold‐crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70–130°C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 110°C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber‐filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 255–268, 2007
Modification of rubber by iodoform
Authors: Bieliński Dariusz M. , Ślusarski Ludomir , Głąb Piotr 
Published: April 2007

AbstractThe activity of iodoform (CHI3) toward unsaturated rubbers was examined. Special attention was devoted to cis‐1,4‐(poly)isoprene (IR). The thermal decomposition of CHI3 was studied by ion mass spectroscopy, and the obtained data were used for the identification of pyrolysis products of CHI3 vulcanizates by pyrolytic gas chromatography. The kinetics of the chemical crosslinking of rubber were studied with a cure meter. The changes observed in the chemical structure of rubber were explained on the basis of 13CNMR and Fourier transform infrared spectroscopy, differential scanning calorimetry, equilibrium swelling, and chemical microanalysis data. Apart from crosslinking, a simultaneous modification of the rubber macromolecules took place, specifically the cis–trans isomerization of IR. This resulted in a significant increase in the rubber hardness, especially after a postheat treatment accompanied by oxidation. CHI3–IR vulcanizates behaved like thermoplastics because of the presence of a trans‐1,4 phase, as confirmed by dynamic mechanical thermal analysis. The structure of the macromolecules treated with CHI3 and its effect on the physical properties of the material were compared with those of peroxide–IR vulcanizates. The influence of the modification on the surface energy, bacteriostaticity, and mechanical properties of the vulcanizates was examined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 177–189, 2007
Studies of the molecular dynamics in polyurethane networks with hyperbranched crosslinkers of different coordination numbers
Authors: Czech Przemyslaw , Okrasa Lidia , Ulanski Jacek , Boiteux Gisele , Mechin Francoise , Cassagnau Philippe 
Published: April 2007

AbstractSeveral new polyurethane networks based on hyperbranched polyesters (trade name Boltorn) were synthesized to investigate the influence of the hyperbranched crosslinking agent on the molecular dynamics of the linear segments containing urethane groups. For comparison, linear polyurethanes as well as polyurethanes crosslinked with the classical crosslinker trimethylolpropane were prepared. Broadband dielectric spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry yielded consistent results concerning the molecular relaxation processes; however, dielectric spectroscopy appeared to be more sensitive concerning the secondary relaxation processes. In the temperature range up to 150°C, the molecular relaxations were very similar in all the investigated samples, despite considerable structural differences. The weak influence of the crosslinking on the molecular properties could be explained by the existence of hydrogen bonds forming a physical network, which was very dense in this temperature range in comparison with the chemical crosslinks and therefore dominated the molecular mobility in all the investigated systems. This hypothesis was confirmed by rheological measurements performed at temperatures above 150°C, when the hydrogen bonds should be thermally destroyed. At these temperatures, the effect of crosslinking was manifested by a strong shift of the flowing point: in the linear polyurethanes, this point occurred at much higher frequencies (and lower temperatures) than in the crosslinked analogues. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 89–98, 2007
Effect of crosslinking on polymer electrolytes based on cellulose
Authors: Chelmecki Marcin , Meyer Wolfgang H. , Wegner Gerhard 
Published: April 2007

AbstractPolymer electrolytes based on biogenic and commercially available substrates have been crosslinked thermally to improve their mechanical properties with only negligible effects on their conductivity. The new materials consist of oligo(ethylene oxide) side chains grafted via ether linkages to a cellulose backbone [poly(ethylene oxide)–2‐hydroxypropylcellulose (PEO–HPC)]. PEO–HPC with a degree of side‐chain substitution up to 3.0, as determined by NMR, has been blended with lithium bis(trifluoromethylsulfone)imide in molar ratios of 0.02 ≤ [Li]/[O] ≤ 0.2. The effect of the salt concentration on the thermal behavior and ionic conductivity has been investigated by impedance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The uncrosslinked materials are viscous liquids. The PEO–HPC/lithium salt blends have been thermally crosslinked with the application of urethane chemistry. The crosslinking reactions have been monitored by dynamic mechanical analysis. Crosslinking renders the liquid materials into mechanically stable films with a storage modulus of 105 Pa at 100°C. Surprisingly, their conductivities remain rather unaffected and reach at best 2.5 × 10−4 S/cm. The applicability of the PEO–HPC/lithium salt blends as separators in lithium‐ion batteries has been demonstrated by the construction of a storage cell that is rechargeable. A freshly constructed cell reveals a voltage of about 3.2 V and can be recharged with a constant direct‐current voltage up to the open circuit voltage of 3.65. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 25–29, 2007
Preparation and dynamic mechanical properties of polyurethane‐modified epoxy composites filled with functionalized fly ash particulates
Authors: Wu Gaohui , Gu Jian , Zhao Xiao 
Published: April 2007

AbstractFly ash (FA) is a porous ceramic, which has proved to have some favorable functions. In this article, we have prepared a series of fly ash filled composites, where the polyurethane‐(PU) modified epoxy (EP) was acted as the matrix. With the purpose of characterizing the effect of the content of PU in the matrices and the surface‐treatment (ST) of fly ash particulates on the dynamic mechanical properties of composites, Fourier transform infrared spectral analysis (FTIR), microstructure observation, impact property test as well as dynamic mechanical analysis (DMA) were systematically investigated. With FTIR test, it can be found that the chemical reactions occur, and new chemical structures are formed between EP and PU, and the functionalized groups existing on the surface of fly ash particulates can also be detected. In fractographs observation of composites, it can be seen that the silane coupling agent improves the interfacial bonding conditions between fly ash particulates and the matrix. Impact property test result reveals that PU improves the toughness of EP. Dynamic mechanical analysis of the composites is carried out from −40 to 150°C using a tension‐compression mode. Results show that the composites, whose matrices are with 10 and 20 wt % PU, may possess better dynamic mechanical properties as compared with the other composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Melt‐electrospinning of poly(ethylene terephthalate) and polyalirate
Authors: Ogata Nobuo , Shimada Naoki , Yamaguchi Shinji , Nakane Koji , Ogihara Takashi 
Published: April 2007

AbstractRodlike polymer samples were made from three kinds of poly(ethylene terephthalate) (PET) pellets with different intrinsic viscosities (IV), and from polyalirate (Vectra) pellets. PET and Vectra fibers were produced using a melt‐electrospinning system equipped with a CO2‐laser melting device from these rodlike samples. The effects of IV value and laser output power on the fiber diameter of PET were investigated. Furthermore, the effect of the laser output power on the fiber diameter of Vectra was investigated. The crystal orientation of these produced fibers was also investigated by X‐ray photographs. The following conclusions were reached: (i) the diameter of PET fiber decreases with increasing laser output power; (ii) the minimum average diameter of PET fibers is scarcely influenced by the value of IV; (iii) the electrospun PET fibers show isotropic crystal orientation; (iv) fibers having an average fiber diameter smaller than 1 μm cannot be obtained from PET and Vectra using the system developed; and (v) preferred liquid crystal orientation can be seen in electrospun Vectra fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Bioinspired Nanodevice Based on the Folic Acid/Titanium Dioxide System
Authors: Gawęda Sylwia , Stochel Grażyna , Szaciłowski Konrad 
Published: April 2007

AbstractA new bioinspired nanomaterial has been obtained by chemisorption of folic acid onto nanocrystalline titanium dioxide. The organic chromophore is linked with the semiconductor surface via the glutamate chain and anchored with the carboxylate group. The geometry and electronic structure of the chromophore was studied in detail with DFT. Photoelectrochemical studies revealed photosensitization of the new material towards visible light. The photoelectrodes composed of the folic acid/titanium dioxide hybrid material generated photocurrent over a 300–600‐nm window. Moreover, the direction of the photocurrent could be changed from anodic to cathodic and vice versa by application of the appropriate photoelectrode potential. Photoelectrochemical and spectroscopic studies allowed the elucidation of the mechanism of photocurrent switching. Photoelectrodes composed of folate‐modified titanium dioxide may serve as a simple model of optoelectronic switches and may constitute the basis for molecular photoelectronic devices.
Nonstereogenic α‐aminoisobutyryl‐glycyl dipeptidyl unit nucleates type I′ β‐turn in linear peptides in aqueous solution
Authors: Masterson Larry R. , Etienne Marcus A. , Porcelli Fernando , Barany George , Hammer Robert P. , Veglia Gianluigi 
Published: April 2007

AbstractThe use of α,α‐disubstituted amino acids represents a valuable strategy to exercise conformational control in peptides. Incorporation of the nonstereogenic α‐aminoisobutyryl‐glycyl (Aib‐Gly) dipeptidyl sequence into i + 1 and i + 2 positions of an acyclic peptide sequence, originally designed and investigated by Gellman and coworkers, [H‐Arg‐Tyr‐Val‐Glu‐Val‐Yyy‐Xxx‐Orn‐Lys‐Ile‐Leu‐Gln‐NH2] nucleates a stable [2:4] left‐handed type I′ β‐turn in water. NMR spectra show that this newly designed β‐hairpin does not aggregate in water up to a concentration of ∼1 mM, and that its backbone conformation is superimposable on corresponding hairpins containing the DPro‐Gly (literature) and Aib‐DAla (this work) sequences. The Aib‐Gly turn‐inducer sequence eliminates complications because of cis–trans isomerization of Zzz‐Pro bonds, and constitutes an attractive alternative to the proteogenic Asn‐Gly and nonproteogenic DPro‐Gly motifs previously suggested as turn‐inducer sequences. These design principles could be exploited to prepare water‐soluble β‐hairpin peptides with robust structures and novel function. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 746–753, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Targeting protein–protein interactions: Lessons from p53/MDM2
Authors: Murray Justin K. , Gellman Samuel H. 
Published: April 2007

AbstractThe tremendous challenge of inhibiting therapeutically important protein–protein interactions has created the opportunity to extend traditional medicinal chemistry to a new class of targets and to explore nontraditional strategies. Here we review a widely studied system, the interaction between tumor suppressor p53 and its natural antagonist MDM2, for which both traditional and nontraditional approaches have been reported. This system has been a testing ground for novel proteomimetic scaffold‐based strategies, i.e., for attempts to mimic the recognition surface displayed by a folded protein with unnatural oligomers. Retroinverso peptides, peptoids, terphenyls, β‐hairpins, p‐oligobenzamides, β‐peptides, and miniproteins have all been explored as inhibitors of the p53/MDM2 interaction, and we focus on these oligomer‐based efforts. Traditional approaches have been successful as well, and we briefly review small molecule inhibitors along with other strategies for reactivation of the p53 pathway, for comparison with oligomer‐ based approaches. We close with comments on an emerging dichotomy among protein–protein interaction targets. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 657–686, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Functional genome‐wide analysis of antibody producing NS0 cell line cultivated at different temperatures
Authors: Swiderek Halina , Al‐Rubeai Mohamed 
Published: April 2007

AbstractLowering culture temperature has been reported as a significant factor in the improvement of mammalian cell productivity. To determine the physiological changes which take place at different temperature cultivations, an NS0 cell line producing human‐mouse chimeric antibody was cultured at 22, 34 and 37°C. Various cellular parameters such as viability, productivity, metabolism, apoptosis and cell cycle were studied and notable changes were shown to be accompanied by changes in metabolic rates. Reduction of the temperature to 22°C resulted in a decrease in the growth rate, inhibition of antibody production, arrest of cell cycle in G2 phase and delay in apoptosis. A slight increase in antibody production was observed at 34°C due to the increase of growth rate and prolonged stationary phase. To better understand and explore the mechanisms underpinning these biological alterations and to identify the genes involved in the genetic reprogramming, genome‐wide analyses were performed using GeneChip Mouse Genome arrays. The examination of differential gene expression induced by temperature reduction demonstrated a specific pattern of gene expression in NS0 cells in response to temperature stress. The effect of temperature on transcription induced changes within a wide range of genes involved in metabolic and signalling pathways. Most deregulated genes involved in essential metabolic pathways (i.e. glycolysis/gluconeogenesis, pentose phosphate pathway and inositol metabolism) were repressed in cells cultured at 22°C. By combining gene expression and physiological changes at different temperatures it was possible to provide greater understanding of cell response to hypothermic conditions. Biotechnol. Bioeng. 2007;98: 616–630. © 2007 Wiley Periodicals, Inc.
Structure and shear strength of microbial biofilms as determined with confocal laser scanning microscopy and fluid dynamic gauging using a novel rotating disc biofilm reactor
Authors: Möhle Roland B. , Langemann Timo , Haesner Marian , Augustin Wolfgang , Scholl Stephan , Neu Thomas R. , Hempel Dietmar C. , Horn Harald 
Published: April 2007

AbstractThe cohesive strength of microbial biofilms cultivated on a rotating disc has been measured using fluid dynamic gauging (FDG). The thickness of heterotrophic mixed culture biofilms was found to depend on substrate concentration and shear force at the biofilm surface during the cultivation. For high substrate concentrations and low shear forces the biofilm thickness increased to several 100 µm within 7 days. Low substrate concentration and higher shear forces yielded thin biofilms of about 100 µm thickness. Independent from cultivation conditions and thickness of the biofilms their cohesive strength ranged between 6.0 and 7.7 N m−2. The ratio between cohesive strength measured with FDG and shear forces applied during biofilm cultivation have ranged from 200 to 1,100. Higher concentrations of iron in the cultivation media has a positive effect on the stability of the biofilms cultivated. By using the CLSM technique a stable base biofilm with a high amount of stained EPS glycoconjugates could be visualized after gauging. The thickness of the base biofilm was about 100 µm for all biofilms cultivated and was not removable under the applied shear conditions used during FDG. Biotechnol. Bioeng. 2007;98: 747–755. © 2007 Wiley Periodicals, Inc.
Optimal fed‐batch cultivation when mass transfer becomes limiting
Authors: Villadsen John , Patil Kiran R. 
Published: April 2007

AbstractIn the design of an aerobic fed‐batch process to produce, for example, a pharmaceutical protein, the volumetric production rate will eventually become limited by mass transfer when the biomass concentration exceeds a certain upper limit x*. It appears to be common practice to switch from exponential feed of substrate to a constant feed rate when x* is reached. This is done to avoid oxygen starvation with a potential risk of undesired stress responses. But with a constant feed rate the carbon source (glucose) concentration may decrease to a low level with a resulting loss of viability and an undesired production of endotoxins. It is shown that an exponential feeding strategy may be continued, but with a smaller exponent than the one used before oxygen limitation occurs. This will diminish the potential detrimental effects on the culture due to low glucose concentration, and the total time to reach a given final biomass concentration will be reduced. Biotechnol. Bioeng. 2007;98: 706–710. © 2007 Wiley Periodicals, Inc.