bluuebunny/crossref_metadata_2025_split huggingface dataset:
Networks in nature
Authors: Burchard Walther 
Published: April 2007

AbstractSynthetic networks, their structure and mechanical properties have been studied since the beginning of polymer science, while the considerable variety of networks in nature has been largely neglected, though use has been made of them as long as human culture has existed. In principle synthetic and natural networks are equivalent, but there are significant differences.(1) The main difference consists in the high polarity of the polymeric components and the related capability of binding large quantities of water. (2) The biosynthesis of covalently linked, macroscopic networks is rare and often too slow a process. In many cases the networks are formed via physical forces between various polymeric components. (3) Often the network formation can be reversed by changing the temperature, or pH, or by adding urea or detergents. (4) The viscoelastic behaviour is often governed by the rigidity of the macromolecular substructures.Examples are given for reversible gels with some charged polysaccharides and with fibrin. Special interactions are demonstrated with the network of connective tissue. The important role of comb‐like macromolecules with protein backbone and polysaccharide side chains is outlined. Special interactions are crucial also for immunologic response, i.e. for cell recognition and antibody‐antigen complex formation. The latter is one of the best examples of a successful application of the Flory‐Stockmayer theory of branching and gelation. Most of the reversible gels are not yet fully understood in their properties, and theory is lacking. This is particularly true for products like gelatin and starch.
Gelation of pectinic acids in the presence of calcium counterions
Authors: Thibault Jean‐Francois , Rinaudo Marguerite 
Published: April 2007

AbstractPectins are polysaccharides which are able to gel in the presence of calcium ions if their degree of esterification is lower than 40%. From a purified pectin, a de‐esterification was carried out by alkali and by enzymes in order to obtain samples with a different charge density and esterification pattern (random or blockwise distribution of carboxylic acid sites). The pectin‐calcium interactions were studied in a dilute solution of calcium pectinates by conductimetry. If the concentration of highly charged polymer is increased, a multichain association can occur: the same process is observed with dilute solutions (cp≤10‐3 eq. 1−1) but in the presence of an excess of calcium ions. This first step of the gelation was followed by light scattering and by viscometry. The gelling system can be described by a power law including a critical ratio (equivalent concentration of calcium ions/pectin carboxylic sites) and quasi‐critical exponents. The values of these critical parameters have been discussed as a function of charge density of the pectins, their esterification pattern, their concentration, and the nature of the divalent counterion.
Electro‐copolymerisation of indene and styrene
Authors: Toppare Levent , Eren Sami , Akbulut Ural 
Published: April 2007

AbstractElectroinitiated cationic copolymerisation of indene and styrene was investigated by constant potential electrolysis. Effects of copolymerisation potential and temperature on the copolymer composition and the reactivity ratios are discussed. The reactivity ratios of the monomers were calculated according to the integrated Lewis‐Mayo equation.
The thermo‐softening process of SBS thermoplastic rubber
Authors: Birley Arthur W. , Canevarolo Sebastiäo V. , Hemsley Derek A. 
Published: April 2007

AbstractThis paper discusses the thermo‐softening process of a triblock copolymer of styrene‐butadiene‐styrene. The specific volume vs temperature curve shows an anomalous expansion above ∼ 165°C, compared with a theoretical curve obtained from applying the simple law of mixtures to the pure components. The amount of crosslinking developed in the copolymer in terms of its gel content is found to increase suddenly, starting from 200°C and being fully developed at 230°C. Form birefringence vs temperature curves obtained during temperature cycling tests, show that a rearrangement takes place in the imperfect original domain structure above 145°C. This significantly increases the birefringence at room temperature. There is a maximum value of birefringence which is not destroyed even when the sample is heated up as high as 290°C. Dynamic mechanical thermo‐analysis shows a large broad peak for the tan δ in the studied region due to this rearrangement. The processes involved are, in general, irreversible although the specific volume vs temperature curve below 150°C is reproducible.
QM polymers and other products derived from parabola vermiculite
Authors: Currell Brian R. , Hayes Peter R. , Midgley Henry G. , Parsonage John R. 
Published: April 2007

AbstractThe trimethylsilylation of parabola vermiculite gives polyorganosiloxanes of the structure QxMy. (Q = SiO42: M = ((CH3)SiO12) which will form gels in a wide range of organic solvents and resins. No other mineral has so far been reported to yield trimethylsilylated products capable of forming gels. The effect on the nature and yields of these QM polyorganosiloxanes' of variation in reaction time, particle size and vermiculite/hexamethyldisiloxane ratio have been investigated. The QM polyorganosiloxanes produced are hydrophobic insoluble powders which gel in a wide range of organic solvents. Reaction with NaOH/EtOH mixtures gives ‘silicone‐silicate’ hybrids by replacement of trimethylsilyl groups with sodium ions. i.e. ‘QMNa’ products. The ability of these products to form films is compared to that of parabola vermiculite itself and also acid‐leached vermiculite. QM polyorganosiloxanes give films which can either be peeled off as an integral film or, after heating on a glass slide at 50°C. will give a hard hydrophobic surface. Preliminary investigation has also shown that QM polymers can be used as fillers in epoxy resins.
Further studies of polycarbonate‐poly(butylene terephthalate) blends
Authors: Birley Arthur W. , Chen Xin Yue 
Published: April 2007

AbstractThe mechanical properties (tensile strength, low temperature falling weight impact strength) of XENOY CL‐100 (a blend of polycarbonate and polybutylene terephthalate) have been studied. This blend is comprised of tough components and the property combinations that result may be useful for certain applications. The hydrolysis resistance of the blend in deionised water at 40°C has been studied. After 30 weeks it did not lose its tensile strength, but subsequently it did lose 50% of the low temperature (−70°C) falling weight impact strength. If the −70°C low temperature toughness is an important quality, this should be taken into account. However, the low temperature (−70°C) falling weight impact strength of pure polycarbonate and of pure poly(butylene terephthalate) is very low, whilst XENOY CL‐100 is still tough material, even after 30 weeks immersion at 40°C. Further study of the composition of XENOY CL‐100 showed that this blend is composed of polycarbonate. poly(butylene terephthalate) and crosslinked acrylic rubber; traces of titanium‐catalyst residue for the poly(butylene terephthalate) polymeristaion and black dye have also been found.
Molecular weights of poly(butyl 2‐cyanoacrylate) produced during nanoparticle formation
Authors: Douglas S. J. , Davis S. S. , Holding S. R. 
Published: April 2007

AbstractThe molecular weights and distributions of poly(buty1 2‐cyanoacrylate) produced during the formation of nanoparticles under a range of polymerisation conditions have been determined by gel permeation chromatography. The data indicate that the type of steric stabiliser and concentration of the monomer added to the polymerisation medium influences the resulting molecular weight of the polymer. In all systems the bulk of the polymer had a low molecular weight (<10000) but nanoparticles stabilised with dextrans or poloxamer 188 also yielded a high molecular weight component (>20000). The results are interpreted with regard to the possible effects on the degradation of nanoparticles and their drug release characteristics. Tentative proposals are made concerning the mechanisms of nanoparticle formation.
Thermal degradation of cinnamoylated poly(vinyl alcohol)
Authors: Caşcaval C. N. , Buruianǎ E. C. , Roşu D. , Rusu E. , Grigoriu G. E. , Bârboiu V. 
Published: April 2007

AbstractThermogravimetry and pyrolysis in combination with gas chromatography and infrared spectroscopy were the experimental techniques applied to the thermal degradation of cinnamoylated poly(vinyl alcohol) samples, constituted from vinyl alcohol‐vinyl cinnamate photocrosslinkable copolymers. The thermal decomposition products include gases, liquids and solids. The gases are formed from saturated and unsaturated volatile hydrocarbons C1C4, carbon monoxide and carbon dioxide. The liquid fraction includes aromatic hydrocarbons and some oxygenated organic compounds. The solid product identified in the greatest amount was cinnamic acid. The content in the thermal decomposition products varies considerably both with copolymer composition and temperature.
Resonance raman spectroscopy of polydiacetylene langmuir‐blodgett films
Authors: Lyall Iain R. J. , Batchelder David N. 
Published: April 2007

AbstractResonance Raman excitation profiles of two vibrational modes have been measured for Langmuir‐Blodgett films of a polydiacetylene. The polymer films were formed by exposing multilayer samples of the Cd salt of 10,12‐pentacosadiynoic acid to ultraviolet radiation. Raman spectra were measured for incident laser photon energies between 1.85 and 2.20 eV (670‐564 nm), the region over which the films exhibited optical absorption associated with an electronic transition of the π‐electrons on the conjugated backbone. The excitation profiles have been used to determine both the strength of the vibronic coupling and the differences in vibrational frequency between the ground and excited states. The results are in reasonable agreement with those obtained previously for polydiacetylene single crystals.
The Use of Dynamic Mechanical Methods to Study the Effect of Absorbed Water on Temperature‐dependent Properties of an Epoxy Resin‐Carbon Fibre Composite
Authors: Barton J. M. , Greenfield D. C. L. 
Published: April 2007

AbstractDynamic mechanical methods were used to study the effect of absorbed moisture on the properties of an epoxy resin matrix CFRP. The glass transition temperature (Tg)of the matrix resin, determined as the onset of the characteristic fall in dynamic modulus with increasing temperature, was found to decrease with increasing moisture content. Maximum shifts in Tg of 80 to 90°C, relative to the dry material, were observed for a resin moisture content of 5.2% by weight. The effects of sample geometry, fibre orientation, and frequency of oscillation, on the dynamic mechanical properties are discussed. Results are given of an analysis of the observed dependence of Tg on water content using two theoretical models.
Group A streptococcus cell‐associated pathogenic proteins as revealed by growth in hyaluronic acid‐enriched media
Authors: Zhang Meng , McDonald Fiona M. , Sturrock Shane S. , Charnock Simon J. , Humphery‐Smith Ian , Black Gary W. 
Published: April 2007

AbstractGroup A streptococcus (GAS), also know as Streptococcus pyogenes, is a human pathogen and can cause several fatal invasive diseases such as necrotising fasciitis, the so‐called flesh‐eating disease, and toxic shock syndrome. The destruction of connective tissue and the hyaluronic acid (HA) therein, is a key element of GAS pathogenesis. We therefore propagated GAS in HA‐enriched growth media in an attempt to create a simple biological system that could reflect some elements of GAS pathogenesis. Our results show that several recognised virulence factors were up‐regulated in HA‐enriched media, including the M1 protein, a collagen‐like surface protein and the glycolytic enzyme glyceraldehyde‐3‐phosphate dehydrogenase, which has been shown to play important roles in streptococcal pathogenesis. Interestingly, two hypothetical proteins of unknown function were also up‐regulated and detailed bioinformatics analysis showed that at least one of these hypothetical proteins is likely to be involved in pathogenesis. It was therefore concluded that this simple biological system provided a valuable tool for the identification of potential GAS virulence factors.
Proteome and phosphoproteome dynamic change during cell dedifferentiation in Arabidopsis
Authors: Chitteti Brahmananda Reddy , Peng Zhaohua 
Published: April 2007

AbstractCell dedifferentiation is a cell fate switching process in which a differentiated cell reverts to a status with competence for cell division and organ regeneration like an embryonic stem cell. Although the phenomenon of cell dedifferentiation has been known for over two and a half centuries in plants, little is known of the underlying mechanisms. Here, we have established the proteome map of Arabidopsis cotyledons and investigated the dynamic change of the cotyledon proteome in the time course of cell dedifferentiation. Among the 353 distinct genes, corresponding to 500 2‐DE gel protein spots identified with high confidence, 12% have over twofold differential regulations within the first 48 h of induction of cell dedifferentiation. The distributions of these genes among different Gene Ontology categories and gene differential regulations within each of the categories have been examined. In addition, we have investigated the cotyledon phosphoproteome using Pro‐Q Diamond Phosphoprotein in Gel Stain followed by mass spectrometry analyses. Among the 53 identified putative phosphoproteins, nine are differentially regulated during cell dedifferentiation. These studies have provided significant new insight into protein and phosphoprotein differential expression during cell dedifferentiation in plants.
Proteomic analysis of roots growth and metabolic changes under phosphorus deficit in maize (Zea mays L.) plants
Authors: Li Kunpeng , Xu Changzheng , Zhang Kewei , Yang Aifang , Zhang Juren 
Published: April 2007

AbstractPhosphorus (P) deficiency is a major limitation for plant growth and development. Plants can respond defensively to this stress, modifying their metabolic pathways and root morphology, and this involves changes in their gene expression. To better understand the low P adaptive mechanism of crops, we conducted the comparative proteome analysis for proteins isolated from maize roots treated with 1000 μM (control) or 5 μM KH2PO4 for 17 days. The results showed that approximately 20% of detected proteins on 2‐DE gels were increased or decreased by two‐fold or more under phosphate (Pi) stress. We identified 106 differentially expressed proteins by MALDI‐TOF MS. Analysis of these P starvation responsive proteins suggested that they were involved in phytohormone biosynthesis, carbon and energy metabolisms, protein synthesis and fate, signal transduction, cell cycle, cellular organization, defense, secondary metabolism, etc. It could be concluded that they may play important roles in sensing the change of external Pi concentration and regulating complex adaptation activities for Pi deprivation to facilitate P homeostasis. Simultaneously, as a basic platform, the results would also be useful for the further characterization of gene function in plant P nutrition.
Transcriptome and proteome analyses in response to 2‐methylhydroquinone and 6‐brom‐2‐vinyl‐chroman‐4‐on reveal different degradation systems involved in the catabolism of aromatic compounds in Bacillus subtilis
Authors: Van Duy Nguyen , Wolf Carmen , Mäder Ulrike , Lalk Michael , Langer Peter , Lindequist Ulrike , Hecker Michael , Antelmann Haike 
Published: April 2007

AbstractBacillus subtilis is exposed to a variety of antimicrobial compounds in the soil. In this paper, we report on the response of B. subtilis to the fungal‐related antimicrobials 6‐brom‐2‐vinyl‐chroman‐4‐on (chromanon) and 2‐methylhydroquinone (2‐MHQ) using proteome and transcriptome analyses. Chromanon, a derivative of aposphaerins from Aposphaeria species caused predominant protein damage in B. subtilis as indicated by the induction of the HrcA, CtsR, and Spx regulons. The expression profile of the ganomycin‐related substance 2‐MHQ was similar to that of catechol as reflected by the common induction of the thiol‐specific oxidative stress response. Several putative ring‐cleavage dioxygenases and oxidoreductases were differentially up‐regulated by 2‐MHQ, catechol, and chromanon including yfiDE, ydfNOP, yodED, ycnDE, yodC, and ykcA. The nitroreductase encoding yodC gene is induced in response to catechol, 2‐MHQ, and chromanon, which depend on the MarR‐type repressor YodB. The yfiDE (catDE) operon encodes a catechol‐2,3‐dioxygenase which is most strongly induced by catechol. The yodED (mhqED), ydfNOP (mhqNOP) operons, and ykcA (mhqA) respond most strongly to 2‐MHQ and encode putative hydroquinone‐specific extradiol dioxygenases. The ycnDE operon was most strongly induced by chromanon. Mutational analyses revealed that the putative hydroquinone‐specific dioxygenases MhqO and MhqA confer resistance to 2‐MHQ in B. subtilis.
Electronic and structural properties of biazulene, terazulene, and polyazulene isomers
Authors: Dias Jerry Ray 
Published: April 2007

AbstractFacile graph theoretical MO solutions are demonstrated. The dihedral angles between the azulene units at the bridging bond in biazulenes were determined by MM2 calculations. Polyazulenes are predicted to be conductive only via the polaron mechanism. Polaron conduction in 1,3‐ and 2,6‐polyazulene is qualitatively predicted to be more facile than in 4,8‐ and 5,7‐polyazulene. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and characterization of poly(L‐lactide)s and poly(D‐lactide)s of controlled molecular weight
Authors: Jalabert Matthieu , Fraschini Carole , Prud'homme Robert E. 
Published: April 2007

AbstractHigh molecular weight poly(L‐lactide)s (PLLAs) and poly(D‐lactide)s (PDLAs) were synthesized in toluene at 70 °C by ring‐opening polymerization of optically pure L‐lactide and D‐lactide, using tin(II) 2‐ethylhexanoate (SnOct2) and 2‐(2‐methoxyethoxy)ethanol as initiator and coinitiator, respectively. Under these conditions, polarimetry as well as 13C NMR spectroscopy indicated that the synthesized poly(lactide)s (PLAs) are more than 99% isotactic. The molecular weight was successfully controlled by adjusting the monomer‐to‐initiator molar ratio. Gel permeation chromatography and MALDI‐TOF mass spectrometry analyses showed that the polydispersity index of the PLAs is below 1.1. Moreover, MALDI‐TOF spectra showed two different chain distributions, one characterized by an even number of lactic acid repeat units and the other by an odd number of lactic acid repeat units. The second distribution, indicative of the presence of intermolecular transesterification reactions, appears at the very beginning of the polymerization and its intensity increases with the polymerization time. Finally, a reversible reaction kinetic model was used to determine the monomer equilibrium concentration ([M]eq = 1.4 ± 0.5%) and the propagation rate constant (kp = 14.4 ± 0.5 L mol−1 h−1) of the polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1944–1955, 2007
Effect of monomer structures and preparation methods on the morphology and properties of UV cured organic–inorganic hybrid films
Authors: Chang Chi‐Jung , Wu Maw‐Song , Kao Pei‐Chun 
Published: April 2007

AbstractThe effects of preparation methods and monomer chemical structures on the microstructure, morphology, and properties of the hybrid films were studied. 7DBPA‐3S was synthesized by the sol–gel reaction of precondensed silica particles with alkoxysilane‐modified polymers DBPA. DBP‐POBG3T3 was prepared by the radiation curing of comb‐like UV curable alkoxysilanes POBG3T3 with UV curable polymer DBP, followed by the sol–gel reaction of alkoxysilanes. The DBP‐POBG3T3 film consisted of polymer matrix and large tethered aggregates with tiny silica connected by organic chains. On the contrary, silica nanoparticles were well‐dispersed in the 7DBPA‐3S hybrid film. The TEM, energy dispersive X‐ray Si‐mapping and P‐mapping images are good experimental approaches to characterize the texture of the tethered aggregates. The 7DBPA‐3S hybrid composite with well‐dispersed silica nanoparticles exhibited smoother surface, higher transparency, and better thermal stability than the DBP‐POBG3T3 composite did. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1152–1165, 2007
Adaptive style and differences in parent and child report of health‐related quality of life in children with cancer
Authors: Jurbergs Nichole , Russell Kathryn M. W. , Long Alanna , Phipps Sean 
Published: April 2007

AbstractThe objective of this study was to examine the self‐reported health‐related quality of life (HRQL) of children with cancer, and the consistency between child and parent reports of child HRQL, as a function of the child's adaptive style. Participants included 199 children with cancer, 108 healthy children, and their parents. Children completed self‐report measures of HRQL and adaptive style. Measures of adaptive style were used to categorize children as high anxious, low anxious, defensive high anxious or repressor. Parents completed measures reporting their children's HRQL. Adaptive style was a significant predictor of child‐reported HRQL, particularly on the psychosocial scales, with children identified as repressors reporting the best HRQL. Adaptive style was also predictive of discrepancies between parent and child report of child HRQL. Repressor and low anxious children reported better HRQL than did their parents, while high anxious children reported poorer HRQL, regardless of health status. Adaptive style is a significant determinant of self‐reported HRQL in children, particularly in psychosocial domains, while health status (i.e. cancer patient vs healthy control) is predictive only of physical health domains. Researchers and clinicians should be aware of the impact of child adaptive style when assessing HRQL outcomes using self‐ or parent report. Copyright © 2007 John Wiley & Sons, Ltd.