bluuebunny/crossref_metadata_2025_split huggingface dataset:
New coordination polymers. III: Oxidation of poly(vinyl alcohol) by permanganate ion in alkaline solutions. Kinetics and mechanism of formation of intermediate complex with a spectrophotometric detection of manganate(vi) transient species
Authors: Hassan Refat M. 
Published: April 2007

AbstractThe kinetics of formation of the [PVA. MnVIO] intermediate complex have been measured by the conventional spectrophotometric technique. The rate of formation of the complex was found to be given by the expression d[Complex]/dt = k1[MnO‐4][PVA−]. The results showed that the rate of formation is dependent on the base concentration. A first‐order reaction in permanganate and fractional order with respect to the poly(vinyl alcohol) (PVA) concentration were observed. The activation parameters have been evaluated and a tentative reaction mechanism has been suggested.
Anionic polymerization of methyl methacrylate initiated by thiophenol
Authors: Takeishi Makoto , Iwasaki Norikazu , Sone Atsushi , Chisaka Yuichi , Sekiya Kenichi , Sato Rikiya 
Published: April 2007

AbstractMethyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non‐radical process. Since other monomers with an x,β‐unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1‐diphenyl‐2‐picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol‐initiated polymerization supporting the postulated mechanism.
Poly(methyl methacrylate) and polyacrylonitrile dispersions stabilized by gelatin
Authors: Stejskal Jaroslav , Kratochvíl Pavel , Urban Josef , Kapur G. S. , Lakshminarayana Y. 
Published: April 2007

AbstractMethyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, MwD ∼ 108‐109 g mol−1) and hydrodynamic radius (RhD ∼ 50‐120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size.Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles.
Fractional composition of partly hydrolysed polyvinyl acetate and its compatibility with hydroxypropyl methylcellulose in aqueous solutions
Authors: Zilberman E. N. , Lerner F. , Joseph H. M. , Grossman D. , Alon M. 
Published: April 2007

AbstractFractionation of partly hydrolysed polyvinyl acetate (PVA) was performed by warming of its aqueous solutions. The following properties of the obtained fractions were determined: viscosity, molecular weight and molecular weight distribution, surface tension, and absorbance in the IR range. The blockiness of the polymer molecules, characterized by their behaviour towards iodine‐containing systems such as I2,‐H3BO3 and I2,‐KI, was estimated. Fractionation of the aqueous solutions of PVA by warming is based mainly on the different internal molecular structure of the separated products, i.e. on the length of the vinyl acetate blocks in the PVA molecules and, to a lesser extent, on the degree of hydrolysis and the degree of polymerization. The more blocklike are the PVA molecules, the less compatible are the polymers in the PVA‐hydroxypropyl methylcellulose (HPMC)‐water system. At phase separation in this sytem the PVA molecules which are not compatible with HPMC are, in the first place, those of the highest blockiness.
Separation characteristics of pervaporation membrane separation processes using modified poly(vinyl alcohol) membranes
Authors: Huang R. Y. M. , Rhim J. W. 
Published: April 2007

AbstractModified poly(vinyl alcohol) (PVA) membranes prepared by the ‘solution technique’ were tested for ethanol‐water mixtures by varying the reaction density (Xcr = 0.05, 0.1) at various temperatures. The results are compared with those of PVA membranes (Xcr = 0.05) prepared by the technique of the GFT Company, Germany.
Modification of poly(vinyl alcohol) using maleic acid and its application to the separation of acetic acid‐water mixtures by the pervaporation technique
Authors: Huang R. Y. M. , Rhim J. W. 
Published: April 2007

AbstractThe ‘solution technique’ modification of poly(vinyl alcohol) (PVA) using maleic acid was carried out with the help of triethanolamine/water catalysts. The resulting PVA membranes were characterized by differential scanning calorimetry, infrared spectroscopy, and tensile studies to investigate the reaction between PVA polymer and maleic acid. It was found that the resulting PVA membranes had two portions, branched and crosslinked, and there were no more branched than cross‐linked portions. For the pervaporation separation of the acetic acid‐water system, two reaction densities (Xcr = mole maleic acid per mole monomeric unit of PVA) of 0.05 and 0.1 were studied for the separation of the entire range of mixture compositions at 25° C. The separation factors of the Xcr = 0.05 modified PVA membranes were higher than those of the Xcr 0.1 modified ones and the highest separation factor of 7.80 was obtained at 70wt% water in the feed with the Xcr = 0.05 modified PVA membrane.
Toward reduced bias and increased utility in the assessment of school refusal behavior: The case for diverse samples and evaluations of context
Authors: Lyon Aaron R. , Cotler Sheldon 
Published: April 2007

AbstractThe current article reviews the literature on school refusal behavior. Definitional inconsistencies, the effects of biased assessment processes, and the consequences of the lack of ethnic, racial, and economic diversity in school refusal research samples are highlighted. An increase in the use of low‐income, ethnic minority, community samples in school refusal research is proposed in order to create a more representative and useful literature. Concerns regarding artificial and impractical divisions between the commonly used labels of school refusal and truancy are also discussed. Suggestions are proposed for a new pragmatic framework of school refusal assessment for research and clinical work that utilizes and enhances Kearney's functional approach. The framework has the potential to incorporate the influences of multiple cultural contexts in order to aid professionals from different disciplines in both prevention and early intervention for school refusal in low‐income, ethnic minority populations. Additional suggestions for future direction in school refusal research are also discussed. © 2007 Wiley Periodicals, Inc.
The controlled homogeneous organic solution polymerization of new hydrophilic cationic exo‐7‐oxanorbornenes via ROMP with RuCl2(PCy3)2CHPh in a novel 2,2,2‐trifluoroethanol/methylenechloride solvent mixture
Authors: Rankin David A. , P'Pool Steven J. , Schanz Hans‐Jörg , Lowe Andrew B. 
Published: April 2007

AbstractThe authors detail herein the synthesis and controlled polymerization of a series of new permanently cationic ammonium exo‐7‐oxanorbornene derivatives via ROMP, with the first generation Grubbs' catalyst RuCl2(PCy3)2CHPh, in a novel solvent mixture composed of 1:1 vol/vol 2,2,2‐trifluoroethanol (TFE)/methylene chloride. It is demonstrated that this cosolvent mixture is a convenient reaction medium facilitating the polymerization of hydrophilic substrates by hydrophobic initiators under homogeneous conditions. Homopolymerizations and copolymerizations proceed yielding materials with controlled molecular masses, and narrow molecular mass distributions. It is also demonstrated that this protocol is not limited to the use of TFE as a cosolvent and that additional halogenated alcohols, such as 2,2,2‐trichloroethanol and 1,1,1,3,3,3‐hexafluoroisopropanol are also effective cosolvents for the controlled polymerization of such cationic substrates. Finally, it is demonstrated that the TFE/methylene chloride mixture has no apparent detrimental effect on Grubbs' catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2113–2128, 2007
Rheological behavior of PET/HDPE in situ microfibrillar blends: Influence of microfibrils' flexibility
Authors: Xu Hong‐Sheng , Li Zhong‐Ming , Wang Song‐Jie , Yang Ming‐Bo 
Published: April 2007

AbstractPoly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) in situ microfibrillar reinforced blends were prepared via a slit die extrusion‐hot stretch‐quenching process. The in situ PET microfibrils contain various contents of a segmented thermoplastic elastomer, Hytrel 5526 (HT), hence having different flexibility as demonstrated by dynamic mechanical analysis. It is interesting that the simple mixing leads to nanoscale particles of the HT phase in PET phase, and the size of the HT particles is almost independent of the HT concentration, as observed from the scanning electron microscope micrographs which show that the microfibrils with different HT concentrations have almost the same diameter and smooth surfaces. The static rheological results by an advanced capillary rheometer show that the entrance pressure drop and the viscosity of the microfibrillar blends both reduced with increasing the microfibrils' flexibility. Furthermore, the data obtained by the temperature scan of the PET/HT/HDPE microfibrillar blends through a dynamic rheometer indicates that the more flexible microfibril leads to lower melt elasticity and slightly decreases the viscosities of blends, presenting a consistent conclusion about influences of the microfibrils' flexibility on the rheological behavior from the static rheometer measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1205–1216, 2007
Superantigen natural affinity maturation revealed by the crystal structure of staphylococcal enterotoxin G and its binding to T‐cell receptor Vβ8.2
Authors: Fernández Marisa M. , Bhattacharya Suparna , De Marzi Mauricio C. , Brown Patrick H. , Kerzic Melissa , Schuck Peter , Mariuzza Roy A. , Malchiodi Emilio L. 
Published: April 2007

AbstractThe illnesses associated with bacterial superantigens (SAgs) such as food poisoning and toxic shock syndrome, as well as the emerging threat of purpura fulminans and community‐associated methicillin‐resistant S. aureus producer of SAgs, emphasize the importance of a better characterization of SAg binding to their natural ligands, which would allow the development of drugs or biological reagents able to neutralize their action. SAgs are toxins that bind major histocompatibility complex class II molecules (MHC‐II) and T‐cell receptors (TCR), in a nonconventional manner, inducing T‐cell activation that leads to production of cytokines such as tumor necrosis factor and interleukin‐2, which may result in acute toxic shock. Previously, we cloned and expressed a new natural variant of staphylococcal enterotoxin G (SEG) and evaluated its ability to stimulate in vivo murine T‐cell subpopulations. We found an early, strong, and widespread stimulation of mouse Vβ8.2 T‐cells when compared with other SAgs member of the SEB subfamily. In search for the reason of the strong mitogenic potency, we determined the SEG crystal structure by X‐ray crystallography to 2.2 Å resolution and analyzed SEG binding to mVβ8.2 and MHC‐II. Calorimetry and SPR analysis showed that SEG has an affinity for mVβ8.2 40 to 100‐fold higher than that reported for other members of SEB subfamily, and the highest reported for a wild type SAg‐TCR couple. We also found that mutations introduced in mVβ8.2 to produce a high affinity mutant for other members of the SEB subfamily do not greatly affect binding to SEG. Crystallographic analysis and docking into mVβ8.2 in complex with SEB, SEC3, and SPEA showed that the deletions and substitution of key amino acids remodeled the putative surface of the mVβ8.2 binding site without affecting the binding to MHC‐II. This results in a SAg with improved binding to its natural ligands, which may confer a possible evolutionary advantage for bacterial strains expressing SEG. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Computational proteomics analysis of HIV‐1 protease interactome
Authors: Kontijevskis Aleksejs , Wikberg Jarl E. S. , Komorowski Jan 
Published: April 2007

AbstractHIV‐1 protease is a small homodimeric enzyme that ensures maturation of HIV virions by cleaving the viral precursor Gag and Gag‐Pol polyproteins into structural and functional elements. The cleavage sites in the viral polyproteins share neither sequence homology nor binding motif and the specificity of the HIV‐1 protease is therefore only partially understood. Using an extensive data set collected from 16 years of HIV proteome research we have here created a general and predictive rule‐based model for HIV‐1 protease specificity based on rough sets. We demonstrate that HIV‐1 protease specificity is much more complex than previously anticipated, which cannot be defined based solely on the amino acids at the substrate's scissile bond or by any other single substrate amino acid position only. Our results show that the combination of at least three particular amino acids is needed in the substrate for a cleavage event to occur. Only by combining and analyzing massive amounts of HIV proteome data it was possible to discover these novel and general patterns of physico‐chemical substrate cleavage determinants. Our study is an example how computational biology methods can advance the understanding of the viral interactomes. Proteins 2007. © 2007 Wiley‐Liss, Inc.
pcaH, a molecular marker for estimating the diversity of the protocatechuate‐degrading bacterial community in the soil environment
Authors: Azhari Najoi El , Chabaud Sylvaine , Percept Anthony , Bru David , Martin‐Laurent Fabrice 
Published: April 2007

AbstractMicroorganisms degrading phenolic compounds play an important role in soil carbon cycling as well as in pesticide degradation. The pcaH gene encoding a key ring‐cleaving enzyme of the β‐ketoadipate pathway was selected as a functional marker. Using a degenerate primer pair, pcaH fragments were cloned from two agricultural soils. Restriction fragment length polymorphism (RFLP) screening of 150 pcaH clones yielded 68 RFLP families. Comparison of 86 deduced amino acid sequences displayed 70% identity to known PcaH sequences. Phylogenetic analysis results in two major groups mainly related to PcaH sequences from Actinobacteria and Proteobacteria phyla. This confirms that the developed primer pair targets a wide diversity of pcaH sequences, thereby constituting a suitable molecular marker to estimate the response of the pca community to agricultural practices. Copyright © 2007 Society of Chemical Industry
Insecticide toxicity and synergism by enzyme inhibitors in 18 species of pest insect and natural enemies in crucifer vegetable crops
Authors: Wu Gang , Miyata Tadashi , Kang Chun Yu , Xie Lian Hui 
Published: April 2007

AbstractThe toxicities of three enzyme inhibitors and their synergistic effects on four insecticides were studied by using the dry film method on field populations of 18 species of insects collected in Jianxin and Shanjie, China, from 2003 to 2005. Meanwhile, the inhibitory effects of these enzyme inhibitors on the activities of acetylcholinesterases (AChE), carboxyesterases (CarE) and glutathione‐S‐transferases (GST), in vivo, were also studied. In general, triphenyl phosphate (TPP) and diethyl maleate (DEM) showed low toxicities to six herbivorous pest insects, four ladybirds and eight parasitoids. Piperonyl butoxide (PB) exhibited low toxicities to the herbivorous pest insects and ladybirds, but high toxicities to the eight parasitoids. The tolerance to the insecticides in 11 pest insects and natural enemies was mainly associated with the tolerance to PB. PB showed the highest synergism on methamidophos, fenvalerate, fipronil and avermectin in nine species of pest insects and natural enemies. In general, TPP and DEM showed significant synergisms to these four insecticides in four parasitoid species. However, in contrast to their effects on the parasitoids, the synergistic effects of TPP and DEM on the four insecticides by TPP and DEM against four pest insects and one ladybird varied depending on the insect species and enzyme inhibitor. Activity of AChE, CarE or GST could be strongly inhibited, in vivo, by PB, TPP or DEM, depending on the insect species and enzyme inhibitors. From the results obtained in this study, mixed‐function oxidase (MFO) was thought to play the most critical role in insect tolerances to the tested insecticides in the field. Low competition existed in the evolution of insecticide resistance in the field populations of parasitoids, as compared with herbivorous pest insects and ladybirds. Possible causes of the high synergistic effects of PB on the four classes of insecticides, based on multiattack on the activity of CarE, GST or AChE in the insect species, are also discussed. Copyright © 2007 Society of Chemical Industry
Effect of Bt cotton expressing Cry1Ac and Cry2Ab, non‐Bt cotton and starvation on survival and development of Trichoplusia ni (Lepidoptera: Noctuidae)
Authors: Li Yuan‐Xi , Greenberg Shoil M , Liu Tong‐Xian 
Published: April 2007

AbstractEffects of Bollgard II® cotton containing two Bacillus thuringensis var. kurstaki Berliner (Bt) toxin proteins (Cry1Ac and Cry2Ab), non‐Bt cotton (DPL 491) and starvation on survival and development of cabbage looper, Trichoplusia ni (Hübner), were determined in the laboratory. Larvae of the first four larval instars died when they fed on the terminal leaves of Bt cotton plants at 50 days after planting (DAP). However, 51.3% of fifth instars that fed on 50 DAP Bt cotton leaves pupated, and 87.1% of the pupae successfully developed into adults. Of the unfed fifth instars (starved), 55.6% pupated and 88.1% of the pupae emerged. Pupae that developed from larvae fed on Bt cotton leaves and unfed were significantly smaller, being 89.7 and 73.2% of the weight of the pupae that developed from larvae fed on non‐Bt cotton leaves. Leaves of 120 DAP Bt cotton were less toxic to T. ni larvae. When the first instars continuously fed on 120 DAP Bt cotton leaves, 75.9, 60.6, 56.4 and 38.4% of larvae survived to second, third, fourth and fifth instars respectively, and 20.9% pupated and 17.9% successfully became adults. However, it took the surviving first instars 37.1 days to become adults, which was 7.2 and 8.9 days longer than those fed on 50 and 120 DAP non‐Bt cottons respectively. Pupae that developed from larvae that fed on 120 DAP Bt cotton leaves were only 50.9 and 52.6% of the weight of those developed from larvae that fed on 50 and 120 DAP non‐Bt cotton respectively. Non‐Bt cotton, both 50 and 120 DAP, did not exhibit significant effects on larval survival and development, except that the pupae in the 50 DAP non‐Bt cotton treatments developed over a significantly longer time than those in the 120 DAP non‐Bt cotton treatment. Copyright © 2007 Society of Chemical Industry
High temperature electrical conductivity in ZnSe:In and in CdSe:In under selenium vapor pressure
Authors: Lott K. , Shinkarenko S. , Volobujeva O. , Türn L. , Nirk T. , Öpik A. , Nisumaa R. , Kallavus U. , Nõges M. , Mikli V. , Viljus M. , Gorokhova E. , Anan'eva G. , Grebennik A. , Vishnjakov A. 
Published: April 2007

AbstractHigh temperature electrical conductivity (HTEC) isotherms and isobars of ZnSe:In and of CdSe:In are compared. There are differencies in In‐doping mechanisms of II–VI compounds. When HTEC isotherms and isobars of ZnSe:In and of CdSe:In, measured under metal component vapour pressure give both n‐type conductivity then differences appear in the results of measurements under the selenium vapor pressure (p). ZnSe:In isotherms in the last case are characterized by the conductivity type conversion but no such drastic change of HTEC type is observed on CdSe:In isotherms. Under the conditions of p, the activation energy of HTEC isobars for ZnSe:In is ΔE ≈ 1.3–1.6 eV and for CdSe:In is ΔE ≈ 1.2 eV. The onefold ionized substitutional In at Zn place is proposed to be compensated by native defects in ZnS:In and in CdSe:In under high p. This native defect may be onefold ionized zinc vacancy for ZnSe:In and twofold ionized cadmium vacancy for CdSe:In. Association of defects occur at lower temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical characterization of He+ irradiated n‐ZnO
Authors: Hayes M. , Auret F. D. , Janse van Rensburg P. J. , Nel J. M. , Wesch W. , Wendler E. 
Published: April 2007

AbstractZnO Schottky barrier diodes (SBD's) were fabricated with 20/80/40/80 nm Ti/Al/Pt/Au ohmic contacts on the O face and circular 0.5 mm in diameter 50 nm thick Ru Schottky contacts in the Zn face. The carrier concentration of the ZnO prior to irradiation was approximately 5 × 1016 cm−3. These diodes were irradiated with 1.8 MeV He+ with fluences ranging from 1 × 1012 cm−2 to 2 × 1013 cm−2. Deep level transient spectroscopy (DLTS) was used to study the defects introduced. These measurements revealed that this irradiation introduced a defect with an energy level at 0.55 eV below the conduction band. The introduction rate of this defect for 1.8 MeV He+ ions was calculated to be 220 ± 20 cm−1. This appears to be the same defect that is introduced during proton irradiation of ZnO. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of Fe doped SiC crystals
Authors: Kuryliszyn‐Kudelska I. , Diduszko R. , Tymicki E. , Dobrowolski W. , Grasza K. 
Published: April 2007

AbstractIn this paper we report on the crystal growth and magnetic as well as structural studies of SiC:Fe. SiC crystals were grown by Physical Vapor Transport method. We used Fe enriched source material to dope crystals. The magnetic properties were examined by AC/DC magnetometry. AC magnetic susceptibility as well as DC magnetization measurements revealed ferromagnetic type of magnetic ordering. The structural measurements using powder X‐ray diffraction were performed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)