bluuebunny/crossref_metadata_2025_split huggingface dataset:
Die energiereichsten kosmischen Teilchen. Ergebnisse des Pierre‐Auger‐Observatoriums
Authors: Blümer Johannes 
Published: June 2010

AbstractSeit Mitte 2008 ist das Pierre‐Auger‐Observatorium in Argentinien zur Beobachtung der kosmischen Strahlung bei höchsten Energien vollständig ausgebaut. Es hat erstmals ein solide kalibriertes Energiespektrum, eine Messung der Schauereigenschaften und Primärmassen sowie eine anisotrope Verteilung der Ankunftsrichtungen der Teilchen geliefert. So gibt es statistisch signifikante Hinweise darauf, dass Teilchen mit Energien von mehr als 1019 eV mit den Positionen von aktiven Galaxien korrelieren. Dennoch bleiben Fragen offen, die mit dem zukünftigen Observatorium Auger‐Nord beantwortet werden sollen.
Cleavages in stable tetrahedral intermediates' bonds and the role of water
Authors: Bethencourt Loengrid , Vivas Daniel , Núñez Oswaldo 
Published: June 2010

AbstractUsing two‐dimensional energy diagrams, results on the formation and cleavage of detectable tetrahedral intermediates are used to predict the position of transition states involved in the cleavages of unstable and stable tetrahedral intermediates (STI). A late transition state (anti‐Hammond) for the former and synchronous cleavage for the latter are predicted and supported with experimental results. For instance, in the case of STI, intrinsic leaving abilities in the order CO > CNHCO ≫ CNH were experimentally observed, confirming the departure of these groups without full heteroatom protonation. The STI designed herein mimics serine proteases enzymes due to the thermoneutral relationship between the enzyme substrate (ES) and enzyme‐acyl tetrahedral intermediate (EATI) analogs. In the STI models, a dramatic change in pKa is observed when changing the lactam ring size due to the strain in the 3‐fused‐ring system of the STI‐H2O complex formed and exo‐anomeric effect. A plot of ΔSo (STI formation) versus pKa provides evidence for the STI–water interaction. Since only one water molecule is required to produce the effect it is also detected when using ‘pure’ CDCl3 as the solvent and therefore may also play a role in the active sites of serine proteases. Copyright © 2010 John Wiley & Sons, Ltd.
Poly[N‐isopropyl acrylamide]‐co‐polyurethane copolymers for controlled release of urea
Authors: Mathews Anu Stella , Narine Suresh 
Published: July 2010

AbstractA novel block copolymer of poly[N‐isopropyl acrylamide]‐co‐polyurethane was designed, synthesized, and applied as controlled release fertilizer coating. Structural confirmation of the copolymer was performed using FTIR and 1H‐NMR spectra and elemental analysis. The coating process consists essentially of immersing urea granules in molten polymer and removing the coated urea from the melt by centrifugal action. The morphology of the coated urea was studied using scanning electron microscope (SEM). The polymer coat of the urea granules was found to swell in water forming pores and enabling the release of urea. The urea released from the granule, monitored using a mass spectroscopy technique, was found to be governed by pH of the aqueous medium. The study anticipates development of a beneficiary fertilizer coat in terms of improving controlled release over a period of time which can be tailored by soil temperature, pH and moisture. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3236–3243, 2010
Poly(lactic acid) brushes grow longer at lower temperatures
Authors: Xu Lebo , Gorman Christopher B. 
Published: July 2010

AbstractPoly(lactic acid) (PLA) brushes prepared by the ring opening of lactide were thicker when polymerized at a lower temperature (25 °C) than was typically used for polymerization in solution. The molecular weight of solution polymerized lactide was also higher when lactide was polymerized at 25 °C compared with polymerization at higher temperatures. However, the yield of PLA was low at this temperature. These results highlight the different requirements for solution polymerization and brush growth. In the former case, both percentage of conversion and molecular weight are important considerations. In the latter case, however, percentage of conversion is unimportant as a brush represents a very small amount of polymer. It was also shown during the course of these studies that the native hydroxy groups on silicon substrates and silanols in solution were equally good initiators when compared with hydroxy terminated self‐assembled monolayers on gold and alcohols, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3362–3367, 2010
The spectrophotometric study of a fluorescence‐enhanced inclusion complex threaded with β‐cyclodextrin: Synthesis and characterization
Authors: Chiu Yi‐Hong , Liu Jui‐Hsiang 
Published: July 2010

AbstractA novel achiral monomer end‐capped with a phenyl‐[1,3,4]oxadiazolyl group and threaded through β‐cyclodextrin was synthesized to investigate the host‐guest interactions in the inclusion complex. 1H NMR studies revealed that one or two cyclodextrin molecules were threaded onto the synthesized achiral monomer, leading to the formation of a fibrous construction of self‐assembled inclusion complexes. The formation of a self‐assembled inclusion complex was identified using SEM and TEM. The highly ordered alignment of self‐assembled supramolecules was confirmed using polarized optical microscopy. We demonstrate an easy process for the fabrication of nano‐structured self‐assembled inclusion complexes in pyridine/ethanol (1 mL/10 mL) as well as the enhancement of photo‐induced fluorescence via monomers end‐capped with a phenyl‐[1,3,4]oxadiazolyl moiety threaded with β‐cyclodextrins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3368–3374, 2010
Selective single monomer addition in living cationic polymerization: Sequential double end‐functionalization in combination with capping agent
Authors: Ida Shohei , Terashima Takaya , Ouchi Makoto , Sawamoto Mitsuo 
Published: June 2010

AbstractAmine‐functionalized and amine‐carboxylate double‐functionalized polymers (I and II, respectively) have been synthesized by a selective single addition of a protected 2‐aminoethyl vinyl ether (BocVE) {CH2 = CH[OCH2CH2N(Boc)2]; Boc = t‐butoxycarbonyl} onto a living cationic poly(n‐butyl vinyl ether) [poly(NBVE)] initiated with the SnCl4/n‐Bu4NCl system: (I) ‐(NBVE)n‐ CH2CH(OCH2CH2NH2)‐H; (II) ‐(NBVE)n‐CH2CH(OCH2CH2NH2)‐CH2CO2H. The single addition was examined with a set of alkene monomers less reactive than NBVE, including BocVE, 2‐chloroethyl vinyl ether, 2‐vinyloxyethylphtalimide, and styrene (St). Upon addition of 10 molar excess of these alkenes onto the living ends, only BocVE led to the intended single adduct, and this was attributed to a chelating interaction of the two carboxylate groups in the terminal BocVE unit with the growing poly(NBVE) terminal, thus sterically hampering further propagation. A simple acid‐catalyzed Boc‐deprotection led to the amino‐functionalized version I. Alternatively, an additional quenching the BocVE‐capped living end (the precursor of I) with sodium malonate, followed by double deprotection of the Boc and the malonate groups gave the double‐functionalized version II. The selective addition of a single monomer molecule is thus a new method for addressable or site‐specific introduction of functional groups along polymer chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3375–3381, 2010
Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores
Authors: Levine Mindy , Song Inja , Andrew Trisha L. , Kooi Steven E. , Swager Timothy M. 
Published: July 2010

AbstractPhotoluminescent energy transfer was investigated in conjugated polymer‐fluorophore blended thin films. A pentiptycene‐containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near‐infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near‐infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn‐on sensors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3382–3391, 2010
Electron microscopic study of the structure of polymers in solutions
Authors: Fakirov S. , Kargin V. A. , Bakeev N. F. 
Published: July 2010

AbstractThe well‐known and widely used methods of samples preparation for electron microscopic studying cannot be employed for polymer solutions. In the present work two techniques have been proposed which are free of the effects produced due to evaporation of the solvent. Their basic principles are as follows: (1) As a solvent a substance which easily goes into a vitreous state on cooling and has glass temperature higher than the room one is used. (2) The solvent is a substance with a low critical temperature (Te). The solvent is condensed in a glass capillary tube containing the polymer and then the capillary tube is heated in a special furnace in vacuo. When the temperature of the furnace is 20–25°C. higher than Te of the polymer solution the capillary tube is broken. Thus the content is “shot” at the grids which can be examined under the electron microscope. Using the described techniques the following systems were studied: polybutene‐1 in colophony, polybutene‐1 in propane, and atactic polypropylene in propane (at concentrations ranging from 0.07 to 3% by weight). Thus, by means of direct electron microscopy, it has been found that in polymer solutions the microscopic structuring of the polymer takes place long before lamination. The appearance of the ordered super‐molecular structures strongly depends on the concentration of the polymer solution.
Mechanism of the polymerization of vinyl chloride and chloroprene in the presence of transition‐metal complexes
Authors: Yamazaki Noboru , Kambara Shu 
Published: July 2010

AbstractTo clarify the polymerization mechanism of vinyl chloride (VCl) and chloroprene (CP) with titanium tetrabutoxide‐aluminum alkylchlorides some work was carried out. Carbon tetrachloride surprisingly enhanced polymerization without decreasing the molecular weight, whereas carbon tetrabromide transferred the polymer chain. The monomer reactivity ratios in the copolymerization of VCl with vinylidene chloride (VdCl), rVCl = 0.30 and rVdCl = 0.90, differed from those in free‐radical polymerizations. In the polymerization of perdeuterovinyl chloride an ethyl radical originating from AlCl(C2H5)2 was found to be incorporated into the polymer. Polymerization of chloroprene with the same catalyst in carbon tetrachloride was kinetically investigated, and a square‐root dependence of the catalyst concentration on the rate was seen. With vanadyl or cobalt acetylacetonate polymers of identical microstructure were obtained. Copolymerization with butadiene and styrene revealed the same behavior as that in free‐radical polymerization. It is suggested that in the polymerization with this catalyst an ionic or coordinated mechanism is included besides the usual radical mechanism.
Electrostatic potential distribution of the gene V protein from Ff phage facilitates cooperative DNA binding: A model of the GVP‐ssDNA complex
Authors: Guan Yue , Zhang Hong , Wang Andrew H.‐J. 
Published: June 2010

AbstractThe crystal structure of the gene V protein (GVP) from the Ff filamentous phages (M13, f1, fd) has been solved for the wild‐type and two mutant (Y41F and Y41H) proteins at high resolution. The Y41H mutant crystal structure revealed crystal packing interactions, which suggested a plausible scheme for constructing the polymeric protein shell of the GVP‐single‐stranded DNA (ssDNA) complex (Guan Y, et al., 1994, Biochemistry 33:7768–7778). The electrostatic potentials of the isolated and the cooperatively formed protein shell have been calculated using the program GRASP and they revealed a highly asymmetric pattern of the electrostatic charge distribution. The inner surface of the putative DNA‐binding channel is positively charged, whereas the opposite outer surface is nearly neutral. The electrostatic calculation further demonstrated that the formation of the helical protein shell enhanced the asymmetry of the electrostatic distribution. A model of the GVP‐ssDNA complex with the n = 4 DNA‐binding mode could be built with only minor conformational perturbation to the GVP protein shell. The model is consistent with existing biochemical and biophysical data and provides clues to the properties of GVP, including the high cooperativity of the protein binding to ssDNA. The two antiparallel ssDNA strands form a helical ribbon with the sugar‐phosphate backbones at the middle and the bases pointing away from each other. The bases are stacked and the Phe 73 residue is intercalated between two bases. The optimum binding to a tetranucleotide unit requires the participation of four GVP dimers, which may explain the cooperativity of the GVP binding to DNA.
Protein destabilization by electrostatic repulsions in the two‐stranded α‐helical coiled‐coil/leucine zipper
Authors: Kohn Wayne D. , Kay Cyril M. , Hodges Robert S. 
Published: June 2010

AbstractThe destabilizing effect of electrostatic repulsions on protein stability has been studied by using synthetic two‐stranded α‐helical coiled‐coils as a model system. The native coiled‐coil consists of two identical 35‐residue polypeptide chains with a heptad repeat QgVaGbAcLdQeKf and a Cys residue at position 2 to allow formation of an interchain disulfide bridge. This peptide, designed to contain no intrahelical or interhelical electrostatic interactions, forms a stable coiled‐coil structure at 20 °C in benign medium (50 mM KCl, 25 mM PO4, pH 7) with a [urea]1/2 value of 6.1 M. Four mutant coiled‐coils were designed to contain one or two Glu substitutions for Gln per polypeptide chain. The resulting coiled‐coils contained potential i to i' +5 Glu‐Glu interchain repulsions (denoted as peptide E2(15,20)), i to i' + 2 Glu‐Glu interchain repulsions (denoted E2(20,22)), or no interchain ionic interactions (denoted E2(13,22) and E1(20)). The stabilities of the coiled‐coils were determined by measuring the ellipticities at 222 nm as a function of urea or guanidine hydrochloride concentration at 20 °C in the presence and absence of an interchain disulfide bridge. At pH 7, in the presence of urea, the stabilities of E2(13,22) and E2(20,22) were identical suggesting that the potential i to i' + 2 interchain Glu‐Glu repulsion in the E2(20,22) coiled‐coil does not occur. In contrast, the mutant E2(15,20) is substantially less stable than E2(13,22) or E2(15,20) by 0.9 kcal/mol due to the presence of two i to i' +5 interchain Glu‐Glu repulsions, which destabilize the coiled‐coil by 0.45 kcal/mol each. At pH 3 the coiled‐coils were found to increase in stability as the number of Glu substitutions were increased. This, combined with reversed‐phase HPLC results at pH 7 and pH 2, supports the conclusion that the protonated Glu side chains present at low pH are significantly more hydrophobic than Gln side chains which are in turn more hydrophobic than the ionized Glu side chains present at neutral pH. The protonated Glu residues increase the hydrophobicity of the coiled‐coil interface leading to higher coiled‐coil stability. The guanidine hydrochloride results at pH 7 show similar stabilities between the native and mutant coiled‐coils indicating that guanidine hydrochloride masks electrostatic repulsions due to its ionic nature and that Glu and Gln in the e and g positions of the heptad repeat have very similar effects on coiled‐coil stability in the presence of GdnHCl.
A proposed structural model of domain 1 of fasciclin III neural cell adhesion protein based on an inverse folding algorithm
Authors: Castonguay Laurie A. , Snow Peter M. , Fetrow Jacquelyn S. , Bryant Stephen H. 
Published: June 2010

AbstractFasciclin III is an integral membrane protein expressed on a subset of axons in the developing Drosophila nervous system. It consists of an intracellular domain, a transmembrane region, and an extracellular region composed of three domains, each predicted to form an immunoglobulin‐like fold. The most N‐terminal of these domains is expected to be important in mediating cell‐cell recognition events during nervous system development. To learn more about the structure/function relationships in this cellular recognition molecule, a model structure of this domain was built. A sequence‐to‐structure alignment algorithm was used to align the protein sequence of the fasciclin III first domain to the immunoglobulin McPC603 structure. Based on this alignment, a model of the domain was built using standard homology modeling techniques. Side‐chain conformations were automatically modeled using a rotamer search algorithm and the model was minimized to relax atomic overlaps. The resulting model is compact and has chemical characteristics consistent with related globular protein structures. This model is a de novo test of the sequence‐to‐structure alignment algorithm and is currently being used as the basis for mutagenesis experiments to discern the parts of the fasciclin III protein that are necessary for homophilic molecular recognition in the developing Drosophila nervous system.
Locations of disulfide bonds and free cysteines in the heavy and light chains of recombinant human factor VIII (antihemophilic factor A)
Authors: Mcmullen Brad A. , Fujikawa Kazuo , Davie Earl W. , Hedner Ulla , Ezban Mirella 
Published: June 2010

AbstractThe locations of disulfide bonds and free cysteines in the heavy and light chains of recombinant human factor VIII were determined by sequence analysis of fragments produced by chemical and enzymatic digestions. The A1 and A2 domains of the heavy chain and the A3 domain of the light chain contain one free cysteine and two disulfide bonds, whereas the C1 and C2 domains of the light chain have one disulfide bond and no free cysteine. The positions of these disulfide bonds are conserved in factor V and ceruloplasmin except that the second disulfide bond in the A3 domain is missing in both factor V and ceruloplasmin. The positions of the three free cysteines of factor VIII are the same as three of the four cysteines present in ceruloplasmin. However, the positions of the free cysteines in factor VIII and ceruloplasmin are not conserved in factor V.
Site‐specific detection and structural characterization of the glycosylation of human plasma proteins lecithin:cholesterol acyltransferase and apolipoprotein D using HPLC/electrospray mass spectrometry and sequential glycosidase digestion
Authors: Schindler Patrick A. , Settineri Christine A. , Collet Xavier , Fielding Christopher J. , Burlingame Alma L. 
Published: June 2010

AbstractSite‐specific structural characterization of the glycosylation of human lecithinrcholesterol acyltransferase (LCAT) was carried out using microbore reversed‐phase high performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC/ESIMS). A recently described mass spectrometric technique involving monitoring of carbohydrate‐specific fragment ions during HPLC/ESIMS was employed to locate eight different groups of glycopeptides in a digest of a human LCAT protein preparation. In addition to the four expected TV‐linked glycopeptides of LCAT, a di‐O‐linked glycopeptide was detected, as well as three additional glycopeptides. Structural information on the oligosaccharides from all eight glycopeptides was obtained by sequential glycosidase digestion of the glycopeptides followed by HPLC/ESIMS. All four potential N‐linked glycosylation sites (Asn20, Asn84, Asn272, and Asn384) of LCAT were determined to contain sialylated triantennary and/or biantennary complex structures. Two unanticipated O‐linked glycosylation sites were identified at Thr407 and Ser409 of the LCAT O‐linked glycopeptide, each of which contain sialylated galactoseβ13N‐acetylgalactosamine structures. The three additional glycopeptides were determined to be from a copurifying protein, apolipoprotein D, which contains potential N‐linked glycosylation sites at Asn43 and Asn78. These glycopeptides were determined to bear sialylated triantennary oligosaccharides or fucosylated sialylated biantennary oligosaccharides. Previous studies of LCAT indicated that removal of the glycosylation site at Asn272 converts this protein to a phospholipase (Francone OL, Evangelista L, Fielding CJ, 1993, Biochim Biophys Acta 7766:301–304). Our results indicate that the carbohydrate structures themselves are not the source of this functional discrimination; rather, it must be mediated by the structural environment around Asn272.
Disulfide bonds in a recombinant protein modeled after a core repeat in an aquatic insect's silk protein
Authors: Smith Stanley V. , Correia John J. , Case Steven T. 
Published: June 2010

AbstractWe constructed a gene encoding rCAS, recombinant constant and subrepeat protein, modeled after tandem repeats found in the major silk proteins synthesized by aquatic larvae of the midge, Chironomus tentans. Bacterially synthesized rCAS was purified to near homogeneity and characterized by several biochemical and biophysical methods including amino‐terminal sequencing, amino acid compositional analysis, sedimentation equilibrium ultracentrifugation, and mass spectrometry. Complementing these techniques with quantitative sulfhydryl assays, we discovered that the four cysteines present in rCAS form two intramolecular disulfide bonds. Mapping studies revealed that the disulfide bonds are heterogeneous. When reduced and denatured rCAS was allowed to refold and its disulfide bonding state monitored, it again adopted a conformation with two intramolecular disulfide bonds. The inherent ability of rCAS to quantitatively form two intramolecular disulfide bonds may reflect a previously unknown feature of the in vivo silk proteins from which it is derived.
Aminolevulinate synthase: Lysine 313 is not essential for binding the pyridoxal phosphate cofactor but is essential for catalysis
Authors: Vajapey Usha , Hafez Osama , Hunter Gregory A. , Barber Michael J. , Ferreira Gloria C. 
Published: June 2010

Abstract5‐Aminolevulinate synthase is the first enzyme of the heme biosynthetic pathway in animals and some bacteria. Lysine‐313 of the mouse erythroid aminolevulinate synthase was recently identified to be linked covalently to the pyridoxal 5′‐phosphate cofactor (Ferreira GC, Neame PJ, Dailey HA, 1993, Protein Sci 2:1959–1965). Here we report on the effect of replacement of aminolevulinate synthase lysine‐313 by alanine, histidine, and glycine, using site‐directed mutagenesis. Mutant enzymes were purified to homogeneity, and the purification yields were similar to those of the wild‐type enzyme. Although their absorption spectra indicate that the mutant enzymes bind pyridoxal 5′‐phosphate, they bind noncovalently. However, addition of glycine to the mutant enzymes led to the formation of external aldimines. The formation of an external aldimine between the pyridoxal 5′‐phosphate co‐factor and the glycine substrate is the first step in the mechanism of the aminolevulinate synthase‐catalyzed reaction. In contrast, lysine‐313 is an essential catalytic residue, because the K313‐directed mutant enzymes have no measurable activity. In summary, site‐directed mutagenesis of the aminolevulinate synthase active‐site lysine‐313, to alanine (K313A), histidine (K313H), or glycine (K313G) yields enzymes that bind the pyridoxal 5′‐phosphate cofactor and the glycine substrate to produce external aldimines, but which are inactive. This suggests that lysine‐313 has a functional role in catalysis.