bluuebunny/crossref_metadata_2025_split huggingface dataset:
Jahrhunderte altes Rätsel des Iapetus gelöst
Authors: Denk Tilmann 
Published: March 2010

AbstractDie Riesenplaneten in unserem Sonnensystem besitzen zahlreiche Monde. Fast alle bestehen im Wesentlichen aus Wassereis, und viele weisen hoch interessante, teilweise überraschende Eigenschaften auf. Die am längsten bekannte Eigentümlichkeit ist die globale Helligkeitsdichotomie des Saturnmondes Iapetus: Während eine Hemisphäre weiß erscheint, ist die andere sehr dunkel (Abbildung 1). Die Ursache dieses Phänomens konnten wir jetzt erklären.
Lehrer in die Forschung
Authors: Rosenzweig Stephan 
Published: March 2010

AbstractDas Leibniz‐Institut für Festkörper‐ und Werkstoffforschung Dresden (IFW) bietet jährlich einem Lehrer die Möglichkeit zu einem Forschungspraktikum. Diese Fortbildungsmaßnahme verlangt von allen Beteiligten eine große Bereitschaft zur Veränderung, bringt aber für beide Seiten viele Vorteile.
Synthesis and properties of bifunctional oligoethers. I. Chiral oligomers from propylene oxide
Authors: Jun C. L. , Leborgne A. , Spassky N. 
Published: March 2010

AbstractRacemic or chiral bifunctional oligoethers of the type H—(O—CH(CH3)—CH2—)n—Cl, n = 4‐10, have been prepared by reacting racemic or optically active propylene oxide with teiraphenyl porphyrin (TPPH2)—AlEt2Cl initiator sysfem. The synthesized products were characterized by IR, elemental analysis, VPO, GPC, and 1H and 13CNMR techniques. The oligomers purified by fractional distillation exhibit narrow MW distributions (M̄w/M̄n ≈ 1.03). Chiroptical properties of the oligomers and their derivatives were examined and compared with those of high molecular weight polyfpropylene oxide). Different possibilities of applicadons of these oligomers are presently under study.
Polvnucleotide analogs with PEI or PEI/polyethyloxazoline backbones
Authors: Ludwick A. G. , Robinson K. S. , McCloud J. 
Published: March 2010

AbstractThe synthesis and characterization of uracil‐ and thy mine‐containing polynucleotide analogs with a linear polyethylenimine backbone is described. Hypochromicity is observed for these analogs in DMSO and in DMSO/H2O solutions and found lo increase as the percent water increases. The influence of water on the 240‐ to 280‐nm absorptions of the analogs and their monomer models is correlated with the mobiliiy of the nucleic‐acid‐base‐con tain ing pendant to the polymeric backbone. An impure 5‐fluorouracil analog has been prepared, and its increased solubility in water relative to the corresponding uracil analog has been noted. A thy mine‐containing analog with a PEI/PEOXZ backbone has been synthesized. The analog consists of water‐soluble and insoluble forms characterized by NMR.
Polyetherimides. II. High‐temperature solution polymerization
Authors: Takekoshi T. , Kochanowski J. E. , Manello J. S. , Webber M. J. 
Published: March 2010

AbstractThe polymerization and characterization of the ether‐containing aromatic polyimides of the following general structure are presented.magnified imageThe polymerization was conducted in one step in homogeneous solution of m‐cresol at high temperatures. Typical polyeterimides (PEI) were noncrystalline and showed excellent thermal stability. Among 46 polymers synthesized, only two were crystalline. PEI had glass transition temperatures from 178° to 277°C and exhibited excellent processibility. Many PEI were also soluble in dipolar aprotic solvents and chlorinated hydrocarbons.
Aromatic polyamides. XIII. effect of the halogen position on the thermal and flammability behavior of halogenated poly (1,3‐phenylene‐isophthalamide)
Authors: Whang W. T. , Kapuscinska M. , Pearce E. M. 
Published: March 2010

AbstractVarious halogen substituted poly (1,3‐phenylene‐isophthalamide)s have been prepared. Their glass transition temperature Tg (DSC), thermal decomposition courses (TGA), and flame resistance (oxygen index) are discussed.The polyamides substituted with halogen in the meta position to NH group showed higher Tg and better thermal stability than those substituted with the same halogen in the ortho position. All halogenated polyamides studied had fairly good flame resistance characteristics: high oxygen indices and high char yields. Halogenated aromatic polyamides with nitrogen ortho to halogen showed the flammability characteristic: limiting oxygen index = 38 + 61 × (weight loss at initial plateau temperature).
Optically active poly(diphenyl‐2‐pyridylmethyl methacrylate): Asymmetric synthesis, stability of helix, and chiral recognition ability
Authors: Okamoto Yoshio , Mohri Haruhiko , Motoshiishikura  , Hatada Koichi , Yuki Heimei 
Published: March 2010

AbstractDipheny‐2‐pyridylmethyl methacrylate (D2PyMA) was anionically polymerized with several organolithium complexes of chiral ligands such as (‐)‐sparteine (Sp), (S,S)‐( + )‐ and (R,R)‐(‐)‐2,3‐dimethoxy‐1,4‐bis(dimethylamino)butane [(+)‐ and (‐ )‐DDB], (S)‐(‐)‐1 ‐ methyl‐2‐(piperi‐dinomethyl)pyrrolidine (MPP), (S,S)‐( + )‐3,4‐dimethoxy‐N‐(2‐(dimethylamino)ethyl)pyrrolidine (DDEP), and (S,S)‐(+ )‐N‐benzyl‐3,4‐dimethoxypyrrolidine (BDP) in toluene at low temperature. Sp complexes gave a polymer of low optical activity. DDB was a better chiral ligand, and its complex, particularly the complex with N,N'‐diphenylethylenediamine monolithium amide (DPEDA‐Li), was effective in preparing a polymer of high optical rotation. A THF‐soluble portion of the polymer obtained with (‐)‐DDB‐DPEDA‐Li showed [α]25/365 about ‐ 1400°, which was comparable to that of poly(triphenylmethyl methacrylate) (PTrMA) with pure one‐handed helical structure. However, in the polymerization with DDB‐DPEDA‐Li, optical rotation of the polymer depended greatly on polymerization conditions, such as monomer and initiator concentrations, reaction temperature, and polar additives. Fractionation by THF and/or gel permeation chromatography of the obtained polymers revealed that poly(diphenyl‐2‐pyridylmethyl methacrylate) (PD2PyMA) consisted of a mixture of (+)‐ and (‐)‐ polymers which probably were not enantiomeric to each other. DDEP‐DPEDA‐Li and DDEP‐fluorenyllithium complexes were also efficient chiral initiators that gave polymer of the same or higher optical rotation in comparison with DDB complexes. The optical rotation of PD2PyMA in CHCl3‐2,2,2‐trifluoroethanol (90:10) slowly changed with time. Optically active PD2PyMA coated on macroporous silica gel resolved racemic compounds as a chiral stationary phase for high‐performance liquid chromatography (HPLC).
A polymeric triarylmethane dye as a sensitizer for photoconductivity
Authors: Mitra Smarajit 
Published: March 2010

AbstractA polymeric analogue of crystal violet in which the triarylmethane moiety is pendent from a polyester backbone has been examined as a sensitizer for photoconductivity in poly‐N‐vinyicarbazole. In both positive and negative surface charging modes, the dark decay rates increase linearly with sensitizer concentration, but are lower than those for monomeric crystal violet sensitization. The photodecay rates, in both modes, show optimal concentration dependence and are higher than those for monomeric crystal violet.
Synthesis and characterization of main‐chain polyaminimides
Authors: Salamone J. C. , Richard R. E. , Watterson A. C. 
Published: March 2010

AbstractThree novel main‐chain polyarninimides were prepared containing rigid and/or flexible groups within the backbone. The polymer precursors were initially synthesized from bis‐dimethylhydrazides and dihalides at room temperature through the Menschulkin reaction, which yielded hydrazinium ionenes. In a similar fashion, low molecular weight model compounds were also prepared in order to confirm the structures of the ionene polymers. It was found that the ionenes were totally, or at least partially, converted o the aminimide form in the presence of water alone, while the model cationic compounds required a strong base before conversion to their corresponding aminimides. These new polymers were characterized by (heir infrared and NMK spectra, as well as dilute solution viscosity. Preliminary solution properties indicate that the hydrazinium form of the polymers behave as poly electrolytes, whereas the aminimide form behaves as a neutral polymer.
NMR study of 9‐anthranylmethyl hexafluorophosphate. Polymerization of styrene monomers
Authors: Toncheva V. D. , Velichkova R. S. , Panayotov I. M. , Markova L. P. 
Published: March 2010

AbstractThe primary carbenium salt 9‐anihranylmethyl hexafluorophosphate is characterized by 1H‐ and 13C‐NMR spectroscopy. The results show that in the temperature range −60°‐15°C the initiator exists as a classical carbenium ion and a protonated anthracenium ion. At higher temperatures the reactions of self‐alkylation and disproportionation proceed, giving bianthracenes, hydroanthracenes, and other dimer forms.The polymerization of α‐methylstyrene and p‐methoxystyrene, initiated by 9‐anthranylmethyl hexafluorophosphate, is investigated. The mechanism of initiation, the stereochemical configuration, and the end groups of the polymer chains are determined.
Exploratory ring‐opening polymerization. XIIL ring‐opening polymerization of 2‐vinyl cyclic sulfones
Authors: Cho Iwhan , Kim Sang‐Keun , Lee Myong‐Hoon 
Published: March 2010

Abstract2‐Vinyllhiolane‐1,1‐dioxide (Ia) and 2‐vinylthiane‐1,1‐dioxide(Ib) have been prepared and polymerized with free radical initiators to obtain poly(sulfonyl‐hex‐2‐enylene) (IIa) and poly(sulfonyl‐hept‐2‐enyIene‐co‐2‐vinylthiane‐1,1‐dioxide) (IIb), respectively, via a ring‐opening mechanism. Structures of the polymers are supported by infrared and 1H‐NMR spectroscopy. Poly(sulfonyl‐hex‐2‐enylene) was insoluble in ordinary organic solvents, but soluble in concentrated sulfuric acid or trifluoroacetic acid, and was white amorphous powder, softening at 168°C. Degradation occurred at 294°C under N2. Ia copolymerized with certain vinyl monomers, such as ethyl acrylate, but its copolymerization behavior was different from those of normal vinyl monomers.
On predicting free radical polymerizability of allyl monomers. MINDO/3 and 13C NMR results
Authors: Vaidya Rajeev A. , Mathias Lon J. 
Published: March 2010

AbstractTwo new methods of predicting free radical polymerizability of allyl monomers have been developed. MINDO/3 calculations of eigenvalues for the C—H bond a to the atlyl substituent allow comparison of relative bond strengths. Monomers known to undergo degradative chain transfer display more positive eigenvalues correlating with weaker α‐C—H bonds. Polymerizable monomers have more negative eigenvalues and stronger α‐C—H bonds. The latter possess strongly polarized or protonated substituents not capable of resonance stabilization of a chain‐terminating allyl radical. The inductive effect of such substituents on the 13C NMR peaks of the vinyl carbons is the basis for the empirical spectroscopic method. Allyl compounds display β‐carbon peaks farther downfield than the γ‐carbon peaks. Polymerizable monomers generally have β peaks shifted upfield and γ peaks shifted downfield from those of poor monomers. This effect brings the two peaks closer together in the spectrum. Thus, the smaller the Δδ value (δβ − δγ), the more likely the monomer is to polymerize well. Monomers with intermediate eigenvalues or Δδ values may polymerize with difficulty or only under special conditions. Combined use of the theoretical and empirical techniques can allow prediction of inherent polymerizability and can facilitate evaluation of reaction media most favorable to polymer formation.
Conformational analysis of poly(tetrahydrofurandiyls)
Authors: Moore J. A. , Wille Roice , Miller Kenneth J. 
Published: March 2010

AbstractThe stereoisomeric configurations of poly(2,5‐tetraliydrofurandiyl), 1, and poly(2,3‐tetrahydrofurandiyl), 2, have been investigated by conformational analysis. Similar results were obtained for 1 and 2, Threodiisotactic (tit) and erythrodisyndiotactic (est) configurations could form low energy helical conformations, whereas erythrodiisotactic (eit) and threodisyndiotactic (tst) configurations generally formed low energy linear conformations. Helical conformations of I placed oxygen atoms at the interior of the helices, but helical conformations of 2 placed oxygen atoms more toward the periphery. The results of ion‐binding experiments are interpreted in terms of the results of conformational analysis. Ion‐binding experiments are consistent with the suggestion that configurations that can form low energy, helical conformations with oxygen atoms at the interior of the helices could bind cations efficiently. Configurations that can form only low energy linear conformations, or that form helices with oxygen atoms toward the periphery of the helices, should be inefficient in binding cations.
Effects of bulky substituents on oxygen permeation behaviors of polystyrene‐based polymers
Authors: Kawakami Y. , Kamiya H. , Yamashita Y. 
Published: March 2010

AbstractPolymers of β‐cyclodextrinyl substituted styrene and 4′‐oligodimethylsiloxanyl‐4‐vinyldiphenyl were synthesized. Their oxygen perm selectivity was studied from the viewpoint of investigating the effects of the introduction of bulky p‐substituents to polystyrene on their permeation behaviors. The bulky substituents were quite effective in enhancing the permeability; however, the selectivity in permeation decreased with the increase in permeability.
A Comparative Mass‐Spectrometric Study of Plasma‐ and Vacuum Ultraviolet Ablation of Selected Polymers
Authors: Nelea Valentin , Vasilets Victor N. , Skurat Vladimir E. , Truica‐Marasescu Florina , Wertheimer Michael R. 
Published: March 2010

AbstractEnergetic photons (UV, VUV radiation and soft X rays), and particles (ions, electrons, metastable excited atoms) from inert gas plasmas possess sufficient energy to induce multiple bond scission reactions in the macromolecular chains of most polymers. As a result, volatile products of varying molecular weights escape from the polymers' surfaces; they can be captured and identified by mass spectrometry (MS). We report an MS‐based study of five commercial polymers, polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(ethylene terephthalate) (PET) and polyamide that were exposed to inert gas (He, Ar) plasmas and to near‐monochromatic (λ = 121.6 nm) VUV irradiation. For the cases of PE and PP, quantitative analyses of the most abundant reaction products (H2, C1–C7 alkanes) are compared among the various polymer/excitation‐source cases, and with regard to literature data for γ irradiation.magnified image
Bridging the gap: A GFP‐based strategy for overexpression and purification of membrane proteins with intra and extracellular C‐termini
Authors: Hsieh Jennifer M. , Besserer Gabriel Mercado , Madej M. Gregor , Bui Ha‐Quyen , Kwon Seunghyug , Abramson Jeff 
Published: March 2010

AbstractLow expression and instability during isolation are major obstacles preventing adequate structure‐function characterization of membrane proteins (MPs). To increase the likelihood of generating large quantities of protein, C‐terminally fused green fluorescent protein (GFP) is commonly used as a reporter for monitoring expression and evaluating purification. This technique has mainly been restricted to MPs with intracellular C‐termini (Cin) due to GFP's inability to fluoresce in the Escherichia coli periplasm. With the aid of Glycophorin A, a single transmembrane spanning protein, we developed a method to convert MPs with extracellular C‐termini (Cout) to Cin ones providing a conduit for implementing GFP reporting. We tested this method on eleven MPs with predicted Cout topology resulting in high level expression. For nine of the eleven MPs, a stable, monodisperse protein‐detergent complex was identified using an extended fluorescence‐detection size exclusion chromatography procedure that monitors protein stability over time, a critical parameter affecting the success of structure‐function studies. Five MPs were successfully cleaved from the GFP tag by site‐specific proteolysis and purified to homogeneity. To address the challenge of inefficient proteolysis, we explored expression and purification conditions in the absence of the fusion tag. Contrary to previous studies, optimal expression conditions established with the fusion were not directly transferable for overexpression in the absence of the GFP tag. These studies establish a broadly applicable method for GFP screening of MPs with Cout topology, yielding sufficient protein suitable for structure‐function studies and are superior to expression and purification in the absence GFP fusion tagging.
Structures of the OmpF porin crystallized in the presence of foscholine‐12
Authors: Kefala Georgia , Ahn Chihoon , Krupa Martin , Esquivies Luis , Maslennikov Innokentiy , Kwiatkowski Witek , Choe Senyon 
Published: March 2010

AbstractThe endogenous Escherichia coli porin OmpF was crystallized as an accidental by‐product of our efforts to express, purify, and crystallize the E. coli integral membrane protein KdpD in the presence of foscholine‐12 (FC12). FC12 is widely used in membrane protein studies, but no crystal structure of a protein that was both purified and crystallized with this detergent has been reported in the Protein Data Bank. Crystallization screening for KdpD yielded two different crystals of contaminating protein OmpF. Here, we report two OmpF structures, the first membrane protein crystal structures for which extraction, purification, and crystallization were done exclusively with FC12. The first structure was refined in space group P21 with cell parameters a = 136.7 Å, b = 210.5 Å, c = 137 Å, and β = 100.5°, and the resolution of 3.8 Å. The second structure was solved at the resolution of 4.4 Å and was refined in the P321 space group, with unit cell parameters a = 215.5 Å, b = 215.5 Å, c = 137.5 Å, and γ = 120°. Both crystal forms show novel crystal packing, in which the building block is a tetrahedral arrangement of four trimers. Additionally, we discuss the use of FC12 for membrane protein crystallization and structure determination, as well as the problem of the OmpF contamination for membrane proteins overexpressed in E. coli.
Steric and thermodynamic limits of design for the incorporation of large unnatural amino acids in aminoacyl‐tRNA synthetase enzymes
Authors: Armen Roger S. , Schiller Stefan M. , Brooks Charles L. 
Published: March 2010

AbstractOrthogonal aminoacyl‐tRNA synthetase/tRNA pairs from archaea have been evolved to facilitate site specific in vivo incorporation of unnatural amino acids into proteins in Escherichia coli. Using this approach, unnatural amino acids have been successfully incorporated with high translational efficiency and fidelity. In this study, CHARMM‐based molecular docking and free energy calculations were used to evaluate rational design of specific protein–ligand interactions for aminoacyl‐tRNA synthetases. A series of novel unnatural amino acid ligands were docked into the p‐benzoyl‐L‐phenylalanine tRNA synthetase, which revealed that the binding pocket of the enzyme does not provide sufficient space for significantly larger ligands. Specific binding site residues were mutated to alanine to create additional space to accommodate larger target ligands, and then mutations were introduced to improve binding free energy. This approach was used to redesign binding sites for several different target ligands, which were then tested against the standard 20 amino acids to verify target specificity. Only the synthetase designed to bind Man‐α‐O‐Tyr was predicted to be sufficiently selective for the target ligand and also thermodynamically stable. Our study suggests that extensive redesign of the tRNA synthatase binding pocket for large bulky ligands may be quite thermodynamically unfavorable. Proteins 2010. © 2010 Wiley‐Liss, Inc.
Novel method for the synthesis of urea backbone cyclic peptides using new Alloc‐protected glycine building units
Authors: Hurevich Mattan , Tal‐Gan Yftah , Klein Shoshana , Barda Yaniv , Levitzki Alexander , Gilon Chaim 
Published: March 2010

AbstractCyclization of bioactive peptides, utilizing functional groups serving as natural pharmacophors, is often accompanied with loss of activity. The backbone cyclization approach was developed to overcome this limitation and enhance pharmacological properties. Backbone cyclic peptides are prepared by the incorporation of special building units, capable of forming amide, disulfide and coordinative bonds. Urea bridge is often used for the preparation of cyclic peptides by connecting two amine functionalized side chains. Here we present urea backbone cyclization as an additional method for the preparation of backbone cyclic peptide libraries. A straightforward method for the synthesis of crystalline Fmoc‐Nα [ω‐amino(Alloc)‐alkyl] glycine building units is presented. A set of urea backbone cyclic Glycogen Synthase Kinase 3 analogs was prepared and assessed for protein kinase B inhibition as anticancer leads. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.
Unveiling the defect levels in SnS thin films for photovoltaic applications using photoluminescence technique
Authors: Sajeesh T. H. , Poornima N. , Kartha C. Sudha , Vijayakumar K. P. 
Published: March 2010

AbstractExploiting the potential of the material for the photovoltaic applications requires an extensive defect level analysis, mandatory. Photoluminescence (PL) technique was employed to probe the defect levels in p‐SnS thin films deposited using chemical spray pyrolysis (CSP) technique. Three PL emissions were recorded at 1.09, 0.76, and 0.75 eV. Systematic investigations performed, focusing the 1.09 eV emission, revealed that the shoulder at 1.093 eV gets completely quenched beyond 110 K. From this study, we could identify a bound exciton associated to a shallow donor level whose activation energy was calculated to be 20 meV from Arrhenius plot. By studying the variation of PL intensity with excitation power, we could zero‐in that the emission at 1.09 eV was a donor–acceptor pair (DAP) transition. Knowing the band gap to be 1.33 eV, we could identify a deep acceptor at 0.22 eV above valence band. The band structure deduced from the present analysis is depicted in the abstract figure. magnified image
Structural details of Ge‐rich and silver‐doped chalcogenide glasses for nanoionic nonvolatile memory
Authors: Mitkova Maria , Sakaguchi Yoshifumi , Tenne Dmitri , Bhagat Shekhar Kumar , Alford Terry L. 
Published: March 2010

AbstractWe are reporting our results of Raman and X‐ray diffraction (XRD) studies on amorphous Ge46S54 thin films and the films after silver photodiffusion. Based on the Raman scattering studies, a structural model for amorphous Ge46S54 is suggested including the formation of single Ge–S chains with a vibrational mode at 410 cm−1. The result of XRD measurement indicates that there exists a medium‐range order with about 6 Å´ even at such Ge‐rich composition. After the introduction of silver, the medium‐range order is lost and there was a change in the diffraction curve indicative of the change in the local atomic order. The experimental results are explained in terms of our structural model, in connection with the application for fast switching memory devices.
Ferromagnetic and ferroelectric quantum phase transitions
Authors: Rowley Stephen , Smith Robert , Dean Mark , Spalek Leszek , Sutherland Michael , Saxena Montu , Alireza Patricia , Ko Chris , Liu Cheng , Pugh Emma , Sebastian Suchitra , Lonzarich Gilbert 
Published: March 2010

AbstractThe applicability of mean field models of ferroelectric and ferromagnetic quantum critical points is examined for a selection of d‐electron systems. Crucially, we find that the tendency of the effective interaction between critical fluctuation modes to become attractive and anomalous as the ordering temperatures tend to absolute zero results in particularly complex and striking phenomena. The multiplicity of quantum critical fields at the border of metallic ferromagnetism, in particular, is discussed here.