bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress in the Palladium‐Catalyzed Cyanation of Aryl Chlorides
Authors: Sundermeier Mark , Zapf Alexander , Mutyala Sateesh , Baumann Wolfgang , Sans Jürgen , Weiss Stefan , Beller Matthias 
Published: April 2003

AbstractThe development of new palladium catalysts for the cyanation of various aryl and heteroaryl chlorides is described. The combination of amine co‐catalysts with chelating phosphine ligands, for example, 1,4‐bis(diphenylphosphino)butane (dppb) or 1,5‐bis(diphenylphosphino)pentane (dpppe), allows an efficient cyanation of chloroarenes with simple potassium cyanide. General palladium‐catalyzed cyanation of nonactivated and deactivated chloroarenes is possible for the first time. Studies of the oxidative addition of aryl halides to palladium triphenylphosphine complexes in the presence and absence of amines suggest that the co‐catalyst is capable of preventing catalyst deactivation caused by the presence of excess cyanide ions in solution.
Criteria for the Elucidation of the Pseudopericyclic Character of the Cyclization of (Z)‐1,2,4,6‐Heptatetraene and Its Heterosubstituted Analogues: Magnetic Properties and Natural Bond Orbital Analysis
Authors: Rodríguez‐Otero Jesús , Cabaleiro‐Lago Enrique M. 
Published: April 2003

AbstractThe electrocyclization of heterosubstituted derivatives of (Z)‐1,2,4,6‐heptatetraene, (2Z)‐2,4,5‐hexatrien‐1‐imine and (2Z)‐2,4,5‐hexatrienal exhibit some features which suggest a pseudopericyclic mechanism. In order to examine this, a comprehensive study including the determination of magnetic properties to estimate aromaticity and an NBO analysis throughout the reaction path was conducted. The cyclization of 5oxo‐2,4‐pentadienal, a process of unequivocal pseudopericyclic nature, was studied for comparison. The results suggest that, although the lone electron pair on the heteroatom in the heptatetraene derivatives seemingly plays a crucial role in the reaction mechanism, it does not suffice to deprive the reaction from the essential features of a pericyclic disrotatory electrocyclization.
Stereodynamics and Characterization of the Hexa(4‐n‐dodecylbiphenylyl)benzene Hexaanion that Includes a Twisted Benzene Core
Authors: Eshdat Lior , Hoffman Roy E. , Fechtenkötter Andreas , Müllen Klaus , Rabinovitz Mordecai 
Published: April 2003

AbstractHexa(4‐n‐dodecylbiphenylyl)benzene (HDBB) was reduced by a series of alkali metals in THF under high vacuum. Three reduction states were identified by NMR spectroscopy, namely the dianion, tetraanion and hexaanion. The NMR spectra of HDBB6− revealed a remarkable distortion of symmetry, which is interpreted by adoption of a twisted conformation of the central benzene ring and a slow rotation of the inner phenylene rings of the biphenyl units. Due to the surprising thermal stability of the hexaanion, a dynamic NMR investigation revealed the pseudorotation of the twisted conformation and the phenylene rotation mentioned above.
[ReO3(bipy)]+[X]−‐Catalyzed Aldehyde Olefination: Carbene and Phosphorane Intermediates
Authors: Zhang Xiangyang , Chen Peter 
Published: April 2003

AbstractThe aldehyde olefination reaction, catalyzed by cationic high‐valent oxorhenium complexes, shows evidence of the intermediacy of both carbene complexes and phosphoranes. The solution‐phase reaction is facile and amenable to tuning and is, hence, likely to prove to be of practical significance. Individual steps in the catalytic cycle are observed in the gas phase. Catalytic competence of each of the putative intermediates can be demonstrated.
The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity
Authors: Floquet Sébastien , Ouali Nadjet , Bocquet Bernard , Bernardinelli Gérald , Imbert Daniel , Bünzli Jean‐Claude G. , Hopfgartner Gérard , Piguet Claude 
Published: April 2003

AbstractThe segmental tris‐tridentate ligand L7 reacts with stoichiometric quantities of LnIII (Ln=La–Lu) in acetonitrile to give the complexes [Ln2(L7)3]6+ and [Ln3(L7)3]9+. Formation constants point to negligible size‐discriminating effects along the lanthanide series, but Scatchard plots suggest that the self‐assembly of the trimetallic triple‐stranded helicates [Ln3(L7)3]9+ is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively [Ln3(L7)3](CF3SO3)9 (Ln=La, Eu, Gd, Tb, Lu) and the Xray crystal structure of [Eu3(L7)3](CF3SO3)9⋅(CH3CN)9⋅(H2O)2 (Eu3C216H226N48O35F27S9, triclinic, P$\bar 1$, Z=2) shows the three ligand strands wrapped around a pseudo‐threefold axis defined by the three metal ions rigidly held at about 9 Å. Each metal ion is coordinated by nine donor atoms in a pseudo‐trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo‐trigonal symmetries in the solid state and in solution. High‐resolution luminescence analyses evidence a low‐lying LMCT state affecting the central EuN9 site, so that multi‐metal‐centered luminescence is essentially dominated by the emission from the two terminal EuN6O3 sites in [Eu3(L7)3]9+. New multicenter equations have been developed for investigating the solution structure of [Ln3(L7)3]9+ by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce–Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second‐rank crystal‐field parameters, obtained by LIS analysis, for the LnN6O3 and LnN9 sites with respect to the parameters extracted for EuIII from luminescence data, suggests that the geometry of the central LnN9 site is somewhat relaxed in solution.
Stabilizing Bolaform Amphiphile Interfacial Assemblies by Introducing Mesogenic Groups
Authors: Wang Mingfeng , Qiu Dengli , Zou Bo , Wu Tao , Zhang Xi 
Published: April 2003

AbstractWe describe the synthesis and characterization of the mesogen‐bearing bolaform amphiphile 4,4′‐dihydroxybiphenylbis(11‐pyridinium‐N‐yl‐undecanoic ester) dibromide (BP‐10) and its solid/liquid interfacial self‐assembly. Cylindrical micelles are directly observed by atomic force microscopy (AFM) at the interface between mica and the aqueous solution above the critical micelle concentration (cmc). In situ and ex situ AFM studies indicate that the cylindrical micelles are stable both at the mica/solution interface and in the dry state. The enhanced stability of the micellar structures enables a detailed investigation of their self‐assembly behavior and supramolecular structures at the interface. The adsorption model proposed here is supported by the variation of the interfacial self‐assemblies on changing the solution concentration and substrate temperature.
Insektizide für die Landwirtschaft: Chemische Schädlingsbekämpfung
Authors: Beckmann Marion , Haack Karl‐Josef 
Published: April 2003

AbstractEin Überblick über chemische Schädlingsbekämpfung in der Landwirtschaft wird geboten, indem Grundlagen zu Schädlingsarten, heute verwendete Wirkstoffe und Substanzklassen, deren biochemische Wirkmechanismen und Wirkprofile dargestellt werden.
Herbizide für die Landwirtschaft: Chemische Unkrautbekämpfung
Authors: Seitz Thomas , Hoffmann Michael G. , Krähmer Hansjörg 
Published: April 2003

AbstractDieser Artikel beschreibt die momentan wichtigsten marktrelevanten Herbizide sowie deren molekulare Wirkmechanismen und pflanzenphysiologische Effekte. Darüber hinaus wird auch auf neue herbizide Wirkmechanismen und die Bedeutung von Safenern eingegangen.
Synthese‐Entwicklung unter speziellen Randbedingungen: Patentsituation und Kostenoptimierung
Authors: Haack Karl‐Josef 
Published: April 2003

AbstractDieser Artikel beschreibt Herstellwege für ausgewählte Wirkstoffe im chemischen Pflanzenschutz. Es werden Methoden und zentrale Zwischenstufen bei den Synthesen von Glyphosate, Glyphosine, Glufosinate, Thiamethoxam, Clothianidin, Fipronil, Kresoxim‐methyl, Trifloxystrobin, Abamectin, Emamectin, (S‐)Metolachlor, Indoxacarb und Deltamethrin vorgestellt.
Moderne Fungizide: Pilzbekämpfung in der Landwirtschaft
Authors: Henningsen Michael 
Published: April 2003

AbstractIn den letzten Jahren wurde eine große Anzahl von neuen Fungiziden in die Landwirtschaft eingeführt. Auf Grund ihres breiten Wirkspektrums haben sich die Strobilurine zu einer der wichtigsten fungiziden Substanzklassen entwickelt. Diese Übersicht stellt die Neuentwicklungen seit 1995 vor, beschreibt die Wirkmechnismen und die wesentlichen Zielkulturen.
Lebensmittelinhaltsstoffe und ‐kontaminanten: Aus toxikologischer Sicht
Authors: Schrenk Dieter 
Published: April 2003

AbstractUnsere Lebensmittel enthalten Stoffen natürlichen Ursprungs, die bei zu häufigem oder übermäßigem Verzehr zu Gesundheitsstörungen führen können. Hierzu zählen beispielsweise die Glucosinolate in Kohlarten oder Trypsin‐Inhibitoren in (ungegarten) Leguminosen. Ferner können bestimmte Inhaltsstoffe wie das Vicin der Ackerbohne oder die Glycyrrhetinsäure in Lakritz für bestimmte Gruppen von Verbrauchern (z.B. mit Erkrankungen wie Bluthochdruck oder bei bestimmten genetischen Defekten) Gefahren bergen. Gesetzlich zugelassene Lebensmittelzusatzstoffe wie Konservierungsstoffe, Emulgatoren oder Farbstoffe sind in der Regel sehr gründlich toxikologisch geprüft und bewertet worden und können daher als sehr sicher gelten. Im Gegensatz dazu stammen Rückstände und Kontaminanten häufig aus unsachgemäßer oder gesetzwidriger Herstellung oder Behandlung von Lebensmitteln oder Rohstoffen. Bei niedrigeren Gehalten können sie Hintergrundkontaminationen z.B. aus der Umwelt widerspiegeln. Schließlich müssen auch Nahrungsergänzungsmittel und ‚funktionelle Lebensmittel’︁ auf toxikologische Eigenschaften überprüft werden, da nicht alle Stoffe, die in einem bestimmten Dosisbereich als ‚gesund’︁ gelten, auch in höherer Dosierung günstig wirken bzw. sicher sind.
(K)ein süßes Leben
Authors: Hübner Karl 
Published: April 2003

AbstractEr war einer der regesten Wissenschaftler im Berlin seiner Zeit. Mit seiner Begründung der industriellen Gewinnung von Zucker aus Rüben schuf er zudem ein gewaltiges praxisrelevantes Erbe. Und doch ist der sein Leben lang von Geldsorgen geplagte heute weitgehend vergessen. Nicht einmal das Römpp‐Chemielexikon führt seinen Namen. Nur unter dem Begriff Saccharose taucht er kurz auf — als derjenige, der 1801 die erste Rübenzuckerfabrik der Welt gründete: In diesem Jahr, am 28. April, jährt sich sein Geburtstag zum 250. Mal.
Berliner Blau: Alte Farbe in neuem Glanz
Authors: Roth Klaus 
Published: April 2003

AbstractDie Entdeckung des Berliner Blaus war reiner Zufall. 1704 erhielt der Berliner Färber Diesbach wohl zu seiner eigenen großen Überraschung aus Eisenvitriol und Kalilauge eine dunkelblaue Lösung. Heute wissen wir, dass die verwendete Kalilauge mit dem damals noch unbekannten Kaliumhexacyanoferrat K4[Fe(CN)6] verunreingt gewesen sein muss. Über die Entdeckung wurde 1710 berichtet [1]: der Farbstoff war ungiftig und ließ sich trotz seiner Unlöslichkeit in Wasser, Öl und anderen Flüssigkeiten sehr fein verteilen. Insgesamt ein ideales Pigment, das als Berliner oder Preußisch Blau die Welt eroberte. Zwar änderte sich mit dem Herstellungsort der Name, aber egal ob Pariser Blau, Miloriblau, Antwerpener Blau, Persischblau, Turnbulls Blau, Hamburger Blau u.s.w., als Mal‐, Druck‐oder Textilfarbe, zum Färben von Leder oder Kunststoffen und in der Kosmetik, Berliner Blau blieb bis heute eines der farbintensivsten und schönsten Blaupigmente.
Höhepunkte aus Liebigs Experimentalvorlesung
Authors: Schwedt Georg 
Published: April 2003

AbstractLiebigs Geburtstag jährt sich am 12. Mai 2003 zum 200. Mal. Aus diesem Anlass werden einzelne Experimente bzw. Versuchsreihen, die noch heute eine grundlegende Bedeutung haben, aus seiner in Gießen entwickelten Experimentalvorlesung vorgestellt. Sie stammen aus dem im Nachlass seines Sohnes, des Arztes Georg von Liebig (1827—1903), im Jahre 1906 aufgefundenen Vorlesungsbuch, das 1983 veröffentlicht wurde.
Phänomene aus der Konserve
Authors: Hildebrandt Henry , Höfker Uwe 
Published: April 2003

AbstractChemische Experimente werden schon seit längerer Zeit auf „Celluloid gebannt”︁, aber auch hier revolutioniert (oder ‚evolutioniert’︁) das Internet die Zugänglichkeit und kann — recht verstanden — die Lehre in Hochschule und Schule bereichern und ein größeres chemieinteressiertes Publikum ansprechen. Neben die Realaufnahmen von chemischen Versuchen treten dabei immer häufiger mehr oder weniger interaktive Veranschaulichungen von Modellvorstellungen durch Computeranimationen.
Sternförmige Hohlschalen aus Metalloxiden
Authors: Feil Sylvia 
Published: April 2003

AbstractSie bilden nicht nur schöne Muster — die Strukturen der Hohlschalen von Kieselalgen (Diatomeen) und Strahlentierchen (Radiolarien) faszinieren auch durch andere Eigenschaften: Diese Einzeller haben hierarchisch geordnete Strukturebenen, die eine biomimetische Nachahmung interessant machen.
Ein Calciumatom als Computer
Authors: Groß Michael 
Published: April 2003

AbstractEin Quantenzustand kann — zumindest theoretisch — der Informationsverarbeitung dienen. Denken Sie etwa an einen Kernspin im Magnetfeld, der sich mittels Anregung mit Radiowellen zwischen zwei verschiedenen Zuständen umschalten lässt. Dafür braucht man nicht mehr als ein handelsübliches NMR‐Spektrometer. Ein solches Zustandspaar definiert ein Qubit, das quantenmechanische Analogon zum Bit der Computertechnik.
Doubly tunable double ring surface coil
Authors: Volotovskyy Vyacheslav , Tomanek Boguslaw , Corbin Ian , Buist Richard , Tuor Ursula I. , Peeling James 
Published: April 2003

AbstractTo perform multinuclear magnetic resonance spectroscopy and imaging, a coil with a high signal‐to‐noise ratio and spatially uniform B1 field that covers the same volume of interest at several frequencies is preferred. The design of a surface coil that reduces contaminating signals from the surface‐lying tissues and improves uniformity of the B1 field within the same preselected volume for both31P and 1H is described. Testing of the coil demonstrated acquisition of proton images and 31P spectra from a selected voxel in rat liver at 7 T. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 11–16, 2003.
The relationship between the Nyquist criterion and the point spread function
Authors: Sarty Gordon E. 
Published: April 2003

AbstractIt is well known that to avoid aliasing in the reconstruction of functions on ℝn that have support on a compact set B (having n‐volume |B|), it is necessary to sample k‐space with a density equal to or higher than one sample per 1/|B| n‐volume of k‐space. It is also well known that undersampling any particular region of k‐space will lead to an aliasing, or “folding in” of image information containing the spatial frequency information of the undersampled region. Here a simple description of what it means to fold in specific spatial frequency information is given in terms of the structure of the point spread function. The description should be useful for designers of k‐space sampling schemes that deliberately incorporate undersampled regions. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 17–24, 2003.
NMR spiral surface microcoils: Design, fabrication, and imaging
Authors: Eroglu Sertac , Gimi Barjor , Roman Brian , Friedman Gary , Magin Richard L. 
Published: April 2003

AbstractNMR investigation of volume‐limited chemical and biological samples requires a radio frequency (RF) microcoil with high signal‐to‐noise ratio (SNR) over the region of interest. Conventional approaches using solenoidal microcoils provide high sensitivity (RF field strength per unit current) and spectral resolution but require the sample and sample container to be enclosed by the coil. Planar surface microcoils provide an alternative configuration that allows direct access to the sample, but with the sacrifice of RF field uniformity. In this study we evaluate a family of planar RF microcoils (500 MHz, Archimedean geometry, 1–6 turns, inner radius 0.75 to 4 mm, and conductor widths of 75, 100, and 200 μm). The design, fabrication, and performance (electrical and NMR) of the coils are described. This coil configuration exhibits a high local SNR, easy fabrication, good electrical properties, and moderate spectral uniformity (suitable for imaging and low resolution NMR spectroscopy). This design can also be scaled to smaller dimensions. These results suggest that planar spiral RF microcoils will find applications in multimodality microscopy and microfludic devices where sample manipulation and coil integration with the microanalysis systems is necessary. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 17B: 1–10, 2003.
CORBA request portable interceptors: analysis and applications
Authors: Baldoni R. , Marchetti C. , Verde L. 
Published: April 2003

AbstractInterceptors are an emerging middleware technology enabling the addition of specific network‐oriented capabilities to distributed applications. By exploiting interceptors, developers can register code within interception points, extending the basic middleware mechanisms with specific functionality, e.g. authentication, flow control, caching, etc. Notably, these extensions can be achievedwithout modifyingeither the application or the middleware code.In this paper we report the results of our experiences with CORBA request portable interceptors. In particular, we point out (i) the basic mechanisms implementable by these interceptors, i.e. request redirection and piggybacking and (ii) we analyze their limitations. We then propose a proxy‐based technique to overcome the interceptors' limitations. Successively, we present a performance analysis carried out on three Java‐CORBA platforms currently implementing the portable interceptors specification. Finally, we conclude our work with a case study in which portable interceptors are used to implement the fault‐tolerant CORBA client invocation semantic without impacting on the client application code and on the CORBA ORB. We also release fragments of Java code for implementing the described techniques. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of a prototype intelligent network interface
Authors: Underwood Keith D. , Ligon Walter B. , Sass Ron R. 
Published: April 2003

AbstractWith a focus on commodity PC systems, Beowulf clusters traditionally lack the cutting edge network architectures, memory subsystems, and processor technologies found in their more expensive supercomputer counterparts. Many users find that what Beowulf clusters lack in technology, they more than make up for with their significant cost advantage. In this paper, an architectural extension that adds reconfigurable computing to the network interface of Beowulf clusters is proposed. The proposed extension, called an intelligent network interface card (or INIC), enhances both the network and processor capabilities of the cluster, which has a significant impact on the performance of a crucial class of applications. Furthermore, for some applications, the proposed extension partially compensates for weaknesses in the PC memory subsystem. A prototype of the proposed architecture was constructed and analyzed. In addition, two applications, the 2D Fast Fourier Transform (2D‐FFT) and integer sorting, which benefit from the resulting architecture, are discussed and analyzed on the proposed architecture. Specifically, results indicate that the 2D‐FFT is performed 15–50% faster when using the prototype INIC rather than the comparable Gigabit Ethernet. Early simulation results also indicate that integer sorting will receive a 21–32% performance boost from the prototype. The significant improvements seen with a relatively limited prototype lead to the conclusion that cluster network interfaces enhanced with reconfigurable computing could significantly improve the Beowulf architecture. Copyright © 2003 John Wiley & Sons, Ltd.
Using multirail networks in high‐performance clusters
Authors: Coll Salvador , Frachtenberg Eitan , Petrini Fabrizio , Hoisie Adolfy , Gurvits Leonid 
Published: April 2003

AbstractUsing multiple independent networks (also known as rails) is an emerging technique which is being used to overcome bandwidth limitations and enhance fault tolerance of current high‐performance parallel computers. In this paper, we present and analyze various algorithms to allocate multiple communication rails, including static and dynamic allocation schemes. An analytical lower bound on the number of rails required for static rail allocation is shown. We also present an extensive experimental comparison of the behavior of various algorithms in terms of bandwidth and latency. We show that striping messages over multiple rails can substantially reduce network latency, depending on average message size, network load and allocation scheme. The methods compared include a static rail allocation, a basic round‐robin rail allocation, a local‐dynamic allocation based on local knowledge and a dynamic rail allocation that reserves both communication endpoints of a message before sending it. The last method is shown to perform better than the others at higher loads: up to 49% better than local‐knowledge allocation and 37% better than the round‐robin allocation. This allocation scheme also shows lower latency and it saturates at higher loads (for long enough messages). Most importantly, this proposed allocation scheme scales well with the number of rails and message size. In addition we propose a hybrid algorithm that combines the benefits of the local‐dynamic allocation for short messages with those of the dynamic algorithm for large messages. Copyright © 2003 John Wiley & Sons, Ltd.
Cover Picture: Ab Initio Calculation of Parity‐Violating Chemical Shifts in NMR Spectra of Chiral Molecules (ChemPhysChem 4/2003)
Authors: Laubender Guido , Berger Robert 
Published: April 2003

AbstractThe cover picture shows an intriguing effect in molecular systems, which is caused by the parity‐violating weak interactions: The chemical shifts of magnetic nuclei are predicted to differ for the two enantiomers of a chiral compound! While in the R enantiomer the nucleus (red) of the yellow center gives rise to the red NMR signal, the corresponding nucleus of the S enantiomer (green) is expected to absorb at a slightly different frequency. The ab initio approach presented by Laubender and Berger on pp. 395–399 allows for a prediction of the resulting parity‐violating line splitting (shown in the black curve) and for the identification of molecular candidates that are well‐suited to the first successful measurement of parity‐violating effects in molecules.
Surface Tension Measurements in Microgravity and their Relevance to Marangoni Convection
Authors: Egry Iván 
Published: April 2003

AbstractThe physical properties of liquids, such as surface tension, Marangoni convection and surface segregation are important in many technical fields and are of fundamental interest. However, inaccuracy of experiments has prevented us from fully understanding these phenomena. Recent advances in experimental techniques, such as the containerless technique and the utilization of microgravity, are described.