bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular Asymmetric Amidations of Sulfonamides and Sulfamates Catalyzed by Chiral Dirhodium(II) Complexes
Authors: Fruit Corinne , Müller Paul 
Published: July 2004

AbstractEnantioselective intramolecular amidation of aliphatic sulfonamides was achieved for the first time by means of chiral carboxylatodirhodium(II) catalysts in conjunction with PhI(OAc)2 and MgO in high yields and with enantioselectivities of up to 66% (Scheme 3, Table 1). The best results were obtained with [Rh2{(S)‐nttl)4] and [Rh2{(R)‐ntv)4] as catalysts ((S)‐nttl=(αS)‐α‐(tert‐butyl)‐1,3‐dioxo‐2H‐benz[de]isoquinoline‐2‐acetato, (R)‐nto=(αR)‐α‐isopropyl‐1,3‐dioxo‐2H‐benz[de] isoquinoline‐2‐acetato). In addition, these carboxylatodirhodium(II) catalysts were also efficient in intramolecular amidations of aliphatic sulfamates esters, although the enantioselectivity of these latter reactions was significantly lower (Scheme 4, Table 3).
Unsymmetrical Unsaturated Ketones from Lactones and Carboxylic Acids in One Step
Authors: Giersch Wolfgang , Naef Ferdinand 
Published: July 2004

AbstractA one‐step transformation of γ‐ and δ‐(spiro)lactones into γ,δ‐ and δ,ε‐unsaturated ketones in the presence of carboxylic acids in the vapor phase at 400° over a supported manganese catalyst is reported for the first time. The scope of this new transformation is exemplified with a series of lactones, and a mechanistic rationale is proposed.
Internal Nucleophilic Termination in Acid‐Mediated Polyene Cyclizations. Part 3
Authors: Snowden Roger L. , Eichenberger Jean‐Claude , Linder Simon , Sonnay Philippe 
Published: July 2004

AbstractTreatment of the unsaturated allenic alcohols (E)‐7, (Z)‐7, 10, 13, and 19 with an excess of FSO3H in 2‐nitropropane at −90° to −30° afforded, in 68–85% yield, diastereoisomer mixtures of racemic tricyclic ethers 14a–d and 20a–d, respectively (Schemes 3 and 5), with high stereoselectivity (see Table and Scheme 6). These stereospecific transformations represent the first reported examples of an acid‐mediated polyene cyclization, in which an alkene is the initiating group and an allenic alcohol serves as the internal terminator. In close analogy to our earlier work, a nonsynchronous process is postulated, whereby the stereochemical course of cyclization is directed by the conformational structure of an intermediate cyclohexyl cation (see Schemes 3 and 6). In addition, the organoleptic properties of 14c and 20c, racemic didehydro and methyl didehydro analogues, respectively, of the known odorant Ambrox® ((−)‐4f), are briefly discussed.
Asymmetric Reaction of Simple Nitro Compounds with Chiral 1,3‐Oxazolidin‐2‐ones
Authors: Kudyba Iwona , Raczko Jerzy , Jurczak Janusz 
Published: July 2004

AbstractThe chiral oxazolidinone 1 (=[(3aS,6R,7aR)‐tetrahydro‐8,8‐dimethyl‐2‐oxo‐4H‐3a,6‐methano‐1,3‐benzoxazol‐3‐yl](oxo)acetaldehyde) was found to react stereoselectively with simple nitro compounds in the presence of Al2O3 or Bu4NF⋅3 H2O (TBAF) as catalysts, affording the diastereoisomeric nitro alcohols 3–6 with good asymmetric induction. When Al2O3 was used, the (S)‐configuration at the center bearing the OH group was generated, with the relative syn‐configuration for the major diastereoisomers. In the case of the nitro‐aldol reaction catalyzed by TBAF, an opposite asymmetric induction was found for two nitro compounds. In contrast to 1, compound 12 (=((4R,5S)‐4‐methyl‐2‐oxo‐5‐phenyl‐1,3‐oxazolidin‐3‐yl)(oxo)acetaldehyde), a derivative of Evans auxiliary, gave rise to poor asymmetric induction in Henry reactions.
Synthesis and Properties of Conformationally Constrained Analogues of Floral‐Type Odorants
Authors: Lamboley Serge , Morel Cédric , de Saint Laumer Jean‐Yves , Boschung André F. , Richards Nigel G. J. , Winter Béat M. 
Published: July 2004

AbstractThe twelve bridged analogues 8–19 of floral‐type odorants related to cyclamenaldehyde (1) were synthesized (Schemes 1–5) to investigate the relationship between the structural and conformational features of these compounds and their odor properties. Comparison of the data from sensory evaluation and molecular modeling suggests that the side chain of both the unconstrained and the constrained active analogues is not extended (anti) but rather folded (gauche) in the ‘bioactive’ conformation. However, it is mainly the nature of the substituents at the α position of the aldehyde function that critically influences the odor quality and strength. These studies provide new information that should aid ongoing efforts to develop models of odorantreceptor interactions.
Studies on the Synthesis of Di‐ and Trisaccharide Analogues of Moenomycin A. Modifications in Unit E and in the Lipid Part
Authors: Yang Guangbin , Mansourova Madina , Hennig Lothar , Findeisen Matthias , Oehme Ramona , Giesa Sabine , Welzel Peter 
Published: July 2004

AbstractRoutes allowing the synthesis of moenomycin analogues with one modified sugar component and with new lipid parts were developed (see 10c, 12c, 16b, and 20b in Schemes 2–4). It is anticipated that such analogues will be useful for studying the mode of action of the moenomycin‐type transglycosylase inhibitors in detail and for preparing analogues with improved pharmacokinetic properties.
Syntheses and Odor Descriptions of Cyclopropanated Compounds. Part 5
Authors: Kiyota Hiromasa , Takigawa Shin‐ya , Kuwahara Shigefumi 
Published: July 2004

AbstractAnalogs of methyl jasmonate (=methyl (1R*,2R*)‐3‐oxo‐2‐[(Z)‐pent‐2‐enyl]cyclopentaneacetate; MJA) bearing a cyclopropane ring, double bond, or a F‐substituent were synthesized, and their odor characteristics were examined. Most of the analogs with the same stereochemical properties as methyl epijasmonate showed odor properties superior to MJA. Interestingly, the enol acetate of MJA had a diffusive orchid‐like note.
Synthesis of 4‐(Phenylamino)quinazoline‐2(1H)‐selones and Diselenides from Isoselenocyanates: Dimroth Rearrangement of an Intermediate
Authors: Atanassov Plamen K. , Linden Anthony , Heimgartner Heinz 
Published: July 2004

AbstractThe reaction of anthranilonitriles 8 with phenyl isoselenocyanates (1a) in dry pyridine under reflux gave 4‐(phenylamino)quinazoline‐2(1H)‐selones 9 (Scheme 2). They are easily oxidized and converted to diselenides of type 11. The analogous reaction of 8a with phenyl isothiocyanate (1b) yielded the quinazoline‐2(1H)‐thione 10 (Scheme 2). A reaction mechanism via a Dimroth rearrangement of the primarily formed intermediate is presented in Scheme 3. The molecular structures of 10 and 11a have been established by X‐ray crystallography. Unexpectedly, no selone or diselenide was obtained in the case of the reaction with 3‐aminobenzo[b]furan‐2‐carbonitrile (14). The only product isolated was the selenide 16 (Scheme 4), the structure of which has been established by X‐ray crystallography.
Photochemistry of Spiro[6H‐[1,3]Oxathiin‐2,2′‐tricyclo[3.3.1.13,7]decan]‐ 6‐one
Authors: Schmidt Kerstin , Margaretha Paul 
Published: July 2004

AbstractOn irradiation (300 nm) in the solid state, the title compound 8 affords tricyclo[3.3.1.13,7]decan‐2‐one (=adamantan‐2‐one; 9) selectively via [4+2] cycloreversion. A similar result is obtained on photolysis in solution (MeCN or acetone), also in the presence of added alkenes. On irradiation in MeOH, a solvent adduct 11 is isolated in addition to 9. From experiments in CD3OD, it can be inferred that 11 is formed via syn‐addition of MeOH to the ground‐state (E)‐heterocycle 16.
Encapsulating chondrocytes in copolymer gels: Bimodal degradation kinetics influence cell phenotype and extracellular matrix development
Authors: Rice Mark A. , Anseth Kristi S. 
Published: July 2004

AbstractHydrogels provide an ideal environment for encapsulating chondrocytes and facilitating the production of cartilaginous tissue. However, the deposition of extracellular matrix (ECM) and ultimate tissue function are significantly affected by degradation of gel scaffolds. It was hypothesized that a bimodal degradation process would capture the critical features necessary for neotissue development. Specifically, most of the initial crosslinks would degrade quickly and enable ECM deposition, whereas a critical amount would remain or degrade much more slowly to provide structural integrity over a longer time period. In this study, chondrocytes were encapsulated in copolymer gels of nondegradable [poly(ethylene glycol) dimethacrylate] and degradable [poly(lactic acid)‐b‐poly(ethylene glycol)‐b‐poly(lactic acid) dimethacrylate] macromers to investigate the effects of gel degradation on ECM evolution. All gels were synthesized from 10 wt % total macromer solutions consisting of 0, 19, 21, 23, 25, or 100 mol % nondegradable units. The copolymer constructs were found to have lower DNA content than completely degradable constructs after 8 weeks. However, total biochemical content was very similar among the various copolymer constructs. Histological analysis gave more interesting insight, showing a more uniform spatial distribution of ECM components in copolymer samples than in constructs with 100 mol % nondegradable units. In addition, a number of major structural defects were present in constructs with 0 mol % nondegradable units that became less apparent as the amount of nondegradable units was increased. Overall, the copolymer gels had a higher compressive modulus during neotissue development and also showed no evidence of chondrocyte dedifferentiation. With their bimodal degradation profile, copolymer gels with carefully selected ratios of degrading to slow or nondegrading crosslinks provide distinct advantages for ECM development in tissue‐engineered cartilage. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 560–568, 2004
Cover Picture: Macromol. Chem. Phys. 11/2004
Authors: Safronov Alexander P. , Smirnova Yelena A. , Pollack Gerald H. , Blyakhman Felix A. 
Published: July 2004

Cover: Partly dehydrated gels of potassium poly(acrylate) change their enthalpy as referred to maximum swollen equilibrium gel, due to the changes in molecular and ionic interactions. Microcalorimetry measurements of swelling to equilibrium for such gels reveal an enthalpy “spectrum”, which makes it possible to evaluate separately main contributions to molecular interactions in polyelectrolytes.Further details can be found in the Full Paper by A. P. Safronov,* Y. A. Smirnova, G. H. Pollack, and F. A. Blyakhman on page 1431.
Hydrodynamic Effect on Secondary Phase Separation in an Epoxy Resin Modified with Polyethersulfone
Authors: Tang Xiaolin , Zhang Linxia , Wang Tao , Yu Yingfeng , Gan Wenjun , Li Shanjun 
Published: July 2004

AbstractSummary: The evolution of the morphologies in blends of epoxy/4,4′‐methylenebis(2,6‐dimethylaniline)/polyethersulfone was followed by time‐resolved light scattering, optical microscopy and scanning electron microscopy. The results suggest that, once the diffusion of epoxy molecules cannot follow the geometrical growth, a secondary phase separation occurs, even in the droplet morphology, in which the size of the epoxy‐rich domain grows as usual. The viscoelastic effect of polyethersulfone is also discussed.Development of morphologies followed by OM: bicontinuous phase separation in the PES‐15.9 blend cured at 140 °C after 80 s.magnified imageDevelopment of morphologies followed by OM: bicontinuous phase separation in the PES‐15.9 blend cured at 140 °C after 80 s.
An integral equation method for a boundary value problem in superconductivity
Authors: Heese Harald 
Published: July 2004

AbstractWe present a mathematical model for transport current carrying superconductors in terms of a boundary value problem for the Laplace equation. A uniqueness and existence result is given via a boundary integral equation method in a Hölder space setting. It's numerical solution is described using a combined collocation method and quadrature rule approach including a convergence analysis and numerical examples. Copyright © 2004 John Wiley & Sons, Ltd.
Coupling of flow simulation and structural analysis for glass‐filled thermoplastics
Authors: Foss Peter H. 
Published: July 2004

AbstractIn the automotive industry, glass‐filled thermoplastics are used in air intake manifolds, radiator tanks, and many other parts. Plastic parts have many advantages over metal parts including mass, design flexibility and parts consolidation. However, widespread application of glass‐filled thermoplastic materials has been limited in many cases by the inability to accurately predict performance and durability. Fiber‐filled injection‐molded parts contain complex fiber orientation patterns. This fiber orientation state affects material properties including elastic modulus and strength and part properties including shrinkage and warpage. Tremendous amounts of time and money can be saved if one can predict the moldability and mechanical properties of a part at the design stage. In this work, we present a method where commercially available injection molding and structural analysis software may be coupled together with appropriate material property data to improve prediction of structural performance for parts molded from short glass fiber‐filled plastics. In addition, we compare the experimental and predicted performance based on simple equations and complex finite element calculations. Two major conclusions may be drawn from this work. In general, the assumption of geometric nonlinearity must be made. Also, an orthotropic material model is generally more robust and accurate than an isotropic analysis. Polym. Compos. 25:343–354, 2004. © 2004 Society of Plastics Engineers.
Rate‐dependent compressive behavior of unidirectional carbon fiber composites
Authors: Salvi Amit G. , Waas Anthony M. , Caliskan Ari 
Published: July 2004

AbstractUnidirectional carbon fiber stitched composites were subjected to off‐axis compression under static and low‐velocity impact loading. Specimens were cut such that the fibers were at angles of 15°, 30°, 45° and 60° to the direction of loading. A modified compression fixture was used to carry out the tests. Static tests were carried out on a hydraulically activated MTS loading frame, where specimens were subjected to displacement controlled loading. Low‐velocity impact tests were conducted on a drop tower facility. A three‐strain‐gauge rosette was used to measure global strains. Load was measured using a load cell. Owing to the unique microstructure of the specimens, a modified three‐parameter characterization of the inelastic response was used, and the constants associated with this characterization were determined uniquely. Independently, Iosipescu shear tests were carried out to determine the shear response of the material under static and low‐velocity impact conditions. The shear response so determined was checked against the off‐axis test results. It is shown that rate‐dependent interfacial effects are predominant in these materials. Polym. Compos. 25:397–406, 2004. © 2004 Society of Plastics Engineers.
Fatigue crack initiation and propagation in polyamide‐6 and in polyamide‐6 nanocomposites
Authors: Bellemare Simon C. , Bureau Martin N. , Denault Johanne , Dickson J. Ivan 
Published: July 2004

AbstractRecent developments in polymer nanocomposites have led to improvements in conventional short‐term, but the long‐term mechanical properties have received little attention. The objective of the present study was to characterize the effect of nanoparticles on the fatigue crack initiation and propagation mechanisms and on the fatigue properties of polyamide‐6 (PA6) nanocomposite (PA6NC) prepared byin situpolymerization with montmorillonite clay. Two approaches were employed: fatigue life measurements and crack growth monitoring. Compared with non‐filled PA6 at the same stress amplitude, the number of cycles to fracture was higher for the nanocomposite, which suggests an increase in the intrinsic resistance of the material to crack initiation. However, the crack growth rate results indicated that nanoparticles decreased the resistance to crack propagation. Post‐fatigue fractographic observations indicated a change in the fatigue crack propagation mechanism resulting from the addition of nanoparticles, primarily attributed to the increase in yield stress, which favors the development of a fibrillated deformation zone. The fibrillation process in the relatively high crack propagation rate regime appeared to be preceded by plastic deformation at approximately constant volume. Most of the effect of nanoparticles on the fatigue behavior and properties results probably from the mechanical reinforcement on the microstructure and its effect on the yield stress and Young's modulus rather than from the effect of the inorganic filler to act as a stress concentrator. Polym. Compos. 25:433–441, 2004. © 2004 Society of Plastics Engineers.
Fatigue testing of polymer membranes
Authors: Mackin Thomas J. , Vernon Paul J. , Begley Matthew R. 
Published: July 2004

AbstractThis paper presents a new impression method for fatigue testing polymer membranes that circumvents many of the problems associated with traditional uniaxial testing of thin, compliant films. The proposed test geometry subjects the polymer membrane to a biaxial stress state by displacing the center of a clamped circular specimen with a spherical indenter. The initiation of fatigue cracks in the membrane is monitored using optical and/or infrared sensing. Finite element and non‐linear membrane theory models, which take into account large‐displacement kinematics, non‐linear material behavior and friction between the indenter and membrane, are used to establish connections between the applied indenter displacement, or load, and the stress in the film. A key result is a closed‐form relationship between applied load and membrane stress, which can be used for a wide range of friction and material response. The broadly applicable approach is demonstrated using two types of laminated polymer membranes. Polym. Compos. 25:442–450, 2004. © 2004 Society of Plastics Engineers.
Solvation effects in the heterolyses of 3‐X‐3‐methylpentanes (X = Cl, Br, I)
Authors: Martins Filomena , Leitão Ruben Elvas , Moreira Luís 
Published: July 2004

AbstractA comparative study of the heterolysis reactions of 3‐X‐3‐methylpentanes (X = Cl, Br, I) in a set of protic and aprotic solvents was performed at 25.00°C. Rate constant values were correlated with solvent descriptors using the TAKA multiparametric equation. Our results point towards a decrease in both hydrogen bond donor acidity (electrophilicity) and hydrogen bond acceptor basicity (nucleophilicity) contributions, and towards an increase in the dipolarity/polarizability term on going from the chloride substrate to iodide. These features suggest the formation of an increasingly early transition state, in contrast to the classical Hughes–Ingold rationale, but in agreement with the Hammond postulate. Furthermore, there seems to be no evidence for a shift in solvation from an electrophilic (or anionic) mode in the chloride substrate to a nucleophilic (or cationic) mode in the iodide, as claimed by some authors. Copyright © 2004 John Wiley & Sons, Ltd.
Chemistry of protonated species in gaseous environments
Authors: Chiavarino Barbara , Crestoni Maria E. , Fornarini Simonetta 
Published: July 2004

AbstractAn overview is presented of gas‐phase studies on the structure and reactivity of protonated species from the authors' research. Specific problems have been addressed operating in different gaseous environments, either in radiolytic systems at atmospheric pressure, enabling the NMR characterization of the neutral end products of gas phase ion–molecule reactions, or in low‐pressure FT‐ICR mass spectrometry, where ions can be trapped and characterized by their reactivity or spectroscopic features. Proton transfer reactions have revealed the role of competing acidic sites leading to biologically relevant C7H7O. radical species and of competing basic sites in substituted benzenes. Proton transfer reactions have also been used as a tool to form elusive cations, e.g. c‐C3H, modulating the reaction energetics, and to unveil the structure and occurrence of degenerate isomerization processes within the benzenium ion. Copyright © 2004 John Wiley & Sons, Ltd.
Substituent and solvent effects on the N‐2—N‐3 hindered rotation of cis‐1,3‐diphenyltriazenes
Authors: Barra Mónica , Srivastava Sonali , Brockman Eleanor 
Published: July 2004

AbstractLaser‐flash photolysis techniques were applied to investigate the dependence of the rotational barrier about the N‐2—N‐3 bond of symmetrically 4,4′‐disubstituted cis‐1,3‐diphenyltriazenes on substituents and solvents. The increase in the rotational barrier with increasing ability of the 4‐substituent to withdraw electrons implies the intramolecular process to be more susceptible to the electronic character of the aryl group attached to N‐1 than of that bonded to N‐3. Furthermore, the increase in the rotational barrier with decreasing solvent polarity implies an increase in dipole moment on rotation from the ground state to the transition state. Copyright © 2004 John Wiley & Sons, Ltd.
Boron trifluoride activated enaminocarbonyl compounds: the influence of intermolecular interactions on theab initiodetermination of structures and vibrational spectra
Authors: Nikolai Joachim , Maas Gerhard , Taubmann Gerhard 
Published: July 2004

AbstractThe structures of the BF3–enaminoaldehyde adducts3a,bhave been determined by quantum‐chemical calculations employing Hartree‐Fock, Møller‐Plesset and density functional methods. The length of the coordinative BO bond ranges between 1.59 and 1.62 Å. The BSSE‐free energy of the BO bond ranges between −14.7 and −16.9 kcal/mol. Taking into account hydrogen bonds and dispersion forces between two molecules of3a,bin the dimeric structure4reduces the BO bond length significantly (BO: 1.52–1.57 Å) thereby reproducing the BO bond length found in the x‐ray structure of1(BO: 1.49 Å) with much better accuracy. Using the calculated IR and Raman spectra of the dimers4as reference, the BO band in the experimental spectra can be assigned. Our approach seems to be of value in discussions comparing structural features gained from gas phaseab initiocalculations and solid state x‐ray structures involving strong dipolar structures which allow for various intermolecular interactions. Copyright © 2004 John Wiley & Sons, Ltd.
From the conformation of a single molecule to physical networks in highly interacting polymers: A small‐angle neutron study
Authors: Perahia Dvora , Jiao Xuesong , Traiphol Rakchart 
Published: July 2004

AbstractSmall‐angle neutron scattering has been used to study the conformation and structure of highly interacting macromolecules in complex fluids. The evolution of the structure has been investigated from the conformation of a single molecule through an association process to the formation of physical networks. Two highly interacting polymers, an ionic polymer (consisting of a perfluorinated backbone and an ionizable hydrophilic side chain dissolved in water/alcohol mixtures) and rodlike, highly conjugated phenylene ethylene molecules (dissolved in toluene), have been studied. Highly interacting polymers often form relatively long lasting physical networks with increasing polymer concentration. The driving force, however, is system‐specific, and so are the micellar systems and physical networks formed. Although the two families of polymers under consideration are entirely different chemically, their strong interaction, either ionic or through π–π coupling, results in similarities in the complex fluids formed when they are dissolved in solutions. These include elongated configurations in dilute solutions, association into micelles, and eventually coalescence into physical networks. The ionic polymers form durable stable networks, whereas the rodlike polymers form a fragile, gel‐like phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3165–3178, 2004