bluuebunny/crossref_metadata_2025_split huggingface dataset:
A robust method for determining 1H–15N long‐range correlations: 15N optimized CIGAR‐HMBC experiments
Authors: Kline Mike , Cheatham Steve 
Published: April 2003

AbstractAn examination of a variety of common nitrogen‐containing systems was undertaken to optimize parameters for observation of 1H–15N long‐range correlations. Because of the diversity of coupling constants encountered with 1H–15N correlations, a modified accordion‐based sequence was used to provide the best results. Optimization of the values for the accordion delay revealed that a range between 3 and 10 Hz provided the best compromise between detection of weak correlations and loss of signal to T2 processes. Multiple bond correlations were readily detected for each class of compound with the exception of anilines. Correlations within heterocyclic systems revealed some general patterns. In general, stronger correlations were observed from protons to ‘pyrrole‐like’ nitrogens than to the ‘pyridine‐type’ nitrogens of imidazoles and pyrazoles. Very long‐range (four‐ and five‐bond) correlations were routinely observed between methyl groups and the nitrogens of aromatic heterocycles. Copyright © 2003 John Wiley & Sons, Ltd.
NMR study of fumarprotocetraric acid, a complex lichen depsidone derivative from Cladonia furcata
Authors: Su Bao‐Ning , Cuendet Muriel , Nikolic Dejan , Kristinsson Hördur , Ingólfsdóttir Kristín , van Breemen Richard B. , Fong Harry H. S. , Pezzuto John M. , Kinghorn A. Douglas 
Published: April 2003

AbstractA lichen depsidone derivative, fumarprotocetraric acid, was obtained as the major constituent of Cladonia furcata (Huds.) Schrad. collected in Iceland. In the 1H NMR spectrum (in DMSO‐d6) of this compound, the trans double bond proton signals of the fumaryl unit appeared as overlapping singlets. To confirm the presence of a trans double bond in the molecule, fumarprotocetraric acid was treated with triethylamine. The 1H NMR spectrum of the resultant triethylamine salt displayed a pair of clear doublets with coupling constants of 15.7 Hz, which are characteristic of a trans double bond. Unambiguous 1H and 13C NMR spectral data for both fumarprotocetraric acid and its triethylamine salt were assigned for the first time based on the interpretation of their 2D NMR (HMQC, HMBC and NOESY) spectra. Copyright © 2003 John Wiley & Sons, Ltd.
Multinuclear magnetic resonance study of chiral mesoionic oxa‐ and thiatriazole and tetrazole derivatives: adducts with dirhodium complexes and chiral recognition
Authors: Jaźwiński Jaroslaw , Rozwadowski Zbigniew , Magiera Damian , Duddeck Helmut 
Published: April 2003

AbstractMesoionic compounds 1–8 were synthesized and their 1H, 13C, 14N, 15N and 17O NMR spectra recorded in the absence and presence of the chiral dirhodium complex Rh*. It is shown that the enantiomers of the mesoionic compounds could be differentiated satisfactorily (‘dirhodium method’). Copyright © 2003 John Wiley & Sons, Ltd.
Structural investigations of three triazines: solution‐state NMR studies of internal rotation and structural information from solid‐state NMR, plus a full structure determination from powder x‐ray diffraction in one case
Authors: Birkett Helen E. , Cherryman Julian C. , Chippendale A. Margaret , Evans John S. O. , Harris Robin K. , James Mark , King Ian J. , McPherson Graham J. 
Published: April 2003

AbstractThree model 2,4,6‐tris(amino)‐1,3,5‐triazines, structurally related to a dyestuff molecule previously studied by NMR, were synthesized in order to enable the effects of rotamer exchange on the NMR spectra to be investigated in more detail. Two of the compounds are novel. Internal rotation of the triazine ring substituents was studied by variable‐temperature solution‐state 1H, 13C and 15N NMR spectroscopy. All the expected rotamers were detected for each molecule. Rotamer exchange rates varied from slow to fast over the temperature range −40 to 90 °C, as observed for the dyestuff molecule itself. Solid‐state 13C and 15N NMR provided information about the structures of the solid molecules. A full crystal structure determination from high‐resolution powder x‐ray diffraction was achieved for one of the molecules using simulated annealing techniques. Ab initio MO and 15N NMR chemical shift calculations, based on energy‐minimized structures derived from the x‐ray structure determination, enabled the effect of intermolecular hydrogen bonding on the 15N NMR chemical shifts to be studied. The results compared favourably with the experimental solid‐state 15N NMR shifts. Copyright © 2003 John Wiley & Sons, Ltd.
Computer‐assisted structure elucidation of natural products with limited 2D NMR data: application of the StrucEluc system
Authors: Blinov Kirill A. , Carlson Dean , Elyashberg Mikhail E. , Martin Gary E. , Martirosian Eduard R. , Molodtsov Sergey , Williams Antony J. 
Published: April 2003

AbstractThis paper considers the strategy of the StrucEluc expert system application for structure elucidation of new natural products when there is a lack of connectivity information that is characteristic of proton‐deficient molecules. It is shown that in this case, a database search for fragments using a 13C NMR spectrum as input allows an investigator to fill gaps in the recorded data. Algorithms and programs have been developed that allow fragments found in the library and/or proposed by the user to be embedded in the molecular connectivities diagrams built on the basis of 2D NMR data analysis. We demonstrate the structure determination of three alkaloids from the cryptolepine series using the principles of construction and application of a user fragment library. The approach described appears to be the most efficient means of structure elucidation for natural products with 2D NMR spectra characterized by sparse responses. Copyright © 2003 John Wiley & Sons, Ltd.
DFT/FPT studies of the structural dependencies of long‐range 1H,1H coupling over four bonds 4J(H,H′) in propanic and allylic systems
Authors: Barfield Michael 
Published: April 2003

AbstractA study is presented of the structural dependencies for scalar J‐coupling across four bonds in propanic and allylic systems. Density functional theory (DFT) and finite perturbation theory (FPT) were used to obtain the Fermi contact (FC) contributions to 1H,1H coupling. Interproton couplings 4J(H,H′) in propane were obtained as functions of the dihedral angles φ1 and φ3, which are measured about the C(1)—C(2) and C(2)—C(3) bonds, respectively, and on the C(1)—C(2)—C(3) internal angle θ2. A four‐term trigonometric expression reproduces the dependence on φ1 and φ3 with a standard deviation of 0.1 Hz. The molecular structures for a series of bicycloalkanes were fully optimized and DFT/FPT results for 4J(H,H′) are in good agreement with the available experimental data. However, in non‐W arrangements of bicyclic systems the propane trigonometric expression for 4J(H,H′) often gives signs opposite to those observed. It is now clear the conformational dependence of coupling constants in propane is not, in general, applicable to bicyclic systems. The DFT/FPT propane‐based results for coupling involving a methyl group (H—C—C—CH3) are in better conformity with the experimental data. The DFT/FPT results for cisoid and transoid allylic coupling 4J(H,H′) in propene were obtained as functions of the dihedral angle φ measured about the C(2)—C(3) bond. Trigonometric expressions with three terms reproduce the calculated propene results with standard deviations 0.1 Hz. The molecular structures for a series of bicycloalkenes were fully optimized and DFT/FPT results for cisoid and transoid coupling are in fairly good agreement with the available experimental data. In contrast to the propanic coupling, the trigonometric expressions for propenic coupling constants are generally applicable to conformational analyses in bicycloalkenes. Copyright © 2003 John Wiley & Sons, Ltd.
13C and 23Na solid‐state NMR spectra of organosodium compounds
Authors: Jost Steffen , Günther Harald 
Published: April 2003

AbstractFor three organosodium complexes, namely triphenylmethylsodium(tmeda) (1), fluorenylsodium(pmdta) (2) and fluorenylsodium(tmeda) (3), 13C and 23Na solid‐state FT‐NMR spectra have been measured for the first time. They were analysed in terms of chemical shifts, δ(13C) and δ(23Na), and 23Na quadrupole coupling constants, χ(23Na). It is shown that the NMR parameters are sensitive to the structural features of the complexes and correlate well with the contact ion‐pair structures of 1–3. 23Na resonances are shielded by ring current effects of the aromatic ligands. Copyright © 2003 John Wiley & Sons, Ltd.
Relative stereochemical determination of β‐hydroxycarbonyl compounds (aldol products) utilizing the J‐based configuration analysis method
Authors: Williamson R. Thomas , Marquez Brian L. , Sosa Ana Carolina Barrios , Koehn Frank E. 
Published: April 2003

Abstractβ‐Hydroxycarbonyl moieties (aldol products) are common features in a variety of molecular structures. Whether this structural motif is synthetically prepared or incorporated into a natural product, the determination of the anti or syn (threo and erythro, respectively) relationship between the α and β centers using previously reported NMR methods has, up to this point, been unreliable. Here, we report a method to determine the relative configuration of aldol products through the combined use of 3JHH homonuclear and, nJCH long‐range heteronuclear coupling constants in tandem with dipolar couplings in a manner related to the previously described J‐based configuration analysis method. Copyright © 2003 John Wiley & Sons, Ltd.
Poly(1‐butene)/clay nanocomposites: Preparation and properties
Authors: Wanjale Santosh D. , Jog J. P. 
Published: April 2003

AbstractThe preparation and properties of poly(1‐butene) (PB)/clay nanocomposites are described for the first time. Nanocomposites were prepared with the melt‐intercalation technique, using organically modified clay. The X‐ray diffraction patterns portrayed well‐defined diffraction peaks at higher d‐spacing than pristine clay, confirming the intercalation of polymer in silicate layers. Because PB exhibits time‐dependent polymorphism, the effect of clay on the phase transformation of PB was examined with thermal analysis. The phase transformation from a metastable tetragonal form to a stable hexagonal form was enhanced because of incorporation of layered silicates in the polymer matrix. The nanocomposites exhibited about a 40–140% increase in storage modulus depending on the clay content and significantly lower coefficient of thermal expansion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1014–1021, 2003
Miscibility level and mechanical characterization of blends of two liquid‐crystalline polymers based on p‐hydroxybenzoic acid
Authors: García M. , Eguiazábal J. I. , Nazábal J. 
Published: April 2003

AbstractInjection‐molded blends composed of two liquid‐crystalline polymers (LCPs) based on 60/40 p‐hydroxybenzoic acid/ethylene terephthalate (R3) and 73/27 p‐hydroxybenzoic acid/2,6‐hydroxynaphthoic acid (VA) copolymers, respectively, were obtained across the whole composition range. The two amorphous phases of the blends contained only slight amounts of the minority component, and the occurrence of some chemical reaction, mainly at high VA contents, was detected by Fourier transform infrared. Synergisms in the modulus of elasticity and in the tensile strength were seen in most of the blend compositions. The largest synergism was in the 50/50 R3/VA blend, which showed a modulus of elasticity 26% higher than that of either of the two components and a 17% positive deviation in the tensile strength with respect to the rule of mixtures. The different orientation of the LCPs in the blends explains the differences in the mechanical behavior. However, contrary to previous works on LCP blends and despite the almost complete immiscibility, the observed negative volume of mixing appears to be the main parameter that determines the synergistic mechanical behavior. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1022–1032, 2003
Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. I. Miscibility and crystallization kinetics
Authors: Zheng Sixun , Zheng Haifeng , Guo Qipeng 
Published: April 2003

AbstractCrystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP)‐cured epoxy resin (ER) and poly(ϵ‐caprolactone) (PCL) were prepared via the in situ curing reaction of epoxy monomers in the presence of PCL, which started from initially homogeneous mixtures of diglycidyl ether of bisphenol A (DGEBA), BAPP, and PCL. The miscibility of the blends after and before the curing reaction was established with differential scanning calorimetry and dynamic mechanical analysis. Single and composition‐dependent glass‐transition temperatures (Tg's) were observed in the entire blend composition after and before the crosslinking reaction. The experimental Tg's were in good agreement with the prediction by the Fox and Gordon–Taylor equations. The curing reaction caused a considerable increase in the overall crystallization rate and dramatically influenced the mechanism of nucleation and the growth of the PCL crystals. The equilibrium melting point depression was observed for the blends. An analysis of the kinetic data according to the Hoffman–Lauritzen crystallization kinetic theory showed that with an increasing amorphous content, the surface energy of the extremity surfaces increased dramatically for DGEBA/PCL blends but decreased for ER/PCL blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1085–1098, 2003
Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon‐13 cross‐polarization/magic‐angle spinning nuclear magnetic resonance spectroscopy
Authors: Zheng Sixun , Guo Qipeng , Chan Chi‐Ming 
Published: April 2003

AbstractCrystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane‐crosslinked epoxy resin (ER) and poly(ϵ‐caprolactone) (PCL) were investigated by means of Fourier transform infrared (FTIR) spectroscopy and high‐resolution solid‐state NMR spectroscopy. FTIR investigations indicated that there were specific intermolecular interactions between ER and PCL and that the intermolecular hydrogen‐bonding interactions were weaker than the self‐association in pure epoxy. The intermolecular hydrogen bonding was considered to be the driving force for the miscibility of the thermosetting blends. For the examination of the miscibility of the thermosetting blends at the molecular level, high‐resolution solid‐state 13C cross‐polarity/magic‐angle spinning (CP‐MAS) NMR spectroscopy was employed. The line width of 13C CP‐MAS spectra decreased with increasing PCL contents, and the chemical shift of the carbonyl carbon resonance of PCL shifted to a low field with an increasing epoxy content in the blends. The proton spin–lattice relaxation experiments in the laboratory frame showed that all the blends possessed identical, composition‐dependent relaxation times (i.e., the proton spin–lattice relaxation times in the laboratory frame), suggesting that the thermosetting blends were homogeneous on the scale of 20–30 nm in terms of the spin‐diffusion mechanism, and this was in a good agreement with the results of differential scanning calorimetry and dynamic mechanical analysis. For the examination of the miscibility of the blends at the molecular level, the behavior of the proton lattice relaxation in the rotating frame was investigated. The homogeneity of the thermosetting blends at the molecular level was quite dependent on the blend composition. The PCL‐lean ER/PCL blends (e.g., 70/30) displayed a single homogeneous amorphous phase, and the molecular chains were intimately mixed on the segmental scale. The PCL‐rich blends displayed biexponential decay in experiments concerning the proton spin–lattice relaxation times in the rotating frame, which was ascribed to amorphous and crystalline phases. In the amorphous region, the molecular chains of epoxy and PCL were intimately mixed at the molecular level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1099–1111, 2003
Fracture and crack profile fictitious crack modeling of porous poly(methyl methacrylate)
Authors: Jiménez‐Piqué E. , Dortmans L. J. M. G. , De With G. 
Published: April 2003

AbstractThis article presents the fracture behavior and applicability of the fictitious crack (FC) model to describe the fracture of a porous poly(methyl methacrylate) material. Two test geometries, wedge‐opening load and single‐edge‐notched beam, were employed under two different test conditions (room temperature and in water at 45 °C); all presented quasibrittle fracture behavior. The crack profile of a wedge‐opening load sample was visualized and measured with the digital image correlation technique. The mechanical response of all the samples, including the crack profile, was successfully modeled with the FC model, and this showed the good applicability of this model to the fracture of this granular poly(methyl methacrylate) material. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1112–1122, 2003
In situ bubble‐stretching dispersion mechanism for additives in polymers
Authors: Daming Wu , Qingyun Meng , Ying Liu , Yumei Ding , Weihong Chen , Hong Xu , Dongyun Ren 
Published: April 2003

AbstractAn in situ bubble‐stretching (ISBS) model has been proposed on the basis of an analysis of the dispersion process of inorganic additives in polymers. The ISBS model is applicable to a dispersion of solid granular aggregates in polymer melts because the dispersed phase itself serves as a nucleation agent, giving rise to bubbles that expand at the surface of the microgranules and their aggregates. In terms of bidirectional stretching, the ISBS process can increase the degrees of freedom of granule dispersion, which favors more homogeneous dispersion. According to theoretical predictions and indirect experimental estimations of the dispersion of nanoscale CaCO3 and nanoscale hydrotalcite in high‐density polyethylene (HDPE), when the bubble expands, the stretching rate of the polymer melt on the bubble wall can reach 105–106 s−1. The field emission scanning electron microscopic images indicated that the granular size of dispersed CaCO3 and hydrotalcite in HDPE with the ISBS method is about 60–80 nm, two orders of magnitude smaller than that attained with a shearing rate of 103 s−1 in a capillary rheometer. It is also predicted that elastic bubble oscillations may be generated through suitable control of process parameters and that their oscillatory frequency can be in the ultrasound range. This type of bubble oscillation can also promote dispersion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1051–1058, 2003
Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites
Authors: Zheng Junrong , Siegel Richard W. , Toney C. Gregory 
Published: April 2003

AbstractThe influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003
Benefits of modeling and simulation in implementing a shared component build strategy
Authors: Componation Paul J. , Gholston Sampson E. , Hyatt Leslie A. , Simmons Brandy B. 
Published: April 2003

AbstractThe push for significantly more affordable Department of Defense programs in a limited budget environment has created a need to better understand the cost impacts of manufacturing decisions made during the early phases of system development. To reduce costs, Department of Defense programs are investigating the benefits of implementing a shared component build strategy. To implement this strategy, program managers need tools that will evaluate how their decision will affect the cost of the systems they are developing. This paper reports on the implementation of a shared component build strategy on two major missile system programs. A simulation model was developed to illustrate the impact of a shared build on the manufacturing system that would construct a component. The simulation models the production line of a common component for two major missile programs. The combination of the simulation and the corresponding user interface demonstrates the ease of experimenting with various manufacturing system architectures and highlights the benefits achieved by utilizing modeling and simulation. The results from this simulation showed that selecting an alternative manufacturing system architecture could result in a $3.04 million cost avoidance. These results support the theory that modeling and simulation is an invaluable decision‐making tool that can support evaluation of a shared production build strategy. © 2003 Wiley Periodicals, Inc. Syst Eng 6: 63–75, 2003
Value streams in science & technology: A case study of value creation and intelligent tutoring systems
Authors: Rouse William B. , Boff Kenneth R. 
Published: April 2003

AbstractScience and technology (S&T) involves a broad community of investors, sponsors, investigators, adopters, and end‐users. This wide range of stakeholders adds value in a variety of ways, resulting in what are termed value streams. This article focuses on elaborating and formalizing S&T value streams. This formulation is evaluated in the context of a case study of computer‐based intelligent tutoring systems. The value streams identified in this context span several decades of S&T investments, R&D in numerous organizations, and deployments in a variety of school settings. Insights gained from this case study enable proposing a general model of value creation in S&T. The phenomena embodied in this model suggest several central hypotheses. Approaches to evaluating these hypotheses are discussed. © 2003 Wiley Periodicals, Inc. Syst Eng 6: 76–91, 2003
Expanding the role of systems engineers in the age of escalating complexity
Authors: Ren Chiang H. 
Published: April 2003

AbstractThe accomplishments of scientists conducting complex systems research could significantly expand the role of systems engineers currently wrestling with more narrowly defined complex systems. The rapid growth of problems extending from newly formed complex systems in society, economic activities, and geopolitical dynamics argues further for the immediate fusion of scientific insight with practical engineering approaches for problem solving. In supporting this new role for systems engineers, a new class of complex systems engineering tools, along with new analytical techniques, are envisioned. Such tools and techniques can further support the continuing efforts of scientists in unraveling the mysteries of highly complex self‐forming and self‐organizing systems. © 2003 Wiley Periodicals, Inc. Syst Eng 6: 116–121, 2003 DOI 10.1002/sys.10039