bluuebunny/crossref_metadata_2025_split huggingface dataset:
Angular group‐induced bond alternation (AGIBA). Part 5—Conformation dependence and additivity of the effect: structural studies of 3,5‐dimethoxybenzaldehyde ­derivatives and related systems
Authors: Krygowski Tadeusz M. , Pindelska Edyta , Anulewicz‐Ostrowska Romana , Grabowski Sławomir J. , Dubis Alina T. 
Published: September 2002

AbstractX‐ray structure analysis of 3,4,5‐trimethoxybenzadehyde and 3,5‐dimethoxy‐4‐(1‐bromoethoxy)benzaldehyde gave their molecular geometries which showed a vague AGIBA effect. To clarify the situation, ab initio optimizations at the MP2/6–31G** level of theory of 12 conformers of 1,3,5‐trimethoxy‐, 1,3‐dimethoxy‐5‐formyl‐, 1,3‐diformyl‐5‐methoxy‐ and 1,3,5‐triformylbenzene derivatives were carried out. The results support the occurrence of additive AGIBA effects, even if some weak interactions are possible between the methoxy and formyl groups. Copyright © 2001 John Wiley & Sons, Ltd.
Olefin epoxidation by dioxiranes and percarboxylic acids: an analysis of activation energies calculated by a density functional method
Authors: Gisdakis Philip , Rösch Notker 
Published: September 2002

AbstractThe activity of dioxiranes, R2CO2, and percarboxylic acids, RCO(O2)H, in olefin epoxidation reactions can be rationalized by a frontier orbital interaction. Barrier heights of these oxygen transfer reactions, as calculated by a density functional method, depend linearly on the energy of the olefin HOMO orbital π (C—C) and of the peroxide LUMO orbital σ*(O—O). Activation barriers can be predicted from linear relationships with the proton affinity of a dioxirane (as measured by the hydrogen fluoride association energy) or the pKa value of a percarboxylic acid. Copyright © 2001 John Wiley & Sons, Ltd.
Enzyme‐catalyzed transesterification of vinyl esters on cellulose solids
Authors: Xie Jiangbing , Hsieh You‐Lo 
Published: September 2002

AbstractEnzyme‐catalyzed transesterification of several cellulose solids in organic media have been investigated. Several protease enzymes were made soluble in organic media through ion‐paired enzyme–surfactant complexes. Subtilisin Carsberg was found to be catalytically active in the transesterification of cellulose with vinyl propionate and vinyl acrylate in anhydrous pyridine. The ester carbonyl groups in acylated cellulose derivatives were confirmed by Fourier transform infrared spectroscopy. The surfaces of these cellulose derivatives became hydrophobic as demonstrated by increased water‐contact angles. The enzyme‐catalyzed transesterification was confirmed to regioselectively target the primary hydroxyl group of cellulose by reactions on specifically substituted cellulose. The cellulose esters from enzyme‐catalyzed transesterification could be hydrolyzed partially by the same enzyme in aqueous media, and were thus biodegradable. Surface grafting of cellulose acrylate was demonstrated using azobisisobutyronitrile‐initiated polymerization of acrylonitrile in dimethylformamide. Polyacrylonitrile (PAN)‐g‐cellulose shows a different thermal behavior from cellulose, homopolymer PAN, and PAN/cellulose blends. The grafted PAN on PAN‐g‐cellulose at a 16% grafting add‐on is incapable of cyclization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1931–1939, 2001
Synthesis and polymerization of functionalized dendritic macromonomers
Authors: Vetter Serge , Koch Sabine , Schlüter A. Dieter 
Published: September 2002

AbstractThe synthesis of dendritic building blocks (dendrons) of the first generation (G1) and the second generation, which carry differently protected amine groups in the periphery, is reported. The dendrons are used for the synthesis of the corresponding acrylic and methacrylic macromonomers. Their polymerization behavior under radical conditions is investigated. The G1 dendronized polymers are decorated at their peripheral amino groups, that is, with the chiral amino acid L‐phenylalanine by the attach‐to approach. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1940–1954, 2001
Epoxy–amine reticulates observed by infrared spectrometry. III. Modifications of the structure and hydration abilities after irradiation in a humid atmosphere
Authors: Ngono Yvette , Maréchal Yves 
Published: September 2002

AbstractThis article is the third part of a series devoted to the study of the responsibilities of both humidity and irradiation in the aging process of amine‐cured epoxy resins. The basic technique used in this study was infrared spectrometry. In previous articles, we described the hydration of two kinds of epoxy resins widely used in the nuclear industry. In the first article, we reported results concerning the hydration of unirradiated resins; in the second article, these resins were first submitted to ionizing radiation in a dry atmosphere. In this article, we describe the effects of irradiation in a humid atmosphere and compare these effects to what was observed after irradiation in a dry atmosphere, as described in the previous articles. These effects were subtle: the humidity of the ambient atmosphere apparently protected the resins from oxidative degradation because, after irradiation in a humid atmosphere, a smaller number of carboxylic groups were formed. However, the water uptake increased after irradiation in a humid atmosphere. Thus, the humidity of the ambient atmosphere at the same time favored the rupture of chains, which released steric hindrances and allowed a greater number of H2O molecules to reach hydrophilic sites in the resin. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1129–1136, 2001
Intercalated clay nanocomposites: Morphology, mechanics, and fracture behavior
Authors: Zerda Adam S. , Lesser Alan J. 
Published: September 2002

AbstractIntercalated nanocomposites of modified montmorillonite clays in a glassy epoxy were prepared by crosslinking with commercially available aliphatic diamine curing agents. These materials are shown to have improved Young's modulus but corresponding reductions in ultimate strength and strain to failure. The results were consistent with most particulate‐filled systems. The macroscopic compressive behavior was unchanged, although the failure mechanisms in compression varied from the unmodified samples. The fracture toughness of these materials was investigated and improvements in toughness values of 100% over unmodified resin were demonstrated. The fracture‐surface topology was examined using scanning electron and tapping‐mode atomic force microscopies and shown to be related to the clay morphology of the system. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1137–1146, 2001
Structural analysis of certain linear operators representing chemical network systems via the existence and uniqueness theorems of spectral resolution. VI*
Authors: Arimoto Shigeru , Spivakovsky Mark , Ohno Hiromu , Zizler Peter , Taylor Keith F. , Yamabe Tokio , Mezey Paul G. 
Published: September 2002

AbstractThe present Part VI of this series of articles provides a mathematical and methodical link between (i) fundamental methodology in the repeat space theory (RST), which is referred to as the approach via the aspect of form and general topology and which has universal unifying power to handle additivity problems of molecules that have many identical moieties, and (ii) frontier electron theory of reactivity indices. Using theoretical tools required to link (i) and (ii), we establish a theorem from which the Generalized Alpha Existence Theorem (a theorem essential in the RST and proved in the previous Part V) directly follows. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 389–400, 2001
A QM/MM/continuum model for computations in solution: Comparison with QM/MM molecular dynamics simulations
Authors: Chalmet S. , Rinaldi D. , Ruiz‐López M. F. 
Published: September 2002

AbstractWe propose a model for fast quantum mechanical computations of molecules and processes in solution. The chemical system is described quantum mechanically (QM) using density functional theory. A few discrete solvent molecules are described using molecular mechanics (MM) force fields. The bulk solvent is described through a dielectric continuum model. The interaction between the QM/MM aggregate and the continuum is computed by using a multipole moment development of the charge distribution of the former. This is an intermediate model between the standard continuum approach and the combined quantum mechanics and molecular mechanics (QM/MM) technique, in which a large number of MM solvent molecules is considered and a statistical simulation of the solution is performed. The method may also be used to estimate long‐range interactions in combined QM/MM Monte Carlo or molecular dynamics simulations. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Improvement of the hybrid density functional method from the viewpoint of effective exchange integrals
Authors: Kitagawa Y. , Soda T. , Shigeta Y. , Yamanaka S. , Yoshioka Y. , Yamaguchi K 
Published: September 2002

AbstractSpin‐unrestricted hybrid density functional theory (DFT) methods are improved to reproduce potential curves and effective exchange integrals ( Jab) of several diradical models, which were calculated by unrestricted post‐Hartree–Fock methods. Particularly, we attempt to reproduce the Jab value of the UCCSD(T) method by using the DFT methods. In general, the magnitude of the calculated Jab values by the conventional DFT methods for radical dimers was too large in comparison with the post‐Hartree–Fock methods values. To overcome the problem, we improve the DFT method for the intermolecular (through‐space) effective exchange integrals by using the hybrid method. Furthermore, the rule for the hybridization is constructed in terms of instability value ysys of the bonding. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Electronic structure calculation by monte carlo diagonalization method
Authors: Shigeta Y. , Nagao H. , Yamaguchi K. 
Published: September 2002

AbstractWe propose an electronic structure calculation scheme for ground and low‐lying excited states of molecular systems by using the generalized coherent state for fermion, where the coefficients of the coherent states are determined by a stochastic approach. This method has both the advantage of the ordinary quantum Monte Carlo and that of the direct diagonalization methods and does not suffer from the negative sign problem. We demonstrate a performance of the present method. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Detection of sulfur‐containing impurities in pharmaceutical samples by high performance liquid chromatography/chemical reaction interface mass spectrometry
Authors: Eckers Christine , Abramson Fred P. , Lecchi Paolo 
Published: September 2002

AbstractThis paper describes the use of chemical reaction interface mass spectrometry (CRIMS) combined with liquid chromatography for the detection of trace level sulfur‐containing impurities in pharmaceutical materials. A mixture of sulfur‐ and non‐sulfur‐containing compounds were analyzed initially to test the system. Then the determination of trace level impurities in a cimetidine drug substance was carried out. Detection of sulfur‐containing impurities at less than 0.1% of the major component was obtained with good linearity. The results obtained are consistent with the expected results for this sample and illustrate the applicability of the technique. Copyright © 2001 John Wiley & Sons, Ltd.
On the fragmentation pathway of the ionized enol of glycine in the gas phase
Authors: Marino T. , Russo N. 
Published: September 2002

AbstractDensity functional and second‐order many body perturbation approaches were used to compute the potential energy surface for the fragmentation of the ionized enol of glycine [H2NCH = C(OH)2]+· into water and aminoketene radical cation [H2N‐HC = CO]+·. Two possible pathways were considered. The potential energy surfaces obtained are very similar and both predict the existence of a molecular complex in which the water is coordinated to the aminoketene moiety in two different fashions with a noticeable binding energy. The fragmentation is kinetically controlled by the step in which the molecular complex is formed from the most stable cation enol of glycine. Our quantum‐mechanical data confirm the hypothesis that the ylide ion [H3NCHCOOH]+· is an intermediate in the water loss. Copyright © 2001 John Wiley & Sons, Ltd.
The effect of the source pressure on the abundance of ions of noncovalent protein assemblies in an electrospray ionization orthogonal time‐of‐flight instrument
Authors: Tahallah Nora , Pinkse Martijn , Maier Claudia S. , Heck Albert J. R. 
Published: September 2002

AbstractThe effect of elevating the pressure in the interface region of an electrospray ionization orthogonal time‐of‐flight mass spectrometer on the ion intensity of different noncovalent protein assemblies has been investigated. Elevating the pressure in the interface region generally led to an enhanced detection of high m/z ions. The optimum pressure was found to be dependent on the m/z value of the ions. This pressure effect should be carefully addressed when relating ion abundance in the mass spectra to solution phase abundance of noncovalent protein assemblies. Copyright © 2001 John Wiley & Sons, Ltd.
Electron impact mass spectral interpretation for some thiophosphoryl‐p‐acetylaminobenzenesulfonamides
Authors: Fenesan I. , Popescu Rodica , Supuran C.T. , Nicoara Simona , Culea Monica , Palibroda N. , Moldovan Z. , Cozar O. 
Published: September 2002

AbstractThis work discusses the synthesis and the fragmentation patterns for 2‐(p‐acetylaminosulfonamido)‐2‐thiono‐(5,5‐dimethyl‐1,3,2‐dioxaphosphorinane)(1) and for the p‐acetylaminosulfonylamides of O,O‐diethylthiophosphoric acid (2), O,O‐diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic‐thiolimidic structure was attributed to compounds 1–5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions. Copyright © 2001 John Wiley & Sons, Ltd.
Deuterium/hydrogen isotope ratio measurement of water and organic samples by continuous‐flow isotope ratio mass spectrometry using chromium as the reducing agent in an elemental analyser
Authors: Kelly Simon D. , Heaton Karl D. , Brereton Paul 
Published: September 2002

AbstractA rapid continuous‐flow technique for quantitative determination of hydrogen isotope ratios in water and organic materials at natural abundance levels is described. Water and organic samples were reduced in a helium stream at temperatures in excess of 1000 °C over chromium metal. δ2H‰ values of water and organic samples were determined by calibration against International Atomic Energy Agency reference materials V‐SMOW and SLAP water. The accuracy of the method was demonstrated through the analysis of the intermediate water standard GISP and IAEA water intercomparison materials OH‐1, OH‐2 and OH‐3. Values obtained using this technique compared well with reference values (maximum difference 2.2‰). The precision of water analyses was less than 2.3‰ (1 σ or 1 standard deviation) in all cases. No apparent memory effect was observed when measuring samples at the natural abundance level. The application of the technique to organic molecules and the salts of organic acids was successfully demonstrated by measuring the δ2H‰ values of an n‐hexadecane laboratory reference and anhydrous calcium formate versus water calibration materials. © Crown copyright 2001. Reproduced with permission of the Controller of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.
Use of a novel nitrification inhibitor to reduce nitrous oxide emission from 15N‐labelled dairy slurry injected into soil
Authors: Dittert Klaus , Bol Roland , King Rosalind , Chadwick David , Hatch David 
Published: September 2002

AbstractRecent recommendations for environmentally sound use of liquid animal manure often include injection of slurry into soil. Two of the most important undesired side effects, ammonia (NH3) volatilisation and odour emissions, are usually significantly reduced by slurry injection. On the other hand, because of the higher amount of nitrogen (N) remaining in soil, the risk of nitrate (NO3−) leaching and nitrous oxide (N2O) emissions is increased. Thus, the reduction of local effects caused by NH3 deposition, e.g. N enrichment and soil acidification, may be at the cost of large‐scale effects such as ozone depletion and global warming as a result of emitted N2O. In this context, nitrification inhibitors can contribute significantly to a reduction in NO3− leaching and N2O production.A field experiment was carried out at IGER, North Wyke, which aimed to evaluate the effect of the new nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP/ENTEC™). For this experiment, 15N enriched dairy slurry was used and the isotopic label in soil N as well as in N2O were studied. After slurry injection into the grassland soil in August 2000, the major emissions of N2O occurred during the first ten days. As expected, high N2O emission rates and 15N content of the emissions were concentrated on the slurry injection slots, showing a steep decrease towards the untreated centre‐point between slurry injection slots. The nitrification inhibitor DMPP proved to be very efficient in reducing N2O emissions. At a rate of 2 kg DMPP ha−1, the total amount of N2O emitted was reduced by 32%, when compared with slurry injection without DMPP. The isotopic label of the emitted N2O showed that during the 22‐day experimental period, emissions from the slurry N pool were strongly reduced by DMPP from 0.93 kg N2O‐N ha−1 (−DMPP) to 0.50 kg N2O‐N ha−1 (+DMPP), while only a minor effect on emissions from the soil N pool was observed (0.69 to 0.60 kg N2O‐N ha−1; −DMPP, +DMPP, respectively). Copyright © 2001 John Wiley & Sons, Ltd.
Development of δ15N stratification of NO3− in soil profiles
Authors: Handley Linda L. , Johnston Andrew M. , Hallett Paul D. , Scrimgeour Charles M. , Wheatley Ronald E. 
Published: September 2002

AbstractNew evidence, obtained using a robust method for measuring the δ15N of NO3−‐N in soil, is consistent with denitrification being the major determinant in the vertical distribution of NO3−‐δ15N in soil profiles. These data also suggest that varying moisture regimes result in different effects of soil NO3−‐N leaching on residual whole soil δ15N. Copyright © 2001 John Wiley & Sons, Ltd.
Strategic environmental assessment for sustainable households in 2050: illustrated for clothing
Authors: Bras‐Klapwijk Remke M. , Knot J. Marjolijn C. 
Published: September 2002

AbstractThis paper discusses the environmental assessment approach that has been developed and applied in the SusHouse project (Strategies towards the Sustainable Household). This project aims at developing and evaluating strategies for a sustainable development of households in the future, for three basic household activities: nutrition, shelter and clothing. The environmental assessment approach in the SusHouse project is different from traditional approaches such as life cycle assessment, due to the system‐level character and due to the focus on future developments. Examples are taken from the clothing research in the Netherlands. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment.
Nanohardness measurement of carbon nitride thin films
Authors: Kojima Isao , Xu Wentao , Fujimoto Toshiyuki 
Published: September 2002

AbstractA nanohardness measurement method using an atomic force microscope equipped with a diamond tip is described and applied to carbon nitride thin films. These films were prepared by radiofrequency magnetron sputtering at various substrate temperatures. Based on the general hardness definition, the hardness of thin films was determined directly from the indentation force and the (residual) indentation depth using fused silica as a standard reference. The hardnesses measured by this technique are quite reproducible. The hardnesses of the carbon nitride thin films with a thickness of ∼35 nm were in the range 31–35 GPa, increasing slightly with substrate temperature. This increase is in good correlation with the film density changes as measured by grazing‐incidence x‐ray reflectivity. Copyright © 2001 John Wiley & Sons, Ltd.
XRD and XPS studies on the ultra‐uniform Raney‐Ni catalyst prepared from the melt‐quenching alloy
Authors: Lei Hao , Song Zhen , Bao Xinhe , Mu Xuhong , Zong Baoning , Min Enze 
Published: September 2002

AbstractWe present a novel method for preparing an ultra‐uniform Raney‐Ni catalyst, which includes melt‐quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X‐ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni–Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen‐pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright © 2001 John Wiley & Sons, Ltd.
Study of the diffusion behaviour of MoO3and ZnO on oxide thin films by SR‐TXRF
Authors: Xu Weiming , Xu Junqian , Wu Nianzu , Yan Jingfeng , Zhu Yongfa , Huang Yuying , He Wei , Xie Youchang 
Published: September 2002

AbstractThe diffusion process of MoO3and ZnO on stable oxide thin films (SiO2, Al2O3, TiO2) was investigated mainly by means of synchrotron‐radiation‐excited total reflection x‐ray fluorescence spectroscopy (SR‐TXRF). A stripe of MoO3or ZnO on the oxide thin film was used as the diffusion source. After thermal treatment, MoO3diffused onto the surface of those films and formed a monolayer or a submonolayer. The diffusion capacity and the diffusion rate of MoO3on each film differed significantly. Sublimation of MoO3also was detected during the diffusion process. A possible explanation for all the phenomena is the combination of surface diffusion onto the surface of the support and transportation via the gas phase. By contrast, ZnO hardly diffuses onto the surface of the film due to its high melting point. Copyright © 2001 John Wiley & Sons, Ltd.
What's in a name.com?: The effects of ‘.com’ name changes on stock prices and trading activity
Authors: Lee Peggy M. 
Published: September 2002

AbstractThis paper uses a market signaling perspective to examine investor reactions to firm announcements of name changes to include ‘.com.’ Firms that change their name as a purely cosmetic technique are contrasted to those that employ other strategic investments. Results show that announcements of ‘.com’ name changes are associated with significant increases in stock prices and trading activity. Furthermore, the magnitude of investor reactions is significantly larger when name changes are accompanied by other strategies. Copyright © 2001 John Wiley & Sons, Ltd.