bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the effects of silicate modification on polymer‐layered silicate nanocomposite morphology
Authors: Kurian Mary , Dasgupta Arnab , Beyer Frederick L. , Galvin Mary E. 
Published: October 2004

AbstractThe morphological behavior of a series of polymer‐layered silicate nanocomposites (PLSNs) has been investigated. The goal was to probe the effect of “textured” silicate surfaces on PLSN morphology. The nanocomposites were fabricated by mixing montmorillonite clay that was carefully modified with tailor‐made polystyrene (PS) surfactants into a PS homopolymer matrix, where the chemical similarity of the matrix polymer and surfactants assures complete miscibility of surfactant and homopolymer. To examine the effect of silicate surface “texture,” clay was modified with combinations of long and short surfactants. The samples were then direct melt annealed to allow the equilibrium morphology to develop, and characterized by small‐angle X‐ray scattering. Based on the implications of the Balazs model and other work on the wetting behavior of polymer melts with longer surfactants and textured surfaces we expected that the intercalation of the homopolymer matrix material into the modified clay would be promoted. Extensive characterization of both the modified clays as well as the resultant nanocomposites clearly show that the modified clays exhibit a high degree of order, but also that only phase‐separated morphologies are formed in the corresponding nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4075–4083, 2004
In‐situ microfibrillar PET/iPP blend via slit die extrusion, hot stretching, and quenching: Influence of hot stretch ratio on morphology, crystallization, and crystal structure of iPP at a fixed PET concentration
Authors: Li Zhong‐Ming , Li Liang‐Bin , Shen Kai‐Zhi , Yang Ming‐Bo , Huang Rui 
Published: October 2004

AbstractThe in situ microfibrillar blend of poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) was fabricated through a slit die extrusion, hot stretch, and quenching process. The morphological observation indicates that while the unstretched blend appears to be a common incompatible morphology, the hot stretched blends present PET in situ fibers whose characteristics, such as diameter and aspect ratio, are dependent on the hot stretching ratio (HSR). When the HSR is low, the elongated dispersed phase particles are not uniform at all. As the HSR is increased to 16.1, well‐defined PET microfibers were generated in situ, whose diameter is rather uniform and is around 0.6 ∼ 0.9 μm. The presence of the PET phase shows significant nucleation ability for crystallization of iPP. Higher HSR corresponds to faster crystallization of the iPP matrix, while as HSR is high up to a certain level, its variation has little influence on the onset and maximum crystallization temperatures of the iPP matrix during cooling from melt. Optical microscopy observation reveals that transcrystalline layers form in the microfibrillar blend, in which the PET microfibers play as the center row nuclei. In the as‐stretched microfibrillar blends, small‐angle X‐ray scattering measurements show that matrix iPP lamellar crystals have the same orientation as PET lamella. The long period of lamellar crystals of iPP is not affected by the presence of PET micofibers. Wide‐angle X‐ray scattering reveals that the β phase of iPP is obtained in the as‐stretched blends, whose concentration increases with the increase of the HSR. This suggests that finer PET microfibers can promote the occurrence of the β phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4095–4106, 2004
First‐order correlation‐kinetic contribution to Kohn–Sham exchange charge density function in atoms, using quantal density functional theory approach
Authors: Sen K. D. , Luque F. Javier 
Published: October 2004

AbstractUsing the static exchange‐correlation charge density concept, the total integrated exchange‐charge density function is calculated within the nonrelativistic spin‐restricted exchange‐only (i) optimized effective potential model, and (ii) nonvariational local potential derived from the exchange‐only work potential within the quantal density functional theory, for the ground‐state isoelectronic series: Ga+, Zn, Cu−; In+, Cd, Ag−; and Tl+, Hg, Au−. The difference between the exchange charge density function derived from these potentials is employed to evaluate the first‐order correlation‐kinetic contribution to the integrated exchange charge density. This contribution is found to be important for both the intra‐ and inter‐shell regions. Screening effects on the contribution due to the nd10 (n = 3–5) subshells are discussed through comparisons with similar calculations on Ca, Sr, and Ba, wherein nd10 electrons are absent. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Supersymmetry approaches to the radial bound states of the hydrogen‐like atoms
Authors: Chenaghlou A. , Fakhri H. 
Published: October 2004

AbstractIntroducing the associated Bessel polynomials in terms of two non‐negative integers, we factorize their corresponding differential equation into a product of first‐order differential operators by four different ways as shape invariance equations. Then, the radial part of the bound states of the Schrödinger equation of a hydrogen‐like atom is derived using one of the factorization methods in the framework of supersymmetric quantum mechanics. In this approach, we regenerate the radial bound states and their corresponding spectrum, which are consistent with the well‐known facts. Based on the generalization of the supersymmetry idea, we shall show that two hydrogen‐like atoms with the same energy of the electron possess three extra supersymmetric structures in addition to an ordinary one. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Electric field gradients in cuprates: Does LDA+U give the correct charge distribution?
Authors: Blaha P. , Schwarz K. , Novák P. 
Published: October 2004

AbstractWe present calculations for the electric field gradients (EFG) on the Cu sites in La2CuO4, YBa2Cu3O6, and YBa2Cu3O7 using standard LDA and GGA exchange‐correlation functionals, but also by using the LDA+U method for the correlated Cu‐d electrons. LDA or GGA calculations yield proper EFGs in agreement with experiment for all sites except the planar Cu(2) site, where the theoretical EFGs are too small by a factor of 2 to 3. This happens for both the metallic (superconducting) YBa2Cu3O7 and the antiferromagnetic insulators. For the latter, these calculations also lead to a nonmagnetic and metallic solution. Application of LDA+U with various double‐counting corrections and varying values for the Hubbard parameter U gives the correct magnetic and insulating ground state and the corresponding EFGs are substantially enhanced. Best agreement with experiment is found using the LDA+U(FLL) method with U around 6 eV, because this method leaves the Cu(1) EFG unchanged, even when U is applied to its d‐states. For the metallic compound YBa2Cu3O7, the EFG results favor the presence of local magnetic moments; however, in bandstructure calculations the necessary long‐range order leads to some artifacts and should be replaced by random spin fluctuations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Soft cohesive forces
Authors: Dobson John F. , Wang Jun , Dinte Bradley P. , McLennan Keith , Le Hung M. 
Published: October 2004

AbstractWe discuss dispersion forces, beginning with toy models that illustrate the limitations of various standard approaches. For metallic cohesion of very thin layers, we show that because the local density approximation (LDA) misses distant dispersion interactions, it also makes significant errors in the maximum cohesive force, a short‐ranged property. Furthermore, perturbative methods fail for such large planar systems, and CI methods are impractical. For large planar and linear systems in the well‐separated limit we show that insulating and metallic systems can exhibit very different dispersion forces, pairwise summation of atomic R−6 terms failing for the metallic cases. This could have implications for the interaction between nanotubes and between graphene planes: these planes are zero‐gap insulators at large separation and weak metals at graphitic equilibrium. Graphitic cohesion and intercalation are fundamental to a hydrogen economy and to various nanotechnologies, yet our arguments strongly suggest that all standard methods are inadequate for these phenomena. We argue that nonlocal RPA‐like correlation energy formulae contain all the required “seamless” physics of long‐ and short‐ranged interaction, as needed for graphitic and other soft‐matter systems. Indeed full calculations of this type are currently being attempted for graphite, and appear to be very delicate. We discuss recent efforts to approximate these calculations, and propose a new scheme. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
DFT calculations of light‐induced excited states and comparison with time‐resolved crystallographic results
Authors: Coppens Philip , Novozhilova Irina V. 
Published: October 2004

AbstractDFT calculations of the ground and first excited states of several transition metal complexes have been performed to complement time‐resolved diffraction experiments. The results from different functionals and relativistic treatments are tested against both diffraction and spectroscopic values. Calculations of the d8–d8complex [Pt2(pyrophosphite)4]4−quantitatively reproduce metal–metal shortening on excitation to the triplet state and support bond formation between the two metal centers, as do calculations on [Rh2(1,3‐diisocyanopropane)4]2+. Results on homoleptic and heteroleptic copper(I) 2,9‐dimethyl−1,10‐phenanthroline (dmp) complexes, which are investigated because of their potential for solar energy capture, confirm considerable molecular deformations on excitation. The distortion calculated for the isolated complex [Cu(dmp)(dmpe)]+(dmpe=1,2‐bis(dimethylphosphino)ethane) is significantly larger than observed in the crystal, indicating the constraining effect of the crystalline environment. The change in the net charge of the Cu atom upon photo‐induced metal‐to‐ligand charge transfer is less than 0.2 e, showing the limitations of the formal Cu(I)→Cu(II) designation. Electron density difference maps show a pronounced change in electronic structure of the Cu atom on excitation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Estimation of physiologically perceived color from TDDFT‐derived excitation spectra
Authors: Beck M. E. 
Published: October 2004

AbstractA new scheme for estimating the physiologically perceived color of a compound from its chemical structure is presented. The first step of this schema was the calculation of electronic excitation energies and probabilities. In this contribution, time‐dependent Density Functional Theory (TDDFT) was used for this purpose. From the excitation energies and oscillator strengths, line shape was approximated by folding with Gaussian functions. Using this spectrum, the CIE1931 chromaticity coordinates were gained by numerical integration. The dependence of the chromaticity coordinates on the band width of the Gaussians was visualized in a chromaticity diagram. From this diagram, the color, as physiologically perceived by a human observer, was estimated. The approach was applied to nine textbook examples of dyes and its limitations are discussed critically. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Density functional theory calculations on microscopic aspects of oxygen diffusion in ceria‐based materials
Authors: Frayret Christine , Villesuzanne Antoine , Pouchard Michel , Matar Samir 
Published: October 2004

AbstractThe critical role of the ionic conductivity properties of materials in the development of Intermediate Temperature Solid Oxide Fuel Cell (IT‐SOFC) technology has been emphasized over the past decade. However, from a fundamental point of view, little is known of the physicochemical parameters influencing ionic diffusion in these conductors. We attempted, through a Density Functional Theory investigation, to develop a new approach for an oxygen diffusion study in solids at the atomic scale. This methodology relies on the evaluation and comparison of steric, energetic, and chemical bonding factors along with the consideration of charge transfers when mixed valences do exist. Microscopic aspects of oxygen diffusion in the ionic conductor ceria‐based materials have been investigated by means of this procedure. It has been demonstrated that steric and polarizability effects prevail over other ones for both nonstoichiometric and doped ceria. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Simulation of UV/visible absorption spectra of (α‐diimine)nickel(II) catalysts by time‐dependent density functional theory
Authors: Cavillot Valérie , Champagne Benoît 
Published: October 2004

AbstractThe metal‐to‐ligand charge‐transfer excited states of (α‐diimine)‐NiII catalysts were simulated using time‐dependent density functional schemes for three reaction intermediates: the active site with a methyl group to mimic the growing alkyl chain, the corresponding π‐complex formed with an ethylene molecule, and the product where the propyl chain displays a γ‐agostic interaction. The simulations provide a basis for analyzing the experimental data in terms of charge‐transfer and enable one to assess the variations of the spectra upon modifications of the bidentate ligand. Moreover, the impact of the atomic basis set and exchange‐correlation functionals on the electronic absorption spectra was addressed in view of a more systematic use on new late transition metal catalysts. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Density functional theory study on the thermodynamic properties of aminophenols
Authors: Gomes José R. B. , Da Silva Manuel A. V. Ribeiro 
Published: October 2004

AbstractDensity Functional Theory was used to investigate several gas‐phase thermodynamic parameters of the o‐, m‐, and p‐aminophenol isomers. Within the DFT approach, the B3LYP method and the 6‐31G(d) and 6‐311+G(2d,2p) basis sets were used to compute standard enthalpies of formation. Calculated data are in excellent agreement with the experimental work of Nuñez et al. [J Chem Thermodyn 1996, 18, 575–579] but differs significantly from the values of Sabbah et al. [Can J Chem 1996, 74, 500–507]. In this work, other properties such as homolytic O‐H and N‐H bond dissociation energies, gas‐phase acidities, and proton or electron affinities were also obtained and confirm the few experimental results available for these properties in these kind of compounds, except the O‐H homolytic dissociation energy of 2‐aminophenol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Energy analysis of the chemical bond in group IV and V complexes: A density functional theory study
Authors: Poleshchuk O. Kh. , Shevchenko E. L. , Branchadell V. , Lein M. , Frenking G. 
Published: October 2004

AbstractWe analyzed the chemical bond between antimony, tin, titanium, and niobium chlorides with several Lewis bases using an energy partitioning analysis (EPA) and Weinhold's NBO method. The optimized geometries are in good agreement with the experimental results. The NQR‐35Cl frequencies appear to be fairly close to the experimental values. Theoretically obtained nuclear quadrupole coupling constants of antimony and niobium atoms are in good agreement with the experimental values. The bonding energies and experimentally known heats of formation are well reproduced by the employed level of theory. All investigated bonds in the donor‐acceptor complexes are highly polar, so that the Townes‐Dailey theory cannot be applied. The NBO approach shows that the donor–acceptor interactions of main‐group elements such as Sb and Sn can basically be described in terms of sp hybridization, just as these interactions of the transition metal elements Ti and Nb can be described by sd hybridization. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Structure by theory and experiment: One nationality, two languages
Authors: Hinchley Sarah L. , Wann Derek A. , Rankin David W. H. 
Published: October 2004

AbstractThe determination of structure in the gas phase is an important technique for obtaining accurate structural information for molecules, free from intermolecular interactions that could affect solid‐state structures. For large asymmetric molecules, obtaining the full gas‐phase structure using experimental data alone is virtually impossible in most cases. The utilisation of theoretical methods in the determination of the experimental molecular structure has allowed many more molecules to be studied, revealing important structural information. This information can be used by theoreticians to develop their methods further, and so both experimentalists and theoreticians benefit. This article describes the development of these methods and uses some examples to demonstrate their importance. These include the determination of the gaseous molecular structures of ferrocene and isopropylferrocene, and of the bis[bis(trimethylsilyl)methyl]phoshido radical, for which Density Functional Theory is realistically the only theoretical method available to aid the determination of the gas‐phase structure. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Metyrapone attenuates the sequential learning deficits but not monoamine depletions following d,l‐fenfluramine administration to adult rats
Authors: Skelton Matthew R. , Blankenmeyer Tracy L. , Gudelsky Gary A. , Brown‐Strittholt Carrie A. , Vorhees Charles V. , Williams Michael T. 
Published: October 2004

AbstractFenfluramine (FEN) is a substituted amphetamine known for its anorectic effects, without the stimulatory or abuse potential associated with other amphetamine derivatives. FEN is a potent serotonin (5‐HT) releaser and reuptake inhibitor and has been shown to cause depletions of 5‐HT that can last days and even weeks after administration. Administration of FEN four times on a single day also causes a prolonged increase of corticosterone (CORT) that lasts ∼72 h following the first FEN dose. This dosing regimen also produces deficits in sequential learning as measured in the Cincinnati water maze (CWM). Adrenalectomy blocks this effect but removes more than CORT. Accordingly, the purpose of this study was to determine whether inhibiting glucocorticoid production, by administration of the 11β‐hydroxylase inhibitor metyrapone (MET), will similarly attenuate or eliminate the sequential learning deficits seen with FEN exposure. MET (50 mg/kg) injections were administered 90 min prior to and for 3 days after FEN (four doses given at 2‐h intervals). Animals pretreated with MET and treated with FEN showed no sequential learning deficits when tested 1 week following FEN administration compared to FEN alone. The depletions of monoamines were similar following FEN administration, regardless of MET treatment. Taken together, this suggests that a potential mechanism for the sequential learning deficits in FEN‐treated animals is a result of prolonged increases in CORT output. Synapse 54:214–222, 2004. © 2004 Wiley‐Liss, Inc.
Characterization of a gene similar to BIK1 in the yeast Kluyveromyces lactis
Authors: Lamas‐Maceiras M. , Cerdán M. E. , Lloret A. , Freire‐Picos M. A. 
Published: October 2004

AbstractIn Saccharomyces cerevisiae, Bik1p is a microtubule plus‐end‐tracking protein that plays several roles in mitosis and ploidy. KlBik1p (from Kluyveromyces lactis) maintains the same structural‐domain organization as does S. cerevisiae Bik1p. As part of its characterization, we constructed a stable klbik1 mutant which is sensitive to benomyl only at 14 °C and has a higher frequency of crescent‐shaped nuclei than S. cerevisiae bik1 mutants. This phenotype is partially rescued by S. cerevisiae BIK1. Other phenotypes associated with bik1 are not present in the K. lactis mutant. By fusion to GFP we were able to show the functionality of the KlBik1p CAP–Gly domain and found that the fusion protein changes its cellular location during the cell cycle. Copyright © 2004 John Wiley & Sons, Ltd.
The cell wall sensor Wsc1p is involved in reorganization of actin cytoskeleton in response to hypo‐osmotic shock in Saccharomyces cerevisiae
Authors: Gualtieri Tania , Ragni Enrico , Mizzi Luca , Fascio Umberto , Popolo Laura 
Published: October 2004

AbstractThe cell wall is essential to preserve osmotic integrity of yeast cells. Some phenotypic traits of cell wall mutants suggest that, as a result of a weakening of the cell wall, hypo‐osmotic stress‐like conditions are created. Consequent expansion of the cell wall and stretching of the plasma membrane trigger a complex response to prevent cell lysis. In this work we examined two conditions that generate a cell wall and membrane stress: one is represented by the cell wall mutant gas1Δ and the other by a hypo‐osmotic shock. We examined the actin cytoskeleton and the role of the cell wall sensors Wsc1p and Mid2p in these stress conditions. In the gas1 null mutant cells, which lack a β(1,3)‐glucanosyltransferase activity required for cell wall assembly, a constitutive marked depolarization of actin cytoskeleton was found. In a hypo‐osmotic shock wild‐type cells showed a transient depolarization of actin cytoskeleton. The percentage of depolarized cells was maximal at 30 min after the shift and then progressively decreased until cells reached a new steady‐state condition. The maximal response was proportional to the magnitude of the difference in the external osmolarity before and after the shift within a given range of osmolarities. Loss of Wsc1p specifically delayed the repolarization of the actin cytoskeleton, whereas Wsc1p and Mid2p were essential for the maintenance of cell integrity in gas1Δ cells. The control of actin cytoskeleton is an important element in the context of the compensatory response to cell wall weakening. Wsc1p appears to be an important regulator of the actin network rearrangements in conditions of cell wall expansion and membrane stretching. Copyright © 2004 John Wiley & Sons, Ltd.
An in vitro assay for (1 → 6)‐β‐D‐glucan synthesis in Saccharomyces cerevisiae
Authors: Vink Edwin , Rodriguez‐Suarez Roberto J. , Gérard‐Vincent Manon , Ribas Juan Carlos , de Nobel Hans , van den Ende Herman , Durán Angel , Klis Frans M. , Bussey Howard 
Published: October 2004

Abstract(1 → 6)‐β‐D‐glucan is a key cell wall component of Saccharomyces cerevisiae and Candida albicans. Many genes are known to affect the levels or structure of this glucan, but their roles and a molecular description of the synthesis of (1 → 6)‐β‐D‐glucan remain to be established and a method to measure (1 → 6)‐β‐D‐glucan synthase activity in vitro would provide an enabling tool. Here, conditions for the detection of in vitro synthesis of this polymer are described. Crude membrane preparations from S. cerevisiae were isolated, and incubated in the presence of UDP‐glucose and GTP. With anti‐(1 → 6)‐β‐D‐glucan‐specific antibodies, a time‐dependent increase in the amount of this glucan was demonstrated in a dot–blot assay, or through an inhibition enzyme immunoassay. Antibody specificity was validated by competition experiments using pustulan, a (1 → 6)‐β‐D‐glucan, laminarin, a (1 → 3)‐β‐D‐glucan, yeast mannan and glycogen. The identity of the reaction product was also demonstrated by its sensitivity to a recombinant (1 → 6)‐β‐D‐glucanase. Extracts from mutants in 10 genes with a wide range of altered cell wall (1 → 6)‐β‐D‐glucan levels were assayed for in vitro synthesis of the polymer. A strong correlation of in vitro synthase activity with in vivo glucan levels was found, providing genetic support for the specificity of the assay. The basis for the GTP‐dependence of the synthase reaction was studied. Extracts from rho2, rho3, rho4 and rho5 null mutants had wild‐type in vitro activity. In contrast, Rho1p overproduction led to increased in vitro synthesis, implicating Rho1p in the regulation of (1 → 6)‐β‐D‐glucan synthesis. Copyright © 2004 John Wiley & Sons, Ltd.