bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical and two‐photon absorption analysis of radiation‐grafted fluoropolymer
Authors: El‐Diasty Fouad , Aly E. Hassan , El‐Sawy N. M. 
Published: September 2010

AbstractGrafting by gamma irradiation has a significant influence on the dispersion properties of polymeric materials. Accordingly, we study the effect of grafting on the material electronic structure parameters such as the fundamental absorption edge and bandgap structure. The optical absorption of grafted polymeric films of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA‐g‐PAAc) is determined in a very wide spectral range of 0.2–3 μm. The nonlinear two‐photon absorption coefficient is determined that showed an increase as a result to the grafting process. Moreover, a significant increase in the optical conductivity for the polymeric films is acquired after grafting. Positron annihilation spectroscopy is used to study polymer structure and volume size of nanoholes of Ps. The data revealed an increase of crosslinking with a smaller average volume size with grafting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2045–2051, 2010
pH‐responsive photoluminescence properties of a water‐soluble copolymer containing quinoline groups in aqueous solution
Authors: Kalogianni Aliki , Pefkianakis Eleftherios , Stefopoulos Andreas , Bokias Georgios , Kallitsis Joannis K. 
Published: September 2010

AbstractThe synthesis of a water‐soluble copolymer containing quinoline groups, P(DMAM‐co‐SDPQ), through free radical copolymerization of N,N‐dimethylacrylamide, DMAM, with 2,4‐diphenyl‐6‐(4‐vinylphenyl)quinoline, SDPQ, is presented and the optical properties of the final product are investigated in aqueous solution as a function of pH. It is found that the emission peak of SDPQ is red‐shifted from 411 to 484 nm with decreasing pH, due to the protonation of quinoline groups at low pH, suggesting that this copolymer may function as a luminescent pH‐indicator. Moreover, the copolymer exhibits the characteristics of a luminescent pH‐detector within the pH range 2 < pH < 4, as in this pH region the ratio of the emission intensity at 411 nm over that at 484 nm changes linearly in a logarithmic scale with the pH of the solution. Finally, the formation of less polar quinoline clusters in the aqueous P(DMAM‐co‐SDPQ) solution upon increasing pH was detected through Nile red probing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2078–2083, 2010
Role of matrix crystallinity in carbon nanotube dispersion and electrical conductivity of iPP‐based nanocomposites
Authors: Jeon Keesu , Warnock Stephen , Ruiz‐Orta Carolina , Kismarahardja Ade , Brooks James , Alamo Rufina G. 
Published: September 2010

AbstractA homopolymer iPP and a series of propylene‐ethylene random copolymers with a content of ethylene from 7 to 21 mol % were used as matrices to prepare single‐walled carbon nanotube (SWCNT) nanocomposites in a range of SWCNT concentration from 0.15 to 1 wt %. The solution blending and melt‐ compression molding procedures were kept identical for all nanocomposites. The poly(propylenes) have crystallinities ranging from 70 to 10%, and serve to test the role of SWCNTs acting as nucleants to preserve in the nanocomposites the uniform dispersion of SWCNTs after sonication. The major role of polymer crystallinity is to mediate toward a more open and more connected SWCNT network structure. Fast nucleation and growth of high crystalline matrices on multiple sites along the surface of the nanotubes prevents SWCNT clustering, and entraps the SWCNT network between the semicrystalline structure reducing the driving force of nanotubes to curl and twist. Depletion of crystallites in the less crystalline matrices (<35% crystallinity) leads to curled and poorly connected nanotubes. A consequence of the gradual loss of SWCNT connectivity is a decreased electrical conductivity; however, the change with crystallinity is not linear. Conductivity decreases sharply with decreasing crystallinity for SWCNT contents near the percolation region, while for contents approaching the plateau region the electrical conductivity is less sensitive to matrix crystallinity. The percolation threshold decreases rapidly for polymers with <∼30% crystallinity and slowly levels off at crystallinities >∼40%. At SWCNT concentrations of 0.15 wt %, SEM images of nanocomposites with the highest crystallinity matrix indicate debundled and interconnected nanotubes, whereas more disconnected and curled SWCNTs remain in the lowest crystallinity nanocomposites. Electrical conductivity in the former is relatively high, whereas the latter are insulators. Also discussed is the nucleating effect of nanotubes and restrictions of the filler to polymer chain diffusion in the crystallization of the polymers. SEM images and Raman spectra in the radial breathing modes region (100–400 cm−1) are complementary tools to extract the quality and details of the SWCNT dispersion in the nanocomposites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2084–2096, 2010
A molecular dynamics simulation study of three polysulfones in dry and hydrated states
Authors: Marque Grégory , Verdu Jacques , Prunier Valéry , Brown David 
Published: September 2010

AbstractMolecular dynamics (MD) simulations of three polysulfones (poly(ether sulfone) PESU, poly(phenylene sulfone) PPSU and polysulfone PSU) in dry and hydrated states were undertaken in order to study the specific interactions between water and glassy polymer matrices of the same structural family. Dry polysulfone models were generated using a hybrid pivot Monte Carlo‐MD single‐chain sampling technique and the resulting relaxed densities were found to be in close agreement with experimental data. Hydrated systems are found to reproduce quite well volumetric changes experimentally observed. The concentrations of sulfonic groups can explain qualitatively their different water solubilities. Water is preferentially hydrogen‐bonded to two sites which either link two polymer sites, or one polymer site and another water, or two other waters. A detailed analysis of these water bridges that are formed is presented. Only a small quantity of potential bridging sites are occupied for water contents near the experimental saturation. The free fractional volumes, the probe accessible volumes, the swelling of the polymers, the water‐polymer interactions and the hydrogen bond lifetimes, are also presented for these polysulfones. Water‐water interactions and water clusters are found to be more important in the more hydrophilic PESU in comparison to the less hydrophilic PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010
Conformational regulation of the EGFR kinase core by the juxtamembrane and C‐terminal tail: A molecular dynamics study
Authors: Mustafa Morad , Mirza Amar , Kannan Natarajan 
Published: September 2010

AbstractThe catalytic domain of epidermal growth factor receptor (EGFR) is activated by dimerization, which requires allosteric coupling between distal dimerization and catalytic sites. Although crystal structures of EGFR kinases, solved in various conformational states, have provided important insights into EGFR activation by dimerization, the atomic details of how dimerization signals are dynamically coupled to catalytic regions of the kinase core are not fully understood. In this study, we have performed unrestrained and targeted molecular dynamics simulations on the active and inactive states of EGFR, followed by principal component analysis on the simulated trajectories, to identify correlated motions in the EGFR kinase domain upon dimerization. Our analysis reveals that the conformational changes associated with the catalytic functions of the kinase core are highly correlated with motions in the juxtamembrane (JM) and C‐terminal tail, two flexible structural elements that play an active role in EGFR kinase activation and dimerization. In particular, the opening and closing of the ATP binding lobe relative to the substrate binding lobe is highly correlated with motions in the JM and C‐terminal tail, suggesting that ATP and substrate binding can be coordinated with dimerization through conformational changes in the JM and C‐terminal tail. Our study pinpoints key residues involved in this conformational coupling, and provides new insights into the role of the JM and C‐terminal tail segments in EGFR kinase functions. Proteins 2010. © 2010 Wiley‐Liss, Inc.
Hydrolysis of organophosphate compounds by mutant butyrylcholinesterase: A story of two histidines
Authors: Amitay Moshe , Shurki Avital 
Published: September 2010

AbstractThis study is aimed at understanding the hydrolysis mechanism of organophosphate (OP) compounds by G117H‐BChE. It is a theoretical study that focuses on the role of the G117H mutation in the dephosphorylation step. Various proposed mechanisms are examined. We show that His117 acts as a general base by activating a water molecule, and thus assisting its nucleophilic attack on the phosphate. The calculated reaction energy profile agrees well with the experimental data. Moreover, analysis of the reaction via its two hypothetical elementary steps, proton transfer and hydroxide attack, supports the role of His117 as a general base. Further support to the proposed mechanism is gained by structural comparison of the active site to RNAse A, which has similar composition of substrate and functional groups. The similarity between these enzymes extends beyond the structure and also becomes evident when comparing functionality of various active sites residues as well as rate–pH dependence obtained in the two cases. Moreover, it is demonstrated that an extended form of Bevilacqua's model (Biochemistry 2003;42:2259–2265) may resolve the apparent contradictions between the proposed mechanism and various experimental observations regarding rate–pH dependence. Finally, that same model is shown to rationalize the hydrolase activity of G117D BChE, an observation which is considered puzzling. It is concluded that G117H‐BChE hydrolyzes echothiophate and possibly other OP compounds via a general acid–base mechanism. On the basis of this mechanism, one can now proceed with rational design aimed at improving the enzyme by exploiting both the structural and mechanistic knowledge. Proteins 2011. © 2010 Wiley‐Liss, Inc.
Self‐organized TiO2 nanotubes: Factors affecting their morphology and properties
Authors: Berger Steffen , Hahn Robert , Roy Poulomi , Schmuki Patrik 
Published: September 2010

AbstractSelf‐organized oxide nanostructures grown by controlled anodic oxidation of a metal substrate attracted wide scientific interest due to a broad number of potential applications. The present work gives an overview on growth principles and mechanistic aspects of self‐organized TiO2 nanotubular layers and related transition metal oxide nanostructures. In particular, key electrochemical factors that control tube geometry and routes to fabricate advanced TiO2 nanotube geometries and morphologies are discussed.
Effect of localized states on internal quantum efficiency of III‐nitride LEDs
Authors: Karpov Sergey Yu. 
Published: September 2010

AbstractA model is suggested accounting for effects of localized electron and hole states formed by composition fluctuations in the InGaN active region of a III‐nitride LED on non‐radiative carrier recombination at threading dislocations. The model enables explanation of the abnormal temperature dependence of internal quantum efficiency (IQE) of a green LED structure recently observed at low current densities. The theoretical predictions are in quantitative agreement with experiment in the temperature range between 200 K and 453 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A prospective double‐blind randomized placebo‐controlled study of the effect of saffron (Crocus sativusLinn.) on semen parameters and seminal plasma antioxidant capacity in infertile men with idiopathic oligoasthenoteratozoospermia
Authors: Safarinejad Mohammad Reza , Shafiei Nayyer , Safarinejad Shiva 
Published: September 2010

AbstractMale factor infertility is a multifactorial disorder that affects a significant percentage of infertile couples; however, many of them remained untreated. In recent years, considerable numbers of infertile men have sought ‘herbal remedies’ as an effective treatment. Among ‘herbal remedies’, saffron is recommended for male infertility in our community. The effect of saffron was evaluated compared with placebo for the treatment of idiopathic male factor infertility. The study included 260 infertile men with idiopathic oligoasthenoteratozoospermia (OAT) who were randomized to saffron 60 mg/day (130, group 1) or a similar regimen of placebo (130, group 2) for 26 weeks. The two groups were compared for changes in semen parameters and total seminal plasma antioxidant capacity. Saffron administration did not result in beneficial effects. At the end of the study no statistically significant improvements were observed in either group in any of the studied semen parameters (sperm density, morphology and motility) (allp= 0.1). At the end of the trial, patients in group 1 had a mean motility of 25.7 ± 2.4%, which was not statistically different from the mean of 24.9 ± 2.8% in the placebo group (p= 0.1). Normal sperm morphology was 18.7 ± 4.7% and 18.4 ± 4.3%, in groups 1 and 2, respectively (p= 0.1). Patients treated with saffron and placebo had a mean sperm density of 20.5 ± 4.6% and 21.4 ± 4.6% per mL, respectively (p= 0.1). Saffron administration did not improve total seminal plasma antioxidant capacity, compared with baseline (p= 0.1) and placebo subjects (p= 0.1). Based on Pearson correlations, each semen parameter did not correlate significantly with treatment duration, including sperm density (r= 0.146,p= 0.13), percent of motile sperm (r= 0.145,p= 0.15) and percent of sperm with normal morphology (r= 0.125,p= 0.30). Saffron does not statistically significantly improve semen parameters in infertile men with idiopathic OAT. If medical professionals want to prescribe herbal remedies for male infertility, previous rigorous scientific investigations, documenting their safety and efficacy are required. Copyright © 2010 John Wiley & Sons, Ltd.
Global potential energy surface for the ground electronic state of H: A DFT approach
Authors: Barragán Patricia , Prosmiti Rita , Villarreal Pablo , Delgado‐Barrio Gerardo 
Published: September 2010

AbstractA ground potential energy surface for the H ion is obtained using density functional theory. The potential was calculated using the B3(H) hybrid functional that has been specifically parametrized for protonated hydrogen clusters. The surface has the appropriate topology to correctly describe equilibrium structures, linearization barrier, and dissociation limits, and its features are compared with previous very high accurate ab initio studies available, as well as with earlier and recent reported analytical potential energy surfaces. It is found that such approach produces a reasonable global potential, representing all aspects of ground‐state H. Such representations are, in particular, interesting for studying high‐lying bound states of H, and thus, for a more accurate description of the PES, further improvement of the density functional used in the present DFT calculations is proposed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
Ab initio study of the structure, spectral, ionochromic, and fluorochromic properties of benzoazacrown‐containing dyes as potential optical molecular sensors
Authors: Freidzon Alexandra Y. , Bagatur'yants Alexander A. , Ushakov Evgeny N. , Gromov Sergey P. , Alfimov Michael V. 
Published: September 2010

AbstractExperimental absorption and emission spectra of benzoaza‐18‐crown‐6‐containing styryl dye 2a and its complexes with Li+, Na+, and Ca2+ are recorded. It is found that complexation causes large hypsochromic shifts of the long‐wave absorption band of the dye. In addition, the spectra of Li+ and Na+ complexes exhibit an additional band or a shoulder with λ virtually coinciding with the absorption band of the free dye. Complexation also enhances the fluorescence of the dye. Simulating the structure and electronic spectra of the dye and its complexes with Li+, Mg2+, Na+, and Ca2+ by DFT and TD DFT allowed us to explain these effects. It is found that cation coordination breaks the conjugation of the crown ether nitrogen with the chromophore, thus reducing the effective chromophore size, and the positive charge of the cation simultaneously decreases the donor nature of the amino group. This explains large hypsochromic shift of the long‐wave absorption band. It is found that Li+ and Na+ complexes can form two types of conformers, with and without cation‐nitrogen bond. The conformers with the cation‐nitrogen bond exhibit a very strong blue shift of the absorption maximum, while the absorption spectra of the complexes without cation‐nitrogen bond are almost unshifted relative to the spectra of the free dye. The ground‐state recoordination of the cation in the macrocycle cavity involves the change between these two forms. Recoordination is promoted by the interaction of the cation with solvent molecules. This explains the presence of the additional long‐wave band or shoulder in the spectra of the complexes. Cation‐induced fluorescence enhancement is explained by the changes in the excited‐state structure of the free dye and its complexes. The free dye changes its structure from the “quinoid” form in the ground state to the “benzenoid” form in the excited state, thus facilitating the rotation of the alkoxyaminophenyl group and causing near‐degeneracy of the potential energy surfaces of the ground and excited states. This results in rapid nonradiative deactivation and fluorescence quenching. Complexation with cations reverses the dye structure to the “benzenoid” form in the ground state and to the “quinoid” form in the excited state thus preventing alkoxyaminophenyl group from rotation, which results in fluorescence enhancement. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
Dressed TDDFT study of low‐lying electronic excited states in selected linear polyenes and diphenylopolyenes
Authors: Mazur Grzegorz , Makowski Marcin , Włodarczyk Radosław , Aoki Yuriko 
Published: September 2010

AbstractDressed TDDFT method is applied to the calculations of low‐lying electronic excited states of selected linear polyenes and α,ω‐diphenylopolyenes. It is shown that proper accounting for doubly excited configurations is necessary to correctly describe excitation energies and geometrical structure of the 21Ag state in these systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
Internal state cooling with a femtosecond optical frequency comb
Authors: Malinovskaya S. , Patel V. , Collins T. 
Published: September 2010

AbstractA single femtosecond optical frequency comb is implemented to induce two‐photon transitions between molecular vibrational levels to form ultracold molecules. The phase across an individual pulse in the pulse train is sinusoidally modulated with a carefully chosen modulation amplitude and frequency. Piecewise population transfer is fulfilled to the final state by each pulse in the applied pulse train providing a controlled population accumulation in the final, ultracold state. The dynamics of rovibrational cooling is discussed on an example of the KRb molecule. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010
Exactly solvable effective mass Schrödinger equation with coulomb‐like potential
Authors: Pacheco‐García C. , García‐Ravelo J. , Morales J. , Peña J. J. 
Published: September 2010

AbstractExactly solvable Schrödinger equation (SE) with a position‐dependent mass distribution allowing Morse‐like eigenvalues is presented. For this, the position‐dependent mass Schrödinger equation is transformed into a standard SE, with constant mass, by means of the point canonical transformation scheme. In that method, the choice of potential for the position‐dependent mass Schrödinger equation allows us to obtain the transformation that should be used to find the exactly solvable SE. As a useful application of the proposal, the equivalent of the Witten superpotential is chosen to be constant to find the position‐dependent mass distribution and the exactly solvable potential V(m(x)) allowing Morse‐type energy spectra. This V(m(x)) is shown to have a Coulomb potential structure and can be useful in the study of the electronic properties of materials in which the carrier effective mass depends on the position. Moreover, the worked example, the approach is general and can be applied in the search of new potentials suitable on the study of quantum chemical systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010
The role of inequalities in the analysis of many‐body systems
Authors: Percus J. K. 
Published: September 2010

AbstractWe discuss the strategy of determining properties of many‐body systems by applying successively more stringent limitations on the domain on which solutions can lie, i.e., sharpening the degree of resolution of the results obtained. A rough division is made into universal, or system‐independent inequalities and system‐dependent ones, which are joined by equalities or sum rules. General examples include Fermion ground states and classical fluids in thermal equilibrium, and for the latter, the effect of estimation by saturating inequalities. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010
Theory of chemical bonds in metalloenzymes. XIV. Correspondence between magnetic coupling mode and radical coupling mechanism in hydroxylations with methane monooxygenase and related species
Authors: Saito Toru , Shoji Mitsuo , Isobe Hiroshi , Yamanaka Shusuke , Kitagawa Yasutaka , Yamada Satoru , Kawakami Takashi , Okumura Mitsutaka , Yamaguchi Kizashi 
Published: September 2010

AbstractBroken‐symmetry (BS) and approximate spin‐projected (AP) BS hybrid density functional theory (DFT) calculations were performed to elucidate possible mechanisms of hydroxylation reactions of methane and alkanes with soluble methane monooxygenase (sMMO) and related metalloenzymes. The BS HDFT (UB3LYP) method was employed to elucidate electronic and spin structures of the key intermediate “Q” and to locate transition structures for hydroxylation reactions in the lowest‐spin (LS) singlet and the highest‐spin (HS) states of sMMO. The spin density populations and chemical indices obtained by the BS B3LYP calculations were found to be consistent with orbital interaction models for hydroxylation with MMO. However these indices in turn indicated significant spin contamination errors in the BS LS solution. The elimination of the errors with the AP procedure indeed reduced the barrier height for the recombination step of alkyl and hydroxyl radicals in the pure LS singlet state, leading to a rebound process. Then present computational results indicated that hydroxylation reactions proceed through the continuous diradical (diradicaloid) mechanism without discreet free radical fragments in the pure LS singlet state. The computational results are, respectively, compatible with local singlet (SD) and local triplet (TD) diradical mechanisms for hydroxylation in the LS and HS states; those were already applied to P450 successfully. Thus magnetic (exchange) coupling modes (LS and HS) in MMO, P450 and related metalloenzymes are directly related to local SD and TD mechanisms for hydroxylation, indicating the correspondence between the magnetic coupling mode and the radical reaction mechanism. These theoretical results enable us to examine recent BS hybrid DFT computational results for hydroxylation reactions with sMMO by several groups. Implications of the present theoretical and computational results are also discussed in relation to several experimental aspects of hydroxylation reactions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010