bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cohesive properties of CeN and LaN from first principles
Authors: Voloshina Elena , Paulus Beate 
Published: May 2008

AbstractThe effect of electron‐correlation on the ground‐state properties of CeN and LaN is studied by ab initio quantum‐chemical methods. The approach which is used combines two separate steps: (1) the ground‐state Hartree‐Fock calculations for the crystal; (2) application of the method of increments to the studied system, which allows an expansion of bulk properties using the information from quantum‐chemical calculations performed for finite clusters. As can be expected, for CeN correlation plays a significant role: with Hartree‐Fock method only 49% of the experimental cohesive energy has been recovered, whereas after correlation corrections (coupled‐cluster approach) the ground‐state properties were found to be in good agreement with the experimental data found in literature. Thus, we obtained about 90% of the expected cohesive energy; the computed lattice constants and bulk moduli also agree well with the experimental values. For comparison, the equivalent treatment has been performed for LaN, where no f orbital is occupied. There the HF contribution to the ground‐state properties is larger and hence the correlation effects weaker. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008
Improved pKa prediction: Combining empirical and semimicroscopic methods
Authors: Kieseritzky Gernot , Knapp E. W. 
Published: May 2008

AbstractUsing three different methods we tried to compute 171 experimentally known pKa values of ionizable residues from 15 different proteins and compared the accuracies of computed pKa values in terms of the root mean square deviation (RMSD) from experiment. One method is based on a continuum electrostatic model of the protein including conformational flexibility (KBPLUS). The others are empirical approaches with PROPKA deploying physically motivated energy terms with adjustable parameters and PKAcal using an empirical function with no physical basis. PROPKA reproduced the pKa values with highest overall accuracy. Differentiating the data set into weakly and strongly shifted experimental pKa values, however, we found that PROPKA's accuracy is better if the pKa values are weakly shifted but on equal footing with that of KBPLUS for more strongly shifted values. On the other hand, PKAcal reproduces strongly shifted pKa values badly but weakly shifted values with the same accuracy as PROPKA. We tested different consensus approaches combining data from all three methods to find a general procedure for most accurate pKa predictions. In most of the cases we found that the consensus approach reproduced experimental data with better accuracy than any of the individual methods alone. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008
Prolonged gene silencing in hepatoma cells and primary hepatocytes after small interfering RNA delivery with biodegradable poly(β‐amino esters)
Authors: Vandenbroucke Roosmarijn E. , De Geest Bruno G. , Bonné Stefan , Vinken Mathieu , Van Haecke Tamara , Heimberg Harry , Wagner Ernst , Rogiers Vera , De Smedt Stefaan C. , Demeester Joseph , Sanders Niek N. 
Published: May 2008

AbstractBackgroundSmall interfering (si)RNA mediated inhibition of oncogenes or viral genes may offer great opportunities for the treatment of several diseases such as hepatocellular carcinoma and viral hepatitis. However, the development of siRNAs as therapeutic agents strongly depends on the availability of safe and effective intracellular delivery systems. Poly(β‐amino esters) (PbAEs) are, in contrast to many other cationic polymers evaluated in siRNA delivery, biodegradable into smaller, nontoxic molecules.Methods and ResultsWe show for the first time that PbAE : siRNA complexes, containing 1,4‐butanediol (PbAE1) or 1,6‐hexanediol (PbAE2) diacrylate‐based polymers, induced efficient gene silencing in both hepatoma cells and primary hepatocytes without causing significant cytotoxicity. Furthermore, carriers that slowly release the siRNA into the cytoplasm and hence induce a prolonged gene silencing are of major clinical interest, especially in fast dividing tumour cells. Therefore, we also studied the duration of gene silencing in the hepatoma cells and found that it was maintained for at least 5 days after siRNA delivery with PbAE2, the polymer with the slowest degradation kinetics.ConclusionsFrom the time‐dependent cellular distribution of these PbAE : siRNA complexes, we suggest that the slowly degrading PbAE2 causes a sustained endosomal release of siRNA during a much longer period than PbAE1. This may support the hypothesis that the endosomal release mechanism of PbAE : siRNA complexes is based on an increase of osmotic pressure in the endosomal vesicles after polymer hydrolysis. In conclusion, our results show that both PbAEs, and especially PbAE2, open up new perspectives for the development of efficient biodegradable siRNA carriers suitable for clinical applications. Copyright © 2008 John Wiley & Sons, Ltd.
The chemical oxidative polymerization of aniline in water: Raman spectroscopy
Authors: Ćirić‐Marjanović Gordana , Trchová Miroslava , Stejskal Jaroslav 
Published: May 2008

AbstractThe structural changes of aniline oligomers and polyaniline, associated with oxidation of aniline with ammonium peroxydisulfate in aqueous solutions without any added acid, were studied. The reaction was quenched at various times and the films deposited on silicon windows have been studied in detail by Raman spectroscopy, at excitation wavelengths 633 and 514 nm. The presence of substituted phenazine structural units, in addition to ordinary benzenoid, quinonoid, and semiquinonoid structures, has been proved by the appearance of characteristic Raman bands at 1645–1630, 1420–1400, 1380–1365, ∼575, and ∼415 cm−1. The remarkable differences of the Raman spectra of oligoanilines, precipitated in the first phase of oxidative polymerization, and polyaniline nanotubes and nanorods, formed in the second stage of reaction, are discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Parahydrogen induced polarization of barbituric acid derivatives: 1H hyperpolarization studies
Authors: Roth Meike , Bargon Joachim , Spiess Hans Wolfgang , Koch Achim 
Published: May 2008

AbstractHomogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the 1H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin–lattice relaxation time T1 of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal‐to‐noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30° pulse experiments and a delay of 10 s. Copyright © 2008 John Wiley & Sons, Ltd.
Microbial transformation of the diterpene mulin‐11,13‐dien‐20‐oic acid by Mucor plumbeus
Authors: Areche Carlos , Loyola Luis A. , Borquez Jorge , Rovirosa Juana , San‐Martin Aurelio 
Published: May 2008

AbstractTwo new mulinane‐type derivatives: 16‐hydroxy mulin‐11,13‐dien‐20‐oic (2) acid and 7α,16‐dihydroxy mulin‐11,13‐dien‐20‐oic (3) acid were obtained by microbial transformation of mulin‐11,13‐dien‐20‐oic acid (1), along with tyrosol (4) using liquid cultures of Mucor plumbeus. The latter compound has not been previously identified in the genus Mucor. Structural elucidation of these metabolites was achieved using 1D‐ and 2D‐NMR spectroscopy. Copyright © 2008 John Wiley & Sons, Ltd.
Synthesis and NMR spectral assignments of novel nitrogen and sulfur heterocyclic compounds
Authors: Chandrashekhar N. , Thomas Bejoy , Gayathri V. , Ramanathan K. V. , Gowda N. M. Nanje 
Published: May 2008

AbstractSynthesis and NMR spectral studies of multidentate N and S heterocycles, 1,3,5‐tris(N‐methylbenzimidazolyl)benzene, 1,3,5‐tris(benzimidazolyl)benzene,1,3,5‐tris(benzothiazolyl) benzene, 2,2′‐bipyridine 3,3′‐bis(benzothiazolyl)benzene and 1,2,4,5‐tetrakis(benzothiazolyl) benzene have been carried out. 2D 1H1H PFG‐COSY as well as 1H13C single and multiple bond correlated (2D GRASP‐HSQC and GRASP‐HMBC) experiments have been employed to characterize the compounds. 1D NOE experiments have been useful in understanding the structure of 1,3,5‐tris(N‐methylenzimidazolyl)benzene. Copyright © 2008 John Wiley & Sons, Ltd.
Macrophage physiological function after superparamagnetic iron oxide labeling
Authors: Hsiao Jong‐Kai , Chu Hung‐Hao , Wang Yu‐Hsiu , Lai Chih‐Wei , Chou Pi‐Tai , Hsieh Sung‐Tsang , Wang Jaw‐Lin , Liu Hon‐Man 
Published: May 2008

AbstractOur goal was to analyze the changes in morphology and physiological function (phagocytosis, migratory capabilities, humoral and cellular response, and nitric oxide secretion) of murine macrophages after labeling with a clinically used superparamagnetic iron oxide (SPIO), ferucarbotran. In SPIO‐treated macrophages, nanoparticles were taken up in the cytoplasm and accumulated in a membrane‐bound organelle. Macrophage proliferation and viability were not modified after SPIO labeling. Phagocytic function decreased after labeling with only 10 µg Fe/mL SPIO, whereas other functions including migration and production of tumor necrosis factor‐α and nitric oxide increased at the highest SPIO concentration (100 µg Fe/mL). Copyright © 2008 John Wiley & Sons, Ltd.
Enabling novel premium service classes in DiffServ over MPLS‐enabled network
Authors: Alshaer Hamada , Elmirghani Jaafar M. H. 
Published: May 2008

AbstractNetwork resources dimensioning and traffic engineering influence the quality in provisioned services required by the Expedited Forwarding (EF) traffic in production networks established through DiffServ over MPLS‐enabled network. By modeling EF traffic flows and the excess of network resources reserved for it, we derive the range of delay values which are required to support these flows at DiffServ nodes. This enables us to develop an end‐to‐end (e2e) delay budget‐partitioning mechanism and traffic‐engineering techniques within a framework for supporting new premium QoS levels, which are differentiated based on e2e delay, jitter and loss. This framework enables ingress routers to control EF traffic flow admission and select appropriate routing paths, with the goal of EF traffic balancing, avoiding traffic congestion and getting the most use out of the available network resources through traffic engineering. As a result, this framework should enable Internet service providers to provide three performance levels of EF service class to their customers provided that their network is DiffServ MPLS TE aware. Copyright © 2008 John Wiley & Sons, Ltd.
Intercalation degree in PP/organoclay nanocomposites: role of surfactant structure
Authors: Bellucci Federica , Terenzi Andrea , Leuteritz Andreas , Pospiech Doris , Frache Alberto , Traverso Giuliano , Camino Giovanni 
Published: May 2008

AbstractThe formation of exfoliated polymer–clay nanocomposites depends upon several factors such as the nature of the polymer, the nature of the clay, as well as the type, packing density, and size of the organic modifier on the silicate layers. The main aim of this work was focused on the role of the chemical structure of the organic modifier on the intercalation properties of the organo‐modified clay into non‐polar polymer matrices such as a polypropylene homopolymer. To achieve this purpose organo‐montmorillonites containing different loadings of organic modifier with increasing molar volume were prepared and used to produce PP based nanocomposites. Morphology studies performed on the composites pointed out that two distinct aspects have to be considered for organic modification of the clays: the interlayer distance and the degree of the inorganic surface coverage, which are the main driving forces for the intercalation process. It was found that an intercalated structure was reached when either a large non‐polar molecule, which ensures an optimal interlayer distance with a partial surface coverage or a mixture of small and large molecules leading to a slightly lower interlayer distance but to a higher surface coverage degree was used. Moreover, rheological, mechanical, and thermal studies indicated that the degree of dispersion and interaction between clay platelets and the polymer chains strongly depended on the interlayer spacing and clay surface coverage. Copyright © 2008 John Wiley & Sons, Ltd.
Linear pentablock quintopolymers (l‐SIDMV) with five incompatible blocks: Polystyrene, polyisoprene‐1,4, poly(dimethylsiloxane), poly(tert‐butyl methacrylate), and poly(2‐vinylpyridine)
Authors: Fragouli Panagiota , Iatrou Hermis , Lohse David J. , Hadjichristidis Nikos 
Published: May 2008

AbstractThree linear pentablock quintopolymers (l‐SIDMV), where S is polystyrene (PS), I polyisoprene‐1,4 (PI), D poly(dimethylsiloxane) (PDMS), M poly(tert‐butyl methacrylate) (PtBuM), and V poly(2‐vinylpyridine) (P2VP), were synthesized by anionic polymerization high vacuum techniques. The approach involves the following: (a) The synthesis of living triblock terpolymer PS‐b‐PI‐b‐PDMSLi and diblock copolymer P2VP‐b‐PtBuMK by sequential polymerizations of the corresponding monomers with sec‐BuLi and benzyl potassium, respectively; and (b) The selective linking of the living triblock terpolymer with the chlorosilane group of 2‐(chloromethylphenyl)ethyldimethylchlorosilane (CMPDMS), followed by linking of the living block copolymer with the remaining chloromethyl group of CMPDMS. Molecular characterization carried out by size exclusion chromatography, membrane osmometry, solution (in CDCl3 or d8‐toluene) and solid‐state 1H‐NMR spectroscopy indicated a high degree of molecular and compositional homogeneity. Differential scanning calorimetry results on the precursors and final polymers were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3938–3946, 2008
Synthesis and properties of sulfonated multiblock copoly(ether sulfone)s by a chain extender
Authors: Nakabayashi Kazuhiro , Matsumoto Kazuya , Ueda Mitsuru 
Published: May 2008

AbstractA new series of sulfonated multiblock copoly(ether sulfone)s applicable to proton exchange membrane fuel cells was synthesized. The multiblock copolymers were synthesized by the nucleophilic aromatic substitution of hydroxyl‐terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender. Because of the high reactivity of DFB, the ether–ether interchange reaction, which could lead to a randomized polymer architecture, was prevented, and multiblock copolymers with high molecular weights were easily produced. The multiblock copolymers gave tough, flexible, and transparent membranes by solution casting. The ion exchange capacity values could be easily controlled by changing the sulfonated block ratios in the copolymers. The resulting membranes demonstrated good oxidative and dimensional stability and significantly higher proton conductivity than sulfonated random poly(ether sulfone) copolymers. The morphologies of the membranes were investigated by tapping mode atomic force microscopy, which showed that the multiblock membranes had a clear hydrophilic/hydrophobic separated structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3947–3957, 2008
End‐group modification of poly(2,6‐dimethyl‐1,4‐phenylene ether) and in situ synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer
Authors: Jéol Stéphane , Fenouillot Françoise , Rousseau Alain , Monnet Christiane , Masenelli‐Varlot Karine , Briois Jean‐François 
Published: May 2008

AbstractThe preparation of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer was performed by the reaction of the 2‐hydroxyethyl modified poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE‐EtOH) with poly(ethylene terephthalate) (PET) by an in situ process, during the synthesis of the polyester. The yield of the reaction of the 2‐hydroxyethyl functionalized PPE‐EtOH with PET was close to 100%. A significant proportion of the PET‐b‐PPE‐EtOH block copolymer was found to have short PET block. Nevertheless, the copolymer structured in the shape of micelles (20 nm diameter) and very small domains with 50–200 nm diameter, whereas unmodified PPE formed much larger domains (1.5 μm) containing copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3985–3991, 2008
Synthesis of porphyrin‐embedded dendronized polymers by Suzuki polycondensation
Authors: Fei Zhuping , Han Yang , Bo Zhishan 
Published: May 2008

AbstractPorphyrin‐embedded high molecular weight dendronized polymers up to fourth generation have been synthesized by Suzuki polycondensation of Fréchet‐type dendritic dibromo macromonomers and porphyrin diboronic pinacol ester. Higher generation lateral dendritic wedges not only endow the dendronized polymers with good solubility in commonly used organic solvents, but also prevent planar porphyrins and conjugated polymer backbones from aggregating by their “site isolation” effect. This type of porphyrin‐embedded dendronized polymers can be used as saturated red light‐emitting materials. With the increase of the generation of the lateral dendrons, the quantum yields of the dendronized polymers also gradually increased. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4030–4037, 2008
Computational evidence for the catalytic mechanism of glutaminyl cyclase. A DFT investigation
Authors: Calvaresi Matteo , Garavelli Marco , Bottoni Andrea 
Published: May 2008

AbstractThe results of a DFT theoretical investigation on the catalytic mechanism of the QC enzyme are presented. A rather large model‐system is used. It includes the most important residues that are believed to play a key‐role in the catalysis. The computational results show that the rate‐determining step of the catalytic process is not the nucleophilic attack leading to the cycle formation (a very easy and fast process with a negligible barrier of 0.8 kcal mol−1), but a proton transfer, which is assisted by the Glu201 residue acting as a proton shuttle (general base and general acid). A complex network of hydrogen bonds (involving Asp248 and other residues) contribute to lower the activation barrier for the proton shift which affords the formation of an ammonia molecule bonded to the substrate. The ammonia molecule is a good leaving group which is easily expelled from the substrate in the last step of the catalytic cycle, but remains anchored to the enzyme as a ligand of the zinc cation. The metal plays a key‐role in assisting the nucleophilic attack (electrostatic catalysis) since it polarizes the substrate γ‐amide carbonyl group (its electrophilic character increases). Also, the strength of the nucleophilic nitrogen (substrate α‐amino group) is enhanced by hydrogen bonds involving the Glu201 residue. The computations outline the important role of Trp329 in helping the substrate binding process and stabilizing the cyclization transition state. Proteins, 2008. © 2008 Wiley‐Liss, Inc.
Targeting the c‐Myc coiled coil with interfering peptides
Authors: Jouaux Eva M. , Schmidtkunz Karin , Müller Kristian M. , Arndt Katja M. 
Published: May 2008

Abstractc‐Myc is one of the most frequently deregulated oncogenes in human cancers, and recent studies showed that even brief inactivation of Myc can be sufficient to induce tumor regression or loss. Consequently, inactivation of Myc provides a novel therapeutic opportunity and challenge, as the dimerization of Myc with Max is crucial for its function. We applied two strategies to specifically target this coiled coil mediated interaction with interfering peptides: a dominant‐negative human Max sequence (Max) and a peptide selected from a genetic library (Mip). Both peptides form coiled coils and were fused to an acidic extension interacting with the basic DNA‐binding region of human Myc. The genetic library was obtained by semi‐rational design randomizing residues important for interaction, and selection was carried out using a protein‐fragment complementation assay. The peptides Max and Mip easily outcompeted the human Myc:Max interaction and successfully interfered with the DNA binding of the complex. Both interfering peptides exhibited higher Tm (ΔTm = 13 and 15 °C) upon interaction with Myc compared to wt Max. The inhibitory effect of the two interfering peptides on human Myc:Max activity makes them promising molecules for analytical and therapeutic Myc‐directed research. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.
Growth, clustering and morphology of intermetallic alloy core‐shell nanodroplets
Authors: Cefalas A. C. , Kobe S. , Sarantopoulou E. , Samardžija Z. , Janeva M. , Drazič G. , Kollia Z. 
Published: May 2008

AbstractSm–Fe–Ta–N core‐shell (CS) nanospheroids were fabricated from hot liquefied nanodroplets by 157 nm pulse laser deposition in nitrogen gas. The Sm13.8Fe82.2Ta4.0 intermetallic alloy was used as the target. At low laser energy (20 mJ), spherical CS of 1–35 nm radius were fabricated on a Si/Ta substrate forming uniform films. The small nanodroplets were grown in the plume from the gas phase, and the larger ones (>50 nm radius) from the target's hydrodynamic ejection. The critical radius of the droplets and their surface energy per unit area was found to be 7.5 nm and 3.8 μJ/cm2 respectively. A number of CS solidified in the plume and consist of 2.5–5 nm radius crystalline nucleus surrounded by a <35 nm radius amorphous spherical shell. This structure prevents the oxidization of the crystalline nucleus because oxidization is confined on the surface of the CS. Furthermore, multi‐crystalline nanodomains (embryos) were identified in a single CS from both homogeneous and heterogeneous nucleation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Si–SiO2 interface band‐gap transition – effects on MOS inversion layer
Authors: Markov Stanislav , Sushko Peter V. , Roy Scott , Fiegna Claudio , Sangiorgi Enrico , Shluger Alexander L. , Asenov Asen 
Published: May 2008

AbstractDensity functional theory simulation results of the atomic structure at the Si–SiO2 interface implies a non‐abrupt transition of the band‐gap within the oxide. The depth of the transition, 2–6 Å, is comparable to the approximately 1 nm oxide thickness in nano‐CMOS devices, and is expected to affect their characteristics. Using hierarchical simulation approach, we combine for the first time ab‐initio density functional theory simulations of the interface, with self‐consistent Poisson–Schrödinger one‐dimensional device simulations, and estimate the impact of interface band‐gap transition on the inversion layer quantisation, capacitance, and tunnelling characteristics of a metal–oxide–semiconductor structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of a constant electric field in cavities of nanotubes. Bloch oscillations and electron confinement
Authors: Jódar Esther , Pérez‐Garrido Antonio , Rojas Fernando 
Published: May 2008

AbstractWe investigate numerically the dynamical properties of electrons in cavities of nanotubes under the influence of an external electric field. In particular, the dynamical behaviour of electrons is studied when the nanostructure is connected to two electrodes at different electric potential.Here it is shown how the phenomenon of Bloch oscillations is produced. Besides this, we study the evolution of electrons when the electric field is placed along different regions of the nanotube, showing that the electron is confined at its initial region instead of spread along the whole structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)