bluuebunny/crossref_metadata_2025 huggingface dataset:
1H and 13 C NMR assignments for two lignans from the heartwood of Streblus asper
Authors: Li Jun , Zhang Yan‐Jun , Jin Bai‐Feng , Su Xiao‐Jian , Tao Yi‐Wen , She Zhi‐Gang , Lin Yong‐Cheng
Published: February 2008

In our ongoing investigation of the bioactive constituents from plants, two new lignans, magnolignan A‐2‐O‐β‐D‐glucopyranoside and strebluslignanol were isolated from heartwood of Streblus asper, along with three known lignans, magnolignan A, magnolol, and magnaldehyde D. 1D and 2D NMR experiments, including COSY, HMQC, and HMBC, and other spectroscopic methods, including UV, IR, and MS were used for the determination of the structures and NMR assignments. Primary bioassays showed that magnolignan A‐2‐O‐β‐D‐glucopyranoside and strebluslignanol have medium cytotoxic activity against HEp‐2 and HepG2 cells, with IC50 of 13.3 µM, 46.4 µM and 10.1 µM, 21.7 µM, respectively. Copyright © 2008 John Wiley & Sons, Ltd.
Spin–spin coupling across intramolecular NH+N hydrogen bonds in models for proton sponges: an ab initio investigation
Authors: Del Bene Janet E. , Alkorta Ibon , Elguero José
Published: February 2008

Ab initio calculations have been performed to obtain structures and coupling constants 1J(NH), 1hJ(HN), and 2hJ(NN) for models of proton sponges with symmetric and asymmetric NH+N intramolecular hydrogen bonds (IMHBs). For a given model, the asymmetric structure has a lower energy, a longer NN distance, and a hydrogen bond which has a greater deviation from linearity. The computed values of 2hJ(NN) for the models are significantly less than predicted values based on the distance dependence of 2hJ(NN) for complexes with intermolecular NH+N hydrogen bonds. However, the reduced values of 2hJ(NN) cannot be attributed solely to the distortion of the hydrogen bond in the models, but also reflect differences in s electron populations at the nitrogens in both the ground state and the excited states which couple to it through the Fermi‐contact (FC) operator. Values of 2hJ(NN) for IMHBs can be related quadratically to the NN distances in the models, and demonstrate that there is no discrepancy between computed values of 2hJ(NN) at the short NN distances found in these systems and experimental data for proton sponges. Copyright © 2008 John Wiley & Sons, Ltd.
Optimal design of pulsed arterial spin labeling MRI experiments
Authors: Xie Jingyi , Gallichan Daniel , Gunn Roger N. , Jezzard Peter
Published: February 2008

Quantitative measurement of cerebral blood flow (CBF) using arterial spin labeling (ASL) MRI requires the acquisition of multiple inversion times (TIs) and the application of an appropriate kinetic model. The choice of these sampling times will have an impact on the precision of the estimated parameters. Here, optimal sampling schedule (OSS) design techniques, based on the Fisher Information approach, are applied in order to derive an optimal sampling scheme for pulsed arterial spin labeling (PASL) experiments. Such an approach should improve the precision of parameter estimation from experimental data, and provide a formal framework for optimally selecting a limited number of samples. In this study, we aimed to optimize the estimation precision of CBF and bolus arrival time from the PASL data. The performance of OSS was compared to a more standard evenly distributed sampling schedule (EDS) using both simulated and measured experimental data sets. It was found that OSS was able to significantly improve the precision of parameter estimation in PASL studies that sought to estimate either both CBF and bolus arrival time, or CBF alone. Magn Reson Med, 2008. © 2008 Wiley‐Liss, Inc.
Proton MR spectroscopic imaging of rhesus macaque brain in vivo at 7T
Authors: Gonen Oded , Liu Songtao , Goelman Gadi , Ratai Eva‐Maria , Pilkenton Sarah , Lentz Margaret R. , González R. Gilberto
Published: February 2008

Due to the overall similarity of their brains' structure and physiology to its human counterpart, nonhuman primates provide excellent model systems for the pathogenesis of neurological diseases and their response to treatments. Its much smaller size, 80 versus 1250 cm3, however, requires proportionally higher spatial resolution to study, nondestructively, as many analogous regions as efficiently as possible in anesthetized animals. The confluence of these requirements underscores the need for the highest sensitivity, spatial coverage, resolution, and exam speed. Accordingly, we demonstrate the feasibility of 3D multi‐voxel, proton (1H) MRSI at (0.375 cm)3 = 0.05 cm3 isotropic spatial resolution over 21 cm3 (≈25%) of the anesthetized rhesus macaques brain at 7T in 25 min. These voxels are ×102–101 times smaller than the 8–1 cm3 common to 1H‐MRS in humans, retaining similar proportions between the macaque and human brain. The spectra showed a signal‐to‐noise‐ratio (SNR) ≈9–10 for the major metabolites and the interanimal SNR spatial distribution reproducibility was in the ±10% range for the standard error of their means (SEMs). Their metabolites' linewidths, 9 ± 2 Hz, yield excellent spectral resolution as well. These results indicate that 3D 1H‐MRSI can be integrated into comprehensive MR studies in primates at such high fields. Magn Reson Med, 2008. © 2008 Wiley‐Liss, Inc.
Shortest path network interdiction with asymmetric information
Authors: Bayrak Halil , Bailey Matthew D.
Published: February 2008

We consider an extension of the shortest path network interdiction problem. In this problem an evader attempts to minimize the length of the shortest path between the origin and the destination in a network, while an interdictor attempts to maximize the length of this shortest path by interdicting network arcs using limited resources. We consider the case where there is asymmetric information, i.e., the evader and the interdictor have different levels of information about the network. We formulate this problem as a nonlinear mixed integer program and show that this formulation can be converted to a linear mixed integer program. Computational results demonstrate improvements in the objective function values over the shortest path network interdiction problem with symmetric information. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008
Minimizing a stochastic maximum‐reliability path
Authors: Pan Feng , Morton David P.
Published: February 2008

We consider a stochastic network interdiction problem in which the goal is to detect an evader, who selects a maximum‐reliability path. Subject to a resource constraint, the interdictor installs sensors on a subset of the network's arcs to minimize the value of the evader's maximum‐reliability path, i.e., to maximize the detection probability. When this decision is made, the evader's origin–destination pair is known to the interdictor only through a probability distribution. Our model is framed as a stochastic mixed‐integer program and solved by an enhanced L‐shaped decomposition method. Our primary enhancement is via a valid inequality, which we call a step inequality. In earlier work [Morton et al., IIE Trans 39 (2007), 3–14], we developed step inequalities for the special case in which the evader encounters at most one sensor on an origin–destination path. Here, we generalize the step inequality to the case where the evader encounters multiple sensors. In this more general setting, the step inequality is tightly coupled to the decomposition scheme. An efficient separation algorithm identifies violated step inequalities and strengthens the linear programming relaxation of the L‐shaped method's master program. We apply this solution procedure with further computational enhancements to a collection of test problems. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008
Price competition with elastic traffic
Authors: Ozdaglar Asuman
Published: February 2008

In this paper, we present a combined study of price competition and traffic control in a congested network. We study a model in which service providers own the routes in a network and set prices to maximize their profits, while users choose the amount of flow to send and the routing of the flow according to Wardrop's principle. When utility functions of users are concave and have concave first derivatives, we characterize a tight bound of 2/3 on efficiency in pure strategy equilibria of the price competition game. We obtain the same bound under the assumption that there is no fixed latency cost, i.e., the latency of a link at zero flow is equal to zero. These bounds are tight even when the numbers of routes and service providers are arbitrarily large. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008
Network search games, with arbitrary searcher starting point
Authors: Dagan Arnon , Gal Shmuel
Published: February 2008

We analyze a zero‐sum game between a blind unit‐speed searcher and a stationary hider on a given network Q, where the payoff is the time for the searcher to reach the hider. In contrast to the standard game studied in the literature, we do not assume that the searcher has to start from a fixed point (known to the hider) but can choose his starting point. We show that for some networks, including trees, the optimal searcher, and hider strategies have a simple structure. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008
A linear programming approach to increasing the weight of all minimum spanning trees
Authors: Baïou Mourad , Barahona Francisco
Published: February 2008

Given a graph where increasing the weight of an edge has a nondecreasing convex piecewise linear cost, we study the problem of finding a minimum cost increase of the weights so that the value of all minimum spanning trees is equal to some target value. Frederickson and Solis‐Oba gave an algorithm for the case when the costs are linear. We give a different derivation of their algorithm, and we slightly extend it to deal with convex piecewise linear costs. We formulate the problem as a combinatorial linear program and show how to produce primal and dual solutions. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008
An iterative regularization method in estimating the unknown energy source by laser pulses with a dual‐phase‐lag model
Authors: Huang Cheng‐Hung , Lin Chien‐Yu
Published: February 2008

In the present study an inverse problem for hyperbolic heat conduction with a dual‐phase‐lag model is solved by the conjugate gradient method (CGM) in estimating the unknown heat generation, due to the ultra‐short duration laser heating, based on the interior temperature measurements. Results obtained in this inverse problem will be justified based on the numerical experiments where two different heat source distributions are to be estimated. Results show that the inverse solutions can always be obtained when choosing the initial guesses of the heat sources equal to zero. Finally, it is concluded that accurate heat sources can be estimated in this study. Copyright © 2008 John Wiley & Sons, Ltd.
Pulmonary nodules discovered during the initial evaluation of pediatric patients with bone and soft‐tissue sarcoma
Authors: Absalon Michael J. , McCarville M. Beth , Liu Tiebin , Santana Victor M. , Daw Najat C. , Navid Fariba
Published: February 2008

Background

Recent technical advances in CT imaging and data processing have improved the ability to detect small pulmonary nodules in children with bone and soft‐tissue sarcoma undergoing radiologic imaging of the chest.

Procedure

We retrospectively studied medical records and CT chest scans at initial diagnosis of 210 children and young adults presenting to a single pediatric tertiary care hospital specialized in oncology for evaluation of bone or soft‐tissue sarcoma. We correlated clinical features and CT scan findings with patient outcome and histologic results, when available.

Results

Pulmonary nodules (diameter ≤3 cm) were identified in 66 patients (31.4%). The median size of the largest nodule in each patient was 5 mm (range, 1–20 mm). Of patients who underwent biopsy or resection of a nodule, 41.7% had metastatic pulmonary disease. Having more than three nodules and a bilateral distribution were associated with histology‐proven metastasis (P = 0.002 and P = 0.011, respectively) and an increased frequency of recurrent or progressive metastatic disease in the lung (P < 0.001 and P = 0.023, respectively). Greater size of the largest nodule present showed a trend towards biopsy‐proven lung metastasis, but did not reach statistical significance (P = 0.06). When biopsy or resection was not performed, increased size was significantly associated with nodules being presumed as malignant (median, 16.8 mm compared to 4.0 mm for biopsied nodules, P < 0.001).

Conclusions

Pulmonary nodules were commonly detected during the initial evaluation of pediatric cases of sarcoma. Number and distribution of nodules were significantly associated with metastatic disease and outcome. Pediatr Blood Cancer 2008;50:1147–1153. © 2008 Wiley‐Liss, Inc.
Team management, twinning, and telemedicine in retinoblastoma: A 3‐tier approach implemented in the first eye salvage program in Jordan
Authors: Qaddoumi Ibrahim , Nawaiseh Ibrahim , Mehyar Mustafa , Razzouk Bassem , Haik Barrett G. , Kharma Saamir , Jaradat Imad , Rodriguez‐Galindo Carlos , Wilson Matthew W.
Published: February 2008

Background

This study evaluated the outcome of retinoblastoma patients, when employing a telemedicine‐based twinning program in Jordan.

Procedure

This cohort study included patients at the King Hussein Cancer Centre (KHCC; Amman, Jordan) who received consultations for retinoblastoma from March 2003 to September 2006. A collaborative program was established with the International Outreach Program at St. Jude Children's Research Hospital in Memphis, Tennessee. Cases were discussed using an Internet consultation service where fundus images, clinical history, and proposed treatment were reviewed. Selected cases were further discussed via videoconferencing and electronic mail.

Results

Thirty‐three children with retinoblastoma (20 bilateral) were treated at KHCC. The median age at diagnosis was 7 months for patients with bilateral retinoblastoma and 35 months for patients with unilateral retinoblastoma. Of the 20 patients with bilateral disease, 12 were newly diagnosed and 8 had received prior treatment. Our success in the bilateral cases was most evident in the previously untreated group, in which only six eyes (25%) were enucleated and four eyes (17%) were irradiated. Of the 13 patients with unilateral retinoblastoma, 12 underwent enucleation, and 6 required radiation. Neither group experienced mortality.

Conclusions

Twinning has positively impacted survival and ocular salvage in Jordan. By partnering a team of professionals with mentors willing to provide close supervision, the highly specialized management of retinoblastoma can be successfully implemented in a developing country. Pediatr Blood Cancer 2008;51:241–244. © 2006 Wiley‐Liss, Inc.
Day hospital versus inpatient management of uncomplicated vaso‐occlusive crises in children with sickle cell disease
Authors: Raphael Jean L. , Kamdar Aditi , Wang Tao , Liu Hao , Mahoney Donald H. , Mueller Brigitta U.
Published: February 2008

Background

Day hospital (DH) management for patients with sickle cell disease (SCD) experiencing uncomplicated vaso‐occlusive pain crises has been utilized as an alternative care delivery system to inpatient hospitalization. The objective of this study was to determine whether DH management results in shorter length of stay compared to inpatient care.

Procedure

We conducted a retrospective cohort study with 35 DH admissions and 35 inpatient admissions for children with SCD presenting with uncomplicated vaso‐occlusive crises (VOCs). A DH admission was defined as a minimum of two consecutive days of aggressive pain management as an outpatient, including intravenous hydration and analgesics, supported by home treatment over night with oral analgesic and anti‐inflammatory agents. We gathered data on demographics, pain scores, length of stay, admission charges, and needs for persistent care.

Results

DH care resulted in a 39% reduction of the average length of stay compared to inpatient admissions. Multivariate linear regression demonstrated that the location of patient care for VOCs was a significant predictor of length of stay (P < 0.0006) after controlling for patient characteristics, severity of illness, and disease history.

Conclusions

We conclude that a dedicated DH facility has the potential to provide efficient and timely management of uncomplicated VOCs through reduction of length of stay. This delivery care system may be particularly relevant for children who are significantly impacted by inpatient hospitalization. Pediatr Blood Cancer 2008;51:398–401. © 2008 Wiley‐Liss, Inc.
Metachronous manifestations of sweet's syndrome in a neutropenic patient with Fanconi anemia
Authors: Chatham‐Stephens Kevin , Devere Theresa , Guzman‐Cottrill Judith , Kurre Peter
Published: February 2008

Sweet's syndrome (SS) is an acute, febrile neutrophilic dermatosis that frequently presents with leukocytosis and erythematous plaques. Lesions show neutrophilic infiltration of the dermis and rarely other organs. We report the case of an adolescent male with chronic pancytopenia secondary to Fanconi anemia (FA) who presented with acute respiratory distress. Despite an exhaustive and ultimately unrevealing work‐up, the diagnosis of pulmonary SS was not made until he developed characteristic cutaneous lesions 4 months later. Comprehensive review of pathological specimens revealed metachronous SS manifestations with infiltrates in lung parenchyma, dermis, and subcutis in this neutropenic patient. Pediatr Blood Cancer 2008;51:128–130. © 2008 Wiley‐Liss, Inc.
The use of questionnaires for measuring patient‐reported side effects of drugs: its importance and methodological challenges
Authors: Foster PhD Juliet M. , van der Molen MD, PhD Thys , Caeser PhD Manfred , Hannaford MD, PhD Philip
Published: February 2008

Patient‐reported outcomes such as Quality of Life often play an important part in the efficacy assessment of drug treatment. Although instruments that measure quality of life can detect the positive effects of treatments on health status, they may not measure the effect of negative treatment‐related symptoms. Patients often fail to spontaneously report common or clinically mild drug‐related symptoms, even though the same symptoms can result in the stopping or skipping of prescribed doses. Therefore, as with quality of life assessments, the perception of patients on possible side effects of treatments is best captured by the use of self‐report questionnaires. There are substantial challenges with creating well‐validated, relevant questionnaires that capture the full range of patient‐reported symptoms and signs. A review of 13 existing instruments showed that many patient‐rated side effect questionnaires had been developed, often to a high standard, using well‐established psychometric methods. However, there were some inconsistencies in the methods used by the questionnaire developers, indicating the need for standardisation when creating new, or adapting previous, instruments. Even with their current deficits, it is important that patient‐reported side effect questionnaires be used more in drug development, health outcomes research and resource allocation; all with the ultimate aim of improving quality of patient care. Copyright © 2008 John Wiley & Sons, Ltd.
Determination of different morphological structures in PC/ABS open spiral injection moldings
Authors: O‐Charoen N. , Leong Y.W. , Hamada H.
Published: February 2008

The internal structure of injection molded polymer blends are complex and greatly affect the mechanical properties. In this work, the microstructure development was observed for a Polycarbonate (PC)/Acrylonitrile‐Butadiene‐Styrene (ABS) blend (60/40 wt% blend ratio) that was injection molded using an open spiral mold. The ABS‐rich phase was chemically etched out, leaving behind cavities of different shapes and sizes. With increasing depth, different morphological structures were observed due to the variation of temperature and shear profiles. The changes in morphology can be abrupt, especially at the regions closest to the external surface of the specimen, while a more gradual transition was observed with increasing specimen depth. Thus, a methodology is developed to segregate these structures into different and distinctive layers (skin, shear, intermediate, and core layers) corresponding to the state of shear flow, cavity pressure and distance from the gate. The thickness of these layers and the characteristics of the cavities (i.e. shapes and sizes) are believed to have a direct impact on the final mechanical properties of the moldings. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
The mastication characteristics of powdered carbon black filled natural rubber during internal mixing
Authors: Zhang Anqiang , Lin Yaling , Wang Lianshi
Published: February 2008

Powdered carbon black filled natural rubber, P(NR/HAF), is a premixture of natural rubber and carbon black in powdered form with good carbon black dispersion throughout the rubber matrix. In this study, the mastication properties of P(NR/HAF) were observed under a wide temperature range (50–110°C) and rotor speed (30–100 rpm) range, using a mixing head attached to Brabender Plasticorder. It was found that P(NR/HAF) showed different mastication characteristic, compared to the traditional internal mastication theories of natural rubber; poor masticating properties of P(NR/HAF) are observed with low rotor speed and high temperature and a ‘‘stable zone’’ with middle rotor speed and lower temperature. The Mooney viscosity of rubber batch under different rotor speed and temperature was almost the same, and mastication properties were unsatisfactory. It was considered that the higher temperature build‐up of the mixing batch of P(NR/HAF) during the early stage of internal mixing results in the special mastication properties. A quadratic mastication model of P(NR/HAF), based on the multivariate regression analysis and stepwise regression analysis, was used to predict the mastication characters of P(NR/HAF) in internal mixer under varied temperature and rotor speed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
The electrical properties of boron‐containing poly(vinyl alcohol) derived ceramic organic semiconductor
Authors: Yakuphanoglu Fahrettin , Schiavon Marco Antônio
Published: February 2008

The direct and alternating current conductivity, space charge limited current, and thermoelectrical properties of boron‐containing poly(vinyl alcohol)‐derived ceramic have been investigated. The electrical conductivity of the sample increases with increase in temperature and the room temperature conductivity of the sample was found to be 3.82 × 10−5 S/cm. The electrical conductivity and thermoelectric power results suggest that the PVAB polymer has p‐type electrical conductivity. The current–voltage characteristics indicate that at higher voltages, the space charge limited conductivity mechanism is dominant in the PVAB sample. The electronic parameters such as the position of the Fermi level bottom of the conduction band, EF, the density of states in conduction band Nc, effective mass of holes ms were found to be 0.44 eV, 2.12 × 1025 m−3, and 0.59 mo, respectively. Alternating current conductivity results suggest that the correlated barrier hopping conductivity is dominant in AC conductivity mechanism of the sample. The imaginary part of the dielectrical modulus at different temperatures shows a relaxation peak, indicating a temperature‐dependent non‐Debye relaxation. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Synthesis and characterization of hollow polyaniline microtubes and microbelts with nanostructured walls in sodium dodecyl sulfate micellar solutions
Authors: Wu Tzong‐Ming , Lin Yen‐Wen
Published: February 2008

Doped polyaniline in its emeraldine salt form (PANI‐ES) were successfully prepared by in situ chemical oxidative polymerization using various concentrations of sodium dodecyl sulfate (SDS) micellar solutions. Structural analysis using field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy showed that the morphologies of fabricated PANI‐ES contain hollow tube‐like and belt‐like structures with thickness in the range of 100–200 nm, diameters in the range of 1–5 μm, and lengths up to several tens and hundreds of micrometers. The changes of morphology from particle‐like into microtube‐like or microbelt‐like structure with nanostructured walls are strongly dependent on the concentration of SDS. The conductivities of fabricated PANI‐ES with 0.1 M SDS content at room temperature are 80% higher than those of PANI‐ES without SDS, perhaps because SDS may serve as a dopant or the formation of one‐dimensional structure to improve the conductivity of PANI‐ES. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Thermal degradation and physical aging of poly(lactic acid) and its blends with starch
Authors: Acioli‐Moura Ricardo , Sun Xiuzhi Susan
Published: February 2008

Poly(lactic acid) (PLA) and its blends with starch and methylenediphenyl diisocyanate (MDI) were extruded in a twin‐screw extruder and compress‐molded in a dog‐bone shaped tensile bars to form test specimens. The thermalgravimetric profile and thermal endurance of these samples were characterized. The effect of physical aging on mechanical and thermal properties of these samples was evaluated. For the aging study, samples were stored at 25°C and relative humidity fluctuating between 90 and 30%, from 2 to 180 days, with or without a polyethylene bag as a moisture barrier. Physical aging of pure PLA samples stored in a controlled environment from 2 to 360 days was also evaluated. The presence of MDI in the PLA/starch composite did not affect the thermal decomposition profile. The PLA showed the highest Arrhenius activation energy and strongest thermal endurance of all samples, followed by PLA/starch/MDI and PLA/starch. Exposure of the samples to storage conditions with fluctuating relative humidity (RH) significantly affects thermal‐mechanical performance of PLA and its composites. But, the samples stored in plastic bags can minimize such effects. Mechanical properties of PLA and PLA/starch‐based composites sealed in plastic bags had no significant change during 30‐day storage in fluctuating humidity conditions (30–90% RH). POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Der Large Hadron Collider – die Entdeckungsmaschine. Teilchenphysik
Authors: Müller Thomas
Published: February 2008

Am Europäischen Zentrum für Teilchenphysik CERN läuft demnächst der Large Hadron Collider, LHC, an. Er soll Protonen mit einer Schwerpunktenergie bis zu 14 TeV und Blei‐Ionen bis zu 1144 TeV miteinander kollidieren lassen. Mehr als 6000 Wissenschaftler und Ingenieure aus rund 500 Instituten aus aller Welt sind am Bau der Detektoren beteiligt. Hauptziele des LHC sind die Entdeckung des Higgs‐Bosons und Teilchen der Supersymmetrie sowie die Erzeugung des Quark‐Gluon‐Plasmas. Auch Fragen nach der Dunklen Materie und kleinen Schwarzen Löchern lassen sich angehen. Der LHC soll mindestens zwanzig Jahre lang arbeiten.
Zweirädrige Energiesparbüchse. Das Fahrrad als alltägliches Verkehrsmittel
Authors: Schlichting H. Joachim , Suhr Wilfried
Published: February 2008

Vergleicht man die energetischen Transportkosten von Laufen, Fahrrad‐ und Autofahren im Stadtverkehr, dann schneidet das Rad am besten ab. Im Vergleich zum Gehen ist Radfahren energetisch etwa fünfmal günstiger. Dabei erlaubt es eine mehr als doppelt so hohe Geschwindigkeit. Das Autofahren ist in der Stadt sogar rund 24‐mal ungünstiger als Radeln, falls es sich um eine Person in einem Kleinwagen handelt.
Kontrollierte Hohlräume in der Nanowelt
Authors: Zacharias Margit
Published: February 2008

Beim Übergang vom Mikro‐ zum Nanobereich können altbekannte Effekte plötzlich ganz erstaunliche Auswirkungen haben. So verändert sich die Diffusion, wenn die diffundierenden Atome in Nanokugeln oder Nanodrähten eingeschlossen sind. Dieser Effekt hat es unserer Gruppe am Max‐Planck‐Institut für Mikrostukturphysik in Halle und der Universität Freiburg ermöglicht, mikrometerlange Hohlräume mit Durchmessern von 30 bis 100 nm in Nanodrähten definiert zu erzeugen.
Highly porous elastomer‐silsesquioxane nanocomposites synthesized within high internal phase emulsions
Authors: Normatov Jenny , Silverstein Michael S.
Published: February 2008

Highly porous elastomeric nanocomposites were successfully synthesized through copolymerization of 2‐ethylhexyl acrylate (EHA), divinyl benzene (DVB), and up to 9 mol % of a polyhedral oligomeric silsesquioxane bearing one propylmethacryl group and seven cyclohexyl groups (MACH‐POSS) within the external phase of high internal phase emulsions (HIPE). The chemical structures, morphologies, thermal properties, and mechanical properties of the polyHIPE were investigated. The mechanical loss peak temperature and full width at half maximum increased with increasing MACH‐POSS content. These changes indicate that copolymerization with MACH‐POSS limits segmental mobility and produces compositional distributions on the nanometer scale. At 9 mol % MACH‐POSS, the reduction in segmental mobility produced a glass transition temperature above room temperature and a significant increase in modulus that can be ascribed to the relatively glassy nature of the polymer. Inorganic monoliths with porosities of around 86%, O/Si of about 1.6, and less than 10% carbon were produced on pyrolysis of the nanocomposite polyHIPE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2357–2366, 2008
Emulsion synthesis of nanoparticles containing PEDOT using conducting polymeric surfactant: Synergy for colloid stability and intercalation doping
Authors: Dai Chi‐an , Chang Chun‐jie , Chi Hung‐yu , Chien Hung‐ta , Su Wei‐fang , Chiu Wen‐yen
Published: February 2008

Poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is a widely used conductive aqueous dispersion synthesized by using emulsion polymerization method. To further enhance its solution processability and conductivity of PEDOT derivatives, we proposed to replace the nonconductive PSS with conductive poly[2‐(3thienyl)‐ethoxy‐4‐butylsulfonate] (PTEB) as surfactant for the emulsion polymerization of PEDOT. The reaction involved colloid stabilization and doping in one step, and yielded PEDOT:PTEB composite nanoparticles with high electrical conductivity. Contrary to its counterpart containing nonconductive surfactant, PEDOT: PTEB showed increasing film conductivity with increasing PTEB concentration. The result demonstrates the formation of efficient electrical conduction network formed by the fully conductive latex nanoparticles. The addition of PTEB for EDOT polymerization significantly reduced the size of composite particles, formed stable spherical particles, enhanced thermal stability, crystallinity, and conductivity of PEDOT:PTEB composite. Evidence from UV–VIS and FTIR measurement showed that strong molecular interaction between PTEB and PEDOT resulted in the doping of PEDOT chains. X‐ray analysis further demonstrated that PTEB chains were intercalated in the layered crystal structure of PEDOT. The emulsion polymerization of EDOT using conducting surfactant, PTEB demonstrated the synergistic effect of PTEB on colloid stability and intercalation doping of PEDOT during polymerization resulting in significant conductivity improvement of PEDOT composite nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2536–2548, 2008
Microstructural evolution in polyacrylonitrile fibers during oxidative stabilization
Authors: Yu Meijie , Wang Chengguo , Bai Yujun , Zhu Bo , Ji Minxia , Xu Yong
Published: February 2008

Microstructural evolution in polyacrylonitrile fibers during oxidative stabilization was investigated by high‐resolution transmission electron microscopy and wide‐angle X‐ray diffraction. Nanocrystallites and two types of amorphous structures, that is, onion‐like spheres and maze‐like matrix, are observed not only in the precursor fibers but also in the fibers stabilized at 230, 255, and 275 °C. During oxidative stabilization, changes take place earlier in the amorphous onion‐like spheres than in the ordered regions. With increasing temperature, the outer layers of the onion‐like spheres gradually interlace with each other, microscopically demonstrating crosslinking reactions among neighboring macromolecules. The interplanar spacing in crystalline regions increases and the crystallite size decreases as a result of an order–disorder transition. The transition in large crystallites is not completed even in the fibers that are stabilized at 275 °C, suggesting that uniform microstructure and fine crystallites are conducive to homogenous stabilization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 759–765, 2008
Critical behavior of brittle‐ductile transition of polymers
Authors: Jiang Wei , Hu Yuexin , Yin Jinghua
Published: February 2008

We report that the brittle‐ductile transition of polymers induced by temperature exhibits critical behavior. When t close to 0, the critical surface to surface interparticle distance (IDc) follows the scaling law: IDc ∝ t−v, where t = 1 − T/T (T and T are the test temperature and brittle‐ductile transition temperature of matrix polymer, respectively) and v = 2/D. It is clear that the scaling exponent v only depends on dimension (D). For 2, 3, and 4 dimension, v = 1, 2/3, and 1/2 respectively. The result indicates that the IDc follows the same scaling law as that of the correlation length (ξ), when t approach to zero. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 766–769, 2008
Solifluction processes in an area of seasonal ground freezing, Dovrefjell, Norway
Authors: Harris Charles , Kern‐Luetschg Martina , Smith Fraser , Isaksen Ketil
Published: February 2008

Continuous monitoring of soil temperatures, frost heave, thaw consolidation, pore water pressures and downslope soil movements are reported from a turf‐banked solifluction lobe at Steinhøi, Dovrefjell, Norway from August 2002 to August 2006. Mean annual air temperatures over the monitored period were slightly below 0°C, but mean annual ground surface temperatures were around 2°C warmer, due to the insulating effects of snow cover. Seasonal frost penetration was highly dependent on snow thickness, and at the monitoring location varied from 30–38 cm over the four years. The shallow annual frost penetration suggests that the site may be close to the limit of active solifluction in this area. Surface solifluction rates over the period 2002–06 ranged from 0.5 cm yr−1 at the rear of the lobe tread to 1.6 cm yr−1 just behind the lobe front, with corresponding soil transport rates of 6 cm3 cm−1 yr−1 and 46 cm3 cm−1 yr−1. Pore water pressure measurements indicated seepage of snowmelt beneath seasonally frozen soil in spring with artesian pressures beneath the confining frozen layer. Soil thawing was associated with surface settlement and downslope soil displacements, but following clearance of the frozen ground, later soil surface settlement was accompanied by retrograde movement. Summer rainfall events caused brief increases in pore pressure, but no further soil movement. Surface displacements exceeded maximum potential frost creep values and it is concluded that gelifluction was an important component of slow near‐surface mass movements at this site. Temporal and spatial variations in solifluction rates across the area are likely to be considerable and strongly influenced by snow distribution. Copyright © 2008 John Wiley & Sons, Ltd.
V domain of RAGE interacts with AGEs on prostate carcinoma cells
Authors: Allmen Edith Uetz‐von , Koch Michael , Fritz Günter , Legler Daniel F.
Published: February 2008

BACKGROUND

The expression of the scavenger receptor for advanced glycation end products (RAGE) and various ligands of RAGE correlate significantly with cancer progression. However, the mechanism of RAGE/sRAGE‐induced cancer cell activation and ligand usage remain largely unknown.

METHODS

Androgen‐independent, highly invasive, as well as androgen‐dependent, non‐invasive human prostate carcinoma (CaP) cells were investigated for their interaction with the soluble form of RAGE (sRAGE). Using neutralizing antibodies and soluble proteins, the ligand for RAGE was identified on CaP cells and ligand binding with sRAGE was biochemically characterized.

RESULTS

Both androgen‐independent, highly invasive and androgen‐dependent, non‐invasive CaP cells interacted with immobilized sRAGE in a surprisingly strong manner. Using C‐terminal truncation variants of RAGE we identified the V domain being responsible for the adhesion of CaP cells to sRAGE. Moreover, we demonstrate that this adhesion cannot be blocked by S100B or neutralizing antibodies against β integrins, or amphoterin. However, the CaP cell–RAGE interaction was inhibited with either AGE‐modified proteins, or with neutralizing antibodies against AGE or RAGE. Despite similar binding kinetics between AGE‐modified BSA and different RAGE domains, only applying an excess of sRAGE, but not the VC1 or V domain of RAGE, was able to block the CaP cell–RAGE interaction.

CONCLUSIONS

We identified AGEs as the ligand for RAGE on both invasive and non‐invasive prostate cancer cells. Prostate 68: 748–758, 2008. © 2008 Wiley‐Liss, Inc.
Deriving protein dynamical properties from weighted protein contact number
Authors: Lin Chih‐Peng , Huang Shao‐Wei , Lai Yan‐Long , Yen Shih‐Chung , Shih Chien‐Hua , Lu Chih‐Hao , Huang Cuen‐Chao , Hwang Jenn‐Kang
Published: February 2008

It has recently been shown that in proteins the atomic mean‐square displacement (or B‐factor) can be related to the number of the neighboring atoms (or protein contact number), and that this relationship allows one to compute the B‐factor profiles directly from protein contact number. This method, referred to as the protein contact model, is appealing, since it requires neither trajectory integration nor matrix diagonalization. As a result, the protein contact model can be applied to very large proteins and can be implemented as a high‐throughput computational tool to compute atomic fluctuations in proteins. Here, we show that this relationship can be further refined to that between the atomic mean‐square displacement and the weighted protein contact‐number, the weight being the square of the reciprocal distance between the contacting pair. In addition, we show that this relationship can be utilized to compute the cross‐correlation of atomic motion (the B‐factor is essentially the auto‐correlation of atomic motion). For a nonhomologous dataset comprising 972 high‐resolution X‐ray protein structures (resolution <2.0 Å and sequence identity <25%), the mean correlation coefficient between the X‐ray and computed B‐factors based on the weighted protein contact‐number model is 0.61, which is better than those of the original contact‐number model (0.51) and other methods. We also show that the computed correlation maps based on the weighted contact‐number model are globally similar to those computed through normal model analysis for some selected cases. Our results underscore the relationship between protein dynamics and protein packing. We believe that our method will be useful in the study of the protein structure‐dynamics relationship. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Glutathione reductase and thioredoxin reductase at the crossroad: The structure of Schistosoma mansoni thioredoxin glutathione reductase
Authors: Angelucci Francesco , Miele Adriana E. , Boumis Giovanna , Dimastrogiovanni Daniela , Brunori Maurizio , Bellelli Andrea
Published: February 2008

Thioredoxin glutathione reductase (TGR) is a key flavoenzyme expressed by schistosomes that bridges two detoxification pathways crucial for the parasite survival in the host's organism. In this article we report the crystal structure (at 2.2 Å resolution) of TGR from Schistosoma mansoni (SmTGR), deleted in the last two residues. The structure reveals the peculiar architecture of this chimeric enzyme: the small Glutaredoxin (Grx) domain at the N‐terminus is joined to the large thioredoxin reductase (TR) one via an extended complementary surface, involving residues not conserved in the Grx superfamily; the TR domain interacts with an identical partner via its C‐terminal domain, forming a dimer with a twisted “W” shape. Although lacking the penultimate Selenocysteine residue (Sec), the enzyme is still able to reduce oxidized glutathione. These data update the interpretation of the interdomain communication in TGR enzymes. The possible function of this enzyme in pathogenic parasites is discussed. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Structural properties of the human respiratory syncytial virus P protein: Evidence for an elongated homotetrameric molecule that is the smallest orthologue within the family of paramyxovirus polymerase cofactors
Authors: Llorente María T. , Taylor Ian A. , López‐Viñas Eduardo , Gomez‐Puertas Paulino , Calder Lesley J. , García‐Barreno Blanca , Melero José A.
Published: February 2008

The oligomeric state and the hydrodynamic properties of human respiratory syncytial virus (HRSV) phosphoprotein (P), a known cofactor of the viral RNA‐dependent RNA polymerase (L), and a trypsin‐resistant fragment (X) that includes its oligomerization domain were analyzed by sedimentation equilibrium and velocity using analytical ultracentrifugation. The results obtained demonstrate that both P and fragment X are homotetrameric with elongated shapes, consistent with electron micrographs of the purified P protein in which thin rod‐like molecules of ∼12.5 ± 1.0 nm in length were observed. A new chymotrypsin resistant fragment (Y*) included in fragment X has been identified and purified by gel filtration chromatography. Fragment Y* may represent a minimal version of the P oligomerization domain. Thermal denaturation curves based on circular dichroism data of P protein showed a complex behavior. In contrast, melting data generated for fragments X and particularly fragment Y* showed more homogeneous transitions indicative of simpler structures. A three‐dimensional model of X and Y* fragments was built based on the atomic structure of the P oligomerization domain of the related Sendai virus, which is in good agreement with the experimental data. This model will be an useful tool to make rational mutations and test the role of specific amino acids in the oligomerization and functional properties of the HRSV P protein. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Toward better refinement of comparative models: Predicting loops in inexact environments
Authors: Sellers Benjamin D. , Zhu Kai , Zhao Suwen , Friesner Richard A. , Jacobson Matthew P.
Published: February 2008

Achieving atomic‐level accuracy in comparative protein models is limited by our ability to refine the initial, homolog‐derived model closer to the native state. Despite considerable effort, progress in developing a generalized refinement method has been limited. In contrast, methods have been described that can accurately reconstruct loop conformations in native protein structures. We hypothesize that loop refinement in homology models is much more difficult than loop reconstruction in crystal structures, in part, because side‐chain, backbone, and other structural inaccuracies surrounding the loop create a challenging sampling problem; the loop cannot be refined without simultaneously refining adjacent portions. In this work, we single out one sampling issue in an artificial but useful test set and examine how loop refinement accuracy is affected by errors in surrounding side‐chains. In 80 high‐resolution crystal structures, we first perturbed 6–12 residue loops away from the crystal conformation, and placed all protein side chains in non‐native but low energy conformations. Even these relatively small perturbations in the surroundings made the loop prediction problem much more challenging. Using a previously published loop prediction method, median backbone (N‐Cα‐C‐O) RMSD's for groups of 6, 8, 10, and 12 residue loops are 0.3/0.6/0.4/0.6 Å, respectively, on native structures and increase to 1.1/2.2/1.5/2.3 Å on the perturbed cases. We then augmented our previous loop prediction method to simultaneously optimize the rotamer states of side chains surrounding the loop. Our results show that this augmented loop prediction method can recover the native state in many perturbed structures where the previous method failed; the median RMSD's for the 6, 8, 10, and 12 residue perturbed loops improve to 0.4/0.8/1.1/1.2 Å. Finally, we highlight three comparative models from blind tests, in which our new method predicted loops closer to the native conformation than first modeled using the homolog template, a task generally understood to be difficult. Although many challenges remain in refining full comparative models to high accuracy, this work offers a methodical step toward that goal. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Prediction of interaction sites from apo 3D structures when the holo conformation is different
Authors: Murga Leonel F. , Ondrechen Mary Jo , Ringe Dagmar
Published: February 2008

The predictability of catalytic and binding sites from apo structures is addressed for proteins that undergo significant conformational change upon binding. Theoretical microscopic titration curves (THEMATICS), an electrostatics‐based method for the prediction of functional sites, is performed on a test set of 24 proteins with both apo and holo structures available. For 23 of these 24 proteins (96%), THEMATICS predicts the correct catalytic or binding site for both the apo and holo forms. For only one of the 24 proteins, THEMATICS makes the correct prediction for the holo structure but fails for the apo structure. The metrics used by THEMATICS to identify functional residues generally are larger in absolute value for the functional residues in the holo forms compared to the corresponding residues in the apo forms. However, even in the apo forms, these identifying metrics are still statistically significantly larger for functional residues than for residues not involved in catalysis or binding. This indicates that some of the unusual electrostatic properties of functional residues are preserved in the apo conformation. Evidence is presented that certain residues immediately surrounding the active catalytic and binding residues impart functionally important chemical and electrostatic properties to the active residues. At least parts of these microenvironments exist in the unbound conformations, such that THEMATICS is able to distinguish the functional residues even in the apo structures. Proteins 2008. © 2008 Wiley‐Liss, Inc.