bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self‐Assembled Sugar‐Substituted Perylene Diimide Nanostructures with Homochirality and High Gas Sensitivity
Authors: Hu Jianchen , Kuang Wenfeng , Deng Ke , Zou Wenjun , Huang Yongwei , Wei Zhixiang , Faul Charl F.J. 
Published: October 2012

AbstractA new symmetrical sugar‐based perylenediimide derivative PTCDI‐BAG is synthesized and its aggregate morphologies and formation mechanisms are studied in detail in the mixed solvent system water/N,N‐dimethylformamide (H2O/DMF) with changing volume ratios. PTCDI‐BAG molecules self‐assemble into planar ribbons in 20/80 and 40/60 H2O/DMF (v/v), but their chiralities are opposite according to recorded circular dichroism (CD) spectra. With a further increase of the water content, only left‐handed helical nanowires are obtained in 60/40 and 80/20 H2O/DMF (v/v) mixtures. By combining density functional theory (DFT) calculations with the experimental investigations, it is proposed that kinetic and thermodynamic factors play key roles in tuning PTCDI‐BAG structures and helicity. The formation of the ribbon is thermodynamically controlled in the 20/80 H2O/DMF system, but kinetically controlled nucleation followed by thermodynamically controlled self‐assembly plays the governing roles for the formation of nanoribbons in 40/60 H2O/DMF. Devices based on single nanoribbons for hydrazine sensing exhibit better performance than nanofiber bundles obtained in this study and achiral nanostructures reported in previous study. This study not only provides an elaborated route to tuning the structures and helicity of PTCDI molecules, but also provides new possibilities for the construction of high‐performance nanodevices.
The Synthesis of N‐Arylated Amides via Copper(II) Triflate‐ Catalyzed Direct Oxygenation and N‐Arylation of Benzylamines with Aryl Iodides
Authors: Xu Mei , Zhang Xiao‐Hong , Shao Yin‐Lin , Han Jiang‐Sheng , Zhong Ping 
Published: October 2012

AbstractAn efficient approach for the synthesis of N‐arylated amides by copper(II) triflate‐catalyzed direct oxygenation and N‐arylation reaction of benzylamines with aryl iodides is reported. Various benzylamines and aryl iodides can participate in the reaction, providing a series of N‐arylated amides in moderate to good yields.
A novel green analytical procedure for monitoring of azoxystrobin in water samples by a flow injection chemiluminescence method with off‐line ultrasonic treatment
Authors: Yang Xin‐an , Zhang Wang‐bing 
Published: October 2012

ABSTRACTA simple and green flow injection chemiluminescence (FI‐CL) method for determination of the fungicide azoxystrobin was described for the first time. CL signal was generated when azoxystrobin was injected into a mixed stream of luminol and KMnO4. The CL signal of azoxystrobin could be greatly improved when an off‐line ultrasonic treatment was adopted. Meanwhile, the signal intensity increases with the analyte concentration proportionally. Several variables, such as the ultrasonic parameters, flow rate of reagents, concentrations of sodium hydroxide solution and CL reagents (potassium permanganate, luminol) were investigated, and the optimal CL conditions were obtained. Under optimal conditions, the linear range of 1–100 ng/mL for azoxystrobin was obtained and the detection limit (3σ) was determined as 0.13 ng/mL. The relative standard deviation was 1.5% for 10 consecutive measurements of 20 ng/mL azoxystrobin. The method has been applied to the determination of azoxystrobin residues in water samples. Copyright © 2012 John Wiley & Sons, Ltd.
Nanoscale structure of type I collagen fibrils: Quantitative measurement of D‐spacing
Authors: Erickson Blake , Fang Ming , Wallace Joseph M. , Orr Bradford G. , Les Clifford M. , Banaszak Holl Mark M. 
Published: October 2012

AbstractThis article details a quantitative method to measure the D‐periodic spacing of type I collagen fibrils using atomic force microscopy coupled with analysis using a two‐dimensional fast fourier transform approach. Instrument calibration, data sampling and data analysis are discussed and comparisons of the data to the complementary methods of electron microscopy and X‐ray scattering are made. Examples of the application of this new approach to the analysis of type I collagen morphology in disease models of estrogen depletion and osteogenesis imperfecta (OI) are provided. We demonstrate that it is the D‐spacing distribution, not the D‐spacing mean, that showed statistically significant differences in estrogen depletion associated with early stage osteoporosis and OI. The ability to quantitatively characterize nanoscale morphological features of type I collagen fibrils will provide important structural information regarding type I collagen in many research areas, including tissue aging and disease, tissue engineering, and gene knockout studies. Furthermore, we also envision potential clinical applications including evaluation of tissue collagen integrity under the impact of diseases or drug treatments.
Thermal Effects on the Synthesis of 1,1‐Dibutoxyethane in a Fixed‐Bed Adsorptive Reactor
Authors: Graça N. S. , Pais L. S. , Silva V. M. T. M. , Rodrigues A. E. 
Published: October 2012

AbstractThe effects of temperature on the synthesis of 1,1‐dibutoxyethane (DBE) in a fixed‐bed adsorptive reactor were studied by performing both adsorption/desorption and reaction/regeneration experiments at 15 and 35 °C. The Langmuir‐type isotherm parameters at 15 and 35 °C were obtained from the adsorption/desorption experiments. The reaction/regeneration experiments showed an increase in both conversion and productivity with increasing temperature. Isothermal and nonisothermal mathematical models were used to simulate the reactor operation with different Damköhler numbers. The simulated results suggest that the reactor productivity can be improved by using the adiabatic operation mode on the fixed‐bed adsorptive reactor, obtaining a productivity for DBE of 71.8 mol kg–1h–1.
Induction of the Columnar Phase of Unconventional Dendrimers by Breaking the C2 Symmetry of Molecules
Authors: Lai Long‐Li , Wang Sheng‐Wei , Cheng Kung‐Lung , Lee Jey‐Jau , Wang Tsai‐Hui , Hsu Hsiu‐Fu 
Published: October 2012

AbstractTwo triazine‐based unconventional dendrimers were prepared and characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD studies showed that these dendrimers display columnar liquid‐crystalline phases during thermal treatment. This is ascribable to breaking of their C2 symmetry. The molecular conformations of prepared dendrimers were obtained by computer simulation with the MM3 model of the CaChe program in the gas phase. The simulation showed that the conformations of the prepared dendrimers are rather flat and disfavor formation of the LC phase. However, due to C2‐symmetry breaking, the prepared dendrimers have structural isomers in the solid state and thus show the desired columnar phases. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks.
Two‐Dimensional Infrared Spectroscopy Reveals the Structure of an Evans Auxiliary Derivative and Its SnCl4 Lewis Acid Complex
Authors: Messmer Andreas T. , Lippert Katharina M. , Steinwand Sabrina , Lerch Eliza‐Beth W. , Hof Kira , Ley David , Gerbig Dennis , Hausmann Heike , Schreiner Peter R. , Bredenbeck Jens 
Published: October 2012

AbstractDetermining the structure of reactive intermediates is the key to understanding reaction mechanisms. To access these structures, a method combining structural sensitivity and high time resolution is required. Here ultrafast polarization‐dependent two‐dimensional infrared (P2D‐IR) spectroscopy is shown to be an excellent complement to commonly used methods such as one‐dimensional IR and multidimensional NMR spectroscopy for investigating intermediates. P2D‐IR spectroscopy allows structure determination by measuring the angles between vibrational transition dipole moments. The high time resolution makes P2D‐IR spectroscopy an attractive method for structure determination in the presence of fast exchange and for short‐lived intermediates. The ubiquity of vibrations in molecules ensures broad applicability of the method, particularly in cases in which NMR spectroscopy is challenging due to a low density of active nuclei. Here we illustrate the strengths of P2D‐IR by determining the conformation of a Diels–Alder dienophile that carries the Evans auxiliary and its conformational change induced by the complexation with the Lewis acid SnCl4, which is a catalyst for stereoselective Diels–Alder reactions. We show that P2D‐IR in combination with DFT computations can discriminate between the various conformers of the free dienophile N‐crotonyloxazolidinone that have been debated before, proving antiperiplanar orientation of the carbonyl groups and s‐cis conformation of the crotonyl moiety. P2D‐IR unequivocally identifies the coordination and conformation in the catalyst–substrate complex with SnCl4, even in the presence of exchange that is fast on the NMR time scale. It resolves a chelate with the carbonyl orientation flipped to synperiplanar and s‐cis crotonyl configuration as the main species. This work sets the stage for future studies of other catalyst–substrate complexes and intermediates using a combination of P2D‐IR spectroscopy and DFT computations.
Palladium(II)‐Catalyzed Oxidative Cyclization of Allylic Tosylcarbamates: Scope, Derivatization, and Mechanistic Aspects
Authors: Joosten Antoine , Persson Andreas K. Å. , Millet Renaud , Johnson Magnus T. , Bäckvall Jan‐E. 
Published: October 2012

AbstractA highly selective oxidative palladium(II)‐catalyzed (Wacker‐type) cyclization of readily available allylic tosylcarbamates is reported. This operationally simple catalytic reaction furnishes tosyl‐protected vinyl‐oxazolidinones, common precursors to syn‐1,2‐amino alcohols, in high yield and excellent diasteroselectivity (>20:1). It is demonstrated that both stoichiometric amounts of benzoquinone (BQ) as well as aerobic reoxidation (molecular oxygen) is suitable for this transformation. The title reaction is shown to proceed through overall trans‐amidopalladation of the olefin followed by β‐hydride elimination. This process is scalable and the products are suitable for a range of subsequent transformations such as: kinetic resolution (KR) and oxidative Heck‐, Wacker‐, and metathesis reactions.
Präkolumbianische Chemie
Authors: Soentgen Jens , Hilbert Klaus 
Published: October 2012

AbstractWir wollen in diesem Essay zeigen, dass besonders auf dem Gebiet der chemischen Praktiken die Erfindungsgabe und technische Intelligenz der indigenen Völker Südamerikas beträchtlich war und ist und zu Erfindungen geführt hat, von denen bis heute etliche Millionen Menschen in der westlichen Welt, insbesondere Chemiekonzerne, profitieren. Wir möchten diese Behauptungen mit einigen Beispielen aus dem Bereich der chemischen Praktiken und der biochemischen Prozesse der Stoffumwandlung belegen, die in der Alten Welt unbekannt waren. Die Fähigkeit der südamerikanischen Indianer, Stoffe zu gewinnen und gezielt umzubilden, soll anhand der Erzeugung von Giften, wie Curare, oder auch der Entgiftung von Pflanzen, wie bei der Herstellung von Maniokmehl, erläutert werden. Erwähnt werden auch andere mehrstufige Prozesse der gezielten Stoffumwandlung und die Entdeckung und Nutzung hochwirksamer Naturstoffe durch indigene Völker Amazoniens, wie Kautschuk, aber auch psychoaktive Drogen.
Positive quadrant dependence testing and constrained copula estimation
Authors: Gijbels Irène , Sznajder Dominik 
Published: October 2012

AbstractPositive quadrant dependence is a specific dependence structure that is of practical importance in for example modelling dependencies in insurance and actuarial sciences. This dependence structure imposes a constraint on the copula function. The interest in this paper is to test for positive quadrant dependence. One way to assess the distribution of the test statistics under the null hypothesis of positive quadrant dependence is to resample from a constrained copula. This requires constrained estimation of a copula function. We show that this use of resampling under a constrained copula improves considerably the power performance of existing testing procedures. We propose two resampling procedures, one based on a parametric constrained copula estimation and one relying on nonparametric estimation of a positive quadrant dependence copula, and discuss their properties. The finite‐sample performances of the resulting testing procedures are evaluated via a simulation study that also includes comparisons with existing tests. Finally, a data set of Danish fire insurance claims is tested for positive quadrant dependence.The Canadian Journal of Statistics41: 36–64; 2013 © 2012 Statistical Society of Canada
Circuit implementation and model of a new multi‐scroll chaotic system
Authors: Chen Diyi , Sun Zaitao , Ma Xiaoyi , Chen Lei 
Published: October 2012

SUMMARYIn this paper, a multi‐scroll chaotic system from the improved Chua's system is proposed. Moreover, non‐linear dynamics are analyzed including phase‐space trajectories, bifurcation diagrams, Poincaré maps and so on. The most important thing is that we discovered phase‐space trajectories, bifurcation diagrams and Poincaré maps are unified and closely related, which can describe different aspects of the multi‐scroll chaotic system. Furthermore, the corresponding improved module‐based circuits are designed for realizing two to four‐scroll chaotic attractors, and the experimental results are also obtained, which are consistent with the numerical simulations. Copyright © 2012 John Wiley & Sons, Ltd.
Decode‐and‐forward two‐way relaying protocol with one retransmission
Authors: Xu Kun , Gao Yuanyuan , Xu Youyun , Fan Zhangjun , Yi Xiaoxin 
Published: October 2012

SUMMARYThis paper investigates the decode‐and‐forward two‐way relaying channel without direct link and proposes a protocol based on the physical‐layer network coding (PNC) protocol. The proposed protocol (termed ORT) introduces one retransmission into PNC, aiming at enhancing its outage performance. To manifest the merits of ORT, we compare it with PNC and the time‐division broadcast (TDBC) protocol, in terms of outage performance, expected rate, and diversity‐multiplexing tradeoff (DMT). Firstly, we derive the outage probability of the three protocols and then the expected rate. Secondly, asymptotic analysis is conducted to shed light on the diversity and coding gains. Finally, the DMT is obtained for the three protocols. The numerical results reveal the following: (i) that ORT performs better than PNC in both outage and expected rate performance when the nodes transmit with different powers. However, it has the same DMT performance with PNC; (ii) that ORT possesses improved DMT performance over TDBC whereas its expected rate is only better than the latter at medium to high signal‐to‐noise ratio. Copyright © 2012 John Wiley & Sons, Ltd.
Polyunsaturated fatty acids production and transformation by Mortierella alpina and anaerobic bacteria
Authors: Ogawa Jun , Sakuradani Eiji , Kishino Shigenobu , Ando Akinori , Yokozeki Kenzo , Shimizu Sakayu 
Published: October 2012

AbstractMicroorganisms are promising as producers of various polyunsaturated fatty acids (PUFAs) and as catalysts transforming them into unique molecular species beyond common PUFAs. This article describes PUFA production through chemical mutant‐ and molecular‐breeding of an oleaginous filamentous fungus Mortierella alpina 1S‐4 and PUFA transformation by anaerobic bacteria. M. alpina 1S‐4 and its mutants and transformants produce oils containing not only common n − 6 and n − 3 PUFAs but also rare PUFAs. Unique PUFA‐transforming activities were found in anaerobic bacteria. They isomerized PUFA to conjugated fatty acids and further transformed to partially saturated fatty acids with hydroxyl fatty acids as intermediates. The functions of these unique PUFAs have been attracting much attention for improving our health and for developing new chemical materials.
Amperometric Response of Alcohols Dissolved in High Resistance Hydrocarbon Media at Microelectrodes Without Supporting Electrolyte
Authors: Kiss László , Nagy Géza , Kovács Barna 
Published: October 2012

AbstractNarrow‐gap cells were fabricated for direct amperometric measurement of alcohol content in liquid hydrocarbon mixtures. Their performance has been investigated using methanol, ethanol, n‐propanol as sample components (ethanol was in most details studied). One type of the insulating materials was applied in order to obtain two copper discs. The surfaces of the copper microdiscs were covered with a CuxS modifying layer. The other cell constructed in the similar way had a carbon disc working electrode (with diameter of 30 µm and copper reference/counter electrode 0.3 mm). The amperometric behaviour of the alcohols have been investigated in toluene and n‐heptane solvents without background electrolyte. The amperometric current was found proportional to the ethanol concentration in the investigated range of 0.5–11 v/v%. The sensor’s performance was also tested with ethanol containing fuel products from a gas station.
Current Advances in Polymer Electrolyte Fuel Cells Based on the Promotional Role of Under‐rib Convection
Authors: Choi K.‐S. , Kim B.‐G. , Park K. , Kim H.‐M. 
Published: October 2012

AbstractLiterature data on the promotional role of under‐rib convection for polymer electrolyte fuel cells (PEFCs) fueled by hydrogen and methanol are structured and analyzed, thus providing a guide to improving fuel cell performance through the optimization of flow field interaction. Data are presented for both physical and electrochemical performance showing reactant mass transport, electrochemical reaction, water behavior, and power density enhanced by under‐rib convection. Performance improvement studies ranging from single cell to stack are presented for measuring the performance of real operating conditions and large‐scale setups. The flow field optimization techniques by under‐rib convection are derived from the collected data over a wide range of experiments and modeling studies with a variety of components including both single cell and stack arrangements. Numerical models for PEFCs are presented with an emphasis on mass transfer and electrochemical reaction inside the fuel cell. The models are primarily used here as a tool in the parametric analysis of significant design features and to permit the design of the experiment. Enhanced flow field design that utilizes the promotional role of under‐rib convection can contribute to commercializing PEFCs.
Proteomic analysis of formalin‐fixed paraffin‐embedded renal tissue samples by label‐free MS: Assessment of overall technical variability and the impact of block age
Authors: Craven Rachel A. , Cairns David A. , Zougman Alexandre , Harnden Patricia , Selby Peter J. , Banks Rosamonde E. 
Published: October 2012

PurposeProtein profiling of formalin‐fixed paraffin‐embedded (FFPE) tissues has enormous potential for the discovery and validation of disease biomarkers. The aim of this study was to systematically characterize the effect of length of time of storage of such tissue blocks in pathology archives on the quality of data produced using label‐free MS.Experimental designNormal kidney and clear cell renal cell carcinoma tissues routinely collected up to 10 years prior to analysis were profiled using LC‐MS/MS and the data analyzed using MaxQuant. Protein identities and quantification data were analyzed to examine differences between tissue blocks of different ages and assess the impact of technical and biological variability.ResultsAn average of over 2000 proteins was seen in each sample with good reproducibility in terms of proteins identified and quantification for normal kidney tissue, with no significant effect of block age. Greater biological variability was apparent in the renal cell carcinoma tissue, possibly reflecting disease heterogeneity, but again there was good correlation between technical replicates and no significant effect of block age.Conclusions and clinical relevanceThese results indicate that archival storage time does not have a detrimental effect on protein profiling of FFPE tissues, supporting the use of such tissues in biomarker discovery studies.
Coarctation of the aorta in the setting of tetralogy of Fallot: an uncommon cause of myocardial dysfunction
Authors: Iannucci Glen J. , Mahle William T. , Clabby Martha L. 
Published: October 2012

AbstractThe combination of both right and left heart obstruction has only rarely been described in the medical literature. We present three cases of coarctation of the aorta in patients with variants of tetralogy of Fallot and hypothesise that this condition may be more common than previously suspected and could represent a hidden cause of morbidity in patients with pulmonary atresia/ventricular septal defect.
Three-Dimensional Chemistry of Multiphase Nanomaterials by Energy-Filtered Transmission Electron Microscopy Tomography
Authors: Roiban Lucian , Sorbier Loïc , Pichon Christophe , Bayle-Guillemaud Pascale , Werckmann Jacques , Drillon Marc , Ersen Ovidiu 
Published: October 2012

AbstractA three-dimensional (3D) study of multiphase nanostructures by chemically selective electron tomography combining tomographic approach and energy-filtered imaging is reported. The implementation of this technique at the nanometer scale requires careful procedures for data acquisition, computing, and analysis. Based on the performances of modern transmission electron microscopy equipment and on developments in data processing, electron tomography in the energy-filtered imaging mode is shown to be a very appropriate analysis tool to provide 3D chemical maps at the nanoscale. Two examples highlight the usefulness of analytical electron tomography to investigate inhomogeneous 3D nanostructures, such as multiphase specimens or core-shell nanoparticles. The capability of discerning in a silica-alumina porous particle the two different components is illustrated. A quantitative analysis in the whole specimen and toward the pore surface is reported. This tool is shown to open new perspectives in catalysis by providing a way to characterize precisely 3D nanostructures from a chemical point of view.
Life's chirality from prebiotic environments
Authors: Gleiser Marcelo , Walker Sara Imari 
Published: October 2012

AbstractA key open question in the study of life is the origin of biomolecular homochirality: almost every life-form on Earth has exclusively levorotary amino acids and dextrorotary sugars. Will the same handedness be preferred if life is found elsewhere? We review some of the pertinent literature and discuss recent results suggesting that life's homochirality resulted from sequential chiral symmetry breaking triggered by environmental events. In one scenario, autocatalytic prebiotic reactions undergo stochastic fluctuations due to environmental disturbances, in a mechanism reminiscent of evolutionary punctuated equilibrium: short-lived destructive events may lead to long-term enantiomeric excess. In another, chiral-selective polymerization reaction rates influenced by environmental effects lead to substantial chiral excess even in the absence of autocatalysis. Applying these arguments to other potentially life-bearing platforms has implications to the search for extraterrestrial life: we predict that a statistically representative sampling of extraterrestrial stereochemistry will be racemic (chirally neutral) on average.