bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asymmetric Rhodium‐Catalyzed Hydrogenation Meets Gold‐Catalyzed Cyclization: Enantioselective Synthesis of 8‐Hydroxytetrahydroisoquinolines
Authors: Hashmi A. Stephen K. , Haufe Patrick , Schmid Christoph , Rivas Nass Andreas , Frey Wolfgang 
Published: May 2006

AbstractDifferent furyl‐substituted (Z)‐dehydroamino acid derivatives were hydrogenated with the rhodium/Mandyphos(OMe)‐system to give enantiomeric excesses between 80 and 98 %. The absolute configuration of the newly formed stereogenic center was determined by anomalous diffraction to be R. These chiral furyl alanines were transferred into 8‐hydroxytetrahydroisoquinolines by employing gold‐catalyzed arene synthesis as the key step. During the latter reaction sequence, also including either a propargylation or a reduction, a protection of the hydroxy group, and a subsequent propargylation, no racemization of the stereogenic center was observed. With very electron‐rich furans, instead of the 8‐hydroxytetrahydroquinolines as products, furans anellated to seven‐membered rings with exocyclic CC double bonds are formed under the same reaction conditions.
Spin‐Density Distribution in the Copper Site of Azurin
Authors: Fittipaldi Maria , Warmerdam Gertrud C. M , de Waal Ellen C. , Canters Gerard W. , Cavazzini Davide , Rossi Gian Luigi , Huber Martina , Groenen Edgar J. J. 
Published: May 2006

AbstractA 95 GHz pulsed deuterium ENDOR study has been performed on single crystals of azurin from Pseudomonas aeruginosa selectively deuterated at the Cβ position of the copper‐coordinating cysteine 112. Complete hyperfine tensors of the two deuterium atoms have been obtained, which reveal identical isotropic parts. Analysis of the hyperfine tensors provides insight into the spin‐density delocalization over the cysteine ligand. Approximately 45 % of the spin density in the paramagnetic site can be attributed to copper and 30 % to sulfur.
Ab Initio Molecular Dynamics Study of the Keto–Enol Tautomerism of Acetone in Solution
Authors: Cucinotta Clotilde S. , Ruini Alice , Catellani Alessandra , Stirling András 
Published: May 2006

AbstractWe have studied the keto–enol interconversion of acetone to understand the mechanism of tautomerism relevant to numerous organic and biochemical processes. Applying the ab initio metadynamics method, we simulated the keto–enol isomerism both in the gas phase and in the presence of water. For the gas‐phase intramolecular mechanism we show that no other hydrogen‐transfer reactions can compete with the simple keto–enol tautomerism. We obtain an intermolecular mechanism and remarkable participation of water when acetone is solvated by neutral water. The simulations reveal that C deprotonation is the kinetic bottleneck of the keto–enol transformation, in agreement with experimental observations. The most interesting finding is the formation of short H‐bonded chains of water molecules that provide the route for proton transfer from the carbon to the oxygen atom of acetone. The mechanistic picture that emerged from the present study involves proton migration and emphasizes the importance of active solvent participation in tautomeric interconversion.
Preparation, antimicrobial activity, and toxicity of 2‐amino‐4‐arylthiazole derivatives
Authors: Morales‐Bonilla Pedro , Pérez‐Cardeña Andrea , Quintero‐Mármol Esther , Arias‐Téllez José Luis , Mena‐Rejón Gonzalo J. 
Published: May 2006

AbstractSeven 2‐amino‐4‐aryl‐1,3‐thiazoles (1a–g) and their corresponding 2‐aminoacetyl (2a–g) and 2‐aminoacetyl‐5‐bromo (3a–g) derivatives were synthesized and tested in vitro against 11 reference strains, three Gram‐positive and four Gram‐negative bacteria, two yeasts, and two moulds. Toxicity of the compounds was also evaluated using the brine shrimp test. Compounds1a, 1b, 1e–g, and3bshowed moderate antimicrobial activity at different concentrations. The results indicated that acetylation of the amino group and bromination at position 5 of the thiazole moiety cause lost of activity. Compounds1a, 1e, and1fshowed toxicity to brine shrimp nauplii below 10 ppm. Most other compounds showed moderate toxicity, LD50above 100 ppm. Structures of all compounds were confirmed by NMR and MS data. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:254–260, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20182
Stereoselective synthesis and conformational analysis of aromatic C‐thionucleosides
Authors: Juárez Ernesto , García Adriana , Hommer Herbert , Salas Magali , Gordillo Barbara 
Published: May 2006

AbstractTetrahydrothiophene derivatives 2a–2d, which are useful intermediates in the synthesis of C‐thionucleosides, were obtained by a tandem strategy that involves the base‐catalyzed conjugate addition of ethyl 2‐mercaptoacetate to trans‐cinnamaldehyde followed by cyclization. The solvent and the nature of the amine used as Lewis base influence the stereo‐ selectivity of the reaction. The reduction of each isolated derivative 2a–2d was performed with LiAlH4 to afford C‐thionucleosides 3a–3d. The configuration and conformation of each diastereomer 2a–2d and 3a–3d was assigned by means of the analysis of vicinal proton–proton coupling constants. The X‐ray structure of 2d, 3a, and 3b confirmed the configuration assigned to each isomeric tetrahydrothiophenes. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:289–298, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20205
New approaches to the synthesis of diphosphine dioxides and hypophosphoric acid esters
Authors: Nycz Jacek E. , Musiol Robert 
Published: May 2006

AbstractAn anion >P–O− has been applied as an efficient synthetic precursor of four coordination compounds of the R2P(O)–(O)PR2 type, namely diphosphine dioxides (R = alkyl, aryl) as well as hypophosphoric acid esters (R = alkoxy, aryloxy), in a one‐pot reaction. Furthermore, there were elaborated some mechanistic aspects of the origin of the >P(O)–O–(O)P< anhydride, as a side‐product of the reaction between the anion >P–O− and >P(O)X (X = Cl, Br) electrophiles. Attention is focused on the synthesis of the >P(O)–(O)P< compounds. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:310–316, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20208
Regioselective N‐alkylation for the synthesis of novel aminotriazolophanes
Authors: Chande M. S. , Uchil Meera H. , Barve P. A. 
Published: May 2006

AbstractRegioselective synthesis of macrocycles, incorporating 3‐oxo‐4‐amino‐1,2,4‐triazole derivatives, has been achieved by reactions involving N‐alkylation, utilizing appropriate 1, ω ‐dihaloalkanes in the presence of metal hydroxide. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:329–336, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20211
A generalized CAD model for the full‐wave modelling of microstrip line and its regular and irregular discontinuities
Authors: Mayouf A. , Mayouf F. , Djahli F. 
Published: May 2006

AbstractIn this paper we present a new theoretical model for the modelling of the microstrip line as well as two types of discontinuities: regular (open end, step, bend and T‐ and cross‐junctions) and irregular (stub and bent‐stub). The two‐dimensional exact dyadic Green function of a grounded dielectric slab has been used with the Galerkin's technique. The subdivision of the discontinuity in a network of juxtaposed unit cells, characterized by their own longitudinal and transversal current distributions, allowed the treatment of a large class of irregular discontinuities in addition to the regular discontinuities. The obtained results have been commented and compared with those of different approaches and with experimental results where a good concordance has been observed. Copyright © 2006 John Wiley & Sons, Ltd.
Biodegradable Heparin‐Loaded Microspheres: Carrier Molecular Composition and Microsphere Structure
Authors: Luo Xianglin , Qiu Di , He Bin , Wang Lijian , Luo Juan 
Published: May 2006

AbstractSummary: Microspheres of amphiphilic triblock polymers PLLA‐PEG‐PLLA were investigated as carriers for heparin delivery. Two series of PLLA‐PEG‐PLLA triblock were synthesized and prepared into microspheres with heparin loaded. The microspheres were hollow and the surface morphology varied from smooth to porous. The pore size increased with increasing PEG content. The microsphere size distribution showed that higher PEG content increased the average microsphere size. The release rate of heparin was closely related to the surface morphology of the microspheres. DSC spectra showed that both cold crystalline temperature (Tc) and crystalline melting temperature (Tm) of heparin‐loaded microspheres were related to the copolymer composition and the Tc was lower than those of corresponding pure microspheres.
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The wet corrosion of molybdenum thin film – Part III: The effect of Ti and Nb
Authors: Tomachuk C. R. , Mitton D. B. , Springer J. , Monetta T. , Bellucci F. 
Published: May 2006

AbstractMagnetron sputtering has become the process of choice for the deposition of a wide range of industrially important coatings. Over the last decade, interest in molybdenum thin films prepared by magnetron sputtering has been increasing; however, little research has been done on molybdenum‐titanium and molybdenum‐niobium alloy thin films. During the current study, electrochemical impedance spectroscopy (EIS) was employed to investigate the effect on the corrosion resistance in basic chloride environments of adding titanium and niobium species to molybdenum thin films deposited by physical vapor deposition. The results indicate that the MoTi alloy thin films exhibit better protective properties than either the molybdenum‐niobium alloy or unalloyed molybdenum thin films.
Acetic acid – direct corrosive mediator in SCC of titanium/ethanol system
Authors: Jiang Y. , Wu Y. , Wang K. 
Published: May 2006

AbstractAlthough so many researchers paid attention on stress corrosion mechanism of titanium/ethanol system, few papers explained why ethanol, a very weak corrosive mediator, caused severe anodic solution. We found that the anodic polarization process of the titanium/ethanol system produced lots of acetic acid, which caused the pH value decreased rapidly. Maybe the acetic acid was the direct reason of stress corrosion susceptibility of titanium alloy in ethanol. And SSR tests proved that acetic acid could accelerate SCC of this system seriously. Also we found that in this system when the specimen was in the yield region, its corrosion potential fluctuated and PDS analysis showed this fluctuation was not a pure random process but a random fluctuation superposed with a definitive quasi‐sine wave. We thought that it was acetic acid made the passive film unstable and this unstable state was the main reason caused SCC in this system.
Neurotization with the brachialis muscle motor nerve
Authors: Palazzi Santos , Palazzi José‐Luis , Caceres Juan‐Pablo 
Published: May 2006

AbstractFunction of the wrist and hand in lower root avulsions is severely impaired. Based on anatomic and experimental studies which suggest that the motor nerve of the brachialis muscle could be used as a selective neurotizator in lower root avulsions with intact C5–C6 ± C7 roots (Klumpke paralysis), we considered its use depending on the target. We describe two techniques for the median nerve (in C8–T1 avulsions) and one for the radial nerve (in C7–C8–T1 avulsions). In all cases, we added the lateral cutaneous nerve of the forearm in the neurotization to improve sensibility in the hand. The present report presents the results of its use in our first five patients. © 2006 Wiley‐Liss, Inc. Microsurgery, 2006.
Saturated double‐angle method for rapid B1+ mapping
Authors: Cunningham Charles H. , Pauly John M. , Nayak Krishna S. 
Published: May 2006

AbstractFor in vivo magnetic resonance imaging at high field (≥3 T) it is essential to consider the homogeneity of the active B1 field (B1+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B1+ magnitude mapping. It combines the double angle method with a B1‐insensitive magnetization‐reset sequence such that the choice of repetition time (TR) is independent of T1 and with a multislice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds. Phantom experiments confirmed the accuracy of this technique even when TR ≪ T1, with the side effect being lowered SNR. The speed of this method enabled B1+ mapping in the chest and abdomen within a single breath‐hold. In human cardiac imaging, the method enabled whole‐heart coverage within a single 16‐s breath‐hold. Results from phantoms and healthy volunteers at 1.5 T and 3 T are presented. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Structural arrangement of crystalline/amorphous phases of polyethylene‐block‐polystyrene copolymer as induced by orientation techniques
Authors: Uehara Hiroki , Yoshida Tomoyuki , Kakiage Masaki , Yamanobe Takeshi , Komoto Tadashi 
Published: May 2006

AbstractA polyethylene‐block‐polystyrene copolymer film having a bicontinuous crystalline/amorphous phases was tensile‐drawn under various conditions for the structural arrangement of these phases. The prepared film could be drawn below the melting temperature of the polyethylene component, with the highest drawability obtained at 60°C. However, the initial bicontinuous structure was gradually destroyed with increasing strain because the drawing temperature was lower than the glass‐transition temperature of the polystyrene component. Correspondingly, a necking phenomenon was clearly recognizable when samples were drawn. In contrast, drawing near the melting temperature of the polyethylene component produced less orientation of both the crystalline and amorphous phases, resulting in homogeneous deformation with lower drawing stress. These results indicated that the modification of the lower ductility of the polystyrene component was key to the effective structural arrangement of both phases by tensile drawing. Here, a solvent‐swelling technique was applied to improve polystyrene deformability even below its glass‐transition temperature. Tensile drawing after such a treatment successfully induced the orientation of both the crystalline and amorphous phases while retaining their initial continuities. A change in the deformation type from necking to homogeneous deformation was also confirmed for the stress–strain behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1731–1737, 2006
Specific heat calculations of III‐N bulk materials
Authors: AlShaikhi A. , Srivastava G. P. 
Published: May 2006

AbstractWe have carried out calculations of the specific heat of the cubic and hexagonal phases of BN, AlN, GaN and InN by employing lattice dynamical results from an adiabatic bond charge model. While each phonon polarization branch contributes equally at high temperatures, it is found that the transverse acoustic branches contribute more at low temperatures. These results, which compare well with available experimental measurements, are used to test the applicability of the routinely employed Debye model based on an isotropic continuum dispersion scheme. The specific heat of the hexagonal phase is predicted to be higher than of the cubic phase at quite low temperatures. A trend in the variation of the specific heat across the sequence BN ‐ AlN ‐ GaN ‐ InN has been established in terms of their molar masses. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of carrier gas on GaN epilayer characteristics
Authors: Cho Y. S. , Hardtdegen H. , Kaluza N. , Thillosen N. , Steins R. , Sofer Z. , Lüth H. 
Published: May 2006

AbstractMetalorganic vapor phase epitaxy (MOVPE) of GaN was performed using hydrogen (H2), nitrogen (N2) and H2/N2mixtures thereof as the carrier gas in the high temperature buffer growth range. The effect of carrier gas on the structural and morphological characteristics of the epilayers was systematically studied using interference and atomic force microscopy (AFM), photoluminescence (PL) measurements at 2 K, Raman spectroscopy and X‐ray diffraction (XRD). The higher the N2 content in the carrier gas, the more pinholes are observed, the lower compressive strain and the higher dislocation density in the layers. A carrier gas composition range was defined at which GaN layers with acceptable structural and morphological characteristics are achieved. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Piezoelectric properties of thin AlN layers for MEMS application determined by piezoresponse force microscopy
Authors: Tonisch K. , Cimalla V. , Foerster Ch. , Dontsov D. , Ambacher O. 
Published: May 2006

AbstractPiezoelectric properties of aluminium nitride thin films were measured using both, the piezoresponse force microscopy and an interferometric technique. Wurtzite AlN thin films were prepared on Si (111) substrates by reactive DC‐sputtering and by metalorganic chemical vapor deposition. Direct measurements of the inverse piezoelectric effect in the picometer range showed that the acceptable tolerance in the crystal orientation is much larger for MEMS applications than expected previously. The value of the piezoelectric coefficient d33for the prepared AlN thin films was determined to be 5.36 ± 0.25 pm/V for highly textured as well as for polycrystalline thin films with a (002) preferential orientation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallization of free standing bulk GaN by HVPE
Authors: Łucznik B. , Pastuszka B. , Grzegory I. , Boćkowski M. , Kamler G. , Domagała J. , Nowak G. , Prystawko P. , Krukowski S. , Porowski S. 
Published: May 2006

AbstractGallium nitride was crystallized on 2 inch MOVPE GaN/sapphire substrates by Hydride Vapor Phase Epitaxy. A stable growth has been achieved in long duration (>10 h) processes at growth rates bigger than 100 μm/h. As a result, entirely transparent and colorless bulk crystals with thickness exceeding 2 mm were obtained. The cracks in the thick HVPE GaN layers deposited on the MOVPE GaN/sapphire substrates can appear especially during cooling of the system after crystallization. It is shown that the formation of cracks at cooling is dependent on the gradients in the layer thickness The relaxation of strains in the resulting crystal coupled to the substrate leads to the self separation of GaN from sapphire. (At present 30 x 30 x 2 mm free standing bulk GaN crystals are obtained). The GaN crystals are characterized by defect selective etching (DSE) and X‐ray diffraction. The density of threading dislocations (measured by DSE of (0001) surface) decreases with the thickness of the HVPE layer and becomes lower than 107 cm–2 in the layers thicker than app. 1 mm. The X‐ray rocking curves for (0002) reflection (slit 0.5 x 0.1 mm) are in the range of 80–95 arcsec. However, larger scans reveal bending of crystallographic {0001} planes. The behavior of these “deformed” free standing crystals used as substrates for HVPE re‐growth is also analyzed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polishing and characterization of thick AlN layers grown on SiC substrates by stress control hydride vapor phase epitaxy
Authors: Mank H. , Amstatt B. , Turover D. , Bellet‐Amalric E. , Daudin B. , Ivantsov V. , Dmitriev V. , Maslennikov V. 
Published: May 2006

AbstractIn this paper, we report new results on polishing and characterization of thick aluminium nitride (AlN) layers grown on 2‐ and 3‐inch electrically conducting 4H‐SiC on‐axis substrate. As thick as 10‐22 µm AlN layers were deposited on Si‐face by stress control hydride vapor phase epitaxy. Rough as‐grown layers were polished to provide epi‐ready surface for device epitaxy. Surface morphology and surface defects of AlN were studied by atomic force microscopy, optical microscopy and scanning electron microscopy. The root mean square surface roughness was drastically decreased from 470 Å for as‐grown surface to less than 3 Å and the peak to valley value was decreased from 345 nm to less than 3 nm. As‐grown and polished epilayer thickness homogeneity, verified by Fourier transform infrared (FTIR) reflectivity, is better than 5%. Structural properties were investigated by X‐ray diffraction (XRD). XRD rocking curves were measured in ω‐scanning mode for the (00.2) and (10.2) reflections. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Robust Regression using Probability Plots for Estimating the Weibull Shape Parameter
Authors: Zhang L.‐F. , Xie M. , Tang L.‐C. 
Published: May 2006

AbstractThe Weibull shape parameter is important in reliability estimation as it characterizes the ageing property of the system. Hence, this parameter has to be estimated accurately. This paper presents a study of the efficiency of using robust regression methods over the ordinary least‐squares regression method based on a Weibull probability plot. The emphasis is on the estimation of the shape parameter of the two‐parameter Weibull distribution. Both the case of small data sets with outliers and the case of data sets with multiple‐censoring are considered. Maximum‐likelihood estimation is also compared with linear regression methods. Simulation results show that robust regression is an effective method in reducing bias and it performs well in most cases. Copyright © 2006 John Wiley & Sons, Ltd.
Development of a Rapid Prototyping System using Response Surface Methodology
Authors: Palmer Kurt , Asiabanpour Bahram , Khoshnevis Behrokh 
Published: May 2006

AbstractThis case study presents an investigation of the relationships between eight process operating variables (factors) and five part performance measures (responses) in a rapid prototyping system. The use of fractional factorial, single‐factor foldover, and central composite designs is demonstrated. Polynomial regression models are constructed for each response, followed by a desirability function model. Canonical and ridge analyses are used to identify a group of factor settings that simultaneously produce improved performance for all responses. Copyright © 2006 John Wiley & Sons, Ltd.
A Comparative Study of Joint Monitoring Schemes for APC Processes
Authors: Jiang Wei , Shu Lianjie , Tsung Fugee 
Published: May 2006

AbstractTo monitor processes under automatic process control (APC), several joint monitoring schemes have recently been proposed, such as the U statistics, $U_{0}$ and $U_{\infty}$, that originate from the uniformly most powerful test. It is known that the $U_{0}$ chart is sensitive to large shift detection whereas the $U_{\infty}$ chart is sensitive to small shift detection. To take advantage of both charts, this paper examines a combined use of the two U charts. A comparative study indicates that the combined procedure improves over a single U chart and performs better than other joint monitoring schemes, including Hotelling's $T^2$ chart for APC processes. Copyright © 2006 John Wiley & Sons, Ltd.