bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reversal of Regioselectivity and Enhancement of Rates of Nitrile Oxide Cycloadditions through Transient Attachment of Dipolarophiles to Cyclodextrins
Authors: Barr Lorna , Lincoln Stephen F. , Easton Christopher J. 
Published: September 2006

AbstractThe reactions of nitrile oxides with monosubstituted dipolarophiles, such as propiolamide, typically afford proportionally 80 % or more of the 3,5‐disubstituted cycloadducts. By contrast, the reactions of 6A‐deoxy‐6A‐propynamido‐β‐cyclodextrin with 4‐tert‐butylbenzonitrile oxide and 4‐phenylbenzonitrile oxide afford >90 % and approximately 85 % of the corresponding 3,4‐disubstituted isoxazoles, respectively. As well as reversing the regioselectivity, the cyclodextrin increases the rates of these cycloadditions. The extent of the acceleration is up to more than three orders of magnitude for the production of the cycloadduct preferred by the cyclodextrin, but even the rate of reaction to give the less favored regioisomer is increased. With 6A‐deoxy‐6A‐propynamido‐β‐cyclodextrin, the cycloadducts are not easily separated from the cyclodextrin, as the amide bond is not readily cleaved. In comparison, the regioselectivity of the cycloadditions of 4‐tert‐butylbenzonitrile oxide with acrylic acid, methacrylic acid, and crotonic acid is also altered by formation of the corresponding cyclodextrin esters, by factors of 500, >10, and >100, respectively. The rates of cycloaddition are also increased by up to 475 times, and in these cases the products of cycloaddition are readily released from the cyclodextrin through ester hydrolysis. Incorporating these processes into a reaction cycle, acylation of β‐cyclodextrin with p‐nitrophenyl acrylate and subsequent treatment first with 4‐tert‐butylbenzonitrile oxide and then with base, the latter to catalyze ester hydrolysis and regenerate the β‐cyclodextrin, affords proportionally fivefold more of the 3,4‐disubstituted isoxazoline than is produced directly from acrylic acid.
The Solution Structure of Stilbenoid Dendrimers: A Small‐Angle Scattering Study
Authors: Rosenfeldt Sabine , Karpuk Elena , Lehmann Matthias , Meier Herbert , Lindner Peter , Harnau Ludger , Ballauff Matthias 
Published: September 2006

AbstractThe spatial structure of a stilbenoid dendrimer is investigated by small‐angle X‐ray scattering (SAXS) and small‐angle neutron scattering (SANS) in dilute solution. All measurements are performed in toluene. The dendrimer consists of a stilbenoid scaffold with appended hexyloxy chains. SAXS is mainly sensitive to the dendrimer scaffold whereas SANS intensity, measured in fully deuterated toluene, derives from the solute molecules. The resulting SAXS and SANS intensities are analyzed by comparison with various models. It is found that the model of a circular disk gives the best description of the data. SAXS data demonstrate that the stilbenoid scaffold is flat as expected for benzene rings conjugated through vinylene units. Thus, it can be described by a circular disk with a radius of 1.6 nm and a thickness of 0.7 nm. SANS, on the other hand, shows that the hexyloxy chains are not confined in the plane defined by the core. This is derived from modeling the SANS data with a much thicker circular disk (radius: 2.4 nm, thickness: 1.8 nm). The structure factor S(q), describing the interaction of the dendrimers at higher concentrations, is modeled quantitatively with the “polymer reference interaction site model” (PRISM) integral equation formalism for hard plates such as particles. Here the structural data obtained from the analysis of the SANS data are used so that no new adjustable parameter is necessary for this description.
Efficient Delaunay‐based localized routing for wireless sensor networks
Authors: Wang Yu , Li Xiang‐Yang 
Published: September 2006

AbstractConsider a wireless sensor network consisting ofnwireless sensors randomly distributed in a two‐dimensional plane. In this paper, we show thatwith high probabilitywe can locally find a path for any pair of sensors such that the length of the path is no more than a constant factor of the minimum. By assuming each sensor knows its position, our new routing method decides where to forward the message purely based on the position of current node, its neighbours, and the positions of the source and the target. Our method is based on a novel structure called localized Delaunay triangulation and a geometric routing method that guarantees that the distance travelled by the packets is no more than a small constant factor of the minimum when the Delaunay triangulation of sensor nodes are known. Our experiments show that the delivery rates of existing localized routing protocols are increased when localized Delaunay triangulation is used instead of several previously proposed topologies, and our localized routing protocol based on Delaunay triangulation works well in practice. We also conducted extensive simulations of another localized routing protocol,face routing. The path found by this protocol is also reasonably good compared with previous one although it cannot guarantee a constant approximation on the length of the path travelled theoretically. Copyright © 2006 John Wiley & Sons, Ltd.
Energy optimization for chain‐based data gathering in wireless sensor networks
Authors: Yen Li‐Hsing , Cai Ming‐Zhou , Cheng Yang‐Min , Yang Ping‐Yuan 
Published: September 2006

AbstractThis paper aims to minimize energy expense for chain‐based data gathering schemes, which is essential to prolong the operation lifetime of wireless sensor networks. Energy expense in chain‐based data gathering schemes consists of two parts. One corresponds to inter‐sensor communications and depends on chain structure. The other corresponds to leader‐BS (base station) communications and depends on leader scheduling policy. To optimize inter‐sensor communications, the notion of virtual chain is utilized, where an edge may correspond to a multi‐hop data propagation path to conserve power. In contrast, an edge in previous work can only be a costly direct communication link. To optimize leader‐BS communications, a leader scheduling rule is presented, where the node with the maximum residual power will be selected to be the leader of the chain. In contrast, nodes in previous work act as leaders by turns, resulting in non‐uniform energy consumption among sensors. Simulation results show that our strategies are nearly optimal in terms of power conservation. Copyright © 2006 John Wiley & Sons, Ltd.
Integration of mobility and intrusion detection for wirelessad hocnetworks
Authors: Sun Bo , Wu Kui , Xiao Yang , Wang Ruhai 
Published: September 2006

AbstractOne of the main challenges in building intrusion detection systems (IDSs) for mobilead hocnetworks (MANETs) is to integrate mobility impacts and to adjust the behaviour of IDSs correspondingly. In this paper, we first introduce two different approaches, a Markov chain‐based approach and a Hotelling'sT2test based approach, to construct local IDSs for MANETs. We then demonstrate that nodes' moving speed, a commonly used parameter in tuning IDS performances, is not an effective metric to tune IDS performances under different mobility models. To solve this problem, we further propose anadaptivescheme, in which suitable normal profiles and corresponding proper thresholds can be selectedadaptivelyby each local IDS through periodically measuring its locallink change rate, a proposed unified performance metric. We study the proposed adaptive mechanism at different mobility levels, using different mobility models such as random waypoint model, random drunken model, and obstacle mobility model. Simulation results show that our proposed adaptive scheme is less dependent on the underlying mobility models and can further reduce false positive ratio. Copyright © 2006 John Wiley & Sons, Ltd.
Alk‐2‐ynyl Trimethylsilyl Chalcogenoethers by Nucleophilic Substitution of Propargyl Bromides
Authors: Taher Deeb , Wallbank Andrew I. , Turner Elizabeth A. , Cuthbert Heather L. , Corrigan John F. 
Published: September 2006

AbstractLithium (trimethylsilyl)chalcogenolates have been generated and used to prepare a series of alk‐2‐ynyl trimethylsilyl chalcogenoethers from the corresponding propargyl bromides in good yield. The thermal decomposition of the telluroethers has also been studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Stereoselective Synthesis of β‐Amino Ketones via Direct Mannich‐Type Reactions, Catalyzed with ZrOCl2·8H2O under Solvent‐Free Conditions
Authors: Eftekhari‐Sis Bagher , Abdollahifar Amir , Hashemi Mohammed M. , Zirak Maryam 
Published: September 2006

AbstractAt room temperature, zirconium oxychloride (ZrOCl2·8H2O) efficiently catalyzes the direct Mannich‐type reaction of a variety of in situ generated aldimines using aldehydes and anilines with ketones in a three‐component reaction under solvent‐free conditions. The reaction proceeds rapidly and affords the corresponding β‐amino ketones in good to high yields with good to excellent stereoselectivities. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Synthesis of Purines Bearing Functionalized C‐Substituents by the Conjugate Addition of Nucleophiles to 6‐Vinylpurines and 6‐Ethynylpurines
Authors: Kuchař Martin , Pohl Radek , Votruba Ivan , Hocek Michal 
Published: September 2006

AbstractPurines bearing diverse β‐substituted ethyl or vinyl groups in position 6 were prepared by the conjugate addition of N‐, O‐ and S‐nucleophiles to 6‐vinylpurines or 6‐ethynylpurines. The scope of this methodology was systematically studied. The addition of amines, alcoholates and thiolates to 6‐vinylpurines gave the corresponsing 6‐(2‐aminoethyl)‐, 6‐(2‐alkoxyethyl)‐ and 6‐[2‐(alkylsulfanyl)ethyl]purines. The addition of amines to 6‐ethynylpurines gave 6‐(2‐aminovinyl)purines, while the addition of alcoholates and thiolates gave 6‐(2‐dialkoxyethyl)‐ and 6‐[2‐bis(alkylsulfanyl)ethyl]purines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Short and Efficient Diastereoselective Synthesis of Enantiopure 1‐Substituted 1H‐2‐Benzopyrans
Authors: Pedrosa Rafael , Sayalero Sonia , Vicente Martina 
Published: September 2006

AbstractThe reaction of homophthaldehyde with (–)‐8‐(benzylamino)menthol is regio‐ and diastereo‐selective, leading to the chiral perhydro‐1,3‐benzoxazine 3 as a single diastereoisomer. The addition of different organometallics to 3 yielded alcohols 4 in excellent yields. Hydrolysis of carbinols, with 2 % HCl in methanol or ethanol, allowed for the synthesis of 1,3‐disubstituted isochromanes, but hydrolysis in toluene led to enantiopure 1‐substituted isochromenes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Restoring identity through outgroup helping: beliefs about international aid in response to the December 2004 tsunami
Authors: van Leeuwen Esther 
Published: September 2006

AbstractIn this paper, the December 2004 tsunami tragedy was used as a background to investigate beliefs about intergroup helping. The general aim of the research was to test the proposal that helping can be used to reaffirm a threatened social identity. Two experiments conducted with Dutch participants (N = 78 and N = 73) tested the hypothesis that a threatened Dutch national identity would result in stronger preferences for help to the victims of the tsunami, but only in a domain that is positively and distinctly related to that national identity (i.e. water management). Results from both studies confirmed this hypothesis. Study 2 also showed a reversal of this effect in a domain negatively related to that identity. Moreover, perceived identity threat in Study 2 reduced over time in the high threat condition but not in the low threat condition, and this reduction was positively associated with the endorsement of water management help. Also, as predicted, in both studies a threatened national identity resulted in stronger beliefs that Dutch relief organisations should stay in control over their aid. Copyright © 2006 John Wiley & Sons, Ltd.
Quantitative‐competitive polymerase chain reaction coupled with slab gel and capillary electrophoresis for the detection of roundup ready soybean and maize
Authors: Dinelli Giovanni , Bonetti Alessandra , Marotti Ilaria , Minelli Maurizio , Navarrete‐Casas Miguel , Segura‐Carretero Antonio , Fernández‐Gutiérrez Alberto 
Published: September 2006

AbstractThe aim of the present study was to develop a quantitative‐competitive PCR (QC‐PCR) method to detect DNA from transgenic herbicide‐resistant (roundup ready, RR) soybean and maize. Since no QC‐PCR system for the quantification of RR maize had been published at the time of writing, a specific competitor DNA for transgenic event was developed. For the QC‐PCR of RR‐soybean, a commercially available competitor was employed. These internal standards were calibrated by coamplifying with mixtures containing RR‐soybean and maize DNAs. The calibrated QC‐PCR systems were applied to certified RR‐soybean and maize flour mixtures in order to demonstrate their suitability not only for the quantification of the glyphosate resistance traits in DNA matrices, but also in practically relevant samples. In addition, a special focus of the present work was to compare the detection of QC‐PCR products by slab gel and CGE with UV detection. CGE permitted the precise detection of transgenic events also below the equivalence points; while in slab gel electrophoresis, due to the low sensitivity the quantification of genetically modified DNA was allowed only at the equivalence point.
Sensitive determination of carbohydrates labelled with p‐nitroaniline by capillary electrophoresis with photometric detection using a 406 nm light‐emitting diode
Authors: Momenbeik Fariborz , Johns Cameron , Breadmore Michael C. , Hilder Emily F. , Macka Miroslav , Haddad Paul R. 
Published: September 2006

Abstractp‐Nitroaniline was explored as a derivatising reagent for UV absorbance detection of carbohydrates after separation by CE. This derivatising agent has three advantages: first, it has excellent water solubility; second, it has high molar absorptivity; and third, it is possible to obtain sensitive detection using a UV or blue light‐emitting diode (LED) as the light source. The labelling reaction took less than 30 min to complete with high reaction yield. The separation process was modelled and optimised using an artificial neural network. Nine carbohydrates were separated by a CE system within 16 min using a 0.17 M boric acid buffer at pH 9.7. On‐column LED detection at 406 nm allowed the detection of carbohydrates with good detection limits (<1.1 µM or 8.8 fmol) and reproducible quantification in the concentration range of 2.6–200 µM. This method was applied successfully to the determination of component carbohydrates in some food samples.
Adaptive contrast enhancement of two‐dimensional electrophoretic protein gel images facilitates visualization, orientation and alignment
Authors: Van Belle Werner , Sjøholt Gry , Ånensen Nina , Høgda Kjell‐Arild , Gjertsen Bjørn Tore 
Published: September 2006

Abstract2‐DE is a powerful technique to discriminate post‐translationally modified protein isoforms. However, all steps of 2‐DE preparation and gel‐staining may introduce unwanted artefacts, including inconsistent variation of background intensity over the entire 2‐DE gel image. Background intensity variations limit the accuracy of gel orientation, overlay alignment and spot detection methods. We present a compact and efficient denoising algorithm that adaptively enhances the image contrast and then, through thresholding and median filtering, removes the gray‐scale range covering the background. Applicability of the algorithm is demonstrated on immunoblots, isotope‐labeled gels, and protein‐stained gels. Validation is performed in contexts of (i) automatic gel orientation based on Hough transformation, (ii) overlay alignment based on cross correlation and (iii) spot detection. In gel stains with low background variability, e.g. Sypro Ruby, denoising will lower the spot detection sensitivity. In gel regions with high background levels denoising enhances spot detection. We propose that the denoising algorithm prepares images with high background for further automatic analysis, without requiring manual input on a gel‐to‐gel basis.
Agarose isoelectric focusing can improve resolution of membrane proteins in the two‐dimensional electrophoresis of bacterial proteins
Authors: Altenhofer Pia , Schierhorn Angelika , Fricke Beate 
Published: September 2006

Abstract2‐D separation of bacterial membrane proteins is still difficult despite using high‐resolution IPG‐IEF/SDS‐PAGE. We were searching for alternative methods to avoid typical problems such as precipitation, low solubility, and aggregation of membrane proteins in the 1‐D separation with IPG‐IEF. Blue native electrophoresis (BNE) and agarose IEF (A‐IEF) were tested for their separation capacity and their capability of replacing IPG‐IEF in the first dimension. SDS‐PAGE was chosen for the second dimension on account of its outstanding resolution. We could confirm that only A‐IEF was a useful replacement for the IPG‐IEF in the first dimension resulting in 2‐D protein distributions with additional membrane protein spots not being found after IPG‐IEF/SDS‐PAGE. A second interesting result was that the agarose IEF mediates the possibility of separation of membrane proteins in a partially native state in the first dimension. This native A‐IEF resulted in drastically changed spot patterns with an acidic shift of nearly all spots and divergent distribution of proteins compared to non‐native A‐IEF and IPG‐IEF. We found out that native and non‐native A‐IEF are powerful tools to supplement IPG‐IEF/SDS‐PAGE.
Capillary electrophoresis of liposomes functionalized for protein binding
Authors: Bilek Gerhard , Kremser Leopold , Blaas Dieter , Kenndler Ernst 
Published: September 2006

AbstractCE enabled assessing the attachment of hexa‐histidine‐tagged proteins to functionalized phospholipid liposomes. The liposomes were made of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine, phosphatidyl‐ethanolamine, cholesterol and distearoyl‐glycero‐3‐phosphoethanolamine‐N‐methoxy(polyethylene glycol) in a molar ratio of 29:26:40:5. The unilamellar vesicles, which had an average diameter of 170 nm, were labelled by inclusion of FITC‐dextran for fluorescence detection. CE was carried out in poly(vinyl alcohol) (PVA)‐coated capillaries at 25°C with a BGE consisting of Tris‐HCl (50 mM, pH 8.0). For conjugation of the liposomes with the proteins (soluble synthetic receptor fragments with molecular mass of 60 and 70 kDa, respectively), Ni2+ was implanted into the vesicle surface by an anchor lipid containing a nitrilotriacetate acid (NTA) group as complexation agent for the metal ions. The difference in surface charge enabled the separation of the different species of interest by CE: plain vesicles, vesicles functionalised with Ni‐NTA, vesicle–protein complexes and the species formed upon removal of the Ni‐ions by complexation with EDTA. Loss of the Ni‐ions resulted in the release of the proteins and the reappearance of the plain Ni‐free NTA‐liposome species in the electropherograms.
An integrated micropump and electrospray emitter system based on porous silica monoliths
Authors: Wang Ping , Chen Zilin , Chang Hsueh‐Chia 
Published: September 2006

AbstractThe work presents the design of an integrated system consisting of a high‐pressure electroosmotic (EO) micropump and a microporous monolithic emitter, which together generate a stable and robust electrospray. Both the micropump and electrospray emitter are fabricated using a sol–gel process. Upon application of an electric potential of sufficient amplitude (>2 kV), the pump delivers fluids with an electroosmotically induced high pressure (>1 atm). The same potential is also harnessed to electrostatically generate a stable electrospray at the porous emitter. Electrokinetic coupling between pump and spray produces spray features different from sprays pressurized by independent mechanical pumps. Four typical spray modes, each with different drop sizes and charge‐to‐mass ratios, are observed and have been characterized. Since the monolith is silica‐based, this integrated device can be used for a variety of fluids, especially organic solvents, without the swelling and shrinking problems that are commonly encountered for polymer monoliths. The maximum pressure generated by a 100 µm id monolithic pump is ˜3 atm at an applied voltage of 5 kV. The flow rate can be adjusted in the range of 100 nL/min to 1 µL/min by changing the voltage. For a given applied voltage across the pump and emitter system, it is seen that there exists one unique flow rate for which flow balance is achieved between the delivery of liquid to the emitter by the pump and the liquid ejection from the emitter. Under such a condition, a stable Taylor cone is obtained. The principles that lead to these results are also discussed.
Electrochromatographic behavior of silica monolithic capillaries of different skeleton sizes synthesized with a simplified and shortened sol–gel procedure
Authors: Puy Guillaume , Demesmay Claire , Rocca Jean‐Louis , Iapichella Julien , Galarneau Anne , Brunel Daniel 
Published: September 2006

AbstractSilica monolithic capillaries (SMCs) were synthesized by a sol–gel process. First, a simplification of the synthesis was proposed by replacing the calcination and the drying steps which can have tremendous effects on chromatographic and physical properties, by a single water or methanol 2 h washing step. The efficiency of such a washing step was demonstrated and the comparison of the chromatographic and electrochromatographic properties between calcined and washed SMCs has shown that such a modification did not impair retention, efficiency, and stability of the monolith. This simplified procedure was carried out to synthesize SMCs with two different skeleton sizes. These capillaries were evaluated in electrochromatography and present high efficiencies (H = 5 µm) at least equal to the best ones reported in the literature. Furthermore, the influence of the skeleton size on the EOF of the second kind (EOF‐2) was investigated with unmodified SMCs used under various experimental conditions including electrical field strength and buffer concentration. The ionic strength of the mobile phase and the applied electrical field that enable this EOF‐2 were related to the size of the skeleton which was tuned by the synthesis conditions.
A self‐contained polymeric 2‐DE chip system for rapid and easy analysis
Authors: Usui Keisuke , Hiratsuka Atsunori , Shiseki Kisho , Maruo Yuji , Matsushima Toshiyuki , Takahashi Katsuyoshi , Unuma Yutaka , Sakairi Koji , Namatame Ichiji , Ogawa Yasuhiro , Yokoyama Kenji 
Published: September 2006

AbstractWe developed a polymeric 2‐DE chip system. The chip consisted of an IEF region, an SDS‐PAGE region, a valveless connection port, and a sample introduction port. A “junction structure” as a valveless connection port, which allowed separating and connecting the first‐ and second‐dimensional gels, was fabricated between their regions. A “solution inlet” as a sample introduction port was fabricated to perform the liquid and sample introductions without solution leakage. Simultaneous sample monitoring was performed using the on‐chip detection system. The performances of the system were demonstrated using commercially available proteins as a standard specimen and tissue‐extracted proteins as the real samples. All procedures were employed without any movement of relocation part. This new 2‐D separation system realized improved labor‐intensive operations and a reduced experimental time.