bluuebunny/crossref_metadata_2025_split huggingface dataset:
Convenient Synthesis of a [1‐14C]Diazirinylbenzoic Acid as a Photoaffinity Label for Binding Studies of V‐ATPase Inhibitors
Authors: Bender Tobias , Huss Markus , Wieczorek Helmut , Grond Stephanie , von Zezschwitz Paultheo 
Published: June 2007

AbstractDiazirine‐tagged systems are considered reliable compounds for photoaffinity labeling (PAL) in biochemical studies as they enable investigation and understanding of biological mechanisms through covalent bonding to the target and subsequent detection. 14C‐labeled 4‐(3‐trifluoromethyl‐3H‐diazirin‐3‐yl)benzoic acid (11) was prepared by a lithium‐bromide exchange on the bis‐silylated 4‐bromophenyldiaziridine 19 with subsequent transformations with electrophiles as key steps of the synthesis. Using 14CO2, which was generated from rather inexpensive Ba14CO3, the desired diaziridinylbenzoic acid 21 was obtained in 78 % yield based on the employed radioactive material. Oxidation under mild conditions then yielded diazirine 11 in a 100 mg scale. This versatile photoaffinity label was selectively attached to the tetrahydropyrane ring of bafilomycin A1 (2) and concanamycin A‐derived 3, which both specifically inhibit the V‐ATPases. Inhibition assays were performed and revealed that the inhibitory capacities of the labeled derivatives are suitable for PAL studies on this important group of enzymes to elucidate the as yet unknown binding sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis and Use of New Substituted 1,3,5‐Hexatrienes in Studying Thermally Induced 6π‐Electrocyclizations
Authors: Sünnemann Hans Wolf , Banwell Martin G. , de Meijere Armin 
Published: June 2007

AbstractAn acyclic, two heterocyclic, and two bicyclic alkenylstannanes, 3, 4a, 4b, 8 and 11, respectively, were synthesized in yields ranging from 43 to 97 %, and each was subjected to a sequence of Stille and Heck couplings with 2‐bromocyclohexenyl triflate (13) and alkyl (tert‐butyl and methyl) acrylate to furnish seven new 1,3,5‐hexatrienes 19, 20, 21, 22‐tBu, 22‐Me, 23 and 43, respectively, in 58–84 % yields. For the alkenylstannanes 4a,b, 8 and 11, customized combinations of catalysts had to be used. The Stille–Heck sequence involving 13, 3 and tert‐butyl acrylate could be performed in a one‐pot mode and proceeded in 75 % yield. The hexatrienes were heated in decalin solutions so as to effect 6π‐electrocyclization. Temperatures and reaction times were optimized individually. The hexatrienes 29, 31 and 36 gave the bi‐ and tricyclic cyclohexadienes 28, 30 and 34, incorporating allylic alcohol and allyl ether termini, by 6π‐electrocyclization and subsequent [1,5]‐hydrogen shift, as single products in good yields (85–93 %). In contrast, the hexatrienes 19, 20, 21 and 39 furnished mixtures of the initial electrocyclization products 26, 32, 37 and 40 as well as the products of a subsequent [1,5]‐hydrogen shift 27, 33, 38 and 41, respectively. The tricyclic hexatrienes 22‐tBu, 22‐Me and 23 bearing alkyl (tert‐butyl, methyl) acrylate termini also selectively gave the tetracyclic dienes 48‐tBu, 48‐Me and 50 in 71–77 % yields by electrocyclizations and subsequent hydrogen shifts.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Bromination and Iodination of 6H,12H‐5,11‐Methanodibenzo[b,f][1,5]diazocine: A Convenient Entry to Unsymmetrical Analogs of Tröger's Base
Authors: Didier Delphine , Sergeyev Sergey 
Published: June 2007

Abstract6H,12H‐5,11‐Methanodibenzo[b,f][1,5]diazocine can easily be prepared from aniline and paraformaldehyde. Its reactions with either N‐bromosuccinimide (NBS) or with iodine monochloride (ICl) in the presence of a suitable activator smoothly afford 2‐bromo‐ and 2‐iodo‐ derivatives, respectively. The combination of these halogenation methods provides access to the 8‐bromo‐2‐iodo derivative, which is an interesting and otherwise inaccessible intermediate for the synthesis of unsymmetrical analogs of Tröger's base. The reported halogenations represent the first examples of electrophilic substitution in 6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Hexaalkylguanidinium Trifluoromethanesulfonates – A General Synthesis from Tetraalkylureas and Triflic Anhydride, and Properties as Ionic Liquids
Authors: Kunkel Helene , Maas Gerhard 
Published: June 2007

AbstractMore than thirty hexaalkylguanidinium trifluoromethanesulfonates 12 were prepared from N,N‐diethyl‐N′,N′‐dimethylurea, N,N‐dibutyl‐N′,N′‐diethylurea, or tetrabutylurea, triflic anhydride, and a dialkylamine or cyclic sec‐amine in two steps. The combination of the urea and triflic anhydride first yields a bis(tetraalkylamidinio)ether bis(triflate) 10, which is then converted into a salt 12 by reaction with the amine component. The reaction sequence can also be carried out as a one‐pot procedure. Eighteen of the prepared guanidinium triflates 12 constitute room‐temperature ionic liquids, which were characterized for their melting point, glass transition temperature, viscosity, and refractive index. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Selective Synthesis of Unnatural α‐, β‐ and γ‐Amino Esters
Authors: Nugent Thomas C. , Ghosh Abhijit K. 
Published: June 2007

AbstractReductive amination of keto esters 1 with α‐methylbenzylamine (α‐MBA) in the presence of hydrogen and Raney‐Ni allows direct access to diastereomeric amino esters 2 in good to high de (72–94 %). For the α‐keto ester 1d and the β‐keto esters 1a, 1b and 1c the reaction is optimally performed in the presence of AcOH, while the γ‐keto ester 1h requires Ti(OiPr)4. The reductive amination product of 1d is an advanced homophenylalanine building block for Angiotensin Converting Enzyme (ACE) inhibitor drugs. The reductive amination product of 1h is converted in two additional steps to a protected chiral 2‐methylpyrrolidine 4h, which is an advanced amine intermediate for pharmaceutical drugs, e.g. ABT‐239. The strategy presented here obviates the need for preforming enamine or imine intermediates for amino ester synthesis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Cover Picture: Procedures for and Possible Mechanisms of Pd‐Catalyzed Allylations of Primary and Secondary Amines with Allylic Alcohols (Eur. J. Org. Chem. 19/2007)
Authors: Muzart Jacques 
Published: June 2007

AbstractThe cover picture shows the palladium‐catalyzed intermolecular reaction of allylic alcohols with amines. The advantages of this process are the easily available substrates, the high atom economy, and the formation of only water as the by‐product. Details of this reaction are presented in the Microreview by J. Muzart on p. 3077 f. The slides that form the frame of the scheme, with the French flag in the background, show the Champagne area and highlight the well‐known sparkling product of the region and the Reims cathedral. Emilie Thiery and Dr. Jean Le Bras are acknowledged for preparing the artwork for the cover picture.
Micellar Effects on the Reduction of 4‐Nitroimidazole Derivative: Detection and Quantification of the Nitroradical Anion
Authors: Jara‐Ulloa P. , Núñez‐Vergara L. J. , Squella J. A. 
Published: June 2007

AbstractThe reductive electrochemistry of 1‐methyl‐4‐nitro‐2‐hydroxymethylimidazole, a 4‐nitroimidazole derivative, was examined in the presence of surfactants anionic as sodium dodecyl sulfate (SDS), nonionic, Triton‐X, Cationic, Hyamine and Cetyl Trimethyl Ammonium Bromide (CTAB). The reductive mechanism of the nitroimidazole derivative was found to be dependent of both, nature and concentration of the surfactants.
The NADH Electrochemical Detection Performed at Carbon Nanofibers Modified Glassy Carbon Electrode
Authors: Arvinte Adina , Valentini Federica , Radoi Antonio , Arduini Fabiana , Tamburri E. , Rotariu Lucian , Palleschi Giuseppe , Bala Camelia 
Published: June 2007

AbstractIn this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10−5 to 2.1×10−3 mol L−1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm2), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors.
Microstructures by Selective Desorption of Self‐Assembled Monolayer from Polycrystalline Gold Electrodes
Authors: Strutwolf Jörg , O'Sullivan Ciara K. 
Published: June 2007

AbstractPotential‐controlled partial reductive desorption of a self‐assembled monolayer of mercaptopropionic acid (MPA) formed on polycrystalline gold electrodes is used to expose subdomains of bare gold to the electrolyte solution. Two sets of cathodic waves are observed in the reduction scan with MPA self‐assembled on a polycrystalline gold electrode. The origin of the two waves is ambiguous but there are indications that the waves are correlated with reductive desorption from the (111) and then simultaneously (100) and (110) index faces of a polycrystalline gold electrode. Consecutive reduction scans with reversing the potential direction after the first peak (but before the onset of the second wave) results in disappearance of the first wave. The exposed domains are then blocked by an assembling process of longer chain alkanethiols to create a mixed self‐assembled monolayer on polycrystalline gold electrodes. Desorption of the remaining MPA creates a partially blocked electrode and the blocking behavior towards hexacyanoferrate(III) is analyzed using the theory of partially blocked electrodes and indicates an array of interacting centers. The approach of partial reductive desorption may be exploited for use in biosensing applications where the exposed gold domains could be used for anchoring of DNA probes.
Determination of Diclofenac in Urine Samples by Molecularly‐Imprinted Solid‐Phase Extraction and Adsorptive Differential Pulse Voltammetry
Authors: Fernández‐Llano Laura , Blanco‐López M. Carmen , Lobo‐Castañón M. Jesús , Miranda‐Ordieres Arturo J. , Tuñón‐Blanco Paulino 
Published: June 2007

AbstractA molecularly imprinted polymer for diclofenac (DCF) was prepared by thermal polymerization over silica beads using 2‐(dimethylamino)ethyl‐methacrylate as functional monomer. After silica elimination by HF treatment, the polymer was applied to the selective solid‐phase extraction of the drug from urine followed by its quantification by adsorptive differential pulse voltammetry. Results indicate that the drug could be selectively extracted from the sample and quantified at clinically relevant concentrations (μg/mL).
Electrochemical Biosensing Platform Using Carbon Nanotube Activated Glassy Carbon Electrode
Authors: Zhang Renyun , Wang Xuemei , Chen Chen 
Published: June 2007

AbstractCarbon nanotube enhanced electrochemically activated glassy carbon electrode (GCE) has been prepared and applied for sensitive electrochemical determination of DNA and DNA bases. The results indicate that the relative activation could efficiently enhance electron transfer at the pretreated GCE so that this carbon nanotube activated glassy carbon electrode could provide relatively low detection limit with good reproducibility for the respective biomolecular determination. Besides, greatly enhanced sensitivity could be obtained for the relevant electrochemical detection of the bio‐recognition process including DNA biosensing by using the carbon nanotube activated GCE. This approach provided a detection limit of 7.5 nM for guanine and 150 ng/mL for acid denatured DNA. These observations suggest that the carbon nanotube activated glassy carbon electrode could be utilized as a very sensitive and stable biosensor for some specific biological process.
CE analysis of the acidic organelles of a single cell
Authors: Chen Yun , Xiong Guohua , Arriaga Edgar A. 
Published: June 2007

AbstractThe properties of organelles within a cell have been shown to be highly heterogeneous. Until now, it has been unclear just how much of this heterogeneity is endemic to the organelle subpopulations themselves and how much is actually due to stochastic cellular noise. An attractive approach for investigating the origins of heterogeneity among the organelles of a single cell is CE with LIF detection (CE‐LIF). As a proof of principle, in this report we optimize and use a single cell CE‐LIF method to investigate the properties of endocytic (acidic) organelles. Our results show that the properties of individual acidic organelles containing Alexa Fluor® 488 Dextran suggest that there are two groups of CCRF‐CEM cells: a group with a high dextran content per cell, and a group with a low dextran content per cell. Furthermore, the individual organelle measurements of the single cells allow us to compare in each group the distributions of doxorubicin content per acidic organelle and electrophoretic mobilities of these organelles.
Investigation of β‐CD‐derivatized erythromycin as chiral selector in CE
Authors: Dai Rongji , Nie Xiaoying , Li Hong , Saeed M. Khalid , Deng Yulin , Yao Guowei 
Published: June 2007

AbstractA novel water‐soluble β‐CD‐derivatized erythromycin (EM) was synthesized and used as an effective chiral selector for the resolution of chiral compounds in CZE. The purpose of substitution at the primary hydroxyl site of β‐CD with 1‐oxygen‐2,3‐epoxypropane is to produce a compound having functions of both β‐CD and EM. β‐CD‐derivatized EM exhibited excellent enantioselectivities compared with single β‐CD and EM for chiral separation in CE. We also investigated the influence of pH and concentration of BGE, concentration of chiral selector, applied potential, and organic modifier on chiral compounds' separation.
A novel LIF‐CE method for the separation of hyaluronan‐ and chondroitin sulfate‐derived disaccharides: Application to structural and quantitative analyses of human plasma low‐ and high‐charged chondroitin sulfate isomers
Authors: Zinellu Angelo , Pisanu Salvatore , Zinellu Elisabetta , Lepedda Antonio J. , Cherchi Gian Mario , Sotgia Salvatore , Carru Ciriaco , Deiana Luca , Formato Marilena 
Published: June 2007

AbstractThe report describes a rapid and simple CE method using LIF detection for the analysis of unsaturated disaccharides obtained from enzymatic depolymerization of plasma chondroitin sulfate (CS) isomers. The disaccharide reducing groups were labeled with 2‐aminoacridone (AMAC). The fluorotagged products can be separated by reversed‐polarity CE using a sodium acetate buffer, pH 3.8, in the presence of 0.05% methylcellulose. The choice of the appropriate electrophoretic conditions was performed after a deep analysis of the most important parameters affecting analyte separation. In particular, the effect of both run buffer concentration and pH on resolution, efficiency, migration times, and peak area was evaluated. The selected electrophoretic conditions allowed us to separate the CS isomers‐derived Δ‐disaccharides in less than 12 min, also resolving the nonsulfated disaccharides released from CS isomers from those released from hyaluronan (HA). Moreover, these conditions gave a good reproducibility of both the migration times (CV%, 0.25) and the peak areas (CV%, 1.4). Intra‐ and interassay CV were 5.37 and 7.23%, respectively, and analytical recovery was about 86%. The applicability of the above method to the quantitative and structural disaccharide analyses of plasma CS isomers was investigated. Data obtained from 44 healthy human subjects were compared with those obtained by a fluorophore‐assisted carbohydrate electrophoresis (FACE) reference assay, by using the Passing and Bablok regression and Bland–Altman tests. The developed method could represent a good tool for an ultrasensitive analysis of CS isomers in biological samples from different sources, particularly when samples are available in very low amounts.
Continuous‐flow single‐molecule CE with high detection efficiency
Authors: Schiro Perry G. , Kuyper Christopher L. , Chiu Daniel T. 
Published: June 2007

AbstractThis paper describes the use of two‐beam line‐confocal detection geometry for measuring the total mobility of individual molecules undergoing continuous‐flow CE separation. High‐sensitivity single‐molecule confocal detection is usually performed with a diffraction limited focal spot (∼500 nm in diameter), which necessitates the use of nanometer‐sized channels to ensure all molecules flow through the detection volume. To allow for the use of larger channels that are a few micrometers in width, we employed cylindrical optics to define a rectangular illumination area that is diffraction‐limited (∼500 nm) in width, but a few micrometers in length to match the width of the microchannel. We present detailed studies that compare the performance of this line‐confocal detection geometry with the more widely used point‐confocal geometry. Overall, we found line‐confocal detection to provide the highest combination of signal‐to‐background ratio and spatial detection efficiency when used with micrometer‐sized channels. For example, in a 2 μm wide channel we achieved a 94% overall detection efficiency for single Alexa488 dye molecules when a 2 μm×0.5 μm illumination area was used, but only 34% detection efficiency with a 0.5 μm‐diameter detection spot. To carry out continuous‐flow CE, we used two‐beam fluorescent cross‐correlation spectroscopy where the transit time of each molecule is determined by cross‐correlating the fluorescence registered by two spatially offset line‐confocal detectors. We successfully separated single molecules of FITC, FITC‐tagged glutamate, and FITC‐tagged glycine.
Off‐line integration of CE and MALDI‐MS using a closed–open–closed microchannel system
Authors: Jacksén Johan , Frisk Thomas , Redeby Theres , Parmar Varun , van der Wijngaart Wouter , Stemme Göran , Emmer Åsa 
Published: June 2007

AbstractIn this work, a new technique for off‐line hyphenation between CE and MALDI‐MS is presented. Two closed fused‐silica capillaries were connected via a silicon chip comprising an open microcanal. The EOF in the system was evaluated using mesityloxide or leucine‐enkephalin as a sample and with a running buffer that rendered the analyte neutrally charged. Comparison was made between the EOF in a closed system (first capillary solely included in the electrical circuit) and in a closed–open system (first capillary and microcanal included in the electrical circuit). It was concluded that the experimental values of the EOF agreed with the theory. The influence of the capillary outer diameter on the peak dispersion was investigated using a closed–open–closed system (first capillary, microcanal and second capillary included in the electrical circuit). It was clearly seen that a capillary with 375 μm od induced considerably higher peak dispersion than a 150 μm od capillary, due to a larger liquid dead volume in the connection between the first capillary outlet and the microcanal. Mass spectrometric analysis has also been performed following CE separation runs in a closed–open–closed system with cytochrome c and lysozyme as model proteins. It was demonstrated that a signal distribution profile of the separated analytes could be recorded over a 30 mm long microcanal.
Inelastic seismic response of stiffening systems and development of demand spectrum: Application to MSSS bridges
Authors: Saadeghvaziri M. Ala , Yazdani‐Motlagh A. 
Published: June 2007

AbstractA stiffening system is a system that increases its stiffness as it goes under large displacements. Such behavioural characteristic can result from constitutive behaviour or at the structural level often from closure of gaps between various components (sub‐systems) of the structure. An example of the latter situation is multi‐span simply supported (MSSS) bridges under horizontal earthquake ground motion. Unlike softening systems, stiffening systems have not been studied. In addition to the need for more understanding of the seismic response of stiffening systems, there is a need to develop response spectrum that can be used in design. Several parameters
including gap size and ratios of sub‐systems stiffness, strength, and mass control the behaviour of a stiffening system. In this study, a simplified stiffening model is developed and over 367 000 cases are analysed to investigate the nonlinear stiffening behaviour and pounding. Parameters considered also include ground motion characteristic. Results are evaluated and compared in terms of displacement and dissipated hysteretic energy. Parameter study results show that, on average, the displacement response is lower for stiffening systems, however, they dissipates higher hysteretic energy, due to higher yield cycles and yield excursions, and can possibly sustain more damage than a bilinear, elastic–plastic system. Using parameter study database, design response spectrum for stiffening systems is also proposed and its practical application is demonstrated through its application to an MSSS bridge. Results of this study goes beyond MSSS bridges and will have application for many structural systems where response is characterized by a stiffening behaviour. Copyright © 2007 John Wiley & Sons, Ltd.
IGF‐1 protects oligodendrocyte progenitors against TNFα‐induced damage by activation of PI3K/Akt and interruption of the mitochondrial apoptotic pathway
Authors: Pang Yi , Zheng Baoying , Fan Lir‐Wan , Rhodes Philip G. , Cai Zhengwei 
Published: June 2007

AbstractProinflammatory cytokine‐mediated injury to oligodendrocyte progenitor cells (OPCs) has been proposed as a cause of periventricular leukomalacia (PVL), the most common brain injury found in preterm infants. Preventing death of OPCs is a potential strategy to prevent or treat PVL. In the current study, we utilized an in vitro cell culture system to investigate the effect of insulin‐like growth factor‐1 (IGF‐1) on tumor necrosis factor‐α (TNFα)‐induced OPC injury and the possible mechanisms involved. OPCs were isolated from neonatal rat optic nerves and cultured in chemically defined medium (CDM) supplemented with platelet‐derived growth factor and basic fibroblast growth factor. Exposure to TNFα resulted in death of OPCs. IGF‐1 protected OPCs from TNFα cytotoxicity in a dose‐dependent manner as measured by the XTT and TUNEL assays. IGF‐1 activates both the PI3K/Akt and the extracellular signal‐regulated kinase (ERK) pathway. However, IGF‐1‐enhanced cell survival signals were mediated by the PI3K/Akt, but not by the ERK pathway, as evidenced by the observation that IGF‐1‐enhanced cell survival was partially abrogated by Akti, the Akt inhibitor, or wortmannin, the PI3K inhibitor, but not by PD98059, the MAPK kinase/ERK kinase inhibitor. The downstream events of IGF‐1‐triggered survival signals included phosphorylation of BAD, blockade of TNFα‐induced translocation of Bax from the cytosol to the mitochondrial membrane, and suppression of caspase‐9 and caspase‐3 activation. These observations indicate that the protection of OPCs by IGF‐1 is mediated, at least partially, by interruption of the mitochondrial apoptotic pathway via activation of PI3K/Akt. © 2007 Wiley‐Liss, Inc.