bluuebunny/crossref_metadata_2025_split huggingface dataset:
Benzannulated Cyclooctanol Derivatives by Samarium Diiodide Induced Intramolecular Carbonyl–Alkene Coupling – Scope, Limitations, Stereoselectivity
Authors: Reißig Hans‐Ulrich , Khan Faiz Ahmed , Czerwonka Regina , Dinesh Chimmanamada U. , Shaikh Aarif L. , Zimmer Reinhold 
Published: August 2006

AbstractA series of γ‐oxo esters 27–34 was prepared from methyl 2‐silyloxycyclopropanecarboxylates 1–9 as key building blocks in a flexible modular synthesis. Their samarium diiodide promoted cyclization to benzannulated cyclooctanol derivatives was systematically investigated. Samarium ketyl compounds derived from aldehydes 27 and 28 mainly provided tricyclic γ‐lactones 38 and 39 as a result of a cis‐selective ring‐closure process, whilst the related ketones 29–31 underwent trans‐selective reductive cyclization to furnish the expected benzannulated cyclooctanol derivatives 43–45 in moderate to excellent yields. With cyclohexanones 33 and 34 an interesting stereochemical matched/mismatched situation was observed. Whereas diastereomers 33a and 34a smoothly afforded tricyclic products 47 and 48 in good yields, compound 33b with apparently mismatched configuration did not undergo the samarium diiodide promoted ring‐closure process. An explanation for this intriguing behaviour is presented, together with an explanation for the cis/trans selectivity. Tricyclic γ‐lactone 38 could be smoothly deprotonated at one bridgehead and the generated lithium enolate was trapped with suitable alkyl halides. Remarkably, a clean α‐hydroxylation of 38 and 39 by direct employment of molecular oxygen was possible, providing high yields of the corresponding tertiary alcohols 54 and 55. These results demonstrate that the cyclization products prepared can easily be converted into higher functionalized benzannulated cyclooctane derivatives.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Photochemical Electron‐Transfer Generation of Arylthiirane Radical Cations with Tetranitromethane and Chloranil — Some Novel Observations
Authors: Puiatti Marcelo , Argüello Juan E. , Peñéñory Alicia B. 
Published: August 2006

AbstractThe radical cations from 2,2,3,3‐tetraphenylthiirane (1a), 2,2‐bis(4‐methoxyphenyl)‐3,3‐diphenylthiirane (1b), and trans‐2,3‐diphenylthiirane (1c) have been generated by photoinduced electron transfer (PET) reactions with tetranitromethane [C(NO2)4] and chloranil (CA). A charge‐transfer complexe (CTC) absorption is observed by UV/Vis spectroscopy between thiiranes (1) and C(NO2)4. On the other hand, quenching studies with azulene suggest that the ET reaction occurs between thiiranes and the triplet CA (3CA). The photochemical reaction of the CTC between thiiranes 1 and C(NO2)4 yields mainly the corresponding alkenes from the fragmentation of the radical‐cation intermediate 1·+, together with the products derived from nitration on the phenyl rings. However, oxygen transfer to afford the sulfoxides is not found. A marked solvent effect is observed in this reaction, with cage coupling favored in CH2Cl2 (nitration derivatives as primary products) and non‐cage coupling observed in CH3CN (the alkene as the primary product). The PET reactions between 1a–b and CA, in the presence of CH3OH (or another possible oxygen‐centered nucleophile), give the ketone derivatives through ring opening, followed by oxidative cleavage. Conversely, under the same experimental conditions, the thiirane 1c affords only trans‐stilbene 2c. This different behavior is ascribed to a different spin density in the corresponding singly occupied molecular orbital (SOMO) of the radical cation. For 1c+·, the spin density is concentrated at the sulfur atom, whereas for 1a·+ and 1b·+, the charge is distributed onto the aromatic rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
RhCl(PPh3)3/DPPF: A Useful and Efficient Catalyst for Cross‐Coupling Reactions of Activated Alkenyl Tosylates with Arylboronic Acids
Authors: Wu Jie , Zhang Liang , Gao Ke 
Published: August 2006

AbstractA useful and effective rhodium catalyst system – [RhCl(PPh3)3/DPPF] – for the Suzuki–Miyaura cross‐coupling of activated alkenyl tosylates is described. The results not only represent the first examples of the rhodium‐catalyzed Suzuki–Miyaura coupling of activated alkenyl tosylates with arylboronic acids under mild conditions, but also provide an efficient route for the synthesis of some natural product‐like compounds, such as furan‐2(5H)‐one, coumarin, pyrone, and quinolin‐2(1H)‐one derivatives.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Asymmetric Synthesis of Arylpropionic Acids and Aryloxy Acids by Using Lactamides as Chiral Auxiliaries
Authors: Ammazzalorso Alessandra , Amoroso Rosa , Bettoni Giancarlo , De Filippis Barbara , Fantacuzzi Marialuigia , Giampietro Letizia , Maccallini Cristina , Tricca Maria L. 
Published: August 2006

AbstractTwo different dynamic kinetic resolution methods have been applied for the asymmetric synthesis of pharmaceutical arylpropionic acids and aryloxy acids by using amides of (S)‐lactic acid as chiral auxiliaries. For arylpropionic acids the esterification mediated by dicyclohexylcarbodiimide (DCC) and 4‐(dimethylamino)pyridine (DMAP) proceeds with good asymmetric induction, while for aryloxyacetic acids the key‐step is a diastereoselective substitution reaction in the presence of triethylamine and n‐hexylammonium iodide as additives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Ammoxidation of straw‐pulp alkaline lignin by hydrogen peroxide
Authors: Qi‐Pei Jiang , Xiao‐Yong Zhang , Hai‐Tao Mo , Zuo‐Hu Li 
Published: August 2006

AbstractA novel method that used hydrogen peroxide as an oxidizer to ammoxidize straw‐pulp alkaline lignin was studied. The purpose of this research was to find a more efficient way to utilize technical lignin, which is a major pollutant in China. The ammoxidation process was employed to nitrogen‐modify straw‐pulp lignin using ammonia liquor and hydrogen peroxide. At the desirable conditions, such as 120°C, 90 min reaction time, 20% hydrogen peroxide charge, and 20% ammonia charge, the nitrogen content of the ammoxidized product reached 11.62% and the ammonia nitrogen was 4.12%. The study showed that hydrogen peroxide could completely substitute for oxygen as an oxidizer for ammoxidizing alkaline lignin. Straw‐pulp alkaline lignin can be effectively converted into slow‐release fertilizer. © 2006 American Institute of Chemical Engineers Environ Prog, 2006
Performance of Alternative Oxide Anodes for the Electrochemical Oxidation of Hydrogen and Methane in Solid Oxide Fuel Cells
Authors: Tu H. , Apfel H. , Stimming U. 
Published: August 2006

AbstractThe electrode performances of the alternative oxides: La0.05Ca0.95Cr0.05Ti0.95O3‐δ‐8YSZ and Ce0.8TM0.2O2‐δ(TM=Mn, Co) for the direct electrochemical oxidation of methane are investigated to assess their potential as anode materials for efficient methane conversion in a SOFC. The electrochemical oxidation of hydrogen was also studied, for comparison. The oxides are characterised electrochemically with impedance spectroscopy in the frequency range from 10 mHz to 1MHz, using a three‐electrode geometry. They are compared to a standard Ni/8YSZ anode for the electrochemical oxidation of hydrogen. It is found that La0.05Ca0.95Cr0.05Ti0.95O3‐δ‐8YSZ demonstrates a poor electrochemical activity in both hydrogen and methane. However, the electrochemical activity of Ce0.8Mn0.2O2‐δ is promising, but the electronic conductivity needs to be increased, e.g., by adding a conducting oxide, before it can be used as an anode material in a SOFC.
Methanol Oxidation on Carbon Supported Pt and Ru – Modified Pt Nanoparticles: a Comparison with Single Crystal and Polycrystalline Electrodes
Authors: Lanova B. , Wang H. , Baltruschat H. 
Published: August 2006

AbstractThe rate of methanol adsorption and oxidation on carbon supported Pt nanoparticles and polycrystalline Pt has been studied by differential electrochemical mass spectrometry (DEMS) under continuous flow. At room temperature, the maximum adsorption rate at polycrystalline Pt is about 0.06 monolayer per second, whereas at Pt nanoparticles it is 0.04 monolayer per second. On polycrystalline Pt it amounts to 56% of a full CO monolayer, obtained by adsorbing CO from a CO saturated electrolyte. On the nanoparticles only 28% of a full CO monolayer can be obtained. The oxidation rate of the adsorbate is of zero order at polycrystalline Pt, whereas at nanoparticles it is of first order with respect to the coverage. Oxidation of methanol starts below the onset of CO2 formation. At polycrystalline Pt and Pt(111), the rate of CO2 formation is determined by the oxidation rate of the adsorbate. At Pt(332) and the nanoparticle electrodes, the rate of CO2 formation from bulk methanol is higher than that from methanol adsorbate, due to the heterogenity of these electrodes.Similarly to Ru modified Pt single crystal electrodes, Ru modified polycrystalline Pt and Pt nanoparticles offer different adsorption sites for CO, which can be selectively populated.
Internal Reforming of Methane at Ni/YSZ and Ni/CGO SOFC Cermet Anodes
Authors: Timmermann H. , Fouquet D. , Weber A. , Ivers‐Tiffée E. , Hennings U. , Reimert R. 
Published: August 2006

AbstractThe internal reforming of methane on Ni/CGO and Ni/YSZ anodes was investigated with single cells operated at steam to carbon ratios from 0 to 3 and at temperatures of 800 °C and 950 °C. The incorporation of gas extraction ports allowed the measurement of the local gas composition in the anode gas compartment by gas chromatography. The methane conversion is presented as a function of feed gas composition, temperature, gas flow velocity, and electrical load. The impact of the anode material on the reforming reaction and on cell performance is shown. Methane conversion along the Ni/CGO anode was calculated with a one‐dimensional model; the required kinetic parameters were obtained by data fitting.
Binary Mixtures of Carbon Supported Pt and Ru Catalysts for PEM Fuel Cells
Authors: Mazurek M. , Benker N. , Roth C. , Fuess H. 
Published: August 2006

AbstractCommercially available carbon‐supported pure Pt and pure Ru catalysts were heat treated in order to modify their individual particle sizes, mixed in a mortar and tested for their suitability as anode catalysts in polymer electrolyte fuel cells (PEMFCs). The procedure chosen for mixing monometallic catalysts should bring more flexibility to the preparation of catalysts, which could thus be easily adjusted to the working conditions. The catalyst mixtures were structurally characterized using a combination of X‐ray diffraction (XRD) and transmission electron microscopy (TEM), and indicated an increase in particle size with heat treatment temperature, while the size distribution remained sufficiently narrow. The particle size effect on the resulting activity of the catalyst mixtures was investigated by current‐voltage measurements (U/i curves) in single cell fuel cells. A mixture of the as‐received platinum and ruthenium gave the best results, which was almost comparable to a commercial Pt‐Ru alloy catalyst purchased from E‐TEK inc. Only a minor decrease in cell performance was seen during long term operation. Following operation, the X‐ray diffraction patterns show reflections of the Pt fcc phase, but not the hcp Ru phase. This may be explained by leaching of the pure ruthenium catalysts and re‐decoration on Pt nanoparticles, or by formation of an amorphous Ru oxide or, less likely, Pt‐Ru alloy during operation. However, these structural changes do not seem to significantly affect the cell performance.
Temperature Dependence of the Oxygen Reduction Kinetics on RuxSey/C Catalysts
Authors: Leveratto D. , Racz A. , Savinova E. R. , Stimming U. 
Published: August 2006

AbstractThe temperature dependence of the oxygen reduction kinetics on carbon‐supported RuxSey catalysts is studied using a rotating disc electrode in 0.5 M H2SO4 in the temperature interval from 25 °C to 65 °C. When the absolute value of the overpotential is below ca. 0.65 V, the reaction is limited by a one‐electron charge transfer step, where the transfer coefficient is independent of the temperature and equal to 0.44. The apparent activation enthalpy at zero overpotential is 0.49 eV and the pre‐exponential factor is independent of the temperature.
In situ fluorescence imaging of glutamate‐evoked mitochondrial Na+ responses in astrocytes
Authors: Bernardinelli Yann , Azarias Guillaume , Chatton Jean‐Yves 
Published: August 2006

AbstractAstrocytes can experience large intracellular Na+ changes following the activation of the Na+‐coupled glutamate transport. The present study investigated whether cytosolic Na+ changes are transmitted to mitochondria, which could therefore influence their function and contribute to the overall intracellular Na+ regulation. Mitochondrial Na+ (Na) changes were monitored using the Na+‐sensitive fluorescent probe CoroNa Red (CR) in intact primary cortical astrocytes, as opposed to the classical isolated mitochondria preparation. The mitochondrial localization and Na+ sensitivity of the dye were first verified and indicated that it can be safely used as a selective Na indicator. We found by simultaneously monitoring cytosolic and mitochondrial Na+ using sodium‐binding benzofuran isophthalate and CR, respectively, that glutamate‐evoked cytosolic Na+ elevations are transmitted to mitochondria. The resting Na concentration was estimated at 19.0 ± 0.8 mM, reaching 30.1 ± 1.2 mM during 200 μM glutamate application. Blockers of conductances potentially mediating Na+ entry (calcium uniporter, monovalent cation conductances, K+ATP channels) were not able to prevent the Na response to glutamate. However, Ca2+ and its exchange with Na+ appear to play an important role in mediating mitochondrial Na+ entry as chelating intracellular Ca2+ with BAPTA or inhibiting Na+/Ca2+ exchanger with CGP‐37157 diminished the Na response. Moreover, intracellular Ca2+ increase achieved by photoactivation of caged Ca2+ also induced a Na elevation. Inhibition of mitochondrial Na/H antiporter using ethylisopropyl‐amiloride caused a steady increase in Na without increasing cytosolic Na+, indicating that Na+ extrusion from mitochondria is mediated by these exchangers. Thus, mitochondria in intact astrocytes are equipped to efficiently sense cellular Na+ signals and to dynamically regulate their Na+ content. © 2006 Wiley‐Liss, Inc.
Invariant mantling of growth cones by Schwann cell precursors characterize growing peripheral nerve fronts
Authors: Wanner Ina B. , Mahoney James , Jessen Kristján R. , Wood Patrick M. , Bates Margaret , Bunge Mary Bartlett 
Published: August 2006

AbstractLittle is known about the cytoarchitecture of growth fronts in developing mammalian nerves. We report here the first quantitative, ultrastructural analysis of growth cones (GCs) and their immediate cellular and tissue environment at tips of growing nerves that are nearing their targets in fore limbs of E14 rat embryos. Schwann cell precursor (SCP) marker, p75 neurotrophin receptor, and growth cone marker, SCG10, were used to identify nerve fronts, respectively. Using confocal 3D reconstructions and immunoelectron microscopy, we found that growth cone and Schwann cell precursor migrate together at the nerve front, where growth cone contact adjacent growth cone and Schwann cell precursor with similar frequency. Schwann cell precursor are extensively connected by adherens junctions and form elaborate scaffolds that enmantle growth cone at nerve fronts, so that 80% of the nerve front surface is covered by Schwann cell precursor. Although they interdigitate in complex ways among growth cone, the total contact area between growth cone and glial membranes is remarkably constant among the 100 growth fronts analyzed. In contrast to this consistency, other growth cone contacts varied markedly from front to front such that the frequencies of GC–GC contacts are increasing proportional to their decreasing contacts with mesenchymal tissue. Thus, at the nerve front, it is the Schwann cell precursor that are most exposed to extracellular environment while forming a surprisingly invariant substrate for advancing growth cone. This study shows for the first time that Schwann cell precursor are close and consistent cellular companions of growth cone in their approach to their final targets in the developing limb and suggests a previously unappreciated role for Schwann cell precursor in growth cone advance through the limb mesenchyme. © 2006 Wiley‐Liss, Inc.
GFAP‐expressing cells in the postnatal subventricular zone display a unique glial phenotype intermediate between radial glia and astrocytes
Authors: Liu Xiuxin , Bolteus Anna J. , Balkin Daniel M. , Henschel Oliver , Bordey Angélique 
Published: August 2006

AbstractNeural stem cells in the adult subventricular zone (SVZ) derive from radial glia and express the astroglial marker glial fibrillary acidic protein (GFAP). Thus, they have been termed astrocytes. However, it remains unknown whether these GFAP‐expressing cells express the functional features common to astrocytes. Using immunostaining and patch clamp recordings in acute slices from transgenic mice expressing green fluorescent protein (GFP) driven by the promoter of human GFAP, we show that GFAP‐expressing cells in the postnatal SVZ display typical glial properties shared by astrocytes and prenatal radial glia such as lack of action potentials, hyperpolarized resting potentials, gap junction coupling, connexin 43 expression, hemichannels, a passive current profile, and functional glutamate transporters. GFAP‐expressing cells express both GLAST and GLT‐1 glutamate transporters but lack AMPA‐type glutamate receptors as reported for dye‐coupled astrocytes. However, they lack 100 μM Ba2+‐sensitive inwardly rectifying K+(KIR) currents expressed by astrocytes, but display delayed rectifying K+currents and 1 mM Ba2+‐sensitive K+currents. These currents contribute to K+transport at rest and maintain hyperpolarized resting potentials. GFAP‐expressing cells stained positive for both KIR2.1 and KIR4.1 channels, two major KIRchannels in astrocytes. Ependymal cells, which also derive from radial glia and express GFAP, display typical glial properties and KIRcurrents consistent with their postmitotic nature. Our results suggest that GFAP‐expressing cells in concert with ependymal cells can perform typical astrocytic functions such as K+and glutamate buffering in the postnatal SVZ but display a unique set of functional characteristics intermediate between astrocytes and radial glia. © 2006 Wiley‐Liss, Inc.
Behavior of in vitro cultured ameboid microglial cells migrating on Müller cell end‐feet in the quail embryo retina
Authors: Tassi Mohamed , Calvente Ruth , Marín‐Teva José L. , Cuadros Miguel A. , Santos Ana M. , Carrasco Maria‐Carmen , Sánchez‐López Ana M. , Navascués Julio 
Published: August 2006

AbstractAmeboid microglial cells migrate tangentially on the vitreal part of quail embryo retinas by crawling on Müller cell end‐feet (MCEF) to which they adhere. These microglial cells can be cultured immediately after dissection of the eye and isolation of sheets containing the inner limiting membrane (ILM) covered by a carpet of MCEF (ILM/MCEF sheets), to which the cells remain adhered. Morphological changes of microglial cells cultured on ILM/MCEF sheets for 4 days were characterized in this study. During the first minutes in vitro, lamellipodia‐bearing bipolar microglial cells became rounded in shape. From 1 to 24 h in vitro (hiv), microglial cells swept and phagocytosed the MCEF on which they were initially adhered, becoming directly adhered on the ILM. MCEF sweep was dependent on active cell motility, as shown by inhibition of sweep after cytochalasin D treatment. From 24 hiv on, after MCEF phagocytosis, microglial cells became more flattened, increasing the surface area of their adhesion to substrate, and expressed the β1 subunit of integrins on their membrane. Morphological evidence suggested that microglial cells migrated for short distances on ILM/MCEF sheets, leaving tracks produced by their strong adhesion to the substrate. The simplicity of the isolation method, the immediate availability of cultured microglial cells, and the presence of multiple functional processes (phagocytosis, migration, upregulation of surface molecules, etc.) make cultures of microglial cells on ILM/MCEF sheets a valuable model system for in vitro experimental investigation of microglial cell functions. © 2006 Wiley‐Liss, Inc.
Functional changes in astroglial cells in epilepsy
Authors: Binder Devin K. , Steinhäuser Christian 
Published: August 2006

AbstractEpilepsy comprises a group of disorders characterized by the periodic occurrence of seizures, and pathologic specimens from patients with temporal lobe epilepsy demonstrate marked reactive gliosis. Since recent studies have implicated glial cells in novel physiological roles in the CNS, such as modulation of synaptic transmission, it is plausible that glial cells may have a functional role in the hyperexcitability characteristic of epilepsy. Indeed, alterations in distinct astrocyte membrane channels, receptors and transporters have all been associated with the epileptic state. This review integrates the current evidence regarding astroglial dysfunction in epilepsy and the potential underlying mechanisms of hyperexcitability. Functional understanding of the cellular and molecular alterations of astroglia‐dependent hyperexcitability will help to clarify the physiological role of astrocytes in neural function as well as lead to the identification of novel therapeutic targets. © 2006 Wiley‐Liss, Inc.
Enhanced Connexin 43 immunoreactivity in penumbral areas in the human brain following ischemia
Authors: Nakase Taizen , Yoshida Yasuji , Nagata Ken 
Published: August 2006

AbstractAstrocytes support neurons not only physically but also chemically by secreting neurotrophic factors and energy substrates. Moreover, astrocytes establish a glial network and communicate through gap junctions in the brain. Connexin 43 (Cx43) is one of major component proteins in astrocytic gap junctions. Heterozygote Cx43 KO mice and astrocyte specific Cx43 KO mice exhibited amplified brain damage after ischemic insults, suggesting a neuroprotective role for astrocytic gap junctions. However, some reports mentioned unfavorable effects of gap junctions in neuronal support. Therefore, the role of astrocytic gap junctions under ischemic condition remains controversial. Since these studies have been performed using animal models, we investigated the Cx43 expression in human brain after stroke. Brain slice sections were prepared from pathological samples in our hospital. Embolic stroke brains sectioned because of the stroke were considered as acute ischemic models. Multiple infarction brains sectioned because of pneumonia or cancer were considered as chronic models. We observed the levels of Cx43 in both lesioned and intact areas, and compared them with acute and chronic models. As the results, astrocytes were strongly activated in penumbral lesions both of acute and chronic ischemic models. The Cx43 immunoreactivity was significantly amplified in the penumbra of chronic model compared to that of the acute model. Neurons were well preserved in chronic model compared to acute model. These findings suggested that the brain may generate neuronal protection by increasing the levels of Cx43 and amplifying the astrocytic gap junctional intercellular communication under hypoxic condition. © 2006 Wiley‐Liss, Inc.