bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Polymerisation of Aniline and Methylsubstituted Derivatives: Electrochemical and Spectroscopic Investigations
Authors: Hochfeld A. , Kessel R. , Schultze J. W. , Thyssen A. 
Published: March 2014

AbstractDuring the potentiostatic polymerisation of aniline (ANI) and 2,6‐dimethylaniline (2,6‐DMA) we measured simultaneously the current densities i, the anodic charge qan, the redox charge qredox, the electrode capacity C, the average thickness d̄ of polymer and the absorption. ANI shows a delayed nucleation with a following autocatalytic polymerisation with hemispherical growth. The polymerisation of 2,6‐DMA takes place after a short period of nucleation. Then it grows homogeneously with a decreasing rate. Finally polymerisation is inhibited by termination reactions after a short period of nucleation. – The thickness of the interfacial double layer d′ is determined by capacity measurements to be d′PANI = 0.4 nm and d′P‐2,6‐DMA = 4 nm. – The Electrochemical Quartz Micro‐Balance (EQMB) yields the thickness d̄ of the total polymer layer, >400 nm in the case of PANI and about 40 nm for P‐2,6‐DMA after 3600 s. The number of electrons z exchanged during a redox cycle per monomer unit can be derived to about 0.1 for PANI and about 0.05 for P‐2,6‐DMA. – Because of a small torsion angle between the aniline rings the electronic conductivity of polyaniline (PANI) is high and the redox charge > 10% of the theoretical charge corresponding to 1 e‐/monomer. The torsion angle of poly‐2,6‐dimethylaniline (P‐2,6‐DMA) is high. Therefore the electronic conductivity is low and the redox charge < 5%. – The stoichiometric and other properties of the polymer films were investigated with XPS.
Temperature Dependence of the Proton‐Discharge Reaction at Gold and Silver Electrodes
Authors: Frese U. , Schmickler W. 
Published: March 2014

AbstractThe kinetics of the Volmer reaction, which is the first step in the hydrogen evolution reaction, have been investigated by means of potentiostatic pulses. Measurements were performed in liquid and frozen HClO4 · 5.5 H2O in the temperature range 180 to 300 K. The apparent transfer coefficient is found to depend strongly on temperature. Classical theories of heterogeneous charge transfer reactions are unable to explain this result. A new model for a “field assisted proton transfer” is presented, which results in a temperature dependent charge transfer coefficient.
The Application of Multi‐Photon Ionization Mass Spectrometry to the Study of the Reactions O + C2H4, F + C3H6, F + c‐C3H6, F + CH3OH, H + CH2OH and O + CH3O
Authors: Heinemann‐Fiedler P. , Hoyermann K. 
Published: March 2014

AbstractThe experimental arrangement of a time‐of‐flight mass spectrometer with multi‐photon ionization and electron impact ionization is described. This set up was combined with a discharge flow reactor and a molecular beam sampling device. The detection of the radicals CH3, C3H5, CH2OH and their deuterated analogs by the wave‐length selective multi‐photon ionization allowed the identification of primary products of elementary reactions in the gas‐phase (around 1 mbar). The branching ratios for the reactions

were determined as (0.5 ± 0.15), (0.5 ± 0.1), (0.95 ± 0.05), respectively. – For the reactions of the CH2OH and CH3O radicals with H and O atoms, the following reaction paths were established:
X‐Ray Characterization of Single Crystals of the Reaction Center I of Water Splitting Photosynthesis
Authors: Witt I. , Witt H. T. , Di Fiore D. , Rögner M. , Hinrichs W. , Saenger W. , Granzin J. , Betzel Ch. , Dauter Z. 
Published: March 2014

AbstractA new type of crystals of the reaction center I complex, RC I, of water splitting photosynthesis has been prepared from the cyanobacterium Synechococcus sp. In contrast to our first crystals (11), the new ones have a length of up to 1 mm, a thickness of up to 50 μm and show X‐ray diffraction patterns with a resolution of about 4 Å. The space group of the hexagonal crystals is probably P6322. One RC I represents the asymmetric unit. The unit cell dimensions are a = b = 285 Å, c = 167 Å, α = β = 90° and γ = 120°. The building block of the crystal lattice is a trimer (diameter ˜19 nm, height ˜6 nm, and apparent mass ˜600 kDa). The trimer is composed of 3 identical RC I units so that the quaternary structure is α3. The unit cell harbors four trimers in two layers with two trimers each.
Excess Gibbs Energies of Some Liquid Mixtures With Polar Components, Effects of Local Polarizability
Authors: van Nhu Nguyen , Nowak G. , Svejda P. 
Published: March 2014

AbstractVapour pressures of binary liquid mixtures of 2‐chloro‐2‐methylpropane, 2‐butanone and ethanenitrile + 2,2,4‐trimethylpentane (isooctane) or + 2,4,4‐trimethyl‐1‐pentene (α‐diisobutylene) were determined by static measurements in an apparatus according to Marsh with an improved vapour pressure cell and a water ebulliometer for the pressure measurements. Also the excess volumes of some of the systems and the isothermal compressibility of 2,4,4‐trimethyl‐1‐pentene were measured by the vibrating tube method. From theses data molar excess Gibbs energies at 293.15 K were determined which could be discussed in terms of different polarizabilities of the structurally closely related compounds isooctane and α‐diisobutylene on mixing with liquids of increasing polarity.
Hydrogen Bonding and Phase Transitions of RbOH · H2O and CsOH · H2O Studied by IR and Raman Spectroscopy
Authors: Lutz H. D. , Henning J. , Jacobs H. , Harbrecht B. 
Published: March 2014

AbstractThe infrared and Raman spectra of RbOH · H2O and of trimorphic CsOH · H2O, LTM, RTM, and HTM, in the range of 95–401 K are presented and discussed in terms of hydrogen bonding, disorder of the hydrogen atoms, and phase transitions. The different behaviour of OH− ions and H2O molecules as hydrogen bond donor and acceptor groups results in strong hydrogen bonding for HOH···OH− linkages and only weak H‐bonds for OH−···OH2 groupings. This is, for example, shown from the very different OH stretching modes of OH− and H2O in CsOH · H2O RTM, viz., 3496 and 2800 cm−1, observed for the same O···O distance of 264 pm. The temperature shifting of the OH− stretching modes in the range 340–395 K of CsOH · H2O can be interpreted by a Landau type order‐disorder phase transition. The halfwidths of the OH− bands exhibit an Arrhenius type behaviour. The activation energies derived reflect the band energies of lattice and librational modes (vibrational dephasing) as well as the energy barriers of proton reorientation processes, i.e., 17 kJ/mol for CsOH · H2O HTM.
Evaluation of agomelatine stability under different stress conditions using an HPLC method with fluorescence detection: application to the analysis of tablets and human plasma
Authors: El‐Shaheny R. N. 
Published: March 2014

ABSTRACTA simple and highly sensitive stability‐indicating HPLC method was developed and validated for the determination of the new antidepressant agent, agomelatine (AGM). Separation of AGM from its stress‐induced degradation products was achieved on a BDS Hypersil phenyl column (250 mm × 4.6 mm i.d., 5 µm particle size) using methanol–0.05 M phosphate buffer of pH 2.5 (35: 65, v/v) as a mobile phase with fluorescence detection at 230/370 nm. Naproxen was used as an internal standard. The method satisfied all the validation requirements, as evidenced by good linearity (correlation coefficient of 0.9999, over the concentration range 0.4–40.0 ng/mL), accuracy (recovery average 99.55 ± 0.90%), precision (intra‐day RSD 0.54–1.35% and inter‐day RSD 0.93–1.26%), robustness and specificity. The stability of AGM was investigated under different ICH recommended stress conditions including acidic, alkaline, neutral, oxidative and photolytic. AGM was found to be labile to acidic and alkaline degradation and a kinetic study was conducted to explore its degradation behavior. First‐order degradation rate constants and half‐life times were calculated in each case. The proposed method was applied for the determination of AGM in tablets and spiked human plasma with mean percentage recoveries of 99.87 ± 0.31 (n = 3) and 102.09 ± 5.01 (n = 5), respectively. Hence, the proposed method was successfully applied for the determination of AGM in human volunteer plasma. The results were compared statistically with those obtained by a comparison HPLC method revealing no significant differences between the two methods regarding accuracy and precision. Copyright © 2014 John Wiley & Sons, Ltd.
Antioxidant defense parameters as predictive biomarkers for fermentative capacity of active dried wine yeast
Authors: Gamero‐Sandemetrio Esther , Gómez‐Pastor Rocío , Matallana Emilia 
Published: March 2014

AbstractThe production of active dried yeast (ADY) is a common practice in industry for the maintenance of yeast starters and as a means of long term storage. The process, however, causes multiple cell injuries, with oxidative damage being one of the most important stresses. Consequentially, dehydration tolerance is a highly appreciated property in yeast for ADY production. In this study we analyzed the cellular redox environment in three Saccharomyces cerevisiae wine strains, which show markedly different fermentative capacities after dehydration. To measure/quantify the effect of dehydration on the S. cerevisiae strains, we used: (i) fluorescent probes; (ii) antioxidant enzyme activities; (ii) intracellular damage; (iii) antioxidant metabolites; and (iv) gene expression, to select a minimal set of biochemical parameters capable of predicting desiccation tolerance in wine yeasts. Our results show that naturally enhanced antioxidant defenses prevent oxidative damage after wine yeast biomass dehydration and improve fermentative capacity. Based on these results we chose four easily assayable parameters/biomarkers for the selection of industrial yeast strains of interest for ADY production: trehalose and glutathione levels, and glutathione reductase and catalase enzymatic activities. Yeast strains selected in accordance with this process display high levels of trehalose, low levels of oxidized glutathione, a high induction of glutathione reductase activity, as well as a high basal level and sufficient induction of catalase activity, which are properties inherent in superior ADY strains.
Quality and antitumour activity evaluation of extract of Hypericum ascyron
Authors: Li Xiu‐Mei , Luo Xue‐Gang , Ma Ning , Li Kun , Li Wen , Ma De‐Yun , Zhang Tong‐Cun 
Published: March 2014

AbstractSimilarity assessment of complex chromatographic profiles is a potential tool for the identification and quality control of herbal medicinal products to guarantee the expected biological activity. In this paper, a high‐performance liquid chromatography method was established for controlling the quality of extract of Hypericum ascyron for the first time. With this method, the correlation coefficients of similarity of 10 batches extract of H. ascyron were >0.97. The extract of H. ascyron displayed steadily inhibitorty activities on the growth of human cervical cancer Hela cell lines. Therefore, the present study successfully set up a sensitive efficient method which might confirm stable biological activity of the extract of H. ascyron. Copyright © 2014 John Wiley & Sons, Ltd.
Liquid chromatography/quadrupole time‐of‐flight mass spectrometry in combination with online hydrogen/deuterium exchange technique for structural elucidation of phase I metabolites of iso‐phenylcyclopentylamine in rat bile
Authors: Liu Xiaoxue , Wang Suilou , Ding Li , Chen Xiaoping , Shen Wenbin , Dong Xin , Yun Changhong , Lin Hongda 
Published: March 2014

ABSTRACTMS/MS experiment and accurate mass measurement are powerful tools in metabolite identification. However, sometimes these data do not provide enough information to assign an unambiguous structure to a metabolite. In combination with MS techniques, hydrogen/deuterium (H/D) exchange can provide additional information for structural elucidation by determination of the number of exchangeable hydrogen atoms in a structure. In this study, the principal phase I metabolites of iso‐phenylcyclopentylamine in rat bile were identified by high‐performance liquid chromatography with electrospray ionization quadrupole time‐of‐flight mass spectrometry (ESI‐Q‐TOF‐MS). Since N‐oxidation may occur because of the existence of the primary amino group in the structure, it was difficult to differentiate the hydroxylated metabolites from N‐oxides by ESI‐Q‐TOF‐MS alone. Therefore, online H/D exchange technique was applied to solve this problem. Finally, 25 phase I metabolites were detected and structurally described, in which 11 were confirmed to be N‐oxides. This study demonstrated the effectiveness of high‐resolution mass spectrometry in combination with an online H/D exchange technique in rapid identification of drug metabolites, especially in discriminating hydroxylated metabolites from N‐oxides. Copyright © 2014 John Wiley & Sons, Ltd.
Nanosecond Dynamics of Calmodulin and Ribosome‐Bound Nascent Chains Studied by Time‐Resolved Fluorescence Anisotropy
Authors: Lamprou Paraskevas , Kempe Daryan , Katranidis Alexandros , Büldt Georg , Fitter Jörg 
Published: March 2014

AbstractWe report a time‐resolved fluorescence anisotropy study of ribosome‐bound nascent chains (RNCs) of calmodulin (CaM), a prototypical member of the EF‐hand family of calcium‐sensing proteins. As shown in numerous studies, in vitro protein refolding can differ substantially from biosynthetic protein folding, which takes place cotranslationally and depends on the rate of polypeptide chain elongation. A challenge in this respect is to characterize the adopted conformations of nascent chains before their release from the ribosome. CaM RNCs (full‐length, half‐length, and first EF‐hand only) were synthesized in vitro. All constructs contained a tetracysteine motif site‐specifically incorporated in the first N‐terminal helix; this motif is known to react with FlAsH, a biarsenic fluorescein derivative. As the dye is rotationally locked to this helix, we characterized the structural properties and folding states of polypeptide chains tethered to ribosomes and compared these with released chains. Importantly, we observed decelerated tumbling motions of ribosome‐tethered and partially folded nascent chains, compared to released chains. This indicates a pronounced interaction between nascent chains and the ribosome surface, and might reflect chaperone activity of the ribosome.
Characterization of a Fluidized Catalytic Cracking Catalyst on Ensemble and Individual Particle Level by X‐ray Micro‐ and Nanotomography, Micro‐X‐ray Fluorescence, and Micro‐X‐ray Diffraction
Authors: Bare Simon R. , Charochak Meghan E. , Kelly Shelly D. , Lai Barry , Wang Jun , Chen‐Wiegart Yu‐chen Karen 
Published: March 2014

AbstractA combination of advanced characterization techniques: synchrotron X‐ray micro‐ and nanotomography, micro‐X‐ray fluorescence, and micro‐XRD have been used to characterize a commercial spent equilibrium fluid catalytic cracking catalyst (ECAT) at both the ensemble and individual particle level. At the ensemble level, X‐ray microtomography was used to determine the average size, shape, and respective distributions of over 1200 individual catalyst particles. This information is important to determine performance in commercial operation. It is shown that a large fraction of the particles contained large internal voids (5–80 μm diameter), and these voids likely aid the accessibility for large hydrocarbon molecules. At the individual particle level, by using X‐ray nanotomography, these voids were visualized at a much smaller scale (≈100 nm–12 μm in diameter). In addition, the individual phases that are present in the particle, for example, TiO2 and clay, are readily visualized in 3 D. Micro‐X‐ray fluorescence (XRF) was used to map, and semiquantitatively determine, both the contaminant (Ni, V, Fe) and inherent (La) catalyst elemental distributions. The distribution of zeolite Y in the ECAT particle was inferred from the La XRF map. Micro‐XRD determined the lattice constant of the zeolite Y at the individual catalyst particle level. This in‐depth characterization study at the ensemble and individual ECAT particle level presents a robust methodology that provides an understanding of the ECAT at both the micro‐ and nanometer scales.
Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron‐Donating Groups
Authors: Ito Akitaka , Kawanishi Kazuyoshi , Sakuda Eri , Kitamura Noboru 
Published: March 2014

AbstractThe spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.
Access to Optically Active 3‐Substituted Piperidines by Ring Expansion of Prolinols and Derivatives
Authors: Gomez Pardo Domingo , Cossy Janine 
Published: March 2014

AbstractThe ring expansion of prolinols via an aziridinium intermediate gives C3‐substituted piperidines in good yields and enantiomeric excess, the substituent at the C3 position being derived from the most reactive nucleophile in the reaction mixture. Depending on the nucleophile, the reaction proceeds under thermodynamic or kinetic control. The regioselectivity of attack of nucleophiles on the aziridinium intermediate depends on the nature of the substituents on the nitrogen atom and the C4 position of the starting prolinols.
Aromatic Superhalogens
Authors: Child Brandon Z. , Giri Santanab , Gronert Scott , Jena Puru 
Published: March 2014

AbstractNo organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzoannulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory revealed that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a metal nor a halogen atom.
Amine‐Catalyzed Enantioselective 1,3‐Dipolar Cycloadditions of Aldehydes to C,N‐Cyclic Azomethine Imines
Authors: Li Wenjun , Jia Qianfa , Du Zhiyun , Zhang Kun , Wang Jian 
Published: March 2014

AbstractAmine‐catalyzed enantioselective 1,3‐dipolar cycloadditions of aldehydes to C,N‐cyclic azomethine imines were developed. The reactions between diversely substituted C,N‐cyclic azomethine imines and aldehydes proceeded smoothly in the presence of chiral prolinol silyl ether catalyst and gave the C‐1‐substituted tetrahydroisoquinolines in a highly stereoselective manner. These tetrahydroisoquinolines could be efficiently transformed to several other useful polycyclic frameworks.
A Practical and Stereoselective Organocatalytic Alkylation of Aldehydes with Benzodithiolylium Tetrafluoroborate
Authors: Gualandi Andrea , Mengozzi Luca , Giacoboni Jessica , Saulnier Steve , Ciardi Moira , Cozzi Pier Giorgio 
Published: March 2014

ABSTRACTRecently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN1‐type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine catalysis) or chiral electrophiles (iminium catalysis, chiral counterion catalysis) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic stereoselective SN1‐type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate 1 can be used for the straightforward organocatalytic stereoselective alkylation of aldehydes. In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials. Chirality 26:607–613, 2014. © 2014 Wiley Periodicals, Inc.
Synthetic and Biological Studies of Tubulin Targeting C2‐Substituted 7‐Deazahypoxanthines Derived from Marine Alkaloid Rigidins
Authors: Scott Robert , Karki Menuka , Reisenauer Mary R. , Rodrigues Roberta , Dasari Ramesh , Smith W. Ross , Pelly Stephen C. , van Otterlo Willem A. L. , Shuster Charles B. , Rogelj Snezna , Magedov Igor V. , Frolova Liliya V. , Kornienko Alexander 
Published: March 2014

AbstractC2‐aryl‐ and C2‐alkyl‐7‐deazahypoxanthines as analogues of marine alkaloid rigidins were prepared utilizing novel synthetic methods developed for the construction of the pyrrolo[2,3‐d]pyrimidine ring system. The new compounds exhibited sub‐micromolar to nanomolar antiproliferative potencies against a panel of cell lines including in vitro models for drug‐resistant tumors, such as glioblastoma, melanoma and non‐small‐cell lung cancer. A selected representative C2‐methyl‐7‐deazahypoxanthine was found to inhibit microtubule dynamics in cancer cells, lending evidence for tubulin targeting as a mode of action for these compounds in cancer cells. The results of the docking studies utilizing the colchicine site on β‐tubulin were consistent with the observed structure–activity relationship data, including an important finding that derivatization at C2 with linear alkyl groups leads to the retention of activity, thus permitting the attachment of a biotin‐containing linker for the subsequent proteomics assays. Because many microtubule‐targeting compounds are successfully used to fight cancer in the clinic, the reported antitubulin rigidin analogues have significant potential as new anticancer agents.