bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of High‐Surface‐Area Zinc Oxide with Ordered Porosity, Different Pore Sizes, and Nanocrystalline Walls
Authors: Polarz Sebastian , Orlov Andrey V. , Schüth Ferdi , Lu An‐Hui 
Published: September 2006

AbstractTransition‐metal‐oxide materials possessing ordered mesoporosity have recently attracted significant research interest due to their numerous potential applications. Among them, ordered mesoporous zinc oxide (ZnO) is a very tempting material because of the importance of ZnO in heterogeneous catalysis. Here, first results of the preparation of ordered mesoporous ZnO materials by using different templates are reported. Porous materials with high surface area, different pore sizes, and nanocrystalline ZnO walls were obtained. Furthermore, we compare the two fundamental templating techniques, involving liquid crystals or ordered mesoporous carbon materials as templates. Regarding the formation of mesoporous ZnO, it was evident that the hard‐matter carbon template is superior.
Photochemistry of Peroxoborates: Borate Inhibition of the Photodecomposition of Hydrogen Peroxide
Authors: Rey Sébastien , Davies D. Martin 
Published: September 2006

AbstractThe UV absorbance and photochemical decomposition kinetics of hydrogen peroxide in borate/boric acid buffers were investigated as a function of pH, total peroxide concentration, and total boron concentration. At higher pH borate/boric acid inhibits the photodecomposition of hydrogen peroxide (molar absorptivity and quantum yield of H2O2 and HO2−, (19.0±0.3) m−1 cm−1 and 1, and (237±7) m−1 cm−1 and 0.8±0.1, respectively). The results are consistent with the equilibrium formation of the anions monoperoxoborate, KBOOH=[H+][HOOB(OH)3−]/([B(OH)3][H2O2]), 2.0×10−8, R. Pizer, C. Tihal, Inorg. Chem. 1987, 26, 3639–3642, and monoperoxodiborate, KBOOB=[BOOB2−]/([B(OH)4−][HOOB(OH)3−]), 1.0±0.3 or 4.3±0.9, depending upon the conditions, with molar absorptivity, (19±1) m−1 cm−1 and (86±15) m−1 cm−1, respectively, and respective quantum yields, 1.1±0.1 and 0.04±0.04. The low quantum yield of monoperoxodiborate is discussed in terms of the slower diffusion apart of incipient .OB(OH)3− radicals than may be possible for .OH radicals, or a possible oxygen‐bridged cyclic structure of the monoperoxodiborate.
Efficient Synthesis of Chiral 1,1′‐Binaphthalenes by the Asymmetric Suzuki–Miyaura Reaction: Dramatic Synthetic Improvement by Simple Purification of Naphthylboronic Acids
Authors: Genov Miroslav , Almorín Antonio , Espinet Pablo 
Published: September 2006

AbstractNaphthylboronic acids prepared as reported in the literature are contaminated with HCl. A very simple purification prior to their use in Suzuki–Miyaura couplings has been found to be crucial, rendering efficient some reactions that had been reported in the literature either to fail or to give extremely poor yields. With this improvement, parent boronic acids can be used instead of esters at moderate temperatures, and bromo derivatives can be used instead of iodo derivatives. Convenient access to chiral sterically hindered binaphthalene derivatives has been achieved through the use of boronic acids, bromonaphthalenes, and ferrocenylphosphane ligands. The products were obtained in good yields (95–55 %) and with good enantioselectivities (90–50 %). Bulkier ligands are less efficient in the coupling of hindered partners.
Dynamic Kinetic Resolution of Secondary Alcohols Combining Enzyme‐Catalyzed Transesterification and Zeolite‐Catalyzed Racemization
Authors: Zhu Yongzhong , Fow Kam‐Loon , Chuah Gaik‐Khuan , Jaenicke Stephan 
Published: September 2006

AbstractHydrophobic zeolite beta containing low concentrations of Zr or Al was found to be a good catalyst for the racemization of 1‐phenylethanol. The formation of styrene as a side product could be minimized by reducing the metal concentration in the zeolite beta. Combined with an immobilized lipase from Candida antarctica, the dynamic kinetic resolution of 1‐phenylethanol to the (R)‐phenylethylester can be achieved with high yield and selectivity. The reaction was best conducted in toluene as solvent at 60 °C, with higher temperatures leading to a loss in the enantioselectivity of the formed ester. By using high‐molecular‐weight acyl‐transfer reagents, such as vinyl butyrate or vinyl octanoate, a high enantiomeric excess of the product esters of 92 and 98 %, respectively, could be achieved. This is attributed to a steric effect: the bulky ester is less able to enter the pore space of the zeolite catalyst where the active sites for racemization are localized. Close to 100 % conversion of the alcohol was achieved within 2 h. If the more common acyl donor, isopropenyl acetate, was used, the enantiomeric excess (ee) of the formed ester was only 67 %, and the reaction was considerably slower.
Solid‐Phase Synthesis, Characterization, and Antibacterial Activities of Metallocene–Peptide Bioconjugates
Authors: Chantson Janine T. , Vittoria Verga Falzacappa Maria , Crovella Sergio , Metzler‐Nolte Nils 
Published: September 2006

AbstractThis work shows how the introduction of an organometallic group enhances and modifies the specificity of biologically active peptides. Ferrocene was chosen as an organometallic group because it has been shown to alter the pharmacodynamic profile of bioactive compounds. A comparison with the isosteric cobaltocenium group allows one to explore the influence of charge and redox potential on the biological activity of the conjugates. Arginine and tryptophan containing peptides H‐WRWRWR‐NH2 and H‐RWRWRW‐NH2 and the metallocene peptide bioconjugates [M]‐C(O)‐RWRWR‐NH2 and [M]‐C(O)‐WRWRW‐NH2, where [M]=[Co(Cp)(C5H4)]+, [Fe(Cp)(C5H4)] were prepared by solid‐phase peptide synthesis (SPPS). They were purified by HPLC, characterized by ESIMS and NMR spectroscopy, and tested for antibacterial properties against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus using the minimum inhibitory concentration (MIC) test. In most cases, no metal‐specific activity could be observed. However, the conjugate [Fe(Cp)(C5H4)‐C(O)‐WRWRW‐NH2] 6 was found to be particularly effective against the Gram‐positive S. aureus. The activity of this metallocene–pentapeptide conjugate (7.1 μM) was even better than the 20 amino acid naturally occurring pilosulin 2, which was used as a positive control. Unlike all other compounds tested, which were most active against the Gram‐negative E. coli strain, the ferrocene conjugate 6 was the only compound in this series that was most active against Gram‐positive bacteria. Given the health concerns resulting from multidrug resistant S. aureus strains, the incorporation of metallocenes may provide a novel line of attack.
Vapor‐Phase Beckmann Rearrangement of Oxime Molecules over H‐Faujasite Zeolite
Authors: Sirijaraensre Jakkapan , Limtrakul Jumras 
Published: September 2006

AbstractThe Beckmann rearrangement (BR) plays an important role in a variety of industries. The mechanism of this reaction rearrangement of oximes with different molecular sizes, specifically, the oximes of formaldehyde (H2CNOH), Z‐acetaldehyde (CH3HCNOH), E‐acetaldehyde (CH3HCNOH) and acetone (CH3)2CNOH, catalyzed by the Faujasite zeolite is investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6‐31G (d,p) basis set. To enhance the energetic properties, single point calculations are undertaken at MP2/6‐311G(d,p). The rearrangement step, using the bare cluster model, is the rate determining step of the entire reaction of these oxime molecules of which the energy barrier is between 50–70 kcal mol−1. The more accurate embedded cluster model, in which the effect of the zeolitic framework is included, yields as the rate determining step, the formaldehyde oxime reaction rearrangement with an energy barrier of 50.4 kcal mol−1. With the inclusion of the methyl substitution at the carbon‐end of formaldehyde oxime, the rate determining step of the reaction becomes the 1,2 H‐shift step for Z‐acetaldehyde oxime (30.5 kcal mol−1) and acetone oxime (31.2 kcal mol−1), while, in the E‐acetaldehyde oxime, the rate determining step is either the 1,2 H‐shift (26.2 kcal mol−1) or the rearrangement step (26.6 kcal mol−1). These results signify the important role that the effect of the zeolite framework plays in lowering the activation energy by stabilizing all of the ionic species in the process. It should, however, be noted that the sizeable turnover of a reaction catalyzed by the Brønsted acid site might be delayed by the quantitatively high desorption energy of the product and readsorption of the reactant at the active center.
The fabrication and evaluation of inline coupling of microdialysis with capillary electrophoresis and its application in the determination of blood glucose
Authors: Chen Hua , Yu Yanlin , Xia Zhining , Tang Shouyuan , Mu Xiaojing , Long Sha 
Published: September 2006

AbstractA novel method of inline coupling of microdialysis (MD) with CE has been investigated. A polysulfone MD membrane was in situ prepared at the inlet end of the separation capillary, which endued the capillary with an additional function of clean‐up sampling and made the pretreatment of complex matrices simple. The properties of the membrane and its influence on electrophoresis were evaluated. The membrane cut off macromolecules and particles efficiently and persistently, and changing the components of membrane‐casting solution could control the molecular weight cutoff of the membrane. Using the capillary having the MD membrane in electrophoresis, column efficiency with little reduction was achieved. The mixture of chlorpheniramine (CPA) and BSA was used to verify the analytical characteristics. Only the peak of CPA appears in the electropherograms and the RSDs of migration times and peak areas of CPA were 0.8 and 4.6%, respectively. The method was applied for the determination of glucose in human blood using an electrochemical detector. Whole blood containing glucose and macromolecules was electrokinetically injected directly into the capillary without pretreatment, and the concentration of glucose in human blood was 5.5 mmol/L. Equilibrium dialysis injection is also investigated in this paper. The results show that the method may be further used for in vivo sampling to monitor the endogenous or exogenous small molecules and their metabolites.
Capillary electrochromatographic separation of proteins on a column coated with titanium dioxide nanoparticles
Authors: Hsieh Yi‐Ling , Chen Tse‐Hsien , Liu Chuen‐Ying 
Published: September 2006

AbstractA TiO2 nanoparticle (TiO2 NP)‐coated open‐tubular column for the capillary electrochromatographic separation of proteins is described. The surface chemistry of the TiO2 NPs on the inner wall of the fused silica was significantly affected by the running buffer. By varying of the phosphate buffer pH, only cathodic EOF was indicated. The results showed that TiO2 NPs are existed as a complexed form with the buffer ligand. Good separation of conalbumin (ConA), apo‐transferrin (apoTf), ovalbumin (OVA), and BSA could be achieved with phosphate buffer (40 mM, pH 8.0) and an applied voltage of 15 kV. Five peaks of glycoisoforms of OVA were observed under these conditions. In comparison with the retention behavior of the analytes on the bare fused‐silica column, the new column's high resolving power seems to be predominantly derived from the ligand exchange of the analytes with the phosphate adsorbed onto the TiO2 NPs. The method was also used to separate egg‐white proteins. Both acidic and basic proteins in egg white were separated in a single run. The microheterogeneities of OVA could also be found in it. The separation efficiency for the main peak of OVA in egg white was around 10 000 plates/m.
Hybrid silica monolithic column for capillary electrochromatography with enhanced cathodic electroosmotic flow
Authors: Hu Jiwei , Xie Chuanhui , Tian Ruijun , He Zhike , Zou Hanfa 
Published: September 2006

AbstractA hybrid silica monolithic stationary phase for RP CEC was prepared by in situ co‐condensation of (3‐mercaptopropyl)‐trimethoxysilane (MPTMS), phenyltriethoxysilane (PTES), and tetraethoxysilane (TEOS) via a sol–gel process. The thiol groups on the surface of the stationary phase were oxidized to sulfonic acids by peroxytrifluoroacetic acid. The introduced sulfonic acid moieties on the monoliths were characterized by a strong and relatively stable EOF in a broad pH range from 2.35 to 7.0 in CEC. Aromatic acids and neutral compounds can be simultaneously separated in this column under cathodic EOF. The CEC column exhibited a typical RP chromatographic mechanism for neutral compounds due to the introduced phenyl groups.
Stereoselective separations of chiral phosphinic acid pseudodipeptides by CEC using silica monoliths modified with an anion‐exchange‐type chiral selector
Authors: Preinerstorfer Beatrix , Lubda Dieter , Mucha Artur , Kafarski Paweł , Lindner Wolfgang , Lämmerhofer Michael 
Published: September 2006

AbstractA nonaqueous CEC method for the simultaneous separation of the four stereoisomers of the N‐benzyloxycarbonyl phosphinic pseudodipeptide methyl ester benzyloxycarbonyl‐homophenylalanine Z‐hPheψ(PO2HCH2)Phe‐OCH3 as well as of the corresponding N‐2,4‐dinitrophenyl (DNP)‐derivative with free C‐terminal carboxylic group DNP‐hPheψ(PO2HCH2)Phe‐OH was developed. For this purpose, a monolithic silica capillary column modified with a cinchona alkaloid‐derived anion‐exchange‐type chiral selector, namely O‐9‐(tert‐butylcarbamoyl)quinidine (tBuCQD) was prepared. The mobile phase composition (ACN/methanol ratio, counterion type) was thoroughly optimized to end up with baseline resolution of all four stereoisomers with critical resolution of as high as about 2. The CEC method proved to be superior over the corresponding HPLC separations primarily due to significantly enhanced plate numbers (between 200 000 and 600 000 m−1 in CEC). Diastereoselectivity contributions arising from electrophoretic mobility differences of the diastereomers facilitated the separation of the later eluted diastereomeric peak pair (peaks III and IV), but had a negative influence on the selectivity of the earlier eluted diastereomeric peak pair (peaks I and II). The stereoselective CEC assay allowed the assessment of the stereoisomeric purity of the individual isomers which were obtained by preparative HPLC on a CHIRALPAK QD‐AX column that is based on the same tBuCQD selector. The present study demonstrates that there exist problems which are hard to solve by HPLC, yet can be conveniently solved by CEC. Moreover, it was intended to prove by this practical application that CEC with monolithic columns is robust enough to be used for solving real‐life problems.
Influence of dynamic soil–structure interaction on the nonlinear response and seismic reliability of multistorey systems
Authors: Bárcena Armando , Esteva Luis 
Published: September 2006

AbstractA set of reinforced concrete structures with gravitational loads and mechanical properties (strength and stiffness) representative of systems designed for earthquake resistance in accordance with current criteria and methods is selected to study the influence of dynamic soil–structure interaction on seismic response, ductility demands and reliability levels. The buildings are considered located at soft soil sites in the Valley of Mexico and subjected to ground motion time histories simulated in accordance with characteristic parameters of the maximum probable earthquake likely to occur during the system's expected life. For the near‐resonance condition the effects of soil–structure interaction on the ductility demands depend mainly on radiation damping. According to the geometry of the structures studied this damping is strongly correlated with the aspect ratio, obtained by dividing the building height by its width. In this way, for structures with aspect ratio greater than 1.4 the storey and global ductility demands increase with respect to those obtained with the same structures but on rigid base, while for structures with aspect ratio less than 1.4 the ductility demands decrease with respect to those for the structures on rigid base. For the cases when the fundamental period of the structure has values very different from the dominant ground period, soil–structure interaction leads in all cases to a reduction of the ductility demands, independently of the aspect ratio. The reliability index β is obtained as a function of the base shear ratio and of the seismic intensity acting on the nonlinear systems subjected to the simulated motions. The resulting reliability functions are very similar for systems on rigid or on flexible foundation, provided that in the latter case the base rotation and the lateral displacement are removed from the total response of the system. Copyright © 2006 John Wiley & Sons, Ltd.
Optimum viscous damper for connecting adjacent SDOF structures for harmonic and stationary white‐noise random excitations
Authors: Bhaskararao A. V. , Jangid R. S. 
Published: September 2006

AbstractThe dynamic behaviour of two adjacent single‐degree‐of‐freedom (SDOF) structures connected with a viscous damper is studied under base acceleration. The base acceleration is modelled as harmonic excitation as well as stationary white‐noise random process. The governing equations of motion of the connected system are derived and solved for relative displacement and absolute acceleration responses of connected structures. The response of structures is found to be reduced by connecting with a viscous damper having appropriate damping. For undamped SDOF structures, the closed‐form expressions for optimum damping of viscous damper for minimum steady state as well as minimum mean square relative displacement and absolute acceleration of either of the connected SDOF structures are derived. The optimum damper damping is found to be functions of mass and frequency ratio of two connected structures. Further, numerical results had indicated that the damping of the connected structures does not have noticeable effects on the optimum damper damping and the corresponding optimized response. This implies that the derived closed‐form expressions for optimum damper damping of undamped structures can also be used in practical applications for damped structures. Copyright © 2006 John Wiley & Sons, Ltd.
Analysis and localization of abnormal partial discharge activity in generator units
Authors: Pemen A. J. M. , van der Laan P. C. T. 
Published: September 2006

AbstractThis paper describes methods to monitor partial discharges (PDs) of important power plant components, such as generator stator windings, generator circuit‐breaker, and step‐up transformer. Two methods have been evaluated under practical conditions, using various sensors: (i) time‐domain measurements followed by signal‐processing to discriminate between PDs and interference, and (ii) a tunable narrow‐bandwidth filter which can be tuned to a frequency where PDs are strong and interference is weak. For several generators, abnormal PD activity was observed. In all cases, the source of these PDs could be located, by means of the transit‐time between various sensors. Examples of identified abnormal discharge activity are: (i) discharge activity between phase separations of a statorwinding, (ii) sparking inside a step‐up transformer, and (iii) large PDs in a generator circuit‐breaker. Copyright © 2006 John Wiley & Sons, Ltd.
Two‐dimensional MHD solver by fluctuation splitting and dual time stepping
Authors: Balcı Şölen , Aslan Necdet 
Published: September 2006

AbstractNumerical solutions of 2D magneto‐hydrodynamic (MHD) equations by means of a fluctuation splitting (FS) scheme (with a new wave model and dual time stepping technique) is presented. The FS scheme, essentially based on the model explained in Proceedings of the Tenth International Conference, vol. 10, Swansea, 21–25 July 1997; Godunov Symposium, University of Michigan, Ann Arbor, 1–2 May 1997; Physics Symposium, Alanya, Turkey, 27–31 October 1998; J. Comput. Phys. 1999; 153:437–466; Ph.D. Thesis, University of Marmara, Istanbul, Turkey, 2000), was extended to include gravitational source effects, limiters to limit oscillations, high order time accuracy through multistage Runge–Kutta steps, and a dual time stepping scheme to drive magnetic field divergence to zero during iterations. The numerical results show that with the new wave model called MHD‐B along with its embedded numerical dissipation, correct limiting viscosity solution has been recovered and that it can safely be used in order to investigate steady or time dependent magnetized or neutral compressible flows in two dimensions. Copyright © 2006 John Wiley & Sons, Ltd.
Vesicular transmitter release from astrocytes
Authors: Montana Vedrana , Malarkey Erik B. , Verderio Claudia , Matteoli Michela , Parpura Vladimir 
Published: September 2006

AbstractAstrocytes can release a variety of transmitters, including glutamate and ATP, in response to stimuli that induce increases in intracellular Ca2+ levels. This release occurs via a regulated, exocytotic pathway. As evidence of this, astrocytes express protein components of the vesicular secretory apparatus, including synaptobrevin 2, syntaxin, and SNAP‐23. Additionally, astrocytes possess vesicular organelles, the essential morphological elements required for regulated Ca2+‐dependent transmitter release. The location of specific exocytotic sites on these cells, however, remains to be unequivocally determined. © 2006 Wiley‐Liss, Inc.
Calcium signaling in invertebrate glial cells
Authors: Lohr Christian , Deitmer Joachim W. 
Published: September 2006

AbstractCalcium signaling studies in invertebrate glial cells have been performed mainly in the nervous systems of the medicinal leech (Hirudo medicinalis) and the sphinx moth Manduca sexta. The main advantages of studing glial cells in invertebrate nervous systems are the large size of invertebrate glial cells and their easy accessibility for optical and electrophysiological recordings. Glial cells in both insects and annelids express voltage‐gated calcium channels and, in the case of leech glial cells, calcium‐permeable neurotransmitter receptors, which allow calcium influx as one major source for cytosolic calcium transients. Calcium release from intracellular stores can be induced by metabotropic receptor activation in leech glial cells, but appears to play a minor role in calcium signaling. In glial cells of the antennal lobe of Manduca, voltage‐gated calcium signaling changes during postembryonic development and is essential for the migration of the glial cells, a key step in axon guidance and in stabilization of the glomerular structures that are characteristic of primary olfactory centers. © 2006 Wiley‐Liss, Inc.