bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model of a pH‐Based Potentiometric Biosensor Immobilizing Organophosphorus Hydrolase
Authors: Lihong W. , Lin Z. , Jinxing H. , Huanlin C. 
Published: March 2006

AbstractA model for predicting the steady‐state response of a pH‐based potentiometric biosensor immobilizing organophosphorus hydrolase (OPH) is developed. The model combines the processes of diffusion and enzymatic reaction in the membrane. Key factors influencing the system response, such as enzyme reaction order, Thiele modulus, and buffer concentration are discussed in detail. It is possible to obtain a good linear response by designing an enzyme electrode with a high enough Thiele modulus and by appropriately controlling added buffer concentrations. It is found that the model is in reasonable agreement with the experiment results.
Optimization of Fischer‐Tropsch Synthesis Using Neural Networks
Authors: Fernandes F. A. N. 
Published: March 2006

AbstractFischer‐Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. Optimization of hydrocarbon products such as diesel and gasoline produced by Fischer‐Tropsch synthesis usually requires the knowledge of the complex polymerization mechanism and the kinetic parameters associated with it in order to optimize production. The Fischer‐Tropsch reaction mechanism is still not fully understood, making optimization a hard task. In this work, a neural network was used in substitution to the reaction mechanism to optimize diesel and gasoline production based on few experimental data for the reaction. The neural network has yielded satisfactory predictions of the product distribution (with prediction errors lower than 5 %) and the optimum operating conditions for gasoline and diesel production were found for a commercial iron based catalyst.
Effect of Alternating Pumping of Two Reactants into a Microchannel on a Phase Transfer Reaction
Authors: Okamoto H. 
Published: March 2006

AbstractAlternating pumping of two reactants into a microchannel was found to provide, in comparison with batch processes, a more effective mixing and an increased yield for a particular organic reaction which uses a phase transfer catalyst. The superiority of the microreactor method increased with the frequency of alternation of the pumping of the two liquids.
Variation of Cell Voltage with Reaction Time in Electrochemical Synthesis Process of Sodium Dichromate
Authors: Li C. W. , Qi T. , Wang F. , Zhang Y. , Yu Z. H. 
Published: March 2006

AbstractTo address the problems existing in the traditional production technique of sodium dichromate, a new green technology of producing sodium dichromate with an electrochemical synthesis method was studied. Using a self‐made electrosynthesis reactor of pure titanium and stainless steel, with a multiple‐unit metal oxides combination anode, a cathode of stainless steel, and a reinforcing combination cation exchange membrane with perfluorosulfonic and perfluorocarboxylic polymers, experiments were carried out on the direct electrochemical synthesis of sodium dichromate from sodium chromate. From the experimental results and electrochemical reaction principles, it was shown that the electrochemical synthesis reaction process of sodium dichromate may be quantitatively determined from the variation of the cell voltage measured macroscopically with reaction time. Cell voltages were experimentally measured at different initial sodium chromate concentrations in the anolyte, and the dependence of the cell voltage on reaction time was discussed. The mathematical model of the variation of cell voltage with reaction time and the change rate equation of cell voltage were established, and satisfactorily formulated the change law of cell voltage in the electrochemical synthesis process of sodium dichromate.
Experimental Study and Analysis on Drag Reduction Mechanisms of Reducing Pressure Drop Stick in a Cyclone Separator
Authors: Liu C. W. , Wang L. Z. , Liu Q. S. 
Published: March 2006

AbstractThe mechanisms of mean mechanical energy losses in a cyclone separator with a Repds (Reducing Pressure Drop Stick) are studied. The results show that the energy losses are mainly caused by direct viscous dissipation, turbulent diffusion, and turbulent energy production, which is the same as in a conventional cyclone separator. In particular, the direct viscous dissipation and the turbulent energy production are of importance. Laser Doppler Velocimetry (LDV) is used to measure the flow field in the cyclone body and the exit pipe of a cyclone separator with and without a Repds, respectively. The drag reduction mechanism of the Repds is analyzed by examining the effects of the Repds on flow parameters which are related to energy loss factors. The measured results and analysis reveal that the drag reduction results from decreases of the direct viscous dissipation, turbulent diffusion, and turbulent production as a whole when a Repds is inserted into a cyclone separator. The resultant drag reduction is a tradeoff between the increase and the decrease of energy losses caused by the Repds.
Study of the Dehydration of Isopropanol by a Pervaporation‐Based Hybrid Process
Authors: Sanz M. T. , Gmehling J. 
Published: March 2006

AbstractThe permeation characteristics of the commercial polymeric membrane PERVAP® 2201 were studied to carry out the dehydration of binary water/isopropanol mixtures. The influence of the composition (2–75 wt % H2O) and temperature of the feed (311.15–348.15 K) on the membrane performance was studied. The selected membrane showed a high selectivity towards water in the entire concentration range. It was found that the permeation rate increased with the water content and the operating temperature. The influence of the temperature on the flux can be described by an Arrhenius‐type expression. The commercial software Aspen Plus was used to simulate the dehydration of isopropanol by means of a hybrid process combining distillation and pervaporation.
Inferential Estimation of Polymer Melt Index Using Sequentially Trained Bootstrap Aggregated Neural Networks
Authors: Zhang J. , Jin Q. , Xu Y. 
Published: March 2006

AbstractThe inferential estimation of a polymer melt index in an industrial polymerization process using aggregated neural networks is presented in this paper. The difficult‐to‐measure polymer melt index is estimated from easy‐to‐measure process variables, and their relationship is estimated using aggregated neural networks. The individual networks are trained on bootstrap re‐samples of the original training data by a sequential training algorithm. In this training method, individual networks, within a bootstrap aggregated neural network model, are trained sequentially. The first network is trained to minimize its prediction error on the training data. In the training of subsequent networks, the training objective is not only to minimize the individual networks' prediction errors but also to minimize the correlation among the individual networks. Training is terminated when the aggregated network prediction performance on the training and testing data cannot be further improved. Application to real industrial data demonstrates that the polymer melt index can be successfully estimated using an aggregated neural network.
Extraction with Spinodal Decomposition – Experiment and Simulation
Authors: Arce J. C. , Schaadt A. , Bart H.‐J. 
Published: March 2006

AbstractExperimental results on the growth and velocity of droplets (up to 0.45 mm/s) during the temperature‐induced phase separation of the 3‐methoxypropionitrile/water solvent system as well as a variety of theoretical methods used to study the demixing dynamics are presented. Due to computational costs, the simulation with Molecular Dynamics (MD) is feasible only for very short times (ps) and miniscule boxes (Å). Dissipative Particle Dynamics (DPD), where a coarse‐grained model of the system is employed, allows nanosecond simulations in a box with more than 13 million atoms in a diffusion‐dominated regime. Finally, the influence of the diffusion/convection ratio during the separation in the μs scale is studied by use of a code based on Model H for both instantaneous and non‐instantaneous quenching cases. Structural information and macroscopic parameters, such as interfacial tension, can be derived from the molecular simulations.
Experimental Investigation and Modeling of Adsorption of Water and Ethanol on Cornmeal in an Ethanol‐Water Binary Vapor System
Authors: Chang H. , Yuan X.‐G. , Tian H. , Zeng A.‐W. 
Published: March 2006

AbstractThe adsorption capacity of water and ethanol on cornmeal in an ethanol‐water binary vapor system was investigated in a fixed‐bed apparatus for ethanol dehydration. Experiments were performed at temperatures of 82–100 °C for different relative humidities of ethanol‐water vapor. Adsorption equilibrium models, including those based on the adsorption potential theory of Polanyi and Sircar's model, have been used to fit the experimental data for water adsorption on cornmeal, and all gave good fits. For ethanol adsorption, pseudo‐equilibrium was defined as the mass adsorbed on the cornmeal within the time needed for the equilibrium for water on the same adsorbent. Based on this limiting condition, adsorption behaviors and mechanisms were analyzed.
Synthesis of Small Tripeptide Molecules through a Catalysis Sequence Comprising Metathesis and Aminohydroxylation
Authors: Streuff Jan , Nieger Martin , Muñiz Kilian 
Published: March 2006

AbstractTripeptidic structures were synthesized by using a combination of two independent consecutive catalytic procedures. Cross‐metathesis of N‐acroyl amino acid esters yields fumaric amide compounds with exclusive E double‐bond geometry. This represents an unprecedented example of complete double‐bond selectivity in this kind of reaction. A subsequent asymmetric aminohydroxylation of the chiral fumaric amides was carried out without the need of any further ligand and gave high yields and no side products. This reaction transforms the central fumaric amide unit into a hydroxy aspartic acid moiety and relies on the inherent stereochemistry of the starting fumaric diamides. An additional feature of our sequence is the ease of generating stereochemical diversification within the aminohydroxylation reaction. As a consequence, rapid conformational and configurational diversification can be achieved from the overall two‐step catalytic sequence. The versatility of this approach is demonstrated by starting from two different N‐acroyl amino esters, which led to the synthesis of eight structurally and stereochemically different tripeptides that could all be identified individually. As such, the present two‐step catalytic approach should serve to efficiently synthesize large families of tripeptidic molecular probes.
Addition of Carbenes to the Sidewalls of Single‐Walled Carbon Nanotubes
Authors: Bettinger Holger F. 
Published: March 2006

AbstractThe addition of carbenes CX2 (X=H, Cl) to single‐walled carbon nanotubes (SWNTs) was investigated by density functional theory and finite, hydrogen‐terminated nanotube clusters or periodic boundary conditions in conjunction with basis sets of up to polarized triple‐ζ quality. For armchair [(3,3) to (12,12)] and zigzag tubes [(3,0) to (18,0)], reaction of CH2 with the CC bond oriented along the tube axis (A) is less exothermic than with those CC bonds having circumferential (C) orientation. This preference decreases monotonically with increasing tube diameter for armchair, but not for zigzag tubes; here, tubes with small band gaps have a very low preference for circumferential addition. Axial addition results in cyclopropane products, while circumferential addition produces “open” structures for both armchair and zigzag tubes. The barriers for addition of dichlorocarbene to a (5,5) SWNT, studied for a finite C90H20 cluster, are higher than that for addition to C60, in spite of similar diameters of the carbon materials. Whereas addition of CCl2 to [60]fullerene proceeds in a concerted fashion, addition to a (5,5) armchair SWNT is predicted to occur stepwise and involve a diradicaloid intermediate according to B3LYP, PBE, and GVB‐PP computations. Addition to C bonds of (5,5) armchair tubes resulting in the thermodynamically more stable insertion products is kinetically less favorable than that to A bonds yielding cyclopropane derivatives.
Structure and Total Synthesis of Aspernigerin: A Novel Cytotoxic Endophyte Metabolite
Authors: Shen Li , Ye Yong‐Hao , Wang Xiao‐Ting , Zhu Hai‐Liang , Xu Chen , Song Yong‐Cun , Li Hai , Tan Ren‐Xiang 
Published: March 2006

AbstractAspernigerin (1), a novel cytotoxic alkaloid consisting of an unprecedented structural framework has been isolated from the extract of a culture of Aspergillus niger IFB‐E003, an endophyte in Cyndon dactylon. Its structure was elucidated on the basis of comprehensive NMR spectral analysis and confirmed by single‐crystal X‐ray analysis. Aspernigerin (1) has been shown to be cytotoxic to the tumor cell lines nasopharynyeal epidermoid KB, cervical carcinoma Hela, and colorectal carcinoma SW1116 with corresponding IC50 values of 22, 46, and 35 μM, respectively. A feasible total synthetic route for aspernigerin (1) has been established for further pharmacological research.
Vacuum‐ultraviolet circular dichroism analysis of biomolecules
Authors: Gekko Kunihiko , Matsuo Koichi 
Published: March 2006

AbstractThe vacuum‐ultraviolet circular dichroism (VUVCD) spectra of various amino acids, saccharides, and proteins were measured using a synchrotron‐radiation CD spectrophotometer at HiSOR/HSRC that is capable of measuring the CD spectra down to 140 nm in aqueous solution. L‐Isomers of amino acids show two successive positive peaks at around 200 and 180 nm depending on the side chain. The ab initio assignment by time‐dependent density functional theory predicts that these peaks are attributed to n–π* and π–π* transitions of the carboxyl group, respectively. Most mono‐ and disaccharides exhibit characteristic peaks at around 170 nm, sensitively depending on the anomeric and axial/equatorial configurations of hydroxyl groups, trans‐gauche conformations of the hydroxymethyl group, and the type of glycosidic linkage. The VUVCD spectra of 31 globular proteins allow us to estimate more accurately the content and number of α‐helix and β‐strand segments by extending the short‐wavelength limit of the analytical program SELCON3 down to 160 nm. These results demonstrate that synchrotron‐radiation VUVCD spectroscopy is a useful tool for structure analyses of biomolecules in solution based on the higher energy transitions of chromophores. Chirality, 2006. © 2006 Wiley‐Liss, Inc.
Absolute configurations of brominated sesquiterpenes determined by vibrational circular dichroism
Authors: Monde Kenji , Taniguchi Tohru , Miura Nobuaki , Vairappan Charles S. , Suzuki Minoru 
Published: March 2006

AbstractTwo brominated sesquiterpenes, majapolene B (1) and acetylmajapolene B (2), isolated from the red algal genus Laurencia were investigated using vibrational circular dichroism (VCD). The ab initio theoretical VCD and IR calculations of 1 and 2 were performed by density functional theory (DFT) using the B3PW91/6–31G(d,p) basis set. The experimental VCD spectra and corresponding population‐weighted theoretical VCD spectra were found to be in excellent agreement in CCl4 solution in the 1800–850 cm−1 region, which allowed unambiguous determination of the absolute configurations of (−)‐1 and (−)‐2 as 7S,10S and 7S,10S, respectively. Chirality, 2006. © 2006 Wiley‐Liss, Inc.
First‐principles calculations of protein circular dichroism in the far‐ultraviolet and beyond
Authors: Oakley Mark T. , Bulheller Benjamin M. , Hirst Jonathan D. 
Published: March 2006

AbstractUnderstanding the relationship between the amino acid sequence of a protein and its unique, compact three‐dimensional structure is one of the grand challenges in molecular biophysics. One exciting approach to the protein‐folding problem is fast time‐resolved spectroscopy in the ultra‐violet (UV). Time‐resolved electronic circular dichroism (CD) spectroscopy offers resolution on a nanosecond (or faster) timescale, but does not provide the spatial resolution of techniques like X‐ray crystallography or NMR. There is a need to underpin fast timescale spectroscopic studies of protein folding with a stronger theoretical foundation. We review some recent studies in this regard and briefly highlight how modern quantum chemical models of aromatic groups have improved the accuracy of calculations of protein CD spectra near‐UV. On the other side of the far‐UV, we describe calculations indicating that charge‐transfer transitions are likely to be responsible for bands observed in the vacuum UV in protein CD. Chirality 18:340–347, 2006. © 2006 Wiley‐Liss, Inc.
Protocols for the analysis of theoretical optical rotations
Authors: Polavarapu Prasad L. 
Published: March 2006

AbstractThe availability of sophisticated quantum mechanical methods for predicting molecular optical rotations has revolutionized the determination of molecular stereochemistry. However, the objectives and approaches used for the applications of optical rotation vary from one laboratory to the other. With the number of applications of optical rotation increasing at an unprecedented rate, it is considered necessary to discuss the protocols for the general use of optical rotations predicted with quantum mechanical methods. A summary of the quantum mechanical methods for predicting optical rotations and protocols for the use of predicted optical rotations are presented in this article. Chirality, 2006. © 2006 Wiley‐Liss, Inc.
For most large underdetermined systems of linear equations the minimal 𝓁1‐norm solution is also the sparsest solution
Authors: Donoho David L. 
Published: March 2006

AbstractWe consider linear equationsy= Φxwhereyis a given vector in ℝnand Φ is a givenn×mmatrix withn<m≤ τn, and we wish to solve forx∈ ℝm. We suppose that the columns of Φ are normalized to the unit 𝓁2‐norm, and we place uniform measure on such Φ. We prove the existence of ρ = ρ(τ) > 0 so that for largenand for all Φ's except a negligible fraction, the following property holds:For every y having a representation y= Φx0by a coefficient vector x0∈ ℝmwith fewer than ρ · n nonzeros, the solution x1of the𝓁1‐minimization problemis unique and equal to x0. In contrast, heuristic attempts to sparsely solve such systems—greedy algorithms and thresholding—perform poorly in this challenging setting. The techniques include the use of random proportional embeddings and almost‐spherical sections in Banach space theory, and deviation bounds for the eigenvalues of random Wishart matrices. © 2006 Wiley Periodicals, Inc.
Coordination Mode of the Zinc(II) and Cadmium(II) Cations with N‐(Diisopropoxyphosphoryl)thiobenzamide
Authors: Sokolov Felix D. , Safin Damir A. , Zabirov Nail G. , Brusko Vasiliy V. , Khairutdinov Bulat I. , Krivolapov Dmitry B. , Litvinov Igor A. 
Published: March 2006

AbstractReaction of the potassium salt of N‐(diisopropoxyphosphoryl)thiobenzamide (iPrO)2P(O)NHC(S)C6H5 (HL) with ZnII and CdII cations in aqueous EtOH leads to three different complexes: [Zn(L‐O,S)2] (1), [Cd2(L‐O,S)4] (2) and [Cd(HL‐O)2(L‐O,S)2] (3). The structures of these compounds were investigated by single‐crystal X‐ray diffraction analysis, EI‐MS and ES‐MS, IR, 1H, 13C and 31P NMR spectroscopy and microanalysis. The zinc(II) atom in complex 1 is in a distorted tetrahedral ZnO2S2 environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated ligands. The cadmium(II) complex 2 is centrosymmetric and consists of dimeric species. Two [Cd(L‐O,S)2] moieties are connected by two bridging [S–Cd–S] units through the sulfur atoms of the ligand C=S groups. Complex 2 has a distorted trigonal‐bipyramidal Cd(Oax)2(Seq)3 core. Complex 3 has a tetragonal‐bipyramidal environment, Cd(Oax)2(Oeq)2(Seq)2, and two neutral ligand molecules are coordinated in the axial positions through the oxygen atoms of the P=O groups. The base of the bipyramid is formed by two anionic ligands in a typical 1,5‐O,S coordination mode. The ligands are in a trans configuration. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Proteomics‐driven progress in neurodegeneration research
Authors: Fountoulakis Michael , Kossida Sophia 
Published: March 2006

AbstractProteomics technologies have been widely used in the investigation of neurodegenerative and psychiatric disorders, and in particular in the detection of differences between healthy individuals and patients suffering from such diseases. Thus, brain and cerebrospinal fluid (CSF) samples from patients with Alzheimer's disease, Down syndrome, Pick's disease, Parkinson's disease, schizophrenia, and other disorders as well as brain and CSF from animals serving as models of neurological disorders have been analyzed by proteomics. 2‐DE followed by MALDI‐TOF‐MS has been mainly applied as this proteomics approach provides the possibility of convenient quantification of protein levels and detection of post‐translational modifications. About 330 unique proteins with deranged levels and modifications have been detected by proteomics approaches to be related to neurodegeneration and psychiatric disorders. They are mainly involved in metabolism pathways, cytoskeleton formation, signal transduction, guidance, detoxification, transport, and conformational changes. In this article, we provide a summary of the major contributions of proteomics technologies in the study of neurodegenerative and psychiatric diseases, in particular, in the detection of changes in protein levels and modifications related to these disorders.
Ligand exchange capillary electrophoresis by cyclodextrin derivatives, a powerful tool for enantiomeric separations
Authors: Cucinotta Vincenzo , Giuffrida Alessandro , Maccarrone Giuseppe , Messina Marianna , Vecchio Graziella 
Published: March 2006

AbstractFive pure CD derivatives synthesized in our laboratory were used as chiral selectors in the presence of copper(II) ion. Three enantiomeric pairs of amino acids were submitted to separation experiments in CE, by exploiting the ligand exchange mechanism. The results obtained in the investigated systems, together with those of the analogous systems previously studied, clearly show the usefulness of this technique in chiral separations. By comparing the ligand exchange CE results with potentiometric results, either reported elsewhere or studied here for the first time (system Cu/CDampy/tyrosine), it has been possible to rationalise the separation results. The importance of the availability of pure selectors, and to characterise them both spectroscopically and thermodynamically is discussed.