bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vinyl Acetate Polymers
Authors: Cordeiro Cajetan F. , Petrocelli Francis P. 
Published: January 2005

AbstractThis article provides information related to the chemistry, manufacture, and use of poly(vinyl acetate). Summary information is provided on vinyl acetate as the primary ingredient in the manufacture of the polymer. This information focuses on the chemical and physical properties of the material and the handling and safety aspects pertinent to its use in a polymerization system. The key material properties of poly(vinyl acetate) homopolymer and copolymers are described. The influences of key components of the polymerization recipe are discussed, such as the effect of the stabilizers, comonomers, and chain‐transfer agents on the reaction and product. Polymerization process aspects are covered with a focus on emulsion polymerization. The mechanisms involved in the vinyl acetate polymerization reaction are discussed. An overview is provided of the applications of the homopolymer and copolymers in adhesives, paint, paper, and other areas. General information is provided in these areas with references which can be used to obtain more specific information.
Temperature‐Controlled Catalytic Growth of ZnS Nanostructures by the Evaporation of ZnS Nanopowders
Authors: Fang X. S. , Ye C. H. , Zhang L. D. , Wang Y. H. , Wu Y. C. 
Published: January 2005

AbstractZnS nanostructures with different morphologies, sizes, and microstructures were synthesized by the evaporation of ZnS nanopowders. Based on the appearance of the as‐synthesized products, we show that substrate temperature and catalyst are the critical factors for controlling the size and the structure of various kinds of ZnS nanostructures, such as nanorods, nanowires, nanobelts, and nanosheets. Within a certain temperature range, products with a specific morphology can be obtained. Therefore, it may be possible to obtain ZnS nanostructures with a specific morphology by controlling the reaction temperature and catalyst. This represents an important step toward the design and control of nanostructures. High‐resolution electron microscopy revealed that most of the nanorods and nanowires grew along the [100] direction, whereas most of the nanobelts and nanosheets grew along [001]. Photoluminescence properties and growth mechanisms of these as‐synthesized ZnS nanostructures are discussed.
Defect‐Related Optical Behavior in Surface Modified TiO2 Nanostructures
Authors: Prokes S. M. , Gole J. L. , Chen X. , Burda C. , Carlos W. E. 
Published: January 2005

AbstractThe surface modification of TiO2 nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Anatase TiO2 structures in the 5–20 nm range, formed by a wet chemical technique, were surface modified and the nitridation of the highly reactive TiO2 nanocolloid surface, as determined by X‐ray photoelectron spectroscopy (XPS) studies, is achieved by a quick and simple treatment in alkyl ammonium compounds. The nitriding process was also simultaneously accompanied by metal seeding resulting in a metal coating layer on the TiO2 structures. The structure of the resultant titanium oxynitride nanostructures remains anatase. These freshly prepared samples exhibited a strong emission near 560 nm (2.21 eV), which red‐shifted to 660 nm (1.88 eV) and dropped in intensity with aging in the atmosphere. This behavior was also evident in some of the combined nitrogen doped and metal seeded TiO2 nanocolloids. Electron spin resonance (ESR) performed on these samples identified a resonance at g = 2.0035, which increased significantly with nitridation. The resonance is attributed to an oxygen hole center created near the surface of the nanocolloid, which correlates well with the observed optical activity.
Growth of Aligned Square‐Shaped SnO2 Tube Arrays
Authors: Liu Y. , Liu M. 
Published: January 2005

AbstractTin dioxide (SnO2) box beams, or tubes with square or rectangular cross‐sections, are synthesized on quartz substrates using a combustion chemical vapor deposition (CVD) method in an open atmosphere at 850 °C to 1150 °C. The cross‐sectional width of the as‐synthesized SnO2 tubules is tunable from 50 nm to sub‐micrometer depending on synthesis temperature. Each tubule is found to be a single crystal of rutile structure with four {110} peripheral surfaces and &&num;60;001&&num;62; growth direction. Although several growth patterns are observed for different samples, the basic growth mechanism is believed to be a self‐catalyzed, direct vapor–solid (VS) process, where most new material is incorporated into the bottom parts of the existing SnO2 tubules through surface diffusion. The tubes are readily aligned in the direction perpendicular to the substrate surface to form tube arrays. These well‐aligned SnO2 tubule arrays with tunable tube size could be the building blocks or templates for fabrication of functional nanodevices, especially those relevant to energy storage and conversion such as nanobatteries, nanofuel cells, and nanosensors. A gas sensor based on a single SnO2 nanotubes demonstrated extremely high sensitivity to ethanol vapor.
Stability and Hydrogenation of “Bare” Gadolinium Nanoparticles
Authors: Aruna I. , Mehta B. R. , Malhotra L. K. , Shivaprasad S. M. 
Published: January 2005

AbstractGadolinium nanoparticles, deposited via an inert gas evaporation method, show improved stability towards oxidation and it is therefore possible to carry out an ex‐situ investigation on “bare” Gd nanoparticles, i.e., in the absence of a protective Pd layer, for the first time. A size‐induced structural transformation from hexagonal close packing to the higher‐symmetry face‐centered cubic structure is observed. The important observation of hydrogen–Gd‐nanoparticle interaction at room temperature and atmospheric pressure, without a Pd catalytic layer, makes Gd nanoparticles a potential candidate for hydrogen‐sensing, switching, and storage applications.
Plastic Electronic Devices Through Line Patterning of Conducting Polymers
Authors: Hohnholz D. , Okuzaki H. , MacDiarmid A. G. 
Published: January 2005

AbstractA novel method for the preparation of transparent conducting‐polymer patterns on flexible substrates is presented. This method, line patterning, employs mostly standard office equipment, such as drawing software, a laser printer, and commercial overhead transparencies, together with a solution or dispersion of a conducting polymer. The preparation of a seven‐segment polymer‐dispersed liquid‐crystal display using electrodes of the conducting polymer poly(3,4‐ethylenedioxythiophene) doped with poly(4‐styrene sulfonate) (PEDOT/PSS) is described in detail. Furthermore, a method to fabricate an eleven‐key push‐button array for keypad applications is presented. Properties of the electrode films and patterns are discussed using microscopy images, atomic force microscopy, conductivity measurements, and tests of film stability.
Multiobjective optimization strategies for linear gradient chromatography
Authors: Nagrath Deepak , Bequette B. Wayne , Cramer S. M. , Messac Achille 
Published: January 2005

AbstractThe increase in the scale of preparative chromatographic processes for biopharmaceutical applications now necessitates the development of effective optimization strategies for large‐scale processes in a manufacturing setting. The current state of the art for optimization of preparative chromatography has been limited to single objective functions. Further, there is a lack of understanding of when to use a particular objective, and how to combine and/or prioritize mutually competing objectives to achieve a true optimal solution. In this paper, these limitations are addressed by using a physical programming–based multiobjective optimization (MO) strategy. A set of Pareto solutions are first generated for model protein separations for both bi‐objective (production rate and yield) and tri‐objective (production rate, yield, and product pool concentration) scenarios. These Pareto frontiers are used to visualize the Pareto optimal surface for different components with various purity constraints and provide a qualitative framework to evaluate the optimal solutions. A physical programming–based multiobjective framework is then used for the quantitative evaluation of the optimal solutions for tertiary protein mixtures. This enables the interpretation of results for different sets of hierarchy and priority values assigned to the objective functions and constraints for the chromatographic processes. This novel multiobjective optimization approach computes the trade‐offs between the conflicting design objectives and helps in choosing an operating condition from infinite feasible optimal solutions. The combined quantitative and visualization framework presented in this paper sets the stage for the development of true optimal solutions for complex nonlinear preparative separations. © 2005 American Institute of Chemical Engineers AIChE J, 51: 511–525, 2005
Die Dihydroxyaceton‐Einheit – ein nützlicher C3‐Baustein in der Organischen Synthese
Authors: Enders Dieter , Voith Matthias , Lenzen Achim 
Published: January 2005

AbstractDihydroxyacetonphosphat (DHAP) dient der Natur als Methylenkomponente in verschiedensten enzymkatalysierten Aldolreaktionen. Das wohl wichtigste Beispiel in diesem Zusammenhang ist die Photosynthese, bei derd‐Glucose, der mengenmäßig bedeutendste Naturstoff, ausgehend von DHAP in nur wenigen Stufen gebildet wird. In den vergangenen Jahren wurde eine Vielzahl von synthetischen DHAP‐Äquivalenten entwickelt, die insofern besondere Aufmerksamkeit verdienen, als ihre Anwendbarkeit nicht auf (stereoselektive) Aldolreaktionen beschränkt ist. Die Reagentien stellten ihr Potenzial auch bei einer Reihe weiterer asymmetrischer elektrophiler α‐Substitutionen in zahlreichen zielgerichteten Synthesen überzeugend unter Beweis. Die verwandten 1,3‐Dioxine sind darüber hinaus nützliche Äquivalente 2‐substituierter Acroleine.
Oligosaccharide Mimics Containing Galactose and Fucose Specifically Label Tumour Cell Surfaces and Inhibit Cell Adhesion to Fibronectin
Authors: Kim Evelyn Y.‐L. , Gronewold Claas , Chatterjee Amitava , von der Lieth Claus‐Wilhelm , Kliem Christian , Schmauser Birgit , Wiessler Manfred , Frei Eva 
Published: January 2005

AbstractWith the aim of establishing a versatile and easy synthesis of branched saccharides for biological applications, we used molecular‐dynamics simulations to model Lewisy to two classes of di‐ or triantennary saccharide mimetics. One set of mimetics was based on 1,3,5‐tris(hydroxymethyl)cyclohexane (TMC) as the core, the other on furan, and both were derivatised with galactose and/or fucose. The TMC‐based saccharides were biotinylated, while the furan disaccharides were treated with maleimide‐activated biotin in a Diels–Alder fashion to yield oxazatricyclodecanes (OTDs). These were then assayed as cell‐surface labels in human colon (SW480 and CaCo‐2), liver (PLC), Glia (U333 CG 343) and ovary (SKOV‐3) tumour cell lines. Discrete staining patterns were observed in all cells, usually at one or two poles of the cells, particularly with the asymmetric 3‐β‐L‐fucopyranosyloxymethyl‐4‐β‐D‐galactopyranosyloxymethyl‐OTD. Normal SV40‐transformed fibroblasts (SV80) showed no staining. Adhesion of the highly metastatic mouse melanoma line B16 F10 to fibronectin was inhibited by 80 % by the TMC‐digalactoside and by 30 % by 3,4‐bis‐(β‐D‐galactopyranosyloxymethyl)furan. None of the saccharide mimetics inhibited the adhesion of the less metastatic B16 F1 line. Migration of B16 F10 cells through MatrigelTM was greatly inhibited by the TMC‐digalactoside and weakly inhibited by the TMC‐trigalactoside. The saccharide mimetics that had shown the best structural agreements with the terminal saccharides of Lewisy in the molecular dynamics simulation were also the most biologically potent compounds; this underlines the predictive nature of molecular dynamics simulations. The use of the non‐saccharide cores enabled us to adapt spacer lengths and terminal saccharides to optimise the structures to bind more avidly to cell‐surface lectins.
Transport Of Surface‐Modified Nanoparticles Through Cell Monolayers
Authors: Koch Annette M. , Reynolds Fred , Merkle Hans P. , Weissleder Ralph , Josephson Lee 
Published: January 2005

AbstractWe synthesized three peptides, aD‐polyarginyl peptide (r8(FITC)), a Tat peptide (Tat(FITC)), and a control peptide (Cp(FITC)) and attached each to amino‐CLIO, a nanoparticle 30 nm in diameter. We then examined the effective permeability,Peff, of all six materials through CaCo‐2 monolayers. The transport of peptide–nanoparticles was characterized by a lag phase (0–8 h) and a steady‐state phase (9–27 h). The steady‐statePeffvalues for peptides were in the order r8(FITC)>Tat(FITC)=Cp(FITC). When r8(FITC) and Tat(FITC) peptides were attached to the nanoparticle, they conferred their propensity to traverse cell monolayers onto the nanoparticle, whereas Cp(FITC) did not. Thus, when the r8(FITC) peptide was attached to the amino‐CLIO nanoparticle, the resulting peptide–nanoparticle had aPeffsimilar to that of this poly‐d‐arginyl peptide alone. ThePeffof r8(FITC)–CLIO (MW∼1000 kDa) was similar to that of mannitol (MW=182 Da), a poorly transported reference substance, with a far lower molecular weight. These results are the first to indicate that the modification of nanoparticles by attachment of membrane‐translocating sequence‐based peptides can alter nanoparticle transport through monolayers. This suggests that the surface modification of nanoparticles might be a general strategy for enhancing the permeability of drugs and that high‐permeability nanoparticle‐based therapeutics can be useful in selected pharmaceutical applications.
Structure and Biosynthesis of Myxochromides S1–3 in Stigmatella aurantiaca: Evidence for an Iterative Bacterial Type I Polyketide Synthase and for Module Skipping in Nonribosomal Peptide Biosynthesis
Authors: Wenzel Silke C. , Kunze Brigitte , Höfle Gerhard , Silakowski Barbara , Scharfe Maren , Blöcker Helmut , Müller Rolf 
Published: January 2005

AbstractThe myxobacterium Stigmatella aurantiaca DW4/3–1 harbours an astonishing variety of secondary metabolic gene clusters, at least two of which were found by gene inactivation experiments to be connected to the biosynthesis of previously unknown metabolites. In this study, we elucidate the structures of myxochromides S1–3, novel cyclic pentapeptide natural products possessing unsaturated polyketide side chains, and identify the corresponding biosynthetic gene locus, made up of six nonribosomal peptide synthetase modules. By analyzing the deduced substrate specificities of the adenylation domains, it is shown that module 4 is most probably skipped during the biosynthetic process. The polyketide synthase MchA harbours only one module and is presumably responsible for the formation of the variable complete polyketide side chains. These data indicate that MchA is responsible for an unusual iterative polyketide chain assembly.
Intramolecular, Reductive Cyclization of β‐Ketoisothiocyanates Promoted by Using Samarium Diiodide
Authors: Cho Min Seok , Lee In Sang , Kang Sung Ho , Kim Yong Hae 
Published: January 2005

AbstractA novel samarium diiodide (SmI2) promoted intramolecular cyclization of β‐ketoisothiocyanate, derived from α,β‐unsaturated esters and ammonium thiocyanate led to α‐hydroxythiolactams and/or thiolactams in high yields. Treatment of β‐ketoisothiocyanate with two equivalents of SmI2 gave a mixture of α‐hydroxythiolactam and thiolactam. Four equivalents of SmI2 afforded only thiolactam in high yields. The intramolecular cyclization took place with high to complete stereoselectivity. A mechanism to explain this transformation is proposed.
Steric Control over Hydrogen Bonding in Crystalline Organic Solids: A Structural Study of N,N′‐Dialkylthioureas
Authors: Custelcean Radu , Gorbunova Maryna G. , Bonnesen Peter V. 
Published: January 2005

AbstractHydrogen bonding in crystalline N,N′‐dialkylthioureas was examined with the help of single‐crystal X‐ray diffraction, DFT calculations, and Cambridge Structural Database (CSD) analysis. A CSD survey indicated that unlike the related urea derivatives, which persistently self‐assemble into one‐dimensional hydrogen‐bonded chains, the analogous thioureas can form two different hydrogen‐bonding motifs in the solid state: chains, structurally similar with those found in ureas, and dimers, that further associate into hydrogen‐bonded layers. The formation of one motif or another can be manipulated by the bulkiness of the organic substituents on the thiourea group, which provides a clear example of steric control over the hydrogen bonding arrangement in crystalline organic solids.
Analytische Basisreaktionen aus einem chemischen Probierkabinett der Goethezeit
Authors: Schwedt Georg 
Published: January 2005

AbstractSchon vor Liebig und Fresenius entwickelte sich eine systematische qualitative Analyse, die erstmals einem breiteren Interessiertenkreis durch das „chemische Probierkabinett”︁ des Chemieprofessors Göttling in Jena ab 1790 bekannt gemacht wurde. Das Anleitungsbuch war zugleich auch das erste Hochschullehrbuch für Analytische Chemie. Ausgewählte, noch heute angewendete Nachweisreaktionen bzw. Reagenzien werden anhand der historischen Texte vorgestellt und mit dem Wissen von heute interpretiert. Goethe war ein Förderer des ehemaligen Apothekenprovisors Göttling in Weimar und hat dessen Probierkabinett im Roman „Die Wahlverwandtschaften”︁ ein literarisches Denkmal gesetzt. Das Probierkabinett ist zugleich ein Vorläufer der chemischen Experimentierkästen unserer Zeit.
Die Chemielehrer‐Ausbildung in Rheinpreußen in der Mitte des 19. Jahrhunderts — Wegweiser in der heutigen Reformdiskussion?
Authors: Schmitz‐Wallrafen Norbert 
Published: January 2005

AbstractVergleicht man die didaktische Konzeption des Seminars für die gesamten Naturwissenschaften an der Universität zu Bonn um 1850 mit den heutigen Forderungen zur Neustrukturierung der Gymnasiallehrerausbildung und den Vorschlägen zur Verbesserung des naturwissenschaftlichen Unterrichts an Schulen, so findet man auffällige Parallelen, auch wenn die Rahmenbedingungen damals und heute nicht vergleichbar sind. Diese Parallelen gilt es aufzuzeigen, denn dadurch wird erst deutlich, welche herausragende Rolle das Seminar zu Bonn bei der Umsetzung seiner didaktischen Konzeption für die Lehrerausbildung in Naturwissenschaften spielte, eine Konzeption, die auch heute noch besticht und von deren ungebrochener Aktualität über die Zeiten hinweg man überrascht wird. Hierbei sei natürlich zugestanden, dass zeitliche Umstände damals wie heute bei der Umsetzung der einen oder anderen Konzeption eine nicht zu unterschätzende Rolle spielen.
Geocryological processes linked to High Arctic proglacial stream suspended sediment dynamics: examples from Bylot Island, Nunavut, and Spitsbergen, Svalbard
Authors: Irvine‐Fynn T. D. L. , Moorman B. J. , Willis I. C. , Sjogren D. B. , Hodson A. J. , Mumford P. N. , Walter F. S. A. , Williams J. L. M. 
Published: January 2005

AbstractRecent research has identified differences in processes contributing to suspended sediment concentration (SSC) dynamics in proglacial streams between High Arctic and alpine catchments, but does not examine processes explicitly linked to the periglacial environment. Three glacierized basins were studied: Austre Brøggerbreen and Midre Lovénbreen, Svalbard (79°N, 12°E) and Glacier B28, unofficially named Stagnation Glacier, Bylot Island, Nunavut (73°N, 78°W). SSC variations were modelled from continuous turbidity, discharge and meteorological data throughout the summer months. Three statistical tools were utilized: principal component analysis, change‐point analysis and multivariate regression. These are shown to be effective in identifying subperiods of distinctive geocryological and glaciofluvial characteristics. Multivariate regression for the subseasons included autoregressive integrated moving‐average modelling, and showed that SSC variations were related not only to discharge variability, but also to fluctuations in energy fluxes. The results are interpreted in terms of spatio‐temporal changes in sediment mobilization and supply associated with changes in the relative importance of fluvial, glacial and periglacial processes. This evidence supports the notion of important linkages between glacial, fluvial and periglacial systems, but exemplifies distinct variability between High Arctic glaciers. Copyright © 2005 John Wiley & Sons, Ltd.
Evaluating runoff generation during summer using hydrometric, stable isotope and hydrochemical methods in a discontinuous permafrost alpine catchment
Authors: Carey S. K. , Quinton W. L. 
Published: January 2005

AbstractResearch on runoff generation in catchments with discontinuous permafrost has focused primarily upon the role of surface organic layers and frozen soils (both permanent and seasonal). Much of this work has been hydrometric, with isotope and hydrochemical methods receiving only limited application in delineating old and new water contributions and chemically inferred hydrological pathways. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, runoff generation processes were studied in the summer of 2001 using a mixed method approach to evaluate the mechanisms and pathways of flow from the hillslopes to the stream during rainfall events. Two storms had δ18O isotopic ratios that differed significantly from baseflow and water within hillslopes, allowing for two‐component hydrograph separation to infer new and old water contributions. Event water contributions ranged between 7 and 9%, exhibiting little variability despite the large differences in event water and stormflow volume. Utilizing δ18O‐dissolved organic carbon and δ18O‐specific conductance data, two tracer three‐component hydrograph separations were attempted to isolate rainfall, water within the organic layer and mineral layer contributions to stormflow. Three‐component separations suggest that water from the mineral soil dominates the stormflow hydrograph, yet the contribution of organic‐layer water varies greatly depending upon the choice of tracers. Hydrometric data indicate that slopes with permafrost likely supply much of the stormflow water due to near‐surface water tables and transmissive organic soils. However, this signal was not clearly discernable in the streamflow hydrochemistry. More integrated studies are required to establish a greater understanding of hillslope processes in mountainous discontinuous permafrost catchments. Copyright © 2005 John Wiley & Sons, Ltd.