bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alkoxy‐Substituted Hexastyrylbenzenes
Authors: Meier Herbert , Holst Hans Christof 
Published: August 2003

AbstractStar‐shaped compounds 2a–e with a central benzene ring and six p‐substituted, (E)‐configured styryl groups have been prepared by a sequence of three‐fold Heck and three‐fold Wittig–Horner reactions. Alkoxy chains (OC3H7, OC6H13, OC10H21, OC12H25) on all six arms guarantee a good solubility of 2a–d, whereas the alternating hexyloxy and cyano substitution in 2e leads to an almost insoluble push‐pull system. Irradiation into the long‐wavelength absorption of 2a–d (with λmax values of 341–342 nm) results in a statistical photocross‐linking, which is characterized by the complete degradation of all stilbene chromophores.
Polymer‐supported palladium(II) complexes and their catalytic study
Authors: Antony R. , Tembe G. L. , Ravindranathan M. , Ram R. N. 
Published: August 2003

AbstractChloromethylated poly(styrene–divinylbenzene) copolymers with 8 and 14% crosslinking was functionalized to a Schiff‐base‐bearing polymer by the sequential oxidation of the chloromethyl group to an aldehydic group and subsequent condensation with a base. The anchoring of the metal ion to the liganded polymer beads was carried out by its reaction with an ethanolic solution of palladium(II) chloride. The physicochemical properties of the supported catalyst, including surface area, bulk density, and the swelling of the polymer in polar and nonpolar solvents, were studied. The catalysts were characterized by various techniques, including elemental analysis, DTA–thermogravimetric analysis, Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. The surface morphology of the catalyst was studied by scanning electron microscopy. The catalytic hydrogenation of cis‐cyclooctene was investigated with the immobilized catalysts. The effects of various reaction parameters, including catalyst concentration, temperature, and hydrogen pressure on the reduction of olefin, were studied. The rate of the reaction was determined from hydrogen uptake measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 370–378, 2003
Small bubbles oxygenation membrane
Authors: Yasuda H. K. , Lin J. N. 
Published: August 2003

AbstractLarge bubbles emerge from porous membranes with small pores because the emerging bubbles spread on the membrane surface before they detache from the surface. If the sessile bubble contact angle (θ) is less than 45°, no spreading occurs, and the bubble size is determined by the size of hole. Even in this case, the equivalent diameter (of spherical bubble) is significantly larger than the pore diameter due to the bubble formation mechanism. If θ > 45°, the spreading of the emerging bubble on the surface occurs, and the bubble size is determined by the size of base of a sessile bubble, which depends on the value of θ, and is independent of the pore size. The equivalent diameter of a bubble could be greater in order of magnitude than the pore diameter. The same principle applies to the bubble formation from an inclined surface; however, the bubble formation is more complicated because of drifting of a developing bubble out of the orifice and the merging of sliding bubbles. In order to create small bubbles, it is necessary to create small orifices on a hydrophilic surface, of which θ < 45°, and two orifices should be separated beyond the maximum diameter of emerging bubble. A horizontal flat surface is the best for the creation of small‐sized bubbles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 387–398, 2003
Morphology of integral‐skin layers in hollow‐fiber gas‐separation membranes
Authors: Carruthers Seth B. , Ramos Gabriela L. , Koros William J. 
Published: August 2003

AbstractThe morphologies of polymeric integrally skinned asymmetric gas‐separation membranes are typically visualized as a thin gas‐selective skin region supported by a nonselective, low‐resistance porous structure. The validity of this visualization for defect‐free and defective membranes was investigated via scanning electron microscopy (SEM) in combination with traditional gas‐permeation measurements for previously reported ultrathin defect‐free hollow‐fiber membranes. Hollow‐fiber membranes were formed via a dry‐jet, wet‐quench process with a spinning solution composed of Matrimid® polyimide and components of varying volatility. For all the defect‐free membranes formed, SEM images revealed a prominent dense skin layer across the fibers' entire outer circumference. Skin‐thickness estimates from 36 SEM images and N2, O2, and He pure gas‐permeation measurements agreed to within 9, 7, and 24% for defect‐free membranes with 150‐, 300‐, and 600‐nm skin thicknesses, respectively. Defective membranes with O2/N2 gas selectivities of Knudsen values, nominally 50 and 80% of dense film values, exhibited a well‐developed nodular, partially developed nodular, and uniform dense layer (no nodules) skin morphologies, respectively. These results provide in‐depth experimental evidence for the existence of a distinct dense integral‐skin layer and suggest that the presence of nodules in the membrane's final skin morphology correlate to gas‐permeation defects. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 399–411, 2003
Measurement of thermal properties of polyaniline/metal from room temperature to 170°C
Authors: Joshi G. P. , Saxena N. S. , Sharma T. P. , Verma S. , Dixit V. , Mishra S. C. K. 
Published: August 2003

AbstractThe heat transfer through polyaniline (PANI) mixed with metals (manganese and iron) is studied by measuring its effective thermal conductivity (λe) and effective thermal diffusivity (χe) from room temperature to 170°C at normal pressure. Simultaneous measurements of the λe and χe values of samples A (100% Fe), B (50% Fe and 50% Mn), and C (100% Mn) of the PANI mixtures with different percentages of Fe and Mn are carried out using the transient plane source technique. It is observed that the λe and χe of the above samples are almost independent of the temperature in a range of temperatures. However, maximum values for the λe and χe are found for sample A at ∼140°C, sample B at ∼130°C, and sample C at ∼120°C. An empirical relationship deduced from a polynomial fit of the experimental data is established for the temperature dependence of the λe and χe values of these samples. Reasonably good agreement is obtained between the theoretically predicted results and the experimental data. This behavior is explained on the basis of bond formation between the metals (Fe and Mn) and nitrogen of the PANI matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 430–435, 2003
Thermotropic liquid‐crystalline copolyester (Rodrun LC3000)/thermoplastic elastomer (SEBS) in situ composites: II. Mechanical properties and morphology of monofilaments in comparison with extruded strands
Authors: Saikrasun S. , Bualek‐Limcharoen S. , Kohjiya S. , Urayama K. 
Published: August 2003

AbstractMonofilaments of in situ composites were prepared from an immiscible blend of a thermotropic liquid‐crystalline polymer (TLCP), Rodrun LC3000, and a thermoplastic elastomer, styrene–(ethylene butylene)–styrene (SEBS), by a melt spinning process. Mechanical properties and the morphology of the composite monofilaments were investigated and compared with those of the extruded strands previously reported. The stresses at all tensile strains of the composite monofilaments were much higher than those of the extruded strands. The tensile strengths of both extruded strands and monofilaments were comparable, but the elongation at break of monofilaments dropped considerably. The tension sets of composite monofilaments were slightly higher than those of extruded strands. All composite monofilaments with TLCP content of ≤15 wt % exhibited good elastic recovery under the applied strain up to 200%. The dynamic mechanical storage modulus at 25°C of 10 wt % TLCP composite monofilament increased fourfold compared with that of the composite extruded strand and fivefold compared with that of the neat SEBS monofilament. The dramatic enhancement in the mechanical properties of in situ composite monofilaments is due to the formation of finer and longer TLCP fibrils (length‐to‐width ratio > 100) than those formed in the extruded strands. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 518–524, 2003
Effect of initiators and ethoxylation degree of non‐ionic emulsifiers on vinyl acetate and butyl acrylate emulsion copolymerization in the loop reactor
Authors: Sarac Ayfer , Yildirim Huseyin 
Published: August 2003

AbstractVinyl acetate and butyl acrylate copolymers were synthesized in the presence of ammonium persulfate and potassium persulfate initiators, mixture of non‐ionic and anionic emulsifiers, and polyvinyl alcohol as protective colloid in a loop reactor. The monomer ratio was chosen 85:15. The series of non‐ionic emulsifiers, which have 10–40 moles ethoxylated nonyl phenol, were combined with Nansa 66 (sodium dodecyl benzene sulfonate). The effects of the initiators on the physicochemical properties of copolymers were investigated by measuring conversion, viscosity, molecular weight, molecular weight distribution, and surface tension, respectively by using gravimetric method, Brookfield viscometer, gel permeation chromatograpy (GPC), and ring method. The effects of ethoxylation degrees of the non‐ionic emulsifiers to the same properties of copolymers were also investigated. It was determined that the copolymer viscosities showed different tendency for two initiators. They were increased by the increasing ethoxylation degree of the non‐ionic emulsifier for ammonium persulfate. In contrast, latex viscosity was decreased by increasing the ethoxylation degree in presence of potassium persulfate. Similar changes were also found in number average molecular weights of copolymers. On the other hand, weight average molecular weights of copolymers increased by increasing the ethoxylation degree of the non‐ionic emulsifier for both initiators. In the case of potassium persulfate, the surface tension values of copolymers increased by increasing the ethoxylation degree, but generally increasing the ethoxylation degree did not affect the surface tension of copolymer very seriously for two initiators. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 537–543, 2003
Anisotropic character and ultrasonic stiffness changes during the natural weathering of LDPE films
Authors: Chabira S. F. , Huchon R. , Sebaa M. 
Published: August 2003

AbstractBlown extruded polyethylene films without stabilizers have been exposed outdoors under severe weathering conditions in the Sahara. The chemical aspect of aging has been followed by IR spectroscopy. The mechanical aspect of aging has been monitored by means of a nondestructive method. It consists of measuring velocities and attenuations of ultrasonic waves propagating in several directions in the film plane. Stiffness constants and energy dissipation terms have been calculated. From the results obtained it is shown that stiffening of the material leads to an increase of velocities and a decrease of wave attenuation. Moreover, the stiffness constants as well as the energy dissipation terms vary with aging and show a changing anisotropic character of the films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 559–564, 2003
High‐Pressure Selectivity Studies—A Simple Route to a Homochiral Wistarin Precursor
Authors: Knappwost‐Gieseke Costanze , Nerenz Frank , Wartchow Rudolf , Winterfeldt Ekkehard 
Published: August 2003

AbstractThe cycloaddition of spirobutenolide 3 to the homochiral cyclopentadiene 1 at 6.5 kbar leads exclusively to cycloadduct 5. Subsequent Diels–Alder or Michael additions again favour the cyclohexenone double bond; this perfect chemo‐ regio‐ and face selectivity was employed for a short and efficient approach to the wistarin framework.
A Density Functional Study To Choose the Best Fluorophore for Photon‐Induced Electron‐Transfer (PET) Sensors
Authors: Chatterjee Abhijit , Suzuki Toshishige M. , Takahashi Yukiko , Pacheco Tanaka David A. 
Published: August 2003

AbstractAnthracenes bearing aliphatic or aromatic amino substituents, which behave as molecular sensors, have shown their potential to act as photon‐induced electron‐transfer (PET) systems. In this PET, the fluorophore moieties are responsible for electron release during protonation and deprotonation. The principle of hard and soft acids and bases (HSAB) deals with both intra‐ and intermolecular electron migration. It is possible to calculate the localized properties in terms of Fukui functions in the realm of density functional theory (DFT) and thus calculate and establish a numerical matchmaking procedure that will generate an a priori rule for choosing the fluorophore in terms of its activity. We calculated the localized properties for neutral, anionic, and cationic systems to trace the course of the efficiency. A qualitative scale is proposed in terms of the feasibility of intramolecular hydrogen bonding. To investigate the effect of the environment of the nitrogen atom on protonation going from mono‐ to diprotonated systems, we calculated the partial density of states and compared the activity sequence with reactivity indices. The results show that location of the nitrogen atom in an aromatic ring does not influence the PET, but for aliphatic chains it plays a role. Furthermore, the protonation/deprotonation scenario has been explained. The results show that the reactivity indices can be used as a suitable property for scaling the activity of fluorophore molecules for the PET process.
Why Does a Ga2 Dimer React Spontaneously with H2, but a Ga Atom Does Not?—A Detailed Quantum Chemical Investigation of the Differences in Reactivity Between Ga Atoms and Ga2 Dimers, in Combination with Experimental Results
Authors: Köhn Andreas , Himmel Hans‐Jörg , Gaertner Benjamin 
Published: August 2003

AbstractThe spontaneous and photoactivated reactions between Ga2 and H2 in a matrix of solid Ar at 12 K have been followed by using IR spectroscopy and have been shown to give access to several isomers of the subvalent hydride Ga2H2. We now present Raman spectra for this system, to complete its characterization on the basis of vibrational spectra. In addition, the differences between the reactivity of a Ga atom and a Ga2 dimer toward H2 are evaluated. The matrix isolation experiments have shown that Ga2 reacts spontaneously with H2, at 12 K, to give the cyclic subvalent hydride Ga(μ‐H)2Ga (D2h symmetry), which can be transformed into two other isomers of Ga2H2 by selective photoactivation. Interestingly, the spontaneous reaction is subject to a marked isotopic effect. In total, the experimental results provide detailed information about the reaction mechanism. In contrast to Ga2, Ga atoms do not react spontaneously with H2; on photoactivation they instead yield the radical species GaH2. The quantum chemical calculations presented herein start with an analysis of the structures and relative energies of the relevant species at the MP2 level, by using extended basis sets, and lead on to a discussion of the correlation diagrams for both reactions. Finally, CASSCF and MRCI methods, in combination with moderate‐sized basis sets, were employed to analyze in detail the mechanisms of the two reactions. It will be shown that the computational results, in concert with the experimental findings, provide a satisfying explanation of the contrasting reactivities of Ga and Ga2.
Synthesis of Hexasaccharide Fragments of Pectin
Authors: Clausen Mads H. , Madsen Robert 
Published: August 2003

AbstractShort syntheses of partially methyl‐esterified hexagalacturonates 1–5 are described as part of the development of strategies for the preparation of larger pectic oligosaccharides. The methodology is based on the repeated coupling of galactose mono‐ and disaccharide donors onto a galactose acceptor until a hexagalactan is obtained. All glycosylations are carried out with n‐pentenyl glycosides to provide good yields of the desired α anomers. Pentenyl disaccharide donors are prepared by the coupling of two pentenyl galactosides controlled by either the armed–disarmed effect or by converting one pentenyl galactoside into the corresponding galactosyl bromide or fluoride. Two orthogonal protecting groups are employed at C6, which makes it possible to oxidize these positions to either the carboxylic acid or to the methyl ester. Each hexagalactan is therefore able to bifurcate into two different hexagalacturonates with a reverse methyl‐esterification pattern. The methyl ester distribution in the hexagalacturonates is confirmed by tandem mass spectrometry.
N⋅⋅⋅Br Halogen Bonding: One‐Dimensional Infinite Chains through the Self‐Assembly of Dibromotetrafluorobenzenes with Dipyridyl Derivatives
Authors: De Santis Alessandra , Forni Alessandra , Liantonio Rosalba , Metrangolo Pierangelo , Pilati Tullio , Resnati Giuseppe 
Published: August 2003

AbstractThe N⋅⋅⋅Br halogen bonding drives the self‐assembly of 1,4‐dibromotetrafluorobenzene (1 a) and its 1,3 or 1,2 analogues (1 b,c, respectively) with dipyridyl derivatives 2 a,b. The isomeric supramolecular architectures 3 a–f are obtained as cocrystals that are stable in the air at room temperature. The solid‐state features of these 1D infinite chains 3 have been fully characterized by single‐crystal X‐ray, Raman, and IR analyses. The occurrence of N⋅⋅⋅Br halogen bonding in solution has been detected with 19F NMR spectroscopy. The N⋅⋅⋅Br halogen bonding is highly selective and directional and the geometry of the single strands of noncovalent copolymers 3 is programmed by the geometry of halogen‐bonding donor and acceptor sites on the starting modules. The composition and topology of the instructed networks can be predicted with great accuracy. Experiments of competitive cocrystal formation established the strength of the N⋅⋅⋅Br interaction relative to other halogen bondings and the ability of different modules 1 to be involved in site‐selective supramolecular syntheses.
Copper–Metallomesogen Structures Obtained by Ionic Self‐Assembly (ISA): Molecular Electromechanical Switching Driven by Cooperativity
Authors: Camerel Franck , Strauch Peter , Antonietti Markus , Faul Charl F. J. 
Published: August 2003

AbstractIn a stepwise noncovalent multiple‐interaction strategy, copper(II) salts were complexed with the sodium salts of bathophenanthrolinedisulfonic acid (BPS) and bathocuproinedisulfonic acid (BCS), and organized into nanostructured materials by the addition of ammonium surfactants by means of the ionic self‐assembly (ISA) route. In the case of the methyl‐substituted BCS complexes, a slow color change from green to brick red was observed. UV and EPR investigations showed that the color change was due to a change in oxidation state, the resulting brick red color is typical for CuI species. It is concluded that steric interactions and mechanical packing into a supramolecular structure drive this electronic transition at the metal center. When complexation is performed with double‐tail ammonium surfactants, these metallomesogenic materials exhibit thermotropic liquid‐crystalline phase behavior, as investigated by polarized light microscopy, differential scanning calorimetry (DSC), and temperature‐dependent wide‐angle and small‐angle X‐ray analyses. The complexity of the observed phases increased with increasing tail length of the surfactants. Complexation with double‐tail C18 surfactants yielded highly organized materials for both the BPS and BCS ligands.
An Efficient One‐Pot Approach to Bridged Bicyclic Ring‐Systems through Consecutive Hetero‐Domino Transformations: A Mechanistic Rationale and Further Rearrangements
Authors: Finet Laure , Candela Lena José I. , Kaoudi Talbi , Birlirakis Nicolas , Arseniyadis Siméon 
Published: August 2003

AbstractThis article describes the design of olefin‐generated/reagent‐modulated consecutive hetero‐domino reactions of 1,2‐unsaturated bicyclic diols, which are potentially of great use, initiated by PhI(OAc)2, continued by [Pb(OAc)4], and completed by use of a mild base (K2CO3). Inversion of a quaternary center has been achieved through a three‐reaction sequence: a domino transformation followed by an m‐CPBA‐mediated Baeyer–Villiger oxidation and subsequent reductive lactone ring opening.
Cover Picture: Coordination Algorithms Control Molecular Architecture: [CuI4(L2)4]4+ Grid Complex Versus [MII2(L2)2X4]y+ Side‐By‐Side Complexes (M=Mn, Co, Ni, Zn; X=Solvent or Anion) and [FeII(L2)3][Cl3FeIIIOFeIIICl3] (Chem. Eur. J. 16/2003)
Authors: Lan Yanhua , Kennepohl Dietmar K. , Moubaraki Boujemaa , Murray Keith S. , Cashion John D. , Jameson Geoffrey B. , Brooker Sally 
Published: August 2003

AbstractThe cover picture shows how differing coordination algorithms control the molecular architecture of complexes of the pyridazine‐containing, two‐armed, acyclic Schiff base ligand L2 (left, prepared from one equivalent of 3,6‐diformylpyridazine and two equivalents of d‐anisidine). Two very different complexes of L2 self‐assemble from tetrahedral copper(I) versus octahedral zinc(II), nickel(II), and cobalt(II) controlled 1 : 1 reactions with L2. In both cases the metal ions are bridged by the pyridazine moieties in L2, but in the case of the tetrahedral copper(II) the result is a tetrametallic [2×2] grid complex ([CuI4(L2)4]4+: top right), whilst in the case of the octahedral metal(II) ions dimetallic side‐by‐side complexes, [MII2(L2)2(X)4]y+ (M = Mn, Co, Ni, Zn; X = solvent or anion), are formed (bottom right). The cover image was kindly generated by M. Crawford (University of Otago) with Strata Studio Pro (Strata). More details are given by S. Brooker and co‐workers on p. 3772 ff.
No‐Barrier Theory: Calculating Rates of Chemical Reactions from Equilibrium Constants and Distortion Energies
Authors: Guthrie J. Peter 
Published: August 2003

AbstractNo‐barrier theory is a new approach to the calculation of rate constants for reactions in solution, from the corresponding equilibrium constants. It requires relatively small molecular orbital theory calculations, and has been very successful. It is in the spirit of Marcus theory, but does not require an “intrinsic barrier”. The approach is explained, with an examination of the way in which the ideas on which it is based were “in the air”.
Fluorescence Spectroscopy of Single Molecules under Ambient Conditions: Methodology and Technology
Authors: Böhmer Martin , Enderlein Jörg 
Published: August 2003

AbstractThis review presents an overview of the fluorescence detection and spectroscopy of single molecules (SMS) in liquids and on surfaces under ambient conditions. The various techniques of SMS, such as confocal epifluorescence detection and wide‐field imaging are presented and discussed, together with the different methods of data analysis such as fluorescence correlation spectroscopy and burst‐by‐burst analysis. Selected applications of the various techniques in physics, chemistry, and biology are described.