bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between volume expansion, solvent‐power, and precipitation in GAS processes
Authors: Striolo Alberto , Elvassore Nicola , Parton Tiziana , Bertucco Alberto
Published: April 2004

Dilute solutions of ethyl cellulose (ETC) in acetone and of poly(ethylene oxide) (PEO) in ethyl acetate, acetonitrile, ethyl acetate‐acetonitrile, and acetonitrile–water mixtures were expanded isothermally by compressed CO2. Onset precipitation pressures were visually measured through a windowed cell.

Toward a rational understanding of the molecular mechanisms involved in gas antisolvent (GAS) processes, saturated‐liquid‐phase volume expansion and solvent power were monitored by UV‐vis spectroscopy for the solvent mixtures considered in the precipitation experiments. Ferrocene absorbance and phenol blue absorption‐peak‐wavelength shifts were used as probes to assess saturated‐liquid‐phase volume expansion and solvent power, respectively.

For the first time, a correlation between a microscopic bulk property, solvent power, and the onset precipitation pressure of a solute is reported. Because of preferential interactions with the dye (hydrogen bonds), the correlation breaks down when even small amounts of water are present in the solvent mixture.

The results presented here suggest that UV‐vis spectroscopy constitutes a valuable tool for understanding some phenomena related to supercritical‐fluid technology.
Mixing of pseudoplastic fluids using helical ribbon impellers
Authors: Shekhar S. Murthy , Jayanti S.
Published: April 2004

Helical ribbon impellers are widely used in chemical and process industries for the mixing of pseudoplastic fluids of high viscosity. The design of such impellers is based on an assumed linear relation between shear rate and the rotation speed of the impeller. A number of computational fluid dynamics (CFD) simulations of the flow field have been carried to verify this hypothesis. It is shown that while the shear rate varies greatly within the mixing vessel, there does exist a linear relationship between the impeller speed and the local shear rate near the tip of the impeller. The proportionality constant Ks associated with this linear relation is found to be dependent on the geometric parameters of the system, but is largely independent of the flow behavior index. Based on these results, a new correlation, applicable to both Newtonian and power‐law fluids for power consumption, is proposed.
Microstreaming effects on particle concentration in an ultrasonic standing wave
Authors: Spengler J. F. , Coakley W. T. , Christensen K. T.
Published: April 2004

It is shown that the magnitude of Rayleigh microstreaming convective drag on microparticles in water in a 3.2‐MHz ultrasonic standing wave can be comparable to the lateral direct radiation force in the nodal plane (DRF1) and can significantly influence the microparticle aggregation. The transducer of a single half‐wavelength chamber was excited to give a single particle aggregate. The estimated sound pressure amplitude was 0.5 MPa. Particle image velocimetry (PIV) measurements gave the average microstreaming velocity in the nodal plane as 450 μm·s−1, which is comparable to the 340‐μm·s−1 value calculated from Rayleigh's theory. Movement of 25‐μm latex particles was primarily determined by DRF1, while that of smaller 1.0 μm, particles was determined by Rayleigh microstreaming. A 15‐μm latex particle velocity map, simulated from microstreaming data, the measured velocity map of 25‐μm particles, and the cube‐dependent relationship between DRF1's on particles of different sizes, was in reasonable agreement with a measured velocity map. Further evidence for the importance of microstreaming came from the result that velocities for 1‐ and 25‐μm particles were of similar magnitude, but were opposite in direction.
Analysis of boundary layer and solute transport in osmotic evaporation
Authors: Romero J. , Rios G. M. , Sanchez J. , Saavedra A.
Published: April 2004

The osmotic evaporation process (OE) is based on the transfer of solvent from a dilute solution to be concentrated to an extraction medium (for example, a highly concentrated brine) separated by a macroporous hydrophobic membrane. Mass transfer takes place in the gas phase through the membrane pores under the influence of the water activity gradient. The OE process has been analyzed before in experiments by Courel et al. in 2000 and models by Romero et al. in 2001. These previous studies take into account the effect of structural membrane parameters and working conditions of water flux performance. An algorithm has been developed to solve the system constituted of the mass‐ and heat‐transfer equations. In order to validate it more easily, the simulation was conducted for the results of pure water evaporation. This provides a lot of interesting information on transfer resistances, temperature, and concentration profiles, as well as the prediction of water flows. A work that is the logical continuation of these previous studies is proposed. First, it aims at explaining the influence of the concentration polarization that develops at the solution–membrane interface when the concentration is applied to a sucrose solution. The transfer of very dilute volatile compounds from the sweetened solution is also analyzed with a view to understanding the mechanism that controls the loss of aroma compounds during the concentration of fruit juices.
Fluid dynamic simulation of O3 decomposition in a bubbling fluidized bed
Authors: Syamlal Madhava , O'Brien Thomas J.
Published: April 2004

Recent advances in dense, multiphase, computational fluid dynamics (CFD) have allowed accurate simulation of the gas and particle motion in bubbling and circulating fluidized beds. Since fluidized‐bed reactors are used for many chemical processes, a simulation must also be able to accurately couple chemical reactions to bed hydrodynamics. The catalytic decomposition of ozone (O3) often has been used to study experimentally the contacting behavior of catalytic reactors. Simulations of laboratory‐scale experiments of premixed O3 decomposition in a bubbling fluidized bed using the multiphase CFD code MFIX were conducted. The grid‐independent results are in very good agreement with reported experimental data on total conversion over a range of fluidization velocities and initial bed heights. This confirms the ability of multiphase hydrodynamic models to capture quantitatively the effect of hydrodynamics on chemical reactions in a bubbling fluidized bed.
Observations and process parameter sensitivities in fluid‐bed granulation
Authors: Cryer S. A. , Scherer P. N.
Published: April 2004

A numerical approach using mechanistic modeling (population balance) for fluid‐bed agglomeration is documented elsewhere. Here important factors for a pilot‐scale fluid‐bed granulater as determined by a 1/2 fraction factorial statistical design of experiment (DOE), Monte Carlo analysis of the mechanistic model, and comparison of experimental observations to model predictions, are summarized. DOE results indicate sensitive primary process parameters affecting granule size include the bed bowl charge, binder spray rate, air flow rate, and input air temperature. Sensitivity analysis of model results suggest the binder spray rate accounts for approximately 65% of the predicted variance, with the next most sensitive parameter the binder droplet diameter (∼11%). Population balance modeling specifically for fluid beds, coupled with a DOE can be combined so the behavior of agglomeration of wettable powders within a fluid bed can be understood and predicted. Good agreement between experiment and simulation results is found for particles grown to sizes of industrial importance.
Scaling and intensification procedures for simulated moving‐bed systems
Authors: Kim Jeung Kun , Wankat Phillip C.
Published: April 2004

Scaling rules and intensification procedures developed for single adsorption or chromatographic columns are extended for both linear and nonlinear isotherms to simulated moving‐bed (SMB) systems. The effects of particle diameter, column length, column diameter, switching time, flow rates, mass transfer, axial dispersion, and dead volume are studied in order to design a new SMB. Changes in the pressure drop, separation, and throughput can be changed as desired. Once an original design has been developed, the scaling procedure requires only algebraic manipulation. Simulations done by Aspen Chromatography showed that the new designs were remarkably good at producing the same product purities and pressure drops as the original design. Intensification is predicted when particle diameter is decreased. The limitations of the technique are that the number of columns per zone cannot be changed, the relative velocities in each zone are fixed, and for nonlinear systems the results apply only for the same feed concentration.
Graphical and stage‐to‐stage methods for reactive distillation column design
Authors: Daza Oscar Sánchez , Pérez‐Cisneros Eduardo S. , Bek‐Pedersen Erik , Gani Rafiqul
Published: April 2004

Based on the element mass‐balance concept, three graphical methods and one stage‐to‐stage computation method for design of reactive distillation columns have been developed. The element‐based approach allows the design of reactive distillation columns by using simple tools similar to those that are typically employed for nonreactive systems. For example, simple design methods employing reactive McCabe‐Thiele‐ and reactive Ponchon‐Savarit‐type diagrams for design of reactive distillation of binary‐element systems—which may be ternary or higher in terms of mixture compounds—are presented. Also, the driving‐force approach has been extended to employ the element concept for reactive systems. For multielement systems, the design is performed by employing a stage‐to‐stage computation method. For combined reactive distillation columns, comprising both reactive and nonreactive stages, a simple design strategy is proposed, based on the stage‐to‐stage computation method considering reactive and nonreactive bubble‐point calculations. This strategy tracks the conversion or generation and temperature between the feed and the end stages of the column, and indicates when and where nonreactive stages should be added to a reactive distillation column in order to achieve the desired separation. Illustrative examples highlight the application of the design methods, as well as the verification of such designs through rigorous simulation.
Thermodynamically equivalent configurations for thermally coupled distillation
Authors: Caballero José A. , Grossmann Ignacio E.
Published: April 2004

In this work a systematic way of generating all the thermodynamically equivalent structures for a given sequence of separation task in N‐1 distillation columns (N is the number of components to be separated) is presented first. The problem is represented through a set of symbolic relations that can be written as propositional logic expressions. Alternatives from fully thermally coupled systems (only one reboiler and one condenser) to conventional columns (each column with a reboiler and a condenser), plus all the intermediate possibilities, are considered. Then all the thermodynamically equivalent structures that do not have control problems associated with the flow transfer among columns are generated. Again the problem is formulated as a set of symbolic relations written as propositional logic expressions. A formula with a detailed derivation to calculate the number of alternatives for a given sequence of tasks is also presented. Logic expressions in propositional logic form or translated into algebraic expressions in terms of binary variables can be integrated in the framework of Disjunctive Programming to extract the best solution for a given objective function. Several results are presented with systems involving mixtures of 4 and 5 components.
Integrated approach to optimization of an ultrasonic processor
Authors: Moholkar Vijayanand S. , Warmoeskerken Marijn M. C. G.
Published: April 2004

In an ultrasonic processor, the input electrical energy undergoes many transformations before getting converted into the cavitation energy, which is dissipated in the medium to bring out the physical/chemical change. An investigation of the influence of free and dissolved gas content of the system on the efficiency of this energy transformation chain is attempted. The results of the experiments reveal that the cavitation intensity produced in the medium varies significantly with the gas content of the system. A unified physical model, which combines basic theories of acoustics and bubble dynamics, has been used to explain the experimental results. An attempt has been made to establish the mechanism of the steps in the energy transformation chain, the involved physical parameters, and interrelations between them. It has been found that the influence of free and dissolved gas content of the medium on the overall energy transformation occurs through a complex inter‐dependence of several parameters. Thus, simultaneous optimization of individual steps in the energy transformation chain, with an integrated approach, is necessary for the optimization of an ultrasonic processor. The present study puts forth a simple methodology, with the gas content of the system as manipulation parameter, for this purpose.
Glucose hydrogenation in a membrane trickle‐bed reactor
Authors: Diakov Victor , Varma Arvind
Published: April 2004

The concept of membrane distributed feed to a packed‐bed reactor is applied to multiphase catalytic reaction systems. The expected benefits of this approach include enhanced reactant conversion. The concept may be applied to a wide variety of reactions conducted over trickle‐beds and is supported experimentally for the reaction of glucose hydrogenation to sorbitol.
Regular solution model for asphaltene precipitation from bitumens and solvents
Authors: Alboudwarej Hussein , Akbarzadeh Kamran , Beck James , Svrcek William Y. , Yarranton Harvey W.
Published: April 2004

A regular solution theory liquid‐liquid equilibrium model was developed to predict asphaltene precipitation from Western Canadian bitumens. The input parameters for the model are the mole fraction, molar volume, and solubility parameters for each component. Bitumens were divided into four main pseudo‐components corresponding to SARA fractions: saturates, aromatics, resins, and asphaltenes. Asphaltenes were divided into fractions of different associated molar mass based on a Schultz‐Zimm molar mass distribution. Asphaltene self‐association was accounted for through the average molar mass of the distribution. The molar volumes and solubility parameters of the pseudo‐components were calculated using solubility, density, and molar mass measurements. The model successfully predicted the effect of solvent type and associated molar mass on asphaltene precipitation for model oil and n‐alkane systems. The model also predicted the onset and amount of asphaltene precipitation from bitumens.
Gas and liquid distribution in the monolith film flow reactor
Authors: Heibel Achim K. , Vergeldt Frank J. , van As Henk , Kapteijn Freek , Moulijn Jacob , Boger Thorsten
Published: April 2004

The gas‐liquid distribution in a monolith film flow reactor is investigated in the scope of this work. Magnetic resonance imaging (MRI) and a customized liquid collection method have been successfully applied to determine the liquid distribution over the monolith cross‐section. Using a well‐positioned spray nozzle liquid distributor, very uniform distributions are found which address the needs for applications that require high single‐pass conversions. Due to the lack of radial convective flow in monoliths, the initial distribution propagates through the reactor. With a correct positioned spray nozzle distributor, a far more uniform distribution than the “natural” one for trickle beds is obtained. MRI, applied to study the local gas‐liquid distribution in a monolith channel, clearly shows the accumulation of the liquid in the corners of the individual channel with an arc‐shaped gas‐liquid interface. Differences in local liquid holdup over the channel corners were found, which is described as channel scale nonuniformities. The experimental results are in good agreement with a fundamental hydrodynamic model based on the Navier‐Stokes equations. The average liquid saturation is conveniently described with an engineering correlation βL = 6.6·(Fr/ReLs)0.46, as a function of the liquid phase Reynolds and Froude number.
Convective heat and mass transfer to a cylinder sheathed by a porous layer
Authors: Sobera Michal P. , Kleijn Chris R. , Van den Akker Harry E. A. , Brasser Paul
Published: April 2004

A systematic study of the flow, heat, and mass transfer around a cylinder sheathed by a second, porous cylinder and placed in a perpendicular turbulent air flow has been performed. The focus of the study was on applications in heat and mass transfer to a clothed human limb in outdoor conditions. Both numerical and experimental investigations have been carried out for the fluid flow. Dimensionless scaling rules have been presented for flow, heat and mass transfer as a function of the free stream Reynolds number, the Darcy number, the dimensionless air resistance of the porous layer, and the dimensionless distance between the outer and inner cylinder. The results have been compared to available data in the literature and to the present experiment. An empirical correlation, which concludes the most important results, has been proposed. The largest reduction of heat and mass transfer due to the sheath layer, compared to that for an uncovered cylinder, was found for intermediate values of the Reynolds number, the flow resistance of the sheath layer, and the thickness of the air gap between solid and sheath cylinder.
Three dimensional model of oxygen transport in a porous diffuser of a PEM fuel cell
Authors: Zhukovsky K. V.
Published: April 2004

Binary molecular diffusion and pressure‐driven fluxes of gas in porous media are studied. A 2‐dimensional model of gas transport in porous media is developed in the field of nonzero gradients of pressure and concentration. Spatial distributions of oxygen concentration and fluxes in a porous diffuser are analyzed for geometric and physical parameters of the electrode. A three‐dimensional generalization of the model is performed. Application to oxygen‐flow modeling in electrodes of polymer electrolyte fuel cells (PEFC) is discussed for two simple configurations of gas supply channels: serpentine and interdigitated. Comparison of the results obtained for the two configurations is carried out. Oxygen flux through the catalytic membrane plane is investigated for physical characteristics of gases and the diffuser, geometry of the gas supply channels, and gas pressure in them. Recommendations for an optimal pressure regime for the specific geometry of the system and its physical characteristics are given.
Effects of fractal trajectory on gas diffusion in porous media
Authors: Zhang Baoquan , Liu Xiufeng
Published: April 2004

A mathematical model was developed to represent the effect of tortuous trajectory and irregular step length on gas diffusion in porous media, and then it was conformed by analyzing the experimentally determined flux with respect to 19 groups of binary gas mixtures in a porous catalyst pellet. Based on the analysis of actual diffusing distance within porous media, the diffusing trajectory of gas molecules was characterized into fractal curves, leading to a novel flux equation of binary gas mixtures. The established model represented the tortuous structure by the only model parameter the fractal dimension of diffusion trajectories dF. A yardstick was devised to account for the influence of pore size, diffusing species, temperature and pressure on the trajectory length of gas diffusion. The size of the yardstick δ could be found after diffusing species, temperature and pressure were specified for a given porous medium. The fitting between the experimentally determined flux and the model equation resulted in a fractal dimension of 1.102. It was evident that the model prediction was in fairly good agreement between the experimental results in the literature and those of the study, and the irregular degree of diffusing trajectory is much less than that of the pore surface. Detailed comparison with the traditional treatment by the tortuosity factor demonstrated that the methodology established here would be especially significant for very tortuous pore systems.
Particle‐size distribution effects in batch adsorption
Authors: Carta Giorgio , Ubiera Antonio
Published: April 2004

Mathematical models for pore‐diffusion‐controlled batch adsorption that take an arbitrary distribution of particle sizes into account are developed and solved for two extreme cases: the linear isotherm case and the irreversible isotherm case. Numerical calculations based on these solutions show that the effects of the particle‐size distribution (PSD) are significant, even for relatively narrow and symmetrical PSDs. The uptake rate is faster initially and slower as equilibrium is approached than is predicted using the volume‐average particle radius. These results are confirmed by comparing model predictions with experimental results obtained for the batch uptake of the protein α‐chymotrypsinogen on SP‐Sepharose‐FF. Although the PSD of this commonly used commercial medium for preparative protein chromatography is fairly narrow, significant effects are observed in both shallow‐bed and stirred batch‐uptake experiments. As a result, the PSD needs to be taken into account when precise predictions are desired, such as when batch‐uptake experiments are used for diffusivity measurements. The PSD also affects the shape of the breakthrough curve in packed beds. The effects are somewhat less pronounced, but still quite significant for the irreversible isotherm case.
Optimal solvent design for batch separation based on economic performance
Authors: Giovanoglou Apostolos , Barlatier Julie , Adjiman Claire S. , Pistikopoulos Efstratios N. , Cordiner Joan L.
Published: April 2004

A mixed‐integer dynamic optimization (MIDO) framework for solvent design in batch processes is presented. Performance measures reflecting process economics and computed on the basis of process dynamics are used to validate candidate solvent structures built from the UNIFAC molecular groups. These define the discrete space in the overall material formulation and are combined according to molecular design feasibility rules to guarantee realistic molecular representations. The algorithm is based on the decomposition of the MIDO primal subproblem into several steps that are solved successively. This allows unsuitable solvents to be detected and discarded quickly and without significant computational cost. Emphasis is placed on problem formulation in order to match accuracy of process model and physical property predictions. The algorithm is applied successfully to an industrial case study dealing with a three‐phase dehydration column and a decantation unit for solvent recovery. The proposed algorithm can be regarded as a promising initial step toward an integrated and simultaneous methodology for material process design in batch separation systems.
Steady‐state process optimization with guaranteed robust stability and feasibility
Authors: Mönnigmann M. , Marquardt W.
Published: April 2004

A new approach is presented to the optimization based design of continuous processes in the presence of parametric uncertainty. In contrast to previous works focusing on process feasibility, it allows to consider both feasibility and stability of the process in the presence of parametric uncertainty. The new approach, therefore, permits an integrated treatment of steady‐state flexibility and robust stability in the optimization of continuous processes. The process optimization problem is extended by constraints that ensure a lower bound on the distance of the nominal point of operation to stability and feasibility boundaries in the space of the uncertain parameters. While previous approaches are based on evaluating constraint violation in the range space of the constraints, the measure for flexibility and robustness used here is given in the domain space of the uncertain parameters. The method is discussed in the context of existing approaches to flexibility in process optimization and is illustrated with a continuous polymerization which is known to have a nontrivial stability boundary resulting from multiple steady states and sustained oscillations.
Hybrid approach to modeling an industrial polyethylene process
Authors: Hinchliffe Mark , Montague Gary , Willis Mark , Burke Annette
Published: April 2004

A hybrid model of a polyethylene production process is developed. The mechanistic model utilizes fundamental material and energy balances to predict important process conditions, such as the reactor temperatures, conversions, and the molecular‐weight distribution (MWD) of the polymer. Using plant data, it is shown that accurate MWD predictions are not obtained from the mechanistic model alone, despite efforts to accurately model the system and improve the accuracy of the input data. Because an accurate prediction of the MWD is required to predict end‐use properties, a hybrid model was developed by adding an empirical layer to the mechanistic model. The empirical layer was developed by using an optimization algorithm to adjust the predicted MWD by manipulating multipliers of the key descriptors (states or functions of states) of the distribution. These multipliers were then predicted from plant data using feedforward artificial neural networks (FANNs). They are then combined with the mechanistic model to allow accurate MWD prediction.
Design and optimization of free‐fall electrostatic separators for plastics recycling
Authors: Wei Jing , Realff Matthew J.
Published: April 2004

Electrostatic separation is a promising technique for separating a mix of plastics, which can acquire different sign charges through triboelectrification. A particular application of growing importance is the separation of plastics with overlapping densities from a waste stream of electronic products. Particle charging, which plays an important role in separation efficiency, has been the topic of much research. However, no systematic method has been proposed for design and optimization of the separation process itself, a gap that this research seeks to fill. The aim is to compare several design options for free‐fall electrostatic separators, taking into account the distribution of the particle charge and initial position. Particle trajectory and recovery models are derived under a set of simplifying assumptions that are carefully analyzed. Optimization models are developed that trade off the strength of the electric field with the size and number of stages of the free‐fall separator. Several different configurations are optimized and compared under various conditions (mean value and standard deviation of particle charges, feed rate, and product prices). Finally, a general guide is proposed for selecting an appropriate design.
Integrated nonlinear optimization of bioprocesses via linear programming
Authors: Vera Julio , Torres Néstor V. , Moles Carmen G. , Banga Julio
Published: April 2004

The problem of integrated design and control of bioprocess plants is considered. A previously presented optimization approach for biochemical systems based on linear programming and modeling using the power law formalism (the Indirect Optimization Method, IOM) is extended. This method is enhanced in order to take into account both static and dynamic measures, and its use for the optimization of the integrated design of a bioprocess is illustrated. The chosen case study is a wastewater treatment plant, a bioprocess which typically presents controllability problems in real practice due to bad design methodologies. After defining an objective function reflecting both investment costs and “paracosts” (such as stability, flexibility, and controllability), a set of constraints determined by the system components and technical and economical factors is defined. A comparison of the results obtained with this new method and with a global optimization method reveals that, in both cases, significant improvements in both controllability and cost reduction are achieved, although the global method yields somewhat better improvements. The advantages and limitations of both methods are evaluated, concluding that the IOM, through its incorporation to a dynamic process simulator, can be successfully used to obtain, in a quick, inexpensive and interactive way, near‐optimal integrated designs for bioprocess plants.
Modeling of hydrogenation of maleic acid in a bubble‐column slurry reactor
Authors: Thakar Nakul N. , Jaganathan Rengaswamy , Chaudhari Raghunath V. , Mills Patrick L.
Published: April 2004

A bubble‐column slurry‐reactor model has been developed for the hydrogenation of aqueous maleic acid (MAC) to tetrahydrofuran (THF). This particular reaction system has recent commercial relevance and represents a case where complex multistep catalytic hydrogenation reactions are conducted at high pressure (>15 MPa) and high temperature (>240°C). It also has additional complexities associated with the reaction chemistry, since the THF reaction product is volatile and the reaction is highly exothermic. The proposed model is derived using the mixing cell approach and incorporates the contributions of gas–liquid and liquid–solid mass transfer, intraparticle diffusion effects, product volatility, heat effects, and complex multistep reaction kinetics. The effect of gas and liquid velocities, catalyst loading, inlet maleic acid concentration, and temperature on the conversion, selectivity, temperature rise, and productivity of the desired products (THF and γ‐butyrolactone (GBL)) is also discussed. Since the reaction step involving the hydrogenation of GBL to THF is relatively slow, severe operating conditions are necessary to achieve high THF selectivity. The distribution pattern of THF in the gas and liquid phases is also discussed. The model proposed could be useful for simulation of existing pilot‐ or industrial‐scale reactors, as well as the design and scale‐up of new reactors for this particular reaction or one that has similar characteristics.
Titelbild: Triple Bond to Lead: Synthesis and Characterization of the Plumbylidyne Complex trans‐[Br(PMe3)4MoPbC6H3‐2,6‐Trip2] (Angew. Chem. 17/2004)
Authors: Filippou Alexander C. , Rohde Holger , Schnakenburg Gregor
Published: April 2004

Die Molybdän‐Blei‐Dreifachbindung im abgebildeten Plumbylidin‐Komplex ist die erste Dreifachbindung zu einem Hauptgruppenelement der 6. Periode. Der kleine Mo‐Pb‐Abstand und die lineare Koordination am Bleiatom sind deutlich erkennbar. Quantenchemische Analysen mithilfe der Elektronenlokalisierungsfunktion (Spiegelung auf der Wasseroberfläche) belegen die elektronische Analogie des Plumbylidin‐Komplexes zu Fischer‐Carbin‐Komplexen. Mehr dazu erfahren Sie in der Zuschrift von A. C. Filippou et al. auf S. 2293 ff.
Beyond Thermodynamic Acidity: A Perspective on the Complex‐Induced Proximity Effect (CIPE) in Deprotonation Reactions
Authors: Whisler Marna C. , MacNeil Stephen , Snieckus Victor , Beak Peter
Published: April 2004

The concept of the complex‐induced proximity effect (CIPE) in deprotonations is helpful in elucidating the mechanisms involved in carbanion chemistry and in planning organic syntheses. In this Review, the consequences of complexation of organolithium bases to functional groups of the substrates before the proton‐transfer step are discussed. Experimental data from kinetic measurements and isotope‐labeling experiments as well as the results of calculations in many cases point to a prelithiation complex as a reaction intermediate. Some examples from natural products synthesis illustrate how this concept can be used to obtain intermediates in a regio‐ or stereoselective manner. Of particular interest is the functionalization of positions that are remote from the coordination group.
Cover Picture: Triple Bond to Lead: Synthesis and Characterization of the Plumbylidyne Complex trans‐[Br(PMe3)4MoPbC6H3‐2,6‐Trip2] (Angew. Chem. Int. Ed. 17/2004)
Authors: Filippou Alexander C. , Rohde Holger , Schnakenburg Gregor
Published: April 2004

The molybdenum–lead triple bond in the plumbylidyne complex shown is the first triple bond to a main‐group element of the sixth period. The small Mo–Pb bond and a linear coordination to the Pb atom are evident in the structure. Quantum‐chemical analysis with the electron localization function (reflected on the water) shows the electronic analogy between the plumbylidyne complex and Fischer carbene complexes. More about this can be found in the Communication by A. C. Filippou et al. on page 2243 ff.
Compatibilization of polypropylene/nylon 6 blends with a polypropylene solid‐phase graft
Authors: Li Duxin , Jia Demin , Zhou Ping
Published: April 2004

The compatibilization of polypropylene (PP)/nylon 6 (PA6) blends with a new PP solid‐phase graft copolymer (gPP) was systematically studied. gPP improved the compatibility of PP/PA6 blends efficiently. Because of the reaction between the reactive groups of gPP and the NH2 end groups of PA6, a PP‐g‐PA6 copolymer was formed as a compatibilizer in the vicinity of the interfaces during the melting extrusion of gPP and PA6. The tensile strength and impact strength of the compatibilized PP/PA6 blends obviously increased in comparison with those of the PP/PA6 mechanical blends, and the amount of gPP and the content of the third monomer during the preparation of gPP affected the mechanical properties of the compatibilized blends. Scanning electron microscopy and transmission electron microscopy indicated that the particle sizes of the dispersed phases of the compatibilized PP/PA6 blends became smaller and that the interfaces became more indistinct in comparison with the mechanical blends. The microcrystal size of PA6 and the crystallinity of the two components of the PP/PA6 blends decreased after compatibilization with gPP. The compatibilized PP/PA6 blends possessed higher pseudoplasticity, melt viscosity, and flow activation energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 420–427, 2004
Factorial experimental design for grafting of vinyl monomers onto natural rubber latex
Authors: Arayapranee W. , Rempel G. L.
Published: April 2004

Graft copolymerization of styrene (St) and methyl methacrylate (MMA) in the presence of natural rubber latex using cumene hydroperoxide/tetraethylenepentamine redox initiator system was prepared at various process variables. The synthesized graft copolymers were purified and then characterized by Fourier transformed infrared spectroscopy analysis. A full 24 factorial experimental design was applied to study the effect of various process variables on grafting efficiency. The following four independent variables considered to be mainly affecting the grafting efficiency were reaction temperature, rubber‐to‐monomer ratio, St‐to‐MMA ratio, and initiator amount used in the secondary polymerization. It was shown in this study that the reaction temperature significantly influenced the grafting efficiency, increasing as the temperature was increased. The amount of grafting increased with increasing rubber‐to‐monomer ratio and St‐to‐MMA ratio, whereas the amount of grafting decreased with increasing amount of initiator. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 455–463, 2004
Effect of polymer density on polyethylene hollow fiber membrane formation via thermally induced phase separation
Authors: Matsuyama Hideto , Hayashi Kentarou , Maki Taisuke , Teramoto Masaaki , Kubota Noboru
Published: April 2004

Microporous high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004
Metabolism of eupatilin in rats using liquid chromatography/electrospray mass spectrometry
Authors: Ji Hye Young , Lee Hye Won , Shim Hyun Joo , Kim Soon Hoe , Kim Won Bae , Lee Hye Suk
Published: April 2004

Eupatilin (5,7‐dihydroxy‐3′,4′,6‐trimethoxyﬂavone) is an active ingredient of an ethanol extract of Artemisia asiatica (DA‐9601) that is used in the treatment of gastritis. In vitro and in vivo metabolism of eupatilin in the rats has been studied by LC‐electrospray mass spectrometry. Rat liver microsomal incubation of eupatilin in the presence of NADPH and UDPGA resulted in the formation of four metabolites (M1–M4). M1, M2, M3 and M4 were tentatively identiﬁed as 3′‐ or 4′‐O‐demethyl‐eupatilin glucuronide, eupatilin glucuronide, 6‐O‐demethyleupatilin and 3′‐ or 4′‐O‐demethyl‐eupatilin, respectively. Those metabolites from in vitro study were also characterized in bile, plasma or urine samples after an intravenous administration of eupatilin to rats. In rat bile, plasma and urine samples, eupatilin glucuronide (M2) was a major metabolite, whereas M3, M4 and M4 glucuronide (M1) were the minor metabolites. Copyright © 2004 John Wiley & Sons, Ltd.
Simultaneous determination of matrine, sophoridine and oxymatrine in Sophora Flavescens Ait. by high performance liquid chromatography
Authors: Li Ke , Wang Huajuan
Published: April 2004

Following a detailed study, a reversed‐phase high performance liquid chromatographic method (HPLC) has been developed and validated for analysis of three bioactive alkaloids, matrine, sophoridine and oxymatrine, in Sophora ﬂavescens Ait. HPLC separation of the alkaloids was performed on a Kromasil C18 column and detected by ultraviolet absorbance at 208 nm. The column temperature was maintained at 40°C. A mobile phase composed of 0.01 mol/L KH2PO4 buffer–methanol–triethylamine in the ratios 94:6:0.01 (v/v) was found to be the most suitable for this separation at a ﬂow‐rate of 1.0 mL/min and enabled the baseline separation of the three analytes free from interferences with isocratic elution. The analysis time was 24 min per injection. The calibration was linear in the range of 0.2–120.0 µg/mL for matrine, 0.2–115.2 µg/mL for sophoridine and 0.2–110.4 µg/mL for oxymatrine, respectively. For assaying Sophora Flavescens Ait. samples, the relative standard deviations were 2.0% for matrine, 2.8% for sophoridine and 1.8% for oxymatrine analysis. The average recoveries of matrine, sophoridine and oxymatrine were 93.9, 95.3 and 93.5% for the Sophora ﬂavescens Ait. samples, respectively. The method has been successfully applied to the simultaneous determination of matrine, sophoridine and oxymatrine in Sophora Flavescens Ait. samples collected in different habitats. Copyright © 2003 John Wiley & Sons, Ltd.
Effects of protein kinase C on M‐phase promoting factor in early development of fertilized mouse eggs
Authors: Yu Bing‐zhi , Zheng Jie , Yu Ai‐ming , Shi Xiu‐yan , Liu Ying , Wu Di‐di , Fu Wei , Yang Jianing
Published: April 2004

The mechanism of development of mouse fertilized eggs from the one‐cell stage to the two‐cell stage remains unclear to date. In the present study, we have evaluated protein kinase C (PKC) and M‐phase promoting factor (MPF) kinase activity in fertilized mouse eggs treated with a PKC modulator. PKC and MPF activity have similar activity. The two subunits of MPF, p34cdc2 and cyclin B, were shown to be included in the substrates phosphorylated by PKC in fertilized mouse eggs, while PKC modulator affected the electrophoretic mobility shift of cdc2 and cdc25C by dephosphorylation and phosphorylation. These results clearly indicate that PKC may affect the progression of the cell cycle through post‐translational modification of MPF activity. Copyright © 2004 John Wiley & Sons, Ltd.
Genetic instability of RBM5/LUCA‐15/H37 in MCF‐7 breast carcinoma sublines may affect susceptibility to apoptosis
Authors: Rintala‐Maki Nina D. , Abrasonis Virginia , Burd Maureen , Sutherland Leslie C.
Published: April 2004

The MCF‐7 human breast carcinoma cell line is widely used as a model system by breast cancer researchers and cell bio logists investigating apoptosis. Since its establishment 30 years ago, from a patient with metastatic breast cancer, the original MCF‐7 cell population has undergone genetic drift to such an extent that numerous genetically diverse sublines now exist. For instance, it has been reported that MCF‐7 cells have lost the region 3p21.3, to which the apoptosis regulatory protein and putative tumour suppressor LUCA‐15 (also called RBM5 and H37) maps; however, LUCA‐15 has been cloned from MCF‐7 cells, and LUCA‐15 expression analyses have been conducted using MCF‐7 cells. To address this discrepancy, we character ized three MCF‐7 sublines by Western blot, RT‐PCR and finally genomic PCR analysis, and determined that one of the three had lost the LUCA‐15 gene. Interestingly, loss of LUCA‐15 was positively correlated with decreased susceptibility to the death‐inducing ligand TNF‐α. Subsequent overexpression of exogenous LUCA‐15 was shown to enhance TNF‐α‐mediated apoptosis, suggesting that LUCA‐15 may play a role in regulating the susceptibility of breast cancer cells to drug‐induced apoptosis. These results not only reinforce the necessity of MCF‐7 subline characterization, but provide the first evidence of an apoptotic modulatory role for LUCA‐15 in a non‐T cell line. Copyright © 2004 John Wiley & Sons, Ltd.
Anion Complexation by Glycocluster Thioureamethyl Cavitands: Novel ESI‐MS‐Based Methods for the Determination of Ka Values
Authors: Oshovsky Gennady V. , Verboom Willem , Fokkens Roel H. , Reinhoudt David N.
Published: April 2004

A series of saccharide‐thiourea functionalized cavitands was prepared in good yields (72–86 %) by reaction of a tetrakis(aminomethyl) cavitand with the thiocyanate derivatives of acetylated glucose, galactose, and cellobiose. The anion complexation behavior of the acetylated and deacetylated glycocluster thioureamethyl cavitands was studied with electrospray ionization mass spectrometry (ESI‐MS) in acetonitrile and in a 1:1 acetonitrile/water mixture, respectively. All compounds show a preference for Cl−. A linear relationship was found between the square root of the intensity and the concentration of the formed host–guest complex. Based on this relationship, novel methods have been developed to determine Ka values, by means of direct titration and competition experiments.
Psychological adjustment and sleep quality in a randomized trial of the effects of a Tibetan yoga intervention in patients with lymphoma
Authors: Cohen Lorenzo , Warneke Carla , Fouladi Rachel T. , Rodriguez M. Alma , Chaoul‐Reich Alejandro
Published: April 2004

BACKGROUND

Research suggests that stress‐reduction programs tailored to the cancer setting help patients cope with the effects of treatment and improve their quality of life. Yoga, an ancient Eastern science, incorporates stress‐reduction techniques that include regulated breathing, visual imagery, and meditation as well as various postures. The authors examined the effects of the Tibetan yoga (TY) practices of Tsa lung and Trul khor, which incorporate controlled breathing and visualization, mindfulness techniques, and low‐impact postures in patients with lymphoma.

METHODS

Thirty‐nine patients with lymphoma who were undergoing treatment or who had concluded treatment within the past 12 months were assigned to a TY group or to a wait‐list control group. Patients in the TY group participated in 7 weekly yoga sessions, and patients in the wait‐list control group were free to participate in the TY program after the 3‐month follow‐up assessment.

RESULTS

Eighty nine percent of TY participants completed at least 2–3 three yoga sessions, and 58% completed at least 5 sessions. Patients in the TY group reported significantly lower sleep disturbance scores during follow‐up compared with patients in the wait‐list control group (5.8 vs. 8.1; P < 0.004). This included better subjective sleep quality (P < 0.02), faster sleep latency (P < 0.01), longer sleep duration (P < 0.03), and less use of sleep medications (P < 0.02). There were no significant differences between groups in terms of intrusion or avoidance, state anxiety, depression, or fatigue.

CONCLUSIONS

The participation rates suggested that a TY program is feasible for patients with cancer and that such a program significantly improves sleep‐related outcomes. However, there were no significant differences between groups for the other outcomes. Cancer 2004. © 2004 American Cancer Society.
Low‐dose weekly paclitaxel for recurrent or refractory aggressive non‐Hodgkin lymphoma
Authors: Rizzieri David A. , Sand Gregory J. , McGaughey Dean , Moore Joseph O. , DeCastro Carlos , Chao Nelson J. , Vredenburgh James J. , Gasparetto Cristina , Long Gwynn D. , Anderson Elizabeth , Foster Tracy , Toaso Bonnie , Adams Donna , Niedzwiecki Donna , Gockerman Jon P.
Published: April 2004

BACKGROUND

Many patients with recurrent, intermediate or high‐grade non‐Hodgkin lymphoma (NHL) may not respond to or are not candidates for aggressive salvage chemotherapy. Effective, less toxic regimens are needed. Although high‐dose taxanes have not been reported to be very effective for the treatment of lymphoma, different delivery rates may allow for different mechanisms of action to be manifest and result in a different toxicity profile and response rate. The current study tested this hypothesis by using low‐dose, weekly paclitaxel in patients with recurrent or refractory NHL.

METHODS

Adults age > 18 years with refractory or recurrent, aggressive NHL who were not considered curable with standard high‐dose therapy received paclitaxel at a dose of 80 mg/m2 weekly for 5 weeks for 2 cycles.

RESULTS

Thirty‐four patients with refractory NHL and 4 patients with recurrent disease were treated. Approximately 45% of the patients had achieved a prior disease remission. The median number of prior regimens received was 3, 74% of the patients had an International Prognostic Index of ≥ 3 at the time of study entry, and 29% had failed high‐dose therapy with autologous hematopoietic support. Only one patient encountered severe toxicity (sepsis). Myelosuppression was reported to occur in approximately 20% of patients. A total of 10 patients (26%) achieved a complete disease response and 4 patients (11%) achieved a partial response.

CONCLUSIONS

In the current study, low‐dose, weekly paclitaxel therapy was found to provide a well tolerated and less toxic approach to the treatment of refractory NHL, with encouraging responses noted in heavily pretreated patients. However, evaluation in patients with an earlier stage of disease is warranted. Cancer 2004. © 2004 American Cancer Society.