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Liquid Solution (liquid + solution)
Selected AbstractsRecent developments in modelling of liquid phase electroepitaxy under applied magnetic fieldCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005S. Dost Abstract Growth of single crystals under magnetic field is of interest for suppressing the adverse effect of natural convection and for better mixing in the liquid solution, which are the favorable conditions for prolonged growth and high quality crystals. In this short review article, recent developments in the modelling of electroepitaxy under magnetic field are presented. An application is given for the liquid phase electroepitaxial growth of GaAs bulk single crystals under a static magnetic field. Experimental results, that have shown that the growth rate under an applied static magnetic field is proportional to the applied magnetic field, and increases with the field intensity level, are predicted from the present model. The model also predicts growth interface shapes accurately. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural Changes in the BODIPY Dye PM567 Enhancing the Laser Action in Liquid and Solid Media,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007I. García-Moreno Abstract In the search for more efficient and photostable solid-state dye lasers, newly synthesized analogs of the borondipyrromethene (BODIPY) dye PM567, bearing the polymerizable methacryloyloxypropyl group at position 2 (PMoMA) or at positions 2 and 6 (PDiMA), have been studied in the form of solid copolymers with methyl methacrylate (MMA). The parent dye PM567, as well as the model analogs bearing the acetoxypropyl group in the same positions, PMoAc and PDiAc, respectively, have been also studied both in liquid solvents and in solid poly(MMA) (PMMA) solution. Although in liquid solution PMoAc and PDiAc have the same photophysical properties as PM567, PDiAc exhibited a photostability up to 10 times higher than that of PM567 in ethanol under 310,nm-irradiation. The possible stabilization factors of PDiAc have been analyzed and discussed on the basis of the redox potentials, the ability for singlet molecular oxygen [O2(1,g)] generation, the reactivity with O2(1,g), and quantum mechanical calculations. Both PMoAc and PDiAc, pumped transversally at 532,nm, lased in liquid solution with a high (up to 58,%), near solvent-independent efficiency. This enhanced photostabilization has been also observed in solid polymeric and copolymeric media. While the solid solution of the model dye PDiAc in PMMA showed a lasing efficiency of 33,%, with a decrease in the laser output of ca.,50,% after 60,000 pump pulses (10,Hz repetition rate) in the same position of the sample, the solid copolymer with the double bonded chromophore, COP(PDiMA-MMA), showed lasing efficiencies of up to 37,%, and no sign of degradation in the laser output after 100,000 similar pump pulses. Even under the more demanding repetition rate of 30,Hz, the laser emission from this material remained at 67,% of its initial laser output after 400,000 pump pulses, which is the highest laser photostability achieved to date for solid-state lasers based on organic polymeric materials doped with laser dyes. This result indicates that the double covalent linkage of the BODIPY chromophore to a PMMA polymeric matrix is even more efficient than the simple linkage, for its photostabilization under laser operation. [source] Supercritical antisolvent micronisation of synthetic all- trans -,-carotene with tetrahydrofuran as solvent and carbon dioxide as antisolventJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2009Miguel A Tavares Cardoso Abstract BACKGROUND: Supercritical antisolvent (SAS) micronisation of synthetic trans -,-carotene was studied using tetrahydrofuran (THF) as solvent and supercritical carbon dioxide (CO2) as antisolvent, with the objective of increasing its bioavailability and facilitating its dispersion in oil and emulsion formulations as a result of its smaller particle size. The micronised powder was analysed by scanning electron microscopy and high-performance liquid chromatography. Micronisation experiments were performed in order to evaluate the effects of temperature (308.15,333.15 K), pressure (6.5,13 MPa) and concentration of the liquid solution (6,9 g L,1). The effect of the supercritical CO2/THF flow ratio in the range between 4 and 44 (on a mass basis) was also analysed. Determinations of equilibrium concentrations of ,-carotene in the CO2/THF mixture were also performed. RESULTS: The particle size obtained ranged from 1 to 500 µm, with mean particle diameters around 100 µm. Three types of morphology were found in the precipitated powder: crystalline with superficial pores and leaf-like appearance; crystalline with regular shapes and blade-like edges; and crystalline without superficial pores and leaf-like apearance. The Peng,Robinson equation of state was used to calculate the density of the CO2/THF binary mixture, and the solubility of ,-carotene in this mixture was correlated with its density. CONCLUSION: The use of the SAS technique to micronise ,-carotene proved to be efficient, and the absence of degradation in the micronised powder allows the industrial application of this technique. Copyright © 2008 Society of Chemical Industry [source] Manipulation of crystal shape by cycles of growth and dissolutionAICHE JOURNAL, Issue 6 2007Ryan C. Snyder Abstract A method for the manipulation of crystal shape by using cycles of growth and dissolution is presented, representing a unique process-based solution to an important product quality concern. Using 3-D shape evolution models for faceted crystal growth and dissolution, results are reported for cycling both an illustrative crystal system, as well as a physical plate-like system. The results show that crystal shape can be manipulated by cycling when the relative growth and dissolution rates are anisotropic, which can be caused by differences in growth mechanism, asymmetry in super/undersaturation, and by the use of surface active additives. Since this method of crystal shape enhancement uses the existing liquid solution, it could be a valuable alternative to the traditional methods which often require changes in the chemical nature of the solution, for example, by changing solvent. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid systemAICHE JOURNAL, Issue 7 2006Izumi Taniguchi Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Delivery of timolol through artificial membranes and pig stratum corneumJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2003D.F. Stamatialis Abstract The in vitro passive and iontophoretic (applied current density: 0.5 mA/cm2) timolol (TM) permeability from a liquid solution through pig stratum corneum (SC) is found to be 0.9,±,0.5,×,10,6 and 3.9,±,0.9,×,10,6 cm/s, respectively. The in vitro iontophoretic TM delivery through the combination of artificial porous membranes with pig SC is investigated as well. When the meso-porous PES-30 membrane is applied, the SC mainly controls the TM delivery. When the microporous NF-PES-10 membrane is applied, both the membrane and the SC contribute to controlling the delivery of TM. When the microporous LFC 1 membrane is applied, the TM delivery is membrane controlled. In all cases, however, the efficiency of the TM delivery is low and would need to be improved for the development of a commercially viable product. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:1037,1039, 2003 [source] Ampicillin micronization by supercritical assisted atomizationJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2003E. Reverchon ABSTRACT The micronization technique called supercritical assisted atomization (SAA) was used to produce ampicillin microparticles with controlled particle size and particle size distribution suitable for aerosol drug delivery. The process is based on the solubilization of supercritical CO2 in a liquid solution. The ternary mixture is then sprayed through a nozzle and, as a consequence of enhanced atomization, solid microparticles are formed. Water and organic solvents were tested with ampicillin to determine the influence of the solvent on the process mechanism. SAA process parameters were studied by testing different supercritical/liquid solvent flow ratios, ampicillin concentrations in the liquid solution and nozzle diameters. The effect of these parameters on morphology, particle size and particle size distribution of microparticles was analysed. Ampicillin particles suitable for aerosol delivery in the size range 1,5 ,m were obtained using buffered water. Moreover, by varying the solute concentration, ampicillin particles in a narrower range (1,3 ,m) than that usually suggested for aerosol deliverable drugs were obtained. This is an example of particle size tailoring by SAA. [source] Determination of the 2,3-pentadienedioic acid enantiomer interconversion energy barrier 1.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15 2006Classical kinetic approach Abstract A classical kinetic method was used to determine the energy barrier for the interconversion of 2,3-pentadienedioic acid enantiomers. Each individual enantiomer was isolated by collecting the appropriate peaks from the HPLC enantiomeric separation, of racemic 2,3-pentadienedioic acid. The isolated enantiomers were racemized at 22°C using various interconversion times. The ratio of enantiomers in each reaction solution was determined by HPLC at 22°C. The corresponding peak areas of the enantiomers and the interconversion times obtained from the HPLC chromatograms were used to calculate both the interconversion rate constants describing (+) , (,) and (,) , (+) interconversions as well as the energy barriers. It was confirmed that the interconversion of 2,3-pentadienedioic acid enantiomers is a first-order kinetic reaction. Both semiempirical and ab initio methods were used to explore the mechanism of the interconversion of 2,3-pentadienedioic acid enantiomers, and to calculate the interconversion energy barrier. Comparison of the interconversion energy barriers found by the ab initio method (,G# = 110.7 kJ/mol) and by classical kinetics in the mobile phase solution at 22°C (,Gapp = 93.9 ± 0.2 kJ/mol) shows a difference which may be attributed to the different conditions assumed in the theoretical calculation (i. e., a gaseous state) and the actual experimental conditions (i. e., liquid solution) and a possible catalytic effect of the solution composition. [source] Conformational states of human H-Ras detected by high-field EPR, ENDOR, and 31P NMR spectroscopy ,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005Michael Spoerner Abstract Ras is a central constituent of the intracellular signal transduction that switches between its inactive state with GDP bound and its active state with GTP bound. A number of different X-ray structures are available. Different magnetic resonance techniques were used to characterise the conformational states of the protein and are summarised here. 31P NMR spectroscopy was used as probe for the environment of the phosphate groups of the bound nucleotide. It shows that in liquid solution additional conformational states in the GDP as well as in the GTP forms coexist which are not detected by X-ray crystallography. Some of them can also be detected by solid-state NMR in the micro crystalline state. EPR and ENDOR spectroscopy were used to probe the environment of the divalent metal ion (Mg2+ was replaced by Mn2+) bound to the nucleotide in the protein. Here again different states could be observed. Substitution of normal water by 17O-enriched water allowed the determination of the number of water molecules in the first coordination sphere of the metal ion. In liquid solution, they indicate again the existence of different conformational states. At low temperatures in the frozen state ENDOR spectroscopy suggests that only one state exists for the GDP- and GTP-bound form of Ras, respectively. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fullerene derivatives encapsulated in carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007W. Plank Abstract We report on the preparation and subsequent Raman analysis of carbon nanotube peapods, using the fullerene C60 and its heterofullerene derivative (C59N)2 as filling materials. The filling with (C59N)2 was done from liquid solution at room temperature and from the gas phase at elevated temperatures. The success of the encapsulation procedure is confirmed through the identification of fingerprint Raman modes and the conversion to double wall nanotubes through heating to 1250 °C. The 2D mode of double wall nanotubes made from (C59N)2 peapods is observed to be downshifted compared to the same mode in double wall nanotubes made from C60 peapods. We interpret this downshift as an evidence for the integration of the nitrogen into the lattice of the inner tube. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical Trends of Diffusion and Reaction into Tubular Nano- and Mesoporous Structures: General Physicochemical and Physicomathematical ModelingCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2008Christian Amatore Prof. Abstract A general and adaptable physicochemical model is presented to evaluate the mass transport within nanopores of mesoporous particles when the mass transport is coupled to heterogeneous kinetics occurring at active sites located onto the nanopore walls surface. The model framework encompasses almost all situations of practical interest in solutions and may be used for characterizing the kinetic rates and constants controlling the system under different sets of experimental conditions. Furthermore, it allows the delineation of simple effective parameters, which should be most useful for optimizing a given material in view of specific applications. For the sake of clarification the simplified model is presented and its results discussed by specializing it for cases where the reactions involve a simple adsorption of a target species on the nanopore immobilized sites as observed for inorganic sponges used in water decontamination. Yet it may easily be extended further to encompass a wider variety of situations where the sites immobilized onto the nanopore walls perform chemical or biochemical transformations as occur in supported catalysis in liquid solution. [source] Chemical reactions in the gas phase and in condensed matter: From wavefunctions to density operatorsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2009David A. Micha Abstract This contribution generalizes the treatment of chemical reactions in the gas phase based on the reaction channel decomposition of the wavefunction, by introducing a similar channel decomposition of the statistical density operator valid also for condensed phases such as liquid solutions and solid surfaces. Coupled equations for the channel components of the density operator are derived and a brief presentation is given of their partial Wigner transform, which leads to a general treatment for coupling quantum and classical variables. This provides a general approach for reactions involving electronically excited states in many-atom systems. It is pointed out that reactions involving coupled quantal and classical variables can be correctly described provided (a) initial conditions for trajectories are generated from quantal distributions and (b) the bundle of trajectories for the whole initial classical phase space is propagated coupled to the quantal elements of the density matrix and used in the calculation of reaction flux averages. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Effect of water treatment on analyte and matrix ion yields in matrix-assisted time-of-flight secondary ion mass spectrometry: the case of insulin in and on hydroxycinnamic acidRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2002Wilfried Szymczak A systematic study was performed to identify the origin of surprisingly high analyte-to-matrix yield ratios recently observed in time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of oligo- and polypeptides mixed in matrices of ,-cyano-4-hydroxycinnamic acid (4HCCA). Several sets of samples of porcine insulin in 4HCCA (1:3100 molar) were prepared from liquid solutions by a nebuliser technique, with more than one order of magnitude variation in sprayed material (substrate silicon). Following different periods of storage in air and/or vacuum as well as exposure to high-purity water, TOF-SIMS analysis was performed under oblique impact of 22 keV SF5+. Treatment with water involved either deposition of a droplet covering the whole sample for times between 1 and 20,min or spraying with water in droplet equivalent quantities. The analyte and matrix molecules were detected as protonated molecules (insulin also in doubly protonated form). Even the as-prepared samples usually showed insulin-to-4HCCA yield ratios exceeding the molar ratio of the mixed material. Upon ageing in vacuum the matrix ion yields remained constant but the analyte yields decreased, partly due to break-up of intrachain disulfide bonds. Water treatment resulted in a pronounced decrease in the 4HCCA yield, typically by a factor of five, in parallel with an increase of the insulin yield, by up to a factor of four. Evidence is provided that these changes occur concurrently with a partial dissolution of 4HCCA at the sample surface. The enhanced insulin yield was not correlated with the Na+ yield. The typically 20-fold increase in the insulin-to-4HCCA yield ratio, generated by water exposure of the samples, provides the explanation for the high yield ratios observed previously with water-treated samples. Spraying with water or repeated exposure to water droplets caused a pronounced degradation of the insulin parent yields in combination with an increasing appearance of signals due to the B- and A-chains of insulin. To clarify the issue of surface segregation, a few samples were prepared by spraying acetone-diluted solutions of insulin on previously deposited layers of 4HCCA. Whereas the insulin yields from as-prepared samples were rather low, the yields observed after water treatment were comparable with those observed with samples of insulin in 4HCCA. The results suggest that a large amount of insulin is present at the surface of samples prepared from liquid mixtures of insulin in 4HCCA. With both methods of sample preparation, however, high secondary ion yields of insulin were only obtained after exposure of the samples to water. The chemical changes responsible for this beneficial effect still need to be identified. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||