Home About us Contact
|
Home About us Contact | ||
|
|
||
Solvent Mixtures (solvent + mixture)
Kinds of Solvent Mixtures Selected AbstractsApplication of QSPR to Binary Polymer/Solvent Mixtures: Prediction of Flory-Huggins ParametersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008Jie Xu Abstract A QSPR study was performed for the prediction of the Flory-Huggins parameters of binary polymer/solvent mixtures. 1,664 descriptors for each polymer and solvent were checked and a cubic multivariable model, with R2,=,0.9638 and s,=,0.146, was produced by using genetic algorithms on a training set of 52 mixtures. The reliability of the proposed model was further validated by satisfactory statistical parameters being obtained using an external test set (,=,0.9565). All descriptors involved in the model can be derived solely from the chemical structures of the polymers and the solvents, which makes it very useful in predicting the Flory-Huggins parameters of unknown or unavailable polymer/solvent mixtures. [source] Organic Single Crystals: Azeotropic Binary Solvent Mixtures for Preparation of Organic Single Crystals (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Mater. The inside cover of this issue illustrates the solution-phase self-assembly of organic single crystals by using azeotropic binary solvent mixtures, described by X. Li et al. on page 3610, and is a snap-shot taken during the self-assembly of tri-isopropylsilylethynyl pentacene single crystals from an azeotropic binary solvent mixture of isopropanol plus toluene, on a silicon substrate. These needle-like crystals were growing with time while floating in the bulk of the solution during solvent evaporation, with bright colors showing their birefringence. [source] Azeotropic Binary Solvent Mixtures for Preparation of Organic Single CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Xiaoran Li Abstract Here, a new approach is introduced to prepare large single crystals of ,-conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri-isopropylsilylethynyl pentacene (TIPS-PEN) with dimensions up to millimeters are facilely self-assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin-films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H-aggregation and promotes an efficient self-assembly of TIPS-PEN is explained. The charge-carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin-films to large single crystals used as active layer in field-effect transistors. Additionally, this approach is extended to other ,,, stacked organic molecules to elucidate its broad applicability. [source] Effects of Solvent Mixtures on the Nanoscale Phase Separation in Polymer Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Yan Yao Abstract The mixed solvent approach has been demonstrated as a promising method to modify nanomorphology in polymer solar cells. This work aims to understand the unique role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non-equilibrium spin-coating process. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology with the additive. Supported by AFM, TEM and XPS results, we proposed a model and identified relevant parameters for the additive such as solubility and vapor pressures. Other additives are discovered to show the ability to improve polymer solar cell performance as well. [source] Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1,g)) Production by 9H -Fluoren-9-one: Solvents and Solvent MixturesHELVETICA CHIMICA ACTA, Issue 2 2003Claudia We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1,g), denoted as 1O2) by 9H -fluoren-9-one (FLU). The normalized empirical parameter E derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production (,,) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (,ISC). Values of ,, of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ,ISC and, therefore, ,, decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ,, to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ,, upon addition of increasing amounts of the latter. [source] Selective Guest Uptake from Solvent Mixtures in the Clathrate Phase of Syndiotactic PolystyreneMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2004Yukihiro Uda Abstract Summary: Selective absorption uptake during the guest-exchange processes in the , form of syndiotactic polystyrene (sPS) was confirmed by IR spectroscopy. When films of the , form were immersed in hexane/decane or chloroform/decane mixtures, decane molecules were incorporated preferentially in the , form. Sorbate uptake by the , form was greatly accelerated when the sorbate was mixed with a solvent penetrable to the amorphous region of sPS. Concentration changes in a , -form film during sorption processes: sorption of a chloroform(D)/decane(H) mixture (1:1 molar ratio). [source] ChemInform Abstract: Copper-Free Sonogashira Coupling in Amine,Water Solvent Mixtures.CHEMINFORM, Issue 13 2009Anna Komaromi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Application of QSPR to Binary Polymer/Solvent Mixtures: Prediction of Flory-Huggins ParametersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008Jie Xu Abstract A QSPR study was performed for the prediction of the Flory-Huggins parameters of binary polymer/solvent mixtures. 1,664 descriptors for each polymer and solvent were checked and a cubic multivariable model, with R2,=,0.9638 and s,=,0.146, was produced by using genetic algorithms on a training set of 52 mixtures. The reliability of the proposed model was further validated by satisfactory statistical parameters being obtained using an external test set (,=,0.9565). All descriptors involved in the model can be derived solely from the chemical structures of the polymers and the solvents, which makes it very useful in predicting the Flory-Huggins parameters of unknown or unavailable polymer/solvent mixtures. [source] Determination of nucleation parameters and the solid liquid interfacial energy of the KCl-ethanol-water systemCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007Waid Omar Abstract The kinetic parameters of homogeneous nucleation of KCl in different ethanol-water solvent mixtures were determined at 25°C from the experimental measurements of the width of the metastable zone at different cooling rates. The ethanol mass ratio in the ethanol water solvent mixture was varied from 0-0.9 and the metastable zone width for each solvent mixture was measured under the cooling rates of 10, 20 and 30 K/h. The influence of ethanol ratio on the activity coefficient was calculated. It was found that increasing the ethanol ratio in the solvent mixture leads to an increase in the mean molal activity coefficient. The experimental results obtained showed that the increase in the ethanol ratio in the solvent widens the metastable zone for the crystallization of KCl. Also it has inferred from the calculations based on the classical nucleation theory that increasing of the ethanol ratio in the solvent mixture resulted in an increase of the nucleation rate order, increase of the critical size of nuclei and increase of the solid liquid interfacial energy. It has been found that the solid liquid interfacial energy can be good correlated with inversely proportionality to the solubility. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] NMR investigations of subunit c of the ATP synthase from Propionigenium modestum in chloroform/methanol/water (4 : 4 : 1)FEBS JOURNAL, Issue 7 2002Ulrich Matthey The subunit c from the ATP synthase of Propionigenium modestum was studied by NMR in chloroform/methanol/water (4 : 4 : 1). In this solvent, subunit c consists of two helical segments, comprised of residues L5 to I26 and G29 to N82, respectively. On comparing the secondary structure of subunit c from P. modestum in the organic solvent mixture with that in dodecylsulfate micelles several deviations became apparent: in the organic solvent, the interruption of the ,,helical structure within the conserved GXGXGXGX motif was shortened from five to two residues, the prominent interruption of the ,,helical structure in the cystoplasmic loop region was not apparent, and neither was there a break in the ,,helix after the sodium ion-binding Glu65 residue. The folding of subunit c of P. modestum in the organic solvent also deviated from that of Escherichia coli in the same environment, the most important difference being that subunit c of P. modestum did not adopt a stable hairpin structure like subunit c of E. coli. [source] Organic Single Crystals: Azeotropic Binary Solvent Mixtures for Preparation of Organic Single Crystals (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Mater. The inside cover of this issue illustrates the solution-phase self-assembly of organic single crystals by using azeotropic binary solvent mixtures, described by X. Li et al. on page 3610, and is a snap-shot taken during the self-assembly of tri-isopropylsilylethynyl pentacene single crystals from an azeotropic binary solvent mixture of isopropanol plus toluene, on a silicon substrate. These needle-like crystals were growing with time while floating in the bulk of the solution during solvent evaporation, with bright colors showing their birefringence. [source] Electrosprayed polymer particles: Effect of the solvent propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Chul Ho Park Abstract Electrospraying technology has been studied in many fields to produce particles of various substances from nanoscale to microscale sizes. Unlike pure liquids, droplets formed by electrospraying that are comprised of polymer solutions undergo additional solidification processes involving solvent evaporation, which primarily determine the particle size and morphology. Herein, the effects of the solvent properties on the morphology and dimensions of solidified particles were systematically studied. In general, the size of the solidified spherical particles with smooth surfaces reflected that of the initially formed liquid droplets, which could partially be estimated by theoretical equations developed for pure liquids. Particle sizes increased with an increase in polymer content and a decrease in the boiling point of the volatile solvent. Inhomogeneous drying processes related to phase separation or skin formation resulted in hollow, cuplike, and porous particle structures, with particle sizes and morphologies that were outside of the scope of the theoretical treatments. The selection of a proper solvent or solvent mixture seemed to be a convenient way to control the particle morphologies, such as hollow, cuplike, or porous structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Solution conformation of a tetradecapeptide stabilized by two di- n -propyl glycine residuesJOURNAL OF PEPTIDE SCIENCE, Issue 8 2010Vijayalekshmi Sarojini Abstract The solution conformation of a designed tetradecapeptide Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (Dpg-14) containing two di- n -propyl glycine (Dpg) residues has been investigated by 1H NMR and circular dichroism in organic solvents. The peptide aggregates formed at a concentration of 3 mM in the apolar solvent CDCl3 were broken by the addition of 12% v/v of the more polar solvent DMSO-d6. Successive NiH Ni+1H NOEs observed over the entire length of the sequence in this solvent mixture together with the observation of several characteristic medium-range NOEs support a major population of continuous helical conformations for Dpg-14. Majority of the observed coupling constants () also support , values in the helical conformation. Circular dichroism spectra recorded in methanol and propan-2-ol give further support in favor of helical conformation for Dpg-14 and the stability of the helix at higher temperature. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. [source] Ethyl-paraben and nicotinamide mixtures: Apparent solubility, thermal behavior and X-ray structure of the 1:1 co-crystal,JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2008S. Nicoli Abstract This work aims at investigating the nicotinamide (NA),ethyl-paraben (EP) binary system both in solution and in the solid state. In particular, the apparent EP solubility in water was studied in the presence of different NA concentrations (between 0.28 and 1.64 M). It was found that the apparent EP solubility increase (nearly twofold) observed at the highest NA concentration tested can be ascribed to a change in the polarity of the solvent mixture, rather than to a direct effect of NA on EP. The effect of fusion and re-crystallization from water or ethanol solutions on EP and NA mixtures was investigated by means of differential scanning calorimetry, elemental analysis and X-ray diffraction both on powder and single crystal. It was discovered that EP and NA form a co-crystal having a 1:1 molar composition that can be easily crystallized from ethanol. Single crystal X-ray analysis of this species revealed that the NA and EP molecules form corrugated layers within which the two components are intimately associated by a dense network of hydrogen bonds. In the presence of an excess NA in solution, the EP-NA co-crystal has lower water solubility with respect to both the single co-crystal formers and precipitates in aqueous solutions at ambient temperature. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4830,4839, 2008 [source] Probing the solvation shell of organic molecules by intermolecular 1H NOESY,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2002Alessandro Bagno Abstract The solvation of some neutral and charged organic molecules (phenol, nitroanilines, tetraalkylammonium) in binary solvent mixtures was investigated by means of intermolecular 1H-NOESY NMR spectroscopy. The solvation shell of the solute is, in most cases, selectively enriched in one of the cosolvents (preferential solvation). The origin of preferential solvation is discussed in terms of solute,solvent interactions and microheterogeneity in the solvent mixture. Copyright © 2002 John Wiley & Sons, Ltd. [source] Synthesis of poly(4-vinylpyridine) by reverse atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007Gregory T. Lewis Abstract Controlled radical polymerization of 4-vinylpyridine (4VP) was achieved in a 50 vol % 1-methyl-2-pyrrolidone/water solvent mixture using a 2,2,-azobis(2,4-dimethylpentanitrile) initiator and a CuCl2/2,2,-bipyridine catalyst,ligand complex, for an initial monomer concentration of [M]0 = 2.32,3.24 M and a temperature range of 70,80 °C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First-order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number,average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29,1.35 were indicative of controlled radical polymerization. The highest number,average degree of polymerization of 247 (number,average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 °C, [M]0 = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70,80 °C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5748,5758, 2007 [source] Cobalt(II) octanoate and cobalt(II) perfluorooctanoate catalyzed atom transfer radical polymerization of styrene in toluene and fluorous media,A versatile route to catalyst recycling and oligomer formationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Marc-Stephan Weiser Abstract Cobalt(II) perfluorooctanoate-catalyzed atom transfer radical polymerization (ATRP) and reverse ATRP were developed to prepare oligostyrenes (Mn < 2500) with low polydispersities Mw/Mn < 1.5. Fluorous biphase catalysis was applied for effective recycling of catalyst and fluorous solvent. The homogeneous polymerization reaction was performed at 90 °C in toluene/cyclohexane/perfluorodecalin mixture (1:1:1) and fluorine-free solvents. Temperature-induced phase separation of this fluorous solvent mixture occurred at room temperature and proved to be the key for the very effective separation of the cobalt(II) perfluorooctanoate from the oligostyrene and fluorine-free solvents. Both the fluorine-tagged cobalt catalysts and the fluorous media were recycled and reused up to three times without encountering catalyst activity losses. The roles of cobalt catalysts, fluorous media, and monomer/initiator ratio were examined with respect to the polymerization kinetics. Fluorine-containing and fluorine-free cobalt(II) octanoate catalyzed controlled styrene oligomerization according to the ATRP mechanism. The molar mass control range was limited in fluorous biphase catalysis most likely because of precipitation of high molar mass polystyrenes in the fluorous reaction medium. To the best of our knowledge, this is the first time temperature-induced phase separation of fluorous and fluorine-free solvents has been successfully applied to polymerization processing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3804,3813, 2005 [source] Effect of temperature on the chromatographic retention of ionizable compounds.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Abstract We propose a general simple equation for accurately predicting the retention factors of ionizable compounds upon simultaneous changes in mobile phase pH and column temperature at a given hydroorganic solvent composition. Only four independent experiments provide the input data: retention factors measured in two pH buffered mobile phases at extreme acidic and basic pH values (e. g., at least ± 2 pH units far from the analyte pKa) and at two column temperatures. The equations, derived from the basic thermodynamics of the acid,base equilibria, additionally require the knowledge of the solute pKa and enthalpies of acid,base dissociation of both the solute and the buffer components in the hydroorganic solvent mixture. The performance of the predictive model is corroborated with the comparison between theoretical and experimental retention factors of several weak acids and bases of important pharmacological activity, in mobile phases containing different buffer solutions prepared in 25% w/w ACN in water and at several temperatures. [source] Determination of phenol using an enhanced chemiluminescent assayLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2003A. D. Ilyina Abstract Enhanced chemiluminescence (ECL) describes the phenomenon of increased light output in the luminol oxidation reaction catalysed by horseradish peroxidase (HRP) in the presence of certain compounds, such as para -iodophenol. In this work, the effects of phenol on the para -iodophenol-enhanced HRP-catalysed chemiluninescent reaction intensity in an aqueous buffer (Tris,HCl buffer, pH 8.5) and in a surfactant,water,octane mixture were compared. Preincubation of HRP at low phenol concentrations stimulated the chemiluminescent intensity in the assay performed in an aqueous buffer, but did not have significant effect in the sodium bis(2-ethylhexyl)sulphosuccinate) (Aerosol OT, AOT) applied system. It was also observed that HRP preincubation with phenol concentration higher than 0.003,mg/mL produced an inhibitory effect on the enzyme activity for both assay systems. Only an inhibitory effect of phenol on the chemiluminescent intensity in the surfactant system in octane (as organic solvent) was observed. Three assays were developed to determine phenol concentration in water and in an organic solvent mixture. The detection limits were 0.006, 0.003 and 0.0005,mg/mL, respectively, for the buffer-containing system, the AOT-applied system with phenol standard solutions in water and for the AOT-applied system with phenol standard solutions in octane. Copyright © 2002 John Wiley & Sons, Ltd. [source] Heteroarm Star Polystyrene- block -Poly(4-vinylpyridine): Multiple Morphologies in Dilute SolutionsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2008Chia-Hung Lin Abstract Synthesis and solution morphologies of four new heteroarm star polystyrene- block -poly(4-vinylpyridine) were studied. As the water content increased, a morphological transformation of heteroarm PS4 -P4VP4 from spheres to cylinders, vesicles, and large compound vesicles was observed. The morphology of PS4 -P4VP4 in the solvent mixture of DMF/water or 1,4-dioxane/water was spherical, but changed to large compound micelles in THF/water. As the P4VP molar ratio decreased, the morphology changed from spherical mixed with cylindrical to vesicles, giant vesicles, and then to LCMs. The present study demonstrated the formation of multiple morphologies through manipulating solvent polarity and block ratio in dilute solution. [source] Reversible Hydrogels from an Ampholytic An(B -b- C)n Heteroarm Star Block TerpolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2008Nikoletta Stavrouli Abstract An asymmetric, amphiphilic, An(B- b -C)n heteroarm star block terpolymer bearing polystyrene and poly(2-vinyl pyridine)- block -poly(acrylic acid) arms, was synthesized by anionic polymerization, using an extending "in-out" method and a post polymerization deprotection reaction. Due to the pH-dependent protonation/deprotonation equilibrium of the P2VP/PAA blocks, a rich phase behavior was observed as a function of pH. At pH,=,2, the star terpolymers form a physical hydrogel through a solvent-induced sol/gel transition in a DMF/water solvent mixture. The gelation mechanism was attributed to a jamming effect mediated by increasing the dielectric permittivity of the medium. [source] Aliphatic Ketones as Photoinitiators for PhotograftingMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2004Huiliang Wang Abstract Summary: The photografting of methacrylic acid (MAA) onto high-density polyethylene (HDPE) initiated by butanone, pentan-3-one, and heptan-3-one is presented. These aliphatic ketones can act as photoinitiators for photografting when they are a component of a suitable solvent mixture with water and ethanol. It is possible that the photoinitiation effect of the aliphatic ketone is induced by the hydrogen bond formed between it and water. The grafting of 2 M MAA in different ketone/water/ethanol (30/30/40) solvents. [source] Reactive processing of syndiotactic polystyrene with an epoxy/amine solvent systemMACROMOLECULAR SYMPOSIA, Issue 1 2003Jaap Schut Abstract Syndiotactic polystyrene (sPS) is a new semi-crystalline thermoplastic which is believed to fill the price-performance gap between engineering and commodity plastics. In order to reduce the high processing temperature of sPS (>290°C), an epoxy-amine model system was used as a reactive solvent. Such a processing aid can be used to achieve a 50 to 500 fold lowering of the melt viscosity. When initially homogeneous solutions of sPS in a stoechiometric epoxy-amine mixture are thermally cured, Reaction Induced Phase Separation (RIPS) takes place, leading to phase separated thermoplastic-thermoset polymer blends. We focus our study on low (wt% sPS < 20%) and high concentration blends (wt% sPS > 60%) prepared by two processing techniques (mechanical stirring in a laboratory reactor or internal mixer/ reactive extrusion respectively). These blends have different potential interests. Low concentration blends (sPS domains in an epoxy-amine matrix) are prepared to create new, tunable blend morphologies by choosing the nature of the phase separation process, i.e. either crystallisation followed by polymerization or polymerization followed crystallisation. High concentration blends (sPS matrix containing dispersed epoxy-amine particles after RIPS) are prepared to facilitate the extrusion of sPS. In this case, the epoxy amine model system served as a reactive solvent. The time to the onset of RIPS is in the order of 7-9 min for low concentration blends, while it increases to 20-45 min for high concentration samples, as the reaction rates are substantially slowed down due to lower epoxy and amine concentrations. During the curing reaction the melting temperature of sPS in the reactive solvent mixture evolves back from a depressed value to the level of pure sPS. This indicates a change in the composition of the sPS phase, caused by (complete) phase separation upon reaction. We conclude that our epoxy amine system is suited for reactive processing of sPS, where final properties depend strongly on composition and processing conditions. [source] Modification of polystyrene properties through grafting with N -vinylcarboxamido-2-methylpropane sulfonic acid monomerPOLYMER INTERNATIONAL, Issue 12 2004A Aggour Abstract Polystyrene (PS) possesses good mechanical properties, but its surface is relatively inert and hydrophobic. Grafting of N -vinylcarboxamido-2-methylpropane sulfonic acid (VCMP) is useful to hydrophilize the PS surface. Grafting was performed using benzoyl peroxide (BPO) as an initiator in toluene:methanol solvent mixture (3:1 volume ratio). The influence of the main factors on grafting, such as temperature, time, concentrations of initiator, PS and VCMP, has been studied. The results show that the initial rate of polymerization and percentage of grafting are enhanced by increased temperature. Furthermore, the specific rate constants of the first order reaction/are determined, and the activation energy of the grafting reaction is estimated. The grafting parameters are established and a suitable mechanism of the reaction is proposed. The grafted PS is to characterized through infrared spectra, intrinsic viscosity, thermogravimetric analysis (TGA) and differential gravimetric analysis (DTG). The kinetics of thermal degradation and the order of the thermal stabilities are given. Also the decomposition activation energies of the thermal degradation are determined, and confirm the thermal stabilities of the polymers used. © 2004 Society of Chemical Industry [source] Biomacromolecular engineering: design, synthesis and characterization.POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9-10 2006One-pot synthesis of block copolymers of arborescent polyisobutylene, polystyrene Abstract Novel arborescent block copolymers comprising of an arborescent rubbery polyisobutylene (PIB) midsegment and glassy polystyrene (PSt) end blocks were prepared by sequential addition of monomers. Synthesis was conducted by the use of 4-(2-methoxyisopropyl) styrene as an inimer-type initiator in conjunction with titanium tetrachloride (TiCl4) in 60:40 (v/v) methylcyclohexane/methyl chloride solvent mixture. Isobutylene was polymerized for 1,2,hr and then prechilled styrene in the same solvent mixture was sequentially added with select additives to the reaction flask. The recovered block copolymers were purified and then characterized by 1H-NMR, size exclusion chromatograph (SEC), tensile test, atomic force Microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Samples with 16.4,32.8,wt% PSt and Mn,=,47,600,125,900,g/mol (Mw/Mn,=,2.02,4.45) displayed thermoplastic elastomeric properties with 5,9.2,MPa tensile strength and 490,920% elongation. The arborescent block copolymers showed surface morphologies ranging from spherical to cylindrical/lamellar nanometer-sized discreet PSt phases dispersed in a continuous PIB matrix, with a 10,nm PIB layer on the surface. Drug release profiles of paclitaxel from two arborescent blocks were found to be similar to that measured from Translute®. Copyright © 2006 John Wiley & Sons, Ltd. [source] Nature of water molecules in hydrogels based on a liquid crystalline cellulose derivativePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003P. Wojciechowski Abstract The status and nature of water molecules in hydrogels with a liquid crystalline organization of the polymer network based on a biopolymer were investigated. Liquid crystalline (LC) hydrogels were obtained in situ by the photopolymerization of acrylic acid into the lyotropic liquid crystalline phase of (2-hydroxypropyl)cellulose in a solvent mixture of water and acrylic acid. The photopolymerization of acrylic acid in the lyotropic liquid crystalline phase at room temperature gives a hydrogel in which liquid crystalline order and water are retained. The liquid crystalline hydrogel contains water, which originates from the composition of the lyotropic liquid crystalline phase, and may also contain water after immersion in liquid water. The water molecule characteristics were examined by means of differential scanning calorimetry, dielectric relaxation spectroscopy, and differential scanning calorimetry coupled with thermo-optical measurements. The swelling data were obtained by using a weighing method. The investigations reveal the different nature of the two above-mentioned water types. For the water from the composition of the lyotropic liquid crystalline phase, the phase transitions,typical for the bulk water,were not observed, in contract to the water after swelling of the liquid crystalline hydrogel in the liquid water. The results of the measurements suggest that water, which comes from the composition of the lyotropic liquid crystalline phase, forms,together with a polymer network,a microstructure, stabilized by this water. The water, after swelling of the LC hydrogel in the liquid water, is separated in the pores of the hydrogel and exhibits the phase transitions of the bulk water. Copyright © 2003 John Wiley & Sons, Ltd. [source] Determination of ligustilide in rat blood and tissues by capillary gas chromatography/mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 10 2006Yunfeng Shi Abstract A gas chromatography/mass spectrometry (GC/MS) method was developed to study the pharmacokinetics of ligustilide following oral administration to rats. The method was used for the analysis of samples taken from rats. Biological samples were prepared by liquid,liquid extraction (LLE) using an n -hexane,ether (2:1) solvent mixture for a sample clean-up step and analyzed by GC/MS with a quadrupole MS detector in selected ion monitoring mode (m/z 190). The calibration curves were linear over the concentration range 0.172,8.60 µg/mL (r > 0.99) for blood samples and a different range (r > 0.99) for different tissue samples. The limit of detection (LOD) was 1.0 ng/mL or 1.0 ng/g (three times the signal,noise ratio). Within- and between-day precision expressed as the relative standard deviation (RSD) for the method was 1.58,3.88 and 2.99,4.91%, respectively. The recovery for all samples was >80%, except for liver samples (>70%). The main pharmacokinetic parameters obtained were: Tmax = 0.65 ± 0.07 h, Cmax = 1.5 ± 0.2 µg/mL, AUC = 34 ± 6 h µg/mL and Ka = 3.5 ± 0.6/h. The experimental results showed that ligustilide was easily absorbed, but its elimination was slow, from 3 to 12 h after oral administration. The concentrations of ligustilide in rat cerebellum, cerebrum, spleen and kidney were higher than those in other organs. Copyright © 2006 John Wiley & Sons, Ltd. [source] Micronization of lysozyme by supercritical assisted atomizationBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2009Renata Adami Abstract Supercritical Assisted Atomization (SAA) has been used to produce lysozyme microparticles. Lysozyme has been micronized using water, buffered water at pH 6.2 and water,ethanol mixtures at different volume percentages. Precipitated lysozyme particles were spherical, with a narrow particle size distribution (PSD) ranging from 0.1 to 4,µm. The concentration of lysozyme in the liquid solvent mixture had a nonlinear effect on the particle distribution, with an increase of the X0.9 from about 1 to 3,µm varying the enzyme concentration from 5 to 20,mg/mL. Precipitation temperature was set as low as possible to avoid enzyme degradation. High-performance liquid chromatography analysis showed no degradation of lysozyme and the enzyme activity, measured by turbidimetric enzymatic assay, only slightly decreased after SAA processing. Depending on the process conditions lysozyme retained from 95% to 100% of the biological activity compared to the untreated enzyme. Biotechnol. Bioeng. 2009; 104: 1162,1170. © 2009 Wiley Periodicals, Inc. [source] Self-Assembled Ionophores from Isoguanosine: Diffusion NMR Spectroscopy Clarifies Cation's and Anion's Influence on Supramolecular StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Tamar Evan-Salem Abstract Cation-templated self-assembly of the lipophilic isoguanosine (isoG,1) with different monovalent cations (M+=Li+, Na+, K+, NH4+, and Cs+) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG,1 forms both pentamers (isoG,1)5,M+ and decamers (isoG,1)10,M+ in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG,1 does not form (isoG,1)5,M+ pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG,1)10,2,M+ and singly charged decamers, (isoG,1)10,M+, are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)4, KB(Ph)4, NaB(Ph)4 and NH4B(Ph)4), depending on the isoG,1:salt stoichiometry of the solution. In the presence of CsB(Ph)4, isoG,1 affords only the singly charged decamers (isoG,1)10,Cs+. By monitoring the diffusion coefficient of the B(Ph)4, ion in the different mixtures of solvents, we also concluded that the anion is more strongly associated to the doubly charged decamers (isoG,1)10,2,M+ than to the singly charged decamers (isoG,1)10,M+. The (isoG,1)10,2,M+ species can, however, exist in solution without the mediation of the anion. This last conclusion was supported by the finding that the doubly charged decamers (isoG,1)10,2,M+ also prevail in 1:1 CD3CN:CDCl3, a solvent mixture in which the B(Ph)4, ion does not interact significantly with the self-assembled complex. These diffusion measurements, which have provided new and improved structural information about these decameric isoG,1 assemblies, demonstrate the utility of combining diffusion NMR techniques with conventional NMR methods in seeking to characterize labile, multicomponent, supramolecular systems in solution, especially those with high symmetry. [source] Aminosilicone Solvents for CO2 CaptureCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 8 2010Robert Abstract This work describes the first report of the use of an aminosilicone solvent mix for the capture of CO2. To maintain a liquid state, a hydroxyether co-solvent was employed which allowed enhanced physisorption of CO2 in the solvent mixture. Regeneration of the capture solvent system was demonstrated over 6 cycles and absorption isotherms indicate a 25,50,% increase in dynamic CO2 capacity over 30,% MEA. In addition, proof of concept for continuous CO2 absorption was verified. Additionally, modeling to predict heats of reaction of aminosilicone solvents with CO2 was in good agreement with experimental results. [source] | ||||||||||||||||||||||||||||||||||