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Solvent System (solvent + system)
Kinds of Solvent System Terms modified by Solvent System Selected AbstractsUltrafine Electrospun Polyamide-6 Fibers: Effects of Solvent System and Emitting Electrode Polarity on Morphology and Average Fiber DiameterMACROMOLECULAR MATERIALS & ENGINEERING, Issue 9 2005Pitt Supaphol Abstract Summary: In the present contribution, polyamide-6 (PA-6) solutions were prepared in various pure and mixed-solvent systems and later electrospun with the polarity of the emitting electrode being either positive or negative. The PA-6 concentration in the as-prepared solutions was fixed at 32% w/v. Some of the solution properties, i.e., shear viscosity, surface tension, and conductivity, were measured. Irrespective of the polarity of the emitting electrode, only the electrospinning of PA-6 solution in formic acid (85 wt.-% aqueous solution) produced uniform electrospun fibers, while solutions of PA-6 in m -cresol or sulfuric acid (either 20 or 40 wt.-% aqueous solution) did not. In the mixed-solvent systems, formic acid (85 wt.-% aqueous solution) was blended with m -cresol, sulfuric acid (either 20 or 40 wt.-% aqueous solution), acetic acid, or ethanol in the compositional range of 10,40 vol.-% (based on the amount of the minor solvent). Generally, the average fiber diameter increased with increasing amount of the minor solvent or liquid. Interestingly, the diameters of the fibers obtained under the negative electrode polarity were larger than those obtained under the positive one. Optical images of electrospun fibers from solutions of polyamide-6 in a mixed solvent of 85 wt.-% formic acid and 20 vol.-% m -cresol under positive (left) and negative (right) electrode polarity. [source] Selective Extraction of Free Astaxanthin from Haematococcus Culture Using a Tandem Organic Solvent SystemBIOTECHNOLOGY PROGRESS, Issue 4 2007Chang Duk Kang A novel tandem solvent process of dodecane and methanol was developed for the selective extraction of free astaxanthin from red encysted Haematococcus culture. The process consists of dodecane extraction for astaxanthin mixture from the culture (stage 1) and methanol extraction for free astaxanthin from the dodecane extract (stage 2). In the first stage, astaxanthin mixture was directly extracted to dodecane from the culture broth without cell harvest process, followed by a rapid separation of the dodecane extract and the culture medium containing cell debris by simple settling. In the second stage, free astaxanthin was selectively collected to methanol from the dodecane extract, accompanied with saponification of astaxanthin-esters by the addition of NaOH to methanol. During saponification, use of the optimum NaOH concentration (0.02 M) and low temperature (4 °C) reaction minimized the degradation of free astaxanthin, resulting in a total recovery yield of free astaxanthin of over 85%. The free-astaxanthin-containing methanol extract was also simply separated from dodecane by gravity settling, after which the astaxanthin-free dodecane was effectively recycled to the first stage, yielding a stable extractability of astaxanthin mixture during repeated extraction. Our results indicate the potential of the proposed tandem solvent process as an alternative extraction technology for the high-value antioxidant Haematococcus astaxanthin. [source] ChemInform Abstract: 3-exo-tet Cyclization of 2,2-Disubstituted 1,3-Dihalopropanes with Indium in Aqueous and Ionic Liquid Solvent System.CHEMINFORM, Issue 3 2010Yuhsuke Tsuchiya Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] ChemInform Abstract: Vicinal Dihydroxylation of Alkenes with Tetradecyltrimethylammonium Permanganate and Potassium Hydroxide in a Two-Phase Solvent System.CHEMINFORM, Issue 15 2002Braja G. Hazra Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] ChemInform Abstract: Can a Fluorous Biphase Solvent System Improve a Polymer Immobilized Heterogeneous Hydrogenation Catalyst?CHEMINFORM, Issue 40 2001Shannon L. Vinson Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Novel Palladium-Catalysed Hydroamination of Myrcene and Catalyst Separation by Thermomorphic Solvent SystemsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Arno Behr Abstract Hydroamination is an elegant and atom economical reaction to convert alkenes into amines. One of the few technical realisations of this reaction is the hydroamination of myrcene to diethylgeranylamine, an important precursor of (,)-menthol. However, this so-called "Takasago process" is catalysed by high amounts of alkali metals, especially lithium, which makes it a relatively expensive approach. In the present work, the hydroamination of myrcene with morpholine is catalysed by palladium complexes with bidentate ligands such as bis(diphenylphosphino)butane (DPPB) or bis(2-diphenylphosphinophenyl) ether (DPEphos). The systematic optimisation of the reaction parameters under single-phase conditions led to yields of the 1,4-adducts of higher than 90%. The only side products proved to be the telomers of myrcene, whose formation could be decreased by using appropriate reaction conditions. The method of temperature-dependent solvent systems was successfully applied to separate the palladium catalyst from the amines with a palladium leaching lower than 1.0%. [source] ChemInform Abstract: Multicomponent Reactions of 1,3-Disubstituted 5-Pyrazolones and Formaldehyde in Environmentally Benign Solvent Systems and Their Variations with More Fundamental Substrates.CHEMINFORM, Issue 42 2010Jia-Neng Tan Abstract A series of substituted tetrahydropyrano[2,3-c]pyrazoles (IV) and (VII) is readily obtained by three-component reaction of pyrazolones with styrenes and paraformaldehyde under solvent-free conditions. [source] In vitro percutaneous penetration of acyclovir from solvent systems and Carbopol 971-P hydrogels: Influence of propylene glycolJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2005O. Díez-Sales Abstract The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER,=,10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increases; this effect could be attributed to the increase of the viscosity in the diffusional pathway. When gels are used skin permeation values of ACV were smaller than those of the solvent systems. This could be attributed to the network structure created by the polymer that increases the length of the diffusional pathway. The maximum ER (=6.8) was for Carbopol gel containing 50% PG. Therefore, these gels can be considered candidates for further research to confirm their usefulness as delivery systems for ACV topical formulations. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1039,1047, 2005 [source] A novel self-consistent Nývlt-like equation for metastable zone width determined by the polythermal methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2009K. Sangwal Abstract Using a power-law relation between three-dimensional nucleation rate J and dimensionless supersaturation ratio S, and the theory of regular solutions to describe the temperature dependence of solubility, a novel Nývlt-like equation of metastable zone width of solution relating maximum supercooling ,Tmax with cooling rate R is proposed in the form: ln(,Tmax/T0) = , + , lnR, with intercept , = {(1,m)/m }ln(,Hs/RGTlim) + (1/m)ln(f/KT0) and slope , = 1/m. Here T0 is the initial saturation temperature of solution in a cooling experiment, ,Hs is the heat of dissolution, RG is the gas constant, Tlim is the temperature of appearance of first nuclei, m is the nucleation order, and K is a new nucleation constant connected with the factor f defined as the number of particles per unit volume. It was found that the value of the term , for a system at saturation temperature T0 is essentially determined by the constant m and the factor f. The value of the factor f for a solute,solvent system at initial saturation temperature T0 is determined by solute concentration c0. Analysis of the experiment data for four different solute-water systems according to the above equation revealed that: (1) the values of , and m for a system at a given temperature depend on the method of detection of metstable zone width, and (2) the value of slope , = 1/m for a system is practically a temperature-independent constant characteristic of the system, but the value of , increases with an increase in saturation temperature T0, following an Arrhenius-type equation with an activation energy Esat. The results showed, among others, that solubility of a solute is an important factor that determines the value of the nucleation order m and the activation energy Esat for diffusion. In general, the lower the solubility of a solute in a given solvent, the higher is the value of m and lower is the value of Esat. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Protein engineering and discovery of lipases,EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 1 2010Robert Kourist Abstract Lipases are widely used in the modification of fats and oils with applications in the production of structured triacylglycerols, selective isolation or incorporation of specific fatty acids, and in oleochemistry for the synthesis of emollient esters and sugar fatty acid esters. Despite the numerous examples for the effective use of lipases, the biocatalysts often need to be optimized to show the desired specificities, stability, operational properties, etc. Beside rather classical methods such as variation of the solvent system or carrier for immobilization, the use of protein engineering methods to modify the protein on a molecular level is an important tool for the creation of tailor-designed enzymes. Protein design is also complemented with the efficient isolation of novel lipases from the metagenome. This article covers concepts and examples for the discovery of novel lipases and their variants by protein engineering and metagenome techniques. [source] Solvatochromic Analysis of Partition Coefficients in the o -Nitrophenyl Octyl Ether (o -NPOE)/Water SystemHELVETICA CHIMICA ACTA, Issue 11 2003Xiangli Liu The objective of this study was to unravel the structural properties responsible for the partitioning of solutes in o -nitrophenyl octyl ether (o -NPOE)/H2O, a new solvent system for the determination of the partition coefficients of ions. A set of 88 compounds (including drugs) was selected to allow a regular and broad distribution of property spaces. Partition coefficients in o -NPOE/H2O (log,Pnpoe) were measured by the shake-flask or the potentiometric method. Linear solvation free-energy relationship (LSER) analyses showed that Van der Waals volume, H-bond-acceptor basicity, and H-bond-donor acidity are the three molecular descriptors of solutes determining their log,Pnpoe values. The partitioning mechanism of the investigated compounds in o -NPOE/H2O is controlled by the same structural properties as it is in 1,2-dichloroethane (DCE)/H2O. ,log,Poct,npoe Values (difference between log,Poct and log,Pnpoe) express mainly dipolarity/polarizability and H-bond-donor acidity. The solvent o -NPOE is shown to be a good candidate to replace DCE in measurements of lipophilicity. [source] Use of TLC-FID and GC-MS/FID to examine the effects of migratory state, diet and captivity on preen wax composition in White-throated Sparrows Zonotrichia albicollisIBIS, Issue 4 2010RAYMOND H. THOMAS Preen wax is important for plumage maintenance and other functions. Its chemical composition is complex, and separating and quantifying its components, commonly by gas chromatography (GC), can be challenging. We present a simple analytical system consisting of thin-layer chromatography/flame ionization detection (TLC-FID) using a solvent system of 100% toluene to analyse the complex compound classes present in preen wax. We used GC and TLC-FID to investigate the effects of migratory status, diet and captivity on the preen wax composition of White-throated Sparrows Zonotrichia albicollis, and to measure the quantity of preen wax on the head, primary and tail feathers. White-throated Sparrows produced preen wax containing only monoesters regardless of migratory state. The monoesters contained several isomers consisting of homologous series of fatty alcohols (C10,C20) and fatty acids (C13,C19) esterified together in different combinations to form monoesters with total carbon numbers ranging from C23 to C38. Weighted average monoester carbon number was greater in captive birds than in wild birds and was greater in captives fed a formulated diet enriched with sesame oil than in birds fed the same diet enriched with fish oil. Captivity and migratory state also affected the complexity of the mixture of monoesters. There was significantly more preen wax on head feathers compared with primary and tail feathers. We suggest that among its many functions, preen wax may play a role in drag reduction by affecting the physical properties of feathers, and/or the fluid flow at their surfaces. [source] Electrospinning of cellulose-based nanofibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Audrey Frenot Abstract Cellulose derivatives of carboxymethyl cellulose sodium salt (CMC), hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and enzymatically treated cellulose have been electrospun, and the microstructure of the resulting nanofibers has been analyzed by scanning electron microscopy (SEM). Before electrospinning, the solutions were characterized by viscometry and surface tension measurements, and the results were correlated with spinnability. Four different CMC derivatives, varying in molecular weight (Mw), degree of substitution (DS), and substitution pattern, have been electrospun in mixtures with poly(ethylene oxide) (PEO), and nanofibers of various characteristics have formed. The CMC-based nanostructures, i.e., the nonwoven sheet and individual nanofibers, proved to be independent of Mw and DS but largely dependent on the substitution pattern. The nonwoven sheets varied in homogeneity, and beads appeared on the individual fibers. Depending on the chemical nature of the CMC, the extraction of PEO resulted in pure CMC nanostructures of varying appearance, indicating that the distribution of PEO and CMC in the nanofibers also varied. Two different HPMC derivatives, varying in DS, were electrospun into nanofibers. Homogeneous nonwoven sheets based on nanofibers of similar appearance are formed, independent of the substitution content of the HPMC sample. Preliminary fibers were obtained from enzymatically treated cellulose in a solvent system based on lithium chloride dissolved in dimethyl acetamide (LiCl: DMAc). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1473,1482, 2007 [source] Distribution of acrylic acid grafted chains introduced into polyethylene film by simultaneous radiation grafting with water and ethanol as solventsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Zhengchi Hou Abstract The graft copolymerization of acrylic acid onto low-density polyethylene films by simultaneous ,-ray irradiation was carried out. The effect of water and ethanol as grafting solvents on the distribution of grafted poly (acrylic acid) in the low-density polyethylene films was studied with optical microscopy observations of dyed and sliced samples and attenuated total reflection/Fourier infrared spectroscopy analysis. When no vigorous homopolymerization occurred, both polyethylene and poly(acrylic acid) existed in the grafted layer, and the thickness of the grafted layer and the poly(acrylic acid) concentration in the grafted layer increased with an increasing degree of grafting, regardless of the grafting conditions, the former increasing faster than the latter. In comparison with water as the solvent, in the absence of the inhibitor, homopolymerization could be suppressed to a certain degree in the ethanol solvent system, whereas in the presence of the inhibitor, obvious homopolymerization occurred at a lower monomer concentration, and both the degree of grafting and the thickness of the grafted layer were lower. Such differences could be explained by the chain transfer and the relatively low solubility of poly(acrylic acid) in ethanol. In addition, an experimental scheme using optical microscopy to observe the dyed and sliced polymers was optimized. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1570,1577, 2007 [source] Computational screening of biomolecular adsorption and self-assembly on nanoscale surfacesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2010Hendrik Heinz Abstract The quantification of binding properties of ions, surfactants, biopolymers, and other macromolecules to nanometer-scale surfaces is often difficult experimentally and a recurring challenge in molecular simulation. A simple and computationally efficient method is introduced to compute quantitatively the energy of adsorption of solute molecules on a given surface. Highly accurate summation of Coulomb energies as well as precise control of temperature and pressure is required to extract the small energy differences in complex environments characterized by a large total energy. The method involves the simulation of four systems, the surface-solute,solvent system, the solute,solvent system, the solvent system, and the surface-solvent system under consideration of equal molecular volumes of each component under NVT conditions using standard molecular dynamics or Monte Carlo algorithms. Particularly in chemically detailed systems including thousands of explicit solvent molecules and specific concentrations of ions and organic solutes, the method takes into account the effect of complex nonbond interactions and rotational isomeric states on the adsorption behavior on surfaces. As a numerical example, the adsorption of a dodecapeptide on the Au {111} and mica {001} surfaces is described in aqueous solution. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] A new method to locate saddle points for reactions in solution by using the free-energy gradient method and the mean field approximationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2004I. Fdez. Abstract A new method for calculating saddle points of reactions in solution is presented. The main characteristics of the method are: (1) the solute,solvent system is described by the averaged solvent electrostatic potential/molecular dynamics method (ASEP/MD). This is a quantum mechanics/molecular mechanics method (QM/MM) that makes use of the mean field approximation (MFA) and that permits one to simultaneously optimize the electronic structure and geometry of the solute molecule and the solvent structure around it. (2) The transition state is located by the joint use of the free-energy gradient method and the mean field approximation. An application to the study of the Menshutkin reaction between NH3 and CH3Cl in aqueous solution is discussed. The accuracy and usefulness of the proposed method is checked through comparison with other methods. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1227,1233, 2004 [source] Cyclopentadienyl technetium (99mTc) tricarbonyl piperidine conjugates: biodistribution and imaging studiesJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 9 2001Mouldi Saidi Abstract Synthesis of organometallic complexes of 99mTc using the precursor ligands N -methylpiperidino-4[(bispentahaptocyclopentadienyl)iron] carboxylate and N -(isopropyl)-piperidino-4[(bispentahaptocyclopentadienyl)iron]carboxylate is described. The labelling method involved reaction of the ligands with 99mTcO in the presence of Mn(CO)5Br in dimethyl formamide at 150°C for 1 h in an oil bath. The purification of the complexes was carried out by preparative TLC using ethery/n -butyl methyl amine (95:5) solvent system. The purified complexes were characterized by HPLC using acetonitrile:water (80:20) solvent system in a PRP-1 column in which both the complexes were eluted as single peaks. Biodistribution studies carried out in rats showed 2.4±0.14 and 1.1±0.42% of the injected activity in the brain tissue 5 min p.i. for cytectrene I and II, respectively. The brain to blood activity ratio was >15:1 for both the complexes at 5 min p.i. Scintigraphic studies in rabbits showed significant uptake of the activity in the brain with fast clearance from blood. The complexes warrant further investigation as agents for brain imaging. Copyright © 2001 John Wiley & Sons, Ltd. [source] Molecular mass determination of plasma-derived glycoproteins by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with internal calibrationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2002Omar Belgacem Abstract Human plasma-derived antithrombin III (AT-III), factor IX (FIX) and vitronectin (VN) were characterized as native glycoproteins and in their de- N -glycosylated form by means of MALDI mass spectrometry. The average molecular masses of the three complex glycoproteins were determined applying internal calibration with high-mass, well-defined protein calibrants. Internal calibration generated for the 47 kDa yeast protein enolase a mass precision in the continuous and delayed extraction mode of ±0.12 and ±0.022%, respectively. The achievable mass accuracy for such a high-mass, unmodified protein was in the range of 0.02% in the continuous mode, which turned out to be better than in the delayed extraction mode. Purification of all (glyco) proteins (even the calibration proteins) by means of ZipTip® technology and direct elution with a solvent system containing the appropriate MALDI matrix turned out to be a prerequisite to measure the exact molecular masses with an internal calibration. The average molecular masses of the two different forms of AT-III, namely AT-III, and AT-III,, were shown to be 57.26 and 55.04 kDa, respectively. The 2.22 kDa mass difference is attributed to the known difference in carbohydrate content at one specific site (Asn-135). After exhaustive de- N -glycosylation (by means of PNGase F) of the ,- and ,-form and subsequent MALDI-MS analysis, average molecular masses of 48.96 and 48.97 kDa, respectively, were obtained. These values are in good agreement (,0.15%) with the calculated molecular mass (49.039 kDa) of the protein part based on SwissProt data. The molecular mass of the heavily post-translational modified glycoprotein FIX was found to be 53.75 kDa with a peak width at 10% peak height of 4.5 kDa, because of the presence of many different posttranslational modifications (N - and O -glycosylation at multiple sites, sulfation, phosphorylation, hydroxylation and numerous ,-carboxyglutamic acids). MALDI-MS molecular mass determination of the native, size-exclusion chromatography-purified, VN sample revealed that the glycoprotein was present as dimer with molecular mass of 117.74 kDa, which could be corroborated by non-reducing SDS-PAGE. After sample treatment with guanidine hydrochloride and mass spectrometric analysis, a single, new main component was detected. The molecular mass turned out to be 59.45 kDa, representing the monomeric form of VN, known as V75. The determined molecular mass value was shown to be on one hand lower than from SDS-PAGE and on the other higher than the calculated amino acid sequence molecular mass (52 277 Da), pointing to the well-known SDS-PAGE bias and to considerable post-translational modifications. Further treatment of the sample with a reducing agent and subsequent MALDI-MS revealed two new components with molecular masses of 49.85 and 9.41 kDa, corresponding to V65 and V10 subunits of VN. PNGase F digest of the V75 and V65 units and MS analysis, exhibiting a molecular mass reduction of 6.37 kDa in both cases, verified the presence of a considerable amount of N -glycans. Copyright © 2002 John Wiley & Sons, Ltd. [source] Synthesis of A,[1-42] and its derivatives with improved efficiencyJOURNAL OF PEPTIDE SCIENCE, Issue 2 2007Márta Zarándi Abstract It has been proved that the principal component of senile plaques is aggregates of ,-amyloid peptide (A,) in cases of one of the most common forms of age-related neurodegenerative disorders, Alzheimer's disease (AD). Although the synthetic methods for the synthesis of A, peptides have been developed since their first syntheses, A,[1-42] is still problematic to prepare. The highly hydrophobic composition of A,[1-42] results in aggregation between resin-bound peptide chains or intrachain aggregation which leads to a decrease in the rates of deprotection and repetitive incomplete coupling reactions during 9-flurenylmethoxycarbonyl (Fmoc) synthesis. In order to avoid aggregation and/or disrupt internal aggregation during stepwise Fmoc solid phase synthesis and to improve the quality of crude products, several attempts have been made. Since highly pure A, peptides in large quantities are used in biological experiments, we wanted to develop a method for a rational synthesis of human A,[1-42] with high purity and adequate yield. This paper reports a convenient methodology with a novel solvent system for the synthesis of A,[1-42], its N -terminally truncated derivatives A,[4-42] and A,[5-42], and A,[1-42] labeled with 7-amino-4-methyl-3-coumarinylacetic acid (AMCA) at the N -terminus using Fmoc strategy. The use of 10% anisole in Dimethylformamide/Dichloromethane (DMF/DCM) can substantially improve the purity and yield of crude A,[1-42] and has been shown to be an optimal coupling condition for the synthesis of A,[1-42]. Anisole is a cheap and simple aid in the synthesis of ,difficult sequences' where other solvents are less successful in the prevention of aggregation during the synthesis. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd. [source] Investigation of penetratin peptides Part 1.JOURNAL OF PEPTIDE SCIENCE, Issue 4 2002The environment dependent conformational properties of penetratin, two of its derivatives Abstract The homeodomain, the DNA-binding domain of Antennapedia homeoprotein, is composed of three ,-helices and one ,-turn between helices II and III. Its third helix from the N -terminal (helix III) can translocate through the cell membrane into the nucleus and can be used as an intracellular vehicle for the delivery of oligopeptides and oligonucleotides. To the best of our knowledge, this helix III, called penetratin, which consists of 16 amino acids, is internalized by cells in a specific, non-receptor-mediated manner. For a better understanding of the mechanism of the transfer, the structure of penetratin was examined in both extracellular matrix-mimetic and membrane-mimetic environments; 1H-NMR and CD spectroscopic measurements were performed in mixtures of TFE/water with different ratios. The molecular conformations of two analogue peptides [(6,14-Phe)-penetratin and a 12 amino acid penetratin derivative (peptide 3)] were also studied. An atomic level comprehensive analysis of penetratin and its two analogues was performed. In a membrane-mimetic solvent system (TFEd2/water = 9 : 1), on the basis of 553 distance restraints, the 4,12 region of penetratin exhibits a bent, irregular helical structure on NMR examination. Interactions between hydrophobic amino acid residues in conjunction with H-bonds stabilize the secondary structure of the molecule. Thus, both derivatives adopt a helix-like conformation. However, while (6,14-Phe)-penetratin displays both ,-helical and 310 -helical features, the structure of peptide 3 is predominantly a 310 -helix. Of the three peptides, surprisingly (6,14-Phe)-penetratin has the largest helical content. An increase in the polarity of the molecular environment gradually disintegrates these helix-like secondary structures. In a highly aqueous molecular system (TFEd2/water = 1 : 9), the fast exchange of multiple conformers leads to too few distance restraints being extracted, therefore the NMR structures can no longer be determined. The NMR data show that only short-range order can be traced in these peptides. Under these conditions, the molecules adopt nascent helix-like structures. On the other hand, CD spectra could be recorded at any TFE/water ratio and the conformational interconversion could therefore be monitored as a function of the polarity of the molecular environment. The CD data were analysed comprehensively by the quantitative deconvolution method (CCA+). All three penetratin peptides display helical conformational features in a low dielectric medium, with significant differences as a function of their amino acid composition. However, these conformational features are gradually lost during the shift from an apolar to a polar molecular environment. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source] Effect of lipid bilayer alteration on transdermal delivery of a high-molecular-weight and lipophilic drug: Studies with paclitaxelJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2004Ramesh Panchagnula Abstract Skin forms an excellent barrier against drug permeation, due to the rigid lamellar structure of the stratum corneum (SC) lipids. Poor permeability of drugs can be enhanced through alteration in partition and diffusion coefficients, or concentration gradient of drug with an appropriate choice of solvent system, along with penetration enhancers. The aim of the current investigation was to assess applicability of lipid bilayer alteration by fatty acids and terpenes toward the permeation enhancement of a high-molecular-weight, lipophilic drug, paclitaxel (PCL) through rat skin. From among the fatty acids studied using ethanol/isopropyl myristate (1:1) vehicle, no significant enhancement in flux of PCL was observed (p,>,0.05). In the case of cis mono and polyunsaturated fatty acids lag time was found to be similar to control (p,>,0.05). This suggests that the permeation of a high-molecular-weight, lipophilic drug may not be enhanced by the alteration of the lipid bilayer, or the main barrier to permeation could lie in lower hydrophilic layers of skin. A significant increase in lag time was observed with trans unsaturated fatty acids unlike the cis isomers, and this was explained on the basis of conformation and preferential partitioning of fatty acids into skin. From among the terpenes, flux of PCL with cineole was significantly different from other studied terpenes and controls, and after treatment with menthol and menthone permeability was found to be reduced. Menthol and menthone cause loosening of the SC lipid bilayer due to breaking of hydrogen bonding between ceramides, resulting in penetration of water into the lipids of the SC lipid bilayer that leads to creation of new aqueous channels and is responsible for increased hydrophilicity of SC. This increased hydrophilicity of the SC bilayer might have resulted in unfavorable conditions for ethanol/isopropyl myristate (1:1) along with PCL to penetrate into skin, therefore permeability was reduced. The findings of this study suggest that the permeation of a high-molecular-weight and lipophilic drug cannot be enhanced through bilayer alteration by penetration enhancers, and alteration in partitioning of drug into skin could be a feasible mode to enhance the permeation of drug. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2177,2183, 2004 [source] Olefin metathesis applied to cellulose derivatives,Synthesis, analysis, and properties of new crosslinked cellulose plastic filmsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2005Nicolas Joly Abstract New crosslinked cellulose-based plastic films were synthesized with olefin metathesis as a crosslinking reaction. Microcrystalline cellulose was first dissolved in a lithium chloride/N,N -dimethylacetamide solvent system and acylated by ,-undecenoyl chloride under microwave irradiation with N,N -dimethyl-4-aminopyridine as the catalyst. Cellulose unsaturated fatty acyl esters with a degree of substitution (DS) ranging from 1.4 to 2.0 were then crosslinked by olefin metathesis with a first generation Grubbs catalyst. Crosslinking ratios (T) ranging from 20 to 90% were obtained for low catalyst amounts (<1.2%), but gels appeared when T was too high. To avoid this gel formation, cellulose was acylated with a mixture of lauroyl and ,-undecenoyl chlorides. This internal dilution allowed us to obtain films of every case and various T (varying from 10 to 80% for a catalyst amount below 3.5%). Plastics were characterized by Fourier transform infrared (FTIR) spectroscopy, and the fatty acid mixture resulting from the hydrolysis of cellulose esters were analyzed by gas chromatography (GC) and NMR spectroscopy. Mechanical properties showed that the elastic modulus and tensile failure stress was higher when the plastic films were crosslinked. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 407,418, 2005 [source] Screening of antioxidant phenolic compounds in Chinese Rhubarb combining fast counter-current chromatography fractionation and liquid chromatography/mass spectrometry analysisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 11 2010Ruilin Hu Abstract In this paper, an effective method combing fast elution-extrusion counter-current chromatography (CCC) and LC/MS for rapid screening of antioxidative phenolic compounds in Chinese Rhubarb is presented. An integrated three-coil CCC column (40,mL each coil) was used to accomplish the optimization of biphasic liquid system. In a single run (approximately 40,min), the solvent system composed of n -hexane/ethyl acetate/methanol/water (1:1:1:1, v/v) was selected as optimum CCC liquid system for fast fractionation of the crude ethanol extract. With a 140,mL-capacity CCC instrument, 100,mg Chinese Rhubarb extract was separated under the optimized conditions, producing six fractions in only 100,min. The quantities of each fraction were ,15,mg. In addition, each fraction was subjected to antioxidant activity assay and characterized by LC/MS analysis. Fifty compounds, including phenolic acids, phenolic glucosides and hydroxyanthraquinones, were detected by LC/MS/MS analysis. As a result, gallic acid together with Fr I showed excellent antioxidant activity, which was well consistent with previous studies and exhibited great potential for natural drug discovery program of the present method. [source] Preparative isolation of flavonoid compounds from Oroxylum indicum by high-speed counter-current chromatography by using ionic liquids as the modifier of two-phase solvent systemJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2010Renmin Liu Abstract A preparative high-speed counter-current chromatography method for isolation and purification of flavonoid compounds from Oroxylum indicum was successfully established by using ionic liquids as the modifier of the two-phase solvent system. Two flavonoid compounds including baicalein-7- O -diglucoside and baicalein-7- O -glucoside were purified from the crude extract of O. indicum by using ethyl acetate,water,[C4mim][PF6] (5:5:0.2, v/v) as two-phase solvent system. 36.4,mg of baicalein-7- O -diglucoside and 60.5,mg of baicalein-7- O -glucoside were obtained from 120,mg of the crude extract. Their purities were 98.7 and 99.1%, respectively, as determined by HPLC area normalization method. The chemical structures of the isolated compounds were identified by 1H-NMR and 13C-NMR. [source] Rapid identification and preparative isolation of antioxidant components in licoriceJOURNAL OF SEPARATION SCIENCE, JSS, Issue 4-5 2010Yeon Sil Lee Abstract This study employed the online HPLC-2,2,-azinobis-(3-ethylbenzothiazoline-6-sulfonate radical cation (ABTS+·) bioassay to rapidly determine antioxidant compounds occurring in the licorice extract of Glycyrrhiza uralensis. The negative peaks of the ABTS+· radical scavenging detection system, which indicated the presence of antioxidant activity, were monitored by measuring the decrease in absorbance at 734,nm. The ABTS+ -based antioxidant activity profile showed that three peaks exhibited antioxidant activity, and then the high-speed counter-current chromatography technique of preparative scale was successfully applied to separate the three peaks I-III in one step from the licorice extract. The high-speed counter-current chromatography was performed using a two-phase solvent system composed of n -hexane,ethyl acetate,methanol,water (6.5:5.5:6:4, v/v). Yields of the three peaks, dehydroglyasperin C (I, 95.1% purity), dehydroglyasperin D (II, 96.2% purity), and isoangustone A (III, 99.5% purity), obtained were 10.33, 10.43, and 6.7% respectively. Chemical structures of the purified dehydroglyasperin C (I), dehydroglyasperin D (II), and isoangustone A (III) were identified by ESI-MS and 1H- and 13C-NMR analysis. [source] pH-Zone-refining centrifugal partition chromatography for preparative isolation and purification of steroidal glycoalkaloids from Solanum xanthocarpumJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2009Anupam Maurya Abstract pH-Zone-refining centrifugal-partition chromatography (CPC) was successfully applied in the separation of complex polar steroidal glycoalkaloids of close Rf values, directly from a crude extract of Solanum xanthocarpum. The experiment was performed with a two phase solvent system composed of ethyl acetate/butanol/water (1:4:5 by volume) where triethylamine (5 mM) was added to the upper organic mobile phase as an eluter and TFA (10 mM) to the aqueous stationary phase as a retainer. Separation of 1 g of crude extract over CPC resulted in two distinct pH-zones. The fractions collected in pH-zone i afforded 72 mg of solasonine while the fractions collected in pH-zone ii were slightly impure, hence were purified over medium pressure LC, which afforded 30 mg of solasonine and further 15 mg of solamargine (SM). The steroidal glycoalkaloids, SM and solasonine were isolated in 93.3 and 91.6% purity, respectively. The isolated alkaloids were characterized on the basis of their 1H, 13C-NMR, and ESI-MS data. [source] Preparative separation and purification of liensinine, isoliensinine and neferine from seed embryo of Nelumbo nucifera GAERTN using high-speed counter-current chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2009Shao Liu Abstract A preparative high-speed counter-current chromatography method for separation and purification of liensinine, isoliensinine and neferine from seed embryo of Nelumbo nucifera GAERTN was successfully established by using n -hexane-ethyl acetate-methanol-water (5:8:4:5, v/v, containing 0.5% NH4OH) as the two-phase solvent system. From 200 mg of crude extract, 18.4 mg of liensinine, 19.6 mg of isoliensinine and 58.4 mg of neferine were obtained with the purity of 96.8, 95.9, and 98.6%, respectively. The identification of the three alkaloids was performed with 1H NMR and 13C NMR. [source] An efficient combination of supercritical fluid extraction and high-speed counter-current chromatography to extract and purify homoisoflavonoids from Ophiopogon japonicus (Thunb.) Ker-GawlerJOURNAL OF SEPARATION SCIENCE, JSS, Issue 11 2009Chengjun Ma Abstract Supercritical fluid extraction (SFE) was used to extract homoisoflavonoids from Ophiopogon japonicus (Thunb.) Ker-Gawler. The optimization of parameters was carried out using an orthogonal test L9 (3)4 including pressure, temperature, dynamic extraction time and the amount of modifier. The process was then scaled up by 100 times with a preparative SFE system under the optimized conditions of 25 MPa, 55°C, 4.0 h and 25% methanol as a modifier. Then crude extracts were separated and purified by high-speed counter-current chromatography (HSCCC) with a two-phase solvent system composed of n -hexane/ethyl acetate/methanol/ACN/water (1.8:1.0:1.0:1.2:1.0 v/v). There three homoisoflavonoidal compounds including methylophiopogonanone A 6-aldehydo-isoophiopogonone A, and 6-formyl-isoophiopogonanone A, were successfully isolated and purified in one step. The collected fractions were analyzed by HPLC. In each operation, 140 mg crude extracts was separated and yielded 15.3 mg of methylophiopogonanone A (96.9% purity), 4.1 mg of 6-aldehydo-isoophiopogonone A (98.3% purity) and 13.5 mg of 6-formyl-isoophiopogonanone A (97.3% purity) respectively. The chemical structure of the three homoisoflavonoids are identified by means of ESI-MS and NMR analysis. [source] Separation and purification of harmine and harmaline from Peganum harmala using pH-zone-refining counter-current chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2008Xiao Wang Abstract pH-zone-refining counter-current chromatography was successfully applied to the separation of alkaloids from a crude extract of Peganum harmala L. using a multilayer coil planet centrifuge. The experiment was performed with a two-phase solvent system composed of methyl tert -butyl ether/THF/water (2:2:3 by volume) where triethylamine (10 mM) was added to the upper organic stationary phase as a retainer and hydrochloric acid (5 mM) to the aqueous mobile phase as an eluter. From 1.2 g of the crude extract, 554 mg harmine and 325 mg harmaline were obtained each with a purity of over 96% as determined by HPLC. The structures of the isolated compounds were identified by electron ionization MS (EI-MS), 1H NMR, and 13C NMR. [source] Nanosized CdSe Particles Synthesized by an Air Pressure Solution Process Using Ethylene-Glycol-Based SolventJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Tao Wang Nanosized CdSe particles were synthesized at a temperature of 115°,175°C by a solution method with air pressure condition. Ethylene glycol (EG) was used as the main solvent and sodium selenite and cadmium nitrate-tetrahydrate as inorganic sources. The influence of refluxing temperature and time on growth morphology and crystallization was investigated by transmission electron microscope, high-resolution transmission electron microscope, and X-ray diffraction. The chemical reaction was deducted based on X-ray photoelectron spectra. The optical absorption property was measured by UV-vis. The CdSe nanoparticles synthesized through this EG solvent system was single wurtzite crystallization and had a nanoscale size below 15 nm diameter with a narrow size distribution. The reduction of Se4+,Se0,Se2,and the disproportionation of Se0 occurred during the synthetic process and dominated the chemical reaction. [source] | ||||||||||||||||||||||||||||||||||||||||