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Different Solvents (different + solvent)
Terms modified by Different Solvents Selected AbstractsCapillary electrophoretic separation and fractionation of hydrophobic peptides onto a pre-structured matrix assisted laser desorption/ionization target for mass spectrometric analysisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2006Johan Jacksén Abstract A CE separation of hydrophobic peptides followed by fractionation onto a prestructured MALDI target and off-line MS analysis was performed. An improved and partially automated manufacturing procedure of the previously described MALDI target is presented. This target is structurally coated with silicone and especially developed for hydrophobic peptides and proteins. Here, the target plate was designed specifically for the CE fraction collection. Different solvents were evaluated to meet the requirements of peptide solubility and compatibility to both the CE and MALDI methods and to the fractionation procedure. CE-MALDI-MS analysis of nine highly hydrophobic peptides from cyanogen bromide-digested bacteriorhodopsin is demonstrated. [source] Comparison of bovine and porcine ,-lactoglobulin: a mass spectrometric analysisJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2006Gaetano Invernizzi Abstract Nano-electrospray-ionization mass spectrometry (nano-ESI-MS) is applied to comparison of bovine and porcine ,-lactoglobulin (BLG and PLG). The conformational and oligomeric properties of the two proteins under different solvent and experimental conditions are analyzed. The pH-dependence of dimerization is described for the pH range 2,11. The results indicate maximal dimer accumulation at pH 6 for BLG and pH 4 for PLG, as well as a lower stability of the PLG dimer at pH 4 compared to BLG at pH 6. Conformational stability appears to be higher for BLG at acidic pH, but higher for PLG at basic pH. The higher stability of BLG at low pH is revealed by means of either chemical or thermal denaturation. Equilibrium folding intermediates of both proteins are detected. Finally, conditions are found that promote dissociation of the BLG dimer at pH 6 into folded monomers. Copyright © 2006 John Wiley & Sons, Ltd. [source] Synthesis and Characterization of Colloidal Core,Shell Semiconductor NanowiresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2010Zhen Li Abstract CdSe colloidal nanowires, generated from solution-liquid-solid approach, have been coated with CdS rods (or ribbons) by using cadmium hexadecyl xanthate (Cd-HDX) as a single source precursor. The use of different solvents and ligands causes pronounced effects on the morphology of the nanowires. The coating process includes nucleation and growth of CdS nanorods onto the core CdSe nanowires, followed by ripening of the CdS nanorods to produce the desired core-shell nanowire structure. [source] Switchable Fluorescent and Solvatochromic Molecular Probes Based on 4-Amino- N -methylphthalimide and a Photochromic DiaryletheneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2008Sergey F. Yan Abstract New fluorescent photochromic compounds (1 -H and 1 -Boc) have been synthesized and characterized in different solvents. The fluorescence emission can be switched "on" and "off" with visible light and UV, respectively, by means of the photochromic reaction. The emission wavelength and efficiency strongly depend on the polarity of the solvent. The compounds show a positive solvatochromic effect in the emission maxima, and their fluorescence quantum yield decreases as the solvent's polarity increases (from cyclohexane to dioxane). In solvents more polar than dioxane the emission is too weak and therefore undetectable, and thus 1 -H and 1 -Boc behave as "normal" photochromic compounds. The photochromic reaction is also sensitive to the environment. A decrease of more than an order of magnitude was found for the quantum yield of the colouring reaction (,OF,CF) for 1 -H in ethanol compared with cyclohexane, and an about threefold decrease in ,OF,CF was observed for the compound 1 -Boc in polar solvents (compared with apolar solvents). For both compounds the ring-opening reaction was found not to dependent on the solvent. The novel fluorescent molecular switches 1 -H and 1 -Boc are able to probe the polarity of their microenvironment. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Systematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of Pyrrole Derivatives through Functionalization of 3,4-Bis(lithiomethyl)dihydropyrrolesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2003José Barluenga Abstract Bis(2-lithioallyl)amines 2, substituted at the double bonds, undergo intramolecular carbolithiation of a lithiated double bond in different solvents to afford dilithiated dihydropyrroles 3. Treatment of these dianions with electrophiles allows the preparation of functionalized pyrrole derivatives 5 and 6. Interestingly, treatment of these dianions with carboxylic esters selectively affords either keto or hydroxy compounds (9 or 10), depending on the conditions. Several experiments have been carried out in order to clarify the mechanism of this selective transformation. Finally, dilithiated dihydropyrrole 3a could be transformed in a three-step procedure into the corresponding 3,4-bis(bromomethyl) derivative 31, which can easily be converted into bicyclic pyrrole compounds 32,33 by treatment with different nucleophiles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Enhanced Antibacterial Activity of Nanocrystalline ZnO Due to Increased ROS-Mediated Cell InjuryADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Guy Applerot Abstract An innovative study aimed at understanding the influence of the particle size of ZnO (from the microscale down to the nanoscale) on its antibacterial effect is reported herein. The antibacterial activity of ZnO has been found to be due to a reaction of the ZnO surface with water. Electron-spin resonance measurements reveal that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals. Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the ZnO itself, is detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small ZnO nanoparticles results in an increased cellular internalization of the nanoparticles and bacterial cell damage. An examination of the antibacterial effect is performed on two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of ZnO are synthesized using ultrasonic irradiation, and the particle sizes are controlled using different solvents during the sonication process. Taken as a whole, it is apparent that the unique properties (i.e., small size and corresponding large specific surface area) of small nanometer-scale ZnO particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles. [source] Epoxidation of Polyunsaturated Fatty Acid Double Bonds by Dioxirane Reagent: Regioselectivity and Lipid Supramolecular OrganizationHELVETICA CHIMICA ACTA, Issue 10 2006Stanislav Abstract The use of dimethyldioxirane (DMD) as the epoxidizing agent for polyunsaturated fatty acids was investigated. With fatty acid methyl esters, this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by-products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome, and the epoxidation showed interesting regioselective features. The CC bonds closest to the aqueous-micelle interface is the most favored for the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid (=,(9Z,12Z)-octadeca-9,12-dienoic acid) to the 9,10-monoepoxy derivative was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid (=,(5Z,8Z,11Z,14Z)-eicosa-5,8,11,14-tetraenoic acid) micelles, the regioselective outcome with formation of the four possible monoepoxy isomers was studied under different conditions. It resulted to be a convenient synthesis of ,cis -5,6-epoxyeicosatrienoic acid' (=,3-[(2Z,5Z,8Z)-tetradeca-2,5,8-trienyl]oxiran-2-butanoic acid), whereas in reverse micelles, epoxidation mostly gave ,cis -14,15-epoxyeicosatrienoic acid (=,(5Z,8Z,11Z)-13-(3-pentyloxiran-2-yl)trideca-5,8,11-trienoic acid). [source] Photophysical and Photochemical Studies of PyridoxamineHELVETICA CHIMICA ACTA, Issue 10 2003Claudio Bueno The absorption and fluorescence emission of pyridoxamine were studied as function of pH and solvent properties. In the ground state, pyridoxamine exhibits different protonated forms in the range of pH,1.5,12. Fluorescence studies showed that the same species exist at the lowest singlet excited state but at different pH ranges. The phenol group is by ca. 8,units more acidic in the excited state than in the ground state. On the other hand, the pyridine N-atom is slightly more basic in the lowest excited state than in the ground state. Excitation spectra and emission decays in the pH range of 8,10 indicate the protonation of the pyridine N-atom by proton transfer from the amine group, in the ground and singlet excited states. Spectroscopic studies in different solvents showed that pyridoxamine in the ground or excited states exhibits intramolecular proton transfer from the pyridine N-atom to the phenol group, which is more favorable in solvents of low hydrogen-bonding capacity. The cationic form with the protonated phenolic group, which emits at shorter wavelength, is the dominant species in nonprotic solvents, but, in strong proton-donor solvents, both forms exist. The fluorescence spectra of these species exhibit blue shift in protic solvents. These shifts are well-correlated with the polarity and the H-donor ability of the solvent. [source] Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4,-bis(dimethylamino)-diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent moleculesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005Kakali Sen Abstract The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4,-bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta-stable Frank,Condon state (,E) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ,E values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ,E value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N-dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H-bonding capability of the protic solvent, methanol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Photochemical cleavage of a tattoo pigment by UVB radiation or natural sunlightJOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 7 2007Eva Engel Summary Background: Millions of people have at least one tattoo. Complex and light absorbing molecules are implanted in the skin. When tattooed skin receives UV radiation or natural sunlight, photochemical cleavage of the pigments may occur. As a first step, we dissolved pigments in a suitable solvent and analyzed them after light irradiation. Methods: The widespread Pigment Red 22 was dissolved in different solvents. The solutions were irradiated with either UVB radiation (up to 8 h) or with natural sunlight (110 days). After irradiation, the solutions were analyzed by means of liquid chromatography and mass spectrometry. Results: A clear cleavage of the pigment was detected in all solvents and the primary decomposition products were identified. In tetrahydrofuran and dioxane, the pigment concentration decreased significantly during UVB irradiation, whereas the pigment was completely destroyed during sunlight exposure. In chloroform and dichloromethane, the pigment concentration decreased slightly during UVB irradiation, whereas the pigment was almost completely destroyed during sunlight exposure. Conclusion: Since chloroform and dichloromethane do not affect the cleavage process, these solvents are optimal for such in vitro experiments. We have shown the cleavage of the tattoo pigment Red 22 when exposed to UVB radiation or natural sunlight. The decomposition products are hazardous showing a potential risk of being toxic or even carcinogenic. At present, a risk assessment is not feasible since the concentration of pigments and their decomposition products in skin are unknown. [source] Synthesis of higher soluble nanostructured polyaniline by vapor-phase polymerization and determination of its crystal structureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Sambhu Bhadra Abstract Higher soluble nanostructured polyaniline was prepared by vapor-phase polymerization after passing aniline vapor through an aqueous acidic solution of ammonium persulfate (PANI-V). Polyaniline was also synthesized by the conventional oxidative polymerization method (PANI-C) in an aqueous medium for the comparison of its properties with PANI-V. PANI-V exhibited lower conductivity but higher hydrophilicity and higher solubility (2,3 times) in different solvents, such as tetrahydrofuran, N -methyl-2-pyrrolidone, dimethylsulfoxide, N,N -dimethyl formamide, and m -cresol at room temperature compared with that of PANI-C. The thermal stability of PANI-V was higher than that of PANI-C. In-depth investigations of the crystal structures of PANI-C and PANI-V were performed through powder X-ray diffraction analysis. The PANI-V showed a less ordered structure with a lower crystallinity and crystallite size and with a higher d-spacing and interchain separation compared with PANI-C. The unit cell volume of PANI-V was significantly higher with a greater number of atoms in the unit cell than that of PANI-C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Dispersion and repulsion contributions to the solvation free energy: Comparison of quantum mechanical and classical approaches in the polarizable continuum modelJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2006Carles Curutchet Abstract We report a systematic comparison of the dispersion and repulsion contributions to the free energy of solvation determined using quantum mechanical self-consistent reaction field (QM-SCRF) and classical methods. In particular, QM-SCRF computations have been performed using the dispersion and repulsion expressions developed in the framework of the integral equation formalism of the polarizable continuum model, whereas classical methods involve both empirical pairwise potential and surface-dependent approaches. Calculations have been performed for a series of aliphatic and aromatic compounds containing prototypical functional groups in four solvents: water, octanol, chloroform, and carbon tetrachloride. The analysis is focused on the dependence of the dispersion and repulsion components on the level of theory used in QM-SCRF computations, the contribution of those terms in different solvents, and the magnitude of the coupling between electrostatic and dispersion,repulsion components. Finally, comparison is made between the dispersion,repulsion contributions obtained from QM-SCRF calculations and the results determined from classical approaches. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source] Heterocyclic compounds from 4h -3,1-benzoxazin-4-one derivatives as anticancer agentJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 7 2005Taha M Abdel-Rahman Behaviour of 2-(4-oxo-4H -benzo[d][l,3]oxazin-2-yl)-benzoic acid (1) towards nitrogen nucleophiles namely, hydrazine hydrate, in different solvents, ammonium acetate, and o -phenylenediamine has been investigated to give aminoquinazolin-4-one, benzotriazepinone, spiro-type compound, and nitrogen bridgehead compounds 3-5, respectively. Also, reactivity of the aminoquinazolin-4-one 2 towards carbon elec-trophiles such as ethyl acetoacetate, ethyl phenylacetate, ethyl chloroacetate, and aromatic aldehydes has been discussed. Reaction of Schiff s base 8 with sulfur nucleophiles namely o -aminothiophenol and/or thio-glycolic acid afforded Michael type adducts. Structural assignments, of products 1-24 have been confirmed by elemental analysis and spectral data (1H- and 13C -NMR and MS fragmentation). The bioassay indicates that some of the target compounds obtained have good selective anticancer activity. [source] Study of the reactivity of ,-acylenaminoketones.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2001Synthesis of pyrazoles The reactions of 4-(methylamino)-3-penten-2-one with diazoketones yielded the ,-acylenaminoketones 1,3 in good yields. Preparation of the ,-acylenaminoketone 4 was carried out by treatment of 4-(t -butyl-amino)-3-penten-2-one with benzoyl chloride being followed by reaction of transamination with methyl-amine. The reactions were carried out in five different solvents and were submitted to gas chromatogra-phy/mass spectrometry analysis, with the goal of obtaining substituted pyrazoles and determining which of the carbonyls would preferentially be attacked by the nucleophile. The reactions of compounds 1,4 with hydrazine reagents led to the formation of the pyrazoles 5,7a-q. Small amounts of 4-methylamino-2-pentenones 10a-q, amides 11a-q and pyrazoles 12a-q were also obtained in these reactions. The unexpected formation of pyrazoles 15d,h,q was detected when methanol and N,N -dimethylformamide were used as solvents in the reactions of ,-acylenaminoketone 4 with hydrazine reagents. [source] Design and synthesis of new trehalose-conjugated pentapeptides as inhibitors of A,(1,42) fibrillogenesis and toxicity,JOURNAL OF PEPTIDE SCIENCE, Issue 3 2009Paolo De Bona Abstract Aggregation of the amyloid A, peptide and its accumulation into insoluble deposits (plaques) are believed to be the main cause of neuronal dysfunction associated with Alzheimer's disease (AD); small molecules that can interfere with the A, amyloid fibril formation are therefore of interest for a potential therapeutic strategy. Three new trehalose-conjugated peptides of the well known ,-sheet breaker peptide iA,5p, were synthesized. The disaccharide was covalently attached to different sites of the LPFFD peptide chain, i.e. at the N-terminus, C-terminus or at the Asp side chain. CD spectroscopy in different solvents was used to assess changes in the peptide conformation of these compounds. The effects of these glycopeptides on the self-assembly and morphology of A, aggregates were investigated by ThT fluorescence assay and dynamic Scanning Force Microscopy, respectively. All the synthesized compounds were tested as inhibitors of A, toxicity toward pure cultures of rat cortical neurons. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] Polymorphism of NCX4016, an NO-releasing derivative of acetylsalicylic acidJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004A. Foppoli Abstract NCX4016 [2-acetoxybenzoic acid 3,-(nitrooxymethyl)phenyl ester] is a recently developed nitrooxy-derivative of aspirin with improved antiinflammatory, analgesic, and antithrombotic activity as well as increased gastrointestinal safety. Systematic polymorphic screening performed with different solvents and preparation methods resulted in the identification of two polymorphs, designated Forms I and II. They were characterized by scanning electron microscopy, powder X-ray diffraction, thermal analyses, and infrared spectroscopy; the crystal structure of polymorph I was solved by single-crystal X-ray analysis and compared with that of aspirin. Finally, intrinsic dissolution rate studies and calculations according to the melting data method were performed to assess the thermodynamic relationship between the two polymorphs. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:521,531, 2004 [source] Study of the solubilization of gliclazide by aqueous micellar solutionsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2003Khouloud A. Alkhamis Abstract It was of interest to increase the solubility of gliclazide in aqueous media. Therefore, solubilization of gliclazide in a variety of surfactants was investigated. Anionic and cationic surfactants exhibited dramatic solubilizing ability for gliclazide, whereas nonionic surfactants showed significantly lower solubilizing ability. It was found that gliclazide solubility increases with increasing the carbon chain length of cationic surfactants and decreases with increasing the carbon chain length of anionic surfactants. The solubilization data were analyzed on the basis of a pseudo-phase model with gliclazide exhibiting moderate partition coefficients into the micellar phase. The possible sites of solubilization of gliclazide in the micelle were examined by studying the effect of NaCl on solubilization and by comparing the absorption spectra of gliclazide in different solvents. The results obtained from these two experiments indicated that gliclazide is solubilized mainly in the inner core of the cationic surfactant micelles and in the outer regions of the anionic surfactant micelles. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:839,846, 2003 [source] Analysis of the Stability and Degradation Products of TriptolideJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2000YAN PING MAO Triptolide is the major active ingredient of the Chinese herbal remedy Tripterygium wilfordii Hook F. (TwHF). As triptolide content is used to estimate the potency of preparations of TwHF, assessment of its stability is warranted. The accelerated stability of triptolide was investigated in 5% ethanol solution in a light-protected environment at pH 6.9, within a temperature range of 60,90°C. The observed degradation rate followed first-order kinetics. The degradation rate constant (K25°C) obtained by trending line analysis of Arrhenius plots of triptolide was 1.4125 times 10,4 h,1. The times to degrade 10% (t1/10) and 50% (t1/2) at 25°C were 31 and 204 days, respectively. Stability tests of triptolide in different solvents and different pH conditions (pH 4,10) in a light-protected environment at room temperature demonstrated that basic medium and a hydrophilic solvent were the major factors that accelerated the degradation of triptolide. Triptolide exhibited the fastest degradation rate at pH 10 and the slowest rate at pH 6. In a solvent comparison, triptolide was found to be very stable in chloroform. The stability of triptolide in organic polar solvents tested at both 100% and 90% concentration was greater in ethanol than in methanol than in dimethylsulphoxide. Stability was also greater in a mixture of solvent: pH 6 buffer (9:1) than in 100% solvent alone. An exception was ethyl acetate, which is less polar than the other solvents tested, but permitted more rapid degradation of triptolide. Two of the degradation products of triptolide were isolated and identified by HPLC and mass spectroscopy as triptriolide and triptonide. This suggested that the decomposition of triptolide occurred at the C12 and C13 epoxy group and the C14 hydroxyl. The opening of the C12 and C13 epoxy is an irreversible reaction, but the reaction occurring on the C14 hydroxyl is reversible. These results show that the major degradation pathway of triptolide involves decomposition of the C12 and C13 epoxy group. Since this reaction is very slow at 4°C at pH 6, stability is enhanced under these conditions. [source] 3H -1,2-Dithiole-3-thione derivatives as novel solvatochromic dyesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2008Alejandro M. Fracaroli Abstract The UV,Vis spectrum of 5-(1-butylthio)-3H -1,2-dithiole-3-thione (1a) and that of the chromium pentacarbonyl complex of 5-methyl-3H -1,2-dithiole-3-thione (3) present significant changes with the solvent polarity. The two absorption bands shown by the compounds in the region above 300,nm were identified by theoretical calculations. For Compound 1a these are n,,* and ,,* transitions and for Compound 3 the longest wavelength absorption corresponds to a charge transfer band and shows a remarkably negative solvatochromism. Not only has the wavelength of maximum absorption changed with the solvent but also the ratio of the absorbances at the two wavelengths. The effect of solvents was correlated with solvatochromic parameters such as ,* and ,. The spectrum of 5-(1-butylthio)-3H -1,2-dithiole-3-one (2) was also measured in different solvents but in this case the changes observed are less significant than for the other two compounds. The spectra of 1a and 3 were also determined in the presence of anionic (SDS), cationic (CTAB), and neutral surfactants (Brig-35) and it is shown that these compounds can be used as probes for the polarity of the binding sites of organized assemblies. Copyright © 2008 John Wiley & Sons, Ltd. [source] Functional colloidal particles stabilized by layered silicate with hydrophilic face and hydrophobic polymer brushesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2009Yani Wu Abstract In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X-ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay-PS particles could be obtained in different solvents. In water, clay-PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay-PS particles formed face-to-face structure. Narrowly dispersed PS colloidal particles stabilized by clay-PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2-vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535,1543, 2009 [source] Atom transfer radical polymerization of n -butyl acrylate catalyzed by CuBr/N -(n -hexyl)-2-pyridylmethanimineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Huiqi Zhang Abstract The homogeneous atom transfer radical polymerization (ATRP) of n -butyl acrylate with CuBr/N -(n -hexyl)-2-pyridylmethanimine as a catalyst and ethyl 2-bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]0/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N -dimethylformamide, and 1-butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index , 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self-regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n -butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N -(n -hexyl)-2-pyridylmethanimine-based system was proven to be applicable to living block copolymerization and living random copolymerization of n -butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549,3561, 2002 [source] Fluoropolyethers end-capped by polar functional groups.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Abstract The kinetics of the dibutyltin dilaurate (DBTDL)-catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z-DOL H-1000 of various molecular weights (100,1084 g mol,1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30,60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl-containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero-order, first-order, second-order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771,3795, 2002 [source] Preparation of amphiphilic statistical copolymers of 2-hydroxyethyl methacrylate with 2-diethylaminoethyl methacrylate, precursors of water-soluble copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2002Gerardo Martinez Abstract Statistical copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2-diethylaminoethyl methacrylate (DEA) were synthesized at 50 °C by free-radical copolymerization in bulk and in a 3 mol L,1N,N,-dimethylformamide solution with 2,2,-azobisisobutyronitrile as an initiator. The solvent effect on the apparent monomer reactivity ratios was attributed to the different aggregation states of HEMA monomer in the different solvents. The copolymers obtained were water-insoluble at a neutral pH but soluble in an acidic medium when the molar fraction of the DEA content was higher than 0.5. The quaternization of DEA residues increased the hydrophilic character of the copolymers, and they became water-soluble at a neutral pH when the HEMA content was lower than 0.25. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2427,2434, 2002 [source] Concentration dependent Raman and IR study on salicylaldehyde in binary mixturesJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2007A. Anis Fathima Abstract A vibrational spectroscopic study of binary mixtures of salicylaldehyde (SA) in three different solvents (polar and nonpolar) is presented. The vibrational modes ,(CO), hydroxyl stretching mode (COH) and aldehydic (CH) stretching vibration were analyzed. Changes in wavenumber position and full width half maximum have been explained for neat as well as binary mixtures with different volume fractions of the reference system, SA, in terms of inter- and intramolecular hydrogen bonding. The IR spectra of these mixtures have also been taken and compared with the Raman data. The spectral changes have been well explained using the concentration fluctuation model and solute,solvent interaction. Copyright © 2007 John Wiley & Sons, Ltd. [source] Changes in spectral features with varying mole fractions of anisaldehyde in binary mixturesJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2007A. Anis Fathima Abstract Raman and IR spectra of neat anisaldehyde (4-methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic , (CH) and ring-breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute,solvent interaction is stronger in 2-propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, , (CO) in 2-propanol and aldehydic , (CH) in acetonitrile, gave a Gaussian-type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute,solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright © 2006 John Wiley & Sons, Ltd. [source] Investigations on 1,5-diaminoanthraquinone by laser excitationJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2003M. Umadevi Abstract Optical absorption and fluorescence emission spectra of 1,5-diaminoanthraquinone (1,5-DAAQ) in different solvents and the surface-enhanced Raman scattering (SERS) spectrum of 1,5-DAAQ in silver sol were investigated. Optical absorption and fluorescence emission studies revealed that the internal and external hydrogen bonds and reorientation of the solvent molecule around the excited state fluorophore are responsible for the observed bathochromic shift and the non-radiative decay process in polar solvents. SERS studies showed that 1,5-DAAQ molecules are chemisorbed through carbonyl groups and the lone pair of electrons on the nitrogen. The orientation of the molecule on the silver surface is found to be stand-on. Copyright © 2002 John Wiley & Sons, Ltd. [source] Reproducible Solvent,Thermal Synthesis, Controlled Microstructure, and Photoluminescence of REPO4:Eu3+, Tb3+ (RE=Y, La, and Gd) NanophosphorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Xiuzhen Xiao By altering the temperature and solvents, we have synthesized hydrated and dehydrated Eu3+/Tb3+ -doped REPO4 (RE=Y, La, and Gd) nanophosphors via a solvo-thermal technology. X-ray powder diffraction and scanning electronic microscopy reveal that they have different structures and different morphologies. REPO4 prepared under subsequent heating at 80°, 120°, and 160°C for 1 day, respectively, present larger particle size than that formed by heating at 160°C for 3 days. Moreover, at the same temperature of 160°C and pH 3, three different solvents (ethanol, N,N -dimethylformamide (DMF), and water) were used, whose influence on the microstructure of LaPO4 has been examined. As a result, LaPO4 samples from anhydrous ethanol solvent show a pure hexagonal phase and nanowire morphology, just like that prepared from the water solvent. On the other hand, the microstructure of LaPO4 samples from DMF,H2O-mixed solvents have been changed: with the increasing volume ratio of DMF to H2O, the crystal phase of LaPO4 has been changed from hexagonal phase to monoclinic phase and the morphology from nanowires to nanoparticles. Finally, the photoluminescence properties of these Eu3+ (Tb3+)-activated rare earth phosphates have been investigated, indicating that the photoluminescent behavior are related to their crystal phases and microstructures. [source] Preferential extractability of ,-oryzanol from dried soapstock using different solventsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 2 2009Raj R Kumar Abstract BACKGROUND: ,-Oryzanol from rice bran has lately gained potential importance because of its proven health benefits. Thus the extractability of ,-oryzanol from the soapstock of crude rice bran oil is important from the perspective of future large-scale production, which would give value addition to this by-product obtained from the rice bran oil industry. The aim of the present study was to investigate the extraction of ,-oryzanol from the drum-dried soapstock of rice bran oil using various solvents. RESULTS: It was found that ,-oryzanol could be extracted most effectively using ethyl acetate, followed by dichloromethane and ethyl methyl ketone. All components of ,-oryzanol have an alcohol group in the ferulate portion giving rise to relatively high polarity, thereby increasing the extraction in more polar solvents efficiently. Ethyl acetate showed maximum extractability of ,-oryzanol by the Soxhlet method. To quantify ,-oryzanol, reverse phase high-performance liquid chromatography (RP-HPLC) was used for fingerprinting the ,-oryzanol analogues with respect to standard ,-oryzanol. CONCLUSION: A new RP-HPLC method for determining the individual components of ,-oryzanol has been reported that can be used for performing an online characterisation of ,-oryzanol analogues by liquid chromatography/mass spectrometry. Copyright © 2008 Society of Chemical Industry [source] Influence of Solvents on the Formation of Honeycomb Films by Water Droplets TemplatingMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2006Ye Tian Abstract Summary: Several solvents were utilized to investigate their influence on the formation of honeycomb patterns. The polymers PPO, PLGA and PLLGA were dissolved in different solvents or mixed solvents to form porous membranes. It was found that a good compatibility between the polymers and their solvents, and an appropriate volatility of the solvent were beneficial for the formation of regular structures. Moreover, C2HCl3 and CH2Cl2, neither of whose PPO solutions could form regular structures at 30,°C, were mixed at different volume ratios to dissolve PPO and fabricate porous structures. The result showed that a regular pattern was achieved when the volume ratio of C2HCl3:CH2Cl2 was 90:10 and that a special structure with big pores surrounded by small pores was obtained when the volume ratio of C2HCl3:CH2Cl2 was 10:90. Based on these phenomena, possible reasons were also proposed. [source] | |||||||||||||||||||||||||||||||||||||