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Same Solvent (same + solvent)
Selected AbstractsPhotophysical and Photochemical Properties of Fluorinated and Nonfluorinated n -Propanol-Substituted Zinc PhthalocyaninesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010lke Gürol Abstract The synthesis of symmetrical fluorinated and nonfluorinated zinc(II) phthalocyanine derivatives obtained from 4,5-dichlorophthalonitrile, 4-nitrophthalonitrile and 3-nitrophthalonitrile substituted with 2,2,3,3-tetrafluoro-1-propanol and n -propanol are described. The comparison of the photophysicochemical properties of fluorinated and nonfluorinated substituted zinc(II) phthalocyanines is reported for the first time. The new compounds have been characterized by elemental analysis, IR, 1H NMR and 19F NMR spectroscopy, electronic spectroscopy and mass spectra. The photophysical and photochemical properties of the compounds were studied in dimethyl sulfoxide (DMSO). The complexes were quenched with benzoquinone (BQ), and their fluorescence-quenching properties were investigated in the same solvent. The effects of the number of the substitution and the position on the photophysical and photochemical parameters of the zinc(II) phthalocyanines 1a,7a are also reported. Photophysical and photochemical properties of phthalocyanine complexes are very useful for photodynamic therapy (PDT) of cancer applications. In particular, high singlet-oxygen quantum yields are very important for Type II mechanisms. These complexes have good singlet-oxygen quantum yields and show potential as Type-II photosensitizers. [source] Chemo- and Enzyme-Catalyzed Reactions Revealing a Common Temperature-Dependent Dynamic Solvent Effect on EnantioselectivityHELVETICA CHIMICA ACTA, Issue 11 2003Gianfranco Cainelli The enantiomeric ratio E of enzyme-catalyzed (Candida antarctica lipase and lipase PS) and chemo-catalyzed (L -proline-based diamines) acylation reactions of 1-(naphthalen-2-yl)ethanol, 2-phenylpropanol, and 2-benzylpropane-1,3-diol is dependent on solvent and temperature. Plots of ln,E vs. 1/T showed the presence of inversion temperatures (Tinv). The Tinv values for the bio-catalyzed and the chemo-catalyzed reactions are fairly in agreement, and correspond as well to the TNMR values obtained by variable-temperature 13C-NMR experiments on the substrates in the same solvent of the resolution. This result demonstrates that clustering effects in the substrate solvation manage the chemical and the enzymatic enantioselectivity, and, moreover, that the solutesolvent cluster is always the real reacting species in solution for chemical as well as for enzymatic reactions. [source] Theoretical investigation of electron transfer transition in tetracyanoethylene-contained organic complexesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2002Xiang-Yuan Li Abstract In this work, the authors use complete active space self-consistent field method to investigate the photoinduced charge-separated states and the electron transfer transition in complexes ethylene-tetracyanoethylene and tetramethylethylene-tetracyanoethylene. Geometries of isolated tetracyanoethylene, ethylene, and tetramethylethylene have been optimized. The ground state and the low-lying excited states of ethylene and tetracyanoethylene have been optimized. The state energies in the gas phase have been obtained and compared with the experimentally observed values. The torsion barrier of tetracyanoethylene has been investigated through the state energy calculation at different conformations. Attention has been particularly paid to the charge-separated states and the electron transfer transition of complexes. The stacked conformations of the donor,acceptor complexes have been chosen for the optimization of the ground and low-lying excited states. Equilibrium solvation has been considered by means of conductor-like screening model both in water and in dichloromethane. It has been found that the donor and tetracyanoethylene remain neutral in complexes in ground state 1A1 and in lowest triplet state 3B1, but charge separation appears in excited singlet state 1B1. Through the correction of nonequilibrium solvation energy based on the spherical cavity approximation, ,,,* electron transfer transition energies have been obtained. Compared with the experimental measurements in dichloromethane, the theoretical results in the same solvent are found higher by about 0.5 eV. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 874,886, 2002 [source] Effect of relative solubility on amino acid crystal purityAICHE JOURNAL, Issue 12 2001Jeffrey C. Givand The ratio of the pure-component solubility of a primary solute to that of an impurity in the same solvent has a dramatic impact on crystal purity when lattice substitution is the dominant mechanism of impurity incorporation in the crystal. This is demonstrated for a model system of isoleucine and leucine in which leucine is the impurity. The pure-component solubility ratios of isoleucine to leucine in mixed solvents were measured and used to select solvents that could affect the lattice substitution of leucine in isoleucine crystals. Addition of electrolytes and/or cosolvents to aqueous solutions of the two amino acids improved the purity of isoleucine crystals obtained by cooling. [source] Nano-Level Mixing of ZnO into Poly(methyl methacrylate)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2010Mukesh Agrawal Abstract A simple, facile and versatile approach is presented for the preparation of PMMA/ZnO nanocomposite materials, which possess high transparency, no color, good thermal stability, UV absorption and improved mechanical properties. The employed process involved mixing of ZnO nanoparticles dispersed in DMAc with the PMMA matrix dissolved in the same solvent. The effect of ZnO content on the physical properties of the PMMA matrix is studied. A significant improvement in mechanical properties was observed with the incorporation of 0.5 wt.-% ZnO particles. The beauty of the described approach lies in the fact that despite being a simple and facile approach, it offers nano-level (2,5,nm) mixing of ZnO nanoparticles into a polymer matrix. [source] On the Lamellar Crystal Structure of Nylons 6,8 and 8,10: A Study Combining Electron Microscopy and Energy AnalysisMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2003Marta Bermúdez Abstract Lamellar crystals of nylon 6,8 and nylon 8,10 with chains in a fully extended conformation were obtained by crystallization in solution, and examined by electron and X-ray diffraction. The same crystal structure appeared to be shared by both nylons crystallized in glycerin. This structure consisted of a mixture of ,- and ,-forms with features similar to that previously described for lamellar crystals of nylon 4,6 grown in the same solvent. Crystallization of nylon 8,10 in hexane-2,5-diol afforded lamellar crystals with sheets stacked in the ,-form. A comparative energy evaluation of the different models that are feasible for the crystal structure of these nylons with fully extended chains indicated very small energy differences among them. The presence of different chain arrangements in the same lamellar crystal, as well as the crystallization of the same nylon in different crystal forms upon slight modification of the crystallization conditions, are fully consistent, therefore, with the results obtained in the energy analysis. Nylon 8,10 crystals grown in hexane-2,5-diol at 150,°C. Inset: The respective electron diffraction patterns. [source] Effect of ,-irradiation on the physical properties and dyeability of poly(vinyl butyral) blends with polystyrene and poly(ethylene glycol)POLYMER COMPOSITES, Issue 6 2008Horia M. Nizam El-Din Cast films of polymer blends essentially based on poly(vinyl butyral) (PVB) and equal ratios of polystyrene (PS) and poly(ethylene glycol) (PEG) were prepared from benzene and butyl alcohol solutions of the individual polymers. The effect of ,-irradiation on the thermal decomposition and tensile mechanical properties was investigated. Moreover, the effect of ,-irradiation on the dye affinity of PVB/PS and PVB/PEG for basic and acid dyestuffs was studied. The thermogravimetric analysis (TGA) study showed that the unirradiated PVB polymer films prepared in benzene displayed higher thermal stability than the same polymer films prepared in butanol. However, in all cases the thermal stability was found to increase with increasing ,-irradiation dose. On the other hand, PVB/PS blend possesses higher thermal stability than PVB/PEG, as shown from the determination of the weight loss (%) at different heating temperatures, the temperatures of the maximum rate of reaction and the activation energy. While, pure PS films showed the stress-strain behavior of brittle polymers, PVB/PS films showed the behavior of tough polymers with yielding properties. The results of dyeing clearly showed that the solvent type, blend composition, and irradiation dose are determining factors for the dye affinity for basic or acid dyes. For example, unirradiated PVB films prepared from butanol displayed a higher affinity for the basic and acid dyes than the same polymer prepared from the same benzene. However, PVB prepared from butanol showed higher affinity to the dyes than PS prepared from the same solvent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Conformational polymorphism in a Schiff-base macrocyclic organic ligand: an experimental and theoretical studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Leonardo Lo Presti Polymorphism in the highly flexible organic Schiff-base macrocycle ligand 3,6,9,17,20,23-hexa-azapentacyclo(23.3.1.111,15.02,6.016,20)triaconta-1(29),9,11,13,15(30),23,25,27-octaene (DIEN, C24H30N6) has been studied by single-crystal X-ray diffraction and both solid-state and gas-phase density functional theory (DFT) calculations. In the literature, only solvated structures of the title compound are known. Two new polymorphs and a new solvated form of DIEN, all obtained from the same solvent with different crystallization conditions, are presented for the first time. They all have symmetry, with the macrocycle positioned on inversion centres. The two unsolvated polymorphic forms differ in the number of molecules in the asymmetric unit Z,, density and cohesive energy. Theoretical results confirm that the most stable form is (II°), with Z, = 1.5. Two distinct molecular conformations have been found, named `endo' or `exo' according to the orientation of the imine N atoms, which can be directed towards the interior or the exterior of the macrocycle. The endo arrangement is ubiquitous in the solid state and is shared by two independent molecules which constitute an invariant supramolecular synthon in all the known crystal forms of DIEN. It is also the most stable arrangement in the gas phase. The exo form, on the other hand, appears only in phase (II°), which contains both the conformers. Similarities and differences among the occurring packing motifs, as well as solvent effects, are discussed with the aid of Hirshfeld surface fingerprint plots and correlated to the results of the energy analysis. A possible interconversion path in the gas phase between the endo and the exo conformers has been found by DFT calculations; it consists of a two-step mechanism with activation energies of the order of 30,40,kJ,mol,1. These findings have been related to the empirical evidence that the most stable phase (II°) is also the last appearing one, in accordance with Ostwald's rule. [source] Fourier transform vibrational circular dichroism as a decisive tool for conformational studies of peptides containing tyrosyl residuesBIOPOLYMERS, Issue 1 2003Attila Borics Abstract Previous UV,circular dichroism (UV,CD) and NMR studies showed that Ac-AAAAAAAEAAKA-NH2 has an ,-helical structure in 50% (v/v) aqueous trifluoroethanol. Replacement of Ala1 to Ala6 with Tyr results in spectra that show an apparent loss of helicity in the same solvent. This apparent loss of helicity could be attributed to the coupling of the tyrosyl side chain chromophore with the backbone amide. However, such electronic coupling does not affect the vibrational CD (VCD) spectra. The VCD spectra of the peptides with tyrosyl residues were identical to that of the peptide containing no Tyr, which shows the same ,-helical structure. Because it is now clear that Tyr replacement does not change the backbone conformation of peptides, UV,CD measurements should be complemented by VCD to determine the secondary structure when electronic effects can disturb the UV,CD spectrum of the inherent structure. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 21,24, 2003 [source] Chain stiffness of heteropolysaccharide from Aeromonas gum in dilute solution by dynamic light scatteringBIOPOLYMERS, Issue 6 2002Xiaojuan Xu Abstract Dynamic light scattering measurements have been made on 15 fractions of aeromonas (A) gum, an extracellular heteropolysaccharide produced by the strain Aeromonas nichidenii, with dimethylsulfoxide containing 0.2M lithium chloride as the solvent at 25°C. Data for the translational diffusion coefficient D covering a molecular weight range from 4.5 × 105 to 2.1 × 106 and ratios of the z -average radius of gyration ,s2,z1/2 to the hydrodynamic radius RH (calculated with previous ,s2,z data) suggest that the polymer behaves like a semiflexible chain in this solvent similar to the stiffness of cellulose derivatives. Thus the D data are analyzed on the basis of the Yamakawa,Fujii theory for the translational friction coefficient of a wormlike cylinder by coarse-graining the heteropolysaccharide molecule. Excluded-volume effects are taken into account in the quasi-two-parameter scheme, as was done previously for ,s2,z and [,] (the intrinsic viscosity) of A gum in the same solvent. The molecular weight dependence of RH is found to be explained by the perturbed wormlike chain with a persistence length of 10 nm, a linear mass density of 1350 nm,1, an excluded-volume strength parameter of 1.3 nm, and a chain diameter of 2.8 nm. These parameters are in substantial agreement with those estimated previously from ,s2,z and [,] data, demonstrating that the solution properties (D, ,s2,z, and [,]) of the heteropolysaccharide are almost quantitatively described by the current theories for wormlike chains in the molecular weight range studied. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 387,394, 2002 [source] A Time-Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3,,5,-Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction PathwayCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2010Chensheng Ma Dr. Abstract 3,,5,-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3,,5,-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH3CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di- meta -methoxybenzylic moieties, for the DMBDP deprotection, comparative fs-TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3,,5,-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady-state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR3 results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection,cyclization mechanism for DMBDP in CH3CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be ,1,ns. This indicates that there is little relevance for the long-lived intermediates (>10,ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3,,5,-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (,2,ps) heterolytic bond cleavage after photoexcitation of meta -methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. [source] Physicochemical characterization of carrageenans,A critical reinvestigationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Gisela Berth Abstract Kappa-, iota-, and lambda-carrageenan (food grade) were analyzed by static light scattering (MALS in batch mode) in 0.1M NaNO3 at 25 and 60°C, earlier heated up to 90°C or not. At 25°C, there was a strong tendency for a concentration-dependent aggregation in the order lambda < kappa < iota. At 60°C, all samples were molecularly dispersed. The strongly temperature-dependent refractive index increments (equilibrium dialysis) differ. Data interpretation in terms of the wormlike chain model using the Skolnik-Odijk-Fixman approach led to an intrinsic persistence length around 3 to 4 nm and expansion factors as high as 1.5 and above in a thermodynamically good solvent for all three types. Triple-detector HPSEC (DRI, MALS, viscometry) on the three commercial samples plus a degraded (by acidic hydrolysis) kappa-carrageenan in the same solvent/eluant at 60°C yielded a uniform and slightly curved [,]- M relationship for 5 × 103 , M/(g mol) , 3 × 106 and a nearly identical molar mass dependence of the radius of gyration. HPSEC at 25°C on kappa-carrageenan confirmed formation of soluble aggregates. Special emphasis was put on analytical and methodological aspects. The reliability of the experimental data was demonstrated by analogous measurements on dextran calibration standards. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Contribution to the Reactivity of N,N, -Diaryl-1,4-diazabutadienes Aryl,N=CH,CH=N,Aryl (Aryl = 2,6-Dimethylphenyl; 2,4,6-Trimethylphenyl) Towards Boron TrichlorideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2006Lothar Weber Abstract The reaction of Aryl,N=CH,CH=N,Aryl (3a: Aryl = 2,6-Me2C6H3; 3b: Aryl = 2,4,6-Me3C6H2) with 2 equiv. BCl3 in a toluene/hexane mixture at ,50 °C led to an inseparable mixture of borolium salts [Aryl,Na=CH,CH=N(Aryl)BCl2(Na,B)]+BCl4, (4a: Aryl = 2,6-Me2C6H3; 9a: Aryl = 2,4,6-Me3C6H2) and [Aryl,Na=CH,C(Cl)=N(Aryl)BCl2(Na,B)]+BCl4, (4b: Aryl = 2,6-Me2C6H3; 9b: Aryl = 2,4,6-Me3C6H2) and the bicyclic species [HCa=N(Aryl)BCl2N(Aryl),Cb=(Ca,Cb)]2 (5: Aryl = 2,6-Me2C6H3; 10: Aryl = 2,4,6-Me3C6H2). Sodium amalgam reduction of borolium salts 4a,b and 9a,b afforded inseparable mixtures of the diazaboroles 2,6-Me2C6H3NaCH=CR,Nb(2,6-Me2C6H3)BCl(Na,B) (1: R = H; 6: R = Cl) and 2,4,6-Me3C6H2NaCH=CR,Nb(2,4,6-Me3C6H2)BCl(Na,B) (2: R = H; 11: R = Cl). In order to obtain pure 1 and 2, diazabutadienes 3a and 3b were slowly combined with 2 equiv. BCl3 in the same solvents at ,78 °C. The acyclic adducts Cl3BN(Aryl)=CH,CH=N(Aryl)BCl3 (7a: Aryl = 2,6-Me2C6H3; 7b: Aryl = 2,4,6-Me3C6H2) were reduced with sodium amalgam to furnish the aminoboranes Cl2BN(Aryl)CH=CH,N(Aryl)BCl2 (8: Aryl = 2,6-Me2C6H3; 12: Aryl = 2,4,6-Me3C6H2). Stirring solutions of 8 and 12 in the presence of CaH2 cleanly gave the diazaboroles 1 and 2, respectively. The novel compounds were characterized by elemental analyses and 1H-, 11B-, 13C NMR and mass spectra. The molecular structures of 1, 4a, 5 and 8 were elucidated by single X-ray diffraction analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Effect of gutta-percha solvents at different temperatures on the calcium, phosphorus and magnesium levels of human root dentinJOURNAL OF ORAL REHABILITATION, Issue 8 2001H. Do The aim of this study in vitro investigation was to evaluate the alterations caused by warmed gutta-percha solvents on the calcium, phosphorus and magnesium levels of root dentin. Extracted human anterior teeth, whose crowns and apical root thirds had been removed were used as root dentin specimens. The roots were sectioned longitudinally into two segments, cleaned and dried. Segments were divided into 12 groups (n=12). In 6 groups, the specimens received treatment with the following solvents at room temperature (22 °C): Chloroform, xylene, eucalyptol, orange oil, halothane and saline (control). Within each group, the specimens were further subgrouped into two to be incubated (100% humidity at 37 °C) for 5 and 10 min, respectively, following treatment with the solvents. The remaining six groups were treated with the same solvents which had been previously warmed to body temperature (37 °C) and received the same experimental procedures. The levels of calcium, phosphorus and magnesium in each specimen were analysed using energy dispersive spectrometric microanalysis. Statistical analysis of the readings showed that neither warming of the solvents nor prolonged incubation (treatment) time was capable of altering the histochemical composition of cut root dentin surfaces. [source] | |||||||||||||