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891.
Renato?Toma?Email author Ivo?Tomini? Marija?Vi?i? Vesna?Sokol 《Journal of solution chemistry》2004,33(11):1397-1410
The emf (electromotive force) of the cell: CdHgx (two phase) | CdCl2 (m) | AgCl | Ag in 2-butanone + water mixtures (containing 5, 10, and 15 mass% 2-butanone) was measured at varying temperature (293.15, 298.15, 303.15, 308.15, and 313.15 K) and in the CdCl2 molality range from 0.002 to 0.02 mol-kg–1. At each temperature the standard emf of the cell (Emo) was determined using potentiometric data and literature values for the stability constants of chlorocadmium complexes. The Emo values were used to calculate the standard thermodynamic quantities for the cell reaction, the stoichiometric mean molal activity coefficients of CdCl2, and the thermodynamic functions for CdCl2 transfer from water to 2-butanone + water mixtures. The transfer process is a forced one and results in an entropy decrease. The transfer functions were compared to those obtained for the same electrolyte in acetone + water mixtures, as well as to those for HBr in ketone + water mixtures. Medium effects upon CdCl2 were calculated and discussed for the examined mixtures (2-butanone + water). 相似文献
892.
Stephan Hagspiel Dren Elezi Merle Arrowsmith Felipe Fantuzzi Alfredo Vargas Anna Rempel Marcel Hrterich Ivo Krummenacher Holger Braunschweig 《Chemical science》2021,12(22):7937
Doubly base-stabilised cyano- and isothiocyanatoborylenes of the form LL′BY (L = CAAC = cyclic alkyl(amino)carbene; L′ = NHC = N-heterocyclic carbene; Y = CN, NCS) coordinate to group 6 carbonyl complexes via the terminal donor of the pseudohalide substituent and undergo facile and fully reversible one-electron oxidation to the corresponding boryl radical cations [LL′BY]˙+. Furthermore, calculations show that the borylenes have very similar proton affinities, both to each other and to NHC superbases. However, while the protonation of LL′B(CN) with PhSH yielding [LL′BH(CN)+][PhS−] is fully reversible, that of LL′B(NCS) is rendered irreversible by a subsequent B-to-CCAAC hydrogen shift and nucleophilic attack of PhS− at boron.Borylenes of the form (CAAC)(NHC)BY (Y = CN, NCS; CAAC = cyclic alkyl(amino)carbene; NHC = N-heterocyclic carbene) coordinate to group 6 carbonyl complexes via Y, and show reversible boron-centered Brønsted basicity and one-electron oxidation. 相似文献
893.
The liquidus temperature was measured in the ammonium nitrate-dimethylsulfoxide-water system over in the concentration range 0–60 mole% ammonium nitrate. The probable formation of the NH4NO3·nDMSO solvate with n=1.3–1.5 and the mixed solvate NH4NO3·DMSO·H2O at 30 mole% ammonium nitrate and a DMSO:H2O ratio of 4∶1 are indicated. The glass transition temperatures T g were measured over a salt concentration range of 0–50 mol% ammonium nitrate and at various compositions of the mixed solvent (y DMSO =0.1–0.9 mole fraction). At a constant mixed solvent composition, the dependence of the glass transition temperature on the salt concentration can be approximated by a linear relationship, as can its dependence on the DMSO content in the solution at constant salt concentration. The glass-forming composition regions were found and the limits of this region are discussed. 相似文献
894.
Schmitt M Böhm M Ratzer C Vu C Kalkman I Meerts WL 《Journal of the American Chemical Society》2005,127(29):10356-10364
The conformational space of tryptamine has been thoroughly investigated using rotationally resolved laser-induced fluorescence spectroscopy. Six conformers could be identified on the basis of the inertial parameters of several deuterated isotopomers. Upon attaching a single water molecule, the conformational space collapses into a single conformer. For the hydrogen-bonded water cluster, this conformer is identified unambiguously as tryptamine A. In the complex, the water molecule acts as proton donor with respect to the amino group. An additional interaction with one of the aromatic C-H bonds selectively stabilizes the observed conformer more than all other conformers. Ab initio calculations confirm much larger energy differences between the conformers of the water complex than between those of the monomers. 相似文献
895.
The reaction product of 4-oxo-4H-[1]benzopyran-3-carbaldehyde and 1,2-benzenediamine is 1,8-dihydro-6,13-bis(2-hydroxybenzoyl)dibenzo[b,i]-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene ( 1 ), and its dehydrogenation product is 3-(2-benzimidazolyl)-4H-[1]benzopyran-4-one ( 2 ) as shown by X-ray structure analysis confirming our earlier report. 相似文献
896.
Determination of total sulfur in diesel fuel employing NIR spectroscopy and multivariate calibration
Breitkreitz MC Raimundo IM Rohwedder JJ Pasquini C Dantas Filho HA José GE Araújo MC 《The Analyst》2003,128(9):1204-1207
A method for sulfur determination in diesel fuel employing near infrared spectroscopy, variable selection and multivariate calibration is described. The performances of principal component regression (PCR) and partial least square (PLS) chemometric methods were compared with those shown by multiple linear regression (MLR), performed after variable selection based on the genetic algorithm (GA) or the successive projection algorithm (SPA). Ninety seven diesel samples were divided into three sets (41 for calibration, 30 for internal validation and 26 for external validation), each of them covering the full range of sulfur concentrations (from 0.07 to 0.33% w/w). Transflectance measurements were performed from 850 to 1800 nm. Although principal component analysis identified the presence of three groups, PLS, PCR and MLR provided models whose predicting capabilities were independent of the diesel type. Calibration with PLS and PCR employing all the 454 wavelengths provided root mean square errors of prediction (RMSEP) of 0.036% and 0.043% for the validation set, respectively. The use of GA and SPA for variable selection provided calibration models based on 19 and 9 wavelengths, with a RMSEP of 0.031% (PLS-GA), 0.022% (MLR-SPA) and 0.034% (MLR-GA). As the ASTM 4294 method allows a reproducibility of 0.05%, it can be concluded that a method based on NIR spectroscopy and multivariate calibration can be employed for the determination of sulfur in diesel fuels. Furthermore, the selection of variables can provide more robust calibration models and SPA provided more parsimonious models than GA. 相似文献
897.
Laan W van der Horst MA van Stokkum IH Hellingwerf KJ 《Photochemistry and photobiology》2003,78(3):290-297
The flavin adenine dinucleotide (FAD)-containing photoreceptor protein AppA (in which the FAD is bound to a novel so-called BLUF domain) from the purple nonsulfur bacterium Rhodobacter sphaeroides was previously shown to be photoactive by the formation of a slightly redshifted long-lived intermediate that is thought to be the signaling state. In this study, we provide further characterization of the primary photochemistry of this photoreceptor protein using UV-Vis and Fourier-transform infrared spectroscopy, pH measurements and site-directed mutagenesis. Available evidence indicates that the FAD chromophore of AppA may be protonated in the receptor state, and that it becomes exposed to solvent in the signaling state. Furthermore, experimental data lead to the suggestion that intramolecular proton transfer (that may involve [anionic] Tyr-17) forms the basis for the stabilization of the signaling state. 相似文献
898.
Vclav Stpn Josef Vodehnal Ivo Kssler Norman G. Gaylord 《Journal of polymer science. Part A, Polymer chemistry》1967,5(3):503-509
The γ-ray-initiated polymerization of butadiene, isoprene, and 2,3-dimethylbutadiene-1,3 was carried out at temperatures of 20°C. and ?78°C. Polymers of butadiene and isoprene with mixed linear and cyclic structure were proved to result from the polymerization at ?78°C. A monocyclic structure was found for the 2,3-dimethylbutadiene-1,3 polymers initiated either at ?78°C. or in the thiourea canal complex at 20°C. 相似文献
899.
Dumitru Baleanu Ivo Petras Jihad H. Asad Maria Pilar Velasco 《International Journal of Theoretical Physics》2012,51(4):1253-1258
In this paper we study the fractional Lagrangian of Pais–Uhlenbeck oscillator. We obtained the fractional Euler–Lagrangian
equation of the system and then we studied the obtained Euler–Lagrangian equation numerically. The numerical study is based
on the so-called Grünwald–Letnikov approach, which is power series expansion of the generating function (backward and forward
difference) and it can be easy derived from the Grünwald–Letnikov definition of the fractional derivative. This approach is
based on the fact, that Riemman–Liouville fractional derivative is equivalent to the Grünwald–Letnikov derivative for a wide
class of the functions. 相似文献
900.