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11.
Udo Kaatze 《Journal of solution chemistry》1997,26(11):1049-1112
A tutorial on dielectric (relaxation) spectrometry of liquids is given in this article. Some methods of measuring complex
(electric) permittivity spectra are briefly described. Results for water are presented and related to characteristic properties
of the liquid structure and to models of the molecular dynamics, particularly as resulting from computer simulation studies.
Dielectric spectra for aqueous solutions of low weight electrolytes, polyelectrolytes, small molecules, and polymers are discussed
to illustrate effects of kinetic depolarization, structure saturation, as well as positive, negative, and hydrophobic hydration.
Reference is also made to fluctuations in the hydrogen bond network of mixtures of water with liquids that are completely
miscible with this unique solvent. 相似文献
12.
F López Arbeloa J Ba?uelos Prieto V Martínez Martínez T Arbeloa López I López Arbeloa 《Chemphyschem》2004,5(11):1762-1771
Absorption and fluorescence (steady-state and time-correlated) techniques are used to study the photophysical characteristics of the pyrromethene 650 (PM650) dye. The presence of the cyano group at the 8 position considerably shifts the absorption and fluorescence bands to lower energies with respect to other related pyrromethene dyes; this is attributed to the strong electron-acceptor character of the cyano group, as is theoretically confirmed by quantum mechanical methods. The fluorescence properties of PM650 are intensively solvent-dependent. The fluorescence band is shifted to lower energies in polar/protic solutions, and the evolution of the corresponding wavelength with the solvent is analysed by a multicomponent linear regression. The fluorescence quantum yield and the lifetime strongly decrease in polar/protic solvents, which can be ascribed to an extra nonradiative deactivation, via an intramolecular charge-transfer state (ICT state), favoured in polar media. 相似文献
13.
14.
Elizabeth P.G. Arêas José A.G. Arêas James Hamburger Warner L. Peticolas Paulo S. Santos 《Journal of colloid and interface science》1996,180(2):578
A remarkably high viscosity has been induced in protein aqueous solutions by the addition of certain structurally related organic solvents. The effect has been observed for lysozyme aqueous solutions containing tetramethylurea (TMU), dimethylsulfoxide (DMSO), dimethylformamide, and hexamethylphosphortriamide. The effect has also been induced in ferrocytochrome c aqueous solutions by TMU. Critical concentrations for both the protein and organic solvent were verified for the onset of the viscosity increase. A common feature of the solvents which were able to induce the effect is a dipolar moiety (C=O, S → O and P → O) and a nonpolar region represented by the methyl groups. The resulting fluids show an extremely restricted flow and a typical non-Newtonian, pseudoplastic behavior. Use was made of1H nuclear magnetic resonance (NMR) and Raman spectroscopy to characterize protein structural modifications and of13C NMR to investigate changes in relaxation times and chemical shifts in the solvent/water solutions. A systematic rheological characterization of the systems was undertaken for some of the solvents, and unusual patterns of viscous effects were identified for the solvent/water systems both with and without protein. The process was found to be at least partially reversible, as concluded from the recovered original solution rheological characteristics and the original protein1H NMR spectrum, after eliminating the organic solvent by ultrafiltration. The whole process was characterized as consisting of two mutually independent stages. The first involves an extensive conformational transition of the polypeptide backbone, from a predominantly α-helical to increased random coiled and β-sheet structures, with the occurrence of nonorthodox protein secondary structures at regions above the solvent critical point. The second stage consists of short-lived interchain contacts leading to an entanglement of the macromolecular system as a whole. A microphase reversion in the organic solvent/water mixture, supported by13C NMR and rheological results, is proposed as the driving force causing the observed behavior. 相似文献
15.
M. Nagy 《Colloid and polymer science》1985,263(3):245-265
16.
Jin-Woong?Kim Jin-Gyu?Park Jee-Hyun?Ryu Ih-Seop?Chang Kyung-Do?SuhEmail author 《Colloid and polymer science》2005,283(11):1233-1240
This study presents a method to produce monodisperse chloromethyl-functionalized macroporous poly(styrene-co-divinylbenzene) polymer particles by seeded polymerization in aqueous media. We observed that the molecular structure of
polystyrene seed particles, the composition of the secondary monomer mixtures, and the type of solvents were very important
factors that determine the morphology and porosity of the final particles. This study proposes that the molecular chemistry
of polystyrene seed polymers, increasing molecular weight or crosslinking, is another factor that can control the porosity
of the final particles. Also, the selection of a poor solvent was effective in forming the larger surface area. In this study,
it was confirmed that the chloromethyl groups introduced on the surface of porous particles were quantified chemically and
their effective incorporation had a close relationship with the surface area. 相似文献
17.
The absorption spectra of isoquinoline-iodine or 2,4-lutidine-iodine solutions in organic solventsn-hexane,n-heptane, cyclohexane, carbon tetrachloride, benzene, toluene, chlorobenzene, ando-dichlorobenzene have been measured and interpreted in terms of the D+I2=DI2 equilibrium, where D is isoquinoline or 2,4-lutidine. Values ofK (288–320°K), ΔHo, and ΔSo for the reaction were calculated. A correlation between theK values and the solubility parameter of the solvent (Buchowski's relation) has been found. 相似文献
18.
Langlet J. Claverie P. Pullman B. Piazzola D. Daudey J. P. 《Theoretical chemistry accounts》1977,46(2):105-116
The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works. 相似文献
19.
The low vapor pressure and the versatility of the physico-chemical properties of ionic liquids make them really attractive as an alternative for conventional molecular solvents. The knowledge of their physico-chemical properties (viscosity, conductivity, miscibility with organic solvents and anion-cation interactions) has appeared mandatory for better targeting their applications, although it is generally still lacking or incomplete.This work promotes capillary electrophoresis instrumentation as an integrated apparatus for measurement of viscosity, conductivity and absorbance of pure ionic liquids and ionic liquid-molecular solvent mixtures. Compared to current conventional techniques, the assets of this instrumentation for this purpose are the combined availability of a pressure delivery system, power supply, diode array absorbance detector and thermoregulation device, allowing unattended, automatic and easy operation, involving minimum sample handling. Most importantly, the required sample volume can be reduced to about 50 μL, making this protocol very cost-effective. A protocol was optimized with respect to time, sample consumption and data reliability for the determination of these physico-chemical parameters. Ionic liquids selected for method development and validation differed in the nature of their cation (butyl- and ethyl-methylimidazolium) and anion (trifluoromethanesulfonate and bis(trifluoromethanesulfonyl)imide). Various molecular solvents were mixed with these ionic liquids (acetonitrile, methanol, dimethylformamide and trifluoroethanol) and the same physico-chemical properties were determined by optimized methods. The knowledge of these data should be of great support in various application areas, including the development of new separation media for capillary electrophoresis and chromatographic techniques. 相似文献
20.
S Katrych A Grytsiv A Bondar T Velikanova M Bohn 《Journal of solid state chemistry》2004,177(2):493-497
Phase equilibria in the Nb-Nb5Si3-NbB region were studied in the melting (crystallization) range by means of light microscopy, XRD, SEM and EMPA on alloys after arc-melting and annealing at 1800°C and at subsolidus temperatures. Phase transition and melting temperatures were determined by DTA and pyrometric Pirani-Alterthum technique resulting in a solidus projection and two isopleths, Nb77Si23-Nb77B23 and Nb99Si1-Nb5Si2B. The T2-phase Nb5Si3−xBx (0?x?2, Cr5B3-type) was found to form equilibria with (Nb), NbB, Nb3Si, and with the T1-phase (Mn5Si3 derivative type). The T2-phase melts incongruently (Nb5Si1.8B1.2 at 2245°C) and forms a quasibinary eutectic with the niobium solid solution on a minimum tie-line at ∼1880°C. 相似文献