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1.
Infinite dilution activity coefficients of sulfur dioxide in various organic solvents were correlated with two basicity scales: the solvent Gutmann donor number and Arnett heat of hydrogen bonding. Linear correlations were observed for both basicity scales, and the accuracy of activity coefficient prediction is estimated to be ±20 to 25%. Infinite dilution activity coefficients of sulfur dioxide in over 80 organic solvents were estimated from the correlations. 相似文献
2.
S. V. Mikheev V. A. Sharnin V. A. Shormanov M. N. Talanova 《Journal of Thermal Analysis and Calorimetry》1995,45(4):715-720
The integral heat effects of CuCl2 dissolution in aqueous DMSO, aqueous ethanol and aqueous acetone solutions at 298. 15 K in the electrolyte concentration range 0.001–0.01M were measured by means of calorimetry. ΔH sol 0 values were obtained by extrapolation to zero electrolyte concentration. Literature data were used to determine the thermodynamic characteristics of Cu2+ transfer from water to aqueous organic solvents. 相似文献
3.
The stability constants of the potassium complex with dibenzo-30-crown-10 have been determined from potentiometric or solubility measurements in the solvents: methanol, iso-propanol, n-butanol, propylene carbonate, acetonitrile and dimethylsulfoxide. The solubility of the ligand in these solvents has also been determined and the transfer activity coefficients of the potassium complex for transfer from methanol to solvent (S), SM(KL+), have been computed. Although solid state studies indicate that dibenzo-30-crown-10 completely surrounds the potassium ion and shields it from water, the transfer activity coefficient of the potassium complex is found to be highly solvent dependent. Dibenzo-30-crown-10 is thus less effective for the removal of the solvation sphere of the potassium ion than previously estimated. 相似文献
4.
T. V. Dorokhova V. A. Mikhailov A. L. Kanibolotskii T. M. Prokop’eva V. A. Savelova A. F. Popov 《Theoretical and Experimental Chemistry》2008,44(5):307-315
A study was carried out on the reversible decomposition of dibromobromate anions in organic solvents and we found the equilibrium
constants for the processes responsible for the distribution of active halogen and hydrogen halide between their different
forms in solution. The capacity of the solvent to form hydrogen bonds with the bromide anion, the feasibility of forming a
molecular complex with bromine, and the structure of the cation (in solutions with low ionizing capacity) were all found to
affect the reversible decomposition of the dibromobromate anion.
Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 298–305, September–October, 2008. 相似文献
5.
L. I. Krishtalik 《Russian Journal of Electrochemistry》2006,42(10):1006-1016
Despite their well-known drawbacks, the approaches of continuum electrostatics are widely used at the analysis of the energies of solvation and reorganization. We propose a method to check the applicability of these approaches in the determination of the solvation energy, which is based on measuring the difference of redox potentials ΔE of two consecutive redox reactions, e.g. for the pairs Co(Cp) 2 + /Co(Cp)2/Co(Cp) 2 ? (here, Cp is cyclopentadienyl). In this difference, the solvophobic effects and the liquid junction potential between the working and reference electrodes, which is impossible to measure, cancel out. From the difference of ΔE in two different solvents, the sum of the electrostatic components of the cation-and anion-transfer energies is determined. It is shown that, for large low-charged ions in aprotic media, the continuum electrostatics proves to be true in a wide range of dielectric permittivities including those typical for proteins. The Stokes shift of fluorescence spectra for proflavine (PF) showed that the water reorganization energy and, hence, the energy of the static dielectric response are anomalously high. To study this effect on the solvation energy, we determined the redox potentials of the Co(Cp) 2 + /Co(Cp)2 pair in a number of water-organic media. The organic cosolvent breaks the water structure and reduces the reorganization energy. Accordingly, the redox potential turns more positive. This allowed us to determine the energy of transfer of Co(Cp) 2 + ions (and, hence, of other ions) nonviolated by the water structure specifics. The experimental energies of the acetate transfer exceed those calculated by an order of magnitude. This demonstrates the incorrectness of the widely used semicontinuum calculations of the pK of ionogenic groups of proteins. A new algorithm, which permits overcoming this discrepancy, is proposed, namely, the short-range interactions are taken into account based on the experimental energies of the transfer to a model DMF solvent, while the transfer energy from this solvent to the protein is calculated electrostatically. The energy of the ion charging in a protein consists of two physically different components, namely, the charging energy in the pre-existing field of protein dipoles and charges and the energy of the dielectric response of the medium. The former energy is determined by the electronic polarization of the protein (its optical dielectric permittivity), while the latter is determined by all kinds of polarization (static permittivity). Taking into account all the aforementioned peculiarities leads to reasonable agreement with the experiment when estimating the pK of certain groups in α-chymotrypsin. These calculations as well as experimental data (both our and taken form the literature (molecular dynamics)) point to the enhanced dielectric permittivity of the outer layers of proteins. 相似文献
6.
Using the isothermal displacement calorimeter, enthalpies of dilution are obtained for solutions of urea in water, methanol, ethanol, formamide, N,N-dimethyl-formamide, and dimethyl sulfoxide. The results are discussed in terms of solute-solvent and solute-solute interactions.Now Diane Beaumont. 相似文献
7.
A Picker flow microcalorimeter was employed in conjunction with asymmetric syringe-type pumps to measure heats of mixing of highly dilute aqueous solutions of organic solvents. These data were used in turn to determine limiting partial molar excess enthalpies of the examined solvents in water. The measurements were carried out at 298.15 K for 29 common, oxygen and/or nitrogen containing solvents exhibiting complete miscibility with water. Except for only one compound, formamide, the limiting partial molar excess enthalpies are exothermic indicating that the process of dissolution is energetically favored. Comparison to literature data (in most cases to solution enthalpies at infinite dilution measured by batch calorimetry) proved the technique applied to be sufficiently accurate. 相似文献
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The effects of some organic solvents and acids on the atomic fluorescence of tin in air-hydrogen flames have been examined. Ketones and alcohols greatly reduced the florescence sensitivity in fuel rich air-hydrogen flame whereas organic acids generally enhanced the fluorescence signal. The depressive effect of organic solvents was found to be highly dependent on the fuel to oxidant ratio in the flame. An attempt has been made to explain these effects, on the basis of possible reactions occurring in the flame.On leave from Institute of Chemistry, University of the Punjab, Lahore 54590, PakistanOn leave from Department of Analytical Chemistry, University of Zaragoza, Zaragoza, Spain 相似文献
10.
Ionic Solvation in Aqueous and Nonaqueous Solutions 总被引:1,自引:0,他引:1
Hitoshi Ohtaki 《Monatshefte für Chemie / Chemical Monthly》2001,132(11):1237-1268
Summary. The history of studies on ionic solvation is briefly reviewed, and structural and dynamic properties of solvated ions in
aqueous and nonaqueous solutions are discussed. An emphasis is placed on ionic solvation in nonaqueous mixed solvents in which
preferential solvation of ions takes place. A new parameter for expressing the degree of preferential solvation of an ion
is proposed.
Received January 16, 2001. Accepted January 31, 2001 相似文献
11.
The application of hydrolases in organic solvents for synthetic purposes is a procedure routinely adopted in organic chemistry, especially for the preparation of chiral building blocks. Numerous studies have shed light on several aspects of the mechanism of hydrolase action in low-water environments. Procedures suitable to improve the catalytic efficiency of enzymes and productivity of the synthetic processes have been reported. These fundamental and applied investigations have made hydrolase-catalyzed reactions in organic solvents of industrial interest. In this article we describe and discuss various approaches adopted to optimize the performance of hydrolases in organic media, with special emphasis on the formulation of the biocatalysts which, under proper conditions, can display an activity equal to that displayed in aqueous buffers. 相似文献
12.
By using the van’t Hoff and Gibbs equations the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, were evaluated from solubility data of naproxen (NAP) determined at several temperatures in octanol, isopropyl myristate, chloroform, and cyclohexane, as pure solvents. The water-saturated organic solvents also were studied except cyclohexane. The excess free energy and the activity coefficients of the solutes, and the mixing and solvation thermodynamic quantities were also determined. The NAP solubilities were higher in chloroform and octanol with respect to those obtained in cyclohexane. In addition, by using literature values for NAP aqueous solubility, the thermodynamic functions relative to transfer of this drug from water to organic solvents were also estimated. 相似文献
13.
Salleh AB Basri M Taib M Jasmani H Rahman RN Rahman MB Razak CN 《Applied biochemistry and biotechnology》2002,102(1-6):349-357
Recent studies on biocatalysis in water—organic solvent biphasic systems have shown that many enzymes retain their catalytic
activities in the presence of high concentrations of organic solvents. However, not all enzymes are organic solvent tolerant,
and most have limited and selective tolerance to particular organic solvents. Protein modification or protein tailoring is
an approach to alter the characteristics of enzymes, including solubility in organic solvents. Particular amino acids may
play pivotal roles in the catalytic ability of the protein. Attaching soluble modifiers to the protein molecule may alter
its conformation and the overall polarity of the molecule. Enzymes, in particular lipases, have been chemically modified by
attachment of aldehydes, polyethylene glycols, and imidoesters. These modifications alter the hydrophobicity and conformation
of the enzymes, resulting in changes in the microenvironment of the enzymes. By these modifications, newly acquired properties
such as enhancement of activity and stability and changes in specificity and solubility in organic solvents are obtained.
Modified lipases were found to be more active and stable in organic solvents. The optimum water activity (a
w
) for reaction was also shifted by using modified enzymes. Changes in enantioselective behavior were also observed. 相似文献
14.
Rong He Xiaogang You Hongye Tian Feng Gao Daxiang Cui Hongchen Gu 《Frontiers of Chemistry in China》2006,1(4):378-383
Nearly monodisperse CdSe quantum dots (QDs) have been prepared by a soft solution approach using air-stable reagents in different
organic solvents. This scheme is a supplement to the conventional thermal decomposition of organometallic compounds at higher
temperatures. CdSe nanocrystals of different sizes could be obtained by simply changing the solvent. This method is reproducible
and simple and thus can be readily scaled up for industrial production. The reaction process was monitored by the temporal
evolution of the UV-Vis absorption and room temperature photoluminensce spectra. The structures of the CdSe quantum dots were
determined by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The phase-transfer of oleic acid-stabilized
CdSe nanocrystals into PBS buffer solutions was also studied for their potentials in biological applications.
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Translated from Journal of Shanghai Jiaotong University, 2005, 39(1) (in Chinese) 相似文献
15.
By the gravimetric method, the solubility of sorbic acid in eight solvents including ethanol, 2-propanol, methanol, 1-butanol, ethyl acetate, methyl tert-butyl ether, acetone and acetonitrile was determined over a temperature range from 285.15 to K at atmospheric pressure. For the temperature range investigated, the solubility of sorbic acid in the solvents increased with increasing temperature. The experimental values were correlated with the linear solvation energy relationship, modified Apelblat equation, λh equation, non-random two-liquid (NRTL) model, and Wilson model. On the other hand, the enthalpy, entropy and Gibbs free energy of dissolution were obtained from these solubility values by using the van’t Hoff and Gibbs equations. The excess enthalpy of solution was estimated on the basis of λh equation. Furthermore, the a priori predictive model COSMO-RS was employed to predict the solubility of sorbic acid in selected solvents and reasonable agreement with experimental values is achieved. 相似文献
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18.
In an attempt to prepare stable dispersions of cellulose nanocrystals in dipolar aprotic solvents, dilute aqueous suspensions
of cellulose nanocrystals were prepared by sulfuric acid hydrolysis of cotton. The aqueous suspensions were freeze-dried,
and then sonicated in the solvent of interest. Dispersions of 1 and 3% w/v concentration were prepared in polar organic solvents
DMSO and DMF. The dispersions showed flow birefringence. The redispersion was incomplete, and there was some evidence for
aggregation in the suspensions. A small amount of water appeared to be critical to suspension stability. Birefringent cellulose
films were prepared from the dispersions by drying under vacuum and at ambient conditions. 相似文献
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20.
Graziano G 《The journal of physical chemistry. B》2005,109(2):981-985
Experimental data for the solvation of water in nonpolar organic solvents indicate that the process is spontaneous under the Ben-Naim standard conditions, due to a large and negative enthalpy change. The process is analyzed by considering that the solvation Gibbs energy change is given by the sum of two opposing terms: the work to create a suitable cavity and the work to turn on the attractive solute-solvent interactions. Basic calculations point out unequivocally that, beyond the van der Waals contributions, additional favorable interactions occur between water and the surrounding solvent molecules. These additional favorable interactions should be nontraditional hydrogen bonds such as those between the delocalized pi-electron cloud of the aromatic ring and the hydrogen atoms of water, and those between the CH groups of both aliphatics and aromatics and the oxygen atom of water. 相似文献