共查询到20条相似文献,搜索用时 15 毫秒
1.
Wojciech Zielenkiewicz 《Thermochimica Acta》2003,405(1):155-169
The experimental enthalpies of solution ΔsolHm∞, van’t Hoff enthalpies of sublimation ΔsgHm0 of solid compounds, partial molar volumes V20, and partial molar heat capacities Cp,20 of aqueous solutions of pyrimidine nucleic acid bases and their derivatives, determined previously and collected here, are discussed in terms of calculated structural parameters. Relations have been established between the calorimetric and volumetric properties. Correlations have been developed to relate both the enthalpies of solvation and the partial molar heat capacities to the polar and apolar parts of the accessible molecular surface areas. 相似文献
2.
Sh. B. Kasenova Zh. K. Tukhmetova A. Zh. Abil’daeva I. M. Oskembekov B. K. Kasenov S. M. Adekenov S. D. Fazylov 《Russian Journal of Applied Chemistry》2008,81(12):2141-2144
The enthalpies of solution of cytisine derivatives (phosphoric acid cytiside dimethyl ester, cytisinovinyloxyethylaminothiourea) in 96% ethanol at various dilutions were determined by isothermal calorimetry. Equations describing the dependences ΔH s 0 = f(m 1/2) (m is the molal concentration) were obtained. The standard enthalpies of solution, combustion, melting, and formation (at 298.15 K) of the compounds were calculated. 相似文献
3.
《The Journal of chemical thermodynamics》2004,36(8):645-658
Saturation molalities m(sat) in H2O(l) have been measured for the substances cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) by using h.p.l.c. The states of hydration were established by performing Karl-Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T≈298 K and then dried with air at T≈296 K for ≈24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Also, molar enthalpies of solution ΔsolHm(cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies Lφ for these substances. These γ and Lφ values were used to adjust the measured values of m(sat) and ΔsolHm(cal) to the standard state and thus obtain values of the standard molar Gibbs free energy ΔsolG∘m and enthalpy changes ΔsolHm∘ for the dissolution reactions of these substances. The values of the pKs and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of ΔsolGm∘ and ΔsolHm∘. Values of standard molar enthalpies of formation ΔfHm∘, standard molar Gibbs free energies of formation ΔfGm∘, and standard partial molar entropies S2,m∘ for the aqueous species of hypoxanthine and xanthine were calculated. A detailed summary and comparison of thermodynamic results from the literature for these substances is presented. 相似文献
4.
V. G. Badelin I. N. Mezhevoi E. Yu. Tyunina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(3):521-524
Calorimetric measurements of enthalpies of solution Δsol H m for glycine, L-cysteine, and glycylglycine in aqueous solutions of sodium dodecyl sulfate (SDS) with concentrations of up to 0.05 mol kg–1 are made. Standard enthalpy of solution Δsol H 0 and enthalpy of transfer Δtr H 0 of the dipeptide from water into mixed solvent are calculated. The calculated enthalpy coefficients of paired interactions of amino acids and dipeptide with SDS prove to be positive. Hydrophobic interactions between the biomolecules and SDS are found to have a major impact on the enthalpies of interaction in the three-component systems under study, within the indicated range of concentrations. 相似文献
5.
For measuring solution enthalpies of the strong hygroscopic double chlorides, an isoperibol solution calorimeter was built. Samples of 2–5 g could be solved to a molar dilution 1 : 3000. The temperature difference between reaction vessel and thermostat was measured by a thermopile; the temperature of the thermostat was constant to 2 · 10?4°C. From the molar enthalpies of solution (ΔHL), enthalpies for the reactions nACl + MCl2 = AsMCl(s + 2) were calculated: ΔHPR = ? ΔHL (double chloride) + ΔHL(n Cl) + ΔHL(MCL2) These values are relatively small: about ? 50 kJ for the Cs-compounds, nearly zero for the K- and Na-compounds. 相似文献
6.
M. Woldan 《Thermochimica Acta》1985,94(2):358
The enthalpies of solution of NaCl, KCl, KBr, KNO3 and CsI have been measured in mixtures of acetamide with water at 298.15 K in the miscibility range. The standard enthalpies of solutions (ΔH0) of the investigated electrolytes have been evaluated The corresponding enthalpies of solvation (ΔHs0) and enthalples of transfer (ΔHt0) from water to water-acetamide mixtures have been calculated The dependence of the standard enthalpies of solution and enthalpies of transfer of the investigated electrolytes on the solvent composition is discussed 相似文献
7.
《The Journal of chemical thermodynamics》2002,34(2):263-275
The standard molar enthalpies of vaporizationΔlgHmo of N -(hydroxyethyl)-piperazine, bis-piperidino-methane, 1,3,5-tri-methyl-hexahydro-s-triazine, and also the enthalpies of sublimation ΔcrgHmoofN,N′ -di(hydroxyethyl)-piperazine, and hexamethylenetetramine were obtained from the temperature dependence of the vapor pressure measured in a flow system. The standard molar enthalpies of formationΔfHmo (l) at the temperatureT = 298.15 K were measured by means combustion calorimetry for bis-piperidino-methane and 1,3,5-tri-methyl-hexahydro-s-triazine. Strain enthalpies (ring-correction terms) of these cyclohexanoid molecules were derived from the experimental enthalpies of formation of the gaseous compounds. These experimental results, together with data available from the literature, provided a quantitative understanding of the interrelations of structure and energetics of a mono- and poly-cyclic cyclohexanoid molecules and strain of their component rings. 相似文献
8.
The results of measurement of equilibrium constants of 30 reactions involving lanthanum and lanthanide fluorides (LnF, LnF2, and LnF3) and 14 reactions involving lanthanum and lanthanide monochlorides (Ln = La-Lu) have been summarized. These constants have been used for calculating the enthalpies of reactions by the second and third laws, from which the enthalpies of atomization Δat H 0 0 of LnCl, LnF, and LnF2 have been determined. Comparison of the calculation results shows that the thermodynamic functions of LnCl and LnF (Ln = Ce-Yb) in which the electronic excitation contribution has been calculated from the excitation energies of Ln+ ions allow one to adequately determined the Δat H 0 0 values from experimental data. Using the trends in the change in Δat H 0 0 as a function of the atomic number of a lanthanide, the enthalpies of atomization of compounds for which experimental data are lacking have been estimated. The Δat H 0 0 values for LnCl+ ions have been calculated. The reliability of the Δat H 0 0 values for LnF+ ions have been assessed. 相似文献
9.
Wenshen C. Yi L. Chuanpei Z. Songsheng Q. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):463-468
The solid-state coordination reaction: Nd(NO3)3·6H2O(s)+4Ala(s) → Nd(Ala)4(NO3)3·H2O(s)+5H2O(l) and Er(NO3)3·6H2O(s)+4Ala(s) → Er(Ala)4(NO3)3·H2O(s)+5H2O(l) have been studied by classical solution calorimetry. The molar dissolution enthalpies of the reactants and the products
in 2 mol L–1 HCl solvent of
these two solid-solid coordination reactions have been measured using a calorimeter. From the results and other auxiliary
quantities, the standard molar formation enthalpies of [Nd(Ala)4(NO3)3·H2O, s, 298.2 K] and[Er(Ala)4(NO3)3·H2O, s,298.2 K] at 298.2 K have been determined to be Δf
H
m
0 [Nd(Ala)4(NO3)3·H2O,s, 298.2 K]=–3867.2 kJ mol–1, and Δf
H
m
0 [Er(Ala)4(NO3)3·H2O, s, 298.2 K]=–3821.5 kJ mol–1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
The integral enthalpies of solution Δsol H m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δsol H 0) of L-serine and of its transfer (Δtr H 0) from water to a mixed solvent were calculated. The dependences of Δsol H 0 and Δtr H 0 on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution. 相似文献
11.
Takakazu Kojima Masahiko Hamada Masa-Aki Miyahara Yoshinobu Hosaka 《Journal of Polymer Science.Polymer Physics》1987,25(7):1481-1489
Studies on solute–solvent interactions of oligo(m-benzamide)s in N,N-dimethylacetamide (DMA) have been carried out. The enthalpies of solution have been measured for oligo(m-benzamide)s and oligo(m-phenylene)s in DMA and benzene. Contributions of enthalpies of cavitation and dispersion interaction to the enthalpy of transfer from benzene to DMA, ΔHtr (Ben → DMA), have been examined for oligo(m-phenylene)s. A considerable contribution of excess enthalpy, ΔHE (Ben → DMA), to ΔHtr (Ben → DMA) has been found, which increases with the number of benzene rings of the solute. By assuming that ΔHE (Ben → DMA) of diphenyl (DP) is equal to that of benzanilide (BA) in DMA, the amide hydrogen bond enthalpy of BA in DMA, ΔH estimated by “the pure base method” corrected for the enthalpies of cavitation and dispersion interaction. The ΔH value has been given by the following expression including the unknown solubility parameter of BA, δBA: The evaluation of δBA has resulted in the conclusion that ?ΔH is smaller than 10.9 kJ mol?1. Moreover, ΔHtr (TMU → DMA) for oligo(m-benzamide)s has been examined. It has been shown that the amide hydrogen bonding ability of DMA is lower than that of TMU. The linearity of the plot of ΔHtr (TMU → DMA) against the number of amide bonds in the molecule has been explained by the increase in hydrogen bond enthalpies with the number of amide bonds in the molecule. 相似文献
12.
The enthalpy of freezing has been measured with DTA using electrical calibration for 33 compositions of indium—lead in the range 6.9–7.9 at.% lead, at which range the electron—lattice interaction causes anomalies in several physical and structural properties. Enthalpies of mixing, ΔHms, have been calculated. The results reveal three maximum and minimum pairs corresponding to partial shift of the Fermi surface to higher Brillouin zones in three steps at 7.1, 7.2 and 7.3–7.4 at.% lead. These details in the overlapping have not been found earlier. The observed change in ΔHms in the steps is about 1 meV atoms?1. 相似文献
13.
《The Journal of chemical thermodynamics》2003,35(10):1681-1702
Saturation molalities m(sat) in H2O(l) have been measured for the substances adenosine(cr), guanosine · 2H2O(cr), inosine(cr), and xanthosine · 2H2O(cr) over the temperature range T=287.91 K to T=308.18 K by using h.p.l.c. The indicated states of hydration of these substances were established by performing Karl–Fischer analyses of samples of these substances which had been equilibrated over H2O(l) and of samples obtained by passing air over the wet crystals (air dried samples). The crystalline phases of these substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Molar enthalpies of solution ΔsolHm for adenosine(cr) and inosine(cr) were measured by using an isoperibol solution calorimeter. A “stacking” or “self-association” model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies Lφ for these substances. These γ and Lφ values were used to adjust the measured values of m(sat) and ΔsolHm to the standard state and obtain values of the standard molar Gibbs free energy and enthalpy changes ΔsolG∘m and ΔsolH∘m, respectively, for the dissolution reactions of these substances. Values of ΔsolH∘m calculated from the temperature dependence of values of ΔsolG∘m were in good agreement with the values of ΔsolH∘m obtained by using calorimetry. 相似文献
14.
For the equilibrium solid phases occurring in the systems: KCl?KBr?H2O, K2SO4?(NH4)2SO4?H2O and KNO3?NH4NO3?H2O, the concentration dependencies of differential solution enthalpies, Δsol H 2 for several crystallization paths, were measured. The limiting differential solution enthalpies, Δsol H 2 0 , were determined by extrapolation of the above dependencies to the ionic strength,I m 0 , corresponding to the appropriate binary solutions. For KCl?KBr?H2O system only, the clear dependence between Δsol H 2 0 andI m 0 values was found and discussed. 相似文献
15.
M. Eugenia Aldea 《Thermochimica Acta》2005,429(2):233-239
Excess molar volumes, VE, isentropic compressibility deviations, ΔκS, and excess molar enthalpies, HE, for the binary mixtures 2-methyl-tetrahydrofuran with 1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane and 2-methyl-2-chloropropane have been determined at temperatures 298.15 and 313.15 K, excess molar enthalpies were only measured at 298.15 K. We have applied the Prigogine-Flory-Patterson (PFP) theory to these mixtures at 298.15 K. 相似文献
16.
Enthalpies of solution of glycine, l-alanine and l-serine in water and aqueous solutions of NaNO3 and NaClO4 have been determined at T = 298.15 K with a calorimeter. Enthalpies of transfer (ΔtrH) from water to aqueous solutions of salts were derived and interpreted in terms of electrostatic interaction and structural interaction. ΔtrH decreases with increasing salt concentration in the composition range studied. The transfer enthalpies of amino acids from water to NaNO3 solution and low concentration NaClO4 solution vary in the sequence l-serine < glycine < l-alanine while glycine < l-serine < l-alanine in NaClO4 solution above 2 mol kg−1. The difference may be due to ion association at high concentration, weakening the interaction with l-serine more than with glycine. 相似文献
17.
Protocatechuic acid, a major metabolite of antioxidant polyphenols found in green tea, has been shown to prevent carcinogenesis or antitumor growth in vitro and in vivo studies. The dilution enthalpies ΔdilHm, dissociation enthalpies ΔdisHm and thermodynamic dissociation constants Ka for protocatechuic acid in aqueous NaCl or KCl solutions were simultaneously determined by mixing-flow microcalorimetry at T = 298.15 K. In order to verify the reliability of the fitted dissociation parameters, the values of dissociation enthalpies and thermodynamic dissociation constants were also determined by isothermal titration calorimetry and electrical conductivity methods. The Ka values obtained through the proposed method agree well with those reported in literatures and obtained by other techniques. Enthalpic interaction coefficients (h2, h3 and h4) were computed according to the McMillan–Mayer model. The trends of h2 and ΔdisHm for protocatechuic acid with increasing salt molality in both the salt solutions were obtained. The different influence of KCl and NaCl on the values of h2 and ΔdisHm were discussed in terms of (solute + solute) and (solute + solvent) interactions. The results showed that it is possible to perform in a single calorimetric experiment the simultaneous determination of dilution enthalpies, dissociation enthalpies and constants in a given solvent. 相似文献
18.
Solid complexes, RE(Et2dtc)3(phen) (RE=La, Pr, Nd, Sm—Lu), were synthesized with sodium diethyldithiocarbamate (NaEt2dtc3H2O), 1,10-phenanthroline (o-phen?H2O) and hydrated lanthanide chlorides in absolute ethanol. The constant-volume combustion energies of complexes, Δ C U, were determined by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion, ΔCHm θ, and standard enthalpies of formation, ΔfHm θ, were calculated for these complexes, respectively. The experiment results showed the “tripartite effect” of rare earth. 相似文献
19.
Ionic liquid (IL) [C7mim][BF4] (1-heptyl-3-methyl-imidazolium tetrafluoroborate) was prepared and characterized. The density and surface tension of the IL were determined in the temperature range of 293.15–343.15 K. In terms of Glasser's theory, the standard molar entropy and lattice energy of the IL were estimated. Using Kabo's method, the molar enthalpy of vaporization of the IL, ΔlgHm0 (298 K), was estimated. According to the interstice model, the thermal expansion coefficient of IL, α, was calculated and in comparison with experimental value, they are within one order of magnitude. 相似文献
20.
I. N. Mezhevoi V. G. Badelin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(4):607-610
The integral enthalpies of dissolution Δsol H m of L-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol under the concentration of organic solvents up to 0.32 mole fraction were measured by means of calorimetry. The standard values of the dissolution enthalpies (Δsol H o) and transfer enthalpies (Δtr H o) of amino acids from water to the mixed solvent were calculated. It was shown that the calculated enthalpic coefficients of pair interactions of L-alanine with cosolvent molecules have positive values. The data obtained are interpreted from the viewpoint of prevalence of different types of interactions in the solutions and influence of the cosolvents nature on the thermo-chemical characteristics of amino acid dissolution. 相似文献