Measurements of the heats of dilution and description of the system H2O/H2SO4/HCl with a solvation model

Heat of dilution measurements have been performed on the system H₂O/H₂SO₄/HCl in the concentration range of 0.3 mol% to 20 mol% electrolyte and in the temperature range of 20°C to 60°C. The constituent binary systems H₂O/H₂SO₄ and H₂O/HCl could be described using the solvation model introduced by Engels [H. Engels, Anwendung des modells der lokalen zusammensetzung auf elektroytlösungen, Dissertation, RWTH Aachen, 1985]. The vapor–liquid-equilibria (VLE) and the thermal properties are described simultaneously by one set of parameters. Applying the solvation model to the ternary system H₂O/H₂SO₄/HCl, the measured heats of dilution as well as VLE-data taken from the literature could be predicted. The heat of dilution data are presented with a mean relative deviation of 3.5%. The boiling temperatures of the three sources of ternary VLE data considered in this paper are predicted with a mean absolute deviation of less than 1.2 K. The corresponding mean absolute deviations of the vapor mole fractions of HCl are within 0.06.     

乙烷/H2O/O2/N2体系中光致过氧化物的产生

采用长光路Fourier红外光谱(LP-FTIR)和高压液相色谱(HPLC)技术研究了乙烷/H2O/O2/N2光化学体系中过氧化物的产生，证实乙烷降解产物中有过氧化氢、乙基过氧化氢(CH3CH2OOH,EHP)和过氧乙酸[CH3C(O)OOH,PAA]，并首次发现了甲基过氧化氢(CH3OOH,MHP)、羟甲基过氧化氢(HOCH2OOH,HMHP)和过氧甲醚(CH3OOCH3,DMP).H2O2,MHP和EHP的最大计算产率分别为6.8%，6.4%和6.7%，是乙烷降解生成的主要过氧化产物。MHP主要来自乙烷降解过程中的中间物乙醛的光解。HMHP的检出表明乙烷降解过程中可能有Criegee中间体.CH2OO.产生。OH自由基引发的乙烷降解反应可能是对流层大气H2O2，MHP及EHP的重要来源之一。     

Experimental isotherms of HCl on H2O ice under stratospheric conditions: connections between bulk and interfacial thermodynamics

The adsorption of HCl on the surface of H(2)O ice has been measured at temperatures and pressures relevant to the upper troposphere and lower stratosphere. The measured HCl surface coverage is found to be at least 100 times lower than currently assumed in models of chlorine catalyzed ozone destruction in cold regions of the upper atmosphere. Measurements were conducted in a closed system by simultaneous application of surface spectroscopy and gas phase mass spectrometry to fully characterize vapor/solid equilibrium. Surface adsorption is clearly distinguished from bulk liquid or solid phases. From 180 to 200 K, submonolayer adsorption of HCl is well described by a Bragg-Williams modified Langmuir model which includes the dissociation of HCl into H(+) and Cl(-) ions. Furthermore, adsorption is consistent with two distinct states on the ice substrate, one in which the ions only weakly adsorb on separate sites, and another where the ions adsorb as an H(+)-Cl(-) pair on a single site with adsorption energy comparable to the bulk trihydrate. The number of substrate H(2)O molecules per adsorption site is also consistent with the stoichiometry of bulk hydrates under these conditions. The ionic states exist in equilibrium, and the total adsorption energy is a function of the relative population of both states. These observations and model provide a quantitative connection between the thermodynamics of the bulk and interfacial phases of HCl/H(2)O, and represent a consistent physicochemical model of the equilibrium system.     

Speciation in the aqueous H+/H2VO4-/H2O2/phosphate system

The speciation in the aqueous H(+)/H(2)VO(4)(-)/phosphate (dihydrogen phosphate, P(-)) and H(+)/H(2)VO(4)(-)/H(2)O(2)/P(-) systems has been determined in the physiological medium of 0.150 M Na(Cl) at 25 degrees C. A combination of multinuclear NMR integral and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and treated simultaneously by the computer program LAKE. The pK(a)-values for phosphoric acid have been determined by potentiometric and (31)P NMR chemical shift data, and have been found to be 1.85 +/- 0.02, 6.69 +/- 0.02 and 11.58 +/- 0.07. The errors given are 3sigma. Altogether nine vanadate-phosphate species have been found in the ternary H(+)/H(2)VO(4)(-)/P(-) system in the pH region 1-11, with the following compositions: VP, VP(2) and V(14)P. Equilibrium is very slow in acidic solutions, requiring more than 3 months for the formation of V(14)P species. On the other hand, less than 15 min are needed for equilibration at neutral and alkaline pH. In the quaternary H(+)/H(2)VO(4)(-)/H(2)O(2)/P(-) system, four new species have been found in addition to all binary and ternary complexes. They are of VXP and VX(2)P compositions, where X denotes the peroxo ligand. (51)V and (31)P NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species is also discussed and physiological conditions are modelled.     

ChemInform Abstract: H2O Nucleation Around Au+

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

1H NMR and DFT study of proton exchange in heterogeneous structures of pyridine-N-oxide/HCl/DCl/H2O

Moderately narrow 1H NMR signals were observed in the solid-phase obtained from pyridine-N-oxide (PyO)...HCl solutions in acetonitrile/H2O after heterogeneous phase separation. High-resolution 1H NMR spectra are compared with those of crystalline PyO...HCl and PyO...DCl. It is concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of the spin system and the presence of different mobile H-bond clusters containing PyO, HCl, DCl and water molecules. Some part of non-bonded water or HCl molecules is captured in the cavities of crystalline samples. The attribution of the 1H NMR signals was based on the density functional theory calculation of proton magnetic screening tensor of the most expected H-bond structures in the 6-311G** basis taking into account the solvent effect by the polarized continuum model.     

Activation energy of hydrogen migration by relay in the O2/Pt19/SnO2/H2 + n H2O system

In the framework of investigation of active and stable electrocatalysts for fuel cells, the hydrogen migration by relay with the consecutive formation of H₂O molecules in the O₂/Pt₁₉/SnO₂/H₂·nH₂O → O/Pt₁₉/SnO₂·nH₂O + H₂O system was simulated. The simulations were performed by the density functional theory (DFT) method with the generalized gradient adjustment (GGA=PBE) under periodic boundary conditions in the projector augmented plane wave (PAW) basis set with a pseudo-potential using the VASP program package. At the cathode on the platinum cluster surface, the oxygen molecules without a barrier form peroxide complexes that dissociate with an energy decrease. The protons transferred via the proton-conducting channels from the anode to cathode form first OH groups bound to the platinum cluster and then H₂O molecules that are easily separated from the cluster (～0.2 eV). The proton transfer process proceeds by relay and involves several water molecules.     

Speciation in the aqueous H+/H2VO4-/H2O2/citrate system of biomedical interest

The speciation in the quaternary aqueous H+/H2VO4-/H2O2/citrate (Cit3-) and H+/H2VO4-/Cit3-/L-(+)-lactate (Lac-) systems has been determined at 25 degrees C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate-citrate species have been found in the ternary H+/H2VO4-/Cit3- system in the pH region 2-10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4-/H2O2/Cit3- system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2-10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4-/Cit3-/Lac- system, two mixed-ligand species have been determined, with the compositions V2CitLac2- and V2CitLac3- (pKa = 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.     

混合电解质中HCl热力学性质——HCl-C3H8O3-NaCl-H2O体系

活度系数;电动势;电极电势;无液接电池;混合电解质中HCl热力学性质——HCl-C3H8O3-NaCl-H2O体系     

Nature and importance of three-body interactions in the (H2O)2HCl trimer

 The nature and importance of nonadditive three-body interactions in the (H₂O)₂HCl cluster have been studied by the supermolecule coupled-cluster method and by symmetry-adapted perturbation theory (SAPT). The convergence of the SAPT expansion was tested by comparison with the results obtained from the supermolecule coupled-cluster calculations including single, double, and noniterative triple excitations [CCSD(T)]. It is shown that the SAPT results reproduce the converged CCSD(T) results within 3% at worst. The SAPT method has been used to analyze the three-body interactions for various geometries of the (H₂O)₂HCl cluster. It is shown that the induction nonadditivity is dominant, but it is partly quenched by the first-order Heitler–London-type exchange and higher-order exchange–induction/deformation terms. This implies that the classical induction term alone is not a reliable approximation to the nonadditive energy and that it will be difficult to approximate the three-body potential for (H₂O)₂HCl by a simple analytical expression. The three-body energy represents as much as 21–27% of the pair CCSD(T) intermolecular energy. Received: 15 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000     

Crystal and molecular structure of aspartame X HCl X 2H2O

The crystal and molecular structure of the hydrochloride salt of the peptide sweetener aspartame (alpha-L-Asp-L-Phe methyl ester) has been determined at 120 K using 3877 reflections with I greater than 2.5 sigma I. Space group P2(1)2(1)2(1), cell dimensions a = 6.768(1), b = 9.796(1) and c = 26.520(3) A; final R factor 0.033. While the N-terminal L-Asp group in the structure of aspartame itself forms a six-membered ring with an intramolecular hydrogen bond between the carboxylate and the protonated amino terminus, the corresponding group in the hydrochloride adopts a completely different conformation with a weak intramolecular hydrogen bond between the carboxyl group and the N atom of the L-Phe residue. The L-Phe methyl ester moiety is rather similar in the two structures. Of the many possible conformations of aspartame, only one may be expected to function as a substrate at the receptor site for sweet taste, and a proposal is made for this active conformation.     

Activity coefficient measurements of the system HCl−ZnCl2−H2O at 25 and 35°C

Electromotive force measurements were carried out on the HCl–ZnCl₂–H₂O system at constant total ionic strengths of 0.1, 0.2, 0.5, 1.0 and 2.0 mol-kg^–1 at 25 and 35°C using a cell consisting of Pt, H₂(g, 1 atm)|HCl(m_A), ZnCl₂(m_B)|AgCl/Ag. The data were interpreted by the mixed electrolyte equations of Pitzer and Kim in order to evaluate mixing ion-interaction parameters. The activity coefficients of ZnCl₂ and the Gibbs excess free energies of mixing are calculated and presented at I=2.0 mol-kg^–1 and compared with similar systems containing transition metal chlorides.     

Thermodynamics of electrolyte solutions. The system HCl + CaCl2 + H2O at 298.15°K

Activity coefficients of hydrochloric acid have been determined from electromotive-force measurements of cells containing mixtures of hydrochloric acid and calcium chloride at constant total ionic strengthsI=0.1, 0.5, 1.0, 2.0, and 3.0 mole-kg^–1 at 298.15°K. Interpretations based on Scatchard's and Pitzer's equations indicate that Pitzer's equations probably provide a more convenient guide to the thermodynamic properties of the mixed-electrolyte solutions. Activity coefficients for calcium chloride were derived from these equations.     

Application of Pitzer's equations on the system HCl+MnCl2+H2O at various temperatures. V.

Activity coefficients of hydrochloric acid in mixed solutions of manganous chloride at twelve ionic strengths, from 0.1 to 5.0 mole-kg^–1, were obtained from emf measurements of cells without liquid junction at five temperatures from 5 to 45°C. The data were interpreted in terms of the simple and convenient Pitzer treatment. Activity coefficients for manganous chloride in the mixtures were also derived using Pitzer's equations. Hydrochloric acid follows Harned's rule fromI=0.1 to 3.0 mole-kg^–1, as concluded by Downes, whereas quadratic terms are warranted fromI=3.5 to 5.0 mole-kg^–1. Contrary to Downes' conclusion, Harned's rule clearly does not hold true for manganous chloride at most ionic strengths.     

Speciation in the aqueous H+/H2VO4-/H2O2/picolinate system relevant to diabetes research

A detailed study of the quaternary aqueous H+/H2VO4-/H2O2/picolinate (Pi-) system has been performed at 25 degrees C in 0.150 M Na(Cl) medium using quantitative 51 V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4-/Pi- system, six complexes have been found in the pH region 1-10. In the quaternary H+/H2VO4-/H2O2/Pi- system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 1)C NMR data and available crystal structures.