Hidekazu Touhara

Thermodynamic properties of aqueous mixtures of hydrophilic compounds 2. Aminoethanol and its methyl derivatives

Abstract The vapour pressures of water + 2-aminoethanol, + N-methyl-2-aminoethanol, and + N,N-dimethyl-2-aminoethanol at 298.15 and 308.15 K were measured over the whole composition range by a static method. The excess enthalpies and densities of the same mixtures at 298.15 K were also measured with an isothermal displacement calorimeter and a pyknometer. The thermodynamic excess functions: GE, HE, TSE, and VE were calculated. Except for aminoethanol-rich region in (water + N,N-dimethyl-2-aminoethanol), where GE is slightly positive, the signs and relative magnitudes of molar excess functions were 0 > G E >TS E >H E , V E These are in accordance with general characteristics of (water + a highly hydrophilic compound). However, hydrophobicity is clearly seen for dilute aqueous solutions where the partial molar volume of aminoethanol exhibits a minimum and the partial molar enthalpy decreases rapidly to a limiting value at infinite dilution. This tendency increases with the introduction of methyl groups into 2-aminoethanol.

Computer experiments on aqueous solutions. III. Monte Carlo calculation on the hydration of tertiary butyl alcohol in an infinitely dilute aqueous solution with a new water–butanol pair potential

Monte Carlo calculations have been carried out for an infinitely dilute aqueous solution of tertiary butylalcohol (TBA) at 298.15 K and ordinary density by the Metropolis scheme in an NVT ensemble. The total number of molecules is 216, one of which is TBA. For water–water interaction, the MCY (Matsuoka–Clementi–Yoshimine) potential is used, whereas a new pair potential is determined for water–TBA interaction from ab initio LCAO SCF MO calculations for more than 380 different dimeric configurations with an STO‐3G basis set and subsequent multiparameter fitting of MO data thus obtained to an appropriate potential function with a nonlinear optimization method. In the Monte Carlo run, 3 600 000 configurations have been generated and final 2 000 000 configurations have been used to obtain energetic and structural information on the hydration structure of TBA. As in the case of the methanol solution studied previously, the potential energy and structure of water tend to be stabilized by the introduction of one TBA molecule, and two strong hydrogen bonds between TBA and the surrounding water molecules favor the formation of a bulky and stable hydration shell which includes cooperatively connected hydrophobic hydration structures. This is clearly shown in density diagrams for water around TBA which visualize remarkable structuration of water. The iceberglike structure around TBA is more pronounced than that of methanol.

Computer experiment on aqueous solution. IV. Molecular dynamics calculation on the hydration of urea in an infinitely dilute aqueous solution with a new urea–water pair potential

A molecular dynamics calculation on aqueous solution of urea has been carried out using constant temperature technique. The total number of molecules was 216, one of which was urea and the temperature was set to 298.15 K and an experimental value was used for the density. For water–water interaction, the MCY (Matsuoka–Clementi–Yoshimine) potential was used, whereas a new potential function was determined for urea–water interaction from SCF LCAO calculations for more than 800 different dimeric configurations with an STO‐3G basis set and subsequent multiparameter fitting of the MO results thus obtained to an appropriate functional form by a nonlinear optimization method. The molecular dynamics calculation has been carried out up to 64 000 time steps and from the final 40 000 time steps, thermodynamic quantities, structural and energetic distribution functions, and time‐dependent properties were obtained. The original water structure in the vicinity of urea molecule is slightly changed energetically by incor...

Computer experiments on aqueous solution. I. Monte Carlo calculation on the hydration of methanol in an infinitely dilute aqueous solution with a new water–methanol pair potential

Monte Carlo calculations have been carried out both for pure water and an infinitely dilute aqueous solution of methanol at 298.15 K and ordinary density by the Metropolis scheme in NVT ensemble. The total number of molecules is 216, one of which is methanol in the case of aqueous solution. For water–water interaction, the MCY (Matsuoka–Clementi–Yoshimine) potential is used, whereas a new pair potential is determined for water–methanol interaction from ab initio LCAO SCF MO calculations for more than 450 different dimeric configurations with a STO‐3G basis set and subsequent multiparameter fitting of MO data thus obtained to an appropriate potential function with a nonlinear optimization method. For the aqueous methanol solution, 4 500 000 configurations have been generated and the final 1 500 000 are used to obtain average quantities for energy and various distribution functions. It is found that, with the introduction of one methanol molecule, the potential energy and structure of water tend to stabiliz...

Computer experiments of aqueous solutions. V. Monte Carlo calculation on the hydrophobic interaction in 5 mol % methanol solution

Monte Carlo calculation has been carried out for 5 mol % aqueous solution of methanol at 298.15 K and experimental density with the Metropolis scheme in NTV ensemble. The total number of molecules is 216, of which 11 are methanol. The three kinds of pair potential function used are all based on SCF MO calculations, namely, water–water interactions with MCY (Matsuoka–Clementi–Yoshimine) potential, water–methanol, and methanol–methanol interactions with those proposed by Okazaki et al. and Jorgensen. Totally 5 800 000 configurations have been generated and final 4 200 000 configurations have been used to the calculation of thermodynamic quantities and various distribution functions. It is found that the mixing is slightly exothermic which can be ascribed to the promotion of water structure around methanol rather than the formation of hydrogen bonding between water and methanol. Evidence is given for the existence of hydrophobic interaction effect and the self‐association of methanol with or without one wate...

Computer experiments on aqueous solutions. VI. Potential energy function for tert‐butyl alcohol dimer and molecular dynamics calculation of 3 mol % aqueous solution of tert‐butyl alcohol

Molecular dynamics (MD) calculation has been carried out for a dilute aqueous solution of tert‐butyl alcohol (TBA) at 298.15 K and with experimental density value by the use of constant temperature technique developed previously. The total number of molecule is 216, seven of which are TBA. The mole fraction of TBA is thus 0.032. For water–water and TBA–water interactions, the MCY (Matsuoka–Clementi–Yoshimine) potential and previously reported potential determined by MO calculation are used. A new potential for TBA–TBA is determined by ab initio LCAO SCF calculations for more than 500 different configurations with an STO‐3G basis set and subsequent multiparameter fitting of the MO data to a 12‐6‐3‐1 type potential energy function. The MD calculation is extended up to 84 000 time steps (26 ps) and final 60 000 time steps are used to calculate both static and dynamic properties of the system. Both hydrophobic hydration and interaction due to TBA molecules are proved to be stronger than those of methanol stud...

Molar excess enthalpies for water + ethanediol, + 1,2-propanediol, and + 1,3-propanediol at 298.15 K

Abstract The molar excess enthalpies for water + ethanediol, + 1,2-propanediol, and + 1,3-propanediol have been measured at 298.15 K over the whole composition range in an isothermal dilution calorimeter. All the mixtures exhibit negative excess enthalpies and their dependence on composition is quite analogous to that of water + monohydric alcohol. The results are interpreted qualitatively in terms of various specific interactions and it is concluded that the methyl group in 1,2-propanediol plays an important role in the lower mole-fraction region of diols.

Computer experiments on aqueous solutions. VII. Potential energy function for urea dimer and molecular dynamics calculation of 8 mol % aqueous solution of urea

Molecular dynamics calculation (MD) has been carried out for an aqueous solution of urea at 298.15 K and with experimental density value at ordinary pressure by the use of constant temperature technique developed previously. The total number of molecules is 216, of which 17 are urea. The mole fraction of urea in the solution is thus 0.078. For water–water and water–urea interactions, the MCY potential and previously determined potential have been used. A new urea–urea pair potential is determined by ab initio LCAO SCF calculations for more than 750 different dimer configurations with an STO‐3G basis set and subsequent multiparameter optimization of the MO data to a 12‐6‐3‐1 potential energy function. The MD calculation is extended up to 76 000 time steps and final 44 000 time steps (17.6 ps) are used to calculate both static and dynamic properties. Among other information, the following results are important and interesting: (1) Urea molecules exhibit appreciable self‐association, (2) such association is ...

Thermodynamic properties of aqueous solutions of hydrophilic compounds 1. Pyridine and methylpyridines

Abstract The vapour pressures of water + pyridine and + 2-methylpyridine at 298.15, 308.15, and 318.15 K, and + 3-methylpyridine, + 4-methylpyridine, and + 2,6-dimethylpyridine at 298.15 and 308.15 K were measured over the whole composition range by a static method. Molar excess Gibbs energies GE were calculated from the vapour pressures and combined with molar excess enthalpies HE from the literature to evaluate molar excess entropies SE. The densities of the same mixtures at 298.15 K were also measured by a pyknometric method and molar excess volumes VE were calculated. For all the systems studied, the signs and relative magnitude of the excess functions were G E >0, TS E E E . These are in accordance with general characteristics of mixtures of water + moderately hydrophilic compounds. The absolute values of all the excess functions were found to increase in the order: pyridine

Discharge reaction mechanism in graphite fluoride-lithium batteries

Abstract The discharge reaction mechanism of graphite fluoride-lithium batteries utilizing a 1M LiClO 4 -propylene carbonate (PC) system was studied by means of X-ray diffraction, ESCA, NMR and transmission electron microscopy, differential thermal analyses and thermal gravimetry. Two types of graphite fluoride flakes, (CF) n and (C 2 F), and (C 2 F) n fibers were used as cathode materials. Based on the full characterization of discharge products of graphite fluoride cathodes, it has been revealed that the discharge reaction proceeds through the formation of an intermediate phase, solvated ternary compound of C-F-Li·PC or C 2 -F-Li·PC, and they then decompose to graphite with low crystallinity and LiF. The decomposition process is not involved in the electrochemical reaction, and this discharge reaction infers the open-circuit voltage of batteries and the stable discharge potential with high utility of graphite fluoride cathode.