Masao Fujisawa

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type.A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented.It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aqueous butanediol isomers and 1-hexanol were very large. Molar enthalpies of infinite dilution of aqueous poly-alcohol (cyclohexaamylose) were endothermic.

The enthalpic stabilization on molecular inclusion of butanediol isomers into cyclodextrin cavities

Abstract The enthalpy of dilution of dilute aqueous solution of meso -2,3-butanediol, x −3 , and enthalpy of inclusion of meso -2,3-butanediol into α - and β -cyclodextrin cavities in dilute aqueous solutions have been determined by using a rocking twin-microcalorimeter of a heat-conduction type at 298.15 K under atmospheric pressure. The enthalpies of inclusion of meso -2,3-butanediol into α - and β -cyclodextrins are exothermic and smallest among three isomers, 1,3-, 1,4- and meso -2,3-butanediols. The correlation between behaviors and molecular shapes are discussed.

Thermodynamic Functions of Molecular Inclusion of Some Isomers of Butanediol in Gas Phase Into α- and β-cyclodextrin Cavities in Aqueous Solutions at 298.15 K

The enthalpies, entropies and Gibbs energies of inclusion of dl-1,3-, 1,4- and meso-2,3-butanediols into α- and β-cyclodextrin cavities from ideal gas phase have been determined on the basis of newly obtained experimental data of the butanediols. The butanediol molecules are stabilised strongly in the cavities due to interactions with inner walls of the cavities. Entropies of the gaseous isomers are greatly decreased in the cavities. The largest decrease is obtained for the case of 2,3-BD. Discussions concerning the1,4-butanediol given in the preceding paper have been changed due to the adoption of new data on the butanediols.

Thermody namic functions of 1,2-alkanediols in dilute aqueous solutions

The heat capacities of binary aqueous solutions of 1,2-ethanediol, 1,2-propanediol and 1,2-butanediol were measured at temperatures ranging from 283.15 to 338.15 K by differential scanning calorimetry. The partial molar heat capacities at the infinite dilution were then calculated for the respective alkanediols. For 1,2-ethanediol or 1,2-propanediol, the partial molar heat capacities at the infinite dilution of increased with increasing temperature. In contrast, the partial molar heat capacities of 1,2-butanediol at the infinite dilution decreased with increasing temperature.Heat capacity changes by dissolution of the alkanediols were also determined. Heat capacity changes caused by the dissolution of 1,2-ethanediol or 1,2-propanediol were increase with increasing temperature. On the other hand, heat capacity changes caused by the dissolution of 1,2-butanediol are decrease with increasing temperature. Thus our results indicated that the structural changes of water caused by the dissolution of 1,2-butanediol differed from that of the two other alkanediols.

Enthalpy and entropy changes on molecular inclusion of 1,3-butanediol into α-and β-cyclodextrin cavities in aqueous solutions

To determine the enthalpies and entropies of inclusion, enthalpies of dilution of dilute aqueous 1,4-butanediol (BD) solutions and those of transfer of 1,4-BD from aqueous to aqueous α- or β-cyclodextrin (CD) solutions have been determined by microcalorimetry at various mole fractions at 298.15 K. Enthalpies of inclusion of 1,4-BD molecules into α- and β-CD cavities are determined, whose values are exothermic and small. However, stabilisation of gaseous 1,4-BD molecules in the CD cavities is large. 1,4-BD molecules must change their conformations to make the closest contacts with the atoms on the wall of α-CD cavities or those on the wall of β-CD cavities and the remaining water molecules in β-CD cavities.

Enthalpic discrimination of R- and S-limonenes in nonpolar solvents at 298.15 K.

Enthalpies of mixing of R- and S-limonene in non-polar solvents in the entire range of mole fractions were measured at 298.15 K. The enthalpies of mixing were negative for all concentrations in dilute concentration, but increased by increasing the concentration of limonenes in solutions. Ultimately positive excess enthalpies were shown in high concentration. Enthalpies of mixing were compared with theoretical estimation by COSMO-RS.

Difference in formation mechanism of inclusion complex between configuration isomers of gallate-type catechin and β-cyclodextrin

The formation mechanism of inclusion complex between (-)-epigallocatechin gallate (EGCg), which is the main catechin in tea leaves, or (-)-gallocatechin gallate (GCg), which is an isomer of EGCg, and β-cyclodextrin (βCD) was studied by isothermal titration microcalorimetry (ITC), NMR and molecular modeling calculation (MMC). ITC measurements revealed that EGCg or GCg interacted with βCD at 1:1 molar ratio driven by enthalpy. Comparing the values of binding constant (7.2 × 103 1/M for EGCg with βCD and 3.9 × 104 1/M for GCg with βCD), it was suggested that GCg interacted with βCD more strongly rather than EGCg. In their ROESY NMR spectra, the cross-peaks were observed between the protons of A, B and B′ ring of EGCg and the protons in the cavity of βCD, and between the protons of B and B′ ring of GCg and the protons in the cavity of βCD. MMC in water showed that EGCg had one kind and GCg had two kinds of most stable conformation (GCg(E) and GCg(A)) in energy. In the stable conformation of EGCg, B ring was coordinated equatorially to C ring, and B′ ring was axially coordinated to C ring. On the other hand, in GCg (E), the coordination of B ring and B′ ring to C ring was both equatorial, and in GCg (A), the coordination of B ring and B′ ring was both axial. MMC also revealed B or B′ ring of GCg(A) was easy to be included in the cavity of βCD more deeply than each ring of EGCg or GCg(E) since the steric hindrance of B ring or B′ ring was small. Therefore, it was found that the difference of B ring’s configuration of gallate-type catechin greatly affected the formation of inclusion complex with βCD.

Interaction Energy Analysis for Drug-Cyclodextrin Inclusion Complexes in Aqueous Solutions

It is vital to elucidate the role of asymmetric intermolecular interactions resulting from the stereospecific structures of molecules in order to understand the mechanisms of chemical and biochemical reactions such as enzyme-substrate reactions, antigen-antibody reactions, etc. In order to reveal the mechanism of the inclusion phenomenon for b-cyclodextrin (CD)-ampicillin complexes and b-CD-ibuprofen complexes, binding free energies were determined using molecular mechanics/Poisson–Boltzmann surface area (MM/PBSA) analysis. To clarify the details of the interaction energies of these complexes, pair interaction energy decomposition analysis (PIEDA) was carried out. The direction of inclusion of drugs into b-CD cavities was clarified on the basis of results obtained using the above-mentioned methods.