Investigation of the structure of and the properties of the potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo[3,4-d]pyridazine-1,4-diones in the gaseous and aqueous phases using the AM1 semi-empirical method

Potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo[3,4-d]pyridazine-1,4-diones and their fixed tautomeric forms have been studied in order to predict their tautomeric equilibrium constants and pK_a values using semi-empirical AM1 quantum-chemical calculations at the SCF level in the gas phase and in aqueous solution. Hydroxy-oxo forms were found to be more stable than dioxo and dihydroxy forms. The results obtained from the tautomeric equilibria and basicity calculations are in good agreement with experimental data.     

Investigation of the structure of and the properties of the potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo[3,4-d]pyridazine-1,4-diones in the gaseous and aqueous phases using the AM1 semi-empirical method

Potentially tautomeric 1,2,3,4-tetrahydro-5,7-dimethyl-6H-pyrrolo[3,4-d]pyridazine-1,4-diones and their fixed tautomeric forms have been studied in order to predict their tautomeric equilibrium constants and pK_a values using semi-empirical AM1 quantum-chemical calculations at the SCF level in the gas phase and in aqueous solution. Hydroxy-oxo forms were found to be more stable than dioxo and dihydroxy forms. The results obtained from the tautomeric equilibria and basicity calculations are in good agreement with experimental data.     

Spectrophotometric and AM1d studies of the equilibria between oxidovanadium(IV) and four isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides in aqueous solution

Complex formation and stability constants for complexes between isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides and oxidovanadium(IV) were determined in aqueous solution by the spectrophotometric method. Complexes of 1?:?2 metal-to-ligand stoichiometry were formed. The impact of the structures of the ligands on the complex formation was discussed. The energetically most favorable structures of the complexes were calculated and visualized by the AM1d method at the semi-empirical level of theory.     

Correlation and prediction of liquid-liquid distribution coefficients in aqueous systems using a modified Wilson model

A modified Wilson model is tested for its ability to correlate and predict distribution coefficients in two representative systems: 1-butanol-water and cyclohexanewater. The model is fitted to ternary equilibrium data for various solutes in these systems using a procedure involving minimization of the least-squares distance between calculated and experimental logarithmic distribution ratios. In addition, benzene-water, hexane-water, and cyclohexane-water distribution coefficients for infinitely diluted liquid solutes are predicted using only binary system information. All computations involve using both van der Waals and molar volumes as structural parameters to account for the geometry of the molecules studied. Satisfactory representations of experimental distribution ratios and fairly accurate distribution coefficients at infinite dilution are obtained for both systems. However, in a number of cyclohexane-water systems, miscibilities of constituent binary mixtures are poorly predicted from ternary system information when van der Waals volumes are used. Replacement of van der Waals volumes by molar volumes has little influence on the fit, but significant improvement is observed for the prediction of both binary miscibility properties and for distribution coefficients at infinite dilution in all the solvent-water systems considered.Presentation to First International Symposium on Solubility Phenomena, University of Western Ontario, London, Ontario, August 21–23, 1984.     

Apparent molar volume, isentropic compressibility and conductivity of di-sodium hydrogen phosphate in water and in aqueous solutions of 1-propanol

Precise measurements on the density and sound velocity of solutions of di-sodium hydrogen phosphate in 1-propanol + water mixed-solvent media with alcohol mass fractions of 0.00, 0.05, 0.10 and 0.15 are reported in the 283.15–303.15 K temperature range at 5 K intervals. Electrical conductivity and refractive index of the solutions are studied at 298.15 K. From the experimental density and sound velocity data, the apparent molar volume and isentropic compressibility values of di-sodium hydrogen phosphate have been evaluated. The results show a positive transfer volume of di-sodium hydrogen phosphate from an aqueous 1-propanol solution to a more concentrated 1-propanol solution. The apparent molar isentropic compression of di-sodium hydrogen phosphate in aqueous 1-propanol solutions is negative and it increases with increasing the concentration of 1-propanol and temperature. The negative values of apparent molar isentropic compression imply that the water molecules around the di-sodium hydrogen phosphate are less compressible than the water molecules in the bulk solutions. The effects of the electrolyte concentration and relative permittivity of the medium on the molar conductivity were also investigated.     

Accurate tracer diffusion coefficients of Na+ and Cl− ions in dilute aqueous sodium chloride solutions measured with the closed capillary method

A simple and absolute closed capillary method is introduced for measuring tracer diffusion coefficients in liquids with both - and -active tracers. In this method a narrow capillary is partially filled with a labelled solution and an unlabelled solution is used to fill the rest of the capillary. The diffusion coefficient is obtained from the time dependence of the monitored activity when the length of the capillary is known. The method has been tested by remeasuring the tracer diffusion coefficients of²²NaCl and Na³⁶Cl for solutions covering a wide range of total NaCl concentration. The average precision of the measurements was about 0.3%. The results obtained for Na³⁶Cl tracer diffusion are in good agreement with the data found in literature. The²²NaCl tracer diffusion coefficients that were measured in dilute solutions agree well with those obtained using the continuous open-ended capillary method but differ from results for solutions between 0.1 and 1M obtained with the diaphragm cell method.