• Archives of Pharmacal Research
• /
• v.20 no.3
• /
• pp.269-274
• /
• 1997

Solubilities of oleanolic acid and ursolic acid in aqueous surfactant solutions, liquid polyethylene glycols (PEG), and solvents of various polarity were measured. The results showed that the solutes were slightly or moderately solubilized in the surfactant solutions and the liquid PEGS. It was also revealed that the solutes were slightly soluble in the solvent of either extreme polarity or nonpolarity, but moderately soluble in solvents of intermediate polarity of which solubility parameters are around 10. The solubility parameters of these solutes were calculated from the group contribution to be 10.2 for both of them. Of the solvents tested, tetramethylurea was exceptionally effective in solubilizing the solutes. The solutes were also moderately soluble in the aqueous cosolvents containing tetramethylurea. This suggests that the mixed systems of tetramethylurea could be employed for the solubilization in the formulation of these compounds as an aqueous system.

• Journal of the Korean Chemical Society
• /
• v.20 no.5
• /
• pp.374-379
• /
• 1976

Apparent molal volumes of urea, 1,3-dimethylurea (DMU), and 1,1,3,3-tetramethylurea(TMU) in dimethylsulfoxide(DMSO) and in methanol have been measured at low concentration by the density measurements at $25^{\circ}C$. It is confirmed that urea molecules in the dilute DMSO solution self-associate to a greater extent than in the concentrated solution, while DMU and TMU molecules in DMSO solutions interact with the solvent molecules. In addition, the molecules of the three solutes also interact predominatingly with methanol molecules.

• Bulletin of the Korean Chemical Society
• /
• v.19 no.1
• /
• pp.110-114
• /
• 1998

The hydrogen-bonding interactions between thioacetamide (TA) and urea derivatives such as tetramethylurea (TMU) and dimethyldiphenylurea (DMDPU) have been studied using near-infrared absorption spectroscopy. Thermodynamic parameters for the interactions between TA and urea derivatives were determined by analyzing the $v^{as}_{N-H}$+Amide Ⅱ combination band of TA at 1970 nm. The ΔH° values, indicating the intrinsic strength of hydrogen bonding, are - 23.0 kJ/mole and - 19.8 kJ/mol for TMU and DMDPU, respectively. This is well explained by the inductive effects of substituents. Ab initio molecular orbital calculations for the proton affinity of TMU, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) in gas phase have been carried out at HF/3-21G ad HF/6-31G(d) levels, showing that the proton affinity of TMU is larger than that of DMA, which agrees well the experimental results.