Saturation Molalities and Standard Molar Enthalpies of Solution of Cytidine(cr), Hypoxanthine(cr), Thymidine(cr), Thymine(cr), Uridine(cr), and Xanthine(cr) in H2O(1)

Published

July 1, 2004

Author(s)

Yadu D. Tewari, Patrick D. Gery, Mark D. Vaudin, Alan D. Mighell, R Klein, Robert N. Goldberg

Abstract

Saturation molalities, m(sat) in H 0(I) have been measure for the substances cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) by using h.p.l.c. The states of hydration were established by performing Karl-Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T 298 K and then dried with air at T 296 K for 24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction with results from the literature. Also, molar enthalpies of solution ? sol Hm (cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients ? and relative apparent molar enthalpies L for these substances. These ? and L values were used to adjust the measured values of m (sat) and ? sol Hm (cal) to the standard state and thus obtain values of the standard molar Gibbs free energy ? sol G m and enthalpy changes ? sol H m for the dissolution reactions of these substances. The values of the pKs and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of ? sol G m and ? sol H m. Values of standard molar enthalpies of formation ?fH m, standard molar Gibbs free energies of formation ?fG , and standard partial molar entropies S 2, m for the aqueous species of hypoxanthine and xanthine were calculated. A detailed summary and comparison of thermodynamic results from the literature for these substances is presented.

Citation

Journal of Chemical Thermodynamics

Volume

36

Pub Type

Journals

Keywords

cytidine, enthalpy of solution, Gibbs free energy, hypoxanthine, saturation molality, solubility, thymidine, thymine, uridine

Citation

Tewari, Y. , Gery, P. , Vaudin, M. , Mighell, A. , Klein, R. and Goldberg, R. (2004), Saturation Molalities and Standard Molar Enthalpies of Solution of Cytidine(cr), Hypoxanthine(cr), Thymidine(cr), Thymine(cr), Uridine(cr), and Xanthine(cr) in H₂O(1), Journal of Chemical Thermodynamics (Accessed October 13, 2024)