Saturation molalities and standard molar enthalpies of solution of adenosine(cr), guanosine · 2H 2O(cr), inosine(cr), and xanthosine · 2H 2O(cr) in H 2O(l)

Abstract

Saturation molalities m(sat) in H 2O(l) have been measured for the substances adenosine(cr), guanosine · 2H 2O(cr), inosine(cr), and xanthosine · 2H 2O(cr) over the temperature range T=287.91 K to T=308.18 K by using h.p.l.c. The indicated states of hydration of these substances were established by performing Karl–Fischer analyses of samples of these substances which had been equilibrated over H 2O(l) and of samples obtained by passing air over the wet crystals (air dried samples). The crystalline phases of these substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Molar enthalpies of solution Δ sol H m for adenosine(cr) and inosine(cr) were measured by using an isoperibol solution calorimeter. A “stacking” or “self-association” model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L φ for these substances. These γ and L φ values were used to adjust the measured values of m(sat) and Δ sol H m to the standard state and obtain values of the standard molar Gibbs free energy and enthalpy changes Δ sol G ∘ m and Δ sol H ∘ m, respectively, for the dissolution reactions of these substances. Values of Δ sol H ∘ m calculated from the temperature dependence of values of Δ sol G ∘ m were in good agreement with the values of Δ sol H ∘ m obtained by using calorimetry.