Saturation molalities and standard molar enthalpies of solution of 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(cr) in H 2O(l)

Abstract

Saturation molalities m(sat) in H 2O(l) have been measured for the substances 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(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 measurements with results from the literature. Also, calorimetric molar enthalpies of solution Δ sol H m(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 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 thus obtain values of the standard molar Gibbs free energy Δ sol G m ∘ and enthalpy changes Δ sol H m ∘ for the dissolution reactions of these substances. The values of the p Ks and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of Δ sol G m ∘ and Δ sol H m ∘ .