Add time:08/11/2019         Source:sciencedirect.com

Saturation molalities m(sat) in H2O(l) have been measured for the substances 2′-deoxyadenosine · H2O(cr), 2′-deoxycytidine · H2O(cr), 2′-deoxyguanosine · H2O(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 ΔsolHm(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 Lϕ for these substances. These γ and Lϕ values were used to adjust the measured values of m(sat) and ΔsolHm to the standard state and thus obtain values of the standard molar Gibbs free energy ΔsolGm∘ and enthalpy changes ΔsolHm∘ 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 ΔsolGm∘andΔsolHm∘.

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