Enthalpies of solution of the nucleic acid bases. 4. Uracil in water

An adiabatic solution calorimeter was used to measure enthalpies of solution in water of 7 uracil samples in a concentration range of 3 to 45 mmol · kg -1 and over a temperature range of 298 K to 325 K. Analytical data for the samples are given. Our best value for the enthalpy of solution is Δ H 0 ( ∞ , 298.15 K ) = ( 29.33 ± 1.2 ) kJmol - 1and for the change in heat capacity for the reaction with temperature, Δ C p 0 = ( 57 ± 13 ) Jmol - 1K - 1No change in the enthalpy of solution with concentration was found in this range. Values were calculated for the entropy of solution, Δ S ° = (68.1 ± 4.2) J · mol -1 · K -1 , and for the apparent molal heat capacity at infinite dilution, C p 2 0 = ( 178 ± 15 ) J m o l - 1K - 1.