Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

Abstract

The standard molar heat capacity C ∘ p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<( T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C ∘ p,m=(142.67±0.29) J · K −1 · mol −1 and the third law entropy S ∘ m=(145.62±0.29) J · K −1 · mol −1. The standard molar Gibbs free energy of formation Δ f G ∘ m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ f G ∘ m=(301.4±1.0) kJ · mol −1. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ f G ∘ m=(313.4±1.0) kJ · mol −1, Δ f H ∘ m=(129.5±1.4) kJ · mol −1, and S m ∘=(217.68±0.44) J · K −1 · mol −1.