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

摘要

The standard molar heat capacity C_(p,m)~o 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)~o=(142.67+-0.29) J·K~(-1)·mol~(-1) and the third law entropy S_m~o=(145.62+-0.29) J·K~(-1)·mol~(-1).The standard molar Gibbs free energy of formation DELTA_fG_m~o at T=298.15 K for crystalline adenine was calculated,using the standard moalr enthalpy of formation of the compound and entropies of the elements from the literature,and found to be DELTA_fG_m~o=(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:DELTA_fG_m~o=(313.4+-1.0) kJ·mol~(-1),DELTA_fH_m~o=(129.5+-1.4) kJ·mol~(-1),and S_m~o=(217.68+-0.44) J·K~(-1)·mol~(-1).