Thermochemistry of inosine

The formation thermodynamic properties of crystalline and aqueous inosine have been determined by using a combination of calorimetric techniques. Oxygen bomb calorimetric measurements on crystalline inosine yielded a standard molar enthalpy of combustion of ΔcHm∘=-(4802.2±4.5)kJ·mol-1. From this, a value for the standard molar enthalpy of formation ΔfHm∘ of −(847.9 ± 4.7) kJ · mol−1 was obtained. The standard molar heat capacity of crystalline inosine has been measured over the temperature interval 11 ⩽ T/K ⩽ 325 by using an adiabatic calorimeter. The heat capacities were fit to a series of polynomials from which smoothed values for the standard thermal properties were calculated for 20 ⩽ T/K ⩽ 320. The standard molar entropy Δ0TSm∘(inosine,cr) at T = 298.15 K is (288.0 ± 0.6) J · K−1 · mol−1 and the standard molar entropy of formation ΔfSm∘ is −(1449.6 ± 0.6) J · K−1 · mol−1. The standard Gibbs free energy of formation ΔfGm∘(inosine,cr)=-(415.7±4.7)kJ·mol-1. By using literature values of the standard molar enthalpy of solution and the saturation molality of inosine(cr), the standard molar thermodynamic properties of aqueous inosine at T = 298.15 K are found to be ΔfHm∘(inosine,aq)=-(819.8±4.7)kJ·mol-1; ΔfGm∘(inosine,aq)=-(409.2±4.8)kJ·mol-1; and Δ0TSm∘(inosine,aq)=(360.1±1.8)J·K-1·mol-1. These results are used to calculate standard thermodynamic properties of various aqueous species involving inosine.