Thermochemistry of Uracil, Thymine, Cytosine, and Adenine

The
goal of this study is to give reliable and accurate thermochemical
data for uracil, thymine, cytosine, and adenine. The gas-phase heats
of formation of these compounds were determined with the diet-HEAT-F12
protocol, which uses explicitly correlated coupled-cluster calculations
along with anharmonic vibrational, scalar relativistic, and diagonal
Born–Oppenheimer corrections. The thermochemically relevant
tautomers of cytosine were also investigated. To derive heats of formation
in the gas and solid phases as well as sublimation enthalpies, the
thermochemical network approach was utilized, i.e., the available
literature data were collected, reviewed, and combined with our theoretical
calculations. Solvation free energies were also determined with various
methods and compared to experimental data.