Thermochemistry of Uracil, Thymine, Cytosine, and Adenine

Abstract

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.

Accurate Structures and Spectroscopic Parameters of Guanine Tautomers in the Gas Phase by the Pisa Conventional and Explicitly Correlated Composite Schemes (PCS and PCS-F12)

“…In the case of uracil, thymine, and adenine, the “canonical” tautomer is significantly more stable than all the “minor” ones also in the gas phase, whereas the situation is more involved for cytosine and guanine . The tautomeric equilibrium of cytosine has been recently investigated by state-of-the-art QC methods. , Therefore, the focus of the present work is on guanine.…”

Heat Capacity and Thermodynamic Functions of Crystalline β-Cytidine from 0 to 300 K

“…Its monomers could be formed in the course of chemical reactions without the involvement of living systems. The work on this hypothesis aroused keen interest − among researchers as it regards all RNA fragments, including nucleosides.…”

Accuracy Meets Feasibility for the Structures and Rotational Constants of the Molecular Bricks of Life: A Joint Venture of DFT and Wave-Function Methods

“…As a matter of fact, the PCS errors are smaller by about 1 order of magnitude than those delivered by standard DFT, MP2, and CCSD­(T)/cc-pVTZ­(- f ) approaches and fulfill the goal of mean unsigned errors below 0.1%, which is considered the gold standard of the most accurate computations even for small semirigid molecules. , Since the SE equilibrium structure of uracil is available, a direct comparison of geometrical parameters is also possible, which shows that the mean unsigned error of bond lengths is reduced from 0.003 to 0.002 and 0.001 Å (the corresponding maximum errors being 0.005, 0.003, and 0.002 Å, respectively) when going from rDSD/j3 to rDSD/3F12 and PCS levels. At the same time, the valence angles are always sufficiently accurate.…”

“…Experimental data are from refs and − for uracil, 2-thiouracil, thymine, adenine, guanine, cytosine, and uridine, respectively. All of the values are given in MHz. b CCSD­(T)/cc-pVTZ­(- f ) from ref . except for 2-thiouracil, CCSD­(T) from ref . …”