Enthalpies of Formation of DNA and RNA Nucleobases from G3X Theory

Abstract

The Gaussian-3X (G3X) method has been used to calculate accurate values of the gas-phase enthalpies of formation of all five DNA and RNA nucleobases: thymine, adenine, cytosine, guanine, and uracil, whose experimental gas-phase study is a difficult problem because of the low vapor pressures. Only for uracil, the published experimental value agrees well with the theoretical one. However, the revision of available experimental data on enthalpies of formation for compounds in the solid phase and enthalpies of sublimation allowed us to recommend a set of self-consistent thermochemical data for thymine, adenine, and cytosine, which lead to good agreement between experimental and theoretical gas-phase enthalpies of formation. To obtain more reliable values of enthalpy of sublimation at 298.15 K, the heat capacity values of gaseous compounds were calculated by standard statistical thermodynamics formulas using molecular parameters determined from B3LYP/6-31G(2df,p) calculations. The following values are recommended based on G3X calculations and a revision of published experimental data:thymine, g, 298.15 K) ) (-338.0 ( 2.5) kJ • mol -1 , ∆ f H 298 °(cytosine, g, 298.15 K) ) (-69.5 ( 3.5) kJ • mol -1 , and ∆ f H 298 °(adenine, g, 298.15 K) ) (225.7 ( 3.5) kJ • mol -1 . Because of a lack of reliable experimental data for guanine, the theoretical G3X value is recommended for this compound: ∆ f H 298 °(guanine, g, 298.15 K) ) (16.0 ( 5.0) kJ • mol -1 .

Thermochemistry of Uracil, Thymine, Cytosine, and Adenine

“…The earliest Δ f H 298 ° (g) value for uracil was determined to be −59.4 ± 10 kJ/mol . After reconsidering the available literature data, Dorofeeva and Vogt suggested a −69.5 ± 3.5 kJ/mol value. The result of Emel’yanenko is somewhat higher, −66.9 ± 2.1, because of their higher sublimation enthalpy value.…”

“…Dorofeeva and Vogt, and Emel’yanenko and co-workers list 225.7 and 225.8 kJ/mol, respectively, as the heat of formation of adenine in the gas phase. The first value is based on the combustion calorimetry results of Kirklin and Domalski combined with the sublimation enthalpy of A. Zielenkiewicz et al, while the other is the original result of ref .…”

“…These data hardly differ from those listed by Pedley. 83 Dorofeeva and Vogt, 7 with the help of G3X calculations and revised literature data, reported Δ f H 298 °(g) = −301.5 ± 2.5 kJ/mol. Emel'yanenko et al 9 also conducted experiments to determine the heats of combustion and sublimation, and their slightly higher sublimation enthalpy All values are in kJ/mol.…”

Enthalpies of formation of β-alanine, sarcosine, and 4-aminobutanoic acid from quantum chemical calculations

“…In previous works, the D f H m ðg; 298:15 KÞ values were calculated for DNA and RNA nucleobases [1] and two amino acids [2] by Gaussian-3X (G3X) method. It has been shown that theoretical calculations could be used to test the accuracy of experimental values and recommend more reliable enthalpies of formation for compounds in the solid phase and enthalpies of sublimation.…”

Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods

“…C2-N1, C4-N3 and C5-N7, C8-N9, may leave the remaining neutral HCN intact.Within the collision energy range studied for adenine and its derivatives, i.e. for the available energy (3.8-68.3 eV), such loss of HCN units is operative since the estimated threshold of the decomposition reaction requires 3.89 eV given that ΔfHg° (C5H5N5) = 225.7 kJ/mol (2.34 eV),41…”