AM1 and PM3 study of tautomerism of hypoxanthine in the gas and aqueous phases

ÜNAL CİVCİR P.

STRUCTURAL CHEMISTRY, cilt.12, sa.1, ss.15-21, 2001 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 12 Sayı: 1
  • Basım Tarihi: 2001
  • Doi Numarası: 10.1023/a:1009253916904
  • Dergi Adı: STRUCTURAL CHEMISTRY
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.15-21
  • Anahtar Kelimeler: hypoxanthine, tautomerism, tautomeric equilibrium constant, dipole moment, ionization potential, AM1, PM3 semiempirical calculation, SEMIEMPIRICAL METHODS, RELATIVE STABILITIES, GUANINE, XANTHINE, OPTIMIZATION, ALLOPURINOL, PROTONATION, PARAMETERS, MOLECULES, SPECTRA
  • Ankara Üniversitesi Adresli: Evet

Özet

Heats of formation, entropies, Gibbs free energies, relative tautomerisation energies, tautomeric equilibrium constants, dipole moments, and ionization potentials for the eight possible tautomers of hypoxanthine have been studied using semiempirical AM1 and PM3 quantum-chemical calculations at the SCF level in the gas and aqueous phases, with full geometry optimization. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the two keto tautomers H17 and H19 are the predominant species at room temperature in the gas and aqueous phase. However, the tautomer H17 is the more dominant species in gas phase, while the H19 tautomer is the more dominant species in the aqueous phase. Comparison. with available experimental data provides support for the results derived From theoretical computations. The entropy effect on the Gibbs free energy of hypoxanthine is very small and there is little significance for the tautomeric equilibria of the base. The enthalpic term is dominant in the determination of the equilibrium constant.