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

ÜNAL CİVCİR P.

JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, cilt.545, ss.7-15, 2001 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 545
  • Basım Tarihi: 2001
  • Doi Numarası: 10.1016/s0166-1280(00)00821-6
  • Dergi Adı: JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.7-15
  • Anahtar Kelimeler: AM1, PM3 semiempirical calculations, dipole moment, ionisation potential, tautomerism, tautomeric equilibrium constant, xanthine, GUANINE, HYPOXANTHINE, NUCLEOSIDES, PROTONATION, ADENINE, ANALOGS, PURINE, FORMS, BASES
  • Ankara Üniversitesi Adresli: Evet

Özet

Heats of formation, entropies, Gibbs free energies, relative tautomerisation energies, tautomeric equilibrium constants, relative proton affinities, dipole moments, and ionisation potentials for the fourteen possible tautomers of xanthine have been studied using semiempirical AMI and PM3 quantum-chemical calculations at the SCF level in the gas and aqueous phases, with full geometry optimisation. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the two diketo tautomers X1,3,7 and X1,3,9 are the predominant species at room temperature in the gas and aqueous phase. But, the first more stable tautomer is the dioxo-7H tautomer, X1,3,7. Comparison with available experimental data provides support for quality of results derived from theoretical computations. The entropy effect on the Gibbs free energy of the xanthine is very small and there is little significance for the tautomeric equilibria of the base. The enthalpic term is dominant also in the determination of the equilibrium constant. (C) 2001 Elsevier Science B.V. All rights reserved.