H Yekeler

Publications (3)10.16 Total impact

• Article: Solvent effects on dimeric self-association of 2-pyrrolidinone: an ab initio study.

  H Yekeler
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  ABSTRACT: Full geometry optimizations were carried out for 2-pyrrolidinone (2-Py) and its dimer structures at the DFT (B3LYP) and HF levels in the gas phase and in solution. Additionally, single-point MP2/6-31G** calculations were performed on the HF/6-3 1G** optimized geometries. The self-association of 2-Py in 1,4-dioxane (epsilon = 2.21) and in water (epsilon = 78.54) were studied using the self-consistent reaction field (SCRF) theory. The calculated relative free energies (deltaG) for the dimerization processes predict the cyclic dimer (CD) to be more stable than the open dimer (OD) at all levels of theory in the gas phase and in solution. The results show that, at least for the properties of the hydrogen-bonded systems studied in this work, the B3LYP/6-31G** calculations give better results than the HF and MP2 calculations with the same basis set. The data obtained from this study were compared with the corresponding experimental results when available.
  Journal of Computer-Aided Molecular Design 05/2001; 15(4):287-95. · 3.39 Impact Factor
• Article: Ab initio study on tautomerism of 2-thiouracil in the gas phase and in solution.

  H Yekeler
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  ABSTRACT: Ab initio geometry optimizations were carried out at the HF/3-21G and HF/6-31+G** levels for the six tautomeric forms of 2-thiouracil (2TU, 2TU1, 2TU2, 2TU3, 2TU4, 2TU5) in the gas phase and in solution. To obtain a more definitive estimate of the relative stabilities for 2-thiouracil tautomers in the gas phase, single-point MP2/6-31+G** calculations were performed on the HF/6-31+G** optimized geometries. The tautomeric equilibria in 1,4-dioxane (epsilon = 2.21), acetonitrile (epsilon = 38), and in water (epsilon = 78.54) were studied using the self-consistent reaction field (SCRF) theory. The calculated relative free energies indicated that 2TU is the energetically preferred tautomer in the gas phase and in solution. The stability order of 2-thiouracil tautomers depends on the level of theory and the dielectric constant of the solvent. The obtained results are compared with the available experimental data.
  Journal of Computer-Aided Molecular Design 04/2000; 14(3):243-50. · 3.39 Impact Factor
• Article: Hydrogen bonding and dimeric self-association of 2-pyrrolidinone: an ab initio study.

  H Yekeler, A Guven, R Ozkan
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  ABSTRACT: Ab initio calculations on the different associated structures of 2-pyrrolidinone with water and with itself were carried out using 3-21G and 6-31G* basis sets at the Hartree-Fock level, including electron correlation using second-order Møller-Plesset perturbation theory. The calculated free energy changes for the intermolecular hydrogen bonded dimer and hydrated species indicated that the molecular systems with cyclic dimerization and association with two water molecules are dominant. The results are compared to the available experimental data in the literature.
  Journal of Computer-Aided Molecular Design 12/1999; 13(6):589-96. · 3.39 Impact Factor