期刊
JOURNAL OF CHEMICAL PHYSICS
卷 135, 期 19, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3658857
关键词
density functional theory; free energy; hydrogen bonds; intermolecular forces; intramolecular forces; molecular configurations; molecular dynamics method; organic compounds; perturbation theory; Raman spectra; solvent effects; water
资金
- Ministerio de Educacion y Ciencia of Spain [CTQ2008-06224/BQU]
- European Regional Development Fund (ERDF)
- Consejeria de Economia
- Comercio e Innovacion of the Junta de Extremadura
The ASEP/MD method has been employed for studying the solvent effect on the conformational equilibrium of the alanine dipeptide in water solution. MP2 and density functional theory (DFT) levels of theory were used and results were compared. While in gas phase cyclic structures showing intramolecular hydrogen bonds were found to be the most stable, the stability order is reversed in water solution. Intermolecular interaction with the solvent causes the predominance of extended structures as the stabilizing contacts dipeptide-water are favoured. Free-energy differences in solution were calculated and PPII, alpha(R), and C5 conformers were identified as the most stable at MP2 level. Experimental data from Raman and IR techniques show discrepancies about the relative abundance of alpha(R) y C5, our results support the Raman data. The DFT level of theory agrees with MP2 in the location and stability of PPII and alpha(R) forms but fails in the location of C5. MP2 results suggest the possibility of finding traces of C7eq conformer in water solution, in agreement with recent experiments. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658857]
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