K. Mohle et Hj. Hofmann, STABILITY ORDER OF BASIC PEPTIDE CONFORMATIONS REFLECTED BY DENSITY-FUNCTIONAL THEORY, JOURNAL OF MOLECULAR MODELING, 4(2), 1998, pp. 53-60
Ab initio density functional methods at the B3LYP/6-311+G(d, p) and 6-
31G(d) levels were performed on several basic peptide conformations re
presenting typical elements of secondary structure (beta-sheets, beta-
and gamma-turns). The results are compared with those from Hartree-Fo
ck and MP2 correlation energy calculations. Whereas the geometries of
the structures are well described at all approximation levels, there a
re considerable discrepancies of the stability orders. Contrary to the
Hartree-Fock calculations, the correlation energy methods provide the
more compact structures with intramolecular hydrogen bonds distinctly
favoured over extended conformations when comparing the energy differ
ences. However, due to considerable compensation of correlation energy
and entropy contributions, the stability order at the Gibbs free ener
gy level closely corresponds to that at the Hartree-Fock level.