Comparison of Structural Types of Proline Pentamer by Quantum Chemical Calculation (QCC)

Comparison of Structural Types of Proline Pentamer by Quantum Chemical Calculation (QCC)

In this study, Proline pentamer model was used to investigate change in the dihedral angle, intramolecular hydrogen bonding and formation energies during structural optimization. L-Proline (LP, as an imino acid residue) pentamers having four conformation types [β: φ/ψ=t−/t+, α: φ/ψ=g−/g−, PPII: φ/ψ=g−/t+ and P-like: φ/ψ= g−/g+] were carried out by QCC [B3LYP/6-31G(d,p)]. The optimized structure and formation energy were examined for designated structure. In LP, P-like and PPII types did not change by optimization, and β types were transformed into PPII having no H-bond independently of the designated ψ values. PPII was more stable than P-like by about 2.2 kcal/mol/mu. The hydrogen bond distances of d2(4-6) type H-bonds were 1.94 - 2.00Å. In order to understand the processes of the transformations, the changes of φ/ψ, distances of NH-OC (dNH/CO) and formation energies (ΔE, kcal/mol/mu) were examined.

In this study, Proline pentamer model was used to investigate change in the dihedral angle, intramolecular hydrogen bonding and formation energies during structural optimization. L-Proline (LP, as an imino acid residue) pentamers having four conformation types [β: φ/ψ=t−/t+, α: φ/ψ=g−/g−, PPII: φ/ψ=g−/t+ and P-like: φ/ψ= g−/g+] were carried out by QCC [B3LYP/6-31G(d,p)]. The optimized structure and formation energy were examined for designated structure. In LP, P-like and PPII types did not change by optimization, and β types were transformed into PPII having no H-bond independently of the designated ψ values. PPII was more stable than P-like by about 2.2 kcal/mol/mu. The hydrogen bond distances of d2(4-6) type H-bonds were 1.94 - 2.00Å. In order to understand the processes of the transformations, the changes of φ/ψ, distances of NH-OC (dNH/CO) and formation energies (ΔE, kcal/mol/mu) were examined.