The energetic stabilization and geometrical parameters of the β-sheet structure of three oligopeptides L-Alan, selected conformers of L-Valn and L-Sern (n=2-10) have been investigated by DFT computations. The data reveal the important effect of long-range interactions operating through hydrogen bonding and dipole-dipole interactions. Compared with related data on Glyn oligopeptides determined in our previous study (V. Horváth, Z. Varga, A. Kovács, J. Phys. Chem. A, 2004, 108, 6869-6873), the methyl, i-propyl and hydroxymethyl substituents lead to a decrease of the long-range interactions. While the energy gain from these interactions of a Gly unit in Gly10 was 2.4 kJ/mol, the contribution decreased to 2.1, 1.8, and 0.4 kJ/mol in Ala10, Val10, and Ser10, respectively. Variations of the geometrical parameters (most important being the lengths of H⋯O hydrogen-bonds and the C-N bonds) are in agreement with the decrease of the stabilization energies. Another important effect of the substituents is that their steric interactions introduce irregularities in the build-up of energetic and geometric trends, in contrast to their monotonous build-up in Glyn.
Bibliographical noteFunding Information:
This research was initiated by Prof István Hargittai and we thank him for advice and discussion. Financial support from the Hungarian Scientific Research Foundation (OTKA No. T046183) and computational time from the National Information Infrastructure Development Program of Hungary is gratefully acknowledged. A.K. thanks the Bolyai Foundation for support.
- Long-range interactions