Viktória Horváth, Zoltán Varga, and Attila Kovács

Long-Range Effects in Oligopeptides.

A Theoretical Study of the b-Sheet Structure of Gly_n (n = 2 - 10)

The Journal of Physical Chemistry A, 108 (2004) 6869-6873

Long-range interactions in the b-sheet structure of oligoglycines Gly_n (n = 2 - 10) have been investigated by DFT computations using the B3LYP exchange-correlation functional in conjunction with a diffuse polarized valence triple-zeta basis set.

The study focused on the evaluation of the title interactions in the Gly_n chain and on the quantitative determination of their consequences in both energy and geometry. It was found that the interactions contribute considerably to the stability of the b-sheet and have a substantial impact on the geometrical parameters. On the basis of the gradual build-up of energetic and geometrical effects, we determined the effective radius of long-range interactions to be around ten Gly units in the b-sheet Gly_n. The energy gain from the long-range interactions of a Gly unit is around 2.5 kJ/mol, stemming to a large extent from the strengthening of the N–H…O=C hydrogen bonds. Among the geometrical parameters, the H…O hydrogen-bond length is the most sensitive to long-range effects, decreasing by several hundredths of an angstrom. Besides, there is a pronounced shortening of the C–N bonds (up to 0.009 Å), while the other bond distances vary within 0.002 Å and the bond angles within 0.5°. Our structure analysis revealed also a small (a few thousands of an angstrom) elongation vs contraction of the chain depending on the parallel vs antiparallel orientation of the NH₂ and COOH end-dipoles. The alterations of the bond distances upon long-range effects are associated with appreciable changes in the magnitude of the main hyperconjugation interactions.