Viktória Horváth, Zoltán Varga, and Attila Kovács
Long-Range Effects in Oligopeptides.
A Theoretical Study of the b-Sheet Structure of Glyn (n = 2 - 10)
The Journal of Physical Chemistry A, 108 (2004) 6869-6873
Long-range interactions in the b-sheet structure of oligoglycines Glyn (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 Glyn 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 Glyn. 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