Underlying Source of the Relation between Polypeptide Conformation and Strength of NH··O Hydrogen Bonds

Document Type

Article

Journal/Book Title

Journal of Molecular Structure

Publication Date

3-2007

Publisher

Elsevier

Volume

844-845

First Page

166

Last Page

172

Abstract

Previous calculations have revealed that the NH···O bond between a dipeptide NH and a proton acceptor is considerably weaker when the dipeptide is in its extended C5 conformation than in the C7 structure. The present work uses quantum chemical methods to determine the underlying reason for this different behavior. With regard to the pertinent NH group, the two dipeptide conformers show very little difference in total electron density or in the character of the low-lying vacant molecular orbitals which might act as sinks for electron density from the proton acceptor. There is also little evidence that a weak intramolecular H-bond within the C5 structure is able to influence the ability of the NH group to participate in an intermolecular bond. Energy decomposition analysis points toward electrostatic interaction as the chief factor in the different behavior of the C5 and C7 structures. Further analysis reveals that the proximity of the carbonyl O atom of the dipeptide, with its partial negative charge, toward the NH group changes the character of the electrostatic potential in the C5 geometry, making NH a less attractive target for an incoming proton acceptor.

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http://www.sciencedirect.com/science/article/pii/S0022286007002803

Publisher PDF is available for download through the link above.

Published by Elsevier in Journal of Molecular Structure.

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