An ONIOM investigation of the effect of conformation on bond dissociation energies in peptides.

J Comput Chem

School of Chemistry, University of Sydney, New South Wales, 2006, Australia.

Published: January 2019

In the present study, we use the ONIOM strategy of Morokuma and coworkers to examine the various CH bond dissociation energies (BDEs) of a small peptide (2ONW) and compare these with values obtained for its component individual amino acid residues. To evaluate suitable methods for ONIOM-based geometry optimizations, we test an "internal consistency" approach against full B3-LYP//B3-LYP results, and find B3-LYP/6-31G(d):AM1 to be appropriate. We find that the BDEs at the α-carbon in 2ONW are generally larger than the corresponding values for the individual residues on their own. This is attributed to the constraints of the peptide backbone leading to conformations that are not ideal for captodative stabilization of the resulting α-radicals. At the more flexible β- and γ-positions, the differences between the BDEs in 2ONW and the individual residues are smaller. Overall, the α-BDEs are smaller than the β- and γ-BDEs in most cases. Thus, to rationalize the inertness of peptide backbones with respect to α-hydrogen abstraction that is frequently found experimentally, it is necessary to consider alternative protection mechanisms such as the polar effect. © 2018 Wiley Periodicals, Inc.

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http://dx.doi.org/10.1002/jcc.25538DOI Listing

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