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Influence of ionization on the conformational preferences of peptide models. Ramachandran surfaces of N ‐formyl‐glycine amide and N ‐formyl‐alanine amide radical cations
Author(s) -
Gil Adrià,
Sodupe Mariona,
Bertran Juan
Publication year - 2009
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.21178
Subject(s) - chemistry , ramachandran plot , oniom , amide , computational chemistry , ionization , peptide , ab initio , solvent , ionization energy , stereochemistry , molecule , ion , protein structure , organic chemistry , biochemistry
Ramachandran maps of neutral and ionized HCO–Gly–NH 2 and HCO–Ala–NH 2 peptide models have been built at the B3LYP/6‐31++G(d,p) level of calculation. Direct optimizations using B3LYP and the recently developed MPWB1K functional have also been carried out, as well as single‐point calculations at the CCSD(T) level of theory with the 6‐311++G(2df,2p) basis set. Results indicate that for both peptide models ionization can cause drastic changes in the shape of the PES in such a way that highly disallowed regions in neutral PES become low‐energy regions in the radical cation surface. The structures localized in such regions, $ \varepsilon^{+\bullet}_{\rm L} $ and $ \varepsilon^{+\bullet}_{\rm D} $ are highly stabilized due to the formation of 2‐centre‐3‐electron interactions between the two carbonyl oxygens. Inclusion of solvent effects by the conductor‐like polarizable continuum model (CPCM) shows that the solute‐solvent interaction energy plays an important role in determining the stability order. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009