Influence of stereochemistry on proton transfer in protonated tripeptide models.

Faculty of Science - National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00, Brno, Czech Republic.
Journal of Molecular Modeling (Impact Factor: 1.98). 05/2011; 18(3):871-9. DOI: 10.1007/s00894-011-1116-2
Source: PubMed

ABSTRACT Vectorial proton transfer among carbonyl oxygen atoms was studied in two models of tripeptide via quantum chemical calculations using the hybrid B3LYP functional and the 6-31++G basis set. Two principal proton transfer pathways were found: a first path involving isomerization of the proton around the double bond of the carbonyl group, and a second based on the large conformational flexibility of the tripeptide model where all carbonyl oxygen atoms cooperate. The latter pathway has a rate-determining step energy barrier that is only around half of that for the first pathway. As conformational flexibility plays a crucial role in second pathway, the effect of attaching methyl groups to the alpha carbon atoms was studied. The results obtained are presented for all four possible stereochemical configurations.

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