title: Influence of stereochemistry on proton transfer in protonated tripeptide models.
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.
authors.affiliation: Faculty of Science - National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00, Brno, Czech Republic.
authors.forename: Namat Ali
authors.initials: NA
authors.lastname: Soliman
authors.forename: Petr
authors.initials: P
authors.lastname: Kulhánek
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Koča
mesh_terms: D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D018583:Pliability; D011487:Protein Conformation; D011522:Protons; D013237:Stereoisomerism
chemical_list: D009842:Oligopeptides; D011522:Protons