Mechanism of Proton Transfer in Short Protonated Oligopeptides. 1. N-Methylacetamide and N2-Acetyl-N1-methylglycinamide

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Authors

KULHÁNEK Petr SCHLAG Edward W. KOČA Jaroslav

Year of publication 2003
Type Article in Periodical
Magazine / Source J. Phys. Chem. A
MU Faculty or unit

Faculty of Science

Citation
Web http://dx.doi.org/10.1021/jp027689+
Field Nuclear and quantum chemistry, photochemistry
Keywords proton transfer; proton exchange; proton interaction; DFT
Description A study of proton transfer in models of a single peptide unit (N-methylacetamide) and diamide (N2-acetyl-N1-methylglycinamide) as well as the influence of a single water molecule on proton transfer is presented here. Three proton pathways in protonated N-methylacetamide are considered: isomerization, inversion, and 1,3-proton shift. The isomerization step exhibits the lowest energy barrier. When a single water molecule was added, no significant influence on proton isomerization was observed. In the diamide model, the isomerization-jump mechanism of proton transfer along diamide carbonyl oxygens was inspected, and the proton isomerization steps were found to be the most energy-demanding processes (~17 kcal mol-1). The presence of a single water molecule leads to a different, lower-energy-barrier proton-transfer mechanism with proton exchange. The highest energy barrier is only 7.6 kcal mol-1. Possible competing pathways are also discussed.
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