Peptide models XXIV: An ab initio study on N-formyl-L-prolinamide with trans peptide bond. The existence or non-existence of α(L) and ε(L) conformations

BALDONI, HECTOR A.; RODRIGUEZ, ANA M.; ZAMORA, MIGUEL A.; ZAMARBIDE, GRACIELA N.; ENRIZ, RICARDO D.; FARKAS, ÖDÖN; CSÀSZÀR, PAL; TORDAY, LADISLAUS L.; SOSA, CARLOS P.; JÀKLI, IMRE; PERZEL, ANDRÀS; PAPP, JULIUS GY.; HOLLOSI, MIKLOS; CSIZMADIA, IMRE G.

JOURNAL OF MOLECULAR STRUCTURE THEOCHEM

ELSEVIER SCIENCE BV

Año: 1999 vol. 465 p. 79 - 91

0166-1280

N-formyl-L-prolinamide was subjected to geometry optimization at three levels of theory: HF/3-21G, HF/6-31G (d) and B3LYP/6-31G (d). At all three levels of computation the global minimum was γ(L) (inverse γ-Turn) backbone conformation with two ring-puckered forms ´UP´ and ´DOWN´. At HF/3-21G level of theory three backbone conformations were found γ(L), ε(L), and α(L). At higher levels of theory the ε(L), and α(L) conformations disappeared. The ´UP´ and ´DOWN´ ring-puckered forms, in the γ(L) backbone conformation, led to practically identical vibrational spectra at the B3LYP/6-31G (d) level of theory.