For-L-Ala-L-Ala-NH2

M. Ramek, C.-H. Yu, and L. Schäfer,
Ab initio conformational analysis of the model tripeptide
N-formyl-L-alanyl-L-alanine amide,
Can. J. Chem. 76, 566-575 (1998).

RHF/6-31G* Structures of Low-Energy Conformers of For-L-Ala-L-Ala-NH₂

Global Minimum two O···H-N hydrogen bonds form two gamma

-turns (7-membered rings closed by H-bond)

Extended Structure second lowest in energy (E_rel = 0.09 kJ/mol) no hydrogen bonds, but two favourable electrostatic interactions with parallel arrangement of the groups C=O and N-H (the so-called C-orientation)

Half Extended Form third in energy (E_rel = 0.33 kJ/mol) one gamma

-turn, one C-orientation

3-Loop fourth in energy (E_rel = 1.60 kJ/mol) one beta

-turn (10-membered ring, closed by a O···H-N hydrogen bond) repetition of this loop produces a 3-helix

RHF/6-31G* Structures of Low-Energy Conformers of For-L-Ala-L-Ala-NH2

Related links:

RHF/6-31G* Structures of Low-Energy Conformers of For-L-Ala-L-Ala-NH₂