An assessment of the chiral environment created by adjacent d- and l-alanyl residues on a glycine unit within the tripeptide N-Ac-Ala-Gly-Ala-NHMe: an ab initio exploratory study

Ab initio Molecular Orbital computations were carried out on the tripeptide models, N-Ac-d-Ala-Gly-l-Ala-NHMe and N-Ac-l-Ala-Gly-l-Ala-NHMe at the RHF/3-21G level of theory. The topologies of conformational Potential Energy Surfaces were explored and analyzed. In addition, global and local minima on the Ramachandran Potential Energy Surfaces, E=f(φ1,ψ1) and E=f(φ3,ψ3) were identified and their geometries optimized. The nearest neighboring effects of d and l amino acids on the conformations of the central glycine residue were also compared. Seven stable minima were found for each system and two conformers (α and ε) were oppositely different due to the influence of the N-terminal d- or l-alanyl residue.