Figure 5.

Semi-log plot of the stabilization energy ΣE_HB due to the NH⋯S H-bonds 5SEE (Tables S3 and S4) against the NH⋯S distance theoretically found for the 7^δ and 6^δ H-bonds (light and yellow symbols resp.) in the 5-7^δ_g+/g−-7_L, 5-7^δ/5_a-π and 6^δ-π_g+-10 backbone conformations of the Ac-Sem-Met-Phe-NH₂ dipeptides, with anti and gauche orientations of the Sem-Phe terminal dihedral χ₃ (square and disk symbols resp.) together with the intermolecular MAA⋯S-SeMe₂ complexes (stars) According to a previous NBO study of amide⋯amide interactions [29], in such plots the points aligned on the same trend illustrate comparable H-bond efficiency of the geometrical approach and enable to assess frustration or enhancement of the H-bond by its environment (see details in text).