Figure 4: Two - dimensional scatter plot in φ - ψ space (θ = ± 60°) for intramolecularly hydrogen bonded β-residues determined in several peptide crystal structures. Specific intramolecular hydrogen bond types and the space for non - hydrogen bonded β3,3Ac6c residue are marked. The arrow indicates the position of the N- and C- terminus residues of the ββ C10 turn. Regions accommodating C12 and C14 helices (ββ) and C11 helices (αβ) are shaded..