Figure 2.

Dihedral angles used to identify the conformations of the N-acetyl-N'-methylamide derivatives of trans-(^βPro)Arg and cis-(^βPro)Arg studied in this work. The (φ,ψ) dihedral angles are defined by the atoms in the backbone, whereas the side-chain dihedral angles χⁱ and ξⁱ are given by the pyrrolidine atoms and the exocyclic side-chain atoms, respectively. In particular, φ and χ⁰ are defined as C(O)–N–C^α–C(O) and C^δ–N–C^α–C^β, respectively. The dihedral angle ξ¹ is given by C^α–C^β–C(H₂)–C(H₂).