Figure 1
Polypeptide backbone and possible rotations. (a) Rotation around the peptide C-N bond is not possible because of the mesomeric equilibrium between two resonance structures. (b) As a consequence the dihedral angle [omega] may assume two values, yielding two conformations: cis ([omega] = 0°) and trans ([omega] = 180°). (c) The rotation around the N-C[alpha] bond can be monitored by the dihedral angle Ci-1-N-C[alpha]-C, which is named [varphi], while the rotation around the C[alpha]-C bond can be measured by the dihedral angle N-C[alpha]-C-Ni+1, which is termed [psi].  [article HTML]

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