C−H⋅⋅⋅O Hydrogen Bond Mediated Chain Reversal in a Peptide Containing a γ-Amino Acid Residue, Determined Directly from Powder X-ray Diffraction Data

Similar to the classical β turn: An intramolecular cyclic 10-atom motif is defined in the molecular conformation of Piv-lPro-γ-Abu-NHMe (see powder X-ray diffraction structure; Piv: pivaloyl, Lpro: L-proline, γ-Abu: γ-aminobutyric acid) by a C−H⋅⋅⋅O interaction. This study emphasizes the considerable potential of powder X-ray diffraction as an alternative to single-crystal X-ray diffraction.