Structural analysis of the foldecture derived from racemic peptide foldamers

The molecular packing structure of an elongated parallelogram plate shaped foldecture composed of a 1:1 racemic mixture of 11-helical peptide foldamers was resolved by powder X-ray diffraction (PXRD) analysis. A comprehensive Rietveld refinement procedure compensated for powder texture and identified the principal face of the foldecture. Each foldamer makes head-to-tail intermolecular hydrogen bonds, creating extended chains of single enantiomers that form a network of hydrophobic close contacts with foldamers of both the opposite and the same chiralities. An isosurface for anisotropic microstrain was calculated and found to be smallest along the x-axis, which is parallel to the network of intermolecular hydrogen bonds. Comparison with the single crystal structure found molecular packing motifs to be almost identical-a result infrequently observed in enantiopure foldectures. This is the first powder X-ray diffraction structural analysis of a foldecture composed of multiple components.