10.1021/ja800355p.s007 Soo Hyuk Choi Soo Hyuk Choi Ilia A. Guzei Ilia A. Guzei Lara C. Spencer Lara C. Spencer Samuel H. Gellman Samuel H. Gellman Crystallographic Characterization of Helical Secondary Structures in α/β-Peptides with 1:1 Residue Alternation American Chemical Society 2008 helix residue NMR data 14 crystal structures backbone amide groups ACPC peptide hydrogen bonds 2008-05-21 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Crystallographic_Characterization_of_Helical_Secondary_Structures_in_Peptides_with_1_1_Residue_Alternation/2937889 Oligomers that contain both α- and β-amino acid residues in a 1:1 alternating pattern have recently been shown by several groups to adopt helical secondary structures in solution. The β-residue substitution pattern has a profound effect on the type of helix formed and the stability of the helical conformation. On the basis of two-dimensional NMR data, we have previously proposed that β-residues with a five-membered ring constraint promote two different types of α/β-peptide helix. The “11-helix” contains <i>i</i>,<i>i</i>+3 CO···H−N hydrogen bonds between backbone amide groups; these hydrogen bonds occur in 11-atom rings. The α/β-peptide “14/15-helix” contains <i>i</i>,<i>i</i>+4 CO···H−N hydrogen bonds, which occur in alternating 14- and 15-atom rings. Here we provide crystallographic data for 14 α/β-peptides that form the 11-helix and/or the 14/15-helix. These results were obtained for a series of oligomers containing β-residues derived from (<i>S,S</i>)-<i>trans</i>-2-aminocyclopentanecarboxylic acid (ACPC) and α-residues derived from α-aminoisobutyric acid (Aib) or l-alanine (Ala). The crystallized α/β-peptides range in length from 4 to 10 residues. Nine of the α/β-peptides display the 11-helix in the solid state, three display the 14/15-helix, and two display conformations that contain both <i>i</i>,<i>i</i>+3 and <i>i</i>,<i>i</i>+4 CO···H−N hydrogen bonds, but not bifurcated hydrogen bonds. Only 3 of the 14 crystal structures presented here have been previously described. These results suggest that longer α/β-peptides prefer the 14/15-helix over the 11-helix, a conclusion that is consistent with previously reported NMR data obtained in solution.