Figure 4
From: Chiral Sulfoxide-Induced Single Turn Peptide α-Helicity
Crystal structure of (R)-19B and calculated structures of (S)-15A, (R)-15B.
(a) X-ray crystal structure of (R)-19B with thermal ellipsoids shown at the 50% probability level with three α-helical hydrogen bonds. (b) Conformers of (R)-diastereomer 15B (R1, R2) and (S)-diastereomer 15A (S1, S2, S3, S4) with increased stability, calculated with density functional theory at PBE1PBE/6-31 + G** level. Relative free energies are given below each structure. (c) Conformations sampled in REMD simulations of (S)-19A and (R)-19B. The x-axis is the backbone RMSD of the conformations, with respect to the X-ray structure of (R)-19B. The y-axis is the radius of gyration of the conformations. The clusters are labelled as R1′(19B), R2′(19B) and S1′-S3′(19A), similar to structures R1(15B), R2(15B), and S1-S3(15A) in (b), see SI Fig. 8 for the structures of R1′(19B), R2′(19B) and S1′-S3′(19A).
