title: N-Methyl peptides. IV. Water and beta-turn in peptides. Crystal structure of N-pivaloyl-L-prolyl-N,N'-dimethyl-D-alaninamide in the anhydrous and monohydrated states.
abstract: The model tripeptide tBuCO-L-Pro-Me-D-Ala-MHMe crystallizes in both anhydrous (1) and monohydrated (2) states: 1, monoclinic space group C2 with a = 20.030 (2) A, b = 5.836 (2) A, c = 14.958 (3) A and beta = 94.11 (1) degrees; 2, orthorhombic space group P212121 with a = 6.971 (6) A, b = 11.766 (3) A, and c = 22.394 (8) A. Both crystal structures were solved by X-ray diffraction in order to characterize the influence of water on the molecular structure. The anhydrous molecule accommodates the well-known, beta II-folded conformation with three trans amide functions and an intramolecular i + 3 leads to hydrogen bond. In the hydrated molecule, water is inserted in a loop containing 12 atoms and induces some conformational changes of the peptide backbone.
mesh_terms: D004151:Dipeptides / Q000138:chemical synthesis; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D011487:Protein Conformation; D014867:Water; D014961:X-Ray Diffraction
chemical_list: D004151:Dipeptides; D014867:Water; C033090:N-pivaloylprolyl-N,N'-dimethylalaninamide