title: Water structure in [Phe4 Val6] antamanide X 12H2O crystallized from dioxane.
abstract: Crystals of [Phe4 Val6] antamanide (cyclic [ValProProPhePhe]2) grown from dioxane/H2O, with space group P21212 and cell parameters a = 15.099(4), b = 22.008(5) and c = 11.024(3) A, are almost identical to crystals grown from H2O/acetone, the structure of which was determined a number of years ago. Per peptide molecule there are the equivalent of 12 water molecules occupying 16 sites in both crystals; however, in the new investigation a number of water molecules present at one-half occupancy have been found in different positions than in the earlier analysis. The interpretation of the hydrogen bonding between peptide/water and between water/water is much more satisfactory. Pentagonal water assemblies are present in the solvent channel. There is a distinct indication of the occurrence of a bifurcated bond between two water molecules, as well as the presence of three-center hydrogen bonds joining three water molecules. This may be the first experimental example of a bifurcated bond between two water molecules.
mesh_terms: D003460:Crystallization; D004146:Dioxanes; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010456:Peptides, Cyclic; D011487:Protein Conformation; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D004146:Dioxanes; D010456:Peptides, Cyclic; C041313:antamanide, Phe(4)-Val(6)-; C025223:1,4-dioxane