title: An asymmetric conformation of 1,3,5-benzene tricarbonyl [Aib4OMe]3.
abstract: Molecules of 1,3,5-benzene tricarbonyl [Aib(4)OMe](3) do not possess any internal symmetry, neither exact nor approximate, in the crystalline state. The Aib(4)OMe moieties each form a 3(10)-helix with an appropriate pair of hydrogen bonds but the sense of rotation is right-handed for two of the helices and left-handed for the third one. The helices are not evenly positioned around the benzene ring, and their helix axes are inclined toward one side of the plane of the benzene ring, giving the molecule the shape of a shallow bowl with an irregular periphery. The molecules are largely surrounded by water and dimethyl sulfoxide (DMSO) solvent molecules that form hydrogen bonds with the CO and NH moieties that protrude from the surfaces of the peptide molecule. The space group is Cc with a = 23.618(4) A, b = 19.708(6) A, c = 17.939(7) A and beta = 100.09(3) degrees.
authors.affiliation: Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC 20375-5341, USA. williams@harker.nrl.navy.mil
authors.forename: I L
authors.initials: IL
authors.lastname: Karle
authors.forename: D
authors.initials: D
authors.lastname: Ranganathan
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*
chemical_list: C502274:1,3,5-benzene tricarbonyl ((aminoisobutyryl)(4)methyl ester)(3); D010455:Peptides