title: Crystallographic characterization of geometry and conformation of TOAC, a nitroxide spin-labelled C alpha,alpha-disubstituted glycine, in simple derivatives and model peptides.
abstract: The molecular and crystal structures of one derivative and two oligopeptides of TOAC, a nitroxide spin-labelled C alpha, alpha-disubstituted glycine, have been determined by X-ray diffraction. The derivative is the 5(4H)-oxazolone from Piv-TOAC-OH; the oligopeptides are Z-TOAC-(L-Ala)2-NHtBu sesquihydrate and pBrBz-TOAC-(L-Ala)2-TOAC-L-Ala-NHtBu hemihydrate. Incipient and fully developed right-handed 3(10)-helical conformations are formed by both independent molecules in the asymmetric unit of the terminally blocked tripeptide amide and the terminally blocked pentapeptide amide, respectively. The average geometry and preferred conformation for the piperidine ring of the TOAC residues are also discussed in detail.
authors: Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC, USA.
authors: J L
authors: JL
authors: Flippen-Anderson
authors: C
authors: C
authors: George
authors: G
authors: G
authors: Valle
authors: E
authors: E
authors: Valente
authors: A
authors: A
authors: Bianco
authors: F
authors: F
authors: Formaggio
authors: M
authors: M
authors: Crisma
authors: C
authors: C
authors: Toniolo
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D013113:Spin Labels; D014961:X-Ray Diffraction
chemical_list: D003497:Cyclic N-Oxides; D013113:Spin Labels; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid