title: Characterization of nanofibers formed by self-assembly of beta-peptide oligomers using small angle x-ray scattering.
abstract: Helical oligomers of beta-peptides represent a particularly promising type of building block for directed assembly of organic nanostructures because the helical secondary structure can be designed to be very stable and because control of the beta-amino acid sequence can lead to precise patterning of chemical functional groups over the helix surfaces. In this paper, we report the use of small angle x-ray scattering measurements (SAXS) to characterize nanostructures formed by the directed assembly of beta-peptide A with sequence H(2)N-beta(3)hTyr-beta(3)hLys-beta(3)hPhe-ACHC-beta(3)hPhe-ACHC-beta(3)hPhe-beta(3)hLys-ACHC-ACHC-beta(3)hPhe-beta(3)hLys-CONH(2). Whereas prior cryo-TEM studies have revealed the presence of nanofibers in aqueous solutions of beta-peptide A, SAXS measurements from the nanofibers were not well-fit by a form factor model describing solid nanofibers. An improved fit to the scattering data at high q was obtained by using a form factor model describing a cylinder with a hollow center and radial polydispersity. When combined with a structure factor calculated from the polymer reference interaction site model (PRISM) theory, the scattered intensity of x-rays measured over the entire q range was well described by the model. Analysis of our SAXS data suggests a model in which individual beta-peptides assemble to form long cylindrical nanofibers with a hollow core radius of 15 A (polydispersity of 21%) and a shell thickness of 20 A. This model is supported by negative stain transmission electron microscopy.
authors.affiliation: Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706-1322, USA.
authors.forename: Claire L
authors.initials: CL
authors.lastname: Pizzey
authors.forename: William C
authors.initials: WC
authors.lastname: Pomerantz
authors.forename: Bong-June
authors.initials: BJ
authors.lastname: Sung
authors.forename: Virany M
authors.initials: VM
authors.lastname: Yuwono
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
authors.forename: Jeffery D
authors.initials: JD
authors.lastname: Hartgerink
authors.forename: Arun
authors.initials: A
authors.lastname: Yethiraj
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Abbott
mesh_terms: D000595:Amino Acid Sequence; D046529:Microscopy, Electron, Transmission; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry*; D010316:Particle Size; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D009842:Oligopeptides