Characterization of nanofibers formed by self-assembly of beta-peptide oligomers using small angle x-ray scattering.
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.
Pizzey
Claire L
CL
Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706-1322, USA.
Pomerantz
William C
WC
Sung
Bong-June
BJ
Yuwono
Virany M
VM
Gellman
Samuel H
SH
Hartgerink
Jeffery D
JD
Yethiraj
Arun
A
Abbott
Nicholas L
NL
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
D009842:Oligopeptides