Characterization of nanofibers formed by self-assembly of β -peptide oligomers using small angle x-ray scattering

• Published in: The Journal of chemical physics 2008-09, Vol.129 (9), p.095103-095103-8
• Main Authors: Pizzey, Claire L., Pomerantz, William C., Sung, Bong-June, Yuwono, Virany M., Gellman, Samuel H., Hartgerink, Jeffery D., Yethiraj, Arun, Abbott, Nicholas L.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Microscopy, Electron, Transmission; Molecular Conformation; Nanostructures - chemistry; Oligopeptides - chemical synthesis; Oligopeptides - chemistry; Particle Size; Scattering, Small Angle; X-Ray Diffraction
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2955745

Helical oligomers of β -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 β -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 β -peptide A with sequence H 2 N - β 3 hTyr - β 3 hLys - β 3 hPhe - ACHC - β 3 hPhe - ACHC - β 3 hPhe - β 3 hLys - ACHC - ACHC - β 3 hPhe - β 3 hLys - C O N H 2 . Whereas prior cryo-TEM studies have revealed the presence of nanofibers in aqueous solutions of β -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 β -peptides assemble to form long cylindrical nanofibers with a hollow core radius of 15 Å (polydispersity of 21%) and a shell thickness of 20 Å . This model is supported by negative stain transmission electron microscopy.