小角X射线散射
纳米纤维
分散性
材料科学
散射
结晶学
结构因子
纳米结构
螺旋(腹足类)
化学
高分子化学
纳米技术
光学
物理
生物
生态学
蜗牛
作者
Claire Pizzey,William C. Pomerantz,Bong June Sung,Virany M. Yuwono,Samuel H. Gellman,Jeffery D. Hartgerink,Arun Yethiraj,Nicholas L. Abbott
摘要
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 H2N-β3hTyr-β3hLys-β3hPhe-ACHC-β3hPhe-ACHC-β3hPhe-β3hLys-ACHC-ACHC-β3hPhe-β3hLys-CONH2. 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 15Å (polydispersity of 21%) and a shell thickness of 20Å. This model is supported by negative stain transmission electron microscopy.
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