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Peptide-Directed Assembly of Single-Helical Gold Nanoparticle Superstructures Exhibiting Intense Chiroptical Activity
- Merg, Andrea
D., Boatz, Jennifer C., Mandal, Abhishek, Zhao, Gongpu, Mokashi-Punekar, Soumitra, Liu, Chong, Wang, Xianting, Zhang, Peijun, van der Wel, Patrick C. A., Rosi, Nathaniel L.
- Journal of the American Chemical Society 2016 v.138 no.41 pp. 13655-13663
- Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy, circular dichroism spectroscopy, models, nanogold, nanoparticles, nuclear magnetic resonance spectroscopy, tomography, transmission electron microscopy
- Chiral nanoparticle assemblies are an interesting class of materials whose chiroptical properties make them attractive for a variety of applications. Here, C₁₈-(PEPAᵤᴹ⁻ᵒˣ)₂ (PEPAᵤᴹ⁻ᵒˣ = AYSSGAPPMᵒˣPPF) is shown to direct the assembly of single-helical gold nanoparticle superstructures that exhibit exceptionally strong chiroptical activity at the plasmon frequency with absolute g-factor values up to 0.04. Transmission electron microscopy (TEM) and cryogenic electron tomography (cryo-ET) results indicate that the single helices have a periodic pitch of approximately 100 nm and consist of oblong gold nanoparticles. The morphology and assembled structure of C₁₈-(PEPAᵤᴹ⁻ᵒˣ)₂ are studied using TEM, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD) spectroscopy, X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. TEM and AFM reveal that C₁₈-(PEPAᵤᴹ⁻ᵒˣ)₂ assembles into linear amyloid-like 1D helical ribbons having structural parameters that correlate to those of the single-helical gold nanoparticle superstructures. FTIR, CD, XRD, and ssNMR indicate the presence of cross-β and polyproline II secondary structures. A molecular assembly model is presented that takes into account all experimental observations and that supports the single-helical nanoparticle assembly architecture. This model provides the basis for the design of future nanoparticle assemblies having programmable structures and properties.