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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.