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Just as peptide function is determined by the position, sequence, and overall arrangement of constituent amino acids, the optical properties of nanoparticle (NP) assemblies are influenced by the size, dimensions, and arrangement of constituent NPs. In this work, we demonstrate that peptide sequence can be programmed to direct the structure and chiroptical activity of chiral helical gold NP (AuNP)superstructures, a growing class of chiral nanomaterials with potential in sensing, detection, and optics-based applications. Gold-binding peptide conjugate families, C 18 -(PEP Au M, x ) 2 and C 18 -(PEP Au M-ox, x ) 2 , that differ in the position ( x = 7, 9, and 11) of methionine (M)/methionine sulfoxide (M-ox) within the peptide sequences (PEP Au = AYSSGAPPMPPF/PEP Au M-ox = AYSSGAPPM ox PPF) are employed to control the aspect ratio and size of AuNPs within helical NP assemblies. Computational modeling reveals that the amino acid variations have a profound effect on peptide-AuNP interactions that ultimately lead to control over NP size. C 18 -(PEP Au M, x ) 2 ( x = 7, 9, and 11) yield irregular double-helical superstructures comprising spherical AuNPs, while C 18 -(PEP Au M-ox, x ) 2 ( x = 9, 11) yield single-helical assemblies comprising oblong or rod-shaped AuNPs. Further, component AuNPs are larger when M/M-ox is placed at x = 11, while smaller component AuNPs are observed when M/M-ox is placed at x = 7. Changes in nanoscale structures manifest themselves in observable differences in chiroptical signal intensity. Ultimately, we achieve dramatic variance in the structure and properties of chiral AuNP superstructures via simple molecular-level tuning of peptide primary sequence.

Atomically precise metal nanoclusters with tailored surface structures are important for both fundamental studies and practical applications. The development of new methods for tailoring the surface structure in a controllable manner has long been sought. In this work, we report surface reconstruction induced by cadmium doping into the [Au 23 (SR) 16 ] - (R = cyclohexyl) nanocluster, in which two neighboring surface Au atomic sites "coalesce" into one Cd atomic site and, accordingly, a new bimetal nanocluster, [Au 19 Cd 2 (SR) 16 ] - , is produced. Interestingly, a Cd(S-Au-S) 3 "paw-like" surface motif is observed for the first time in nanocluster structures. In such a motif, the Cd atom acts as a junction which connects three monomeric -S-Au-S- motifs. Density functional theory calculations are performed to understand the two unique Cd locations. Furthermore, we demonstrate different doping modes when the [Au 23 (SR) 16 ] - nanocluster is doped with different metals (Cu, Ag), including (i) simple substitution and (ii) total structure transformation, as opposed to surface reconstruction for Cd doping. This work greatly expands doping chemistry for tailoring the structures of nanoclusters and is expected to open new avenues for designing nanoclusters with novel surface structures using different dopants.

Systematically controlling the assembly architecture within a class of chiral nanoparticle superstructures is important for fine-tuning their chiroptical properties. Here, we report a family of chiral gold nanoparticle single helices, varying in helical pitch and nanoparticle dimensions, that is assembled using a series of peptide conjugate molecules C x -(PEP Au M-ox ) 2 (PEP Au M-ox = AYSSGAPPM ox PPF; x = 16-22). We demonstrate that the aliphatic tail length (i) can be used as a handle to systematically tune the helical pitch from 80 to 130 nm; and (ii) influences the size, shape, and aspect ratio of the component nanoparticles. Certain members of this family of materials exhibit intense plasmonic chiroptical activity. These studies highlight the multiple levels of structural control that can be achieved within a class of chiral nanoparticle superstructures via careful design and selection of peptide conjugate precursor.

Chiral nanoparticle assemblies are an interesting class of materials whose chiroptical properties make them attractive for a variety of applications. Here, C 18 -(PEP Au M-ox ) 2 (PEP Au M-ox = AYSSGAPPM ox PPF) 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 C 18 -(PEP Au M-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 C 18 -(PEP Au M-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.