While discrete nanoparticles (NPs) have interesting, unique properties at the atomic and macroscale, assembling those NPs into well-defined structures can lead to emergent collective properties. Harnessing fine-tuned control over these structures’ morphologies and therefore properties is key to fulfilling their potential in a variety of applications, from optoelectronic technology to sensing. Biological molecules, such as peptides, are frequently used to direct NP assembly because of their inherent programmability. Our previous work on peptide-based AuNP assembly has led to a variety of achiral and chiral superstructures. We use peptide conjugates (PCs) designed both assemble in aqueous media and bind to AuNPs. The PCs contain an aliphatic tail conjugated to at least one peptide sequence; within the peptide sequence (AYSSGAPPMPPF, referred to as PEPAu) there are two distinct regions: AYSSGA, which has a high propensity to form b-sheet secondary structures, and PPMPPF, which binds AuNPs. Small molecular changes in the PC can manifest in nanoscale structural changes. At the finest level, within a family of divalent PCs (Cx-(PEPAu)2, oxidation of the methionine residue to methionine sulfoxide results in the transition from roughly double-helical one-dimensional superstructures to pristine AuNP single helices with a strong chiroptical signal. In order to understand this phenomenon in which a single atomic addition leads to dramatic morphological change in the product nanoparticle superstructure, we aimed to test the hypothesis that the polarity of the 9th amino acid influences peptide assembly and the helical morphology of the resultant NP superstructure. We therefore synthesized a family of divalent PCs with mixed oxidation states and varying dipole moment at the 9th position and examined how these modifications affected peptide assembly and superstructure morphology.

Atomic and molecular level control over nanoscale structure of helical nanoparticle assemblies

ACS Fall 2021

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