Design principles for cadmium chalcogenide nanoparticle assembly via peptoids

Abstract

Self-assembled organic nanomaterials can be generated by bottom-up assembly pathways where the structure is controlled by the organic sequence and altered using pH, temperature, and solvation. These nanomaterials have been used as scaffolds for assembly of inorganic materials but are limited to architectures accessible by the organic monomers. In contrast, self-assembled structures based on inorganic nanoparticles typically rely on physical packing and drying effects to achieve uniform superlattices. By combining these two chemistries to access inorganic-organic nanostructures, we aim to understand the key factors that govern the assembly pathway and structural outcomes in hybrid systems. This dissertation focuses on the assembly of peptidomimetic poly-N-substituted glycines, also known as peptoids. We explore the combination of peptoids with cadmium chalcogenide clusters and quantum dots (QDs) to generate hybrid materials. By creating a set of design principles for controlling the structure and structural evolution of hybrid peptoid-QD assemblies we are closer to the predictive synthesis of complex hybrid matter.Chapter 1 introduces the field of hybrid nanomaterials with a focus on peptoids and semiconducting nanoparticles. The properties, functions, and assembly of peptoids and nanoparticles are reviewed and the inherent challenges in coupling these two disparate building blocks are highlighted. Chapter 2 demonstrates the use of preformed peptoid nanostructures as scaffolds for CdSe nanoparticle assembly via an irreversibly formed covalent linkage. The structure of the resulting hybrid materials is explored using ex-situ transmission electron microscopy (TEM) and atomic force microscopy (AFM), and methods to control the density of nanoparticles on the peptoid surfaces are developed. Furthermore, we probe the chemistry underlying the covalent conjugation using 1H NMR spectroscopy. Chapter 3 describes a bottom-up approach to QD assembly with peptoids that relies on reversible peptoid monomer coordination to QD surfaces. The synthesis of hybrid QD/peptoid monomers is developed. The surface chemistry and size of the QD were demonstrated as viable handles to alter the hybrid monomer solubility in various solvents, ultimately resulting in rational access to different hybrid morphologies.