Surface Functionalization and DNA-Mediated Colloidal Crystal Engineering of Metal-Organic Framework Nanoparticles


Metal-organic frameworks (MOFs) are a class of highly modular materials with welldefined three-dimensional architectures, permanent porosity, and diverse chemical functionalities, which show promise for a wide range of applications, including gas storage and separation, drug delivery, chemical sensing, and catalysis. Nanoparticle forms of MOFs have similar properties but are dispersible in solution, and therefore could serve as useful components in biological probes, membrane separation materials, and building blocks for colloidal crystal engineering. In this dissertation, we present a series of fundamental studies centered on the synthesis and surface functionalization of MOF nanoparticles (MOF NPs), with an emphasis on the realization of uniform NP size and phase, surface functionalization of MOF NPs with DNA, and the incorporation of MOF NPs as a new class of building blocks for colloidal crystal engineering strategies. The first chapter provides a history and introduction to the study of MOF NPs, with an emphasis on how such structures form and grow, and ways to address their external surface architectures with organic ligands. Chapter two describes two chemical approaches that we developed to control the size, shape, and phase uniformity of MOF NPs. The critical role of a series of chemical modulators in the crystallization process of MOF NPs is evaluated. These 3 modulators significantly influence the resulting MOF NP polydispersity and colloidal stability. Next, we introduce a straightforward electrostatic based purification strategy to separate mixedphase MOF NPs, which allows one to access pure phase MOF NPs for further investigations. In chapter three, we discuss a post-synthetic surface functionalization strategy that selectively modifies the external surface of MOF NPs with phosphate-terminated lipids. Strong coordination between coordinatively unsaturated metal sites and phosphate surface ligands promotes efficient surface modification under mild conditions with retained internal porosity. The fourth chapter describes the first general and direct method to interface MOF NPs with DNA employing terminal phosphate modified oligonucleotides appended to nine archetypical MOFs at high surface coverage. Design rules emerge from this study that predict the surface DNA coverage as a function of MOF surface metal node density, metal cluster connectivity, and metal-phosphate bond strength. Further, we show that nucleic acid-MOF NP conjugates are promising for the intracellular delivery of functional proteins. Taking advantage of the unique programmability of DNA surface ligands, we describe in chapter five the realization of hierarchical colloidal crystal engineering incorporating DNA functionalized MOF NPs as a novel class of building blocks. Finally, chapter six summarizes these data and their impact, and puts them in context regarding future opportunities. Descriptions of the materials and methods used to synthesize these materials are included at the end of each chapter.

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