As the fields of chemistry, biology, materials science and physics converge upon one another the demands for new materials and technologies continue to run high. Nanotechnology continually emerges as a plausible area of research in which these demands can be met. Specifically, the role of magnetic nanoparticles in new sensors, biomedical, materials and separations technologies has seen extraordinary growth over the past 15 years.
With this growth has also emerged new expectations of the control necessary to form these advanced materials and the challenges faced with their syntheses. For magnetic nanoparticles these challenges exist in the realm of particle surface chemistry and functionalization. The field as a whole has given enormous attention to the shape, size and monodispersity of magnetic nanomaterials while leaving their surface functionality comparatively untouched. The following chapters seek to address the development of new general surface chemistries for monolayer protected nanoparticles while envisioning their eventual adaptation to magnetic nanoparticles.
In this regard, Au nanoparticles are used as a model system with which to develop general organic transformations on monolayer protected nanoparticles. Au nanoparticles are ideal for this purpose owing to the fact that a large volume of literature exists detailing the particles physical and reactive properties. In addition, unlike magnetic nanoparticles, NMR spectroscopy may be used to directly investigate products still bound to the nanoparticle surface. Two new surface chemistries for Au nanoparticles, 1,3-dipolar cycloaddition and Grignard reagent addition to Weinreb amides are introduced as general methods by which to append multiple functionalities to Au nanoparticles.
Chapter 2 describes uncatalyzed 1,3-dipolar cycloaddition as a mild general method by which to attach, electroactive, fluorescent, and solubilizing species to the surface of small (~ 2 nm) Au nanoparticles bearing mixed monolayers of decane thiol and 11-azido-ω-undecane thiol. A modest reaction of the azide terminated Au nanoparticles with functional small molecules bearing an alkyl ketone moiety is observed in dioxane after a 60 h period at room temperature. In addition detailed kinetic studies of the reaction are presented in chapter 3, establishing the kinetic trends of the cycloaddition on the surface of Au nanoparticles. These studies revealed an analogous rate of reaction on the particle surface as compared to free reactants in solution. Furthermore, the azide surface concentration was found to exert more control over the extent of reaction than the reactive termini's proximity to the thiol monolayer.
Addition of alkylmagnesium halides or Grignard reagents to Au nanoparticles bearing mixed monolayers of methyl and N-methoxy- N'-methyl amides (Weinreb amides) was investigated in chapter 4. The reaction was found to produce excellent surface yields on short time scales. Additionally, the effect of the organometallic species on the stability of the particles was assessed. Small organometallic nucleophiles were found to bypass the monolayer causing significant particle decomposition while bulkier nucleophiles caused no decomposition with respect to controls.
In chapter 5, trifluoroethyl ester chemistry for surface functionalization of Au and FePt nanoparticles is adopted for the synthesis of pH sensitive magnetic nanoparticles using fluorescein amine. A modification of the method of standard addition to quantitate the fluorescein amine surface concentration is presented. Initial studies suggest that the particle fluorophore conjugate quantum yield remained unchanged with respect to the small molecule and that the pH sensitivity is reversible over a biologically relevant pH range. Finally, future goals for these studies are suggested and placed in the context of broader impacts.