Master of Science
Workentin, Mark S.
Thiolate-protected Au144 nanoclusters (NCs) are an intriguing member of the gold NC family. Their geometric structure, distinct electrochemical features, and susceptibility to structural rearrangement under the duress of ligand exchange have been studied. However, there are currently no established protocols for surface modification or tuning of their ligand shells post synthesis. Here, the direct synthesis of three regioisomers of azide-modified Au144 NCs with 60 azide moieties, i.e., Au144(SC2H4C6H4-N3)60, is reported, in which the azide functionality is located at the ortho-, meta-, or para position of the ligand’s phenyl ring. The regioisomeric effect of the azide group on Au144(SC2H4C6H4-N3)60 synthesis and physical properties are described. A proof-of-concept cluster surface strain promoted alkyne-azide cycloaddition (CS-SPAAC) reaction is also demonstrated, revealing all 60 azides can be accessible in the para derivative. The CS-SPAAC chemistry was further extended to append a functional TEMPO group, which can be utilized towards an alcohol electro-oxidation application.
Summary for Lay Audience
At the macro scale, bulk gold is known to be an excellent material for making lustrous jewelry and coinage. However, at the nanoscale, a scale too small for the naked eye to perceive, gold materials acquire new size and structure-dependent properties that suit various technological and medical applications. Among these ultrasmall materials are gold (Au) nanoclusters (NCs), a class of nano-sized compounds. Au NCs have a core-shell configuration that can be tuned to target different optical or chemical properties. Their cores contain a geometric framework of a precise number of Au atoms, and the shell is made up of ligands (organic small molecules). Existing knowledge of tunable NC features focuses mainly on their gold cores. However, it has recently been demonstrated that NC ligand shells can be modified following NC synthesis via “click chemistry”; a means of connecting molecules together using rapid, high-yielding and highly selective reactions. By incorporating a robust functional group amenable to click chemistry into the ligand structure of NCs, i.e. an azide (N3) group, new molecules can be tethered to the surface of NCs following their synthesis. This thesis focuses on the development of a NC containing 144 gold atoms in its core and 60 azide-containing ligands in its shell. The 60 ligands are each capable of undergoing a click reaction, specifically the cluster surface strain-promoted alkyne-azide cycloaddition (CS-SPAAC) reaction, to attach new functionality to the NC at 60 different sites within its ligand shell. This azide-functionalized Au144 NC can be used as a template to introduce new properties to NCs and therefore expand the scope of their applications.
de Jong, Johanna A., "Expanding the Scope of Clickable Azide-Functionalized Nanoclusters to include Au144" (2022). Electronic Thesis and Dissertation Repository. 9008.