Understanding synthetic route impact on NHCAuNP stability

Gold nanoparticles are a very promising nanomaterial which currently finds applications in sensing, optoelectronics, photonics, catalysis, and even photothermal cancer therapy. However, gold nanoparticles are typically not stable on their own but rely on a protective layer (typically organic surfactants) to stabilize them in solution. Further, to impart functionality for e.g. sensing or catalysis, surface modifications need to be performed. Current technology relies on a sulfur-gold bond to bind active moieties onto the gold nanoparticle surface. Though these interactions are strong, it is not complete inert and nanoparticles can decompose in a complex matrix. Recent advancements address this issue by replacing the sulfur gold bond with a much more stable carbene-gold interaction. Although these novel gold nanoparticles show great promise with regards to thermal and chemical stability, recent reports suggest that the stability of gold nanoparticles not only depends on the inertness of the gold linker strength, but also that the way the nanoparticles are synthesized play a crucial role. We recently showed that N-heterocyclic carbene stabilized gold nanoparticles contain both elemental and gold ions, which might have implications for the stability of the nanoparticles. In this project we therefore aim to investigate in detail the synthetic route impact on the exact composition of such gold nanoparticles. To do so, a series of molecular N-heterocyclic carbene gold complexes will be synthesized and utilized for gold nanoparticles synthesis (bottom up synthesis). At the same time, surface ligand exchange reactions (top down synthesis) will be conducted and the composition of both gold nanoparticles will be characterized in detail. Further, reactivity studies will give an insight into differences between bottom up and top down synthesis. By comparing bottom up vs. top down synthesis approaches we expect to gain significant insight into the gold nanoparticle composition and reactivity. The second part of this project aims to utlize the gained knowledge of gold nanoparticle composition for the development of nanocatalysts. Although N-heterocyclic carbenes are a versatile ligand for molecular catalysis, there are only a few examples utilizing N- heterocyclic carbenes stabilized gold nanoparticles for catalysis. Through mechanistic investigations and through the proposed reactivity studies, this project will pave they way for the rational design of nanocatalysts. To summarize, this project should lead to a detailed understanding of N-heterocyclic carbene stabilized gold nanoparticle formation and stability. Furthermore, rationally designed nanocatalysts will pave the way for novel catalytic processes.