Functionalizing au25 nanoclusters with crown ether ligands for the detection of dissolved heavy metals

Gold nanoclusters are an intermediate form between molecular and bulk gold. In some respects, they retain a physical appearance to gold nanoparticles but possess molecular-like properties unique to them. One notable example is the highly stable and symmetrical Au25(SCH2CH2Ph)18 (Au25) nanocluster, which has captivated many owing to its rich electronics and optical properties. Like their nanoparticle counterparts, gold nanoclusters are capable of undergoing surface modifications by ligand exchange. Here, we attempt to tailor Au25 through ligand exchange with crown ether ligands for the detection of bismuth(III), cadmium(II), lead(II), mercury(II), and thallium(III) by ion recognition methods. Crown ethers are well known for their chelating properties, in some cases generating “sandwich” complexes with appropriate ions. Here we attempt to exploit this property on the crown ether functionalized nanoclusters to induce aggregations, detectable by UV-Vis. Instead, we report the unusual outcomes of the ligand exchange reactions and unexpected reactions between the Au25 clusters and the active metal ions. In addition to these studies, we explore diffusion-ordered 1H-NMR spectroscopy (DOSY) as an alternative to transmission electron microscopy (TEM), an important technique used for determining particle diameter. DOSY addresses some of the limitations of TEM while providing equally, if not more, precise measurements.