Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology

A comparative study of structural, electronic, and optical properties of thiolated gold clusters with icosahedral vs face-centered cubic cores

The structural, electronic, and optical properties of the protected Au clusters with icosahedral (Ih) and face-centered cubic (FCC)-like Au₁₃ cores were studied to understand the origin of the difference in the optical gaps of these clusters. It has been demonstrated that the choice of density functionals does not qualitatively affect the properties of Au₂₃ and Au₂₅ clusters with Ih and FCC cores. The density of states, molecular orbitals, and natural charges were analyzed in detail using the B3LYP functional. The substantial energy difference in the lowest-energy absorption peaks for the clusters with the Ih and FCC cores is attributed to the difference in the natural charges of the central Au atoms (Au_c) in the Ih and FCC cores, the former of which is more negative than the latter. Natural population analysis demonstrates that the excess negative charge of the Au_c atom in clusters with Ih cores occupies the 6p atomic orbitals. This difference in Au_c is attributed to the smaller size of the Ih core compared to the FCC core, as a less bulky ligand allows a smaller core with increased electron density, which, in turn, increases the highest occupied molecular orbital energy and decreases the optical gap.

Gold nanoparticles stabilized with sulphonated imidazolium salts in water and reverse micelles

Herein we describe the synthesis of gold nanoparticles (Au-NPs) in presence of sulphonated imidazolium salts [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazolium (L1), 1-mesityl-3-(3-sulfonatopropyl)imidazolium (L2) and 1-(3-sulfonatopropyl)imidazolium (L3)] in water and in a confinement environment created by reverse micelles (RMs). The Au-NPs were characterized-with an excellent agreement between different techniques-by UV-vis spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential. In homogeneous media, the Au-NPs interact with the imidazolium ring and the sulphonate groups were directed away from the NPs' surface. This fact is responsible for the Au-NPs' stability-over three months-in water. Based on the obtained zeta potential values we assume the degree of coverage of the Au-NPs by the imidazolium salts. In n-heptane/sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT)/water RMs, the Au-NPs formed in presence of sulphonated imidazolium salts present different patterns depending on the ligand used as stabilizer. Interestingly, the Au-NPs are more stable in time when the salts are present in AOT RMs (three weeks) in comparison with the same RMs system but in absence of ligands (less than an hour). Clearly, the sulphonated imidazolium salts are very effective Au-NPs stabilizers in a different medium and this generates a plus to be able to use them for multiple purposes.