Racemization of a Chiral Nanoparticle Evidences the Flexibility of the Gold–Thiolate Interface

Thiolate-protected gold nanoparticles and clusters combine size-dependent physical properties with the ability to introduce (bio)­chemical functionality within their ligand shell. The engineering of the latter with molecular precision is an important prerequisite for future applications. A key question in this respect concerns the flexibility of the gold–sulfur interface. Here we report the first study on racemization of an intrinsically chiral gold nanocluster, Au₃₈(SCH₂CH₂Ph)₂₄, which goes along with a drastic rearrangement of its surface involving place exchange of several thiolates. This racemization takes place at modest temperatures (40–80 °C) without significant decomposition. The experimentally determined activation energy for the inversion reaction is ca. 28 kcal/mol, which is surprisingly low considering the large rearrangement. The activation parameters furthermore indicate that the process occurs without complete Au–S bond breaking

Facile Synthesis, Size-Separation, Characterization, and Antimicrobial Properties of Thiolated Copper Clusters

Metal nanomaterials have attracted extensive attention in biological labeling and imaging due to their controllable physical and chemical properties. Recently, a lot of effort has been devoted to preparing various ultrasmall and functional copper nanoclusters (CuNCs) with different emissions from blue to red, soluble both in organic and aqueous phases. Herein, a novel one-step synthetic method is proposed for the preparation of stable water-soluble glutathione-capped (GSH-capped) CuNCs. The resulting nanoclusters have a good dispersibility and stability in aqueous media. The stability was examined by several test experiments. The mass detection in ESI-HRMS mode allowed ionization of several doubly charged species with formula Cu₅L₆, Cu₆L₆, Cu₇L₆, Cu₈L₆, and Cu₉L₆ (L = C₁₀H₁₆N₃O₆S). The use of advanced separation techniques including liquid chromatography (HPLC), gel electrophoresis (PAGE), and capillary electrophoresis (CE) allowed the separation of several clusters, some of which are larger than Au₂₅(GS)₁₈, as shown by PAGE. To the best of our knowledge, this is the first report on successful size-separation of CuNCs. Moreover, the synthesized CuNCs show a dose-dependent antimicrobial effect. At lower cluster concentration the growth of bacteria is partially reduced. However, at higher concentrations, the bacterial growth is completely restricted