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

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journal contribution
posted on 20.02.2016, 15:06 by Stefan Knoppe, Igor Dolamic, Thomas Bürgi
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.