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

Abstract

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