Small thiol protected gold nanoparticles (< 2nm), also known as gold cluster, are self-assembled systems formed by Au(0) core and a thiol protecting monolayer. The latter is fundamental not only for stabilization and solubility of the clusters themselves, but also is the principal responsible for their reactivity.[1] One of the most frequent reactions used to functionalized the monolayer are the thiol-exchange reactions.[2]. These reactions usually present difficulties in controlling the number of substitutions and the reaction time can vary from minutes to days. In this study we investigated the thiol-exchange reaction using nuclear magnetic resonance (NMR) spectroscopy and MALDI analysis.[3] Kinetic studies were performed on Au₂₅(SC₂H₄Ph)₁₈ exchange with butane thiol and vice versa (Au₂₅(SButane)₁₈ exchange with HSC₂H₄Ph, Figure 1). By these studies, were possible to understand: 1) the affinity of different thiol ligands towards the Au₂₅ cluster, 2) calculating the number of thiols exchange, 3) the position of exchange and 4) obtaining the relative binding constants. From this information was possible to gain a clearer picture on the mechanism of this reaction that can help in fine-tuning the functionality of the monolayer.

[1] H. Häkkinen, Nat. Chem., 2012, 4, 443–55.
[2] T. Ni, M. Tofanelli, B. Philips, C. J. Ackerson, Inorg. Chem., 2014, 53, 6500–6502.
[3] P. Pengo, C. Bazzo, M. Boccalon, L. Pasquato, Chem. Commun., 2015, 51, 3204–3207.