Glutathione capped gold AuN(SG)M clusters studied by isotope-resolved mass spectrometry

In this manuscript, we report the synthesis and mass spectrometry study of small gold liganded clusters ranging from Au4(SG)4 to Au25(SG)18 (SG = glutathione peptide). Collision induced dissociation pathways of liganded clusters involve formation of Au4(SG)4 cluster ion products and, successive losses of pyroglutamic acid coming from a cleavage and reorganization of the glutamic acid side chain. We used isotope-resolved mass spectrometry to determine the charge state of the clusters and eventually the number of electrons in the core. Au15(SG)13 is the first size for which electron count and fragmentation spectra suggest the formation of a gold core. A geometry built around a trimeric gold core with Au4(SG)4 staple as the nanoparticle's protecting structure is proposed. Clusters with sizes superior to Au22(SG)17 are negatively charged showing that, in this case, the gold core is sufficiently large to accommodate one excess electron.

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► We synthesized small gold liganded clusters.
► We recorded isotope-resolved mass spectra of the clusters.
► The charge state of the gold core was determined.
► Collision induced dissociation pathways of liganded clusters was determined.
► A possible structure for Au15(SG)13 is given.