"Blebbing" of a Gold Nanocluster by Dioxygen Insertion into Thiolate Staples during Self-Photooxidation

In our work with a Au thiolate nanocluster (Au₂₀(SG)₁₆, where SG is the tripeptide glutathione), we noticed that it underwent a self-photooxidation reaction in the presence of white light and oxygen. We now report on mechanistic studies using photophysical, photochemical, theoretical, and indirect trapping methods. We find rapid total quenching of singlet oxygen (¹O₂) by ground-state Au₂₀(SG)₁₆, with evidence of dioxygen insertion into the nanocluster. Supported by analyses with IR, ESI-MS, and density functional theory, we propose the formation of Au-O-O-SG bonds in the Au nanocluster. The expansion of the staple motif from dioxygen insertion is attributed to heightened lability and blebbing (a protrusion) arising from the O-O group. We then demonstrated that the self-photooxidized Au₂₀(SG)₁₆ undergoes oxygen-atom transfer to a phosphine trap in the dark.