Oxygen'S Role In Aqueous Gold Cluster Synthesis

The presence of oxygen in thiolate-protected gold nanoparticle synthesis influences product distribution. Oxygen's diradical nature underlies this effect, and oxygen can be replaced with radical initiators in the synthesis of organosoluble gold nanoclusters. The role of O-2 in the synthesis of water-soluble clusters such as Au-102(p-MBA)(44), Au-25(SR)(18), as well as the thiol etching of water-soluble colloidal gold particles is not yet established. Herein it is shown that radicals, either from O-2 or from radical initiators such as 4-hydroxy-TEMPO, are necessary components for synthesis of water-soluble thiolate-protected gold nanoclusters, as well as the etching of aqueous colloidal gold by thiols. Furthermore, air-free synthetic routes to watersoluble gold nanoclusters Au-102(SR)(44) and Au-25(SR)(18) are described. Overall, the understanding of the role of radicals in the synthesis of water-soluble gold clusters will allow standardization of often difficult to reproduce syntheses that attract increasing attention for biological applications.