Fig. 3

Schematic for proposed Cu(II) azurin–Ag ENM reaction mechanism. a Cu(II) azurin (blue protein with Cu(II) shown as blue sphere in active site) and Ag ENM (large grey sphere) bind to form a complex. b Redox reaction oxidizes Ag ENM surface to form Ag(I) (black sphere) and reduces Cu(II) azurin to Cu(I) azurin (light grey protein with Cu(I) azurin shown with a light grey sphere in active site). Weakly bound Cu(I) is displaced from the active site via one of two mechanisms, either via c direct displacement to form Ag(I) azurin and dissolved Cu(I)(aq) or via d two dissolution equilibria to form apo-azurin with dissolved Cu(I)(aq) and Ag ENMs with dissolved Ag(I)(aq)