Chiral Monolayer-Protected Bimetallic Au–Ag Nanoclusters: Alloying Effect on Their Electronic Structure and Chiroptical Activity

Abstract

Chiral glutathione (GSH)-protected bimetallic Au–Ag nanoclusters (AuAg(SG)) are synthesized by the reduction of mixtures of Au and Ag salts at the feed mole ratio of Au/Ag = 3/1 in the presence of GSH and isolated by gel electrophoretic separation, yielding a family of magic-numbered bimetallic Au–Ag nanoclusters. The PAGE pattern similarity between Au(SG) and AuAg(SG) as well as the analyses based on small-angle X-ray scattering and X-ray photoelectron spectroscopy (XPS) allow comparisons of their chemical compositions for each family of nanoclusters, and the fractioned nanocluster compounds (three samples) are identified as Au12.2Ag2.8(SG)13, Au14.4Ag3.6(SG)14, and Au17.6Ag7.4(SG)18. The XPS study also suggests that (i) incorporation of Ag heteroatoms into smaller-sized Au nanoclusters is less favorable and (ii) Ag heteroatoms preferentially occupy sites on the cluster’s core (including the core-surface and center) rather than the peripheral semiring shell. Optical spectroscopy shows that the electronic...