Magic-numbered Au(n) clusters protected by glutathione monolayers (n = 18, 21, 25, 28, 32, 39): isolation and spectroscopic characterization.

Small gold clusters (<1 nm) protected by a glutathione (GSH) monolayer were fractionated into six components by polyacrylamide gel electrophoresis, and their chemical compositions were investigated by electrospray ionization mass spectroscopy. The results demonstrate isolation of a series of magic-numbered gold clusters, Au18(SG)11, Au21(SG)12, Au25+/-1(SG)14+/-1, Au28(SG)16, Au32(SG)18, and Au39(SG)23. Their optical absorption spectra are highly structured with clear absorption onsets, which shift toward higher energies with reduction of the core size. These molecular-like gold clusters exhibit visible photoluminescence. The results reported herein provide helpful guidelines or starting points for further experimental and theoretical studies on structures, stabilities, and optical properties of monolayer-protected gold clusters.