Formation of alkanethiolate-protected gold clusters with unprecedented core sizes in the thiolation of polymer-stabilized gold clusters

Octadecanethiolate-protected gold (Au:SC₁₈) clusters were prepared by the reaction of C₁₈SH and Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) (PVP). Four samples were fractionated by recycling size exclusion chromatography of the as-prepared Au:SC₁₈ clusters, and their core sizes were determined to be 8, 11, 21, and 26 kDa by using laser desorption ionization mass spectrometry. Unexpectedly, the sequence of these core sizes is different from that (8, 14, 22, and 29 kDa) obtained by conventional reduction of Au(I)-SC₁₈ polymers, which is governed by kinetic factors. The present finding shows that the Au:SR (R = organic group) clusters with a high tolerance to thiol etching can be systematically synthesized by first populating precursory Au clusters in a PVP matrix with subsequent thiolation of the preformed Au clusters.