Giant Gold−Glutathione Cluster Compounds: Intense Optical Activity in Metal-Based Transitions

A series of giant metal-cluster compounds, each composed of a gold core and a glutathione (GSH) adsorbate layer, have been prepared from Au(I)SG polymers and separated by gel electrophoresis, using methods reported in a recent Letter [J. Phys. Chem. B 1998, 102, 10643−6]. Identification of the separated compounds by core mass is accomplished through laser desorption mass spectrometry of matrix-diluted films. Three principal compounds have core masses of ca. 4.3, 5.6, and 8.2 kDa (in the range of ∼20−40 Au atoms), and show structured optical absorption spectra with clear optical absorption onsets near 1.7, 1.3, and 1.0 eV, respectively. Each of these shows unusually strong chiroptical activity in the metal-based electronic transitions across the near-infrared, visible, and near-ultraviolet regions, whereas neither the crude (unseparated) mixture nor its higher molecular weight components possess such strong optical activity. The location and strength of the optical activity suggest a metal electronic struc...