Chiral 38-gold-atom nanoclusters: synthesis and chiroptical properties.

Enantioselective synthesis of chiral Au-38 nanoclusters is achieved with chiral 2-phenylpropane-1-thiol (abbreviated as R/S-PET, organic soluble), captopril and glutathione (water soluble) as the respective ligand. The circular dichroism (CD) spectra of Au-38(R-PET)(24) and Au-38(S-PET)(24) show multiple bands which are precisely mirror-imaged, while their normal optical absorption spectra are identical with each other and also superimposable with that of the racemic Au-38(SCH2CH2Ph)(24) nanoclusters. The observed CD signals are not from the chiral ligands themselves (which only give rise to CD signals in the UV (<250 nm), rather than in the visible wavelength region). Chiral Au-38 nanoclusters with different types of ligands are further compared. Although the Au-38 core is intrinsically chiral, different chiral ligands are found to largely influence the chiroptical response of the overall nanocluster. Thus, the chiral response of ligand-protected nanoclusters has both contributions from the metal core and the ligand shell around it. These optically active nanoclusters hold promise in future applications such as chiral sensing and catalysis.