Influence of the Spatial Conformation of Charged Ligands on the Optical Properties of Gold Nanoclusters

Photoluminescent gold nanoclusters (Au NCs) were synthesized in one step in aqueous conditions using a mixture of glutathione and (mono or multivalent) glutathione-modified arginine peptides. By controlling the ratio of coligands, we investigated how the multivalency and the amount of arginines influenced the growth of Au NCs, their surface chemistry, their colloidal stability, and their optical properties. We demonstrated using two-dimensional nuclear magnetic resonance spectroscopy that the organization of the ligand on the Au surface was composed by an inner rigid layer and an outer flexible part via inter- and/or intraligand spatial proximity. This directly impacted the structure of the Au NCs, as confirmed by gel electrophoresis, high-resolution transmission electron microscopy, diffusion-ordered spectroscopy, and mass spectrometry. Increasing arginine content also induced an increase of positive surface charge and an enhancement of the near infrared emission intensity at ∼670 nm with quantum yield up to 10% validating the significant influence of the ligands to the optical properties of Au NCs.