The Interaction of Amines with Gold Nanoparticles.

Understanding the interactions between amines and the surface of gold nanoparticles is important because of their role in the stabilization of the nanosystems, in the formation of the protein corona and preparation of semisynthetic nanozymes. By using fluorescence spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and molecular simulation we obtained a detailed picture of these interactions. We show for the first time that amines interact with surface Au(0) atoms of the nanoparticles with their lone electron pair with a strength linearly correlating with their basicity corrected for steric hindrance. The kinetic of binding depends on the position of the gold atoms (flat surfaces or edges) while the mode of binding involves a single Au(0) with nitrogen sitting on top of it. We also found that the presence of a small fraction of surface Au(I) atoms, resulting from the non-complete reduction of gold salts when citrate is used as the reducing agent in the nanoparticle preparation, is reduced by the amines yielding a much stronger Au(0)-RN .+ (RN . , after the loss of a proton) interaction. DFT calculations reveal that, in this case, the mode of binding involves two Au(0) atoms with a bridging nitrogen placed between them. The strength of the interaction of the amines with gold nanoparticles may be quite different depending on whether they have been used for the reduction of the gold salt or were introduced after the reduction had occurred. The implications for the passivation of the nanoparticles and their interaction with the amino groups of proteins are significant. Stable Au nanoparticles, as those required for robust semisynthetic nanozymes preparation, are better obtained when the protein is involved (at least in part) in the gold ions reduction. This article is protected by copyright. All rights reserved.