Surface modification of adamantane-terminated gold nanoclusters using cyclodextrins

Abstract

The surface functionality of Au₃₈S₂(SAdm)₂₀ nanoclusters (−SAdm = adamantanethiolate) in the presence of α-, β-, and γ-cyclodextrins (CDs) is studied. The supramolecular chemistry and host–guest interactions of CDs and the protecting ligands of nanoclusters are investigated using UV-vis and NMR spectroscopies, MALDI mass spectrometry, and molecular dynamics simulations. In contrast to α- and γ-CDs, the results show that β-CDs are capable of efficiently chemisorbing onto the Au₃₈S₂(SAdm)₂₀ nanoclusters to yield Au₃₈S₂(SAdm)₂₀–(β-CD)₂ conjugates. MD simulations revealed that two –SAdm ligands of the nanoparticle with the least steric hindrance are capable to selectively be accommodated into hydrophobic cavity of β-CDs, as furthermore confirmed by NMR spectroscopy. The conjugates largely improve the stability of the nanoclusters in the presence of strong oxidants (e.g., TBHP). Further, the electrochemical properties of Au₃₈S₂(SAdm)₂₀ nanoclusters and Au₃₈S₂(SAdm)₂₀–(β-CD)₂ conjugates are compared. The charge transfer to the redox probe molecules (e.g., K₃Fe(CN)₆) in solution was monitored by cyclic voltammetry. It is found that β-CDs act as an umbrella to cover the fragile metal cores of the nanoclusters, thereby blocking direct interaction with destabilizing agents and hence quenching the charge transfer process.