Mercaptocalixarene-Capped Gold Nanoparticles via Postsynthetic Modification and Direct Synthesis: Effect of Calixarene Cavity-Metal Interactions

Abstract

Evidence for interactions between π-electron-rich calixarene cavities and the surface of gold nanoparticles is demonstrated using a comparative synthetic approach involving the capping of the nanoparticles with thiol ligands. In one approach, thiol ligands are systematically titrated onto existing 5.3 nm gold nanoparticles in solution (postsynthetic synthesis approach), whereas in the other a gold solution is reduced in the presence of thiol ligands (direct synthesis approach). The calixarene cavity is placed in close proximity and facing toward the gold nanoparticle surface upon adsorption of ligand 5,11,17,23-tetrakis-mercaptomethyl-25,26,27,28-tetrapropoxylcalix[4]arene (MMC), which comprises four upper-rim thiol groups. The other two ligands used in this investigation contain either four thiol groups on the calixarene lower-rim, 25,26,27,28-tetrakis(4-mercaptobutyloxy)calix[4]arene (MBC), or a model monodentate thiol, 4-methoxybenzenemethanethiol (MBM), as controls. The orientation of the cavity in MM...