Accessibility in Calix[8]arene-Bound Gold Nanoparticles: Crucial Role of Induced-Fit Binding

Abstract

Metal nanoparticles bound with polymeric and oligomeric ligands are commonly employed in areas where accessibility to the underlying metal is critical, such as in catalysis. Developing a fundamental understanding of molecular-scale factors that control accessibility to the metal surface in these systems enables approaches for ligand design. Here, we implement a comparative synthetic approach to investigate the role of an induced-fit binding mechanism on accessibility, which reduces to elucidating the correlation between ligand flexibility and accessibility. Four nm gold nanoparticles are bound with a calix[8]arene phosphine ligand in the comparative series 3a−c, and ligand molecular footprints of ∼230 A2/calix[8]arene are measured on the gold surface using UV−vis spectroscopy of the surface plasmon resonance absorption band. Ligand flexibility in CDCl3 solution is characterized using variable-temperature 1H NMR spectroscopy, and results demonstrate 3c to be the most rigid of all three ligands. This is fur...