Carboxylate-Imidazole Cooperativity in Dipeptide-functionalized Gold Nanoparticles with Esterase-like Activity

We report here the first example of peptide-functionalized gold nanoparticles hydrolytically active against carboxylate esters. The active units are constituted by His-Phe-OH terminating thiols. The confinement of the catalytic units in the monolayer covering the nanoparticles triggers a cooperative hydrolytic mechanism operative at pH < 7 in which a carboxylate and an imidazolium ion act as general base and general acid, respectively. Such a mechanism is absent with an analogous monomeric dipeptide, and this results in a more than 300-fold rate acceleration of the hydrolytic process at low pH in the presence of the functional nanoparticles.