  Gold nanoparticles are unique electrocatalysts for oxygen reduction, carbon
dioxide reduction, and alcohol oxidation. Electrocatalytic processes are
influenced by the interaction with the solvent, yet the direct investigation of
the solvation of nanoparticles is scarce. Here we select gold nanoparticles as
10 nm sized solutes of which we can control the charge. We perform mid-infrared
and terahertz spectroscopy to compare the behavior of the water in solution
with micelles loaded with neutral and positive gold nanoparticles. We find
indications that the hydration water around the gold-loaded micelles is
characterized by weaker hydrogen bonds than bulk water. A positive nanoparticle
charge is observed to result in a larger blue shift of the OH stretch, quenches
the intensity of the collective translational mode, and increases the
absorption by librating water molecules. Water at the interface of a positive
gold nanoparticle could experience a stiffer potential energy surface which, in
turn, might unveil local thermodynamic properties.
