We present a joint computational and experimental study on the adsorption of pyruvic acid on hydroxylated silica particles. Under dry conditions (&lt;1% relative humidity, RH), transmission Fourier transform infrared (FTIR) spectroscopy reveals the presence of both the trans–cis (Tc) and trans–trans (Tt) pyruvic acid conformers as well as the (hydrogen bonded) pyruvic acid dimers. Under higher relative humidity conditions (above 10% RH), adsorbed water competes for surface adsorption sites, changing the relative populations of the different adsorbed pyruvic acid configurations. The detailed surface interactions are further discussed with the help of ab initiomolecular dynamics simulations. Our results highlight the importance of the environment (relative humidity and co-adsorbed water) in the adsorption, partitioning, and configurations of pyruvic acid at the surface. Using a free energy perturbation approach in combination with ab initiomolecular dynamics simulations, we also show how the acidity of pyruvic acid at the quartz/water interface is increased by almost two units. Such increased acidity is the result of the specific microsolvation at the interface and, in particular, of the stabilization of the deprotonated form by the silanols on the quartz surface and the special interfacial water layer. This result shows that, at difference with the water/vapor interface where molecular acidity is generally reduced, at a hydrophilic solid/liquid interface the acidity can indeed also increase.

Heterogeneous molecular interactions at the silica/water interface

2019 Fall National Meeting

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