Adsorption of constitutional isomers of cyclic monoterpenes on hydroxylated silica surfaces.

ABSTRACT

We present a study of four monoterpene isomers (limonene, γ-terpinene, terpinolene, and α-pinene) that are prevalent in indoor environments and their interaction with the hydroxylated SiO2 surface, a model for the glass surface, by combining infrared spectroscopy and computational simulations. These isomers are molecularly adsorbed onto SiO2 through π-hydrogen bonds with surface hydroxyl groups. However, experimental results suggest that the strength of interaction of these compounds with the SiO2 surface varies for each isomer, with α-pinene showing the weakest interaction. This observation is supported by molecular dynamics simulations that α-pinene adsorbed on the SiO2 surface has lower free energy of desorption and a lower mass accommodation coefficient compared to other isomers. Additionally, our ab initio molecular dynamics simulations show lower π-hydrogen bonding probabilities for α-pinene compared to the other three constitutional isomers. Importantly, these interactions are most likely present for a range of other systems involving organic compounds and solid surfaces and, thus, provide a thorough framework for comparing the interactions of organic molecules on indoor relevant surfaces.