Solvation Structure of Surface-Supported Amine Fragments: A Molecular Dynamics Study

SJ Sheng and J Fu and BM Wong and JZ Wu, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 22156-22163 (2017).

DOI: 10.1021/acs.jpcc.7b07178

Amine-grafted silica gel is an efficient heterogeneous catalyst for the Knoevenagel condensation and draws much attention in green chemistry for applications like heavy metal adsorption and CO2 fixation. Despite its successful usage in diverse areas, fundamental questions remain on how the silica substrate affects the local chemical environment of the tethered amines. In this work, we use all-atom molecular dynamics simulation to investigate the solvation structures of two primary amines tethered onto a silica surface at different pHs of aqueous solutions. The atomic density profiles in the solvation shell are analyzed with a spherical harmonics expansion method for both isolated and silica- supported amines in different aqueous environments. The simulation results provide direct evidence for the strong influence of the silica surface on the hydration structure that is often ignored in the theoretical analysis of surface reactions. The surface effect becomes less prominent on the tethered amine as the alkyl chain length increases.

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