Water Plays a Dynamical Role in a Hydrogen-bonded, Hexameric Supramolecular Assembly

The hexameric resorcin[4]arene supramolecular assembly has attracted significant interest as a self-assembled capsule that exhibits dynamic host-guest chemistry. Many studies have been carried out to investigate the structure and thermodynamics of the assembly, but considerably less is known about its dynamical properties. Here, molecular dynamics simulations are used to investigate the timescales of water encapsulation in this assembly in wet chloroform. We have previously shown [A. Katiyar et al., Chem. Commun. 2019, 55, 6591-6594] that at low water content there are three distinct populations of water molecules present, while at higher water content an additional population, long water chains interacting with the assembly, appears. The relative free energies of these different water positions are calculated and time correlation functions are used to determine the timescales for interconversion between the populations. This analysis demonstrates that the water molecules are in rapid exchange with each other on timescales of tens of ps to a few ns, and suggests that water molecules might be acting as a critical component in the guest exchange mechanism.