Cavitation energies can outperform dispersion interactions. Issue 12 (December 2018) - He, Suhang
Abstract The accurate dissection of binding energies into their microscopic components is challenging, especially in solution. Here we study the binding of noble gases (He–Xe) with the macrocyclic receptor cucurbit[5]uril in water by displacement of methane and ethane as1 H NMR probes. We dissect the hydration free energies of the noble gases into an attractive dispersive component and a repulsive one for formation of a cavity in water. This allows us to identify the contributions to host–guest binding and to conclude that the binding process is driven by differential cavitation energies rather than dispersion interactions. The free energy required to create a cavity to accept the noble gas inside the cucurbit[5]uril is much lower than that to create a similarly sized cavity in bulk water. The recovery of the latter cavitation energy drives the overall process, which has implications for the refinement of gas-storage materials and the understanding of biological receptors. Binding interactions, whether between a biological receptor and ligand or between a synthetic host and guest, are frequently stronger for larger molecules than for smaller ones. This is commonly believed to arise from increased dispersion interactions, but it has now been shown that cavitation energies—always required to dissolve molecules in solution—can be more important.