Correlating solution binding and ESI-MS stabilities by incorporating solvation effects in a confined cucurbit[8]uril system.

The high-throughput characterization of solution binding equilibria is essential in biomedical research such as drug design as well as in material applications of synthetic systems in which reversible binding interactions play critical roles. Although isothermal titration calorimetry (ITC) has been widely employed for describing such binding events, factors such as speed, concentration, and sample complexity would principally favor a mass spectrometry approach. Here, we show a link between ITC and electrospray ionization mass spectrometry (ESI-MS) by incorporating solvation free energies in the study of the ternary complexes of the macrocyclic host cucurbit[8]uril (CB[8]). The binding affinities of 32 aromatic reference complexes were studied by ITC and ESI-MS and combined with solvation data of the guests from an implicit solvation model (SM8) to obtain a correlation between aqueous and gas-phase measurements. The data illustrates the critical importance of solvation on the binding strength in CB[8]'s ternary complexes. Finally, this treatment enabled us to predict association constants that were in excellent agreement with measured values, including several highly insoluble guest compounds.