A New Perspective on Ion Receptors – Spectroscopy of Isolated Supramolecular Ion Complexes in Vacuo and Solution

The effectiveness and selectivity of molecular ion receptors, most of which are applied in solutions, depends on the competition of ion binding and ion solvation. Experiments in solutions, however, suffer from drawbacks such as speciation, broadening of spectroscopic features, and the obscurement of important spectroscopic signatures by the response of the bulk solvent, all of which can hinder molecular-level insight into the interactions at play. Moreover, effects of ion-receptor interactions and of ion solvation cannot be cleanly separated by experiments in solutions alone.



Gas phase experiments on mass-selected, cryogenically prepared ions can shed light on the intrinsic interactions between ion and receptor, offering a unique level of experimental control over the molecular environment of the ion binding site. At the same time, this approach circumvents many of the challenges associated with experiments in solutions. I will present experimental results from cryogenic ion vibrational spectroscopy of ion receptors based on calix[4]pyrrole macrocycles, together with their computational analysis. These studies highlight the influence of the immediate chemical environment around the ion binding site on the ion-receptor interactions.