Halide anion solvation and recognition by bambusurils: A DFT study

• A strategy for computational (DFT) study of anion binding by macrocyclic hosts is proposed. • The strategy relies on two-step mechanism: the desolvation of the guests precedes the inclusion. • Unfavourable guest desolvation opposes favorable host-guest interactions. • DFT predicted affinities for solvated anions and experimental results in solution are in line. The phenomenon of ion solvation in water has received considerable attention in recent years as the most common species used in the study of aqueous ionic solvation are halide anions and alkali cations. The solvation of the halide ions appears to have great impact on the complex formation processes with the neutral macrocyclic dodecamethylbambus[6]uril host system. Bambusuril host system binds halide ions, preferably in the order I > Br > Cl > F. Various theoretical approaches (different DFT functionals, quite large basis sets, implicit/explicit consideration of the solvent) were employed unsuccessfully in an attempt to overcome the discrepancy between DFT predicted affinities and those experimentally observed in solution (reversed ordering for all or for some of the halide anions). A strategy for calculating the thermodynamic parameters by taking into account two sequential reactions of the guest anion (1) desolvation and (2) inclusion inside the cavity of the host system is applied in our computational study of the dodecamethylbambus[6]uril – halide ions complex formation process. DFT predicted affinities for solvated halide anions are fully in line with available experimental results in solution.