Accumulated Proton-Donating Ability of Solvent Molecules in Proton Transfer

Solvent-inventory experiments on the excited-state proton transfer of a 7-hydroxyquinoline molecule complexed cyclically with two alcohol molecules in the host medium of n-alkane have been carried out with various combinations of alcohols having different proton-donating abilities. Alcohol molecules participating in the hydrogen-bonded chain of the cyclic complex accelerate proton transfer in a concerted fashion by accumulating their proton-donating abilities. The rate-determining deprotonation of the alcohol molecule hydrogen-bonded directly to the imino group of 7-hydroxyquinoline is stimulated by the push-ahead effect of the next alcohol molecule in the hydrogen-bonded chain. Our results provide a clue at the level of molecules on the fundamental mechanistic elucidation of proton transport occurring through a proton wire consisting of diverse amino acids.