The concentrations used to estimate ∆G •/ * are in agreement with the experimental conditions described in ref. 20 in order the results to be comparable. Thereby, the following gasphase concentrations were used: 5.54 M for water, 15.36 M for ethanol, 2.4x10 -3 M for QH 2 and its derivatives, 2x10 -3 M for DPPH• and its derivatives, 0.2 M for Al 3+ and its derivatives, and different proton concentrations according to the pH in each situation. Limiting reagent's concentration is the one that defines the concentration of any formed intermediate specie. See Supporting Information (SI) for further details.