Takin into account precedent experimental studies, the one-electron reduction potential of DPPH• in the presence of Al 3+ has been studied here considering a solution with a pH value of 5.5. As it happened for hydroquinones, the presence of Al 3+ reduces the original pH of the solution without Al 3+ (for the DPPH• case the reduction goes from 7.5 to 5.5 pH units). Globally, the pH of the DPPH• solution with the presence of Al 3+ is more basic than the pH of equivalent hydroquinone solutions and it has an -0.28 -0.09 0.27 effect in the relative stability of the Al 3+ complexes that may be formed. As it can be observed in Table , when the solution becomes more basic, an extra stabilization of less charged complexes is achieved. We This could be expected from the chelation of alcohol ligands to aluminum, which causes important shifts in their pKa values. Table 6 reports all the one-electron reduction potentials analyzed for DPPH• considering Al 3+ present in solution. In all Al 3+ -complexes where DPPH• is coordinated to Al 3+ , the coordination is done through an orto nitro group of the picryl substituent of DPPH•, kO, (Figure ) because this coordination mode is always more stable than the diazane coordination, kN (see Table ).