The key role of the sequential proton loss electron transfer mechanism on the free radical scavenging activity of some melatonin-related compounds

The role of the acid-base equilibria and the sequential proton loss electron transfer mechanism (SPLET) on the free radical scavenging activity of six melatonin-related compounds was investigated using the density functional theory. It was found that this chemical route is particularly important for about half of the studied compounds. Some of their pKa values are reported here for the first time. In addition, our results also indicate that anionic species, presenting the phenolate moiety, may be crucial to scavenge peroxyl radicals albeit their populations are relatively low at physiological pH. The key number to consider in this context should be the product of the molar fraction of the reacting compound, at the pH of interest, by the corresponding rate constant.