QSAR and mechanisms of radical scavenging activity of phenolic and anilinic compounds using structural, electronic, kinetic, and thermodynamic parameters

Antiradical and reductant activities of anthocyanidins and anthocyanins, structure–activity relationship and synthesis

“…Radicals formed on 5-, 7-or 4 0 -hydroxyl groups can also be stabilized by the same resonance in the opposite direction. This resonance effect is similar to that reported for the catechol structure where stable semiquinone radicals are formed leading to stable diketones (Ali & Ali, 2015;Castaň eda-Ovando et al, 2009). The presence of the 3-OH group conjugated with a 2-3 double bond was previously reported to enhance the antioxidant activity in other classes of flavonoids; this structural feature permits coplanarity of ring B with rings A and C, allowing extension of conjugation and electron delocalization leading to extra stability of the resulting radicals (Balasundram, Sundram, & Samman, 2006;Heim, Tagliaferro, & Bobilya, 2002).…”

“…As peonidin, malvidin (Mv) lacks a catechol structure but has more 5 0 -OMe groups; it gave a higher activity (%DPPH 68.64). The electronic effect of substituents has a large influence on both the activation energy and O-H bond dissociation energy of phenols (Foti, Daquino, Mackie, DiLabio, & Ingold, 2008 the resulted radicals of phenolic compounds, leading to an increase in their antioxidant activity with a greater effect shown by the methoxy group than hydroxyl substituent (Ali & Ali, 2015;Balasundram et al, 2006;Heim et al, 2002). Therefore, comparing the activity of compounds lacking the catechol structure, we find the activity against the three radicals (DPPH, ABTS and OH) decreases in the order of Mv > Pn > Pg > Ap > 4-OH-flavylium respective to the presence of 6, 5, 4, 3 and 1 hydroxyl and/or methoxy groups; the difference is significant in most cases.…”

Investigation of radical scavenging effects of acetaminophen, <i>p</i>-aminophenol and their <i>O</i><i>-</i>sulfated conjugates

“…The lower reactivity of APAP towards DPPH radical, compared to that of p-AP, could be due to the presence of the electron-withdrawing acetamido group, which may destabilize the phenoxyl radical (Alisi et al, 2012). Moreover, the amino group of p-AP, rather than its phenolic hydroxyl group, may also play an important role as a strong electron donor in the reaction with DPPH radical (Bendary et al, 2013;Ali et al, 2013;Ali and Ali, 2015). Based on the above-mentioned rationalization, it is likely that p-AP has a higher antioxidant capacity than APAP.…”

Use of quantum-chemical descriptors to analyse reaction rate constants between organic chemicals and superoxide/hydroperoxyl (O2•−/HO2•)

“…For a better estimate of the kinetics, a more thorough knowledge of the oxidative scavenging mechanism is required [66]. For complex (poly)phenols a combination of descriptors such as E HOMO , pK a , BDE, hydrogen bonding, as well as geometrical descriptors may be needed [67,68,79]. For example, the pK a 's of hydroquinone are indicators of the electron density (e.g.…”