Quantitative Kinetic Analysis of Hydrogen Transfer Reactions from Dietary Polyphenols to the DPPH Radical

Abstract

Diphenylpicrylhydrazyl (DPPH) is widely used for quickly assessing the ability of polyphenols to transfer labile H atoms to radicals, a likely mechanism of antioxidant protection. This popular test generally pays no attention to the kinetics of H atom transfer, which however could be even more important than the total H-atom-donating capacities (stoichiometry, EC50) typically evaluated. In the present work, a series of dietary polyphenols belonging to the most representative families (flavonols from onion, flavanol monomers and oligomers from barley, and caffeic acid and caffeoyl esters from artichoke and endive) are characterized not only by their total stoichiometries (n(tot)) but also by their rate constants of first H atom abstraction by DPPH (k(1)), deduced from the kinetic analysis of the decay of the DPPH visible band following addition of the antioxidant. The mildly reactive DPPH radical allows a good discrimation between polyphenols, as demonstrated by the relatively large ranges of k(1) (ca. 400-5000 M(-)(1) s(-)(1)) and n(tot) (ca. 1-5) values typically measured with antioxidants having a single polyphenolic nucleus. With antioxidants displaying more than one polyphenolic nucleus (procyanidin oligomers, dicaffeoyl esters), the kinetic analysis makes it possible to demonstrate significant differences in reactivity between the subunits (two distinct k(1) values whose ratio lies in the range 3-10) and nonadditive stoichiometries.

The Methodology Applied in DPPH, ABTS and Folin-Ciocalteau Assays Has a Large Influence on the Determined Antioxidant Potential

“…Apart from their structural characteristics (number and position of -OH groups, inductive effects of other substituents present in the antioxidant molecule, steric hindrance/accessibility, packaging of an antioxidant around reactive species) the reactivity of an antioxidant depends significantly on reaction conditions such as solvent polarity, pH, temperature, type and concentration of reactive species. 3,[6][7][8][9][10][11][12][13][14] Since the selection of the method, the time and reaction conditions adopted to evaluate the content of antioxidants in a given sample significantly impact the determined values and, due to the fact that these parameters in a number of articles are relatively poorly described, it is very difficult to compare the results of AOP obtained for similar samples in different studies.…”

Kinetic and Stoichiometric Evaluation of Free Radicals Scavengers Activities Based on Diphenyl-Picryl Hydrazyyl (Dpph) Consumption

“…The values range from 4.4 x 10 3 to 0,1 M -1 s -1 for quercetagein to apigenin, respectively. This emphasizes the great sensitivity of the kinetic process to the scavenger structure 19 . On the other hand, stoichiometric factors derived from titration experiments were rather similar for all the compounds considered.…”

Synthesis, anticonvulsant, antioxidant and binding interaction of novel N-substituted methylquinazoline-2,4(1H,3H)-dione derivatives to bovine serum albumin: A structure–activity relationship study

“…The stable free radical DPPH is a useful reagent to investigate the scavenger properties of phenols, catechols and anilines. This assay evaluates the ability of the substance under examination to donate hydrogen atoms or electron donating (conceivable) and quench the visible absorption at 517 nm of the nitrogen radical of DPPH [31]. There are many reports describing the antiradical effect of phenolic compounds by DPPH assay [32,33].…”