Use and Abuse of the DPPH(•) Radical. Foti Mario C Journal of agricultural and food chemistry The 2,2-diphenyl-1-picrylhydrazyl (DPPH(•)) radical is approaching 100 years from its discovery in 1922 by Goldschmidt and Renn. This radical is colored and remarkably stable, two properties that have made it one of the most popular radicals in a wide range of studies. First, there is the evaluation of the antioxidant abilities of phenols and other natural compounds (A-H) through a "test" that-at a closer look-is utterly inappropriate. In fact, the test-derived EC50, that is, the concentration of A-H able to scavenge 50% of the initial DPPH(•), is not a kinetic parameter and hence its purported correlation with the antioxidant properties of chemicals is not justified. Kinetic measurements, such as the second-order rate constants for H-atom abstraction from A-H by DPPH(•), in apolar media, are the only useful parameters to predict the antioxidant ability of A-H. Other applications of DPPH(•) include kinetic and mechanistic studies, kinetic solvent effects, EPR spectroscopy, polymer chemistry, and many more. In this review these applications are evaluated in detail by showing the usefulness of some and the uselessness of others. The chemistry of DPPH(•) is also briefly reviewed. 10.1021/acs.jafc.5b03839

Contribution of trans-aconitic acid to DPPH scavenging ability in different media. Piang-Siong William,de Caro Pascale,Marvilliers Arnaud,Chasseray Xavier,Payet Bertrand,Shum Cheong Sing Alain,Illien Bertrand Food chemistry The antioxidant properties of trans-aconitic acid (TAA) alone or in the presence of usual antioxidants were assessed by DPPH assay. The IC50 value equal to 70mM was very high compared to usual antioxidants (vitamin C and trolox). A joint experimental/theoretical study suggested that hydrogen atom abstraction in TAA by DPPH was located on -CH2- methylene bridge because the corresponding radical was more stabilized than COO(·) and CC(·) radicals. In combination with antioxidants (vitamin C, gallic acid, caffeic acid, trolox), synergy or additivity effects were noticed. The magnitude of the synergistic effect varied between 1.06 and 1.24 depending on the type and concentration of antioxidant for a concentration of TAA equal to 22.3mM. Especially, the addition of TAA at a concentration below 32mM to a solution containing 20μM of vitamin C had a synergy effect. Beyond this concentration, TAA showed an additive effect. 10.1016/j.foodchem.2016.07.083

Contribution of individual flavonoids in Lysimachia species to the antioxidant capacity based on HPLC-DPPH assay. Toth Anita,Riethmuller Eszter,Vegh Krisztina,Alberti Agnes,Beni Szabolcs,Kery Agnes Natural product research Quantitative phytochemical characterisation of the chief flavonoid aglycones in the hydrolysed Lysimachia extracts revealed the dominance of kaempferol, quercetin and myricetin in L. vulgaris, L. nummularia, L. punctata, L. christinae, L. ciliata and L. clethroides, respectively. Due to the significant radical scavenging capacity of the samples, the contribution of the individual aglycones to the total antioxidant activity became of interest. Therefore, a HPLC method coupled to pre-column DPPH scavenging assay was developed. Differences in the six Lysimachia species' phenolic composition regarding their participation to the antioxidant activity were revealed. The participation of the three investigated flavonoids to the radical quenching activity was the highest (91.2%) in the L. vulgaris sample, the lowest in L. christinae sample with 29.6%. In L. vulgaris sample, the 76.3% contribution of quercetin to the scavenger capacity was the highest peak area decrement ratio among the investigated samples. 10.1080/14786419.2017.1359176

Paper-based DPPH Assay for Antioxidant Activity Analysis. Sirivibulkovit Kitima,Nouanthavong Souksanh,Sameenoi Yupaporn Analytical sciences : the international journal of the Japan Society for Analytical Chemistry We report on a paper-based 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH) assay for a simple, inexpensive, low reagent and sample consumption and high throughput analysis of antioxidant activity. The paper-based device was fabricated using a lamination method to create a 5-mm in diameter circular test zone that was embedded with a DPPH reagent. The analysis was carried out in one-step by dropping an antioxidant/sample onto the test zone. After reduction by the antioxidant, the DPPH radicals become stable DPPH molecules, resulting in a change in color from deep violet to pale yellow. The violet color intensity of DPPH was inversely proportional to the antioxidant activity of the samples, and was measured using imaging software. A high precision and a low limit of detection were found in the analysis of six standard antioxidants including gallic acid, trolox, ascorbic acid, caffeic acid, vanilliic acid and quercetin. The device was then validated against the traditional spectrophotometric DPPH assay by analyzing the antioxidant activity of 7 tea samples. The results showed no significant difference for gallic acid equivalent for all 7 samples obtained from the two methods at the 95% confidence level, indicating that the developed method was reliable for antioxidant activity analysis of real samples. Finally, the paper-based DPPH device was found to be stable over 10 days when stored in a refrigerator (2 - 4°C), making it an easy-to-use device for end-users. 10.2116/analsci.18P014