Relevance of Secondary Processes in Orac Values Obtained Employing Pyrogallol Red as Target Molecule

López-Alarcón, Camilo; Aspée, Alexis; Lissi, E. A.

doi:10.4067/s0717-97072009000100003

Cited by 3 publications

(1 citation statement)

References 7 publications

(11 reference statements)

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“…The reactivity of C 314 +• , expressed as a bimolecular rate constant, toward some selected phenolic compounds that we have chosen due to their proven antioxidant ability − are summarized in Table (values were measured under N 2 and N 2 O). Additionally, in this table, we have also included p K a and redox potential values for the antioxidants employed here.…”

Section: Resultsmentioning

confidence: 99%

Coumarin 314 Free Radical Cation: Formation, Properties, and Reactivity toward Phenolic Antioxidants

et al. 2011

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We have explored the photogeneration of the coumarin 314 radical cation by using nanosecond laser excitation at wavelengths longer than 400 nm in benzene, acetonitrile, dichloromethane, and aqueous media. In addition, time-resolved absorption spectroscopy measurements allowed detection of the triplet excited state of coumarin 314 (C(314)) with a maximum absorption at 550 nm in benzene. The triplet excited state has a lifetime of 90 μs in benzene. It is readily quenched by oxygen (k(q) = 5.0 × 10(9) M(-1) s(-1)). From triplet-triplet energy transfer quenching experiments, it is shown that the energy of this triplet excited state is higher than 35 kcal/mol, in accord with the relatively large singlet oxygen quantum yield (Φ(Δ) = 0.25). However, in aqueous media, the coumarin triplet was no longer observed, and instead of that, a long-lived (160 μs in air-equilibrated solutions) free radical cation with a maximum absorbance at 370 nm was detected. The free radical cation generation, which has a quantum yield of 0.2, occurs by electron photoejection. Moreover, density functional theory (DFT) calculations indicate that at least 40% of the electronic density is placed on the nitrogen atom in aqueous media, which explains its lack of reactivity toward oxygen. On the other hand, rate constant values close to the diffusion rate limit in water (>10(9) M(-1) s(-1)) were found for the quenching of the C(314) free radical cation by phenolic antioxidants. The results have been interpreted by an electron-transfer reaction between the phenolic antioxidant and the radical cation where ion pair formation could be involved.

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Section: Resultsmentioning

confidence: 99%

Coumarin 314 Free Radical Cation: Formation, Properties, and Reactivity toward Phenolic Antioxidants

et al. 2011

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Influence of the Target Molecule on the ORAC Index

López-Alarcón

Aspée

Lissi

2012

ACS Symposium Series

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New insights into the antioxidant activity of hydroxycinnamic and hydroxybenzoic systems: Spectroscopic, electrochemistry, and cellular studies

Mura

Silva

Castro

et al. 2014

Free Radical Research

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A series hydroxycinnamic and gallic acids and their derivatives were studied with the aim of evaluating their in vitro antioxidant properties both in homogeneous and in cellular systems. It was concluded from the oxygen radical absorbance capacity-fluorescein (ORAC-FL), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and cyclic voltammetry data that some compounds exhibit remarkable antioxidant properties. In general, in homogeneous media (DPPH assay), galloyl-based cinnamic and benzoic systems (compounds 7-11) were the most active, exhibiting the lowest oxidation potentials in both dimethyl sulfoxide (DMSO) and phosphate buffer. Yet, p-coumaric acid and its derivatives (compounds 1-3) disclosed the highest scavenging activity toward peroxyl radicals (ORAC-FL assay). Interesting structure-property- activity relationships between ORAC-FL, or DPPH radical, and redox potentials have been attained, showing that the latter parameter can be a valuable antioxidant measure. It was evidenced that redox potentials are related to the structural features of cinnamic and benzoic systems and that their activities are also dependent on the radical generated in the assay. Electron spin resonance data of the phenoxyl radicals generated both in DMSO and phosphate buffer support the assumption that radical stability is related to the type of phenolic system. Galloyl-based cinnamic and benzoic ester-type systems (compounds 9 and 11) were the most active and effective compounds in cell-based assays (51.13 ± 1.27% and 54.90 ± 3.65%, respectively). In cellular systems, hydroxycinnamic and hydroxybenzoic systems operate based on their intrinsic antioxidant outline and lipophilic properties, so the balance between these two properties is considered of the utmost importance to ensure their performance in the prevention or minimization of the effects due to free radical overproduction.

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Relevance of Secondary Processes in Orac Values Obtained Employing Pyrogallol Red as Target Molecule

Cited by 3 publications

References 7 publications

Coumarin 314 Free Radical Cation: Formation, Properties, and Reactivity toward Phenolic Antioxidants

Coumarin 314 Free Radical Cation: Formation, Properties, and Reactivity toward Phenolic Antioxidants

Influence of the Target Molecule on the ORAC Index

New insights into the antioxidant activity of hydroxycinnamic and hydroxybenzoic systems: Spectroscopic, electrochemistry, and cellular studies

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