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The Flow of the Redox Energy in Quercetin during Its Antioxidant Activity in Water.

ABSTRACT: Most studies on the antioxidant activity of flavonoids like Quercetin (Q) do not consider that it comprises a series of sequential reactions. Therefore, the present study examines how the redox energy flows through the molecule during Q's antioxidant activity, by combining experimental data with quantum calculations. It appears that several main pathways are possible. Pivotal are subsequently: deprotonation of the 7-OH group; intramolecular hydrogen transfer from the 3-OH group to the 4-Oxygen atom; electron transfer leading to two conformers of the Q radical; deprotonation of the OH groups in the B-ring, leading to three different deprotonated Q radicals; and finally electron transfer of each deprotonated Q radical to form the corresponding quercetin quinones. The quinone in which the carbonyl groups are the most separated has the lowest energy content, and is the most abundant quinone. The pathways are also intertwined. The calculations show that Q can pick up redox energy at various sites of the molecule which explains Q's ability to scavenge all sorts of reactive oxidizing species. In the described pathways, Q picked up, e.g., two hydroxyl radicals, which can be processed and softened by forming quercetin quinone.

SUBMITTER: Li Z

PROVIDER: S-EPMC7504380 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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The Flow of the Redox Energy in Quercetin during Its Antioxidant Activity in Water.

Li Zhengwen Z Moalin Mohamed M Zhang Ming M Vervoort Lily L Hursel Erik E Mommers Alex A Haenen Guido R M M GRMM

International journal of molecular sciences 20200821 17

Most studies on the antioxidant activity of flavonoids like Quercetin (Q) do not consider that it comprises a series of sequential reactions. Therefore, the present study examines how the redox energy flows through the molecule during Q's antioxidant activity, by combining experimental data with quantum calculations. It appears that several main pathways are possible. Pivotal are subsequently: deprotonation of the 7-OH group; intramolecular hydrogen transfer from the 3-OH group to the 4-Oxygen a ...[more]

PMID: 32825576

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Project description:It was recently shown that, when tested in cellular systems, quercetin oxidized products (Qox) have significantly better antioxidant activity than quercetin (Q) itself. The main Qox identified in the experiments are either 2,5,7,3',4'-pentahydroxy-3,4-flavandione (Fl) or its tautomer, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Bf). We have now performed a theoretical evaluation of different physicochemical properties using density functional theory (DFT) calculations on Q and its main Qox species. The most stable structures (for Q and Qox) were identified after a structural search on their potential energy surface. Since proton affinities (PAs) are much lower than the bond dissociation enthalpies (BDEs) of phenolic hydrogens, we consider that direct antioxidant activity in these species is mainly due to the sequential proton loss electron transfer (SPLET) mechanism. Moreover, our kinetic studies, according to transition state theory, show that Q is more favored by this mechanism. However, Qox have lower PAs than Q, suggesting that antioxidant activity by the SPLET mechanism should be a result of a balance between proclivity to transfer protons (which favors Qox) and the reaction kinetics of the conjugated base in the sequential electron transfer mechanism (which favors Q). Therefore, our results support the idea that Q is a better direct antioxidant than its oxidized derivatives due to its kinetically favored SPLET reactions. Moreover, our molecular docking calculations indicate a stabilizing interaction between either Q or Qox and the kelch-like ECH-associated protein-1 (Keap1), in the nuclear factor erythroid 2-related factor 2 (Nrf2)-binding site. This should favor the release of the Nrf2 factor, the master regulator of anti-oxidative responses, promoting the expression of the antioxidant responsive element (ARE)-dependent genes. Interestingly, the computed Keap1-metabolite interaction energy is most favored for the Bf compound, which in turn is the most stable oxidized tautomer, according to their computed energies. These results provide further support for the hypothesis that Qox species may be better indirect antioxidants than Q, reducing reactive oxygen species in animal cells by activating endogenous antioxidants.

Project description:Production of sugarcane and more recently of energy cane strengthen renewable bioenergy production capacity. However, droughts resulting from climate change have limited the production of these crops. One of the strategies to attenuate water deficit damage in these crops is the use of silicate, which contributes to plant physiology. This strategy is likely to increase water use efficiency, thus promoting crop sustainability. Notwithstanding, studies on this issue are still incipient. This study assesses whether Si applied via fertigation and foliar spraying in the seedling production phase and as a complement after seedling transplanting to the soil is efficient in attenuating water deficit in sugarcane and energy cane. The study further elucidates physiological and biochemical mechanisms involved in this process. For this, the authors conducted two experiments: one with sugarcane and the other with energy cane. Treatments were arranged in randomized blocks with 5 replications, in a 2 × 2 factorial scheme. Factors consisted of the absence (-Si) and presence of Si (+ Si) applied via fertigation and foliar spraying; and two water regimes: 70% (without water deficit) and 30% (severe water deficit) of the soil water retention capacity. Silicon was supplied during the formation phase of presprouted seedlings and during the transplanting of seedlings to pots filled with samples of Entisol (Quartzipsamment). In these pots, water regimes were induced from 7 to 160 days after transplanting. Severe water deficit reduced the water content and water potential of plants. This situation induced oxidative stress and impaired gas exchange and photosynthetic water use efficiency, reducing plant growth. Silicon supply via fertigation in association with foliar spraying in the seedling formation phase with complementation after transplanting was efficient in increasing Si accumulation in the plants. Silicon was effective in attenuating severe water deficit damage up to initial culm formation through mechanisms that maintain water and physiological balance by favoring the antioxidant defense system in sugarcane and energy cane plants.

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The Flow of the Redox Energy in Quercetin during Its Antioxidant Activity in Water.

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The Flow of the Redox Energy in Quercetin during Its Antioxidant Activity in Water.

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