Flavonoids and the Structure-Antioxidant Activity Relationship
The structures that conferred flavonoids with the most antioxidant activity in the Knowledge of structure−activity relationships in the CAA assay may be helpful . Phenolic Composition and Antioxidant Activity in Seed Coats of 60 Radical and Inhibition of the Heme-Induced Peroxidation of Linoleic Acid. PDF | Flavonoids and phenolic acids make up one of the most pervasive groups of plant phenolics. Due to their stresses on antioxidant accumulation in relation to plant metabolites of plants with polyphenolic structure. The antioxidant and prooxidant activities of flavonoids belonging to several classes were studied to establish their structure-activity.
The structure of flavonoids is a key determinant of their antioxidant activities.
Flavonoids and the Structure-Antioxidant Activity Relationship
The antioxidant activity of flavonoids increases with increasing degree of hydroxylation. However, substitution of the hydroxyl groups at the 3- and 5-position with methoxyl groups reduces the activity. Some structural features and nature of substitutions on rings B and C determine the antioxidant activity of flavonoids.
The degree of hydroxylation and the positions of the -OH groups in the B ring, as an ortho-dihydroxyl structure of ring B catechol group leads to higher activity, or acts as the preferred binding site for trace metals [ 8 ]. The presence of hydroxyl groups at the 3'- 4'- and 5'-positions of ring B a pyrogallol group was found to enhance the antioxidant activity.
promovare-site.info | STRUCTURE-ANTIOXIDANT ACTIVITY RELATIONSHIPS OF FLAVONOIDS AND PHENOLIC ACIDS
A double bond between C-2 and C-3, conjugated with the 4- oxo group in ring C improves the radical scavenging capacity of flavonoids [ 8 ] and the double bond between C-2 and C-3, combined with a 3-OH ring Calso increases the active radical scavenging capacity of flavonoids.
The substitution of hydroxyl groups in ring B by methoxyl groups alters the redox potential, which affects the radical scavenging capacity of flavonoids [ 89 ].
It was demonstrated that in flavonoids the O-glycosylation decreases their antioxidant potential in in vitro assays, whereas the C-glycosylation in most cases increases their antioxidant potential [ 1011 ]. Blocking the hydroxy group at the C-3 position or removing the 3-OH group decreases antioxidative properties of flavonoids.
Further studies are focused on the discovery of new flavonoids from plant material and their structure-activity relationship. Due to the traditional medicine, plants still represent a large source of natural compoundsnew chemical entities, for the development of novel drugs [ 12 ]. Further studies are focused on the discovery of new bioactive compounds as flavonoids [ 13 ] from plant material and their structure-activity relationship.
Antioxidant activity was calculated as follows: The log P value was measured in pH values of 3. The val- idant, respectively, and Winh and W0 are the oxidation rates the ues of log P ranged from 0.
More hydrophobic phenolic compounds and absence of an antioxidant, respectively. The phenolic acids containing protonated car- boxyl group at the lower pH value exhibited higher hydrophobici- All determinations were carried out in triplicate, and data were ties, whereas the esterified ones were undergone no significant subjected to analysis of variance ANOVA.
This indicates that 3. Partition coefficient Log P o-hydroxyl groups and, to a lesser amount, o-methoxy groups make p-HBA more hydrophilic.
Less effective role of o-methoxy Measuring the log P value provides helpful information about groups in increasing the polarity of phenolic acids can be the polarity-based antioxidative behavior of phenolic antioxidants. A schematic kinetic curve of peroxide accumulation during oxidation of lipid systems, and the corresponding kinetic values. IHBs have been shown to possess a ate such hydrogen bonds, which will be established only in polar large contribution to lowering the O—H BDE value of polyphenols.
Meanwhile, the semiquinone free radical was higher than that in the hydrophilicity due to the o-hydroxyl resulted from the hydrogen abstraction in PCA and GA can be sta- and o-methoxy groups. It is expected that the bigger alkyl ester bilized by forming one and two IHBs Schemes 2 and 3respec- group is, the more hydrophobic is the molecule. It has been reported that the introduc- 3. Radical scavenging activity tion of more than two hydroxyl groups to a monophenol will not improve the antioxidant efficiency Pokorny, Electron-donating between the phenolic O—H and o-methoxy groups increased from o-hydroxyl substituents on the aromatic ring lower the O—H BDE 3.
Following the hydrogen abstraction, polyphenols hydroxyl group cannot be stabilized by forming IHB Scheme 4. This capable of producing highly reactive hydroxyquinone intermedi- can be due to the more effective role of o-dimethoxy moiety in ates which can scavenge the radicals more efficiently.
Formation of semiquinone radical intermediates and quinones from dihydroxyphenols. Intramolecular hydrogen bonds in the catechol moiety of polypheols. Plausible radical scavenging mechanism of methyl protocatechuate in alcoholic solvents. Intramolecular hydrogen bonds in the pyrogallol moiety of polypheols.Health Facts - Phenolic Antioxidant
IPinhb Winhc Ad Control Intramolecular hydrogen bond in an o-methoxyphenol. The negative effect of the IHBs formed in o-methoxyphenols on the O—H BDE value can be removed to some extent by the intermolecular hydrogen bonds with polar solvents, the fish oil and even exerted pro-oxidant activity to some extent. In their study on a series of synthesized phenolic-based antioxi- Interestingly, the comparison between the RSA value of PCA and dants in olive oil using Rancimat test, Torres de Pinedo, Penalver, GA with their esters indicated different influence of the esterifica- and Morales observed no comparable stabilizing potency tion reaction on the antiradical behavior of catechol-type PCA for the monophenolic antioxidants experimented.
Saito, Okamoto, and Kawabata reported that respectively, could stabilize the fish oil more tangibly than the methyl protocatechuate dramatically inhibits DPPH free radicals other phenolics studied. These values were much greater than that when changing solvent from aprotic e. They tocopherol formula conventionally used to oxidatively stabilize showed that the intermediate protocatechuquinone methyl ester fish oils.
As can be seen in Tables 2 and 3, the antioxidant perfor- is highly susceptible to nucleophilic attack of the alcohol molecule mance of GA in preventing the formation of hydroperoxides was to C-2 position, resulting in a regeneration of the catechol struc- by far higher than in scavenging the DPPH free radical, so that ture capable of scavenging two additional radicals Scheme 5.
It is possible that the additional hydroxyl group present in Hydrogen bonds are primarily electrostatic interactions that their the o-quinone produced from GA could enhance the reactivity of stability depends on the dielectric constant of the environment.
Lipid systems with dielectric constants extremely lower than those of aqueous systems provide anhydrous conditions in which IHBs 3. Similar results have been reported by Torres de formance of the phenolic compounds. The kinetic parameters of Pinedo et al. The results found in the bulk oil system for p-HBA and Unlike showing the different behaviors in the DPPH free radical its methyl ester was very similar to those observed in the DPPH assay, the alkyl esters of both PCA and GA presented higher antiox- free radical assay, so that they showed no stabilizing ability in idant activities than their parent molecules in the bulk fish oil R.
However, EPC possessed a much higher stabilizing effect system. This can be due to the hydrophobic nature of its methyl than its parent molecule a ratio of 2. It can molecules to the interface, agreeing with the polar paradox theory.
Therefore, when the affinity to interface predominates, the chain, resulting in a well-stabilized phenoxy radical Torres de ultimate efficiency of antioxidants possessing different polarity Pinedo et al. In general, the performance of the phenolic depends to a lesser amount on the electronic phenomena of the acid antioxidants and their alkyl esters in the bulk oil system functional groups attached.
Meanwhile, the polar paradox theory, denoting that less alkyl ester from 1. As can be seen in Table 2, the overall hydrophobicity of the phenolic ring has increased more by introducing alkyl ester 3. The antioxidant a lower tendency to absorb phenolic acids existing as negatively efficiency of the phenolic compounds in the emulsion was almost charged molecules, or a higher tendency to incorporate the completely different from that in the alcoholic environment of uncharged alkyl esters of the phenolic acids.
In contrast to the high activities observed The influence of o-hydroxyl, o-methoxy, and alkyl ester groups in the previous systems, GA was among the weakest antioxidants on the antioxidant activity of p-HBA as a function of the type of in the emulsion system with no significant difference with PCA. Hence, ening effect on the electron-withdrawing activity of the carboxyl it is expected that GA with the highest polarity among the pheno- substituent, alkyl ester groups were able to increase the antioxi- lics studied Table 2 incorporates a larger portion of its molecules dant activity, although their effectiveness was extensively affected to the aqueous phase of the emulsion system than to the water—oil by the environmental conditions of the test used to evaluate the interface.
This is in agreement with the polar paradox theory antioxidant performance. As for the polyphenolic derivatives, denoting that more polar antioxidants are less effective in more IHBs were considered as improving causes of the antioxidant per- polar media Porter, The obtained and lipid media experimented, exerted the same performance as results indicated the opposite roles for the hydrogen bonds in the PCA statistically and an activity close to that of GA in the emulsion o-methoxy phenolic derivatives.
Structure-antioxidant activity relationships of flavonoids: a re-examination
The anhydrous conditions of the bulk oil system caused the IHBs to form more extensively, whereas Table 4 the polar medium of the solvent used enhanced the intermolecular Kinetic parameters of hydroperoxide formation during the oxidation of the fish oil-in- hydrogen bonds. Mechanisms of the cardioprotective Methyl gallate Pathophysiology, Vanillic acid Oxidative kinetics of salmon oil in a-Tocopherol Process Biochemistry, a 45, — Establishment of a quantitative d Antioxidant activity, dimensionless.
Journal of Nenadis, N. Structure—antioxidant activity Pharmaceutical Sciences, 92, — The role of fish oils in the treatment of groups. Journal of Agricultural and Food Chemistry, 51, — Paradoxical behavior of antioxidants in food and biological Amsterdam: Chemical, physiological, nutritional de Heer, M.
Poly methoxy phenols in solution: