Antioxidant Activity of Selected Phenolic Acids–Ferric Reducing Antioxidant Power Assay and QSAR Analysis of the Structural Features

Abstract

<jats:p>Phenolic acids are naturally occurring compounds that are known for their antioxidant and antiradical activity. We present experimental and theoretical studies on the antioxidant potential of the set of 22 phenolic acids with different models of hydroxylation and methoxylation of aromatic rings. Ferric reducing antioxidant power assay was used to evaluate this property. 2,3-dihydroxybenzoic acid was found to be the strongest antioxidant, while mono hydroxylated and methoxylated structures had the lowest activities. A comprehensive structure–activity investigation with density functional theory methods elucidated the influence of compounds topology, resonance stabilization, and intramolecular hydrogen bonding on the exhibited activity. The key factor was found to be a presence of two or more hydroxyl groups being located in ortho or para position to each other. Finally, the quantitative structure–activity relationship approach was used to build a multiple linear regression model describing the dependence of antioxidant activity on structure of compounds, using features exclusively related to their topology. Coefficients of determination for training set and for the test set equaled 0.9918 and 0.9993 respectively, and Q2 value for leave-one-out was 0.9716. In addition, the presented model was used to predict activities of phenolic acids that haven’t been tested here experimentally.</jats:p>

Approach to Optimization of FRAP Methodology for Studies Based on Selected Monoterpenes

“…In accordance with Spiegel et al [ 17 ], lower FRAP assay activity was observed for methylated compounds compared to their nonmethylated counterparts. The authors explained this phenomenon by stating that the methylation process decreases the activity of electron- and hydrogen-donating groups.…”

“…In the presented studies, the highest reduction activity was observed for cyclic hydrocarbon terpenes with conjugated double bonds without single electron transfer (SET) moiety characteristics (with the exception of γ-terpinene without the moiety) ( Figure 3). In accordance with Spiegel et al [17], lower FRAP assay activity was observed for methylated compounds compared to their nonmethylated counterparts. The authors explained this phenomenon by stating that the methylation process decreases the activity of electron-and hydrogen-donating groups.…”

“…Simultaneously, they noticed that along with decreasing distance between carboxylic groups and ring formation, the influence of methylation increased. In a study of the terpene structure, it was In accordance with Spiegel et al [17], lower FRAP assay activity was observed for methylated compounds compared to their nonmethylated counterparts. The authors explained this phenomenon by stating that the methylation process decreases the activity of electron-and hydrogen-donating groups.…”

L‐Carnitine‐Based Bio‐Ionic Liquids as Antioxidants

“…Methylation of the cinnamic acid derivatives has no significant influence on the antioxidant activity. The opposite relationship occurs in the case of IL 5 based on syringic acid, which has much lower activity compared to the ILs containing the anions derived from non‐methylated benzoic acids [59] …”

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“…Mono-hydroxy phenols are also fairly ineffective at this reduction, generally at least two orders of magnitude lower, as the monohydroxy compounds do not easily oxidize to the quinone form, and meta-dihydroxy compounds are also weak for the same reason. [ 17 ].…”