Abstract
The antioxidant capacity of an antioxidant reflects its ability to remove reactive oxygen species (ROS). In this study, the hydrophilic oxygen radical absorbance capacity (H-ORAC) method was used to quantitatively evaluate the antioxidant capacities of natural phenols and their derivatives against peroxyl radicals. This method was comprehensively applied to low-molecular-weight phenols to construct a database. Although no macroscopic correlation was observed for values related to the antioxidant capacity expression, we observed a difference in the trend of the H-ORAC values for each functional group. Thus, this database will serve as a new benchmark and tool for molecular design.
Highlights
In organisms, the oxygen consumed by breathing is converted to reactive oxygen species (ROS), including hydroxyl radicals, peroxides, singlet oxygen species, peroxy radicals, and hydroperoxide, and this process is promoted by external stimuli.[1]
The ionization potential (IP) and electron-transfer enthalpy (ETE) values do not correlate with the hydrophilic oxygen radical absorbance capacity (H-oxygen radical absorbance capacity (ORAC)) values because the reactions occur in a neutral environment with the involvement of electrons, while the steric factors of the molecules do not participate (Fig. 3 and 4)
It is inferred that there is a negative correlation between a small bond dissociation enthalpy (BDE) and a HORAC value, even though there is no correlation in reality (Fig. 5)
Summary
The oxygen consumed by breathing is converted to reactive oxygen species (ROS), including hydroxyl radicals, peroxides, singlet oxygen species, peroxy radicals, and hydroperoxide, and this process is promoted by external stimuli.[1]. The oxygen radical absorbance capacity (ORAC) assay is a key method employed to measure the antioxidant capacities of compounds against peroxyl radicals In this method, the antioxidant capacity is measured by evaluating the inhibition of the uorescent probe degradation by the peroxyl radicals produced from 2,20-azobis(2-amidinopropane) dihydrochloride (AAPH).[2] In this method, radical species that mimic lipid peroxyl radicals are generated, and the uorescence decay over time is measured. Depending on the type of antioxidant, the decay behavior of the uorescence intensity can change in the ORAC measurement In this context, a previous study reported an induction or lag time before the decrease in the uorescence intensity, with some compounds exhibiting a rapid decrease a er the lag time (e.g., trolox or trans-ferulic acid) or a gradual decrease without the lag time (e.g., catechin).[11] This phenomenon is observed due to the structural differences between the antioxidants, which allow them to react rapidly or persistently with peroxyl radicals. We estimate the effect of each functional group by examining changes in the ORAC value
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