Structure-antioxidant activity (oxygen radical absorbance capacity) relationships of phenolic compounds

Antioxidant capacity is the extent to which a compound can eliminate reactive oxygen species, and in vitro methods for its chemical evaluation have been proposed. Among these methods, the oxygen radical absorbance capacity (ORAC) assay comes close to the oxidation reaction in the living body because it generates radical species that mimic the lipid peroxyl radical involved in the peroxidation reaction of biological components and react in a phosphate buffer. In this study, PM7, a semi-empirical molecular orbital method, was used to calculate the thermodynamic properties (bond dissociation enthalpy, ionisation potential and proton affinity) associated with ORAC. We also applied the clusterwise linear regression analysis as a statistical method for grouping the antioxidants by structure. By analysing the data for antioxidants, the trend in the hydrophilic ORAC values was determined using the calculated structures and bond dissociation enthalpies of the groups classified according to the presence or absence of oxygen functional groups in the ortho position of phenol. Further studies of indicators other than bond dissociation enthalpy are needed to predict the ORAC of other antioxidants such as flavonoids and indoles.

Automated summary

This study used the semi-empirical molecular orbital method PM7 to calculate the thermodynamic properties associated with ORAC, and applied clusterwise linear regression analysis to group antioxidants based on their structure. By analyzing the data, the trend in hydrophilic ORAC values was determined based on the presence or absence of oxygen functional groups in the ortho position of phenol. Further research is needed to predict the ORAC of other antioxidants using indicators other than bond dissociation enthalpy.