Influence of the geometric isomers on the radical scavenging properties of 3,5-dicaffeoylquinic acid: A DFT study in vacuo and in solution

3,5-Dicaffeoylquinic acid (diCQA) is a part of the chlorogenic acid group of compounds, largely isolated from food sources and possessing potent antioxidant activity. Only the trans-trans isomer exists in nature, however, abiotic stresses, such as UV-radiation, give rise to cis isomers. There have been no reports on the antioxidant activity of the cis isomers. The current study, performed using the B3LYP/6-311+G(d,p) method, is aimed at investigating and comparing the antioxidant properties of the geometrical isomers of 3,5-diCQA. The study is conducted by checking the molecules' ability for two main radical scavenging mechanisms, hydrogen atom transfer (HAT) and electron transfer (ET). A separate DPPH assay experimental study performed in this study shows that all the geometrical isomers are potent radical scavengers. The lowest O-H bond dissociation enthalpy value (70.599 kcal/mol) corresponds to the trans-trans isomer and is comparable to that of gallic acid, a commercially available antioxidant. The lowest ionization potential value corresponds to the cis-cis isomer (149.54kcal/mol), indicating that it is best antioxidant, in terms of ET mechanism.