Syringic acid (SA) is a natural phenolic acid found in vegetables, fruits, and other plant-based foods. A range of biological activities were proposed for this compound including anticancer, antimicrobial, anti-inflammation, and anti-diabetic activities, as well as antioxidant and antinitrosant properties. In this study, the focus is on the latter two. The HO • , HOO • , NO, and NO 2 scavenging activities of SA were evaluated in physiological environments by kinetic and thermodynamic calculations. The computed rate constants of the HO • radical scavenging of SA were 4.63 × 10 9 and 9.77 × 10 7 M −1 s −1 in polar and nonpolar solvents, respectively. A comparison with the experimentally determined rate constant in aqueous solution yields a k calculated /k experimental ratio of 0.3, thus the computed kinetic data are reasonably accurate. SA exhibited excellent HOO • and NO 2 scavenging activity in water (k overall (HOO • ) = 1.53 × 10 8 M −1 s −1 and k overall (NO 2 ) = 1.98 × 10 8 M −1 s −1 ), whereas it did not show NO scavenging activity in any of the studied environments. In lipid medium, SA exhibited weak activity. Thus, in polar environments, the HOO • radical scavenging of SA is 1.53 times higher than that of ascorbic acid. Consistently, SA is a promising antioxidant and antinitrosant agent in polar environments.

The antiradical properties of 5-HMF in the gas-phase and in physiological environments were examined by thermodynamic and kinetic calculations.

Oxidative stress is implicated in aging and aging-related diseases, including cancer.

Antioxidants are a diverse group of chemicals with proven health benefits and thus potential preventive medicine and therapeutic applications. While most of these compounds are natural products, determining their mechanism of radical scavenging and common motifs that contribute to antioxidant activity would allow the rational design of novel antioxidants. Here the origins of the antioxidant properties of ten natural products of the lignan family were studied in silico by calculating their thermochemical properties by using ROB3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) model chemistry. Three conditions were modelled: gas phase, ethanol and water solvents. The results allowed assigning the antioxidant activity to specific moieties and structural features of these compounds. It was found that the benzylic hydrogen atoms are the most likely to be abstracted to form radicals and hence define antioxidant properties in most of the studied compounds. The results also suggested that the most likely mechanism of HOO• radical scavenging differs by the key moiety: it is hydrogen atom transfer in case the benzylic C-H bonds, however it is proton coupled electron transfer in case of the compounds where O-H bonds are responsible for radical scavenging.