Theoretical and Experimental Studies of the Antioxidant and Antinitrosant Activity of Syringic Acid

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 center dot, HOO center dot, NO, and NO2 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 x 10(9) and 9.77 x 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(culculated)/k(experimental) ratio of 0.3, thus the computed kinetic data are reasonably accurate. SA exhibited excellent HOO center dot and NO 2 scavenging activity in water (k(overall)(HOO center dot) = 1.53 x 10(-8) M-1 s(-1) and k(overa)(ll) (NO2) = 1.98 x 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 center dot 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.