Antioxidant, pro-oxidant, cytotoxic and antimicrobial properties of selected plant phenolic compounds and resulting structure-activity relationships.

This study provides a comprehensive evaluation of the biological properties of six selected phenolic compounds: chlorogenic, caffeic, p-coumaric, rosmarinic, gallic and tannic acids. Their antioxidant potential was determined using DPPH, ABTS, FRAP, CUPRAC, lipid peroxidation inhibition and pro-oxidant assays, while antimicrobial activity was tested against Staphylococcus aureus and Candida albicans. In addition, cytotoxicity toward human skin melanoma A-375 cells and normal fibroblasts was examined, together with the assessment of intracellular ROS, GSH/GSSG ratio, thiol group content, and lipid peroxidation products. The results revealed clear structural dependence of biological activity, with the number and distribution of hydroxyl groups playing a decisive role. Tannic acid exhibited the strongest antioxidant and antimicrobial properties, while gallic and tannic acids showed the most pronounced cytotoxicity toward melanoma cells, accompanied by elevated oxidative stress and redox imbalance, with limited toxicity toward normal fibroblasts. These findings support the potential application of plant-derived phenolic compounds as natural agents with antioxidant, antimicrobial and anticancer activity, making them promising candidates for pharmaceutical and cosmetic use.