Green Synthesis of Silver Nanoparticles from Stachys setifera subsp. lycia: Characterization, Antioxidant Activity,...

In this study, the antioxidant activities (DPPH˙, ABTS˙⁺, and FRAP) of water extract and synthesized silver nanoparticles (AgNP) from Stachys setifera subsp. lycia (Ss) were investigated for the first time. UV-vis spectroscopy, FT-IR, XRD, and TEM were used to characterize the nanoparticles. In addition, the interactions of the compounds determined as major components in the LC-ESI-MS/MS analysis of extract with antioxidant enzymes (glutathione reductase and superoxide dismutase) were theoretically calculated in silico studies. According to the results of the antioxidant assay, AgNP (12.19 µg/mL, 5.78 µg/mL, and 3.61 μ mol TE/mg) showed higher activity than the extract (15.10 µg/mL, 12.71 µg/mL, and 2.78 μ mol TE/mg) in DPPH˙, ABTS˙⁺, and FRAP analysis, respectively. Chlorogenic acid (203.1989 µg/g extract) was determined as the major component in the LC-ESI-MS/MS analysis. The main compound, chlorogenic acid, was oxidized and silver ions (⁺¹) were reduced to silver. In addition, the silver was stabilized and capped by the corresponding compound. Chlorogenic acid and possible chlorogenic acid-AgNP complex showed a high affinity for the enzyme glutathione reductase. The results showed that the AgNPs obtained from S. setifera had higher antioxidant properties than the extract and that the chlorogenic acid was theoretically a glutathione reductase inhibitor.