## 4 Discussion
Larger variations in the size and shape of AgNPs that were mentioned when detailing the obtained results may be due to the presence of different plant extract molecules found on the surface of nanoparticles [42]. This can be explained by the different parts of the plant taken into study (flowers vs. leaves), the different obtaining conditions for both the extract and the AgNPs, and, therefore, by a different chemical composition of the extract and, implicitly, of the AgNPs surface. A larger size of AgNPs determined by DLS compared to TEM can be explained by the different principles of the two methods and by the fact that DLS measures the hydrodynamic size of AgNPs, which also includes the biomolecules found on the surface of nanoparticles. In both cases, the obtained Zeta potential values are negative and relatively high, which contributes to the stabilization of the nanoparticles' dispersion in solvents, given the similar surface charge that leads to electrostatic repulsion between nanoparticles, thus preventing agglomeration. Researchers suggest that secondary metabolites present in the extract may be involved in the stabilization of AgNPs, which, in our case, can be represented by polyphenic acids, flavonoids, carotenoids, and terpenes [44]. The Zeta potential of AgNPs-H\({}_{2}\)O and of AgNPs-EtOH is similar to the value obtained by [PERSON] et al. (\(-\)27.63 mV) for AgNPs synthesized using an aqueous extract from _T. erecta_ flowers [23]. 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH) has the ability to generate peroxyl radicals and induce oxidative stress by affecting the cell and its subcellular structures. Peroxyl radicals increase the rigidity of the red cell membrane and reduce its resistance. Studies in rats have shown the capacity of AAPH to induce hemolysis and to increase the number of carbonyl groups in proteins, thus, impairing tissue function. Peroxyl radicals cause the oxidation of fatty acids found in the structure of phospholipid membranes and the reduction of erythrocyte resistance [45]. The ethanolic extract and the AgNPs obtained using the aqueous extract show the best capacity to block the prooxidant action of AAPH, thus, protecting erythrocytes against peroxyl radicals. The protection induced by the ethanolic extract is close to that of gallic acid. The AgNPs synthesis increases the protective capacity of the aqueous extract from 48.48% (5 mg/mL) to 75.25% (5 mg/mL), but reduces that of the ethanolic extract by about five times, if considering EC\({}_{50}\) values. These variations could be determined by the different composition of the ethanolic and aqueous extracts, given the different solubility of natural compounds in the two used solvents. A recent study carried out by [PERSON] et al. indicated the ability of peptides in brown rice extract to block the action of AAPH by reducing the hemolysis from 70% (in the absence of the extract) to a maximum of 20% (in the presence of the extract) [46]. All peptides analyzed contained tyrosine, therefore, the phenolic hydroxyl group may be considered to be involved in the AAPH neutralization process. Such groups are also present in the structure of polyphenols and flavonoids found in the extracts analyzed in this study. The neutralization of peroxyl radicals generated by AAPH is usually performed by compounds that possess hydrogen donor functional groups such as hydroxyl and carboxyl groups, but especially hydroxyl groups [47]. Polyphenols from plant extracts have the capacity of neutralizing peroxyl radicals generated by AAPH, but at the same time, due to their ability to penetrate or attach to the hydrophilic region of the red cell membrane, can also slightly increase membrane fluidity and erythrocyte osmotic resistance, therefore, increasing the resistance to pro-oxidants [48].