ИСТИНА

Plant extracts contain a potent array of various metabolites, including terpenoids, polyphenols, sugars, alkaloids, phenolic acids, and proteins, which can bioreduce metal ions into nanoparticles. We report the synthesis of amorphous iron nanoparticles from iron salts in aqueous extracts of dicotyledonous (Nicotiana benthamiana) and monocotyledonous (Hordeum vulgare) plants, and also discuss their characterization using TEM, SAED, DLS, XRD and EELS. H. vulgare extracts produced smaller nanoparticles (average diameter of 10 nm) than was observed in N. benthamiana (average diameter of 20 nm). Subsequent XPS analysis of the nanoparticles revealed that the binding energies for 2p iron electrons were typical for Fe3O4 iron oxide, where iron atoms were contained in combined (II and III) oxidation states. These iron nanoparticles were found to be intrinsically unstable and prone to aggregation: one hour after synthesis the hydrodynamic diameter of the nanoparticles increased by more than 10 times. It was subsequently found that addition of 40 mM citrate buffer pH 3.0 into plant extracts leads to longterm nanoparticle stability. The differences in the sizes of nanoparticles measured using TEM and DLS methods, likely indicates the presence of organic components in their composition. Using AFM analysis, textural differences between the extracts were identified: H. vulgare contained smaller nanosized organic aggregates to a higher level than N. benthamiana. We suggest that these aggregates might act as nucleation sites, with their different morphologies and numbers likely accounting for the differential modulation of iron nanoparticle formation. This research was supported by the RFBR grant 14-04-01448 A and Grant of the President of the Russian Federation for supporting of young scientists MK-2072.2014.4