ИСТИНА

Humic substances (HS) are natural macroligands with major functionalities presented by carboxylic groups and phenolic moieties. As a result, HS enter redox and complexing interactions with metals mediating their migration and bioavailability in the environment. Recently, it has been revealed that these interactions can also facilitate formation and stabilization of metal-containing nanoparticles in natural waters and soils. Understanding of these processes might shed light on migration and toxicity of nanoparticles released into the environment. On the other side, reproduction of these processes in the lab might open new possibilities for a use of natural macromolecular compounds – humic substances – for synthesis of biocompatible and stabilized nanoparticles. The objectives of this study were to realize humics-assisted synthesis of nanoparticles of iron oxyhydroxide nanoparticles, and to study their structural properties, colloidal stability, and bioavailability. We conducted the humics-assisted synthesis of iron oxohydroxides nanoparticles – feroxyhyte (δ' FeOOH) and lepidocrocite (γ FeOOH). The synthesis was carried out by precipitation and oxidation of Fe(OH)n2-n + Fe(OH)m3-m suspension directly in the aqueous solutions of HS. The study of nanoparticles morphology in the presence of HS was conducted using transmission electron microscopy (TEM), X-ray absorption (XANES), and Moessbauer-spectroscopy. It was shown that in the presence of HS, plate-like feroxyhyte NPs with transversal size 20-30 nm and thickness up to 3 nm were formed. The NPs were encapsulated into humic associates composing organo-inorganic composites. In the absence of HS in the reaction mixture, uncontrolled growth of NPs up to submicron sizes (300-400 nm) was observed. It should be specifically noted that the encapsulated NPs of feroxyhyte possessed superparamagnetic properties. The assessment of bioavailability of the feroxyhyte nanoparticles stabilized by HS was studied using vegetation experiments. We used wheat plants (Triticun aestivum) as a test plant. We assesses biometric parameters such as weight of roots and sprouts, as well as chlorophyll fluorescence to judge on the plant conditions. We also measured the content of iron in the plants exposed to the control medium without iron, with inorganic iron (FeCl3) and with feroxyhyte stabilized with HS. It was shown that in the presence of the HS-stabilized feroxyhyte the biometric parameters were much better than in the control. The iron was substantially accumulated by roots and to the lesser extent – translocated into the leaves. The presented results allowed us to conclude on a substantial role of HS in the synthesis and transport of nanoparticles in the environment. The practical applications of this research might be a use of natural macroligands – humic substances – for synthesis of biocompatible and bioavailable nanoparticles of biogenic metals, which can serve as alternative to synthetic chelates in the production of microfertilizers.