ИСТИНА

This study was aimed to estimate of the effect of hydrodynamic diameter and surface charge on bioactivity of Fe3O4 NPs modified by various ligands (humic acids, HA and 3-aminopropyltriethoxysilane, APTES). Behaviors of NPs were investigated in the aspects of their toxicity to Sinapis alba and Paramecium caudatum. Fe3O4 NPs were prepared by a chemical coprecipitation in situ from FeCl2 and FeCl3 in the presence of NH4OH. The NPs formulated by sol-gel method were Fe3O4-APTES (Ar) and Fe3O4-APTES (air) (various formulation conditions: in argon or air atmosphere, drying in at 70 °C in vacuum or 150 °C). The zeta potential and hydrodynamic diameter data were determined by dynamic light scattering. According data of FTIR spectroscopy, there are free aminogroups onto the Fe3O4-APTES NPs surface. With HA increasing, the isoelectric point (IEP, pH at ξ=0) for Fe3O4 shifts to the acid region. The charge of Fe3O4-HA at pH=6 changes and becomes negative. Thus, at a Fe3O4-HA ratio as 1: 4 (full coverage of Fe3O4 NPs with HA), the surface charge at pH=6 equals −39 mV. At similar amount of HA for Fe3O4-APTES ξ~ equals +2 mV at pH 6. The EC20 parameter for NPs with positive charge (Fe3O4, Fe3O4-APTES (air) and Fe3O4- APTES (Ar), ξ= +10 mV and +17 mV, respectively) higher then EC20 for NPs with negative charge (HA, ξ= −37 mV). It means that NPs with positive charge surface are less toxic towards infusorians in compare with ones for negative charge surface, and Fe3O4-HA demonstrated stimulation towards infusorians. The greater toxicity of Fe3O4-APTES-HA in comparison with other negatively charged NPs can be explained by the insufficient coating of the surface with HA. So, HA has mitigation effect on toxicity of magnetite NPs. It has been shown that nanoparticles with zeta potential near IEP have greater toxicity. The primary amines on the surface of the Fe3O4-APTES give rise to the large positive surface charge and have previously been reported to cause a toxic effect. The reduction in toxicity observed in the humic acids coated particles arises due to the decreased surface charge. Higher plants turned out to be less sensitive to the selected nanoparticles at all range of concentrations, while the nanoparticles showed toxic effects in relation to the ciliates at concentrations of more than 0.1%. Acknowledgement. This research has been financed by the Russian Foundation for Basic Research (#19-33-90149). Thanks to Pavel Uchanov for providing test cultures