Spectral, experimental-toxicological and quantum-chemical studies of predictors of biological activity of titanium-containing nanoparticles doped with silver

The aim: to study the influence of structural, spectral and quantum-chemical parameters of the synthesized TiO2, TiO2/Ag (4 wt. %) and TiO2/Ag (8 wt. %) nanosystems on biological activity. Materials and methods. The structural-morphological, spectral, toxicological and cytotoxic properties of TiO2 nanomaterials with silver content in the range from 0 wt % to 8 wt. % for the direction of human biosafety were investigated. The TiO2/Ag composites were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and the results of high-level quantum chemical calculations. Results. The optical activity of the TiO2/Ag composite was determined by Raman spectroscopy, which is confirmed by the shift in the Eg1 mode frequency from 143 cm-1 to 157 cm-1 and the FWHM in the range from 12 cm-1 to 19 cm-1 due to the decrease in the size of the TiO2 crystallites. The mode shift in nano-TiO2/Ag reflects a certain deformation of the anatase-modified titanium dioxide crystal lattice upon doping with silver. This leads to an increase in the ability to produce reactive oxygen species on the surface of the TiO2/Ag nanoparticle and to an increase in biological activity (4 wt. % Ag; 8 wt. % Ag) compared to undoped TiO2, providing an increase in their toxicity, which is confirmed by the values LD50, CC50 parameters, respectively. According to the results of quantum chemical calculations, it was established that during the adsorption of the Ag2 dimer on the surface of anatase in the Ti15O41H22Ag2 adsorption complex, two Ag atoms are involved with the formation of four Ag–O bonds, the length of which with the two-coordinated oxygen atoms of the TiO2 surface is 2.44 Å, and the Ag–Ag bond length increases to 2.75 Å, compared to the equilibrium distance in the diatomic Ag2 molecule (2.53 Å). This indicates the vibrationally excited state of the Ag2 diatomic fragment in the Ti15O41H22Ag2 adsorption complex. It should also be noted that the ionization potential of the adsorption complex decreased from 7.35 eV to 5.72 eV. The result of such changes is the increased reactivity of argentum atoms compared to their reactivity in the diatomic Ag2 molecule. Due to the fact that silver atoms adsorbed on the surface of anatase nanoparticles act as electron traps, the efficiency of separation of photogenerated electron-hole pairs (excitons) with interphase electron transfer increases, which increases the photocatalytic and biocidal properties of silver-doped anatase. Conclusions. There is a certain objective relationship between the physicochemical parameters of nanoparticles and their biological activity, which can be characterized not only qualitatively, but also quantitatively. Thus, in the materials of our research, the influence of their size, specific surface area, the presence of hydroxyl groups on the surface of the nanoparticle, the size of crystallites, the size of interatomic bonds, and the ionization potential on the toxicity of nanoparticles has been demonstrated. These data are of great scientific importance not only in terms of their hygienic regulation, but also in terms of further synthesis of safer nanomaterials.