# Antimicrobial Effect of Submicron Complex Oxide Particles CsTeMoO\({}_{6}\) under Visible Light
## 4 Discussion  
This section presents data enabling us to postulate and elucidate the potential mechanisms of the antimicrobial activity of the compound under investigation, as well as the uncertainty in demonstrating the antimicrobial effect based on the metal's nature and on the anatomical-morphological and physio-biochemical characteristics of the microorganism group under investigation. Previously [24], the antimicrobial properties of submicron particles of WO\({}_{3}\) and RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) were studied. It has been shown that the survival rate of bacteria and fungi decreased under dark and light conditions. Moreover, under the conditions of using light sources in the visible spectrum of different powers, there was an observed improvement in the antimicrobial ability of these compounds. It has been shown that reducing the particle size of RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) enhances its antimicrobial effect. The duration of exposure also influenced the degree of vital activity of bacteria and fungi. Regarding the mechanisms of antimicrobial action on the metabolism of microorganisms, the literature provides the following information. Nano- and submicron particles of metal oxides can cause the death of microorganisms, and they exhibit an antimicrobial effect without light exposure [22; 23; 25; 26; 27; 28]. Nano- and submicron particles of oxides can not only lead to the destruction of the cell wall and membrane of microorganisms due to electrostatic interactions, but they can also penetrate inside the cell and damage organelles (mitochondria and ribosomes) and, causing condensation and margination of chromatin, lead to the apoptotic death of the cell [29]. Also, nanoparticles can permeate through the cell membrane of microorganisms and bind to transport proteins to disrupt the operation of proton pumps [30], and they can inactivate phosphorus- and sulfur-containing enzymes and DNA. Nanoparticles play an important role in inhibiting ATP and reducing the number of copies of the bacterial 16S rDNA gene [31]. The toxicity of nano- and submicron metal oxides particles against fungi and bacteria increases under light. This means that there is the formation of reactive oxygen species (ROS) as a result of photocatalytic activity that can inhibit the vital activity of microorganisms [32; 33]. According to [34], complex oxide CsTeMoO\({}_{6}\) has a wide band gap of \(\sim\)3.1 eV, which corresponds to the UV range. However, combining the results of reflection and transmission spectroscopy allows us to conclude that the compound inside the band has two impurity-defect levels with energies of 2 and 2.6 eV [34; 35]. Due to these levels, the CsTeMoO\({}_{6}\) compound can absorb visible light with the formation of electron-hole pairs on its surface, which lead to oxidation reactions and organic compounds, which we have shown using the example of methylene blue and methyl orange dyes [34] (Figure 6). Figure 6 illustrates the mutual arrangement of the electronic levels of the CsTeMoO\({}_{6}\) and RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) compounds relative to the main redox potentials of water \(\bullet\)O\({}_{2}\)\({}^{-}\)/O\({}_{2}\) (\(-\)0.2 V) and \(\bullet\)OH/H\({}_{2}\)O (2.37 V) [36]. Both complex oxides can form simultaneously hydroxyl and superoxide radicals upon absorption of visible light.