The abuse of tetracycline antibiotics (TCs) has caused serious environmental pollution and risks to public health. Degradation of TCs by cold atmospheric plasmas (CAPs) is a high efficiency, low energy consumption and environmentally friendly method. In this study, a reactive molecular dynamics (MD) simulation is applied to study the interactions of reactive oxygen species (ROS) produced in CAPs and TCs (including tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and demeclocycline (DMC)). As revealed by the simulation data at the atomic level, the main reaction sites on TCs are the C2 acylamino, the C4 dimethylamine, the C6 methyl group, the C8 site on the benzene ring and the C12a tertiary alcohol. The interaction between ROS and TCs is usually initiated by H-abstraction, followed by the breaking and formation of the crucial chemical bonds, such as the breaking of C-C bonds, C-N bonds and C-O bonds and the formation of C=C bonds and C=O bonds. Due to the different structures of TCs, when the ROS impact OTC, CTC and DMC, some specific reactions are observed, including carbonylation at the C5 site, dechlorination at the C7 site and carbonylation at the C6 site, respectively. Some degradation products obtained from the simulation data have been observed in the experimental measurements. In addition, the dose effects of CAP on TCs by adjusting the number of ROS in the simulation box are also investigated and are consistent with experimental observation. This study explains in detail the interaction mechanisms of degradation of TCs treated by CAPs with the final products after degradation, provides theoretical support for the experimental observation, then suggests optimization to further improve the efficiency of degradation of TCs by CAPs in applications.
Antibiotic pollution has received increasing global and scientific attention in recent years due to its serious impact on ecosystems and human health. As a new advanced oxidation method, Cold Atmospheric Plasmas (CAPs) have been successfully applied to degrade oxytetracycline (OTC) with a large removal rate, high energy efficiency, and environment-friendly requirements; however, the reaction pathways are still unclear. In this study, a reactive Molecular Dynamics (MD) simulation is performed to investigate the mechanisms of OTC degradation induced by Reactive Oxygen Species (ROS) in CAPs. The simulations showed the breaking of chemical bonds upon the impact of ROS, such as C–C, C–N, and C–O. In particular, the removal of important functional groups, including the acylamino at the C2 site, the dimethylamine at the C4 site, and the tertiary alcohol at the C12a site, is observed, and the destruction of these key structures indicates the degradation of OTC by reducing the antibacterial ability. The final products revealed by the computational data agree well with the experimental measurements. The dose effects on OTC degradation are also examined by adjusting the numbers of ROS in the simulation box. This study can further enhance the understanding of OTC degradation induced by CAP according to the reactive MD simulation results, unveiling the key pathways of OTC degradation.
Low-energy radiation is primarily involved in the spent fuel treatment process in a specific nuclear facility, but if it is not shielded, it will still have an impact on worker health. In light of this unique low-energy environment, the Monte Carlo simulation software geant4 is used to simulate and calculate the effect of doping many rare earth elements into glove rubber materials on the shielding effect of low-energy gamma radiation. The results show that some rare earth elements have a good gamma radiation shielding effect, and their chemical toxicity is lower than that of the traditional shielding material lead. This paper demonstrates that selecting rare earth materials for glove box gloves in a suitable energy range is reasonable, and that incorporating suitable rare earth elements into glove materials can improve the energy attenuation rate of composite protective materials. Experiments are used to create the material that can be used to make glove box gloves. The radiation shielding experiment shows that this material's shielding rate to 59.5keV energy can reach 33%~41%, and its other physical properties are good. Based on this finding, we believe that this material can be used to replace lead-containing gloves in some situations and can be used to design related shielding and protective equipment.
Plasma medicine is a rapidly growing multidisciplinary field, which mainly focuses on the application of Cold Atmospheric Plasma (CAP) in bioengineering. Several experiments have suggested that amino acids in proteins are excellent targets for plasma-derived chemical species. To gain a deep insight into the oxidative modification of proteins induced by CAP, a ReaxFF-based reactive Molecular Dynamics simulations are performed to investigate the reaction mechanism of Reactive Oxygen Species produced in CAP and the model peptides. The simulation results show that sulfur-containing amino acids with high reactivity could be oxidized to sulfuric acid moiety through sulfonation, and only H-abstraction reaction can take place for aromatic amino acids. The oxidation of five-membered ring amino acids could be observed by yielding the ring-open products in the simulations. Additionally, the dehydrogenation and hydroxylation of carbon-chain amino acids were also found from the simulations, with the formation of the hydroxyl group. The polar amino acids with the electron-rich structure were oxidized to a variety of products, such as di-hydroxylated lysine and hydroxylated asparagine. This study provides a crucial step to understand the processes of oxidative modifications and inactivation of proteins induced by CAP, showing a deep insight on the mechanism of plasma medicine.
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