Organophosphorus compounds (OP) are chemicals widely used as pesticides in different applications such as agriculture and public health (vector control), and some of the highly toxic forms have been used as chemical weapons. After application of OPs in an environment, they persist for a period, suffering a degradation process where the biotic factors are considered the most relevant forms. However, to date, the biodegradation of OP compounds is not well understood. There are a plenty of structure-based biodegradation estimation methods, but none of them consider enzymatic interaction in predicting and better comprehending the differences in the fate of OPs in the environment. It is well known that enzymatic processes are the most relevant processes in biodegradation, and that hydrolysis is the main pathway in the natural elimination of OPs in soil samples. Due to this, we carried out theoretical studies in order to investigate the interactions of these OPs with a chosen enzyme-the phosphotriesterase. This one is characteristic of some soils' microorganisms, and has been identified as a key player in many biodegradation processes, thanks to its capability for fast hydrolyzing of different OPs. In parallel, we conducted an experiment using native soil in two conditions, sterilized and not sterilized, spiked with specific amounts of two OPs with similar structure-paraoxon-ethyl (PXN) and O-(4-nitrophenyl) O-ethyl methylphosphonate (NEMP). The amount of OP present in the samples and the appearance of characteristic hydrolysis products were periodically monitored for 40 days using analytical techniques. Moreover, the number of microorganisms present was obtained with plate cell count. Our theoretical results were similar to what was achieved in experimental analysis. Parameters calculated by enzymatic hydrolysis were better for PXN than for NEMP. In soil, PXN suffered a faster hydrolysis than NEMP, and the cell count for PXN was higher than for NEMP, highlighting the higher microbiological toxicity of the latter. All these results pointed out that theoretical study can offer a better comprehension of the possible mechanisms involved in real biodegradation processes, showing potential in exploring how biodegradation of OPs relates with enzymatic interactions.

Department of Chemistry Faculty of Science University of Hradec Kralove 50003 Hradec Kralove Czech Republic

Federal Institute of Education Science and Technology Avenida Ministro Salgado Filho 1000 Soteco Vila Velha 29106 010 Espírito Santo Brazil Federal University of Espirito Santo Unit Goiabeiras Vitória 29075 910 Espírito Santo Brazil

Institute of CBRN Defense Avenida das Américas 28705 Rio de Janeiro 23020 470 Brazil

Laboratory of Molecular Modeling Applied to Chemical and Biological Defense Praça General Tibúrcio 80 Rio de Janeiro 22290 270 Brazil

Laboratory of Molecular Modeling Applied to Chemical and Biological Defense Praça General Tibúrcio 80 Rio de Janeiro 22290 270 Brazil Department of Chemistry Faculty of Science University of Hradec Kralove 50003 Hradec Kralove Czech Republic

Natural Products Research Institute Avenida das Américas 28705 Rio de Janeiro 23020 470 Brazil

Natural Products Research Institute Avenida das Américas 28705 Rio de Janeiro 23020 470 Brazil Department of Chemistry Faculty of Science University of Hradec Kralove 50003 Hradec Kralove Czech Republic

Natural Products Research Institute CCS Bloco H Cidade Universitária Rio de Janeiro 21941 902 Brazil

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