Aguiar Antônio S N, Costa Luiz B, Borges Igor D, Aguirre Gerardo, Tejerina-Garro Francisco L, Dutra E Silva Sandro, Napolitano Hamilton B
Programa de Pós-Graduação em Recursos Naturais do Cerrado, Universidade Estadual de Goiás, Anápolis, Brazil.
Programa de Pós-Graduação em Sociedade, Tecnologia e Meio Ambiente, Universidade Evangélica de Goiás, Anápolis, Brazil.
Front Chem. 2023 Sep 19;11:1267634. doi: 10.3389/fchem.2023.1267634. eCollection 2023.
The green revolution model that is followed in the Brazilian Cerrado is dependent on mechanization, chemical fertilization for soil dressing and correction, and the use of herbicides. Paraquat is a methyl viologen herbicide marketed as bipyridylium dichloride salts and used (in low doses) to combat weeds in their post-emergence stage. It is a non-selective pesticide that causes the peroxidation of the lipids that make up the cell membrane, and when it comes into contact with foliage, it results in the death of the plant. The effect of water molecules co-crystallized in Paraquat salt structures was analyzed in anhydrous, dihydrate, and trihydrate forms to understand those physicochemical properties in its redox activity. The frontier molecular orbitals were also carried out using DFT to obtain the chemical reactivity of the bipyridylium cation. Finally, the supramolecular arrangements were evaluated to analyze the physicochemical stability and acquire insights on superoxide anions. The electronic structure indicated that the BP cation presents an acidic character due to its low ELUMO value, while the salt has a more basic character due to its high EHOMO value. For this reason, the BP ion is more susceptible to reduction during the weeds' photosynthesis process. During the process of plant photosynthesis, PQ is reduced to form a stable radical cation. In the supramolecular arrangement, the presence of water molecules increases the number of strong H-bonds, while the weak/moderate H-bonds are stabilized. PQ's toxic effects are observed in wildlife, domesticated animals, human populations, and ecosystems. The influence of PQ on the terrestrial environment is limited because of the soil adsorption capacity associated with good agricultural practices. The current use of good agricultural practices in the Cerrado seems not to prevent the environmental impacts of herbicides like PQ because it aims for the expansion and profitability of large-scale farming based on input-intensive practices instead of sustainable agriculture processes.
巴西塞拉多地区采用的绿色革命模式依赖于机械化、用于土壤改良和校正的化学施肥以及除草剂的使用。百草枯是一种甲基紫精除草剂，以二氯化联吡啶盐的形式销售，（低剂量）用于防治杂草出苗后的生长。它是一种非选择性农药，会导致构成细胞膜的脂质发生过氧化反应，当它与叶片接触时，会导致植物死亡。分析了百草枯盐结构中共结晶的水分子在无水、二水合物和三水合物形式下的作用，以了解其氧化还原活性中的那些物理化学性质。还使用密度泛函理论（DFT）对前沿分子轨道进行了研究，以获得联吡啶阳离子的化学反应性。最后，对联分子排列进行了评估，以分析物理化学稳定性并深入了解超氧阴离子。电子结构表明，由于其较低的最低未占分子轨道（ELUMO）值，联吡啶阳离子具有酸性特征，而盐由于其较高的最高已占分子轨道（EHOMO）值而具有更强的碱性特征。因此，在杂草的光合作用过程中，联吡啶阳离子更容易被还原。在植物光合作用过程中，百草枯被还原形成稳定的自由基阳离子。在超分子排列中，水分子的存在增加了强氢键的数量，而弱/中等氢键则得到了稳定。百草枯的毒性作用在野生动物、家畜、人类群体和生态系统中都有观察到。由于与良好农业实践相关的土壤吸附能力，百草枯对陆地环境的影响是有限的。目前在塞拉多地区采用的良好农业实践似乎无法防止像百草枯这样的除草剂对环境的影响，因为它旨在通过投入密集型实践实现大规模农业的扩张和盈利，而不是可持续农业过程。
