Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, United States.
Environ Sci Technol. 2013 Feb 5;47(3):1357-64. doi: 10.1021/es303895w. Epub 2013 Jan 15.
Manganese(III) geocomponents are commonly found in the soil environment, yet their roles in many biogeochemical processes remain unknown. In this study, we demonstrated that Mn(III) generated from the reaction of MnO(2) and oxalic acid caused rapid and extensive decompositions of a quinoxaline-di-N-oxide antibiotics, viz carbadox. The reaction occurred primarily at the quinoxaline-di-N-oxide moiety resulting in the removal of one -O from N1-oxide and formation of desoxycarbadox. The reaction rate was accelerated by increasing amounts of Mn(III), carbadox and oxalate. The critical step in the overall reaction was the formation of a quinoxaline-di-N-oxide/Mn(III)/oxalate ternary complex in which Mn(III) functioned as the central complexing cation and electron conduit in which the arrangement of ligands facilitated electron transfer from oxalate to carbadox. In the complex, the C-C bond in oxalate was cleaved to create CO(2)(-•) radicals, followed by electron transfer to carbadox through the Mn(III) center. This proposed reaction mechanism is supported by the reaction products formed, reaction kinetics, and quantum mechanical calculations. The results obtained from this study suggest that naturally occurring Mn(III)-oxalic acid complexes could reductively decompose certain organic compounds in the environment such as the antibiotic quinoxaline-di-N-oxide.
锰(III)地质成分在土壤环境中很常见，但它们在许多生物地球化学过程中的作用仍然未知。在这项研究中，我们证明了 MnO(2)和草酸反应生成的 Mn(III)会导致喹喔啉二 N-氧化物抗生素（如卡巴多）迅速广泛分解。反应主要发生在喹喔啉二 N-氧化物部分，导致 N1-氧化物上的一个-O 被去除，并形成去氧卡巴多。增加 Mn(III)、卡巴多和草酸盐的量会加速反应速率。整个反应的关键步骤是形成喹喔啉二 N-氧化物/Mn(III)/草酸盐三元络合物，其中 Mn(III)作为中心配位阳离子和电子导管，其配体的排列促进了电子从草酸盐向卡巴多的转移。在该络合物中，草酸盐中的 C-C 键被切断，生成 CO(2)(-•)自由基，然后通过 Mn(III)中心向卡巴多转移电子。这一反应机制得到了反应产物、反应动力学和量子力学计算的支持。这项研究的结果表明，天然存在的 Mn(III)-草酸复合物可能会在环境中还原分解某些有机化合物，如抗生素喹喔啉二 N-氧化物。
