Manganese oxides, typically similar to δ-MnO₂, form in the aquatic environment at near neutral pH via bacterially promoted oxidation of Mn(II) species by O₂, as the reaction of [Mn(H₂O)₆]²⁺ with O₂ alone is not thermodynamically favorable below pH of ~ 9. As manganese oxide species are reduced by the triphenylmethane compound leucoberbelein blue (LBB) to form the colored oxidized form of LBB (λ_max = 623 nm), their concentration in the aquatic environment can be determined in aqueous environmental samples (e.g., across the oxic–anoxic interface of the Chesapeake Bay, the hemipelagic St. Lawrence Estuary and the Broadkill River estuary surrounded by salt marsh wetlands), and their reaction progress can be followed in kinetic studies. The LBB reaction with oxidized Mn solids can occur via a hydrogen atom transfer (HAT) reaction, which is a one-electron transfer process, but is unfavorable with oxidized Fe solids. HAT thermodynamics are also favorable for nitrite with LBB and MnO₂ with ammonia (NH₃). Reactions are unfavorable for NH₄⁺ and sulfide with oxidized Fe and Mn solids, and NH₃ with oxidized Fe solids. In laboratory studies and aquatic environments, the reduction of manganese oxides leads to the formation of Mn(III)-ligand complexes [Mn(III)L] at significant concentrations even when two-electron reductants react with MnO₂. Key reductants are hydrogen sulfide, Fe(II) and organic ligands, including the siderophore desferioxamine-B. We present laboratory data on the reaction of colloidal MnO₂ solutions (λ_max ~ 370 nm) with these reductants. In marine waters, colloidal forms of Mn oxides (< 0.2 µm) have not been detected as Mn oxides are quantitatively trapped on 0.2-µm filters. Thus, the reactivity of Mn oxides with reductants depends on surface reactions and possible surface defects. In the case of MnO₂, Mn(IV) is an inert cation in octahedral coordination; thus, an inner-sphere process is likely for electrons to go into the empty e ^*_g conduction band of its orbitals. Using frontier molecular orbital theory and band theory, we discuss aspects of these surface reactions and possible surface defects that may promote MnO₂ reduction using laboratory and field data for the reaction of MnO₂ with hydrogen sulfide and other reductants.

中文翻译：

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还原锰的氧化物：一对两个电子转移步骤的热力学，动力学和机理考虑

锰的氧化物，典型地类似于δ -MnO ₂经由锰（II）物质的细菌促进氧化被O，形式在接近中性pH值的水生环境₂，作为[锰（H反应₂ O）₆ ] ²⁺与ø ₂作为氧化锰物种是由三苯基甲烷化合物leucoberbelein蓝色（LBB）还原以形成LBB的着色氧化形式单独不低于〜9的pH值热力学有利的（λ_最大 = 623 nm），可以在水性环境样品中确定它们在水生环境中的浓度（例如，切萨皮克湾，半劳斯河圣劳伦斯河口和被盐沼湿地包围的Broadkill河口的有氧-缺氧界面），在动力学研究中可以跟踪它们的反应进程。Mn固体氧化物的LBB反应可以通过氢原子转移（HAT）反应发生，这是一个单电子转移过程，但对Fe固体氧化物不利。HAT热力学对LBB的亚硝酸盐和NH _3的MnO ₂也是有利的。NH ₄ ⁺和硫化物与氧化的Fe和Mn固体以及NH _3的反应不利与氧化的铁固体。在实验室研究和水生环境中，即使二电子还原剂与MnO ₂反应，锰氧化物的还原也会导致形成大量浓度的Mn（III）-配体络合物[Mn（III）L] 。关键还原剂是硫化氢，Fe（II）和有机配体，包括铁载体去铁敏胺-B。我们对胶体的MnO的反应本实验室数据₂溶液（λ_最大 〜370 nm）的与这些还原剂。在海水中，未检测到胶体形式的Mn氧化物（<0.2 µm），因为Mn氧化物被定量捕集在0.2 µm的过滤器上。因此，Mn氧化物与还原剂的反应性取决于表面反应和可能的表面缺陷。在MnO ₂的情况下，Mn（IV）是八面体配位的惰性阳离子；因此，内球过程很可能使电子进入其轨道的空e ^* _g导带。使用前沿分子轨道理论和能带理论，我们讨论了这些表面反应的各个方面以及可能利用MnO ₂与硫化氢和其他还原剂反应的实验室和现场数据来促进MnO ₂还原的表面缺陷。