Ruiz-Garcia Mismel, Richards Mark, Ballerini Ribeiro Gomes Giovanna, Anagnostopoulos Vasileios
Department of Chemistry, University of Central Florida, Orlando FL, 32816, USA.
Environ Sci Pollut Res Int. 2024 Mar;31(12):18540-18548. doi: 10.1007/s11356-024-32319-9. Epub 2024 Feb 12.
Although Mn(III) complexes with organic ligands have been previously identified, the information about their stability and reactivity is scarce. In the present study, we analyzed the formation and stability of three different complexes: Mn(III)-citrate, Mn(III)-tartrate, and Mn(III)-humic acid (HA), as well as their reactivity toward an element of high environmental concern, lead (Pb).Our results indicate that the stability of studied complexes is highly dependent on pH. The Mn(III) complexes with citrate and tartrate degrade below pH 8, due to the electron transfer reaction between Mn(III) and the ligand, while the Mn(III)-HA complex's degradation is slower and less sensitive to pH. At pH 4, less than 40% of the initial Mn(III)-HA was found to be stable.The reactivity of the complexes was different depending on the ligand and its concentration. The Mn(III)-citrate and Mn(III)-tartrate complexes effectively reduced PbO and releases aqueous Pb, although significant differences were found with increasing ligand concentration. There was no evidence of the reduction of PbO by Mn(III) when it forms a complex with HA. This is likely due to the large size of HA moieties that prevent the Mn(III) component of the complex from getting close enough to the PbO surface to initiate electron transfer and lead to the reduction of Pb(IV) by HA itself.
尽管之前已鉴定出锰（III）与有机配体形成的配合物，但关于它们稳定性和反应活性的信息却很少。在本研究中，我们分析了三种不同配合物的形成与稳定性：锰（III）-柠檬酸盐、锰（III）-酒石酸盐和锰（III）-腐殖酸（HA），以及它们对一种备受环境关注的元素铅（Pb）的反应活性。我们的结果表明，所研究配合物的稳定性高度依赖于pH值。锰（III）与柠檬酸盐和酒石酸盐形成的配合物在pH值低于8时会降解，这是由于锰（III）与配体之间发生了电子转移反应，而锰（III）-HA配合物的降解较慢且对pH值不太敏感。在pH值为4时，发现初始锰（III）-HA中只有不到40%是稳定的。配合物的反应活性因配体及其浓度而异。锰（III）-柠檬酸盐和锰（III）-酒石酸盐配合物能有效还原PbO并释放出溶解态的Pb，不过随着配体浓度增加发现了显著差异。当锰（III）与HA形成配合物时，没有证据表明其能还原PbO。这可能是由于HA部分的尺寸较大，阻止了配合物中的锰（III）成分与PbO表面充分靠近以引发电子转移，从而导致HA本身无法将Pb（IV）还原。
