Designing Green Oxidation Catalysts for Purifying Environmental Waters

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• 作者：W. Chadwick Ellis ; Camly T. Tran ; Riddhi Roy ; Marte Rusten ; Andreas Fischer ; Alexander D. Ryabov ; Bruce Blumberg ; Terrence J. Collins
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：July 21, 2010
• 年：2010
• 卷：132
• 期：28
• 页码：9774-9781
• 全文大小：300K
• 年卷期：v.132,no.28(July 21, 2010)
• ISSN：1520-5126

文摘

We describe the synthesis, characterization, aqueous behavior, and catalytic activity of a new generation of Fe^III−TAML (tetraamido macrocycle ligand) activators of peroxides (2), variants of [Fe{(OC)₂(o,o′-NC₆H₄NCO)₂CMe₂}(OH₂)⁻] (2d), which have been designed to be especially suitable for purifying water of recalcitrant oxidizable pollutants. Activation of H₂O₂ by 2 (k_I) as a function of pH was analyzed via kinetic studies of Orange II bleaching. This was compared with the known behavior of the first generation of Fe^III−TAMLs (1). Novel reactivity features impact the potential for oxidant activation for water purification by 2d and its aromatic ring-substituted dinitro (2e) and tetrachloro (2f) derivatives. Thus, the maximum activity for 2e occurs at pH 9, the closest yet to the EPA guidelines for drinking water (6.5−8.5), allowing 2e to rapidly activate H₂O₂ at pH 7.7. In water, 2e has two axial water ligands with pK_a’s of 8.4 and 10.0 (25 °C). The former is the lowest for all Fe^III−TAMLs developed to date and is key to 2e’s exceptional catalytic activity in neutral and slightly basic solutions. Below pH 7, 2d was found to be quite sensitive to demetalation in phosphate buffers. This was overcome by iterative design to give 2e (hydrolysis rate 2d > 100 × 2e). Mechanistic studies highlight 2e’s increased stability by establishing that to demetalate 2e at a comparable rate to which H₂PO₄⁻ demetalates 2d, H₃PO₄ is required. A critical criterion for green catalysts for water purification is the avoidance of endocrine disruptors, which can impair aquatic life. Fe^III−TAMLs do not alter transcription mediated by mammalian thyroid, androgen, or estrogen hormone receptors, suggesting that 2 do not bind to the receptors and reducing concerns that the catalysts might have endocrine disrupting activity.