Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate
| Autor: | Julian A. Rees, Julie A. Kovacs, Maike N. Blakely, Gloria Villar-Acevedo, Abbie S. Ganas, Erin M. Hanada, Priscilla Lugo-Mas, Werner Kaminsky |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Nitrile
Stereochemistry Molecular Conformation chemistry.chemical_element 010402 general chemistry Photochemistry Ligands 01 natural sciences Biochemistry Ferric Compounds Catalysis Article Metal chemistry.chemical_compound Colloid and Surface Chemistry Reactivity (chemistry) Sulfhydryl Compounds 010405 organic chemistry Cobalt General Chemistry 0104 chemical sciences Oxygen chemistry Catalytic cycle visual_art Chemical Sciences visual_art.visual_art_medium Quantum Theory Density functional theory Derivative (chemistry) Cysteine |
| Zdroj: | Journal of the American Chemical Society, vol 139, iss 1 |
| Popis: | Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [FeIII(S2Me2N3-(Pr,Pr))]+ (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [FeIII(η2-SMe2O)(SMe2)N3(Pr,Pr)]+ (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)Cys114 proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [FeIIIS2Me2NMeN2amide(Pr,Pr)]− (8), shows that oxo atom donor reactivity correlates with the metal ion’s ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3−) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined. |
| Databáze: | OpenAIRE |
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