| Autor: |
White CJ; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Lengel MO; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Bracken AJ; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Kampf JW; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Speelman AL; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Alp EE; Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States., Hu MY; Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States., Zhao J; Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States., Lehnert N; Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, United States. |
| Abstrakt: |
Flavodiiron nitric oxide reductases (FNORs) carry out the reduction of nitric oxide (NO) to nitrous oxide (N 2 O), allowing infectious pathogens to mitigate toxic levels of NO generated in the human immune response. We previously reported the model complex [Fe 2 (BPMP)(OPr)(NO) 2 ](OTf) 2 ( 1 , OPr - = propionate) that contains two coplanar NO ligands and that is capable of quantitative NO reduction to N 2 O [White et al. J. Am. Chem. Soc. 2018 , 140 , 2562-2574]. Here we investigate, for the first time, how a distortion of the active site affects the ability of the diiron core to mediate N 2 O formation. For this purpose, we prepared several analogues of 1 that contain two monodentate ligands in place of the bridging carboxylate, [Fe 2 (BPMP)(X) 2 (NO) 2 ] 3+/1+ ( 2-X ; X = triflate, 1-methylimidazole, or methanol). Structural data of 2-X show that without the bridging carboxylate, the diiron core expands, leading to elongated (O)N-N(O) distances (from 2.80 Å in 1 to 3.00-3.96 Å in 2-X ) and distorted (O)N-Fe-Fe-N(O) dihedral angles (from coplanarity (5.9°) in 1 to 52.9-85.1° in 2-X ). Whereas 1 produces quantitative amounts of N 2 O upon one-electron reduction, N 2 O production is substantially impeded in 2-X , to an initial 5-10% N 2 O yield. The main products after reduction are unprecedented hs-Fe II /{Fe(NO) 2 } 9/10 dinitrosyl iron complexes (DNICs). Even though mononuclear DNICs are stable and do not show N-N coupling (since it is a spin-forbidden process), the hs-Fe II /{Fe(NO) 2 } 9/10 DNICs obtained from 2-X show unexpected reactivity and produce up to quantitative N 2 O yields after 2 h. The implications of these results for the active site structure of FNORs are discussed. |
