Non-heme diiron
China Scholarship Council (CSC)/University of Michigan Post-Doctoral Program.
Non-heme diiron enzymes catalyze the activation of dioxygen to cleave the C bonds of a range of substrates. This class includes soluble methane monooxygenase (sMMO), connected bacterial multi-component monooxygenases, and fatty acid desaturases.1 High-valent intermediates are implicated inside the oxygen activation mechanisms for these enzymes.3,5 One example is, intermediate Q of sMMO can be a two-electron oxidant that effects the hydroxylation of methane84 and has been proposed to have an [FeIV2(-O)2] diamond core on the basis of extended x-ray absorption fine structure (EXAFS) research.15 Associated diiron(IV) oxidants might also be involved inside the catalytic cycles of fatty acid desaturases and other diiron monooxygenases resulting from cleavage in the O-O bond in observed peroxo intermediates,168 but direct proof for such diiron(IV) species has not but been obtained. Related oxygen activation chemistry is utilized by ribonucleotide reductases (RNR) with diiron and iron-manganese centers, which produce an intermediate named X that may be used for the one-electron oxidation of a particular Cys residue that is definitely needed to initiate the deoxygenation of ribonucleotides to deoxyribonucleotides.19 For these enzymes, FeIII MIV (M = Fe or Mn) oxidants have already been trapped,202 plus the greatest structurally characterized may be the intermediate for the RNR from Chlamydia tranchomatis, which has been shown to have an [FeIIIMnIV(-O)(-OH)] diamond core on the basis of Fe and Mn K-edge EXAFS experiments and linked density functional theory (DFT) calculations.22 In our work to get synthetic analogs of such high-valent diiron species, we’ve got characterized the very first examples of complexes with [FeIIIFeIV(-O)2]23 (1 in Scheme 1) andXue et al.Page[FeIV2(-O)2]24 core structures, providing synthetic precedents for the [FeIV2(-O)2] core proposed for Q.15 Far more lately, we reported the generation of 1-OH, a complicated with an open HO eIII eIV=O core structure (Scheme two), by the addition of hydroxide to 1 or by the one-electron reduction of its HO eIV eIV=O precursor 2 (Scheme 1).Ganciclovir 25 As EXAFS characterization of two shows an Fe-Fe distance of 3.32 and an Fe e angle of 130 it is clear that the Fe e unit is bent,26 implicating a hydrogen bonding interaction involving the hydroxo proton on a single Fe to the oxo around the other Fe. By extension, 1-OH can also be proposed to have such an H-bond. Indeed direct spectroscopic evidence for the hydrogen bond in 1-OH has not too long ago been obtained by 1H-ENDOR experiments.PS10 27 Within this paper, we examine the reactivities of 1-OH and 1-F, one more open-core complicated derived in the addition of F- to 1, and find that 1-F is definitely an order of magnitude extra reactive than 1-OH in both H-atom abstraction and oxo-atom transfer.PMID:26780211 Unlike the hydroxo ligand in 1-OH, the iron(III)-bound fluoride need to not be capable of hydrogen bonding to the terminal FeIV=O unit, so the distinction in reactivity might be associated for the presence from the hydrogen bond. Certainly EXAFS analysis establishes the presence of a linear Fe e unit in 1-F. DFT calculations have been carried out on both 1-OH and 1-F to shed additional light on this reactivity behavior. Experimental and Computational Particulars Complexes 1 and 2 were ready according to reported procedures.24,26 9,10dihydroanthracene (DHA, 97 ), Fluorene (99 ) and ferrocene (Fc, 98 ) bought from Aldrich had been recrystallized (from EtOH for the former two and MeOH for the l.
