Saddle-shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of Fe hemes with hydrogen peroxide (H O ) to form high-valent Fe-oxo species remains uncertain. Through examination of the ESI-MS spectra, absorption changes and H NMR chemical shifts, we investigated the reactions of two Fe porphyrins with different degrees of saddling deformation, namely Fe (OETPP)ClO (1 ) and Fe (OMTPP)ClO (1 ), with tert-butyl hydroperoxide (tBuOOH) in CH Cl at -40 °C, which quickly resulted in O-O bond homolysis from a highly unstable Fe -alkylperoxo intermediate, Fe -O(H)OR (2) into Fe -oxo porphyrins (3).
View Article and Find Full Text PDFThe formation of [(N4Py)Fe =O] species was accomplished by the reaction of [Fe (N4Py)] with 20 equivalents of tBuO H (TBHP, 70 % in H O). The temperature, [Fe (N4Py)] -concentration and H O-concentration in anhydrous TBHP (5.5 m in decane) dependences of its yields and rates were analyzed to indicate that the proton migration from [(N4Py)Fe -HOOtBu] to [(N4Py)Fe -OO HtBu] is the rate-determining step followed by rapid heterolytic O-O bond cleavage of Fe -OO HtBu to Fe =O complex.
View Article and Find Full Text PDFProton delivery to the prosthetic group is a crucial step to sustain the activity of nitrite reductase. An iron N-confused porphyrin (NCP) complex, which is capable of relaying protons from the outer pyrrolic nitrogen (N-H) of the inverted pyrrole ring to the axial coordinated ligand, has been demonstrated to facilitate facile nitrite reduction. Time-dependent FTIR studies on the reaction between [Fe(HCTPPMe)Br] (1) and a nitrite anion revealed a two-step process involving conversion of the starting complex 1 to an {Fe(NO)} intermediate, [Fe(CTPPMe)(NO)] (5), before the detection of [Fe(CTPPCH)(NO)] (3), an {Fe(NO)} end product.
View Article and Find Full Text PDFA series of straight-chain oligoarylamines were synthesized and examined by electrochemical, spectroelectrochemical, electron paramagnetic resonance techniques, and density functional theory (DFT) calculation. Depending on their electrochemical characteristics, these oligoarylamines were classified into two groups: one containing an odd number and the other an even number of redox centers. In the systems with odd redox centers (N1, N3, and N5), each oxidation was associated with the loss of one electron.
View Article and Find Full Text PDFSaddle-shaped Co(II)[OET(p-R)PP] (R = CF3, H, CH3) can be readily oxidized with Cl2, Br2, and I2 to the corresponding one-electron-oxidation product Co[OET(p-R)PP]X (X = Cl, Br, I) with the clear character of a ring cation radical. With the series of (1)H and (13)C NMR spectra of these related complexes, both the axial ligand and peripheral substituent of the ring macrocycle are proven to act as a dual channel to tune spin coupling between low-spin Co(II) and a porphyrin π-cation radical. Density functional theory calculations have shown that the antiferromagnetic coupling between spins residing in d(z)(2) and a(2u) are expected to exist as the ground state.
View Article and Find Full Text PDFInvestigations on the transfer of the ligand, imidazole (HIm), between two covalently linked redox centres--zinc porphyrin and phenylenediamine (PD)--and the influence of the length of the linker are reported. Since the binding affinity of the ligand with zinc porphyrin is different from that of the ligand with the phenylenediamine moiety, the transfer of the ligand could be electrochemically controlled by adjusting the oxidation potentials. Changes in cyclic voltammograms and absorption spectra of the complexes revealed the site of ligand binding in the various oxidation states of the modified zinc porphyrins.
View Article and Find Full Text PDFAn amino-linked nitrogen heterocyclic carbene (amino-NHC), 1-tBu, has been shown to mediate carbon-carbon coupling through the direct C-H functionalization of benzene and pyridine in the absence of a metal catalyst. Using EPR, the first spectroscopic evidence corroborating the single electron transfer mechanism for the metal-free carbon-carbon coupling manifold, as reported by others, is introduced.
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