74507-62-3Relevant articles and documents
Direct Determination of the Number of Electrons Needed to Reduce Coenzyme F430 Pentamethyl Ester to the Ni(I) Species Exhibiting the Electron Paramagnetic Resonance and Ultraviolet-Visible Spectra Characteristic for the MCRredl State of Methyl-coenzyme M Reductase
Piskorski, Rafal,Jaun, Bernhard
, p. 13120 - 13125 (2003)
The UV-visible and electron paramagnetic resonance (EPR) spectra of MCRred1, the catalytically active state of methyl-coenzyme M reductase, are almost identical to those observed when free coenzyme F430 or its pentamethyl ester (F430M) are reduced to the Ni(I) valence state. Investigations and proposals concerning the catalytic mechanism of MCR were therefore based on MCRred1 containing NiIF430 until, in a recent report, Tang et al. (J. Am. Chem. Soc. 2002, 124, 13242) interpreted their resonance Raman data and titration experiments as indicating that, in MCRred1, coenzyme F430 is not only reduced at the nickel center but at one of the C=N double bonds of the hydrocorphinoid macrocycle as well. To resolve this contradiction, we have investigated the stoichiometry of the reduction of coenzyme F430 pentamethyl ester (F430M) by three independent methods. Spectroelectrochemistry showed clean reduction to a single product that exhibits the UV-vis spectrum typical for MCRred1. In three bulk electrolysis experiments, 0.96 · ± 0.1 F/mol was required to generate the reduced species. Reduction with decamethylcobaltocene in tetrahydrofuran (THF) consumed 1 mol of (Cp*)2Co/mol of F430M, and the stoichiometry of the reoxidation of the reduced form with the two-electron oxidant methylene blue was 0.46 ± 0.05 mol of methylene blue/mol of reduced F430M. These experiments demonstrate that the reduction of coenzyme F430M to the species having almost identical UV-vis and EPR spectra as MCRred1 is a one-electron process and therefore inconsistent with a reduction of the macrocycle chromophore.
Synthesis, structure, and bonding of stable complexes of pentavalent uranyl
Nocton, Gregory,Horeglad, Pawel,Vetere, Valentina,Pecaut, Jacques,Dubois, Lionel,Maldivi, Pascale,Edelstein, Norman M.,Mazzanti, Marinella
, p. 495 - 508 (2010/03/25)
Stable complexes of pentavalent uranyl [UO2(salan- tBu2)(py)K]n (3), [UO2(salan- tBu2)(py)K(18C6)] (4), and [UO2(salophen- tBu2)(thf)]K(thf)2}n (8) have been synthesized from the reaction of the complex {[UO2py 5][KI2py2]}n (1) with the bulky amine-phenolate ligand potassium salt K2(salan-tBu 2) or the Schiff base ligand potassium salt K2(salophen- tBu2) in pyridine. They were characterized by NMR, IR, elemental analysis, single crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, low-temperature EPR, and variable-temperature magnetic susceptibility. X-ray diffraction shows that 3 and 8 are polymeric and 4 is monomeric. Crystals of the monomeric complex [UVO2(salan- tBu2)(py)][Cp*2Co], 6, were also isolated from the reduction of [UVIO2(salan-tBu 2)(py)], 5, with Cp*2Co. Addition of crown ether to 1 afforded the highly soluble pyridine stable species [UO2py5]I ?py (2). The measured redox potentials E1/2 (U VI/UV) are significantly different for 2 (-0.91 and -0.46 V) in comparison with 3, 4, 5, 7 and 9 (in the range -1.65 to -1.82 V). Temperature-dependent magnetic susceptibility data are reported for 4 and 7 and give μeff of 2.20 and 2.23 μB at 300 K respectively, which is compared with a μeff of 2.6(1) μB (300 K) for 2. Complexes 1 and 2 are EPR silent (4 K) while a rhombic EPR signal (g x = 1.98; gy = 1.25; gz = 0.74 (at 4 K) was measured for 4. The magnetic and the EPR data can be qualitatively analyzed with a simple crystal field model where the f electron has a nonbonding character. However, the temperature dependence of the magnetic susceptibility data suggests that one or more excited states are relatively low-lying. DFT studies show unambiguously the presence of a significant covalent contribution to the metal-ligand interaction in these complexes leading to a significant lowering of the πu*. The presence of a back-bonding interaction is likely to play a role in the observed solution stability of the [UO 2(salan-tBu2)(py)K] and [UO 2(salophen-tBu2)( py)K] complexes with respect to disproportionation and hydrolysis.
Organometallic crystal engineering with multidentate building blocks and template guest size effect. Supra-anionic organic framework obtained from cyclobutane-1,2,3,4-tetracarboxylic and trans-acootinic acids
Braga, Dario,Benedi, Oscar,Maini, Lucia,Grepioni, Fabrizia
, p. 2611 - 2618 (2007/10/03)
The organic acids cyclobutane-1,2,3,4-tetracarboxylic C4H4(CO2H)4, and trans-acotinic acid C3H3(CO2H)3, have been treated in thf with the organometallic hydroxides [Co(η5-C5H5)2]+[OH]-, [Co(η5-C5Me5)2]+[OH]-, and [Cr(η6-C6H6)2]+[OH]- prepared in situ from the oxidation of the corresponding neutral complexes to yield the novel organic-organometallic crystalline materials [Co(η5-C5H5)2]+[C4H4(CO2H)3COO]- 1, [Cr(η6-C6H6)2][C4H4(CO2H)3(CO2]-*H2O 2, and [Co(η5-C5Me5)2]+[C3H3(CO2H)2CO2(H)*C3H3(CO2H)2CO2]-*H2O 3. Self-assembly of the monodeproptonated organic acid C4H4(CO2H)4 generates supra-anionic framework structures held together by O-H...O and O-H...O- hydrogen bonds which accomodate the diamagnetic [Co(η5-C5H5)2]+ and paramagnetic [Cr(η6-C6H6)2]+ cations, respectively. Crystalline 1 does not form single crystals with defined shapes but rather an enamel like material which grows parallel to the crystallographic bc plane. The same reaction between trans-acotinic acid and [Co(η5-C5Me5)2]+[OH]- generates a large honeycomb-type structure in [Co(η5-C5Me5)2]+[C3H3(CO2H)2(CO2(H)*C3H3(CO2H)2CO2]-*H2O 3. The effect of the size of the templating units [Co(η5-C5H5)2]+ and [Co(η5-C5Me5)2]+ is discussed. The previously unknown structure of the starting material [Co(η5-C5Me5)2]+[PF6]- 4, used for the preparation of [Co(η5-C5Me5)2]+[OH]-, has also been determined.
