Fe\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e Precipitation in Magnetotactic Bacteria

Using Mössbauer resonance spectroscopy of 57Fe, we have determined the nature and distribution of major iron compounds in the magnetotactic bacterium Aquaspirillum magnetotacticum. In addition to magnetite (Fe3O4), cells contained a low-density hydrous ferric oxide, a high-density hydrous ferric oxide (ferrihydrite), and ferrous iron. Analysis at different temperatures of whole cells harvested early and late in growth, of mutant cells unable to synthesize magnetite, and of cell fractions enriched in 57Fe indicated that Fe3O4 precipitation resulted from partial reduction of the high-density hydrous ferric oxide precursor

A thermally stable {FeNO}(8) complex: properties and biological reactivity of reduced MNO systems

Reduced nitrogen oxide ligands such as NO−/HNO or nitroxyl participate in chemistry distinct from nitric oxide (NO). Nitroxyl has been proposed to form at heme centers to generate the Enemark–Feltham designated {FeNO}8 system. The synthesis of a thermally stable {FeNO}8 species namely, [Co(Cp*)2][Fe(LN4)(NO)] (3), housed in a heme-like ligand platform has been achieved by reduction of the corresponding {FeNO}7 complex, [Fe(LN4)(NO)] (1), with decamethylcobaltocene [Co(Cp*)2] in toluene. This complex readily reacts with metMb, resulting in formation of MbNO via reductive nitrosylation by the coordinated HNO/NO−, which can be inhibited with GSH. These results suggest that 3 could serve as a potential HNO therapeutic. Spectroscopic, theoretical, and structural comparisons are made to 1 and the {CoNO}8 complex, [Co(LN4)(NO)] (2), an isoelectronic analogue of 3

Mossbauer Spectroscopy of Fe\u3csup\u3e2+\u3c/sup\u3e Binding to Apo and Holo Mammalian Ferritin

The anaerobic binding of Fe2+ to apo and holo Mammalian ferritin has been studied in the pH range from 6.0 to 10.0. Mossbauer spectroscopy of samples in which the added Fe 2+ is enriched in Fe-57 shows that the Fe2+ ions bind to the ferritin core and exchange electrons with Fe3+ ions in the core

Combined Mössbauer Spectral and Density Functional Study of an Eight-Coordinate Iron(II) Complex

The iron-57 Mössbauer spectra of the eight-coordinate complex, [Fe(LN4)2](BF4)2, where LN4 is the tetradentate N1(E),N2(E)-bis[(1-methyl-1H-imidazol-2-yl)methylene]-1,2-benzenediimine ligand, have been measured between 4.2 and 295 K and fit with a quadrupole doublet. The fit at 4.2 K yields an isomer shift, δFe, of 1.260(1) mm/s and a quadrupole splitting, ΔEQ, of 3.854(2) mm/s, values that are typical of a high-spin iron(II) complex. The temperature dependence of the isomer shift yields a Mössbauer temperature, θM, of 319(27) K and the temperature dependence of the logarithm of the Mössbauer spectral absorption area yields a Debye temperature, θD, of 131(6) K, values that are indicative of high-spin iron(II). Nonrelativistic single point density functional calculations with the B3LYP functional, the full 6-311++G(d,p) basis set, and the known X-ray structures for [Mn(LN4)2]2+, [Mn(LN4)2](ClO4)2, 1, [Fe(LN4)2]2+, and [Fe(LN4)2](BF4)2, 2, yield small electric field gradients for the manganese(II) complexes and electric field gradients and s-electron densities at the iron-57 nuclide that are in good to excellent agreement with the Mössbauer spectral parameters. The structure of 2 with a distorted square-antiprism C1 iron(II) coordination symmetry exhibits four different Fe-Nimid bonds to the imidazole nitrogens with an average bond distance of 2.253(2) Å and four different Fe-Nimine bonds to the benzenediimine nitrogens, with an average bond distance of 2.432(2) Å; this large difference yields the large observed ΔEQ. An optimization of the [Fe(LN4)2]2+ structure leads to a highly symmetric eight-coordination environment with S4 symmetry and four equivalent Fe-Nimid bond distances of 2.301(2) Å and four equivalent Fe-Nimine bond distances of 2.487(2) Å. In contrast, an optimization of the [Mn(LN4)2]2+ structure leads to an eight-coordination manganese(II) environment with D2d symmetry and four equivalent Mn-Nimid bond distances of 2.350(3) Å and four equivalent Mn-Nimine bond distances of 2.565(3) Å. (Graph Presented)