Electron paramagnetic resonance spectra complexes

The [Fe =0(TMP+ )]+ complex exhibited a characteristic bright green color and corresponding visible absorbance in its UV-vis spectrum. In its NMR spectrum, the meta-proton doublet of the porphyrin mesityl groups were shifted more than 70 ppm downfield from tetramethylsilane (TMS) because they were in the presence of the cation radical, while the methyl protons shift between 10 and 20ppm downfield. In Mossbauer spectroscopy, the isomer shift, 5 of 0.06 mm/s, and A q value of 1.62mm/s were similar to those for other known Fe(IV) complexes. Electron paramagnetic resonance (EPR), resonance Raman (RR), and EXAFS spectroscopies provided additional indications of an Fe =0 n-cation radical intermediate. For instance,... 

Figure 2. Electron paramagnetic resonance spectra of Mr bound to the single catalytic site on (Na + K )-ATPase. The X-hand spectrum (9.5 GHz) is shown in A, while the K-band spectrum (35 GHz) of the same complex is shown in B. The enzyme-Mn2 complex was centrifuged out of 20mM Tes-TMA, pH 7.5, and then combined with buffer so that the final concentrations were 0.15mM (Ha 4-K )-A TPase, 0.1 mM MnCl, 20mM Tes-TMA, pH 7.5. T = 23°C.

Three membrane-bound adenosine triphosphatase enzymes have been characterized using Mn(II) and Gd(III) electron paramagnetic resonance (EPR) and a variety of NMR techniques. Mn(II) EPR studies of both native and partially delipidated (Na+ + K+)-ATPase from sheep kidney indicate that the enzyme binds Mn2+ at a single, catalytic site with Kq = 0.21 x 10- M. The X-band EPR spectrum of the binary Mn(II)-ATPase complex exhibits a powder line shape consisting of a broad transition with partial resolution of the 55 n nuclear hyperfine structure, as well as a broad component to the low field side of the spectrum. ATP, ADP, AMP-PNP and Pj all broaden the spectrum, whereas AMP induces a substantial narrowing of the hyperfine lines of the spectrum. 

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique to explore the electronic state of iron complexes. EPR spectroscopy of the non-heme iron component in the electron transfer system of mitochondria has been extensively used and discussed by Beinert (9), who showed that this type of iron has a so-called g = 1.94 type signal upon reduction. Consideration of the EPR spectrum of adrenodoxin has been described previously (68). 

Electron Paramagnetic Resonance Spectra. Only two of these complexes exhibit well-resolved EPR spectra. A narrow, isotropic signal observed at g = 2.005 for the trinuclear complex 12 at low temperatures is consistent with an S = 1/2 ground state169), but a detailed description of the electronic properties of the complex remains to be developed. The [Fe(MoS4)2]3 ion shows a rhombic S = 3/2 EPR spectrum that is very solvent dependent and, under certain conditions, is somewhat similar in apperance to that of FeMo-com). For example, in frozen aqueous solution, the apparent g values are 5.3,2.6, and 1.7181). If complex 14 also proves to have an S = 3/2 ground state, a somewhat similar EPR spectrum at low temperature would be expected as well. 

The ESR spectrum of a Cu complex with hydrolyzed ascidiacyclamide suggested that a ligandimetal ratio of 1 1, a single monomeric copper(ll) complex, is formed in solution while computer simulation of electron paramagnetic resonance (EPR) spectra indicated a 1 2 ratio <1996IC1095>. 

Tris[bis(trimethylsilyl)amido] vanadium(III) crystallizes from benzene as dark-brown, soft needles, extremely sensitive to air and moisture. This complex is paramagnetic 2.4 BM) but does not show electron paramagnetic resonance absorption at temperatures above that of liquid nitrogen. The compound is thermally unstable but gives a mass spectrum containing the parent molecular ion. Infrared spectra and electronic absorption spectra are given in Table II. The crystalline complex has the same trigonal structure as the Fe compound. ... 

Deuterium quadrupole coupling constants can also be obtained from electron nuclear double resonance (ENDOR).19 30 An observation of the hyperfine structure caused by quadrupole coupling in the electron paramagnetic resonance (EPR) spectrum, as for many lanthanide complexes, has not been reported for deuterium. The determination of nuclear quadrupole coupling constants from Mossbauer spectroscopy is not applicable to the deuterium nucleus. 

Electron paramagnetic resonance spectroscopy is one of the primary tools in studying the electronic structure of polynuclear complexes (341). Whereas magnetic susceptibility studies are capable of detecting electronic interactions as small as a wavenumber (discussed earlier), the EPR spectrum of a polynuclear complex may be sensitive to intramolecular exchange couplings as small as 0.001 cm even at room temperature. Additionally, the °Mn nucleus has a nuclear spin... 

A zeolite with MFI structure was synthesised with 3 different amounts of niobium ammonium complex (NAC) in the reaction mixture. The samples obtained were characterised by scanning electron microscopy (SEM) using secondary electron detector and energy dispersive spectrum (EDS) detector, X-ray diffraction (XRD), differential thermal analysis (DTA), and electron paramagnetic resonance (EPR). The increase of NAC in the reaction mixture results in the decrease of the crystal size of the zeolite. The characterisation shows evidence that the niobium was incorporated into MFI structure. 

We have mentioned earlier the dissimilarities between the spectral properties of chromophoric metal ions at the active sites of metalloen-zymes and the properties of simple bidentate model complexes of the same metals. Cobalt phosphatase has served well to illustrate such a dissimilarity and, in Figure 9, the data for phosphatase, representative of a cobalt enzyme, are shown again along with those for plastocyanin, a copper enzyme, and ferredoxin, an iron enzyme. Each enzyme spectrum is unusual compared with the simple model complexes shown at the bottom of the figure. More detailed spectral data as well as comparison of other physical properties of metalloenzymes—e.g., electron paramagnetic resonance spectra—with those of model complexes have been summarized previously (10). 

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