A high‐resolution view of the coordination environment in a paramagnetic metalloprotein from its magnetic properties

Metalloproteins constitute a significant fraction of the proteome of all organisms and their characterization is critical for both basic sciences and biomedical applications. A large portion of metalloproteins bind paramagnetic metal ions, and paramagnetic NMR spectroscopy has been widely used in their structural characterization. However, the signals of nuclei in the immediate vicinity of the metal center are often broadened beyond detection. In this work, we show that it is possible to determine the coordination environment of the paramagnetic metal in the protein at a resolution inaccessible to other techniques. Taking the structure of a diamagnetic analogue as a starting point, a geometry optimization is carried out by fitting the pseudocontact shifts obtained from first principles quantum chemical calculations to the experimental ones

Interaction of high-power microwave beams with metal-dielectric media

Results of experimental investigation of powerful microwave beams action on the metal-dielectric compositions are presented. Dielectric surfaces with introduced metallic grains as well as dielectric powder containing small admixtures of a metallic one have been explored as an objects of irradiation. At a relatively small microwave power ($P \le 1$ mW) all investigated targets were practically completely transparent for incident electromagnetic wave. At a relatively high power (microwave generators based on the gyratrons and powerful magnetrons) the irreversible changes in the electric and radiophysical properties of metal-dielectric composites exposed to microwave radiation whose intensity is below the threshold intensity for plasma production have been observed (sharp increase of conductivity and microwave absorption coefficient)

Hyperfine interactions and electron distribution in Fe(II)Fe(I) and Fe(I)Fe(I) models for the active site of the [FeFe] hydrogenases: Mössbauer spectroscopy studies of low-spin Fe(I)

[[abstract]]Mössbauer studies of [{μ-S(CH2C(CH3)2CH2S}(μ-CO)FeIIFeI(PMe3)2(CO)3]PF6 (1 OX ), a model complex for the oxidized state of the [FeFe] hydrogenases, and the parent FeIFeI derivative are reported. The paramagnetic 1 OX is part of a series featuring a dimethylpropanedithiolate bridge, introducing steric hindrance with profound impact on the electronic structure of the diiron complex. Well-resolved spectra of 1 OX allow determination of the magnetic hyperfine couplings for the low-spin distal FeI ( FeI D ) site, A x,y,z = [−24 (6), −12 (2), 20 (2)] MHz, and the detection of significant internal fields (approximately 2.3 T) at the low-spin ferrous site, confirmed by density functional theory (DFT) calculations. Mössbauer spectra of 1 OX show nonequivalent sites and no evidence of delocalization up to 200 K. Insight from the experimental hyperfine tensors of the FeI site is used in correlation with DFT to reveal the spatial distribution of metal orbitals. The Fe–Fe bond in [Fe2{μ-S(CH2C(CH3)2CH2S}(PMe3)2(CO)4] (1) involving two dz2 -type orbitals is crucial in keeping the structure intact in the presence of strain. On oxidation, the distal iron site is not restricted by the Fe–Fe bond, and thus the more stable isomer results from inversion of the square pyramid, rotating the dz2 orbital of FeI D . DFT calculations imply that the Mössbauer properties can be traced to this dz2 orbital. The structure of the magnetic hyperfine coupling tensor, A, of the low-spin FeI in 1 OX is discussed in the context of the known A tensors for the oxidized states of the [FeFe] hydrogenases.[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]DE