Change In Coordination Structure Research Articles

The effect of crystallographic orientation on the transformation of the structure in aluminum single crystals upon exposure to shock waves

In this work, the influence of the crystallographic orientation of high-purity aluminum single crystals of grade A999 on the transformation of the initial structure as a result of exposure to shock waves at a temperature of −196°C was experimentally investigated. It was found that when the shock front propagates in the [110] direction at pressures of 40 GPa and 50 GPa, structural changes in aluminum single crystals are observed in the form of dislocation slip lines along the (111) and (110) planes. The impact of the shock front in the direction of [113] at a pressure of 50 GPa leads to coordination structural changes. It was found that a nanocrystalline structure with an average grain size of 80 nm is formed in the near-surface layers at a depth of 1–3 mm, and a subgrain structure is formed at a depth of 6–7 mm. In fact, a gradient type structure is formed. The reasons for the pronounced effect of the influence of the crystallographic orientation of high-purity aluminum single crystals on structural changes under the action of shock waves are discussed.

Energy transition in Germany: a case study on a policy-driven structural change of the energy system

The German energy transition (“Energiewende”), i.e., shifting the basis of the energy system from fossil and nuclear fuels to renewable energy constitutes a policy-driven structural change of the energy systems. The fundamental political decisions on nuclear phase-out and the deep decarbonisation of the energy system were based on specific risk considerations in German society, formed by political and learning processes over more than two decades, including the experiences made with the roll-out of renewable energies from 1990 to 2010 that created significant technology optimism in this field. The major challenges for the energy transition do not arise from technological issues or the system costs of a renewables-based system if the once-only investments in innovation are taken into account (that contributed significantly to the massive cost decrease of wind and solar energy at global level). Structural challenges arise first from the dominance of variable renewable energies, which changes generation patterns and shifts cost structures to high shares of capital and low or even zero marginal costs. This triggers the need for restructured power market design that enables price-based system coordination as well as the payback of investments in a low marginal cost environment and re-adjusts the cost allocation among the different consumer groups. Second, the increasing diversity in the power system brings in a broad range of new players and new economic appraisals (self-generation, etc.) that also requires—beyond new dimensions of coordination—structural changes in the regulatory framework. Third, the spatial patterns of the electricity system necessitate large-scale structural changes in the network infrastructures, which demand a sensitive reflection of public acceptance and network regulation approaches. A successful energy transition beyond its present stage requires stringent and holistic policy approaches that are based on four pillars: paving the way for clean energy, designing the exit game for the high-carbon assets, triggering the network infrastructures and making innovation work in time.

Effect of pressure on the coordination structure of acetate-rare earth complex in water

Pressure-induced coordination structural changes of the acetate-rare earth complex in water (LnCl3·20H2O·CH3COOLi) have been investigated using Raman spectroscopy. From the analysis of Raman CC stretching band of acetate ion, the integrated Raman intensity of polymeric chain structure decreases with increasing pressure throughout the rare-earth series. The monodentate ligand appears at around 0.6 GPa in the meddle-heavy rare earth region. We have determined the difference in the partial molar volume (PMV) (ΔV) among three coordination structures. The rank ordering of the PMV of three coordination structures is as follows: monodentate ligand <bidentate ligand <polymeric chain structure. The absolute values ΔVPolymeric→ Bidentate and ΔVBidentate→Monodentate become larger with decreasing ionic radius of Ln3+ ion, and theses are probably due to the size effect of Ln3+ ion.

Photochromism of metal complexes composed of diarylethene ligands and Zn(II), Mn(II), and Cu(II) hexafluoroacetylacetonates.

Metal complexes composed of bidentate 1,2-bis(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (1a) and monodentate 1-(2-methyl-5-phenyl-3-thienyl)-2-(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (2a) photochromic ligands and M(hfac)(2) (M = Zn(II), Mn(II), and Cu(II)) were prepared, and their photoinduced coordination structural changes were studied. X-ray crystallographic analyses showed the formation of coordination polymers and discrete 1:2 complexes for bidentate and monodentate ligands, respectively. The complexes underwent reversible photochromic reactions by alternate irradiation with UV and visible lights in solution as well as in the single-crystalline phase. Upon photoirradiation with UV and visible light, the ESR spectra of the copper complexes of 1a reversibly changed. While the open-ring isomer gave an axial-type spectrum, the photogenerated closed-ring isomer showed a rhombic-type spectrum. This indicates that the photoisomerization induced the change in the coordination structure.

In vivo coordination structural changes of a potent insulin-mimetic agent, bis(picolinato)oxovanadium(IV), studied by electron spin-echo envelope modulation spectroscopy

Bis(picolinato)oxovanadium(IV) [VO(pic) 2] is one of the most potent insulin-mimetic vanadium complexes. To probe coordination structural changes of this complex in vivo and provide insights into the origin of its high potency, an electron spin-echo envelope modulation (ESEEM) study was performed on organs (kidney, liver and bone) of VO(pic) 2- and VOSO 4-treated rats. Kidney and liver samples from both types of rats exhibited a 14N ESEEM signal that could be attributed to equatorially coordinating amine nitrogen. The relative intensity of the amine signal was larger for the organs of the rat treated with the less potent VOSO 4, suggesting that this amine coordination inhibits the insulin-mimetic activity. The spectra of kidney and liver from the VO(pic) 2-treated rat contained a weak signal due to the picolinate imine nitrogen. This suggests that some picolinato species (including both the bispicolinato and a partially decomposed monopicolinato species) still exist in the organs as a minor species, where the proportions of the picolinato species to the total amount of the EPR-detectable V IVO species are estimated as 8–16% in the kidney and 12–24% in the liver. The picolinate ligand presumably serves to prevent VO 2+ from being converted into the inactive amine-coordinated species. Bone samples from both types of rats exhibited an ESEEM signal due to 31P nuclei. The VO 2+ in bone is therefore most likely incorporated into the hydroxyapatite Ca 10(PO 4) 6(OH) 2 matrix, which is consistent with the hypothesis that the bone-accumulated VO 2+ is gradually released and transported to other organs as is Ca 2+. No 14N signals were observed, even in the bone samples of the VO(pic) 2-treated rats, indicating that vanadium uptake by bone requires complete decomposition of the complex.

Effects of cyanogen bromide modification of the distal histidine on the spectroscopic and ligand binding properties of myoglobin: magnetic circular dichroism spectroscopy as a probe of distal water ligation in ferric high-spin histidine-bound heme proteins

Magnetic circular dichroism (MCD) spectroscopy has been utilized to characterize the change in coordination structure in native ferric sperm whale myoglobin upon cyanogen bromide-modification. Comparison of the MCD properties of the ferric high-spin state of cyanogen bromide-modified myoglobin (BrCN-Mb) with those of native ferric horseradish peroxidase and Aplysia myoglobin suggests that ferric BrCN-Mb is a potential MCD model for the pentacoordinate state of ferric high-spin histidine-ligated heme proteins. These five-coordinate heme proteins afford a relatively weak and unsymmetric signal in the Soret region of the MCD spectrum. In contrast, native ferric myoglobin and the benzohydroxamic acid adduct of ferric horseradish peroxidase show a strong and symmetric derivative-shaped Soret MCD signal which is indicative of hexacoordination with water and histidine axial ligands. Therefore it seems that MCD spectroscopy could be used to probe the presence of water ligated to the distal side of ferric high-spin heme proteins. The MCD spectra of the ferric-azide, ferrous-deoxy and ferrous-CO forms of BrCN-Mb have also been measured and compared to those of analogous native myoglobin complexes. The present MCD study has been extended to include new ligands, NO, thiocyanate and cyanate, which bind to ferric BrCN-Mb. With exogenous ligands such as CO, NO and thiocyanate, the coordination structures of the BrCN-Mb complexes are similar to those of the respective native myoglobin adducts. In the case of ferrous-deoxy and ferric-cyanate BrCN-Mb, however, the altered MCD spectra (and EPR for the latter) reveal changes in electronic structure which likely correlate with alterations of the coordination environment of these BrCN-Mb derivatives. Data are also presented which support the proposed tetrazole-bound structure for azide-treated BrCN-Mb (Hori, H., Fujii, M., Shiro, Y., Iizuka, T., Adachi, S. and Morishima, I. (1989) J. Biol. Chem. 264, 5715-5719) and the inability of the distal histidine of BrCN-Mb to stabilize the ferric ligand-bound state.