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61.
Ana Valria Colnaghi Simionato Marcelo Delmar Cantú Emanuel Carrilho 《Microchemical Journal》2006,82(2):214-219
Siderophores are low molecular weight non-ribosomal peptides with extremely high affinity by iron. However, other metals present affinity for siderophores but to a smaller degree. Deferoxamine is an example of a bacterial hydroxamic siderophore, which was investigated herein. Capillary zone electrophoresis (CZE) was used as a new approach in the continuous variation method for the characterization of metal-deferoxamine complexes. A set of samples containing both metal (e.g., Fe(III), Fe(II) or Ni(II)) and siderophore with different molar ratios was prepared and analyzed by both CZE and UV-vis spectrophotometry. A phosphate buffer pH 8.0 was used as the background electrolyte in the first case due to best complex and free ligand peaks resolution. The Job's plots obtained from complex peak areas (complex concentration) versus metal molar fraction revealed complexes stoichiometries of M : L of 2 : 3, 1 : 2 and 1 : 1 for Fe(III), Fe(II) and Ni(II) complexes, respectively. Conditional formation constants could also be calculated for Fe(III) and Fe(II) complexes as Kf = 1.03 × 1013 and 2.47 × 104, respectively. UV-visible spectrophotometric analysis confirmed the data obtained for Fe(III)-complex. 相似文献
62.
Size exclusion chromatography (SEC) was coupled on-line to inductively coupled plasma mass spectrometry (ICP-MS) for speciation study of trace metals in cancerous thyroid tissues in comparison to healthy thyroids aimed to estimation of changes in metalloprotein speciation in pathological tissue. The study showed a presence of species binding Cu, Zn, Cd and Pb in healthy thyroid tissue with a good reproducibility of chromatographic results, whereas the same species could not be detected in cancerous tissues. Thus, remarkable differences with respect to metal-binding species were revealed between healthy and pathological thyroid samples, pointing out a completely different distribution of trace metals in cancerous tissues. The metal-binding species could not be identified in the frame of this work because of a lack of appropriate standards. Nevertheless, the results obtained confirm the suitability of SEC-ICP-MS for monitoring of changes in trace metal distribution in cancerous tissue and will help to better understand the role of metal-containing species in thyroid pathology. 相似文献
63.
Molecular electron transfer of protein junctions characterised by conducting atomic force microscopy 总被引:1,自引:0,他引:1
The transport characteristics of the blue copper metalloprotein, azurin, have been characterised by conducting atomic force microscopy (C-AFM) at molecular level. Tunnel junctions have been constructed by sandwiching chemisorbed protein molecules between a conducting AFM tip and a planar conducting substrate. Asymmetric current curves with respect to the polarity of the bias (I–V) have been observed. The modulation of I–V behaviour with compressional force has been examined and is described by a modified Simmons model within which both tunnel distance (protein dimensions) and tunnel barrier are modulated. The modified Simmons formula, which considered unequal Fermi level shifts on two electrodes as being responsible for the asymmetric I–V curves, accurately describes the behaviour observed. 相似文献
64.
Jong Bum Lee Soong Ho Um Jeong-Woo Choi Kee-Kahb Koo 《Colloids and surfaces. B, Biointerfaces》2003,30(4):307-314
The self-assembled ferredoxin monolayer onto the (100) surface of the silicon substrate was prepared and the nonspecifically adsorbed aggregates of ferredoxin on the substrate were successfully eliminated by using a zwitterionic surfactant, 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). The AFM image of the self-assembled ferredoxin monolayer on the silicon substrate treated with CHAPS clearly shows that the size of ferredoxin clusters is about 20–30 nm, which is on the order of an aggregate of about five ferredoxin molecules, whereas the size of ferredoxin aggregates on the substrate without CHAPS treatment was measured to be about 100–200 nm. Those results offer a useful method for the elimination of the nonspecific adsorption of proteins onto inorganic substrates, which has been a long-term problem in the fabrication of biomolecular electronic devices by the self-assembly technique. 相似文献
65.
《Arabian Journal of Chemistry》2023,16(3):104546
Boron-rich yttrium borides are an exceptional group of compounds not only with excellent mechanical properties, but also with particular superconducting and thermoelectric properties. Although the Y–B compounds with integral components have been extensively investigated experimentally and theoretically, the yttrium borides with the fractional stoichiometries are rarely observed. Herein, utilizing a combination of the CALYPSO method for crystal structure prediction and first-principles calculations, we made an investigation on a broad range of stoichiometries of yttrium borides. An extraordinary stable Y2B5 compound possessing the fractional stoichiometry with the monoclinic P121/c1 phase is firstly uncovered. Structurally, the P121/c1-Y2B5 crystalline consists of the distorted B6 octahedrons and seven-member B rings. Remarkably, the B–B covalent network following the increment of the boron content in six concerned yttrium borides undergoes an increasing dimension, quasi one-dimensional chain → two-dimensional B ring → a combination of two-dimensional B ring and three-dimensional B6 octahedron → three-dimensional B24 cage. According to a microscopic hardness model, P121/c1–Y2B5 is considered as an incompressible and hard material with the hardness of 18.83 GPa. More importantly, Fm-3 m-YB12 can be classified into an ultra-incompressible material with the appreciable Vickers hardness of 33.16 GPa. The present consequences can provide important insights for understanding the complex crystal structures of boron-rich yttrium borides and stimulate further experimental synthesis of novel multifunctional materials with the fractional compositions. 相似文献
66.
M.D. Carvalho L.P. Ferreira J.C. Waerenborgh A.B. Lopes 《Journal of solid state chemistry》2008,181(9):2530-2541
Ca2Fe1−xMnxAlO5 (0?x?1) compounds were prepared by a self-combustion method under air (x=0, 0.1, 0.2 and 0.3) and nitrogen (x=0.5, 0.7 and 1.0). The samples prepared under nitrogen were successfully oxidized after short annealing under air. Both X-ray powder diffraction (XRD) Rietveld analysis and electron diffraction revealed that all compounds adopt the brownmillerite-type structure. All samples present an overall antiferromagnetic behaviour and data from magnetic measurements and Mössbauer spectroscopy allowed to conclude that the transition temperature decreases as Mn content increases for x?0.3 and increases in the case of the x?0.5 compounds. Except for x=1, chemical disorder due to the occupancy of both octahedral and tetrahedral sites by different metals as well as the competition between different moments’ orientation induce a complex magnetic behaviour characterized by magnetic frustration and canted antiferromagnetism. Mössbauer spectroscopy and chemical titrations also allowed to conclude about the preferential oxidation of Mn3+ over Fe3+, obtained by thermal treatment under air of the x=0.5 and 0.7 compositions. 相似文献
67.
The iron chelation stoichiometries of a dendritic iron(III) chelator with N(1), N(3), N(5)-trimethylbenzene-1,3,5-tricarboxamide at its core, and containing 3 identical hexadentate tris-hydroxypyridinone branches D was studied by MALDI mass spectrometry. At pH 7.2, the speciation of the system included FeD, Fe(2)D and Fe(3)D species with the respective conditional stability constants of 26.74, 26.03 and 25.36. The differences in the stepwise affinity constants arise from the statistical distribution of iron(III), and there was no evidence for cooperativity between the iron-binding sites. 相似文献
68.
The structural changes accompanying small stoichiometric variations around 1–2–3 composition in the Y-Ba-Cu-O compound have
been investigated. Ba-deficient composition is found to give considerable orientation along (001). This oriented powder gives
a higher current density compared to the unoriented powder. The temperature has been correlated with stoichiometry. 相似文献
69.
Ibon Alkorta María Teresa Benito José Elguero Elisa García Doyagüez Monika R. Patterson María Luisa Jimeno H. V. Rasika Dias Felipe Reviriego 《Magnetic resonance in chemistry : MRC》2022,60(4):442-451
A series of DOSY experiments have been carried out to determine the solution stoichiometry of silver(I) 3,5-bis (trifluoromethyl)pyrazolate species. This compound exists as a trimer in the solid state (n = 3) but in solutions of chlorinated solvents, the DOSY data suggest the presence of a mixture of solvent stabilized monomer (n = 1) and dimer (n = 2) in equilibrium. Different approximations have been used including the Stokes–Einstein and the Stokes–Einstein–Gierer–Wirtz equations. Some methodological problems are discussed. 相似文献
70.
Significance of epoxy network properties for the toughening effect of flaky and fullerene‐like WS2 nanoparticles
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Dietmar Haba Michel Barbezat Santhosh Ayalur‐Karunakaran Sandra Schlögl Andreas J. Brunner Gerald Pinter 《Journal of Polymer Science.Polymer Physics》2016,54(17):1738-1747
This work deals with the toughening effect of flaky WS2 and fullerene‐like WS2 (IF‐WS2) nanoparticles on epoxy with varying network properties. Reducing the amount of curing agent resulted in decreased crosslink density as measured by dynamic‐mechanic analysis and double‐quantum nuclear magnetic resonance spectroscopy. Although that lead to moderate changes in the epoxy's tensile properties, its fracture toughness dropped drastically, probably due to an increased defect fraction. IF‐WS2 could be dispersed significantly more effectively within epoxy resin than flaky WS2, possibly due to its spherical shape, but caused less toughening. IF‐WS2 tended to debond from the epoxy, while flaky WS2 introduced more secondary cracks. Both increased the fracture toughness of the (brittle) substoichiometric, but not that of the (tough) stoichiometric epoxy, possibly due to their interaction with molecular defects. Irrespective of which mechanism resulted in the toughening effect, its effectiveness depended strongly on the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1738–1747 相似文献