Concept: Transition metal
The aim of the study was evaluation of metal ions (nickel and chromium) released from orthodontic appliances in cleft lip and palate patients and the usefulness of non-invasive matrices (saliva and hair).
Microparticles containing substantial amounts of radiocesium collected from the ground in Fukushima were investigated mainly by transmission electron microscopy (TEM) and X-ray microanalysis with scanning TEM (STEM). Particles of around 2 μm in diameter are basically silicate glass containing Fe and Zn as transition metals, Cs, Rb and K as alkali ions, and Sn as substantial elements. These elements are homogeneously distributed in the glass except Cs which has a concentration gradient, increasing from center to surface. Nano-sized crystallites such as copper- zinc- and molybdenum sulfide, and silver telluride were found inside the microparticles, which probably resulted from the segregation of the silicate and sulfide (telluride) during molten-stage. An alkali-depleted layer of ca. 0.2 μm thick exists at the outer side of the particle collected from cedar leaves 8 months after the nuclear accident, suggesting gradual leaching of radiocesium from the microparticles in the natural environment.
Research progress to understand the role of vitamin C (ascorbic acid) in human health has been slow in coming. This is predominantly the result of several flawed approaches to study design, often lacking a full appreciation of the redox chemistry and biology of ascorbic acid. In this review, we summarize our knowledge surrounding the limitations of common approaches used in vitamin C research. In human cell culture, the primary issues are the high oxygen environment, presence of redox-active transition metal ions in culture media, and the use of immortalized cell lines grown in the absence of supplemental ascorbic acid. Studies in animal models are also limited due to the presence of endogenous ascorbic acid synthesis. Despite the use of genetically altered rodent strains lacking synthesis capacity, there are additional concerns that these models do not adequately recapitulate the effects of vitamin C deprivation and supplementation observed in humans. Lastly, several flaws in study design endemic to randomized controlled trials and other human studies greatly limit their conclusions and impact. There also is anecdotal evidence of positive and negative health effects of vitamin C that are widely accepted but have not been substantiated. Only with careful attention to study design and experimental detail can we further our understanding of the possible roles of vitamin C in promoting human health and preventing or treating disease.
- Langmuir : the ACS journal of surfaces and colloids
- Published about 5 years ago
Epitaxial graphene is expected to be the only way to obtain large-area sheets of this two-dimensional material for applications on an industrial scale. So far, there are different recipes for epitaxial growth of graphene, using either intrinsic carbon, such as the selective desorption of silicon from a SiC surface, or using extrinsic carbon, as via the chemical vapor deposition (CVD) of simple hydrocarbons on transition metal surfaces. In addition, even liquid precursor deposition (LPD) provides well-ordered graphene monolayers. It will be shown that graphene formation on transition metal surfaces by LPD synthesis is a very robust mechanism that even works if carbon is provided in a quite undefined way, namely by using a human fingerprint as a liquid precursor. Graphene growth from fingerprints provides well-ordered monolayers with the same quality as LPD grown graphene using ultrapure synthetic single precursors. The reliability of the self-assembly process of graphene growth on transition metals by LPD therefore offers a simple and extremely robust synthesis route for epitaxial graphene and may give access to production pathways for substrates for which the CVD method fails.
The increasing human need for clean and renewable energy has stimulated research in artificial photosynthesis, and in particular water photoelectrolysis as a pathway to hydrogen fuel. Nanostructured devices are widely regarded as an opportunity to improve efficiency and lower costs, but as a detailed analysis shows, they also have considerably disadvantages. This article reviews the current state of research on nanoscale-enhanced photoelectrodes and photocatalysts for the water splitting reaction. The focus is on transition metal oxides with special emphasis of Fe(2)O(3), but nitrides and chalcogenides, and main group element compounds, including carbon nitride and silicon, are also covered. The effects of nanostructuring on carrier generation and collection, multiple exciton generation, and quantum confinement are also discussed, as well as implications of particle size on surface recombination, on the size of space charge layers and on the possibility of controlling nanostructure energetics via potential determining ions. After a summary of electrocatalytic and plasmonic nanostructures, the review concludes with an outlook on the challenges in solar fuel generation with nanoscale inorganic materials.
A total of nine tin-contained ancient glass beads were characterized by a combination of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry and Raman spectroscopy. These glass beads dated from 1st century BC to 10th century AD were excavated from the Xinjiang and Guangxi provinces of China. Two kinds of tin-based opacifiers/colorants included crystalline cassiterite (SnO(2) ) and lead-tin yellow types II were first found in these soda lime glass beads. The tentative chronology of the tin-based opacifiers/colorants used in ancient glasses from China and the West was compared. In addition, several transition metal ions colorants were also found in these beads. The detailed study of the glassy matrices, crystalline inclusions, and the microstructural heterogeneities for these glass beads has revealed some valuable information to trace the possible making technology and provenances. Microsc. Res. Tech., 2013. © 2012 Wiley Periodicals, Inc.
Intrinsic deviations in fluorescence yield detected x-ray absorption spectroscopy: the case of the transition metal L(2,3) edges.
- Journal of physics. Condensed matter : an Institute of Physics journal
- Published over 6 years ago
Fluorescence yield (FY) detected x-ray absorption spectra (XAS) of 3d transition metal ions are calculated from the integrated 2p3d resonant x-ray emission spectra. The resulting FY-XAS spectra are compared with the normal XAS spectra corresponding to the absorption cross section and significant deviations between the two spectra are found. This implies that the assumption that the FY-XAS spectrum identifies with the XAS spectrum is disproved. Especially for the early transition metal systems the differences between the FY-XAS and XAS are large, due to the opening of inelastic decay channels from selected x-ray absorption final states. The theoretical calculations show that the difference between FY detection and XAS is largest for the detection in depolarized geometry. The calculations are compared with experimental spectra for oxides and coordination compounds for Fe(2+), Co(2+) and Ni(2+) systems. The implications for the sum rules in XAS and magnetic circular dichroism experiments are discussed.
Glycolytic interconversion of phosphoglycerate isomers is catalysed in numerous pathogenic microorganisms by a cofactor-independent mutase (iPGM) structurally distinct from the mammalian cofactor-dependent (dPGM) isozyme. The iPGM active site dynamically assembles through substrate-triggered movement of phosphatase and transferase domains creating a solvent inaccessible cavity. Here we identify alternate ligand binding regions using nematode iPGM to select and enrich lariat-like ligands from an mRNA-display macrocyclic peptide library containing >10(12) members. Functional analysis of the ligands, named ipglycermides, demonstrates sub-nanomolar inhibition of iPGM with complete selectivity over dPGM. The crystal structure of an iPGM macrocyclic peptide complex illuminated an allosteric, locked-open inhibition mechanism placing the cyclic peptide at the bi-domain interface. This binding mode aligns the pendant lariat cysteine thiolate for coordination with the iPGM transition metal ion cluster. The extended charged, hydrophilic binding surface interaction rationalizes the persistent challenges these enzymes have presented to small-molecule screening efforts highlighting the important roles of macrocyclic peptides in expanding chemical diversity for ligand discovery.
Trianionic pincer and pincer-type ligands are the focus of this review. Metal ions from across the periodic table, from main group elements, transition metals, and the rare earths, are combined with trianionic pincer ligands to produce some of the most interesting complexes to appear in the literature over the past decade. This review provides a comprehensive examination of the synthesis, characterization, properties, and catalytic applications of trianionic pincer metal complexes. Some of the interesting applications employing trianionic pincer and pincer-type complexes include: (1) catalyzed aerobic oxidation, (2) alkene isomerization, (3) alkene and alkyne polymerization, (4) nitrene and carbene group transfer, (5) fundamental transformations such as oxygen-atom transfer, (6) nitrogen-atom transfer, (7) O2 activation, (8) C-H bond activation, (9) disulfide reduction, and (10) ligand centered storage of redox equivalents (i.e. redox active ligands). Expansion of the architecture, type of donor atoms, chelate ring size, and steric and electronic properties of trianionic pincer ligands has occurred rapidly over the past ten years. This review is structured according to the type of pincer donor atoms that bind to the metal ion. The type of donor atoms within trianionic pincer and pincer-type ligands to be discussed include: NCN(3-), OCO(3-), CCC(3-), redox active NNN(3-), NNN(3-), redox active ONO(3-), ONO(3-), and SNS(3-). Since this is the first review of trianionic pincer and pincer-type ligands, an emphasis is placed on providing the reader with in-depth discussion of synthetic methods, characterization data, and highlights of these complexes as catalysts.
A series of luminescent ion exchanged zeolite are synthesized by introducing various ions into NaY zeolite. Monometal ion (Eu(3+) , Tb(3+) , Ce(3+) , Y(3+) , Zn(2+) , Cd(2+) , Cu(2+) ) exchanged zeolite, rare earth ion (Eu(3+) , Tb(3+) , Ce(3+) ) exchanged zeolite modified with Y(3+) and rare earth ion (Eu(3+) , Tb(3+) , Ce(3+) ) exchanged zeolite modified with Zn(2+) are discussed here. The resulting materials are characterized by FTIR, XRD, SEM, PLE, PL and luminescence lifetime measurements. The photoluminescence spectrum of NaY indicates that emission band of host matrix exhibits a blue shift of about 70 nm after monometal ion exchange process. The results show that transition metal ion exchanged zeolites possess a similar emission band due to dominant host luminescence. A variety of luminescence phenomenon of rare earth ion broadens the application of zeolite as a luminescent host. The Eu(3+) ion exchanged zeolite shows white light luminescence with a great application value and Ce(3+) exchanged zeolite steadily exhibits it characteristic luminescence in ultraviolet region no matter in monometal ion exchanged zeolite or bimetal ions exchanged zeolite. This article is protected by copyright. All rights reserved.