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At least 487 records · Page 27Linked to original sources
PubMed2003

The vanadium environment in blood cells of Ascidia ceratodes is divergent at all organismal levels: an XAS and EPR spectroscopic study.

K-edge X-ray absorption and EPR spectroscopies were used to test the variation in blood cell vanadium between and within specimens of the tunicate Ascidia ceratodes from Bodega Bay, California. Intracellular vanadium was speciated by fitting the XAS spectra of whole blood cells with linear combinations of the XAS spectra of models. Blood cell samples representing one specimen each, respectively, revealed 92.5 and 38.7% of endogenous vanadium as [V(H(2)O)(6)](3+), indicating dissimilar distributions. Conversely, vanadium distributions within blood cell samples respectively representing one and six specimens proved very similar. The derived array of V(III) complexes was consistent with multiple intracellular regions that differ both in pH and c(sulfate), both within and between specimens. No systematic effect on vanadium distribution was apparent on mixing blood cells. EPR and XAS results indicated at least three forms of endogenous vanadyl ion, two of which may be dimeric. An inverse linear correlation was found between soluble and complexed forms of vanadyl ion, implying co-regulation. The EPR A value of endogenous vanadyl ion [A(0)=(1.062+/-0.008)x10(-2) cm(-1)] was marginally different from that representing Monterey Bay A. ceratodes [A(0)=(1.092+/-0.006) x10(-2) cm(-1)]. Comparisons indicate that Bodega Bay A. ceratodes maintain V(III) in a more acidic intracellular environment on average than do those from Monterey Bay, showing variation across populations. Blood cell vanadium thus noticeably diverges at all organismal levels among A. ceratodes.

Animals↗
PubMed1997

The uptake of particulates by an urban woodland: site description and particulate composition.

Woodlands may improve local air quality by increasing the uptake rates of gaseous, particulate and aerosol pollutants from the atmosphere and can also act as relatively permanent sinks for some pollutants. Rough Wood, Walsall was selected for a study of the material which accumulates on tree foliage because of its location in a densely populated urban area, and its proximity to a motorway with high traffic flow (the M6) and to other pollutant sources. Methods were developed for leaf washing to allow determination of the quantity of dust and the identification of the dust particles present on oak leaves. Elemental analysis of particles was also undertaken using scanning electron microscopy coupled with electron probe microanalysis. A large proportion of particles were organic in origin. Of the inorganic particles, the majority contained silicon and aluminium in varying proportions suggesting that they were soil derived. Some particles were clearly identified as the products of combustion, and sea or road salt was present on leaf surfaces. Some particles contained copper, tin and titanium which may reflect the proximity of Rough Wood to local metal workings. The number of particles counted on leaf surfaces decreased as distance from the motorway increased.

Journal Article↗
PubMed1987

Size dependent enzyme activities of multinucleated (osteoclastic) giant cells in bone tumors.

In osteoclastic giant cells of six different tumors of bones and joints (fibrous dysplasia, proliferating giant cell tumor, malignant giant cell tumor, osteosarcoma after chemotherapy, malignant synovioma and Ewing's sarcoma) activities of tartrate-resistant acid phosphatase, NADH-tetrazolium-oxidoreductase and, in three of them, of non-specific esterase are determined by enzyme histochemical methods. Quantitative microphotometry makes it possible to determine relative enzyme activities in the cut sections of giant cells of different sizes. Giant cells of the various tumors reveal similar trends: With an increase in cell size, mean extinctions of NADH-tetrazolium-oxidoreductase and non-specific esterase decrease. Mean extinctions of tartrate-resistant acid phosphatase increase in cells of medium size, whereas the large cells reveal in part low activities. An additional ultrastructural examination of the giant cells in the proliferating giant cell tumor as well as in the osteosarcoma shows morphological signs of degeneration in the large cells. Electron probe microanalysis of the proliferating giant cell tumor exhibits evidence of phagocytosis of Ca and/or Fe containing particles. The similar size dependent reaction pattern of enzymes in osteoclastic giant cells of different tumors favors the concept of a common histogenesis, i.e. a host reaction.

Acid Phosphatase↗
PubMed2002

Electron beam patterning of biomolecules.

The patterning of biomolecules on semiconducting surfaces is of central importance in the fabrication of novel biodevices. In the process of patterning, it is required that the biomolecule preserves its properties and the substrate is not damaged by the chemicals, the temperatures or the patterning beams involved in the procedure. Recently, both DUV and electron beam microlithography have been used in order to deposit protein layers in predefined patterns. Various approaches have been used, some involving photoresists. Contrast between exposed and unexposed regions, resolution of adjacent features and sensitivity to dose variation, are the key issues. The approach followed in this paper consists of a direct patterning of a biotin layer, deposited on an amino-silane primed silicon nitride surface, using an electron beam. After irradiation, the surface is covered by bovine serum albumin (BSA), which acts as a blocking material to protect the exposed areas from streptavidin adsorption. Using 20 keV e-beam energy and doses, in the range 100-1000 microC/cm(2), submicrometer dense lines of 1-microm pitch have been obtained. The results have been tested by fluorescence optical microscopy.

Biotin↗
PubMed2001

Keynote Address: The Time of Pioneers.

This article, dedicated to the memory of the late professor Raimond Castaing, will evoke the birth and the first developments of electron probe microanalysis in France.

Journal Article↗
PubMed2002

Bismuth nanowires for potential applications in nanoscale electronics technology.

Nanowires of bismuth with diameters ranging from 10 to 200 nm and lengths of 50 microm have been synthesized by a pressure injection method. Nanostructural and chemical compositional studies using environmental and high resolution transmission electron microscopy with electron stimulated energy dispersive X-ray spectroscopy have revealed essentially single crystal nanowires. The high resolution studies have shown that the nanowires contain amorphous Bi-oxide layers of a few nanometers on the surface. In situ environmental high resolution transmission electron microscopy (environmental-HRTEM) studies at the atomic level, in controlled hydrogen and other reducing gas environments at high temperatures demonstrate that gas reduction can be successfully applied to remove th oxide nanolayers and to maintain the dimensional and structural uniformity of the nanowires, which is key to attaining low electrical contact resistance.

Bismuth↗
PubMed2002

Synthesis of electron energy loss spectra for the quantification of detection limits.

We describe a method for predicting detection limits of minority elements in electron energy loss spectroscopy (EELS), and its implementation as a software package that gives quantitative predictions for user-specified materials and experimental conditions. The method is based on modeling entire energy loss spectra, including shot noise as well as instrumental noise, and taking into account all the relevant experimental parameters. We describe the steps involved in modeling the entire spectrum, from the zero loss up to inner shell edges, and pay particular attention to the contributions to the pre-edge background. The predicted spectra are used to evaluate the signal-to-noise ratios (SNRs) for inner shell edges from user-specified minority elements. The software also predicts the minimum detectable mass (MDM) and minimum mass fraction (MMF). It can be used to ascertain whether an element present at a particular concentration should be detectable for given experimental conditions, and also to quickly and quantitatively explore ways of optimizing the experimental conditions for a particular EELS analytical task. We demonstrate the usefulness of the software by confirming the recent empirical observation of single atom detection using EELS of phosphorus in thin carbon films, and show the effect on the SNR of varying the acquisition parameters. The case of delta-doped semiconductors is also considered as an important example from materials science where low detection limits and high spatial resolution are essential, and the feasibility of such characterization using EELS is assessed.

Calcium↗
PubMed2003

Compositional averaging of backscatter intensities in compounds.

We present high-precision measurements of pure element stable isotope pairs that demonstrate mass has no influence on the backscattering of electrons at typical electron microprobe energies. The traditional prediction of average backscatter intensities in compounds was pragmatically based on elemental mass fractions. Our isotopic measurements establish that this approximation has no physical basis. We propose an alternative model to mass fraction averaging, based on the number of electrons or protons, termed "electron fraction," which predicts backscatter yield better than mass fraction averaging. We also present an improved backscatter (electron loss) factor based on a modified electron fraction average for the ZAF atomic number correction that provides a significant analytical improvement, especially where large atomic number corrections are required.

Copper↗
PubMed2003

Investigation of winter atmospheric aerosol particles in downtown Katowice using XPS and SEM.

X-ray photoelectron spectroscopy (XPS) was used to determine the surface chemical composition of atmospheric particles (PM-10 and PM-2.5), collected in downtown Katowice, Upper Silesia, Poland, in the winter season (November and December 2000). Carbon- and oxygen-containing species dominated the particulate surface with traces of N, S, Si, Cl, Na, Zn, Al, Cu, Fe, Ca, K, Mg, Pb, and P present. Additionally, the size, morphology, and chemical composition of about 300 of the individual atmospheric particles were analyzed by high-resolution scanning electron microscopy and electron probe microanalysis. A number of aluminosilicates and metallic elements such as Fe, K, Mg, Zn, as well as rare earth elements, were detected by SEM. The results obtained show that the analyzed aerosol is of natural and anthropogenic origin. Particles containing sulfur compounds as well as oxygen and sodium in downtown Katowice come mainly from the east and southeast sectors.

Journal Article↗
PubMed2006

Practical aspects of carbon content determination in carburized steels by EPMA.

The carbon contents in carburized steels were investigated by electron probe microanalysis (EPMA) for a range of carbon levels in the solid solution less than 1 wt%. This article describes the difficulties encountered with the classic analytical procedure using the k ratio of X-ray intensities and the phi(rhoz) model. Here, a suitable calibration curve method is presented with emphasis on the metallographic study of standard specimens and on the carbon decontamination of samples.

Journal Article↗
PubMed2006

The determination of the efficiency of energy dispersive X-ray spectrometers by a new reference material.

A calibration procedure for the detection efficiency of energy dispersive X-ray spectrometers (EDS) used in combination with scanning electron microscopy (SEM) for standardless electron probe microanalysis (EPMA) is presented. The procedure is based on the comparison of X-ray spectra from a reference material (RM) measured with the EDS to be calibrated and a reference EDS. The RM is certified by the line intensities in the X-ray spectrum recorded with a reference EDS and by its composition. The calibration of the reference EDS is performed using synchrotron radiation at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt. Measurement of RM spectra and comparison of the specified line intensities enables a rapid efficiency calibration on most SEMs. The article reports on studies to prepare such a RM and on EDS calibration and proposes a methodology that could be implemented in current spectrometer software to enable the calibration with a minimum of operator assistance.

Journal Article↗
PubMed1998

Going Nondispersive.

: The energy-dispersive Si(Li) X-ray spectrometer, introduced 30 years ago into electron probe microanalysis (EPMA) by R. Fitzgerald et al., has profoundly affected the development of microanalysis. It offers many advantages over the wavelength-dispersive crystal spectrometer. It has no moving parts and covers the full energy range of interest in EPMA. There is no defocusing over large distances on the specimen, the efficiency of the device is high, varies slowly and continuously with atomic number, and can be predicted fairly accurately, and, most importantly, all emission lines are detected and can be observed simultaneously. The one remaining disadvantage of the Si(Li) spectrometer is its poorer energy resolution. Solid-state detection devices now under development promise to achieve resolution comparable to that of the crystal spectrometer.

Journal Article↗
PubMed2003

Topochemical speciation of intercalated palladium in graphite by valence band X-ray spectrometry in the electron microprobe.

The binding state of palladium was studied within the frame of an investigation on the mechanism of analyte fixation during the pyrolysis step in graphite furnace atomic spectrometry. One approach was the determination of the palladium intercalated in the pyrolytic coating of the graphite tube. Due to the low concentrations of intercalated palladium in the pyrolytic coating, precise determination of the shift of certain X-ray lines was chosen. From several investigated valence state sensitive X-ray transitions, the Pd Lbeta2/15 (L3-N4,5) line shift was the one best determinable. The measured line shifts are in the range of -0.14 to 0.71 eV at line widths of 13 eV (fwhm) and a line energy of 3.1729 keV. These very small line shifts were determined by electron probe microanalysis. The detection of the small line shifts was performed with a new method-by evaluation of the change of the intensity in the flanks of the X-ray line. The measurements yielded the following results: inside the pyrolytic graphite, the palladium is distributed inhomogeneously in the form of clusters or islands and in the form of particles on the surface of the pyrolytic graphite. The differentiation between particles and clusters is a very practical one: as long as a particle can be seen in the SEM we talk of particles. Often, however, Pd is detected in an area on the tube or platform surface without detection of a particle. Hence, it can be assumed that the Pd is present in the form of clusters which might even be intercalated in the uppermost graphite layers. The valence state inside these clusters does not appear to be uniform. It can be interpreted as a mixture of Pd with PdO in the center of the clusters or particles (positive peak shift) and of Pd bound to the graphite (strong negative peak shift). On the basis of these observations, a way is proposed to determine how activated Pd atoms in intercalated Pd domains are forming strong covalent bonds to analytes. These bonds are responsible for the analyte fixation of even very volatile analytes.

Journal Article↗
PubMed1995

Evidence for the proximity of calcium to the manganese cluster of photosystem II: determination by X-ray absorption spectroscopy.

The photosynthetic oxygen-evolving complex contains a cluster of four manganese atoms and requires both Ca and Cl for activity. The question of Ca proximity to the Mn cluster has been investigated by performing Mn X-ray absorption experiments on native samples of photosystem II (PS II) and on samples depleted of Ca and reconstituted by either Ca or Sr. Analysis of X-ray K-edge spectra demonstrates no significant differences in oxidation state or symmetry between Ca- and Sr-reactivated preparations. Differences are observed in the extended X-ray absorption fine structure (EXAFS). The amplitude of a Fourier transform peak due to scatters at distances greater than 3 A is larger for samples reactivated with strontium than for calcium-reactivated samples. Taking into account the stoichiometry of Mn and Ca atoms in PS II, and considering physically reasonable structures, curve-fitting analyses of the EXAFS data using FEFF5-calculated parameters favor a model where both manganese and calcium (or strontium) scatterers contribute to the Fourier peak at approximately 3 A. Other models for the approximately 3 A peak with multiple Mn-Mn interactions or multiple Mn-Ca(Sr) interactions can also be fit to the data, but are considered less likely. This result provides confirmation for the structural proximity of Ca to the Mn cluster suggested previously [Yachandra, V. K., et al. (1993) Science 260, 675-679]. Possible structural arrangements for a calcium-binding site are discussed.

Binding Sites↗
PubMed2000

Domains I and III of the human copper chaperone for superoxide dismutase interact via a cysteine-bridged Dicopper(I) cluster.

Copper binding to the human copper chaperone for superoxide dismutase (hCCS) has been investigated by X-ray absorption spectroscopy. Stoichiometry measurements on the dialyzed, as-isolated protein indicated that up to 3.5 Cu ions bound per hCCS molecule. Reduction with either sodium dithionite or dithiothreitol decreased the copper binding ratio to 2 coppers per hCCS monomer. Analysis of the as-isolated EXAFS data indicated coordination of Cu by a mixture of S and N backscatterers, suggestive of heterogeneous binding of copper between Cu-cysteine binding sites of domain I or III and copper-histidine SOD1-like metal binding sites of domain II. The best fit was obtained with 1.6 Cu-S (cysteine) at 2.24 A (2sigma(2) = 0.011 A(2)) and 1.1 N (histidine) at 1.98 A (2sigma(2) = 0.005 A(2)). A peak of variable intensity in the Fourier transform (FT) of the as-isolated protein at 2.7 A was suggestive of the presence of a heavy atom scatterer such as Cu. Analysis of the dithionite- and DTT-reduced derivatives indicated that copper was lost from the histidine coordinating sites, resulting in a S-only environment with copper coordinated to three S backscatterers at 2. 26 A. The heavy atom scatterer peak was now prominent in the FT and could be well fit by a Cu-Cu interaction at 2.72 A. The data were best interpreted by a dinuclear mu(2)()-bridged cluster with doubly bridging cysteine ligands similar to the cluster proposed to exist in the cytochrome c oxidase chaperone COX17. Analysis of primary sequence and X-ray structural information on yeast CCS strongly suggests that this cluster bridges between domains I and III in hCCS. A mechanism for copper translocation is briefly discussed.

Chloroplast Proteins↗
PubMedDate not supplied

Directed-sorting method for synthesis of bead-based combinatorial libraries of heterogeneous catalysts.

The synthesis and analysis of inorganic material combinatorial libraries by a directed-sorting, split-pool bead method was demonstrated. Directed-sorting, split-pool, metal-loaded libraries were synthesized by adsorbing metal salts (H2PtCl6, SnCl2, CuCl2, and NiCl2) and metal standards (Pt, Cu, Ni in HCl) onto 2-mg porous gamma-alumina beads in 96- or 384-well plates. A matrix algorithm for the synthesis of bead libraries treated each bead as a member of a row or column of a given matrix. Computer simulations and manual tracking of the sorting process were used to assess library diversity. The bead compositions were analyzed by energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, electron probe microanalysis, inductively coupled plasma atomic emission spectroscopy, and inductively coupled plasma mass spectroscopy. The metal-loaded beads were analyzed by laser-activated membrane introduction mass spectroscopy (LAMIMS) for catalytic activity using methylcyclohexane dehydrogenation to toluene as a probe reaction. The catalytic activity of individual beads that showed minimal (approximately 20% of that of Pt on alumina) to high conversion could be determined semiquantitatively by LAMIMS. This method, therefore, provides an alternative to screening using microreactors for reactors that employ catalysts in the form of beads. The directed-sorting method offers the potential for synthesis of focused libraries of inorganic materials through relatively simple benchtop split-pool chemistry.

Catalysis↗
PubMed2001

Artificial peptidase with an active site comprising a Cu(II) center and a proximal guanidinium ion. A carboxypeptidase A analogue.

An immobile artificial metallopeptidase having a well-defined active site was constructed on the backbone of cross-linked polystyrene by adjoining a guanidinium moiety to the Cu(II) complex of a tetraaza ligand. The catalyst (CABP) and intermediate polymers were characterized by elemental analysis, IR, inductively coupled plasma measurement, electron probe microanalysis, test for primary amines, binding of Cu(II) ion, and complexation of p-nitrobenzoate ion. CABP effectively catalyzed amide hydrolysis of carboxyl-containing N-acyl amino acids. The catalytic rate of CABP in the hydrolysis of unactivated amides was comparable to that of the catalytic antibody with the highest peptidase activity reported to date. It is proposed that the guanidinium moiety of CABP recognizes the carboxylate anion of the substrate whereas the Cu(II) center participates in the cleavage of the amide bond of the complexed substrate. Several characteristic features of carboxypeptidase A were reproduced by CABP: catalytic action of the metal ion, participation of guanidinium in substrate recognition, hydrolysis of small unactivated amides, and substrate selectivity toward amide bonds adjacent to a carboxylate group.

Amides↗