X-ray Absorption Edge Studies Research Articles

X-ray absorption edge studies of the electronic structure of metal catalysts

Studies of x-ray absorption threshold resonance at L[sub III] and Lu[sub II] absorption edges can provide useful information on the electronic structure of a metal catalyst, if complications associated with sample thickness effects are recognized and corrected. One can measure the d-band occupancies of various metals of interest in catalysis, thereby providing a quantitative basis for relating catalytic activity to this parameter. One can also determine whether or not this parameter is influenced by the state of dispersion of the metal on a support, by the chemical nature of the support itself, or by alloying. Moreover, the resonances are useful for probing the oxidation states of precursor species during various stages in the preparation of a metal catalyst. Such information can be used in the optimization of a preparation procedure. For these reasons, among others, absorption edge studies provide a valuable probe for the characterization of metal catalysts.

Reactivity of the laccase trinuclear copper active site with dioxygen: an x-ray absorption edge study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactivity of the laccase trinuclear copper active site with dioxygen: an x-ray absorption edge studyJames L. Cole, Grace O. Tan, Edward K. Yang, Keith O. Hodgson, and Edward I. SolomonCite this: J. Am. Chem. Soc. 1990, 112, 6, 2243–2249Publication Date (Print):March 1, 1990Publication History Published online1 May 2002Published inissue 1 March 1990https://doi.org/10.1021/ja00162a025RIGHTS & PERMISSIONSArticle Views419Altmetric-Citations60LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (966 KB) Get e-Alerts Get e-Alerts

New structural insights into the iron-molybdenum cofactor from Azotobacter vinelandii nitrogenase through sulfur K and molybdenum L x-ray absorption edge studies

The electronic and structural nature of sulfur and molybdenum in the FeMO cofactor (FeMO-co) isolated from Azotobacter vinelandii MoFe protein has been studied by X-ray absorption edge and near-edge spectroscopy (referred to herein collectively as XANES) at the sulfur K and molybdenum L/sub 3/ and L/sub 2/ absorption edges. In contrast to the relatively poor resolution found for X-ray absorption edges at higher energies (e.g., several electronvolts at the molybdenum K edge at 20 keV), resolution in the 2.5-3.0-keV region is significantly improved (e.g., 0.5 eV at the sulfur K edge at 2.47 keV), resulting in more edge structure with higher sensitivity to changes in electronic and structural environment. In order to record spectra from dilute samples at these low energies, an experimental method that takes advantage of the higher flux synchrotron radiation from an undulator magnet has been developed. XANES spectra have been recorded for FeMo-co in the oxidized (ox) and semireduced (s-r) forms and, for comparison, a number of inorganic complexes containing molybdenum and sulfur. To remove the interference of dithionite, its decomposition products, and other small, unbound molecules from the FeMo-co spectrum, an anaerobic column chromatographic method of purification has been developed. The spectrum of dithionite-free FeMo-comore » in the oxidized form could thus be recorded.« less

Oxygen excess in layered lanthanide nickelates

Density measurements on large single-crystal specimens of La 2NiO 4+δ and Pr 2NiO 4+δ show that oxygen nonstoichiometry arises from the presence of excess lattice oxygen. X-ray photoelectron spectra as well as X-ray absorption edge studies provide no evidence for the existence of Ni 3+ in these oxygen-excess nickelates under the conditions of the measurements. Transmission electron microscopy has revealed a novel type of exsolution process of the stoichiometric phase out of nonstoichiometric La 2NiO 4 during heating in CO 2 at 870 K for 3 h. An interpretation of the results in terms of the existence of peroxide species within the conducting layers is proposed.

Spectrophotometric and x-ray absorption edge study of complexation of carbon monoxide with ferric tetrasulfophthalocyanine in alkaline solution

Spectrophotometric and x-ray absorption edge study of complexation of carbon monoxide with ferric tetrasulfophthalocyanine in alkaline solution

QUANTITATIVE Cu X-RAY ABSORPTION EDGE STUDIES : OXIDATION STATE AND SITE STRUCTURE DETERMINATION

X-ray absorption edge studies of Cu(I) complexes with different coordination number and covalency reveal that the 8983-8984 eV feature (assigned as the 1s→4p transition) can be correlated with ligation and site geometry. These Cu(I) features have been qualitatively interpreted using a Ligand Field model, and this has been applied to analyze the polarized single crystal, pH dependent edge spectra of reduced plastocyanin. In addition, normalized difference X-ray absorption edge analysis has been used to quantitatively determine the percent of Cu(I) in several derivatives of the multicopper oxidase, laccase.

X-ray absorption studies of laccase and ceruloplasmin

Determination of oxidation state is essential to interpretation of the spectroscopy and chemistry of metal ions. We will describe the use of X-ray absorption edges to quantitatively determine the percent of Cu(I) in samples of mixed Cu(I)/Cu(II) composition, and specific applications of this technique to characterization of copper oxidation states in various derivatives of the multicopper oxidases laccase and ceruloplasmin. It has long been recognized that the energy and the shape of an X-ray absorption edge are correlated, respectively, with the effective charge on the absorbing atom and with the geometry of the absorbing site. Cu complexes, in particular, have X-ray absorption edges which change dramatically with metal oxidation state. Cuprous complexes show an intense transition at approximately 8984 eV which is absent for complexes in the +2 oxidation state. In addition, the peak absorbance for Cu(I) complexes is less intense that for Cu(II) complexes. The different edge shapes for Cu(I) and Cu(II) have previously been used as a qualitative indicator of the presence of Cu(I) in a variety of metalloproteins [1–4], and in particular, in a study of the multicopper oxidase Rhus vernicifera laccase [5]. Laccase, which contains four copper ions at its active site, is the least complicated of the multicopper oxidases and is the current focus of our binuclear copper research. While study of the coupled binuclear site in this enzyme is complicated by the presence of blue and normal copper centers, a reversible procedure exists for T2 copper removal to yield type 2 depleted laccase (T2D) [6], wherein the binuclear site is only complicated by the additional blue copper site. Much controversy has ensued over the chemical and spectroscopic properties of the prepared T2D laccase [7]. Our preliminary X-ray absorption edge studies [5] indicated that T2D contained approximately 70% cuprous copper, while H 2O 2 treated (met) T2D and native laccase contained essentially no Cu(I). Together with EPR evidence that the T1 copper remains oxidized in T2D laccase, these edge studies demonstrated that T2D laccase contains a reduced T3 site which can be reoxidized by peroxide. We will present evidence that the properly normalized difference between two Cu X-ray absorption edges, under certain circumstances, can also be used to quantitatively determine the Cu(I) concentration in a sample [8]. We have studied an extensive series of Cu model complexes in order to determine the limitation of the different-edge technique. We have then used this technique to quantitatively determine the Cu(I) concentration in native and T2D laccase as well as their ferricyanide, nitrite, and hydrogen peroxide treated forms. Preliminary results on ceruloplasmin will also be presented. An Extended X-ray Absorption Fine Structure (EXAFS) study of met and met-N − 3 T2D laccase is also discussed. The EXAFS data are analysed to determine the average environment of the three Cu atoms in the T2D laccase derivatives, and also compared with the EXAFS data for plastocyanin, which is an appropriate model for the blue copper site in laccase [9].

ChemInform Abstract: STATE OF MANGANESE IN THE PHOTOSYNTHETIC APPARATUS. 2. X‐RAY ABSORPTION EDGE STUDIES ON MANGANESE IN PHOTOSYNTHETIC MEMBRANE

Chemischer InformationsdienstVolume 12, Issue 50 Physical Organic Chemistry ChemInform Abstract: STATE OF MANGANESE IN THE PHOTOSYNTHETIC APPARATUS. 2. X-RAY ABSORPTION EDGE STUDIES ON MANGANESE IN PHOTOSYNTHETIC MEMBRANE J. A. KIRBY, J. A. KIRBYSearch for more papers by this authorD. B. GOODIN, D. B. GOODINSearch for more papers by this authorT. WYDRZYNSKI, T. WYDRZYNSKISearch for more papers by this authorA. S. ROBERTSON, A. S. ROBERTSONSearch for more papers by this authorM. P. KLEIN, M. P. KLEINSearch for more papers by this author J. A. KIRBY, J. A. KIRBYSearch for more papers by this authorD. B. GOODIN, D. B. GOODINSearch for more papers by this authorT. WYDRZYNSKI, T. WYDRZYNSKISearch for more papers by this authorA. S. ROBERTSON, A. S. ROBERTSONSearch for more papers by this authorM. P. KLEIN, M. P. KLEINSearch for more papers by this author First published: December 15, 1981 https://doi.org/10.1002/chin.198150045AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue50December 15, 1981 RelatedInformation

State of manganese in the photosynthetic apparatus. 2. X-ray absorption edge studies on manganese in photosynthetic membrane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTState of manganese in the photosynthetic apparatus. 2. X-ray absorption edge studies on manganese in photosynthetic membraneJ. A. Kirby, D. B. Goodin, T. Wydrzynski, A. S. Robertson, and M. P. KleinCite this: J. Am. Chem. Soc. 1981, 103, 18, 5537–5542Publication Date (Print):September 1, 1981Publication History Published online1 May 2002Published inissue 1 September 1981https://doi.org/10.1021/ja00408a043RIGHTS & PERMISSIONSArticle Views196Altmetric-Citations99LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (799 KB) Get e-Alerts Get e-Alerts

XPS and X-ray absorption edge studies of the surface and bulk valence states of cerium in CeCo2

XPS and LIII X-ray absorption edge studies regarding the valence state of cerium have been carried out on the intermetallic compounds CeCo2, which becomes superconducting at low temperatures. It is observed from XPS that the surface shows both Ce3+ and Ce4+ valence states, while the X-ray absorption edge studies reveal only Ce4+ in the bulk. Thus valence fluctuation and superconductivity do not coexist in the bulk of this compound.

X-ray absorption edge studies on oxidized and reduced cytochrome c oxidase.

The x-ray absorption edge spectra of the Cu and Fe-centers in oxidized and reduced cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase: EC 1.9.3.1) have been obtained using synchrotron radiation from the SPEAR storage ring at the Stanford Linear Accelerator Center. In addition, oxidized and reduced plastocyanin as well as a number of model copper compounds in various oxidation states were also examined. A comparison of the absorption edge fine structure of cytochrome oxidase with those of the models indicates that one of the two coopers in the oxidized protein is in the +1 oxidation state. Upon reduction of the protein with dithionite, the second copper becomes Cu(I). The shift in the Fe K-edge of cytochrome oxidase upon reduction is small (about 2 e V or 3 times 10(-19 J) and is comparable to that previously observed for the reduction of the heme iron of cytochrome c.

An X-ray absorption edge study of zeolite-supported platinum

Platinum in a large pore zeolite (Linde SK-200: 0.5% Pt Ca Y zeolite) was characterized by X-ray absorption edge spectroscopy, acid solubility studies, X-ray diffraction line-broadening, and hydrogen adsorption measurements. The absorption edge data show that, all the platinum was reduced to a zero-valent state, and that on the average this platinum is smaller in size than that found in conventional reforming catalysts. Sixty percent of the reduced platinum is small enough in size to dissolve in acid; X-ray diffraction shows the remaining 40% is present as 60 Å metal crystals. These data in conjunction with hydrogen adsorption data showing an uptake of 0.5 hydrogen atom per platinum atom lead to an estimate of 10 Å for the size of the acid-soluble platinum, small enough to fit inside the zeolite cages. The exposure of zero-valent platinum to hydrogen leaves the platinum with a negative charge. The exposure of zeolite-supported platinum to hydrogen at 300 °C and 1 atm pressure for 1–2 hr produces a larger change in the platinum X-ray absorption edge spectrum than does a similar exposure at 100 °C. This has been interpreted to mean that a stronger platinum-hydrogen bond is formed at 300 °C. For every platinum atom in the sample 0.5 hydrogen atom is adsorbed after a 1-hr exposure at either 100 ° or 300 °C and 1 atm pressure. This hydrogen affects the X-ray absorption edge spectrum. Therefore, it is this hydrogen that is bonded to platinum and serves as a measure of its size. An additional 1.2 hydrogen atoms can be adsorbed per sample platinum atom at 300 °C under 1 atm pressure by waiting 20 or more hours. This additional hydrogen does not affect the platinum absorption edge spectrum and is therefore interpreted to be not adsorbed by the catalyst platinum.