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Pieter Glatzel

Publications and source records attributed to Pieter Glatzel.

12 recordsLinked to original sources
PubMed2006

Structure and orientation of the Mn4Ca cluster in plant photosystem II membranes studied by polarized range-extended x-ray absorption spectroscopy.

X-ray absorption spectroscopy has provided important insights into the structure and function of the Mn(4)Ca cluster in the oxygen-evolving complex of Photosystem II (PS II). The range of manganese extended x-ray absorption fine structure data collected from PS II until now has been, however, limited by the presence of iron in PS II. Using a crystal spectrometer with high energy resolution to detect solely the manganese Kalpha fluorescence, we are able to extend the extended x-ray absorption fine structure range beyond the onset of the iron absorption edge. This results in improvement in resolution of the manganese-backscatterer distances in PS II from 0.14 to 0.09A(.) The high resolution data obtained from oriented spinach PS II membranes in the S(1) state show that there are three di-mu-oxo-bridged manganese-manganese distances of approximately 2.7 and approximately 2.8A in a 2:1 ratio and that these three manganese-manganese vectors are aligned at an average orientation of approximately 60 degrees relative to the membrane normal. Furthermore, we are able to observe the separation of the Fourier peaks corresponding to the approximately 3.2A manganese-manganese and the approximately 3.4A manganese-calcium interactions in oriented PS II samples and determine their orientation relative to the membrane normal. The average of the manganese-calcium vectors at approximately 3.4A is aligned along the membrane normal, while the approximately 3.2A manganese-manganese vector is oriented near the membrane plane. A comparison of this structural information with the proposed Mn(4)Ca cluster models based on spectroscopic and diffraction data provides input for refining and selecting among these models.

Calcium↗
PubMed2006

Valence-to-core X-ray emission spectroscopy identification of carbide compounds in nanocrystalline Cr coatings deposited from Cr(III) electrolytes containing organic substances.

Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.

Journal Article↗
PubMed2006

On the presence of Fe(IV) in Fe-ZSM-5 and FeSrO3-x --unequivocal detection of the 3d4 spin system by resonant inelastic X-ray scattering.

The contribution of a 3d(4) spin configuration to the valence electronic structure of Fe compounds can be probed via spin-selective Fe K-pre-edge absorption spectra, using resonant inelastic X-ray scattering (RIXS). The 3d(4) configuration of Fe(IV) can be unequivocally detected even in a mixture with the high-spin 3d(5) configuration of Fe(III). This is demonstrated on the perovskite FeSrO(3-x) with formal oxidation state Fe(IV). When the technique was applied to an Fe-ZSM-5 catalyst during reaction with N(2)O, no 3d(4) configuration was detected. The formation of Fe(IV) upon reaction of Fe-ZSM-5 with N(2)O can, therefore, be ruled out.

Biophysics↗
PubMed2006

Identification of CO adsorption sites in supported Pt catalysts using high-energy-resolution fluorescence detection X-ray spectroscopy.

High-energy-resolution fluorescence detection (HERFD) X-ray spectroscopy is presented as a new tool for the identification of the bonding sites of reactants in supported metal catalysts. The type of adsorption site of CO on an alumina-supported platinum catalyst and the orbitals involved in the bonding are identified. Because X-ray absorption spectroscopy (XAS) is element-specific and can be used under high pressures and temperatures, in situ HERFD XAS can be applied to a swathe of catalytic systems, including alloys.

Letter↗
PubMed2006

Unusual coordination behavior of Cr3+ in microporous aluminophosphates.

A CrAPO-5 molecular sieve has been investigated with X-ray absorption spectroscopy (EXAFS-XANES) as dehydrated material and after loading with water and ammonia to unravel the coordination geometries of Cr3+ in the framework of a microporous crystalline aluminophosphate, more particularly of the AFI-type. A comparison of the XANES data, a preedge analysis with crystal field multiplet calculations and EXAFS data, pointed toward the presence of framework Cr3+ which, on dehydration, takes on a distorted tetrahedral coordination state. Due to the 3d3 configuration of Cr3+, this unusual tetrahedral coordination environment strongly tends to transform into the more stable 6-fold coordination geometry by binding two extraframework water molecules during hydration. In the presence of ammonia, tetrahedral Cr3+ readily transforms into a 5-fold coordination geometry by binding one ammonia molecule. Therefore, depending on the environmental conditions, the Cr3+ ions can occur in a 4-, 5-, or 6-fold coordination. This observation underlines the flexibility of transition metal ions, such as Cr3+, to cope with unusual coordination geometries in inorganic hosts, making them interesting as potential active sites in heterogeneous catalysis.

Journal Article↗
PubMed2005

1s2p resonant inelastic X-ray scattering of iron oxides.

1s2p resonant inelastic X-ray scattering (RIXS) spectroscopy has been measured for a series of iron oxides, including octahedral and tetrahedral Fe(II) and Fe(III) systems. Their spectral shapes have been analyzed and explained using crystal-field multiplet simulations. The RIXS planes and the K-edge and L-edge X-ray absorption spectra related to these RIXS planes will be discussed with respect to their analytical opportunities. It is concluded that the full power and possibilities of 1s2p RIXS needs an overall resolution of 0.3 eV. This will yield a technique with more detailed information than K-edge and L-edge X-ray absorption combined, obtained in a single experiment. Another major advantage is that 1s2p RIXS involves only hard X-rays, and experiments under essentially any condition and on any system are feasible.

Electrons↗
PubMed2005

High-resolution Mn EXAFS of the oxygen-evolving complex in photosystem II: structural implications for the Mn4Ca cluster.

The biological generation of oxygen by the oxygen-evolving complex in photosystem II (PS II) is one of nature's most important reactions. The recent X-ray crystal structures, while limited by resolutions of 3.2-3.5 A, have located the electron density associated with the Mn4Ca cluster within the multiprotein PS II complex. Detailed structures critically depend on input from spectroscopic techniques, such as EXAFS and EPR/ENDOR, as the XRD resolution does not allow for accurate determination of the position of Mn/Ca or the bridging and terminal ligand atoms. The number and distances of Mn-Mn/Ca/ligand interactions determined from EXAFS provide important constraints for the structure of the Mn4Ca cluster. Here, we present data from a high-resolution EXAFS method using a novel multicrystal monochromator that show three short Mn-Mn distances between 2.7 and 2.8 A and, hence, the presence of three di-mu-oxo-bridged units in the Mn4Ca cluster. This result imposes clear limitations on the proposed structures based on spectroscopic and diffraction data and provides input for refining such structures.

Calcium↗
PubMed2005

X-ray damage to the Mn4Ca complex in single crystals of photosystem II: a case study for metalloprotein crystallography.

X-ray absorption spectroscopy was used to measure the damage caused by exposure to x-rays to the Mn(4)Ca active site in single crystals of photosystem II as a function of dose and energy of x-rays, temperature, and time. These studies reveal that the conditions used for structure determination by x-ray crystallography cause serious damage specifically to the metal-site structure. The x-ray absorption spectra show that the structure changes from one that is characteristic of a high-valent Mn(4)(III(2),IV(2)) oxo-bridged Mn(4)Ca cluster to that of Mn(II) in aqueous solution. This damage to the metal site occurs at a dose that is more than one order of magnitude lower than the dose that results in loss of diffractivity and is commonly considered safe for protein crystallography. These results establish quantitative x-ray dose parameters that are applicable to redox-active metalloproteins. This case study shows that a careful evaluation of the structural intactness of the active site(s) by spectroscopic techniques can validate structures derived from crystallography and that it can be a valuable complementary method before structure-function correlations of metalloproteins can be made on the basis of high-resolution x-ray crystal structures.

Calcium↗
PubMed2004

The electronic structure of Mn in oxides, coordination complexes, and the oxygen-evolving complex of photosystem II studied by resonant inelastic X-ray scattering.

Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p(3/2) RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (Mn(III)(acac)3 and Mn(IV)(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital.

Electrons↗
PubMed2002

Electronic structure of Ni complexes by X-ray resonance Raman spectroscopy (resonant inelastic X-ray scattering).

The potential of 1s2p resonant inelastic (Raman) X-ray scattering (RIXS) is demonstrated for a series of Ni coordination complexes. In this technique, incident and scattered photon energies lie in the hard X-ray range (>5 keV). The 1s2p RIXS contour plots provide information that is complementary to K-edge and L-edge spectroscopy. RIXS spectroscopy promises to be a valuable probe of electronic structure

Nickel↗
PubMed2002

Site-selective EXAFS in mixed-valence compounds using high-resolution fluorescence detection: a study of iron in Prussian Blue.

A quantitative analysis is presented for the site-selective Fe K-edge absorption spectra of Prussian Blue: Fe(4)[Fe(CN)(6)](3) x xH(2)O (x = 14-16). The site-selective spectra were recorded using high-resolution fluorescence detection of the K beta emission from a polycrystalline sample. The K beta fluorescence lines arising from the high-spin and low-spin sites are shifted in energy. Since the emission features partially overlap, fluorescence-detected absorption spectra using different emission energies represent different linear combinations of the pure high-spin and low-spin EXAFS. A numerical method was used to extract the individual site EXAFS spectra from the experimental data. The analysis yields a range of solutions. A unique solution can be obtained if homovalent model compounds are used to simulate the K beta fluorescence emission from the two Fe sites in Prussian Blue. EXAFS analysis of the range of spectra obtained in the numerical method yields almost identical interatomic distances for the different spectra while the Debye-Waller factors vary considerably. The distances obtained in the EXAFS fit correspond to the crystallographic distances.

Crystallography, X-Ray↗