Search

Abstract: Acutolysin-C, a snake-venom zinc metalloproteinase, displays a distinct pH-dependent proteolytic activity, which has been tentatively assigned to a structural change of the zinc-containing catalytic center. In this work we compare X-ray absorption near-edge structure (XANES) experimental spectra at the Zn K-edge and theoretical calculations of solutions at different pH values. The experimental data show clear differences confirmed by a best fit using the MXAN procedure. The results show that, when pH decreases from pH 8.0 to pH 3.0, the zinc-coordinating catalytic water molecule moves far from the Glu143 residue that is considered to play an essential role in the proteolytic process. Data suggests that this is the possible mechanism that deactivates the metalloproteinase. [Copyright &y& Elsevier]

Abstract: This contribution investigates the effect on the imaging contrast of the small angle scattering and of the rocking curve in the entire angular range. We show that based on the small angle scattering properties, the reflectivity of the crystal analyzer and the rocking curve of the monochromator–analyzer, in a diffraction enhanced imaging (DEI) experimental setup the contrast of the image collected at the top of the rocking curve is always higher than that of the apparent absorption image. Moreover, our experimental data confirm that the quality of a refraction image is superior to a refraction-like image. In order to understand the observed behavior we introduce and discuss the contribution of a new term in the classical DEI equation. [Copyright &y& Elsevier]

Abstract: Diffraction enhanced imaging (DEI) with two crystals has been performed at the 4W1A beamline at Beijing Synchrotron Radiation Facility (BSRF). Two different crystal geometrical layouts were used to collect images, in the first layout the rotation axis of the crystal has been set perpendicular to the orbital plane while in the second the axis is parallel to the orbital plane. Performance comparison between the two layouts is discussed in terms of thermal expansion of the crystal induced by the heat load, imaging homogeneity, spatial resolution and angular resolution. From both experimental and theoretical data we show that the best images may be obtained with the optical layout in which the rotation axis of the crystals is perpendicular to the orbital plane. [Copyright &y& Elsevier]

Abstract: A monolithic half focusing polycapillary X-ray lens (MHFPXRL) composed of 289,000 capillaries is used to produce a synchrotron radiation microbeam. The energy dependence of the output focal distance, focal spot size, transmission efficiency, vertical beam position, and gain in flux density of this microbeam is studied in detail. There is a slight change in the output focal distance of the MHFPXRL when the X-ray energies change. [Copyright &y& Elsevier]

Abstract: The recent discovery of the magnesium diboride superconductor, a system characterized by a remarkably high transition temperature (), has renewed interest towards experimental and theoretical research of the superconductivity in isostructural systems, such as transition-metal diborides. Here we present an X-ray-absorption fine-structure investigation in AlB2-type 4d transition-metal diborides TMB2 (TM=Y, Zr, Nb) at the transition-metal K-edge. The vibrational behavior of these transition-metal diborides has also been investigated by analyzing the extended X-ray-absorption fine-structure (EXAFS) spectra. The change of the bond length and Debye–Waller factors of TM–B, TM–TM (in-plane) and TM–TM (out-plane) with the covalent radii of the transition-metal atoms has been shown. Data clearly demonstrate that the chemical stability is in the following order for the 4d transition-metal diborides: ZrB2>NbB2>YB2. The chemical stability of YB2 must be much less than that of the two other compounds. It suggests that the species difference of the transition metals influences the vibrational behavior of TM–B and TM–TM bonds. In particular, a clearly different behavior of the vibration is observed for the transition-metal atoms in and out of plane. The results suggest the importance of the metal atoms in the diborides for superconductivity of these compounds and an intimate relationship between the local atomic displacements and the superconductivity. [Copyright &y& Elsevier]

Abstract: A new diffraction-enhanced imaging (DEI) set-up was designed and constructed at Beijing Synchrotron Radiation Facility. The size of imaging beam cross section is the same as that of incident “white” X-ray beam in the new set-up. While in the original set-up, the size is always limited in one direction. Thus, larger samples can be imaging in a single exposure without need for scanning of the sample and detector in the new set-up. Choosing a fly as sample, DEI and DEI-computed-tomography (CT) experiments were carried out using the new set-up. Experimental results show that the spatial resolution of the CT image is in the tens of microns. [Copyright &y& Elsevier]

Abstract: The 4W1A beamline at the Beijing Synchrotron Radiation Facility (BSRF) had been dedicated to researches in the field of X-ray phase contrast imaging. In both available layouts, e.g., in-line imaging and diffraction enhanced imaging, a spatial resolution better than 10μm has been achieved and an X-ray phase contrast CT system has been installed and tested on the beamline. With or without analyzer, it can work either in in-line or the diffraction enhanced mode. [Copyright &y& Elsevier]

Abstract: Peptide deformylase (PDF, EC 3.5.1.27) is essential for the normal growth of eubacterium but not for mammalians. Recently, PDF has been studied as a target for new antibiotics. In this paper, X-ray absorption spectroscopy was employed to determine the local structure around the zinc ion of PDF from Leptospira Interrogans in dry powder, because it is very difficult to obtain the crystallized sample of LiPDF. We performed X-ray absorption near edge structure (XANES) calculation and reconstructed successfully the local geometry of the active center, and the results from calculations show that a water molecule (Wat1) has moved towards the zinc ion and lies in the distance range to coordinate with the zinc ion weakly. In addition, the sensitivity of theoretical spectra to the different ligand bodies was evaluated in terms of goodness-of-fit. [Copyright &y& Elsevier]

Abstract: A method of measuring energy spectrum of synchrotron radiation (SR) based on attenuation is described in this paper. Tikhonov regularized method is applied to reconstruct the spectral distribution of SR. The feasibility of the method is studied in detail by using a hypothetical SR spectrum. The applied results of the spectrum of 4W1B beamline in BSRF (Beijing Synchrotron Radiation Facility) are shown. [Copyright &y& Elsevier]

Abstract: ZrO2-doped CuZnO catalyst prepared by successive-precipitation method was investigated by ICP-AES, BET, TEM, XRD, EXAFS, H2-TPR and CO/CO2 hydrogenation. The active phase of copper in CuZnO catalyst prepared by co-precipitation method was well-crystallized. The presence of ZrO2 led to a high copper dispersion, which was distinctive from CuZnO. Though the activity for carbon monoxide hydrogenation was little lower than that of CuZnO catalyst, ZrO2-doped CuZnO catalyst showed much higher activity and selectivity towards methanol synthesis from carbon dioxide hydrogenation. Moreover, ZrO2-doped CuZnO catalyst showed high performance for methanol synthesis from CO2-rich syngas. [Copyright &y& Elsevier]

Abstract: γ-Alumina-supported β-Mo2N0.78 catalyst was synthesized by the temperature-programmed nitriding reaction and tested to determine its catalytic activity and selectivity during the hydrodesulfurization (HDS) of dibenzothiophene. The results indicated that the conversion increases with reaction temperature and hydrogen pressure. And increasing the hydrogen pressure results in more hydrogenation, but increasing reaction temperature can improve the two parallel pathways of direct desulfurization and hydrogenation desulfurization at same degree. Sulfur can replace the surface oxygen of passivated nitride in the HDS reaction although the bulk structure is preserved. [Copyright &y& Elsevier]

The structure of the extraction complexes of light lanthanides (La(III), Nd(III), Eu(III)) with bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HBTMPDTP) have been characterized with extended X-ray absorption fine structure spectroscopy (EXAFS), IR, and MS; the tR spectrum of the extraction complex of [sup 241]Am with HBTMPDTP has been studied too. The molecular formula of the extraction complexes of lanthanides is deduced to be HML[sub 4]·H[sub 2]O (M = La, Nd, Eu; L = anion of HBTMPDTP). The coordination number of Ln(III) in the complexes is 8; the coordinated donor atoms are 7 sulfur atoms from 4 HBTMDTP molecules and 10 atom from a hydrated water molecule. With the increase of the atomic number of Ln, the coordination bond lengths of Ln-O and Ln-S decrease in the complexes. For La(III), Nd(III), and Eu(III), the coordination bond lengths of Ln-O are 2.70, 2.56, and 2.50, respectively, the coordination bond lengths of Ln-S are 3.01, 2.91, and 2.84, respectively, and the average distances between Ln and P atoms are 3.60, 3.53, and 3.46, respectively. The structure of the extraction complexes of Ln(III) with HBTMDTP is different from that of the Am(III) extraction complex. The results of IR show that there is no water coordinated with Am in the extraction complex. The molecular formula of the complex of Am(III) is deduced as being HAmL[sub 4], and there are 8 S atoms from 4 HBTMPDTP molecules coordinated with Am. Composition and structure differences of the extraction complexes may be one of the most most important factors affecting the excellent selectivity of HBTMPDTP for Am(III) over Ln(III). [ABSTRACT FROM AUTHOR]

Fe7C3 nanocrystals encapsulated in carbon nanoparticles, with sizes ranging from 10 to 40 nm, were synthesized via the explosion of a hybrid xerogel containing oxidized pitch and iron nitrate. Explosion of the hybrid xerogel was induced by heat treatment. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were employed to determine the structure of the nanoparticles in the explosion product. The results show that the Fe7C3 nanocrystals are nested inside amorphous carbon shells that protect them from oxidation by air. [Copyright &y& Elsevier]

VUV-UV and Eu-L3 edge XANES spectra were measured for europium-doped strontium tetraborate prepared by solid state reaction at high temperature in air. The VUV-UV spectra show that the host absorption band of SrB4O7 appears below 170 nm. The charge transfer band of Eu3+ doped in SrB4O7 is peaked at 272 nm. The 4f–5d transitions of Eu2+ consist of a band peaked at 310 nm with a shoulder at 280 nm and also include the bands peaked at 238 (weak) and 203 (strong) nm. The result of XANES spectrum at Eu-L3 edge of the synthesized sample indicates that Eu3+ and Eu2+ coexist in SrB4O7:Eu prepared in air, which is consistent with the results of the VUV-UV spectra. [Copyright &y& Elsevier]

XAFS (EXAFS and XANES) at Eu–L3 edge were used to determine the local structure and the valences of europium in CaBPO5:Eu prepared in air. The results of EXAFS showed that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu–O were 2.39 A˚ in the host lattice. XANES at Eu–L3 edge exhibited that Eu2+ and Eu3+ coexisted in the matrix. The luminescent spectrum of the material excited by VUV at 147 nm presented a similar spectrum with that excited by f–f transition of Eu3+ at 396 nm and f–d transition of Eu2+ at 312 nm. The broad emission band due to both 4f65d – 4f7 transition of Eu2+ and f – f transition of Eu3+ could be observed in emission spectra, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [VCa]″ formed by aliovalent substitution between Ca2+ and Eu3+ ions. The UV excitation spectrum showed the typical f–f transition of Eu3+ and f–d transition of Eu2+. The bands with the maxima at about 113 and 158 nm in VUV excitation spectrum were assigned to originate from the absorption of the host lattice. [Copyright &y& Elsevier]

The structure of extraction complexes of Am(III) with di-n-octyldithiophosphinic acid and di(2,4,4-trimethylpentyl)dithiophosphinic acid in kerosene have been studied by extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS spectra demonstrate that the two extraction complexes are analogous in coordination structure with eight sulfur atoms coordinated in inner sphere. The coordination numbers and distances from the central Am atom to the nearest shell and the second shell atoms are: S, n=7.8±1, R=2.92 A˚; P, n=3.8±0.5, R=3.47 A˚ for di-n-octyldithiophosphinic acid and S, n=7.8±1, R=2.98 A˚; P, n=3.7±0.4, R=3.58 A˚ for di(2,4,4-trimethylpentyl)dithiophosphinic acid. [Copyright &y& Elsevier]

Abstract: The growth mechanism of glutathione (GSH) capped ZnSe quantum dots (QDs) obtained from the aqueous synthesis method is studied by in situ X-ray absorption fine structure (XAFS) utilizing a flow reactor and synchrotron radiation. Detailed analysis of the Se K-edge EXAFS data reveals that the growth of ZnSe QDs from aqueous synthesis undergoes a fast nucleation process and then a slow growth stage, which follows the two-stage growth mechanism. The ZnSe QDs are strained to minimize the total free energy, and the contraction of Se–Zn bond relaxes with time. This shows the promising capability of in situ XAFS to investigate the growth process of nano-materials synthesized by chemical solution method. [Copyright &y& Elsevier]

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of 'Ni(OH) 2 -clothed Pt-tetrapods' with an amorphous Ni(OH) 2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH) 2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. The markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N 4 structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H 2 O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A g metal -1 and a large turnover frequency of 5110 h -1 at a low overpotential of 216 mV (10 mA cm -2 ), 480-510 times larger than those of the commercial IrO 2 . More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium., (© 2021. The Author(s).)

Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes that are vital for improving energy utilization efficiency and mitigating the aggravating global warming challenge. The noble metals such as platinum are generally the most frequently used electrocatalysts to drive these reactions and facilitate the relevant energy conversion processes. The high cost and scarcity of these materials pose a serious challenge for the wide-spread adoption and the sustainability of these technologies in the long run, which have motivated considerable efforts in searching for alternative electrocatalysts with reduced loading of precious metals or based entirely on earth-abundant metals. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts, such as high activity, selectivity, stability, maximized atom utilization efficiency and easy separation from reactants/products. The graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts for various electrochemical energy conversion processes. In this review, we highlight the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities.

The quaternary compound Cu 2 ZnSnSe 4 (CZTSe), as a typical candidate for both solar cells and thermoelectrics, is of great interest for energy harvesting applications. Materials with a high thermoelectric efficiency have a relatively low thermal conductivity, which is closely related to their chemical bonding and lattice dynamics. Therefore, it is essential to investigate the lattice dynamics of materials to further improve their thermoelectric efficiency. Here we report a lattice dynamic study in a cobalt-substituted CZTSe system using temperature-dependent X-ray absorption fine structure spectroscopy (TXAFS). The lattice contribution to the thermal conductivity is dominant, and its reduction is mainly ascribed to the increment of point defects after cobalt substitution. Furthermore, a lattice dynamic study shows that the Einstein temperature of atomic pairs is reduced after cobalt substitution, revealing that increasing local structure disorder and weakened bonding for each of the atomic pairs are achieved, which gives us a new perspective for understanding the behavior of lattice thermal conductivity.

A new quick-scanning X-ray absorption fine-structure (QXAFS) system has been established on beamline 1W1B at the Beijing Synchrotron Radiation Facility. As an independent device, the QXAFS system can be employed by other beamlines equipped with a double-crystal monochromator to carry out quick energy scans and data acquisition. Both continuous-scan and trapezoidal-scan modes are available in this system to satisfy the time scale from subsecond (in the X-ray absorption near-edge structure region) to 1 min. Here, the trapezoidal-scan method is presented as being complementary to the continuous-scan method, in order to maintain high energy resolution and good signal-to-noise ratio. The system is demonstrated to be very reliable and has been combined with in situ cells to carry out time-resolved XAFS studies.

In this report, AI-BL1.0, an open-source Labview-based program for automatic on-line beamline optimization, is presented. The optimization algorithms used in the program are Genetic Algorithm and Differential Evolution. Efficiency was improved by use of a strategy known as Observer Mode for Evolutionary Algorithm. The program was constructed and validated at the XAFCA beamline of the Singapore Synchrotron Light Source and 1W1B beamline of the Beijing Synchrotron Radiation Facility.

Crossed Fe2O3 nanosheets supported cobalt oxide nanoparticles on three-dimensionally macroporous nickel foam substrate (xCo/Fe-NF) was designed and successfully prepared through a facile hydrothermal and impregnation route. These catalysts showed high catalytic soot combustion activities under self-capture contact mode. The three-dimensional macroporous structures of Ni foam and the crossed Fe2O3 nanosheets constituted macroporous voids can greatly increase the contact efficiency between soot particulates and catalysts. The interaction between Co and Fe facilitated the activation of the Fe-O bond and increased the amounts of active oxygen species, thus improving the redox property of the catalysts. The 0.6Co/Fe-NF catalyst exhibited the highest turnover frequency (TOF) for soot combustion, which is in good accordance with the largest amount of active oxygen species. Based upon the catalytic performance and multiple characterization results, two reaction pathways for soot oxidation are identified, namely, the direct oxidation by the activated oxygen species via oxygen vacancies and the NOx-aided soot oxidation.

Vanadium(V)-doped hexagonal turbostratic birnessites were synthesized and characterized by multiple techniques and were used to remove Pb(2+) from aqueous solutions. With increasing V content, the V(V)-doped birnessites have significantly decreased crystallinity, i.e., the thickness of crystals in the c axis decreases from 9.8 nm to ∼0.7 nm, and the amount of vacancies slightly increases from 0.063 to 0.089. The specific surface areas of these samples increase after doping while the Mn average oxidation sates are almost constant. V has a valence of +5 and tetrahedral symmetry, and exists as oxyanions, including V₆O₁₆(2-), and VO4(3-) on birnessite edge sites by forming monodentate corning-sharing complexes. Pb LIII-edge extended X-ray absorption fine structure (EXAFS) spectra analysis shows that, at low V contents (V/Mn≤0.07) Pb(2+) mainly binds with birnessite on octahedral vacancy and especially edge sites whereas at higher V contents (V/Mn>0.07) more Pb(2+) associates with V oxyanions and form vanadinite [Pb₅(VO₄)₃Cl]-like precipitates. With increasing V(V) content, the Pb(2+) binding affinity on the V-doped birnessites significantly increases, ascribing to both the formation of the vanadinite precipitates and decreased particle sizes of birnessite. These results are useful to design environmentally benign materials for treatment of metal-polluted water., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A facile heating cell has been designed for in situ transmittance and fluorescence X-ray absorption spectroscopy (XAS) measurements up to 1273 K under vacuum or an inert atmosphere. These high temperatures are achieved using a tantalum heating element by ohmic heating. Because of the small specific heat capacity, the temperature can be changed in a matter of minutes from room temperature to high temperature. Furthermore, a commercial power controller was adapted to provide stable temperature control. The construction of the heat shielding system provides a novel approach to reducing the beam's path length and the cell's size. The cell is inexpensive and easy to build. Its performance was evaluated by in situ XAS measurements of the temperature-dependent structure of ceria nanocrystals. Some preliminary results for the structural mechanism in ceria nanocrystal redox applications are given.

When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.

The hydrotalcite-based Mn(x)Mg(3-x)AlO catalysts with different Mn:Mg atomic ratios were synthesized by coprecipitation, and employed for soot combustion, NOx storage and simultaneous soot-NO(x) removal. It is shown that with the increase of Mn content in the hydrotalcite-based Mn(x)Mg(3-x)AlO catalysts the major Mn-related species vary from MnAl(2)O(4) and Mg(2)MnO(4) to Mn(3)O(4) and Mn(2)O(3). The catalyst Mn(1.5)Mg(1.5)AlO displays the highest soot combustion activity with the temperature for maximal soot combustion rate decreased by 210 degrees C, as compared with the Mn-free catalyst. The highly reducible Mn(4+) ions in Mg(2)MnO(4) are identified as the most active species for soot combustion. For NO(x) storage, introduction of Mn greatly influences bulk NO(x) storage, with the adsorbed NO(x) species varying from linear nitrites to ionic and chelating bidentate nitrates gradually. The coexistence of highly oxidative Mn(4+) and highly reductive Mn(2+) in Mn(1.0)Mg(2.0)AlO is favorable to the simultaneous soot-NO(x) removal, giving a NO(x) reduction percentage of 24%. In situ DRIFTS reveals that the ionic nitrate species are more reactive with soot than nitrites and chelating bidentate nitrates, showing higher NO(x) reduction efficiency.

Big changes in resistivity along with the changing of local structure in some oxide systems, such as high-temperature superconductors and colossal magnetoresistance system, strongly suggest the need of a systematic investigation of their local electronic and atomic structures. In this work we present the high-resolution X-ray emission spectra and the spin-polarized X-ray absorption near-edge spectroscopy (SPXANES) data at the Mn K-edge in the La(1-x)Sr(x)MnO(3). This experiment is based on a high-resolution large-acceptance crystal analyzer based on Si (111) and optimized for X-ray fluorescence spectroscopy. With a spherical bent crystal monochromator, a Mn Kbeta emission spectra with high resolution was obtained with a short collection time and SPXANES spectra of La(1-x)Sr(x)MnO(3) at room temperature were also measured at high temperature.

Although the Gd ion in Gd@C(82) has been shown to lie above the C-C bond on the C(2) axis as an anomalous structure from the MEM/Rietveld analysis, the present XANES study reveals that it lies above the hexagon on the C(2) axis as a normal structure, and Gd oscillates around its equilibrium position with an amplitude increasing with temperature increase.

Previously performed studies have shown that Pseudomonas putida CZ1 biomass can bind an appreciable amount of Cu(II) and Zn(II) ions from aqueous solutions. The mechanisms of Cu- and Zn-binding by P. putida CZ1 were ascertained by chemical modifications of the biomass followed by Fourier transform infrared and X-ray absorption spectroscopic analyses of the living or nonliving cells. A dramatic decrease in Cu(II)- and Zn(II)-binding resulted after acidic methanol esterification of the nonliving cells, indicating that carboxyl functional groups play an important role in the binding of metal to the biomaterial. X-ray absorption spectroscopy was used to determine the speciation of Cu ions bound by living and nonliving cells, as well as to elucidate which functional groups were involved in binding of the Cu ions. The X-ray absorption near-edge structure spectra analysis showed that the majority of the Cu was bound in both samples as Cu(II). The fitting results of Cu K-edge extended X-ray absorption fine structure spectra showed that N/O ligands dominated in living and nonliving cells. Therefore, by combining different techniques, our results indicate that carboxyl functional groups are the major ligands responsible for the metal binding in P. putida CZ1.

Peptide deformylase (PDF, EC 3.5.1.27) is essential for the normal growth of eubacterium but not for mammalians. Recently, PDF has been studied as a target for new antibiotics. Its activity is strongly dependent on the bound metal ion. The crystallographic studies did not show any significant structural difference upon various bound metal ions. In this paper, X-ray absorption spectroscopy was employed to determine the local structure around the zinc ion of PDF from Leptospira interrogans in dry powder. XANES (X-ray absorption near-edge structure) calculations were performed and the local geometry of the active center was reconstructed successfully. By comparing with the crystal structure of an enzyme-product complex, the results from calculations show that a water molecule has moved towards the zinc ion and lies in the distance range to coordinate with the zinc ion weakly.

Synchrotron radiation extended X-ray absorption fine structure (SR EXAFS) was employed to study the transformation of coordination environment and the redox speciation of arsenic in a newly discovered arsenic hyperaccumulator, Cretan brake (Pteris cretica L. var nervosa Thunb). It showed that the arsenic in the plant mainly coordinated with oxygen, except that some arsenic coordinated with S as As-GSH in root. The complexation of arsenic with GSH might not be the predominant detoxification mechanism in Cretan brake. Although some arsenic in root presented as As(V) in Na2HAsO4 treatments, most of arsenic in plant presented as As(III)-O in both treatments, indicating that As(V) tended to be reduced to As(III) after it was taken up into the root, and arsenic was kept as As(III) when it was transported to the above-ground tissues. The reduction of As(V) primarily proceeded in the root.

Microscopic structures of Zn(II) surface complexes adsorbed at a delta-MnO2-water interface were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. In a 0.1 mol/L NaNO3 solution of pH 5.50, Zn(II) was adsorbed onto the solid surface in the form of octahedral hydrous Zn(II) ions. The octahedral Zn(II) was linked to the structural unit of octahedral MnO6 of the delta-MnO2 surface by sharing the O atoms. The average bond length of RZn-O was (2.071 +/- 0.007)A (n = 3) and the Zn-Mn atomic distance was (3.528 +/- 0.006) A (n = 3), which corresponded to a corner-sharing linkage adsorption mode (weaker adsorption). Macroscopic adsorption-desorption isotherm experiments showed that, in contrast to that of Zn-manganite, adsorption of Zn(II) on delta-MnO2 was highly reversible and no apparent adsorption hysteresis was observed. EXAFS results indicated that the microscopic mechanism for the high adsorption reversibility was corresponded to the weak adsorption sites of corner sharing linkage between the adsorbate and adsorbent polyhedra.

Microscopic structures of Zn(II) surface complexes adsorbed at the manganite(gamma-MnOOH)-water interface were studied using extended X-ray absorption fine structure(EXAFS) spectroscopy. Quantitative analysis of the EXAFS spectra showed that, in a 0.1 mol/L NaNO3 solution of pH 7.5, Zn(II) was adsorbed onto the solid surface by sharing the oxygen atom in the hydrous Zn2+ ions and in the structural unit MnO6 on the manganite surface. Most of the adsorbed Zn(II) was in the form of octahedral Zn(H2O2)(6)2+, but part of Zn(II) was adsorbed as tetrahedral Zn(OH)2 or Zn(OH)(4)2-. The average Zn-O bond length was 1.998 +/- 0.010 A (n = 3). The ZnO polyhedron of the hydrous Zn2+ ions was linked to the octahedron MnO6 of the manganite in two modes by sharing two O atoms on the edges of the polyhedral and/or one O atom on the corners of the polyhedral. EXAFS analysis of the second sphere indicated that Zn (II) adsorbed on the manganite resulted in two Zn-Mn atomic distances of 3.08 +/- 0.024A (n = 3) (R1) and 3.54 +/- 0.018 A (n = 3) (R2), corresponding to the edge-linkage (stronger adsorption site) and corner-linkage (weaker adsorption site), respectively. This result confirmed the basic hypothesis of Metastable Equilibrium Adsorption (MEA) theory from a molecular level that adsorption density gamma (mol/m2) is not a state variable, because adsorption density for the same adsorbate may have different chemical potential values due to different microscopic structure and adsorbate energy status. Macroscopic adsorption-desorption experiments showed that adsorption of Zn(II) onto manganite was largely irreversible (big adsorption hysteresis). EXAFS results indicated that the microscopic mechanism for the adsorption irreversibility was corresponded to the strong adsorption sites of edge sharing linkage between the adsorbate and adsorbent polyhedra.