Meijuan Yu

Speciation of zinc in secondary fly ashes of municipal solid waste at high temperatures

The evaporation aerosols produced during the vitrification process of municipal solid waste incinerators (MSWI) fly ash represent a potential environmental risk owing to their high content of heavy metals. In this research, high-temperature heating processes were carried out on fly ashes collected from bag houses in a Chinese MSWI plant and the secondary fly ashes (SFA) were separately collected at three high temperatures (1273 K, 1423 K and 1523 K) below the melting range. Elemental analysis showed that high contents of both zinc and chlorine were present in these SFA samples and, according to the standard of the heavy metals industrial grade of ore, SFAs can be re-used as metallurgical raw materials or rich ore. Moreover, as shown by XAS analysis and for different high temperatures, zinc environments in the three SFA samples were characterized by the same local structure of the zinc chloride. As a consequence, a zinc recycling procedure can be easily designed based on the configuration information.

Enhanced Thermoelectricity in High-Temperature β-Phase Copper(I) Selenides Embedded with Cu2Te Nanoclusters

We report remarkably enhanced thermoelectric performance of Te doped Cu2Se in midtemperature range. Through ball-milling process followed by spark plasma sintering (SPS), nanoscale Cu2Te clusters were embeded in the matrix of Cu2Se, inducing a drastic enhancement of thermoelectric performance by reducing the thermal conductivity without degrading the power factor. A large ZT value of 1.9 was achieved at 873 K for Cu2Se1.9Te0.1, which is about 2 times larger than that of the pure Cu2Se. The nanoscale heat management by Cu2Te nanoclusters in superionic conductors opens up an avenue for thermoelectric materials research.

Local structure investigation of the active site of the imidazolonepropionase from Bacillus subtilis by XANES spectroscopy and ab initio calculations.

Imidazolonepropionase is an important enzyme that plays a crucial role in the degradation of the histidine in mammals and bacteria. In this contribution a detailed structural investigation is presented of the imidazolonepropionase from Bacillus subtilis at the zinc site by X-ray absorption near-edge structure (XANES) spectroscopy combining experimental data with ab initio calculation in the framework of the multiple-scattering theory. The resolved local structure leads to a modification of the data set in the Protein Data Bank (PDB) (PDB code 2BB0). Actually, data suggest that the carboxyl of the Asp324 moves far away from the zinc ion at the center, while the water molecule and the nearest-neighbor histidines move towards it. This new conformation and the occurrence of a short water-to-zinc bond length support the nucleophilic attack catalytic mechanism proposed for this enzyme.

How water molecules affect the catalytic activity of hydrolases--a XANES study of the local structures of peptide deformylase.

Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å.

Spectroscopic study and electronic structure of prototypical iron porphyrins and their μ-oxo-dimer derivatives with different functional configurations

Metalloporphyrins are networking molecules with strong internal N-H hydrogen bonds that may be used to substitute a metal ion inside a porphyrin ring, forming a metallo complex. The understanding of electronic structures and charge dynamics of porphyrin based molecular architectures is mandatory to clarify biological functions, catalytic processes, and opto-electrical responses in which these molecules are involved. We present here a systematic analysis of the electronic structures and the charge dynamics of two different iron-porphyrins (i.e. protoporphyrin IX and meso-tetraphenylporphine) with different functional architectures. We investigated these prototypical porphyrins and their mu-oxo-dimer derivatives by means of Fe K-edge X-ray Absorption Near-Edge Spectroscopy (XANES) combined with theoretical calculations. The electronic structure, namely the partial projected density of states and the polarization components were discussed in terms of orbital hybridizations among metal and local ligands. Data show that hydrogens are electron donors while the central metal irons accept electrons. Moreover, the metal axial ligands exhibit different electron behaviors: donors for Cl in prototypical porphyrins and acceptors for O in mu-oxo-dimer derivatives. Actually, the charge dynamics are affected by local metal ligands, but also strongly depend on the mid-range atomic ordering of the porphyrins network. The charge dynamics, evaluated from the self-consistent local potential, is associated with charge transfer mechanisms involving interactions with the axial ligands as well as with the substituents. The quantum chemical topology analysis of the electron localization function (ELF) has been used to identify the distribution of the electron pairs. They are localized around Cl atoms regardless of porphyrin configurations. Charge dynamics and electron localization are fundamental information for a deep understanding of the role of porphyrin and porphyrin-like molecules in a wide range of molecular biophysical mechanisms and in materials science processes.

Correlation between local vibrations and metal mass in AlB2-type transition-metal diborides.

Lattice vibrations have been investigated in TiB2, ZrB2 and HfB2 by temperature-dependent extended X-ray absorption fine structure (EXAFS) experiments. Data clearly show that the EXAFS oscillations are characterized by an anomalous behavior of the Debye-Waller factor of the transition-metal-boron pair, which is suggested to be associated with a superposition of an optical mode corresponding to phonon vibrations induced by the B sublattice and an acoustic mode corresponding to the transition-metal (TM) sublattice. Data can be interpreted as a decoupling of the metal and boron vibrations observed in these transition-metal diborides (TMB2), a mechanism that may be responsible for the significant reduction of the superconducting transition temperature observed in these systems with respect to the parent MgB2 compound. The vibrational behavior of TM-TM bonds has also been investigated to study the occurrence of anisotropy and anomalies in the lattice vibrational behavior of TM-TM bonds.

Solution structure of human DESR1, a CSL zinc‐binding protein

Solution structure of human DESR1, a CSL zinc-binding protein Fangming Wu, Jiahai Zhang, Jianping Sun, Hongda Huang, Peng Ji, Wangsheng Chu, Meijuan Yu, Feifei Yang, Ziyu Wu, Jihui Wu,* and Yunyu Shi* 1National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China 2 Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

3D local structure around Zn in Kti11p as a representative Zn-(Cys)4 motif as obtained by MXAN.

Zinc is an important component of many proteins that play key roles in transcription, translation, and catalysis. Kti11p, DESR1, both belonging to a protein family characterized by a CSL zinc finger domain, and the co-catalytic zinc-protein PML containing a Zn(2+) binding domain called RING or C(3)HC(4) finger are all structurally determined by NMR although the zinc sites are silent to this spectroscopical method. The comparison of X-ray absorption near-edge spectroscopy (XANES) data for the three proteins demonstrates that fingerprints effect is a reliable method for a primary characterization of ligand species. Ab initio full MS calculations performed by MXAN are applied to obtain chemical and stereo structural information around the Zn ion in Kti11p. For the first time this high-spatial resolution technique confirms the formation of a stable Zn tetrahedral configuration with four sulfur ligands, and returns extremely accurate bond angle information between ligands.

Chemical speciation of lead in secondary fly ash using X-ray absorption spectroscopy

In this study, fly ash samples were collected from bag houses in a Chinese municipal solid waste incinerator (MSWI) and secondary fly ash (SFA) samples were collected from a high-temperature tubular electric furnace by thermal treatment of MSWI fly ash at 1050, 1100, 1150, 1200, and 1250 °C.We determined the speciation and atomic coordinates of lead in SFA using X-ray absorption spectroscopy (XAS) techniques. The results obtained by X-ray absorption near edge structure (XANES) spectra revealed that the mass fraction of PbO in MSWI fly ash was 57.9% (wt %) while PbCl2 and PbS were the dominant species in SFA. Extended X-ray absorption fine structure (EXAFS) data analysis indicated the atomic coordinates of Pb were proportional to the weights of PbCl2 and PbS, in good agreement with the XANES spectra. These findings highlight lead evaporation processes in the MSWI fly ash during heat treatment and provide a method for consistent speciation analysis of environmental samples using XAS.

New insight on the local structure of Cu2+ ion in the solution of CuBr2 by EXAFS studies

CuBr2 solutions at different concentrations were studied by extended X-ray absorption fine structure (EXAFS) at the Cu K edge. In the saturated solution Cu2+ ions have chemical bonds with 3.0 oxygen atoms and 0.9 Br ion at about 1.96 A and 2.42 A, respectively. It indicates that the CuBr4-2 configuration exists with a ratio of 25% under this condition. In the dilute solutions no evidence of Br ions contributions in the first shell around Cu2+ ions occurs. The almost identical X-ray absorption near edge structure (XANES) and EXAFS characters address similar local environments around Cu2+ in agreement with results of the EXAFS fit taking into account only the contributions of Cu-O bonds.