X-ray absorption near-edge structure study on the configuration of Cu2＋/histidine complexes at different pH values

The local configurations around metal ions in metalloproteins are of great significance for understanding their biolog- ical functions. Cu2＋/histidine （His） is a typical complex existing in many metalloproteins and plays an important role in lots of physiological functions. The three-dimensional （3D） structural configurations of Cu2＋/His complexes at different pH values （2.5, 6.5, and 8.5） are quantitatively determined by x-ray absorption near-edge structure （XANES）. Generally Cu2＋/His complex keeps an octahedral configuration consisting of oxygen atoms from water molecules and oxygen or nitrogen atoms from histidine molecules coordinated around Cu2＋. It is proved in this work that the oxygen atoms from water molecules, when increasing the pH value from acid to basic value, are gradually substituted by the Ocarboxy1, Nam, and Nim from hisitidine molecules. Furthermore, the symmetries of Cu2＋/His complexes at pH 6.5 and pH 8.5 are found to be lower than at pH 2.5.

Landscape of s-triazine molecule on Si(100) by a theoretical x-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectra study

The chemisorbed structure for an aromatic molecule on a silicon surface plays an important part in promoting the development of organic semiconductor material science. The carbon K-shell x-ray photoelectron spectroscopy（XPS） and the x-ray absorption near-edge structure（XANES） spectra of the interfacial structure of an s-triazine molecule adsorbed on Si（100） surface have been performed by the first principles, and the landscape of the s-triazine molecule on Si（100） surface has been described in detail. Both the XPS and XANES spectra have shown their dependence on different structures for the pristine s-triazine molecule and its several possible adsorbed configurations. By comparison with the XPS spectra, the XANES spectra display the strongest structural dependency of all of the studied systems and thus could be well applied to identify the chemisorbed s-triazine derivatives. The exploration of spectral components originated from non-equivalent carbons in disparate local environments has also been implemented for both the XPS and XANES spectra of s-triazine adsorbed configurations.

A theoretical study of the oxygen K-edge near-edge X-ray absorption fine structure of N_2O/Ir(110)

A multiple-scattering chtster method is employed to calculate the oxygen K-edge near-edge X-ray absorption fine structure of N20/Ir（110） and its monolayer. Two peaks and one weak resonance appear in both cases. The self- consistent field DV-Xa calculations of the peaks and resonance show that the physical origin of the pre-edge peak x is different from those of the main peak 1 and the other weak resonance al. This setup is intrinsic to the N20 monolayer, owing to the interaction between the neighbouring molecular chains in the monolayer and partly to the adsorbed atomic oxygen, according to both the theoretical and experimental data.

Theoretical characterization of the adsorption configuration of pyrrole on Si(100)surface by x-ray spectroscopy

The possible configurations of pyrrole absorbed on a Si(100)surface have been investigated by x-ray photoelectron spectroscopy(XPS)and near-edge x-ray absorption fine structure(NEXAFS)spectra.The C-1s XPS and NEXAFS spectra of these adsorption configurations have been calculated by using the density functional theory(DFT)method and fullcore hole(FCH)approximation to investigate the relationship between the adsorption configurations and the spectra.The result shows that the XPS and NEXAFS spectra are structurally dependent on the configurations of pyrrole absorbed on the Si(100)surface.Compared with the XPS,the NEXAFS spectra are relatively sensitive to the adsorption configurations and can accurately identify them.The NEXAFS decomposition spectra produced by non-equivalent carbon atoms have also been calculated and show that the spectral features vary with the diverse types of carbon atoms and their structural environments.

Equation of state for warm dense lithium： A first principles investigation

The quantum molecular dynamics based on the density functional theory has been adopted to simulate the equation of state for the shock compressed lithium. In contrary to some earlier experimental measurement and theoretical simulation,there is not any evidence of the ‘kink＇ in the Hugoniot curve in our accurate simulation. Throughout the shock compression process, only a simple solid-to-liquid melting behavior is demonstrated, instead of complicated solid–solid phase transitions. Moreover, the x-ray absorption near-edge spectroscopy has been predicted as a feasible way to diagnose the structural evolution of warm dense lithium in this density region.

Microwave-assisted synthesis of photoluminescent glutathione-capped Au/Ag nanoclusters： A unique sensor-on-a-nanoparticle for metal ions, anions, and small molecules

Even though great advances have been achieved in the synthesis of luminescent metal nanoclusters, it is still challenging to develop metal nanoclusters with high quantum efficiency as well as multiple sensing functionalities. Here, we demonstrate the rapid preparation of glutathione-capped Au/Ag nanoclusters （GS-Au/Ag NCs） using microwave irradiation and their unique sensing capacities. Compared to bare GS-Au NCs, the doped Au/Ag NCs possess an enhanced quantum yield （7.8% compared to 2.2% for GS-Au NCs）. Several characterization techniques were used to elucidate the atomic composition, particulate character, and electronic structure of the fabricated NCs. According to the X-ray photoelectron spectroscopy （XPS） and X-ray absorption near-edge structure （XANES） spectra, a significant amount of Au exists in the oxidized state as Au（I）, and the Ag atoms are positively charged. In contrast to those nanoclusters that detect only one analyte, the GS-Au/Ag NCs can be used as a versatile sensor for metal ions, anions, and small molecules. In this manner, the NCs can be regarded as a unique sensor-on-a-nanoparticle.

Stabilization of the Anatase Phase of Ti_(1-x)Sn_(x)O_(2) (x < 0.5) Nanofibers

We experimentally investigate the stabilization of the anatase phase of Ti_(1-x)Sn_(x)O_(2)(x<0.5)nanofibers when synthesized by an electrospinning method.The as-spun nanofibers became nano-grained,polycrystalline nanofibers after calcination and the diameters of the nanofibers depend on Sn content.Stabilization of the anatase phase in Ti-rich compositions and incorporation of Sn ions were confirmed by X-ray diffraction,Raman,X-ray absorption near-edge structure,and photoluminescence(PL)spectroscopies.Results from the PL study also demonstrated the tunable nature of the optical properties,with the emission maximum shifting towards higher wavelength with increasing Sn concentration.

Analysis of nickel distribution by synchrotron radiation X-ray fluorescence in nickel-induced early- and late-phase allergic contact dermatitis in Hartley guinea pigs

Background: Nickel-induced allergic contact dermatitis (Ni-ACD) is a global health problem. More detailed knowledge on the skin uptake of haptens is required. This study aimed to investigate the penetration process and distribution of nickel in skin tissues with late phase and early phase of Ni-ACD to understand the mechanisms of metal allergy. Methods: Forty Hartley guinea pigs were divided into four groups according to the NiSO4 sensitizing concentration and the NiSO4 challenged concentration: the 5% NiSO4-group, 5% to 10%(sensitization-challenge;late phase group);10% NiSO4-group, 10% to 10%(sensitization-challenge;early-phase group);and the positive and negative controls. Pathological biopsies were performed on each group. The depth profile of nickel element concentration in the skin of guinea pigs was detected by synchrotron radiation micro X-ray fluorescence spectroscopy (SR-μ-XRF) and micro X-ray absorption near-edge spectroscopy (μ-XANES). Results: In each section, the nickel element concentration in both the 5% NiSO4-group and 10% NiSO4-group was significantly higher than that in the negative control group. In the upper 300-μm section of skin for the early phase group, the nickel element concentration was significantly higher than that in the lower section of skin. In deeper sections (>200 μm) of skin, the concentration of nickel in the early phase group was approximately equal to that in the late phase group. The curve of the late phase group was flat, which means that the nickel element concentration was distributed uniformly by SR-μ-XRF. According to the XANES data for the 10% NiSO4 metal salt solution, structural changes occurred in the skin model sample, indicating that nickel was not present in the Ni^2+ aqueous ionic state but in the nickel-binding protein. Conclusions: This study showed that the distribution of the nickel element concentration in ACD skin tissue was different between the early phase and late phase groups. The nickel element was not present in the Ni^2+ aqueous ionic state but bound with certain proteins to form a complex in the stratum corneum in ACD model tissue.

Extreme biomimetic approach for developing novel chitin-GeO2 nanocomposites with photoluminescent properties

This work presents an extreme biomimetics route for the creation of nano- structured biocomposites utilizing a chitinous template of poriferan origin. The specific thermal stability of the nanostructured chitinous template allowed for the formation under hydrothermal conditions of a novel germanium oxide- chitin composite with a defined nanoscale structure. Using a variety of analytical techniques （FTIR, Raman, energy dispersive X-ray （EDX）, near-edge X-ray absorption fine structure （NEXAFS）, and photoluminescence （PL） spectroscopy, EDS-mapping, selected area for the electron diffraction pattern （SAEDP）, and transmission electron microscopy （TEM））, we showed that this bioorganic scaffold induces the growth of GeO2 nanocrystals with a narrow （150-300 nm） size distri- bution and predominantly hexagonal phase, demonstrating the chitin template＇s control over the crystal morphology. The formed GeO2-chitin composite showed several specific physical properties, such as a striking enhancement in photo- luminescence exceeding values previously reported in GeOR-based biomaterials. These data demonstrate the potential of extreme biomimetics for developing new-generation nanostructured materials.

Quasi-freestanding graphene on Ni（110）： A graphene/ metal contact with suppressed interface states

Graphene/Ni（110） has been studied by time-resolved X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. The C ls core level shows a splitting typical of periodically rippled interfaces. The analysis of the C K-edge reveals that the interface states previously observed for graphene/Ni（111） are suppressed in graphene/Ni（110）. This suppression is due to the reduced hybridization of the Dirac-cone electrons in graphene with the d-bands of the （110）-oriented nickel contacts. Our results show that, contrary to commensurate growth of graphene on Ni（111）, epitaxially grown graphene on Ni（110） behaves as a quasi-freestanding sheet, as the lattice mismatch gives rise to a moir6 reconstruction.

Formation of Extended Covalently Bonded Ni Porphyrin Networks on the Au（lll） Surface

The growth and ordering of {5,10,15,20-tetrakis（4-bromophenyl）porphyrinato}nickel（II） （NiTBrPP） molecules on the Au（111） surface have been investigated using scanning tunnelling microscopy, X-ray absorption, core-level photoemission, and microbeam low-energy electron diffraction. When deposited onto the substrate at room temperature, the NiTBrPP forms a well-ordered close-packed molecular layer in which the molecules have a flat orientation with the porphyrin macrocycle plane lying parallel to the substrate. Annealing of the NiTBrPP layer on the Au（111） surface at 525 K leads to dissociation of bromine from the porphyrin followed by the formation of covalent bonds between the phenyl substituents of the porphyrin. This results in the formation of continuous covalently bonded porphyrin networks, which are stable up to 800 K and can be recovered after exposure to ambient conditions. By controlling the experimental conditions, a robust, extended porphyrin network can be prepared on the Au（111） surface that has many potential applications such as protective coatings, in sensing or as a host structure for molecules and clusters.

Friction-condition-dependent sulfide and sulfate evolution on dialkylpentasulfide tribofilm studied by XANES

The effects of friction conditions, such as rotational speed, frictional time, and applied load, on the evolution mechanism of sulfide and sulfate on the top and bottom layers of tribofilm were investigated by total electron yield (TEY) and fluorescence yield (FY) mode X-ray absorption near-edge structure (XANES) spectra in the same beam line (4B7A). The results demonstrated that the top and bottom layers of tribofilms were covered by sulfide and sulfate. The addition of dialkylpentasulfide (DPS) could form complex nonuniform tribofilm. In addition, the friction condition (speed, load, or time) has its unique role in the generation of sulfide and sulfate at a specific depth on the tribofilm surface. The enhancement of friction conditions could promote the sulfur tribochemical reaction in a comparatively large range and alter the relative intensity of sulfurization and the sulfur-oxidizing process.