X-ray Photoabsorption Research Articles

Quantitative Determination of a Contrast Agent by Multispiral Computed Tomography and Targeted Absorption Spectroscopy in the K-Jump Region of X-Ray Photoabsorption

Quantitative Determination of a Contrast Agent by Multispiral Computed Tomography and Targeted Absorption Spectroscopy in the K-Jump Region of X-Ray Photoabsorption

Chromium-Doped Nickel Cobaltite Nanoneedles as a Cathodic Material for Li–O2 Cells: An X-ray Photoemission and Photoabsorption Spectroscopy Investigation

Chromium-Doped Nickel Cobaltite Nanoneedles as a Cathodic Material for Li–O₂ Cells: An X-ray Photoemission and Photoabsorption Spectroscopy Investigation

Ionizing radiation induces cross-linking of two noncovalently bound collagen mimetic peptide triple helices in the absence of a molecular environment.

Cross-linking is a fundamental molecular process that is highly important for many applications, in particular, to tune the properties of collagen-based biomaterials. Chemical reagents, the action of enzymes or physical factors such as heat or radiation can facilitate collagen cross-linking. Ionizing radiation has the advantages of being fast, efficient and free from potentially toxic reagents. Collagen cross-linking by ionizing radiation is thought to occur via a water-mediated pathway. In the past, synthesized collagen mimetic peptides have proven to be of great value for understanding the influence of the amino acid sequence on the stability of tertiary (fibrous) as well as secondary (triple helical) structures of collagen. Cross-linking of synthetic collagen mimetic peptides is often used for modifying the properties of biomaterials. In this work, for the first time, we apply radiation-induced cross-linking to synthetic collagen mimetic peptides and present an experimental and theoretical study of peptide hexamers consisting of two noncovalently bound triple helices in the absence of a molecular environment, i.e. in the gas phase. Our results show that X-ray photoabsorption of the hydroxylated hexamer leads to ionization and cross-linking of the two triple helices: thus, we found evidence that cross-linking can be achieved by ionizing radiation, without the presence of any reagent or water. We propose a cross-linking mechanism involving the creation of two radicals on hydroxyproline side-chains and their recombination, ultimately leading to covalent bond formation between the triple helices.

Evaluation of Antifungal Properties of Titania P25.

Commercial titania photocatalyst—P25 was chosen for an antifungal property examination due to it exhibiting one of the highest photocatalytic activities among titania photocatalysts. Titania P25 was homogenized first (HomoP25) and then annealed at different temperatures. Additionally, HomoP25 was modified with 0.5 wt% or 2.0 wt% of platinum by a photodeposition method. The obtained samples were characterized by diffuse-reflectance spectroscopy (DRS), X-ray photoabsorption spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy. Moreover, photocatalytic activity was tested for methanol dehydrogenation under UV/vis irradiation. The spore-destroying effect of photocatalysts was investigated against two mold fungal species, i.e., Aspergillus fumigatus and Aspergillus niger. Both the mycelium growth and API ZYM (estimation of enzymatic activity) tests were applied for the assessment of antifungal effect. It was found that annealing caused a change of surface properties of the titania samples, i.e., an increase in the noncrystalline part, a growth of particles and enhanced oxygen adsorption on its surface, which resulted in an increase in both the hydrogen evolution rate and the antifungal effect. Titania samples annealed at 300−500 °C were highly active during 60-min UV/vis irradiation, inhibiting the germination of both fungal spores, whereas titania modification with platinum (0.5 and 2.0 wt%) had negligible effect, despite being highly active for hydrogen evolution. The control experiments revealed the lack of titania activity in the dark, as well as high resistance of fungi for applied UV/vis irradiation in the absence of photocatalysts. Moreover, the complete inhibition of 19 hydrolases, secreted by both tested fungi, was noted under UV/vis irradiation on the annealed P25 sample. It is proposed that titania photocatalysts of large particle sizes (>150 nm) and enriched surface with oxygen might efficiently destroy fungal structures under mild irradiation conditions and, thus, be highly promising as covering materials for daily products.

Synchrotron µ-XRF mapping analysis of trace elements in in-situ cultured Japanese red coral, Corallium japonicum.

Precious corals belong to the family Coralliidae (Cnidaria, Octocorallia), and their axis, which consists of high magnesian calcium carbonate, has long been used in jewelry. With its low growth rate and long lifespan, precious coral is a representative taxon of the vulnerable marine ecosystem. Due to years of overfishing, coral fishery has become a controversial issue. To estimate the growth rate and clarify the uptake process of trace elements in relation to the growth of the carbonate axis, Japanese red coral (Corallium japonicum) was cultured at a depth of 135 m off Takeshima Island, Kagoshima, Japan for 98 months and analyzed by microscopic X-ray fluorescence/soft X-ray photoabsorption (µ-XRF/XAS) speciation mapping. The growth rate was estimated to be 0.37 mm/year in diameter, and 10–11 growth rings were observed in a cross section of the axis. This estimated growth-rate value is the first ever to be obtained from the in-situ culture of Japanese precious coral. The fluctuation in water temperature near the in-situ-culture site was recorded for part of the culture period and then compared with the changes in the growth ring and the distribution of trace elements in a cross section of the coral axis during the same period. When the water temperature was increasing, the growth ring was light in color, sulfur and phosphorus concentrations were low, and magnesium was high. Conversely, a dark band in the growth ring, high sulfur and phosphorus, and low magnesium concentrations were observed when the water temperature was decreasing. In a cross section of the coral axis, the distribution of sulfur and magnesium from the center to the surface corresponded, respectively, to dark and light bands in the annual growth ring. Sulfur concentration was high in the dark band and low in the light band, while magnesium was negatively correlated with sulfur.

UPS, XPS, NEXAFS and Computational Investigation of Acrylamide Monomer

Acrylamide is a small conjugated organic compound widely used in industrial processes and agriculture, generally in the form of a polymer. It can also be formed from food and tobacco as a result of Maillard reaction from reducing sugars and asparagine during heat treatment. Due to its toxicity and possible carcinogenicity, there is a risk in its release into the environment or human intake. In order to provide molecular and energetic information, we use synchrotron radiation to record the UV and X-ray photoelectron and photoabsorption spectra of acrylamide. The data are rationalized with the support of density functional theory and ab initio calculations, providing precise assignment of the observed features.

Extreme-ultraviolet- and X-Ray-driven Photochemistry of Gaseous Exoplanets

Abstract The interaction of exoplanets with their host stars causes a vast diversity in bulk and atmospheric compositions and physical and chemical conditions. Stellar radiation, especially at the shorter wavelengths, drives the chemistry in the upper atmospheric layers of close orbiting gaseous giants, providing drastic departures from equilibrium. In this study, we aim at unfolding the effects caused by photons in different spectral bands on the atmospheric chemistry. This task is particularly difficult because the characteristics of chemical evolution emerge from many feedbacks on a wide range of timescales, and because of the existing correlations among different portions of the stellar spectrum. In describing the chemistry, we have placed particular emphasis on the molecular synthesis induced by X-rays. The weak X-ray photoabsorption cross sections of the atmospheric constituents boost the gas ionization to pressures inaccessible to vacuum and extreme-ultraviolet photons. Although X-rays interact preferentially with metals, they produce a secondary electron cascade able to ionize efficiently hydrogen- and helium-bearing species, giving rise to a distinctive chemistry.

Development of Depth-resolved Soft X-ray Photoabsorption Spectroscopy

Development of Depth-resolved Soft X-ray Photoabsorption Spectroscopy

Exploring the x-ray photoabsorption spectrum of sodium in the energy range 1070–1090 eV by elucidating the inner shell excitation transition probabilities

The researchers report on a new study of the x-ray photoabsorption spectrum of sodium near the K-edge, involving the calculations of the excitation energies and the excitation transition probabilities for K-shell and M-shell electron excitations transitions in atomic sodium. The calculations were carried out by employing the ‘multi configuration Dirac–Fock method’, Breit interactions and ‘finite nuclear size corrections’ are included in the calculations, the transition probabilities were convoluted into ‘Breit–Wigner’ line shapes, and single 1s photoionization was also taken into account. In addition, the [1s]np and the [1s3s]ns n′p singlet–triplet energy splitting was calculated. Results of the calculations were compared with previous measurements of the photoabsorption spectrum of sodium near the K-edge, and a very good agreement was observed.

MXAN: A new program for ab-initio structural quantitative analysis of XANES experiments

X-ray absorption spectroscopy (XAS) is a powerful method for obtaining electronic and structural information around a well-defined absorbing atom site of different types of matter, from biological systems to condensed materials in almost all possible thermodynamics conditions. The low energy part of the XAS spectrum, from the rising edge up to few hundreds eV, the so called XANES (X-ray absorption near-edge structure) region, is extremely rich of electronic and structural information, like, for example, the oxidation state, overall symmetry, interatomic distances and angles. In this paper we present in details the MXAN method and a new reengineered release of the code proposed in the literature some years ago which allows a complete fit of the XANES energy region in term of well-defined set of structural parameters. This approach is based on the comparison between experimental data and many theoretical calculations performed by varying selected structural parameters starting from a putative structure, i.e. from a well-defined initial geometrical configuration around the absorber. The X-ray photo-absorption cross sections are derived using full multiple-scattering theory, i.e. the scattering path operator is calculated exactly without any series expansion. In this way the analysis can start from the edge without any limitations in the energy range and polarization conditions. Here we present in detail the theoretical background behind the code and new capabilities implemented from theory in this last version of the program as the analysis of XANES data coming from time-dependent spectra. The code is provided with modern technology for rapid deployment of binaries based on Docker runtime so that, without source compiling, its execution reduces to just a command line striking for a full parallel (shared memory) run even using complex construct like memory filesystem in a transparent way to the end-user. Program summaryProgram Title: MXANCPC Library link to program files:https://doi.org/10.17632/4k9363vcvh.1Licensing provisions: GPLv3Programming language: FORTRAN90External routines/libraries: MKL or OpenBLAS libraryNature of problem: In MXAN (Minuit XANES) program we implemented a fitting procedure based on a full Multiple Scattering (MS) theory [1] able to extract local structural information around the absorbing atom from experimental XANES data. The MXAN method has been successfully used for studying many known and unknown molecular systems, yielding structural geometries and metrics comparable to X-ray diffraction and/or EXAFS results [2–4]. The release of this new code paves the route to new possibilities available now in the latest version of the program, as the analysis of XANES data coming from time-dependent and structural disordered systems.Solution method: MXAN program is based on the comparison between experimental data and iterative theoretical calculations performed by varying selected structural parameters starting from a well-defined initial geometrical configuration around the absorber. The calculation of XANES spectra is performed within the so-called full MS approach, i.e. the inverse of the scattering path operator is computed exactly, avoiding any “a-priori” selection of the relevant MS paths [5,6]. The fit procedure is performed in the energy space without the use of any Fourier transform algorithm; polarized spectra can be easily analyzed because the calculation is performed using the full MS approach [1]. The optimization in the space of the parameters is achieved using the CERN-library MINUIT [7] routines minimizing the square residual.Additional comments including restrictions and unusual features: Depending on the molecular system under study and on the operating runtime conditions the program may or may not fit into available host RAM memory. The present release of the code is limited to a single SMP machine by running in parallel using OpenMP and/or the multi-threaded version of MKL or OpenBLAS.

X-ray photoabsorption-induced processes within protonated rifamycin sodium salts in the gas phase

Up to now, the response of antibiotics upon ionizing radiation has been very scarcely reported. Here, we present the results of X-ray photoabsorption experiments on isolated rifamycin, a broad-range antibiotic against Gram-positive and Gram-negative bacteria. A mass spectrometer has been coupled to a synchrotron beamline to analyze cationic products of photoabsorption on protonated rifamycin dimer and monomer sodium salts. Absorption of a single photon in the 100–300eV energy range leads to ionization of the molecular system, followed by vibrational energy deposition and subsequent inter- and/or intramolecular fragmentation. Interestingly, we observe a proton transfer from sodiated rifamycin to rifamycin, a widely observed process in ionized molecular systems in the gas phase. Moreover, we show that another charge-transfer process occurs in both dimer and monomer: intramolecular sodium transfer, which has not been reported yet, to the best of our knowledge.

PPT Isolated Molecule and Its Building Block Moieties Studied by C 1s and O 1s Gas Phase X-ray Photoelectron and Photoabsorption Spectroscopies

The present study is focused on the comprehensive gas phase electronic structure characterization of 2,8-bis(diphenylphosphoryl)-dibenzo[b,d]thiophene (PPT), a promising ambipolar phosphorescent ho...

Elucidating the theoretical X-ray photoabsorption spectrum of Argon near the KM edge: Transition probabilities calculations.

We report new calculations of the transition probabilities for double electron photo-excitations near the KM edge in atomic Argon in the energy range 3220-3238eV. The calculations were performed to study the X-ray photoabsorption spectrum of Argon near the KM edge using Multi-configurational Dirac-Hartee Fock method. Configuration interaction calculations showed that excitations to the doubly excited state [1s3p]3d2 is almost small compared to [1s3p]4p2 excitations, thus [1s3p]4p2 is the dominant transition in this energy range. The transition probabilities were convoluted into Breit-Wigner line shapes and compared to previous measurements of the X-ray photoabsorption spectrum of Argon near the KM edge, the comparison showed good agreement with experiment. The results of the calculations presentded herein therefore shed light on understanding of near KM edge features, and thereby the preferred excitation channels of the atom.

Soft x-ray photoabsorption spectra of photoionized CH4 and CO2 plasmas

In this work we report soft x-ray (SXR) photoabsorption measurements in neutral methane and carbon dioxide molecules and their corresponding photoionized plasmas. The SXR radiation was generated by a table-top laser produced plasma source based on a double stream gas puff target. At low SXR intensities only features related to neutral molecules are present in the absorption spectrum. On the other hand, as the radiation intensity increases, we observe new absorption features in the low photon energy side of the spectrum. In that case fragments such as neutral and ionized molecules, atoms and atomic ions are found to contribute to the absorption spectrum of the plasmas. To our knowledge these are the first measurements where this laser plasma based SXR source is used to both create and probe a molecular plasma. Emphasis is placed on identifying the fragment species and the corresponding transitions.

Evidence for a core-shell structure of hydrothermal carbon

Hydrothermal carbonisation (HTC) has been demonstrated to be a sustainable thermochemical process, capable of producing functionalised carbon materials for a wide range of applications. In order to better apply such materials, the local chemistry and reaction pathways governing hydrothermal carbon growth must be understood. We report the use of scanning transmission X-ray microscopy (STXM) to observe chemical changes in the functionality of carbon between the interface and bulk regions of HTC. Spatially-resolved, element-specific X-ray photo-absorption spectra show the presence of differing local carbon chemistry between bulk “core” and interface “shell” regions of a glucose-derived hydrothermal carbon spherule. STXM provides direct evidence to suggest that mechanistic pathways differ between the core and shell of the hydrothermal carbon. In the shell region, at the water-carbon interface, more aldehyde and/or carboxylic species are suspected to provide a reactive interface for bridging reactions to occur with local furan-based monomers. In contrast, condensation reactions appear to dominate in the core, removing aryl-linking units between polyfuranic domains. The application of STXM to HTC presents opportunities for a more comprehensive understanding of the spatial distribution of carbon species within hydrothermal carbon, especially at the solvent-carbon interface.

Influence of ionizing radiation on molecular recognition in the gas phase: VUV and X-ray photoabsorption of antibiotic-receptor non-covalent complexes

SynopsisThe intrinsic effects of ionizing radiation on molecular recognition between an antibiotic and its re-ceptor have been probed by coupling a synchrotron beamline to a tandem mass spectrometer. Protonated vanco-mycin-receptor non-covalent complexes in the gas phase undergo inter-as well as intramolecular bond cleavage due to internal energy transfer after photoabsorption in the VUV-X energy range. The deprotonated complex undergoes electron detachment, but the native interactions underlying molecular recognition are not systematically lost.

Sulfur speciation in growth layers of shell cross section of the long-lived bivalve Margaritifera laevis using synchrotron spectromicroscopy analysis

To reliably utilize the information on growth and environment stored within the hard carbonate shells of long-lived bivalves, it is necessary to accurately count the annual growth lines from their shell cross-sections. In this study, we investigated the relationship between the distribution of minor elements and visual lines in the shell cross-sections of the long-lived mussel Margaritifera laevis collected from the Chitose River in Hokkaido, Japan. The distribution of minor elements, such as sulfur (S), phosphorus (P), strontium (Sr), magnesium (Mg), and sodium (Na), in a cross-section of the umbo was determined by X-ray fluorescence analysis using synchrotron soft X-ray radiation. The chemical properties of S and P were analyzed in-situ using soft X-ray photoabsorption spectroscopy, and the chemical form dependence of S distribution was determined by speciation mapping. In addition, the annual and disturbance lines were visualized by staining shell cross-sections. Our results showed that the distribution of reduced S (i.e., SC and SH) corresponded to the annual lines, whereas the distribution of oxidized S (i.e., SO42−) corresponded to the disturbance lines. Overall, this study revealed that speciation analysis of S in shell cross-sections can be used to determine the origin of visual lines in chronological studies.

Parameters optimization for synthesis of Al-doped ZnO nanoparticles by laser ablation in water

Al-doped ZnO crystalline colloidal nanoparticles were synthesized by a laser ablation of ZnO:Al2O3 in MilliQ water. Experiments were performed systematically by changing the number of applied laser pulses and laser output energy with the aim to affect the nanoparticle size, composition (Al/Zn ratio) and characteristics (band-gap, crystallinity). Distinctly, set of nanoparticle syntheses was performed in deionized water for comparison. SEM investigation of colloidal nanoparticles revealed that the formed nanoparticles are 30 nm thick discs with average diameters ranging from 450 to 510 nm. It was found that craters in the target formed during the laser ablation influence the size of synthesized colloidal nanoparticles. This is explained by efficient nanoparticle growth through diffusion process which take place in spatially restricted volume of the target crater. When laser ablation takes place in deionized water the synthesized nanoparticles have a mesh-like structure with sparse concentration of disc-like nanoparticles. Al/Zn ratio and band-gap energy of nanoparticles are highly influenced by the number and output energy of applied laser pulses. In addition, the procedure how to calculate the concentration of colloidal nanoparticles synthesized by laser ablation in liquids is proposed. The Al-doped ZnO colloidal nanoparticles properties were obtained using different techniques like scanning electron microscopy, optical microscopy, energy-dispersive X-ray spectroscopy, grazing-incidence X-ray diffraction, photoabsorption, photoluminescence and X-ray photoelectron spectroscopy.

Theoretical investigation of the X-ray photoabsorption spectrum of Potassium near K, KN and KM edges: Transition probabilities for single and double electron excitations

We present new calculations for the transition probabilities and transition energies for single electron K shell excitations and double electron KN and KM shell excitations in atomic Potassium in the energy range 3610–3650 eV. The calculations were carried out to investigate the X-ray photoabsorption spectrum of atomic Potassium using Multi-configurational Dirac-Hartee Fock method. The transition probabilities were convoluted in Lorentzian line shapes, a rough estimate of the effect of photoionization was also taken into account, comparison of the calculations with previous measurements of the X-ray photoabsorption spectrum of atomic Potassium near K, KN and KM edges showed relatively good agreement.

An energy dispersion scheme based on a semiconductor X-ray spectrometer and a broadband monochromator for determining the content of heavy elements from the absorption spectra

An energy-dispersion scheme for determining the conсentrations of impurities of heavy elements from the absorption spectra in the regions of X-ray photoabsorption jumps is described. A semiconductor X-ray spectrometer and a pyrolytic graphite monochromator were used to record data in a spectral band of width up to 1 keV. The initial shape of the absorption spectrum in the approximation of an isolated atom was reconstructed by means of a numerical solution of the convolution equation. The scheme provides a sharp increase in the data acquisition and measurement sensitivity. The results of measurements of the Bi and Pb contents in samples with organic matrices and determination of the thicknesses of thin Mo films on diamond substrates are presented.