Probing Iodine Atom Interactions in 4-Iodo-L-phenylalanine Crystals by X-Ray Absorption Near-Edge Structure Spectroscopy.

X-ray absorption near-edge structure (XANES) spectroscopy of fullerenes: inner-shell excitonic effects in fullerenes and the XANES spectrum of a higher fullerene C 76

X-ray absorption near-edge structure (XANES) spectroscopy is a new method for the characterization of active pharmaceutical ingredients. XANES spectra show unique features depending on the electronic states of the X-ray absorbing elements and provide information about the chemical environment that affects the electronic states. In this study, six bisphosphonate hydrate crystals were used to investigate, for the first time, how the phosphorus K-edge XANES spectra are affected by the interatomic interactions and charged states of phosphonate moieties. Phosphorus K-edge XANES spectra showed several differences among the bisphosphonates. In particular, the chlorine atoms covalently bonded near the phosphonate and the number of electric charges of the phosphonate moieties seemed to have large effects on peak shape in XANES spectra. Unique shapes of the XANES spectra demonstrated that differences in interactions at the oxygen atoms of the phosphonate moieties could change the shapes of the XANES spectrum peaks to the extent that each material was distinguished based on the spectra. Since slight differences in interatomic interactions and charged states lead to variations in the spectra, XANES spectroscopy could be widely applied as the fingerprint method to evaluate active pharmaceutical ingredients.

Synchrotron radiation S K- and L-edge X-ray absorption near-edge structure (XANES) spectra are reported for the cubic, rocksalt (B1) structure sulfides niningerite (MgS), alabandite (MnS), and oldhamite (CaS), and for their solid solutions (Mn,Fe)S and (Mg,Mn)S, and S L-edge XANES spectra are reported also for (Mg,Fe)S solid solutions. Pre-edge features at the S K-edge are attributed to transition of S 1s electrons to the lowest available unoccupied S 3p σ* antibonding states hybridized with metal 3d(e g ) states, and at the S L-edge to transition of S 2p electrons to unoccupied S 3s σ*, 4s σ*, and 3d antibonding states hybridized with metal 3d(e g ) states, and to a lesser extent 3d(t 2g ) states. The S K-edge XANES spectra for the solid solutions show a progressive participation of 3d orbitals in metal-S bonding with increase in substitution by Fe in (Mn,Fe)S and (Mg,Fe)S and Mn in (Mg,Mn)S through progressive increase in the area of the pre-edge feature. However, the pre-peak area does not increase linearly in each solid solution series showing that a real change in bulk electronic properties has occurred. Increase in pre-peak area reflects an increase in overall attainability of metal 3d states for hybridization with S 3p σ* antibonding states as proportionally more metal 3d orbitals become available. The S L-edge XANES spectra show progressive evolution of pre-edge features at the L 3 - and L 2 -edges (a 1 and a 2 , respectively). Only a 2 is present in the S L-edge XANES spectrum of FeS (troilite), and with progressive decrease in Fe content in (Mn,Fe)S and (Mg,Fe)S solid solutions, a 1 first appears, then becomes dominant. Since a 1 is attributed to transition of S 2p 3/2 electrons to S 3s σ* states hybridized with metal 3d(e g ) and 3d(t 2g ) states, this appears to represent an increased contribution from metal-S π-bonding. The results show that the size and position of the pre-edge features to the S K- and L-edges are controlled more by the DOS of hybridized 3d(e g β ) and 3d(t 2g β ) states and nearest-neighbor coordination of the metal atoms than by the precise coordination of S and the extended structure of the sulfide. The full multiple scattering approach has been applied to the calculation of the S K-edge XANES spectra of MgS, MnS, and CaS. Results are consistent with experimental XANES spectra, especially for the pre-edge features, which are often neglected in such calculations.

Polymorphic crystals of ambroxol, forms I and II, and form A ambroxol hydrochloride crystals were characterized with bromine K-edge X-ray absorption near-edge structure (XANES) spectroscopy and single-crystal X-ray structure analysis. The XANES spectra had unique shapes depending on the crystal forms. Refined single-crystal structures revealed different interatomic interactions around bromine atoms, such as C-H…Br and N-H…Br hydrogen bonds, Br…O halogen bonds, and N-H…π interactions. Differences in these weak interactions could affect the electronic states of the bromines, resulting in differences in the XANES spectra. The results demonstrated that weak non-conventional interatomic interactions could alter the shape of XANES spectra. Hence, the spectra could be used for evaluating polymorphs of active pharmaceutical ingredients.

We measured Pd L3-edge X-ray absorption near-edge structure (XANES) spectra for small Pd particles dispersed on inorganic oxide supports (SiO2 and Al2O3) and the spectra changes induced by the adsorption and the absorption of hydrogen. When the XANES spectra were measured under the atmosphere of H2, a new peak appeared at about 8 eV above the inflection point of the absorption edge. The peak position was invariant but its intensity decreased with the decrease of Pd particle size. This peak is caused by hydrogen absorption in the Pd particles. Hydrogen at the subsurface region little affected the Pd L3-edge XANES spectra. A new peak also appeared for the Pd sample accompanied with hydrogen adsorbed on the surface. The peak energy relative to the edge was independent of the Pd particle size and the peak intensity increased with the amount of adsorbed hydrogen. The XANES spectra can quantify the adsorbed and absorbed hydrogen atoms. We presented a model of Pd particles composed of surface, subsurface and bulk atoms.

High-sensitive XANES analysis at Ce L2-edge for Ce in bauxites using transition-edge sensors: Implications for Ti-rich geological samples

Gold (Au) clusters with well-defined geometrical structures have attracted substantial attention due to their unique optical and catalytic properties, which are drastically changed by the ligands, compositions, and geometric structures. Here, we investigated the effect of ligand on the electronic state of Au in [Au9(PPh3)8]3+ (Au9) and [Au25(SC2H4Ph)18]− (Au25) by X-ray absorption spectroscopy using high energy resolution fluorescence detection (HERFD) and theoretical calculations. Au L3-edge X-ray absorption near-edge structure (XANES) spectra revealed that the white-line intensity of Au9 was comparable to that of Au25, while the white-line peak of Au25 was 3 eV lower than that of Au9. The total area of the white line of Au9 corresponded to that of Au25, which is explained by the natural bond orbital analysis, showing that the occupancy of Au 5d orbitals of Au9 was close to that of Au25. The simulated XANES spectra using finite difference method near-edge structure software resembled the experimental XANES spectra. The projected density of state profiles and molecular orbitals indicated that the unoccupied 5d orbitals of the surface Au in Au9 and of surface and oligomer Au in Au25 interacted with P/S 3s+3p orbitals. The difference in peak locations in Au L3-edge XANES between phosphine- and thiolate-protected gold clusters was ascribed to the energy shift of unoccupied Au 5d orbitals, which are modulated by the Au 5d and P/S 3s+3p interaction.

Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

“A spectroscopic picture paints 1000 words” mapping iron speciation in brain tissue with “full spectrum per pixel” X-ray absorption near-edge structure spectroscopy

Iron local structure in tektites and impact glasses by extended X-ray absorption fine structure and high-resolution X-ray absorption near-edge structure spectroscopy

Ce(III) and Ce(IV) (re)distribution and fractionation in a laterite profile from Madagascar: Insights from in situ XANES spectroscopy at the Ce LIII-edge

Calcium carbonate minerals are frequently found in biomineral structures and are the predominant mineral in invertebrates. While there are several calcium carbonate polymorphs, aragonite and calcite are the two most commonly found in biogenic systems. Currently, calcium L-edge X-ray absorption near-edge structure (XANES) spectra are used to distinguish between different calcium carbonate polymorphs, including calcite and aragonite, while oxygen and carbon K-edge XANES spectra are often used to determine the c axis orientation of a given calcium carbonate crystal. By doing a full analysis of the calcite and aragonite calcium L-edge XANES spectrum for both geologic and biogenic systems, we were able to show that aragonite has a polarization-dependent peak while calcite does not. Analysis based on both multiplet models and density functional calculations show how the polarization dependence arises from directional bonds between the calcium and oxygen atoms within aragonite. These data not only enable an interpretation of the aragonite calcium L-edge XANES spectrum but also the ability to determine the orientation of the c and b axes of aragonite crystals within a biomineral sample.

The microstructure and composition, including chemical speciation of sulphur (S), of two mollusc shells were investigated using a combination of scanning electron microscopy, X-ray absorption near-edge structure spectroscopy (XANES) and electron probe microanalysis (EPMA). The shell of Pinna is composed of monocrystalline, and Pinctada, of polycrystalline, calcite prisms separated by organic-rich walls. Sulphur speciation information from XANES spectra using a scanning X-ray microscope showed that the protein S content of the interprismatic walls is higher than the SO4 content, whereas the reverse is true for the intraprismatic structures. High-spatial-resolution XANES maps for the different S species across adjacent calcite prisms confirm their distinctive distributions in the molluscan shells and illustrate the presence of narrow, submicron transverse growth features. On a larger scale, a series of wider growth zones, incorporating the submicron zones, are aligned parallel to each other and cross-cut many calcite prisms. EPMA element maps for magnesium (Mg) and S demonstrate that these growth increments are compositionally zoned, comprising alternating layers of high mineral (Mg-rich) and high organic (S-rich) components. Additionally, these maps confirm that the organic interprismatic walls have lower Mg and higher S than the intraprismatic structures.

Investigating binary oil additive systems containing P and S using X-ray absorption near-edge structure spectroscopy

Tc-gluconate complexes in aqueous systems were recently reported and characterized by Tc L3-edge X-ray absorption near-edge structure (XANES) measurements [Dardenne, K.; Inorg. Chem. 2021, 60, 12285-12298]. The puzzling result was reported that the Tc L3-edge XANES of the sample containing Tc(IV)-gluconate species differs substantially from that of the Tc(IV)O2(am,hyd) hydrous oxide reference sample, whereas the Tc K-edge XANES spectra did not differ significantly. We studied this observation theoretically and tracked the unknown Tc(IV)-gluconate species in a three-step procedure: (1) developing chemical models, (2) optimizing the equilibrium structures of the models, and (3) simulating the corresponding Tc L3-edge XANES spectra. We identified the [Tc(IV)(Glu-2H)2(H2O)2]2- structure as the most likely Tc(IV)-gluconate species present in our samples and explain the substantial difference between the two Tc L3-edge XANES spectra. Additionally, we revisited the Tc(V)-gluconate species and identified the [Tc(V)O(Glu-H)2]- structure as the most likely Tc(V)-gluconate species in our sample.