X-ray Absorption Fine-structure Spectroscopy Measurements Research Articles

Direct detection of the crystal form of an active pharmaceutical ingredient in tablets by X-ray absorption fine structure spectroscopy

Different crystal forms of active pharmaceutical ingredients (APIs) may display variations in physicochemical properties. During the drug development process, the definitive purpose is to maintain homogeneous quality in a single crystalline form. Hence, it is important to evaluate and understand the properties of each crystal form of APIs in pharmaceutics. In this study, forms 0, Ⅰ, Ⅱ, III of bromhexine hydrochloride, and form S of bromhexine were characterized by the commonly used methods X-ray powder diffraction, thermogravimetry–differential thermal analysis, and single crystal structure X-ray diffraction. Additionally, X-ray absorption fine structure spectroscopy (XAFS), a seldom used method in the pharmaceutics discipline was also applied to explore the chemical environment of bromine atoms in forms 0, Ⅰ, Ⅱ and S as well as chloride ions in forms 0 to Ⅱ. The XAFS spectra of each form were different from each of the other forms which indicated the chemical environment around target elements in the crystal polymorphs were distinct. Then, we measured the commercial bromhexine hydrochloride tablets with XAFS measurement and found that XAFS could distinguish the crystal form in the tablets. Hence, we demonstrated that XAFS measurements would be applicable as one of the methods for the direct detection of APIs in the tablets.

Mechanism of the photoreduction of carbon dioxide catalyzed by the benchmarking rhenium dimethylbipyridine complexes; operando measurements by XAFS and FT-IR

The photoreduction of CO2 catalyzed by [fac-Re(dmbpy)(CO)3Cl] was precisely investigated through operando measurements of X-ray absorption fine structure spectroscopy (XAFS) and laser-flash FT-IR transient spectroscopy. In the early stage of the photoreaction, Re0-species assigned as penta-coordinated complex, [Re0(dmbpy)(CO)3], appeared and a delayed rise of ReII-species, [ReII(dmbpy)(CO)3CO2] (3)/[ReII(dmbpy)(CO)3COOH]+ (3′), were observed in XAFS measurements. The valence state of Re-center in the catalytic cycle changed as ReI → Re0 → ReII to be a clear evidence of an oxidative addition of CO2 to the Re0 center. In the laser-flash induced FT-IR measurements, a rise and decay of 3 followed by a delayed rise and decay of 3′ was observed. The second electron transfer from the carbon radical of triethylamine (TEA•) to 3′ induced the formation of [ReI(dmbpy)(CO)4]+ through [ReI(dmbpy)COOH]. The rate determining step of the catalytic cycle was revealed to be the protonation process of forming 3′ from 3.

Propane Dehydrogenation on Single-Site [PtZn4] Intermetallic Catalysts

Summary Propane dehydrogenation (PDH) is a commercial propylene production technology that has received much attention, but high reaction temperatures result in a decrease of propylene selectivity and catalyst stability. This paper describes a single-site [PtZn4] catalyst by assembling atomically ordered intermetallic alloy (IMA) as a selective and ultrastable PDH catalyst. The catalyst enables more than 95% of propylene selectivity from 520°C to 620°C. No obvious deactivation is observed within the 160-h test, superior to PtSn/Al2O3 and state-of-the-art Pt-based catalysts. Based on in situ X-ray absorption fine structure, X-ray photoelectron spectroscopy measurements, and density functional theory calculations, we reveal that the surface [PtZn4] ensembles in PtZn IMAs serve as the key active site structures, wherein the geometry-isolated and electron-rich Pt1 site in [PtZn4] ensembles readily promotes the first and second C–H cleavage of propane but inhibits further dehydrogenation of surface-bounded propylene. This significantly improves the selectivity and stability by prohibiting coke side reactions.

Operando NRIXS and XAFS Investigation of Segregation Phenomena in Fe-Cu and Fe-Ag Nanoparticle Catalysts during CO2 Electroreduction.

Operando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO2 reduction (CO2RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO2RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO3 at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H2 production.

Operando NRIXS and XAFS Investigation of Segregation Phenomena in Fe‐Cu and Fe‐Ag Nanoparticle Catalysts during CO2 Electroreduction

AbstractOperando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO2 reduction (CO2RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO2RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO3 at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H2 production.

Operando Evolution of the Structure and Oxidation State of Size-Controlled Zn Nanoparticles during CO2 Electroreduction.

We explored the size-dependent activity and selectivity of Zn nanoparticles (NPs) for the electrochemical CO2 reduction reaction (CO2RR). Zn NPs ranging from 3 to 5 nm showed high activity and selectivity (∼70%) for CO production, whereas those above 5 nm exhibited bulk-like catalytic properties. In addition, a drastic increase in hydrogen production was observed for the Zn NPs below 3 nm, which is associated with the enhanced content of low-coordinated sites on small NPs. The presence of residual cationic Zn species in the catalysts was also revealed during CO2RR via operando X-ray absorption fine-structure spectroscopy measurements. Such species are expected to play a role in the selectivity trends obtained. Our findings can serve as guidance for the development of highly active and CO-selective Zn-based catalysts for CO2RR.

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Program and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form PdxSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. They may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.

Role and Evolution of Nanoparticle Structure and Chemical State during the Oxidation of NO over Size- and Shape-Controlled Pt/γ-Al2O3 Catalysts under Operando Conditions

The structure and chemical state of size-selected Pt nanoparticles (NPs) supported on γ-Al2O3 were studied during the oxidation of NO using X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy measurements under operando conditions. The data revealed the formation of PtOx species in the course of the reaction that remained present at the maximum temperature studied, 350 °C. The PtOx species were found in all samples, but those with the smallest NPs showed the highest degree of oxidation. Moreover, NO-induced nanoparticle redispersion was observed at temperatures below 150 °C for all catalysts studied. Catalytic tests showed activity toward the oxidation of NO for all samples. Nevertheless, the catalyst with the smallest NPs was found to be the least active, which is explained by a more extensive formation of PtOx species in this catalyst and their detrimental contribution to the oxidation of NO.

Metal induced crystallization of amorphous silicon thin films studied by x-ray absorption fine structure spectroscopy

The role of thin metallic layer (Chromium or Nickel) in the crystallization of a-Si film has been studied using X-ray absorption fine structure spectroscopy (XAFS). The films were grown at different substrate temperatures in two different geometrical structures : (a) a 200 nm metal layer (Cr or Ni) was deposited on fused silica (FS) followed by 400 nm of a-Si and (b) the 400 nm a-Si layer was deposited on FS followed by 200 nm of metal layer. XAFS measurements at Cr K-edge and Ni K-edge were done at BM08 – GILDA beamline of the European Synchrotron Research Facility (ESRF, Grenoble, F) in fluorescence mode. To understand the evolution of the local structure of Cr/Ni diffusing from bottom to top and from top to bottom, total reflection and higher incidence angles were employed. The relative content of metal, metal oxide and metal silicides compounds on the upper surface and/or in the bulk of different films has been evaluated as a function of thermal treatment.

High-sensitivity x-ray absorption fine structure investigation of arsenic shallow implant in silicon

High-sensitivity fluorescence-yield x-ray absorption fine structure spectroscopy (XAFS) has been investigated to characterize the local structure around arsenic shallow implant in silicon. Fluorescence-yield XAFS experiments were performed using a high-brilliance synchrotron radiation beam from an in-vacuum-type undulator in a third-generation light source. In addition to investigating the efficiency of high-brilliance undulator x-rays during the fluorescence-yield XAFS measurements, we compared the analytical performance of both the wavelength dispersive spectrometer (WDS) and the energy dispersive spectrometer (EDS) based on the silicon drift detector (SDD). It was confirmed that the WDS reduces the influence of scattering background due to the high spectral resolution. Another advantage of the WDS is high counting rate measurements. It was found that fluorescence-yield XAFS using undulator x-rays combined with the WDS permits superior sensitivity measurements.

A fast energy-dispersive multi-element detector for X-ray absorption spectroscopy

In this paper results are presented from fluorescence-yield X-ray absorption fine-structure spectroscopy measurements with a new seven-cell silicon drift detector (SDD) module. The complete module, including an integrated circuit for the detector readout, was developed and realised at DESY utilizing a monolithic seven-cell SDD. The new detector module is optimized for applications like XAFS which require an energy resolution of approximately 250-300 eV (FWHM Mn Kalpha) at high count rates. Measurements during the commissioning phase proved the excellent performance for this type of application.

An Overview of Synchrotron Radiation Applications to Low Temperature Geochemistry and Environmental Science

The availability of synchrotron radiation (SR) to the scientific community has literally revolutionized the way X-ray science is done in many disciplines, including low temperature geochemistry and environmental science. The key reason is that SR provides continuum vacuum ultraviolet (VUV) and X-ray radiation five to ten orders of magnitude brighter than that from standard sealed or rotating anode X-ray tubes (Winick 1987; Altarelli et al. 1998). Although SR was first observed indirectly by John Blewitt in 1945 (Blewitt 1946) and directly by Floyd Haber in 1946 at the General Electric 100-MeV Betatron in Schenectady, NY (see Elder et al. 1947; Baldwin 1975), it took 10 to 15 years before the first systematic applications of SR, which involved spectroscopic studies of the VUV absorption of selected elements (Tomboulian and Hartman 1956) using the 300-MeV synchrotron at Cornell University and of rare gases (Madden and Codling 1963) using the National Bureau of Standards SURF I synchrotron. As of September 2002, there are about 75 storage ring-based SR sources in operation, in construction, funded, or in advanced planning in 23 countries, with 10 fully dedicated SR storage ring facilities in the U.S.. A listing of these sources can be obtained at the following web site: http://www-ssrl.slac.stanford.edu/sr_sources.html . The first SR experiments relevant to low temperature geochemistry and environmental science, although not performed on earth or environmental materials, were X-ray absorption fine structure (XAFS) spectroscopy measurements on amorphous and crystalline germanium oxide conducted on the SPEAR storage ring at the Stanford Synchrotron Radiation Project in 1971 by Dale Sayers, Farrel Lytle, and Edward Stern (Sayers et al. 1971). Prior to the availability of SR in the hard X-ray energy range (> 5 keV), XAFS spectroscopy measurements were impractical because of the high X-ray flux required and the need for a continuously tunable …