FOCAL: X-ray optics for accurate spectroscopy

A crystal spectrometer has been constructed in the Focusing Compensated Asymmetric Laue geometry covering the energy range between 30 and 120 keV. We summarize the crystal optics and show the usefulness of the instrument for spectroscopy of stationary and fast moving X-ray sources. Results are reported from several tests employing a ¹⁶⁹Yb gamma-ray source and the Lyman radiation of one-electron Au⁷⁸⁺ ions travelling at a velocity corresponding to β=v/c_o≈0.44.     

Surface properties of the Ni-Cu-Cr oxide catalyst for dehydrogenative hydrolysis of amines

Catalysts for dehydrogenative hydrolysis of amines, prepared by sorption of copper ions from a solution on a preformed Ni-Cr oxide system, were studied by Auger electron spectroscopy, X-ray photoelectron spectroscopy, and IR spectroscopy of adsorbed CO and NH₃ probe molecules. It was shown that on adsorption copper blocked the chromium ions in the Ni-Cr catalyst with concomitant stabilization as Cu⁺. The incorporation of copper into the Ni-Cr system increased the ability of nickel to reduce water with the formation of oxygen-containing complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 288–291, February, 1993.     

Structure of the blue forms of bisphthalocyanines of rare-earth elements

Using electron spectroscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy, the blue forms of bisphthalocyanines of rare-earth elements were found to have structures of sandwich-type complexes with isoelectronic phthalocyanine ligands linked with tetravalent metal ions, [Pc^2–Ln⁴⁺Pc^2–]⁰. A comparative spectral and electrochemical study of the blue and green forms oftert-butyl-substituted bisphthalocyanines was carried out for almost the whole series of rare-earth metals. Lutetium octa(perfluoro-tert-butyl)- and perchlorobisphthalocyanines were synthesized for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 425–430, March, 1995.This study was financially supported by the Russian Foundation for Basic Research (grant No. 94-03-08903).     

X-ray photoelectron spectroscopic studies of the charged state of 3d metal ions in CuCr1?xVxS2 (x = 0–0.4)

The charged state of the 3d metal ions in layered cation-substituted disulfides CuCr_1−x V _x S₂ was studied by X-ray photoelectron spectroscopy. An analysis of the energy positions and structure of the Cu2p _3/2 and Cr2p _3/2 X-ray photoelectron lines showed that the corresponding polycrystalline samples of CuCr_1−x V _x S₂ contained mixed-valence chromium and copper ions. It was shown that the charged states of chromium and copper ions depended on the concentration of vanadium cations (x). The presence of mixed-valence Cu¹⁺ and Cu²⁺ ions in CuCr_1−x V _x S₂ may be correlated with the crystal structure of the corresponding layered disulfides. Original Russian Text Copyright ? 2009 by L. N. Mazalov, V. V. Sokolov, N. A. Kryuchkova, E. I. Vovk, I. Yu. Filatova, and G. M. Abramova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 461–467, May–June, 2009.     

Heteroorganic betaines. 7. Synthesis and structure of a germanium-containing organophosphorus betaine Et3P+—CHMe—GeMe2—S–

Germanium-containing organophosphorus betaine Et₃P⁺—CHMe—GeMe₂—S^– was synthesized by the reaction of hexamethylcyclotrigermatrithiane with Et₃P=CHMe. The structure of the betaine was established by X-ray diffraction analysis and multinuclear NMR spectroscopy. In the crystal, the P⁺—C—Ge—S^– main chain of the molecule adopts a folded cis-gauche conformation due to strong Coulomb interactions between the anionic and cationic centers. The equilibrium geometry of the isolated molecule was calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set). The calculated geometric characteristics are in qualitative agreement with the X-ray data. The structure of the betaine is compared with the structure of its silicon-containing analog studied previously.     

Ionic conductivity, structural and thermal properties of pure and Sr doped Y2Ti2O7 pyrochlores for SOFC

In the present study, SrO doped Yttrium titanate pyrochlore was synthesized using solid state reaction technique. The sintering characteristics, crystal structure, thermal and conductivity behavior of doped and undoped pyrochlores have been studied to find their suitability in solid oxide fuel cells (SOFC). The as-prepared samples were characterized using X-ray diffraction (XRD), Fourier-Transform-Infrared spectroscopy (FT-IR), thermal-gravimetric analysis (TGA) and ac conductivity up to 900 °C. The results are discussed in light of oxygen vacancy formation and structural disordering. Undoped and doped yttrium titanate with SrO (x = 0.1) exhibits single Y₂Ti₂O₇ phase with relative density of 94%. It was observed that further doping of SrO (x = 0.2–0.4) leads to formation of Y₂Ti₂O₇ phase along with SrTiO₃ phase. Excessive SrO (x = 0.4) results in increase in ionic conductivity to 1.50 × 10⁻¹ S cm⁻¹ whereas it impedes the densification process with relative density of 85%.     

Uranium's Valency in U3S5

U₃S₅ has been prepared by chemical transport reaction and investigated using X-ray powder diffraction, FTIR spectroscopy, electrical resistivity measurements, and X-ray photoelectron spectroscopy. U₃S₅ is a semiconductor with a thermal band gap E_g=78.1(4) meV (298 K<T<50 K), which closes gradually to 3.4(4) meV for T<25 K. Photoelectron spectroscopy on single crystals of U₃S₅ and β-US₂ suggest a mixed valency of uranium in U₃S₅. Physical and structural data are consistent with a mixed-valent model (U³⁺)₂U⁴⁺ (S²⁻)₅. A brief survey of literature data on crystal structure and physical properties of uranium sulfides and selenides is given.     

Study of alkaloids from the flora of the Siberian and Altai regions. 6. Crystal and molecular structure of songorine Z-oxime

Oximation of songorine afforded a mixture of its Z- and E-oximes. The crystal and molecular structure of the Z-isomer was established by X-ray diffraction analysis. Its structure was also confirmed by the spectral data (2D ¹H—¹H and ¹³C—¹H NMR spectroscopy and mass spectrometry). The structure of isomeric E-oxime was established by comparing its NMR spectroscopic data (¹H and ¹³C) with the data for the Z-isomer.     

Ion-beam irradiation effects on polyimide-UV–vis and infrared spectroscopic study

Ion-beam irradiation effects on polyimide, Kapton™, were studied with respect to optical and electronic properties. Stack films of Kapton™ (12.5 μm thick) were irradiated to various ion beams in air or vacuo at room temperature and subjected to ultraviolet–visible (UV–vis) spectroscopy, and change in absorbance and energy gap is discussed. The UV–vis absorption spectrum, which is assigned to the transition of electrons in benzene rings from π to π* orbital, upon He²⁺ (6 MeV/u) irradiation in air, shifted towards longer wavelength direction for all cases, and the shift was more obvious for higher linear energy transfer (LET) ion beams. The energy gap of the transition was estimated, and the H⁺ and He²⁺ ion beams caused little change in the transition energy gap Eg, while the heavier ions such as C⁶⁺ and Si¹⁴⁺ caused more significant decrease. This decrease is assumed to the structural changes around benzene rings, and the infrared spectroscopy revealed breakage in imide groups next to benzene ring in the repeating unit of polyimide.     

Synthesis, infrared spectra, thermal analyses and structural studies of half-sandwich Fe(III)/Fe(II) complex containing pyridine-2,6-dicarboxylate and 1,10-phenanthroline

A new pyridine-2,6-dicarboxylate iron(III)/iron(II) complex [Fe(phen)₃][Fe₂(PDC)₄]·3CH₃OH was synthesized and characterized (where PDC = pyridine-2,6-dicarboxylate, phen = 1,10-phenanthroline) by using elemental analysis, IR spectroscopy and thermal analyses (TGA and DTA). The molecular structure of the complex has been determined by single-crystal X-ray diffraction. The complex is mixed-ligands and the IR spectra display bands characteristic of coordinated mixed-ligand bases. All the IR results are in agreement with the X-ray crystal result. The bond lengths indicate that this complex has [Fe(phen)₃]²⁺ cation where Fe(II) ion is in typical low-spin state, and in counter ions, [Fe(PDC)₂]⁻ are both in high-spin state.     

Redox Reaction in Ti−Mn Redox Flow Battery Studied by X-ray Absorption Spectroscopy

We performed X-ray absorption studies for the electrolytes of a Ti−Mn redox flow battery (RFB) to understand the redox reaction of the Ti/Mn ions and formation of precipitates in charged catholyte, because suppression of the disproportionation reaction is a key to improve the cyclability of Ti−Mn RFB and enhance the energy density. Hard X-ray absorption spectroscopy with a high transmittance and soft X-ray absorption spectroscopy to directly observe the 3d orbitals were complementarily employed. Moreover, the Ti/Mn 3d electronic structure for each precipitate and solution in the charged catholyte was investigated by using scanning transmission X-ray microscopy: the valence of Mn in the precipitate is mostly attributed to 4+, and the solution includes only Mn²⁺. This charge disproportionation reaction should occur after the Mn ions in the catholyte should be oxidized from Mn²⁺ to Mn³⁺ by charge.     

IR Spectroscopic Study of the Interaction of Transition Metal Ions with Hydroxyapatite Modified by Potassium Ferrocyanide

IR spectroscopy was used to study the modification of hydroxyapatite by potassium ferrocyanide and the interaction of transition metal ions with the modified adsorbent. The structural changes of hydroxyapatite upon the adsorption of Zn²⁺ ions were studied by X-ray phase analysis. Potassium ferrocyanide was found to interact with the surface hydroxyl groups of hydroxyapatite through the nitrogen unshared electron pair. Co²⁺, Ni²⁺, and Zn²⁺ ions were found to eliminate outer-sphere K⁺ ions of adsorbed ferrocyanide to give Fe²⁺— CN—M²⁺— NC—Fe²⁺ bridging structures. Zn²⁺ cations additionally eliminate a part of the Ca²⁺ ions from structural positions of hydroxyapatite, which leads to the appearance of a two-phase hydroxyapatite–sholzite system with heterogeneous distribution of the Ca²⁺ ions in the mot her mineral phase, while the Zr²⁺ ions are found in the new sholzite phase.     

XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

Influence of coordination on N-H X hydrogen bonds. Part II. Zn(NH3)2Br2 and Ni(NH3)2X2 (X is Cl and Br)

Microcrystalline samples of Zn(NH₃)₂Br₂ and Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻) have been investigated from 100 to 293 K using X-ray diffraction and IR spectroscopy measurements (range 400–4000 cm⁻) performed with isotopically dilute (5% deuterated) samples. Values of Δν(ND)/ΔT for all compounds hint at the existence of hydrogen bonds. Zn(NH₃)₂Br₂ shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molecules takes place in Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻). A comparison between octahedrally coordinated ammoniates [Ni(NH₃)₆]Br₂, Ni(NH₃)₂Br₂ and [Zn(NH₃)₆]Br₂ with tetrahedrally coordinated ones [Zn(NH₃)₂Br₂] leads to the conclusion that the lower coordination number increases the strength of the hydrogen bonds. Because this effect is small, it is not possible to separate the influence of the type of coordinating ions for one coordination number from the influence of the coordination number itself.     

Infrared spectroscopy of isolated nucleotides. 1. The cyclic 3′,5′-adenosine monophosphate anion

The intracellular second messenger deprotonated adenosine 3′,5′-cyclic monophosphate anion (cAMP-H)⁻, generated as gaseous species by electrospray ionization (ESI) and stored in a Paul ion-trap mass spectrometer, has been investigated by mass-resolved infrared multiple photon dissociation (IRMPD) spectroscopy in the 900–1800 cm⁻¹ fingerprint wavenumber range, exploiting the powerful and continuously tunable radiation from a free electron laser (FEL) at the Centre Laser Infrarouge d’Orsay (CLIO). The IRMPD features are interpreted by comparison with the IR spectra obtained by quantum chemical calculations for different low-lying conformers, allowing an assignment for the observed IRMPD bands. It is to be noted that the calculated IR spectra for the most stable conformers look all rather similar and do not allow an unambiguous structural assignment, based exclusively on the IRMPD spectrum. However, the positions and intensities of the IRMPD features of isolated (cAMP-H)⁻ ions are consistent with a species deprotonated at the phosphate group and compatible with the main equilibrium structures lying within 18 kJ mol⁻¹ from the lowest lying conformation, the anti-chair form with a C3′-endo sugar twist.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Phosphate desorption kinetics from goethite as induced by arsenate

The kinetics of the arsenate-induced desorption of phosphate from goethite has been studied with a batch reactor system and ATR-FTIR spectroscopy. The effects of arsenate concentration, adsorbed phosphate, pH and temperature between 10 and 45 °C were investigated. Arsenate is able to promote phosphate desorption because both oxoanions compete for the same surface sites of goethite. The desorption occurs in two steps: a fast step that takes place in less than 5 min and a slow step that lasts several hours. In the slow step, arsenate ions exchange adsorbed phosphate ions in a 1:1 stoichiometry. The reaction is first order with respect to arsenate concentration and is independent of adsorbed phosphate under the experimental conditions of this work. The rate law is then r = k_r[As], where r is the desorption rate, k_r is the rate constant and [As] is the arsenate concentration in solution. The values of k_r at pH 7 are 1.87 × 10⁻⁵ L m⁻² min⁻¹ at 25 °C and 7.95 × 10⁻⁵ L m⁻² min⁻¹ at 45 °C. The apparent activation energy of the desorption process is 51 kJ mol⁻¹. Data suggest that the rate-controlling process is intraparticle diffusion of As species, probably As diffusion in pores. ATR-FTIR spectroscopy suggests that adsorbed phosphate species at pH 7 are mainly bidentate inner-sphere surface complexes. The identity of these complexes does not change during desorption, and there is no evidence for the formation of intermediate species during the reaction.     

Vibrational spectroscopic study of the arsenate mineral strashimirite Cu8(AsO4)4(OH)4·5H2O—Relationship to other basic copper arsenates

The basic copper arsenate mineral strashimirite Cu₈(AsO₄)₄(OH)₄·5H₂O from two different localities has been studied by Raman spectroscopy and complemented by infrared spectroscopy. Two strashimirite mineral samples were obtained from the Czech (sample A) and Slovak (sample B) Republics. Two Raman bands for sample A are identified at 839 and 856 cm⁻¹ and for sample B at 843 and 891 cm⁻¹ are assigned to the ν₁ (AsO₄³⁻) symmetric and the ν₃ (AsO₄³⁻) antisymmetric stretching modes, respectively. The broad band for sample A centred upon 500 cm⁻¹, resolved into component bands at 467, 497, 526 and 554 cm⁻¹ and for sample B at 507 and 560 cm⁻¹ include bands which are attributable to the ν₄ (AsO₄³⁻) bending mode. In the Raman spectra, two bands (sample A) at 337 and 393 cm⁻¹ and at 343 and 374 cm⁻¹ for sample B are attributed to the ν₂ (AsO₄³⁻) bending mode. The Raman spectrum of strashimirite sample A shows three resolved bands at 3450, 3488 and 3585 cm⁻¹. The first two bands are attributed to water stretching vibrations whereas the band at 3585 cm⁻¹ to OH stretching vibrations of the hydroxyl units. Two bands (3497 and 3444 cm⁻¹) are observed in the Raman spectrum of B. A comparison is made of the Raman spectrum of strashimirite with the Raman spectra of other selected basic copper arsenates including olivenite, cornwallite, cornubite and clinoclase.     

Photoactivity of mechanochemically prepared nanoparticulate titanium dioxide investigated by EPR spectroscopy

Titanium dioxide nanopowders were prepared by mechanochemical synthesis in a high-energy ball mill using TiOSO₄·xH₂O and Na₂CO₃ followed by annealing in the temperature range 200–800 °C. The UVA photonic efficiency of radical processes on synthesized TiO₂ powders was determined by in situ EPR spectroscopy, using, as indicators, the N-oxide spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide and 5-(diisopropoxy-phosphoryl)-5-methyl-1-pyrroline N-oxide) or the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate, ABTS⁺). The results obtained by monitoring the photoinduced generation of hydroxyl radical spin adducts correlated with those found by the investigation of the photoreduction of ABTS⁺. The presence of iron and chromium ions, which were evidenced in samples milled in steel, decreased the photonic efficiency of radical processes. The presence of a sulfate salt matrix during the annealing process distinctly inhibits the transformation of anatase to rutile. The highest photocatalytic activity was shown by anatase samples which were prepared by milling in corundum and annealed at 700 °C. They were composed of crystallites with a mean size of 25–30 nm and well developed crystal faces.     

Spectroscopic studies on binding of Puerarin to human serum albumin

The interaction between Puerarin with human serum albumin has been studied for the first time by spectroscopic methods including fluorescence quenching technology, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. The results of fluorescence titration revealed that Puerarin can strongly quench the intrinsic fluorescence of HSA by static quenching and there is a single class of binding site on HSA. In addition, the studies of CD spectroscopy and FT-IR spectroscopy showed that the binding of Puerarin to HSA changed slightly molecular conformation of HSA. Furthermore, the thermodynamic functions ΔH⁰ and ΔS⁰ for the reaction were calculated to be −9.067 kJ mol⁻¹ and 54.315 J mol⁻¹ K⁻¹ according to van’t Hoff equation. These data suggested that both hydrogen bond and hydrophobic interaction play a major role in the binding of Puerarin to HSA, which is in good agreement with the result of molecular modeling study.