EXAFS Study Research Articles

Palladium immobilized on functionalized halloysite: A robust catalyst for ligand free Suzuki–Miyaura cross coupling and synthesis of pyrano[2,3-c]pyrazole motifs via four component cascade reaction and their in-silico antitubercular screening

This research introduces a novel organically functionalized halloysite-supported palladium catalyst, HMF-EDA-TMS@HAL-Pd(II) that was synthesized and thoroughly characterized using various analytical techniques like HR-TEM, FEG-SEM, EDX, XPS, FTIR, XRD, TGA, ICP-AES, EXAFS and DFT studies. The catalyst exhibited exceptional performance in Suzuki–Miyaura cross coupling reactions, demonstrating high efficiency and reusability up to seven cycles in aqueous ethanol medium. Motivated by its promising catalytic activity, we extended our investigation to explore its applicability in the synthesis of pyrano[2,3-c]pyrazole motifs via a four-component cascade reaction affording the desired products in good to excellent yields with broad substrate scope under green reaction conditions. In-silico antitubercular screening of pyrano[2,3-c]pyrazole motifs against DprE1 enzyme have shown promising results with inhibition constants ranging between 0.030 and 0.1 μM for compounds 5b, 5k and 5 l. This protocol has the advantages of wide substrate scope, high yield, excellent functional group tolerance, high efficiency and environmental benign procedure. These findings emphasized the catalyst's versatility and potential in diverse organic transformations, highlighting its importance in advancing sustainable synthetic methodologies.

Kinetics of Oxygen Catalyst Based on Pyrochlore Oxide Nano-Particles for Low Temperature Water Electrolysis

Alkaline water electrolysis is carried out at 60 to 80 oC using nickel-based electrode materials and highly concentrated KOH solutions, which make highly corrosive environment against the electrodes, the separator, the current collector, and the others of the cell. Reduction in operating temperature would be preferable to suppress corrosion, although it would also make the catalytic activity for OER and HER down, making the cell voltage up. Since oxygen evolution is known as a high overpotential reaction which is more than 400 mV with nickel-based oxides at 60 oC or more, and alternative materials with lower overpotential and higher stability for OER in AWE have been needed. This paper presents a novel oxygen catalyst nano-particles based on bismuth ruthenium oxide, in which ruthenium at the B site in the pyrochlore structure is partly replaced with manganese1).Mn-doped bismuth ruthenium oxide (MBRO) was prepared by precipitation of metal hydroxide precursor, which had been obtained by addition of NaOH solution into the metal salt solution containing Bi(III) and Ru(III) with Mn(II), followed by calcination at 600 oC. XRD, EDX, EXAFS, ICP-AES, and RBS were used for structural and compositional analyses of MBRO. The obtained oxide was added into distilled water and the solution was treated by ultrasonic vibration to make a suspension, which was then dropped on a titanium disk (4 mm diam.) and dried at RT for 24 h, resulting in oxide particles-coated titanium disk, in which no binders or ionomers were used in the process. The disk was mounted in a commercial rotating disk electrode and was used as the working electrode with a platinum counter electrode, an Hg/HgO reference electrode, and 0.1 mol/L KOH solution. Polarization curves were measured by LSV for OER, of which the results were analyzed to obtain the onset potential, Tafel slope, exchange current density. All measurements were performed at RT (25 oC).EDX and EXAFS studies of MBRO showed that Ru(IV) was replaced with Mn(IV) at the B-site of pyrochlore structure, and this doping made a single phase of pyrochlore structure oxide without sub-product up to 30 at% replacement . Linear sweep voltammetry revealed the overpotential of MBRO for OER was less than 200 mV and the Tafel slope analysis of the LSV curve gave 40 mV/dec or less. The onset potential and the Tafel slope were almost the same when Ru:Mn atomic ratio of MBRO was changed from 100:0 to 70:30 at%. Further analysis of the polarization curve indicated the exchange current density slightly decreased with increasing Mn ratio. These results suggest that Ru is the active site for OER but Mn is as well. The Tafel slope of OER catalysts reported in literatures is mostly 60 mV/dec or more, including more than 200 mV/dec of nickel-based oxides2,3). Therefore, MBRO is a hyper catalytic oxide for OER in alkaline media and can significantly reduce the overpotential of the anode in AWE even at ambient temperature.Ref.1) M. Morimitsu, Patent US.2022085387.A1.2) T. Shinagawa, A. T. Garcia-Esparza, K. Takanabe, Scientific Reports, Vol. 5, Article No.13801 (2015).3) S. Yagi, et al., Nature Communications, Vol. 6, Article No. 8249 (2015).

Growth of copper-nickel (Cu-Ni) dual atom catalysts over graphene variants as active anodes for clean oxygen generation: Integrative experimental and computational validation

The development of atomically precise metals on the surface of graphene has led to superior electrocatalytic properties for the clean oxygen production. In this study, Cu single-atom and NiCu dual-atom catalysts supported on different graphene variants were effectively developed as electrocatalysts for the production of clean oxygen. Various techniques, including XRD, SEM, Raman, HR-TEM, EXAFS and XPS, were used to characterize these synthesized electrocatalysts. The extent of reduction in graphene oxide (GO) support was confirmed using Raman analysis which demonstrated a greater ID/IG-apparent intensity ratio, indicating that the GO (ID/IG=0.9) has more sp3-hybridized carbon with respect to the rGO (ID/IG= 0.6). The HR-TEM analysis with EDX and STEM data confirmed the dispersion of Cu and NiCu dimer over the surface of graphene variants. XPS and EXAFS studies revealed predominant metallic nature of Cu and NiCu dimer with the synergistic interplay between the constituent atoms. Copper-nickel dimer catalyst supported on reduced graphene oxide (CuNi/rGO) demonstrated the best electrocatalytic performance, where a lower overpotential of 320 mV was observed to reach a current density of 10 mA cm−2 with lowest Tafel slope of 110 mV/dec for oxygen evolution reaction. Good stability was observed after 1000 CV cycles and 50 h of electrolysis in 1.0 M KOH electrolytic solution at an oxidation potential of 1.62 V (vs RHE). Control experiments were also performed using borosilicate pyrex glass and Teflon made electrochemical cells in order to over rule the probable involvement of leached out impurities in OER reaction under extreme alkaline conditions. The calculations obtained from Density Functional Theory (DFT) suggest that the dual-atom catalysts have lower overpotential (0.33 V at Cu-site) with respect to the single-atom catalysts, which agreed well with the experimental results. Also, the Cu-site OER was found to have lower overpotential (0.33 V) than the Ni-site (0.47 V). Thus, this study can provide valuable insights into developing low-cost dual-atom electrocatalysts, where the synergism between constituent elements in the dimer and their stabilization by graphene matrix can be exploited for various electrochemical reactions.

Molecular geochemistry of radium: A key to understanding cation adsorption reaction on clay minerals

Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra2+ adsorbed on clay minerals and showed that Ra2+ forms inner-sphere complexes on vermiculite, which can be surprising because Ra2+ is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra2+ by clay minerals and the controlling factors can effectively predict cation environmental behavior.

EXAFS study of the local environment of lead and iron sorbed onto volcanic ash

This work focuses on the EXAFS investigation of the local environment of lead and iron sorbed onto volcanic ash materials previously studied using XANES technique. Different compounds found in the composition of volcanic ash were used as the models in the EXAFS fitting procedure of the experimental EXAFS spectra collected at the Fe K edge and Pb L3 edge in the Fe- and Pb-sorbed volcanic ash samples. The results showed two types of interactions involving in the adsorption process of both samples. The first is related to iron or lead absorber with oxygen atoms in the first coordination shell. The second interaction occurred between the absorbers (Fe or Pb) and the backscatters (Fe or Pb) in the second shell. The local environment of the iron-sorbed element may have a cubic geometry with different crystallographic sites related to oxygen and iron atoms. On the other hand, the lead-sorbed element may be in orthorhombic geometry with different sites related to oxygen atoms and lead atoms. The adsorption mechanisms involved in the process of iron and lead sorption are ion exchange with probable chemisorption for iron and microprecipitation for lead.

Entrapping aliphatic and heterocyclic gaseous amines on copper-exchanged montmorillonite: A straight and green process to reduce air pollution

The capture of a number of aliphatic (APAs) and heterocyclic (HCAs) amines, known as widespread pollutants, by Cu2+-exchanged montmorillonite (Mt-Cu) was studied through elemental analysis diffuse-reflectance ultraviolet-visible and infra-red spectroscopies, X-rays diffraction, thermal analysis coupled with mass spectrometry of the evolved gases, XANES and EXAFS spectroscopy, and solid-state NMR. The investigated APAs and HCAs were: ethylamine (EtNH2), triethylamine (Et3N), ethylenediamine (En) and morpholine (Morph), piperidine (Piper), and pyridine (Py), respectively. Mt-Cu saturation occurred within 25 h at worst, the immobilized amount was relevant and involved the binding of the amino nitrogen to the interlayer Cu2+ ions. While for APAs the entrapped amount changed with the structure of the molecule, for HCAs it did not. The EXAFS and XANES studies showed that the interlayer Cu2+ ions are strongly coordinated to the amino groups. This resulted in the coordination number changing from four to five coordination, with the exception of En for which the CuII ions remained tetra-coordinated as in pristine Mt-Cu. Residual water molecules were found to be bound to the copper also after exposure to the amines. For EtNH2, En, Morph, and Piper the coordination to CuII occurred without the deprotonation of the amino group. NMR measurements showed the presence of physisorbed amines whose amount depended on the structure: while En was mostly bound to CuII (physisorption was negligible), for EtNH2, Et3N, Morph, and Piper the physisorbed amount ranged from 55 to 30% and for Py it was even the 70%. In addition, En was found to be the amine entrapped with the highest strength and covalent character. The obtained results supported the effectiveness of Cu2+-modified layered silicates as an air/gas purification system. The exploitation of devices based on Cu2+-exchanged montmorillonite could therefore become a very appealing future challenge as the interlayer modification was very simple and fast and the entire process turned out to be green and economic.

Crystallization kinetics and structural studies of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics based solid state electrolyte

The crystallization kinetics and structural behaviour of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics system have been investigated. Glass was prepared by melting the calcined initial charges at 1450 °C using conventional quenching technique. From model free crystallization kinetics, the value of activation energy obtained was 165 kJ mol−1. The nature of nucleation and the dimension of growth of the NASICON crystal were estimated from the kinetics parameters. This glass was converted to glass-ceramics using suitable heat schedule as per DTA data. X-ray diffraction analysis confirmed the formation of desired NASICON phase along with AlPO4 as minor phase. Raman spectroscopy and EXAFS studies showed that molybdenum ions moved to the desired tetrahedral sites in glass-ceramic. The dimension of the crystal growth was clearly seen in SEM image of LAGPM glass-ceramics sample. Impedance spectroscopy was carried out to evaluate the dc ionic conductivity (σdc) of LAGPM glass-ceramics based solid electrolyte. The value of σdc evaluated from the Nyquist plot was found as ∼4.64 × 10−4 S.cm−1 at room temperature.

Structural changes in Ti1-xAlxN coatings during turning: A XANES and EXAFS study of worn tools

Structural changes in Ti1-xAlxN coated tool inserts used for turning in 316L stainless steel were investigated by XANES, EXAFS, EDS, and STEM. For coarse-grained fcc-structured Ti1-xAlxN coatings, with 0 ≤ x ≤ 0.62, the XANES spectrum changes with Al-content. XANES Ti 1s line-scans across the rake face of the worn samples reveals that TiN-enriched domains have formed during turning in Ti0.47Al0.53N and Ti0.38Al0.62N samples as a result of spinodal decomposition. The XANES spectra reveal the locations on the tool in which the most TiN-rich domains have formed, indicating which part of the tool-chip contact area that experienced the highest temperature during turning. Changes in the pre-edge features in the XANES spectra reveal that structural changes occur also in the w-TiAlN phase in fine-grained Ti0.38Al0.62N during turning. EDS shows that Cr and Fe from the steel adhere to the tool rake face during machining. Cr 1s and Fe 1s XANES show that Cr is oxidized in the end of the contact length while the adhered Fe retains in the same fcc-structure as that of the 316L stainless steel.

Unraveling the Magnetic Ground State and Local Lattice Distortions in Z2XY-Type Full Heusler Compounds: An EXAFS Study

Unraveling the Magnetic Ground State and Local Lattice Distortions in Z₂XY-Type Full Heusler Compounds: An EXAFS Study

XANES, EXAFS, Voltammetric, and Microhardness Studies of Manganese Dioxide-Lead-Lead Dioxide Vitroceramics.

In this work we investigated the electrochemical performances and mechanical behavior of the manganese dioxide–lead dioxide–lead vitreous system. The structural and electrochemical properties of vitroceramics were investigated by the analysis of X-ray diffraction (XRD) spectra, X-ray absorption spectroscopy (XAS), and measurements of cyclic voltammetry and linear sweep voltammetry. The mechanical properties of the studied samples were determined by Vickers hardness values using the indentation method. The analysis of X-ray absorption near edge structure (XANES) data for the L3 edge of the lead and the radial distribution function data for the PbO2 and Pb model indicate the modification of Pb-O interatomic distances by the doping process. The voltammetric study reveals the vitroceramic with x = 90 mol% Pb as the most suitable for application as a lead acid battery electrode.

EXAFS Study of Radiation-Induced Defects in Molybdenum and Tantalum Metals

EXAFS Study of Radiation-Induced Defects in Molybdenum and Tantalum Metals

Tuning CO2 to CO Conversion on Metal-Doped Carbon Catalysts

One of the significant challenges faced during electrochemical CO2 reduction (ECO2RR) is the low selectivity of the products obtained. The best example is polycrystalline Cu, which can electrochemically produce hydrocarbons and alcohols but with poor selectivity.1, 2 To date, high selectivity has been achieved only towards CO and formate on Au and Sn surface, respectively but scalability and commercialization are limited owing to their cost and stability. Metal-nitrogen-carbon (MNC) materials are comparable to Au or Ag catalysts, albeit with their lower overpotentials, higher mass activity and high selectivity toward CO.3 , 4 During the pyrolysis of N-containing carbon molecules, different chemical functionalities such as pyridinic, pyrrolic and graphitic N atoms can be formed, each behaving as a product-specific active site. 5 It is still debatable whether pyrdinic or pyrrolic N is responsible for CO2RR activity; thus, it remains unclear how to favor CO2 reduction over hydrogen evolution.In this work, we aimed to synthesize C2N-like covalent organic frameworks, with 8-10 Å pore size, tailored to host dual atoms coordinated to nitrogen. Such sites are expected to favor C-C coupling and produce multi-carbon products during ECO2RR. A step-by-step synthetic approach was employed to optimize the CO2RR:HER ratio through: Tuning carbon:nitrogen ratio using two different synthetic approaches.Reducing nitrogen in the carbon matrix through pyrolyzing at different temperatures (700, 800 and 900 oC),Doping phosphorus and nitrogen into the carbon matrixTuning CO2RR product distribution through different metals (Fe and Ni) doping. EXAFS and STEM studies revealed the presence of a mixture of single and dual atomic sites. XPS and ICP results showed that Fe and Ni loadings <2 wt% could be obtained in the C2N materials. Higher hydrogen evolution, owing to the higher N-content, was observed at a lower pyrolysis temperature which decreased at a pyrolysis temperature of 900 oC. Both Fe-NC and Ni-NC selectively produced CO, thus suppressing FE H2 to <5%. Fe-NC also exhibited lower overpotential for CO production compared to its Ni-NC counterpart. A small percentage of ethanol and 2-propanol (FE<5%) was observed indicating the favoured C-C coupling on the dual-atomic sites. Further optimization of the metal-N coordination environment may allow for an improved selectivity for >C2 products. References K. P. Kuhl, E. R. Cave, D. N. Abram and T. F. Jaramillo, Energy Environ. Sci., 5, 7050 (2012). S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo and I. Chorkendorff, Chem. Rev., 119, 7610 (2019). A. S. Varela, N. Ranjbar Sahraie, J. Steinberg, W. Ju, H.-S. Oh and P. Strasser, Angew. Chem. Int. Edit., 54, 10758 (2015). A. S. Varela, W. Ju, A. Bagger, P. Franco, J. Rossmeisl and P. Strasser, ACS Catal., 9, 7270 (2019). Y. Lum and J. W. Ager, Nat. Catal., 2, 86 (2019).

Using thiol-functionalized montmorillonites for chemically immobilizing Hg in contaminated water and soil: A comparative study of intercalation and grafting functionalization

Mercury (Hg) contamination in water and soil is of great concern due to its high toxicity and biomagnification in food chain. In this study, clay mineral montmorillonites (Mt) was thiol-functionalized via 2–mercaptoethylammonium intercalation (ISH–Mt) and 3–mercaptopropyltrimethoxysilane surface grafting (GSH–Mt) for enhancing remediation ability of Hg contamination. Characterization results indicated that surface grafting significantly changed surface morphology and porous structure, with rougher surface, larger specific surface area and more porous structure. The adsorption capacity of Hg2+ was significantly enhanced by thiol functionalization, being 141.55 and 136.92 mg g−1 for ISH–Mt and GSH–Mt, respectively. Fitting results of pseudo-second-order kinetic models (R2 = 0.879– 0.930) and Freundlich isotherms (R2 = 0.900– 0.950) indicated that Hg2+ was adsorbed on heterogeneous surfaces with chemical processes as the rate-limiting step. TCLP-Hg concentrations in soils after applying ISH–Mt and GSH–Mt (0.1%–1% dosage, m/m) were < 200 μg L−1 (The Leaching Standards of Hazardous Wastes, USEPA). Hg fractionation shifted from mobile fractions (exchangeable and carbonate-bound) to stable forms (organic matter-bound). XPS and Hg LIII-edge EXAFS studies revealed that the complexation of –SH toward Hg was the primary mechanism for Hg adsorption and stabilization. These results illustrated that thiol-functionalized Mts prepared by intercalation and surface grafting are promising for the remediation of Hg-contaminated water and soil.

Single-atom V-N charge-transfer bridge on ultrathin carbon nitride for efficient photocatalytic H2 production and formaldehyde oxidation under visible light

Solar-driven hydrogen evolution and formaldehyde oxidation are highly appealing, but insufficient active sites and restricted charge transfer channel resulted in limited photocatalytic efficiency for most reaction systems. Herein, we designed coordinating single-atomic-site V on ultrathin carbon nitride (namely, SAVCN) with V-N charge-transfer bridge as the reaction switch for photocatalytic H2 production and formaldehyde oxidation under visible light. The formation of V single-atoms was certified by spherical aberration-corrected HAADF-STEM, EXAFS, and DFT study. The electronic structure of the V-N bridge enables a stable photocatalytic hydrogen evolution activity, which is nearly 3 times above that of pristine carbon nitride under 420 nm, and further elevates the green light driven H2 generation by over 11-fold. Remarkably, the SAVCN system exhibits comparably high photocatalytic activity for gaseous formaldehyde oxidation, which is superior to most reported carbon nitride-based photocatalysts. The photocatalytic mechanistic prediction confirms that the introduced unsaturated V-N coordination favorably reduces the activation energy barrier of the hydrogen evolution, and enhances the rate-determining step of intermediates for mineralization of gaseous formaldehyde.

Quantitative description of the role of Cr on the ordering characteristics of a single phase Ni-16 wt.% Mo- 7wt.% Cr alloy

Binary and ternary Ni-Mo based alloys under the service conditions of high temperature show precipitation and chemical ordering which influence their microstructure, mechanical and corrosion properties. In the present work, the phase transformation behaviour of Ni-Mo and Ni-Mo-Cr alloys is studied to identify the role of Cr in altering the stability of brittle ordered intermetallic phases. TEM characterization demonstrates that the addition of Cr destabilizes not only the long-range ordered D1a phase but also the short-range order represented by <1 ½ 0> ordering wave vectors. EXAFS studies on Ni-Mo and Ni-Mo-Cr alloys establish preferential bonding of Cr with Ni as the first nearest neighbour in the fcc lattice replacing Mo. The cluster-expansion based calculations on Ni-Mo, Ni-Cr and Cr-Mo systems show that the nearest neighbour pair and multisite interaction energies are changed in magnitude as well as in sign for Ni-Mo and Ni-Cr systems signifying that the D1a type ordering tendency is reduced with Cr addition and the disordered fcc phase is stabilised. A combination of experimental and theoretical studies unequivocally establishes the stability of the disordered fcc structure, which is crucial for the long-term use of the selected Ni-Mo-Cr alloy at elevated temperatures.

Effect of pretreatment with hydrogen on the structure and properties of carbon-supported Pd-Ag-nanoalloys for ethylene production by acetylene hydrogenation

• Pd-Ag/Sibunit catalysts are promising in C 2 H 4 production by acetylene hydrogenation. • ~ Pd 0.6 Ag 0.4 particles are formed during treatment in H 2 at t = 400–500 °C. • The Pd-Pd distance in the ~ Pd 0.6 Ag 0.4 particles is 2.78–2.80 Å. • The sample treated in H 2 at t = 400 °C have an average particle size of 2.9 nm. • The ethylene selectivity of the Pd-Ag/Sibunit treated with H 2 at 400–500 °C is 77–78%. The formation process of the active component of 0.5%Pd-0.5%Ag catalysts supported on the carbon black/pyrolytic synthetic carbon composite «Sibunit», which were synthesized by joint impregnation, was studied. XRD and EXAFS studies revealed that heating of the Pd-Ag/Sibunit catalyst in hydrogen at 400–500 °C results in the formation of bimetallic solid solution Pd 0.6 Ag 0.4 . The bimetallic particles are characterized by an increased distance between neighboring palladium atoms (2.78–2.80 Å), as compared to metallic palladium and by an increase in the electron density on palladium atoms under the action of silver (according to XPS data). The synthesized samples with supported Pd-Ag nanoparticles make it possible to obtain С 2 Н 4 by ethyne hydrogenation with the selectivity of 77–78%.

Electron structure and magnetic properties of self-doped Pr 1-xMnO3+δ manganites: XANES and EXAFS study. Comparing with A- and B-site doped perovskites

The local electronic and crystal structures of self-doped Pr1-xMnO3+δ (x = 0.0 and 0.2) perovskites are studied by x-ray absorption spectroscopy at Mn K-, Mn L- and O K-edges. The Mn K-edge shifts towards higher energy with increasing x indicating the increase in average manganese valence, which, in turn, leads to an increase in magnetization. The Mn L-edge spectra display a splitting into L3(2p3/2) and L2(2p1/2) peaks which is caused by core hole spin-orbit coupling. The intensities of 2p3/2 and 2p1/2 peaks increase with x, which correlates with the increase in magnetization and results from the change in hybridization between O 2p and Mn 3d orbitals. Altering x do not affect the O K-pre-edge spectra indicating no changes in Fermi level. Difference in relation of magnetic properties to electron structure in self-doped manganites and oxides doped in A- and B-positions of perovskites ABO3 cell is underlined. The Fourier transform of EXAFS spectra shows the decrease in oxygen and praseodymium contents and the formation of trivalent manganese anti-site defects in praseodymium position with increasing x.

Identification of a copper ion recognition peptide sequence in the subunit II of cytochrome c oxidase: a combined theoretical and experimental study

The role of the pentapeptide, NHSFM, derived from the surface exposed part of the metal ion binding loop of the subunit II of cytochrome c oxidase on the maturation of the binuclear purple CuA center of the enzyme has been investigated using several experimental and computational methods. The copper ion was found to form 1:1 complex of the pentapeptide with a binding constant ~ 104M-1 to 105M-1,where a 4 ligand coordination from the peptide in a type 2 copper center was revealed. The pH dependence of the metal-peptide was associated with a [Formula: see text] of ~ 10 suggesting deprotonation of the N-terminal amine. EXAFS studies as well as DFT calculations of the metal-peptide complexes revealed pH dependent changes in the metal-ligand bond distances. Spectroscopic properties of the metal peptides calculated from TDDFT studies agreed with the experimental results. Restrained molecular dynamics (RMD) simulations indicated coordination of a carbonyl oxygen from the asparagine (N) side chain and of water molecules apart from histidine (H), methionine (M)and terminal amine of asparagine (N) in a distorted square planar geometry of Cu-NHSFM. Analyses of the backbone distances as well as B-factors for the metal peptide suggested that the peptide backbone becomes more compact and rigid on binding of the metal ion. This indicated that binding of copper ion to this pentapeptide in the protein possibly cause movement of the protein backbone bringing other coordinating residues closer to the copper ion, and thus helping in sequential uptake of copper ions to the protein.

Studies on the uranium speciation in zinc iron phosphate (ZnIP) glass using Mössbauer and EXAFS spectroscopic investigations

5–15 mol % UO3 loaded zinc iron phosphate glass was prepared by melt quench process. The solubility of UO3 in ZnIP was determined by XRD and was found to be below 15 mol %; beyond which separation of UP2O7 compound was observed. Mössbauer spectroscopy unraveled the ratio of Fe (II)/Fe(III) and was found to decrease from 0.071 (ZnIP) to 0.029. EXAFS studies unraveled the prevalence of two type of coordination for U–O (i.e U–O1 and UO2) and Fe–O (Fe–O1 and Fe–O2) in the ZnIP glass matrix, whereas a single chemical environment for Zn–O in the same glass matrix.

A solvent-free solid catalyst for the selective and color-indicating ambient-air removal of sulfur mustard

Bis(2-chloroethyl) sulfide or sulfur mustard (HD) is one of the highest-tonnage chemical warfare agents and one that is highly persistent in the environment. For decontamination, selective oxidation of HD to the substantially less toxic sulfoxide is crucial. We report here a solvent-free, solid, robust catalyst comprising hydrophobic salts of tribromide and nitrate, copper(II) nitrate hydrate, and a solid acid (NafionTM) for selective sulfoxidation using only ambient air at room temperature. This system rapidly removes HD as a neat liquid or a vapor. The mechanisms of these aerobic decontamination reactions are complex, and studies confirm reversible formation of a key intermediate, the bromosulfonium ion, and the role of Cu(II). The latter increases the rate four-fold by increasing the equilibrium concentration of bromosulfonium during turnover. Cu(II) also provides a colorimetric detection capability. Without HD, the solid is green, and with HD, it is brown. Bromine K-edge XANES and EXAFS studies confirm regeneration of tribromide under catalytic conditions. Diffuse reflectance infrared Fourier transform spectroscopy shows absorption of HD vapor and selective conversion to the desired sulfoxide, HDO, at the gas–solid interface.