Cr3+ electron paramagnetic resonance study of Sn(1-x)CrxO(2) (0.00 <= x <= 0.10)

This paper reports on the liquid-helium-temperature (5 K) electron paramagnetic resonance (EPR) spectra of Cr3+ ions in the nanoparticles of SnO2 synthesized at 600 degrees C with concentrations of 0%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 5.0%, and 10%. Each spectrum may be simulated as overlap of spectra due to four magnetically inequivalent Cr3+ centers characterized by different values of the spin-Hamiltonian parameters. Three of these centers belong to Cr3+ ions in orthorhombic sites, situated near oxygen vacancies, characterized by very large zero-field splitting parameters D and E, presumably due to the presence of nanoparticles in the samples. The fourth EPR spectrum belongs to the Cr3+ ions situated at sites with tetragonal symmetry, substituting for the Sn4+ ion, characterized by a very small value of D. In addition, there appears a ferromagnetic resonance line due to oxygen defects for samples with Cr3+ concentrations of <= 2.5%. Further, in samples with Cr3+ concentrations of >2.5%, there appears an intense and wide EPR line due to the interactions among the Cr3+ ions in the clusters formed due to rather excessive doping; the intensity and width of this line increase with increasing concentration. The Cr3+ EPR spectra observed in these nanopowders very different from those in bulk SnO2 crystals.

3d and 4d core level X-ray photoelectron spectroscopy of mixed-valence CePd3

3d and 4d core-level XPS spectra for CePd3, a mixed-valence system, have been measured. Each spectrum exhibits two sets of structures, each corresponding to one of the valence states of cerium. Thus the usefulness of XPS, which has so far not been used extensively to investigate the mixed-valence cerium systems, is pointed out.

Optical Properties of Nanocrystalline Potassium Lithium Niobate in the Glass System (100-x) TeO2-x(1.5K(2)O-Li2O-2.5Nb(2)O(5))

Optically clear glasses of various compositions in the system (100-x) TeO2-x(1.5K(2)O-Li2O-2.5Nb(2)O(5)) (2 <= x <= 12, in molar ratio) were prepared by the melt-quenching technique. The glassy nature of the as-quenched samples was established via differential scanning calorimetry (DSC). The amorphous and the crystalline nature of the as-quenched and heat-treated samples were confirmed by the X-ray powder diffraction and transmission electron microscopic (TEM) studies. Transparent glasses comprising potassium lithium niobate (K3Li2Nb5O15) microcrystallites on the surface and nanocrystallites within the glass were obtained by controlled heat-treatment of the as-quenched glasses just above the glass transition temperature (T-g). The optical transmission spectra of these glasses and glass-crystal composites of various compositions were recorded in the 200-2500 nm wavelength range. Various optical parameters such as optical band gap, Urbach energy, refractive index were determined. Second order optical non-linearity was established in the heat-treated samples by employing the Maker-Fringe method.

X-ray and IR characterisation of Nasicon solid solution, Na1+xZr2SixP3−xO12

X-ray and IR studies on Nasicon solid solutions, Na1+xZr2SixP3−xO12, are carried out as a function of composition x. X-ray diffraction studies show that the unit cell volume increases as x increases and exhibits a maximum at x ≈ 2. On further increase in x the unit cell volume decreases. The infrared absorption peak positions and the splitting of these absorption peaks suggest a distortion of the PO4 and SiO4 tetrahedra. But the distortion is not large enough to change the local symmetry around the phosphorus or silicon ion from Td to C3v.

X-Ray Structure Of A Ternary Metal-Complex - Copper(Ii) Inosine 5'-Monophosphate Imidazole - Metal-Binding To The N(7) Atom Of The Nucleotide In A Mixed-Ligand System Containing An Aromatic Amine

A ternary metal-nucleotide complex, Na2[Cu(5’-IMP)2(im)o,8(H20)l,2(H20)2h]as~ 1be2e.n4 pHr2ep0a,r ed and its structure analyzed by X-ray diffraction (5’-IMP = inosine 5’-monophos hate; im = imidazole). The complex crystallizes in space group C222, with a = 8.733 (4) A, b = 23.213 (5) A, c = 21.489 (6) 1, and Z = 4. The structure was solved by the heavy-atom method and refined by full-matrix least-squares technique on the basis of 2008 observed reflections to a final R value of 0.087. Symmetry-related 5’-IMP anions coordinate in cis geometry through the N(7) atoms of the bases. The other cis positions of the coordination plane are statistically occupied by nitrogen atoms of disordered im groups and water oxygens with occupancies 0.4 and 0.6, respectively. Water oxygens in axial positions complete the octahedral coordination of Cu(I1). The complex is isostructural with C~S-[P~(S’-IMP),(NH~)~a] m”,o del proposed for Pt(I1) binding to DNA. The base binding observed in the present case is different from the typical ”phosphate only” binding shown from earlier studies on metal-nucleotide complexes containing various other ?r-aromatic amines.

In Situ Phase Separation Following Dehydration in Bimetallic Sulfates: A Variable-Temperature X-Ray Diffraction Study

Phase separation resulting in a single-crystal-single-crystal transition accompanied by a polycrystalline phase following the dehydration of hydrated bimetallic sulfates [Na2Mn1.167(SO4)(2)S0.33O1.167 center dot 2H(2)O and K4Cd3-(SO4)(5)center dot 3H(2)O] has been investigated by in situ variable-temperature single-crystal X-ray diffraction. With two examples, we illustrate the possibility of generating structural frameworks following dehydration in bimetallic sulfates, which refer to the possible precursor phases at that temperature leading to the mineral formation. The room-temperature structure of Na2Mn1.167(SO4)(2)S0.33O1.167 center dot 2H(2)O is trigonal, space group R (3) over bar. On heating the crystal in situ on the diffractometer, the diffraction images display spherical spots and concentric rings suggesting phase separation, with the spherical spots getting indexed in a monoclinic space group, C2/c. The structure determination based on this data suggests the formation of Na2Mn(SO4)(2). However, the diffraction images from concentric rings could not be indexed. In the second example, the room-temperature structure is determined to be K4Cd3(SO4)(5)center dot 3H(2)O, crystallizing in a monoclinic space group, P2(1)/n. On heating the crystal in situ, the diffraction images collected also have both spherical spots and diffuse rings. The spherical spots could be indexed to a cubic crystal system, space group P2(1)3, and the structure is K4Cd3(SO4)(3). The possible mechanism for the phase transition in the dehydration regime resulting in this remarkable single-crystal to single-crystal transition with the appearance of a surrogate polycrystalline phase is proposed.

Ce1-xRuxO2-delta (x=0.05, 0.10): A New High Oxygen Storage Material and Pt, Pd-Free Three-Way Catalyst

Nanocrystalline Ce1-xRuxO2-delta (x = 0.05 and 0.10) of 8-10 nm sizes have been synthesized by hydrothermal method using melamine as complexing agent. Compounds have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray analysis (EDX) and their structures have been refined by the Rietveld method.The compounds crystallize in fluorite structure and the composition is Ce1-xRuxO2-x/2 where Ru is in +4 state and Ce is in mixed-valence (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen. Ce1-xRuxO2-x/2 reversibly releases 0.22[O] and 0.42[O] for x = 0.05 and 0.10, respectively, which is higher than the maximumpossible OSC of 0.22 [O] observed for Ce0.50Zr0.50O2. Utilization of Higher OSC of Ce1-xRuxO2-delta (x = 0.05 and 0.10) is also reflected in terms of low-temperature CO oxidation with these catalysts, both in the presence and absence of feed oxygen. The Ru4+ ion acts as an active center for reducing molecules (CO, hydrocarbon ``HC'') and oxide ion vacancy acts as an active center for O-2 and NO, leading to low-temperature NO conversion to N-2. Thus due to Ru4+ ion, Ce1-xRuxO2-delta is not just a high oxygen storage material but also shows high activity toward CO, hydrocarbon ``HC'' oxidation, and NO reduction by CO at low temperature with high N-2 selectivity for three-way catalysis.

Surface segregation and oxidation studies of Cu-Sn and Cu-Pd alloys by x-ray photoelectron and auger spectroscopy

X-ray photoelectron and Auger spectroscopic techniques have been employed to study surface segregation and oxidation of Cu-1 at%Sn, Cu-9at%Pd and Cu-25at%Pd alloys. Both Cu-Pd(9%) and Cu-Pd(25%) alloys show segregation of Cu when heated above 500 K. The Pd concentration was reduced by 50% at 750 K compared to the bulk composition; the enthalpy of segregation of Cu is around - 6kJ/mol. Sn segregation is seen from 470 to 650 K in the Cu-Sn(1%) alloy, and a saturation plateau of Sn concentration above 650 K is observed. Surface oxidation of Cu-Sn(1%) and Cu-Pd(9%) alloys at 500 K showed the formation of Cu2O on the surface with total suppression of Sn or Pd on the respective alloy surfaces. On vacuum annealing the oxidised Cu-Sn alloy surface at 550 K, a displacement reaction 2Cu2O+Sn→4Cu+SnO2 was observed. However, under similar annealing of the oxidised Cu-Pd(9%) alloy surface at 500 K, oxide oxygen was totally desorbed leaving the Cu-Pd alloy surface clean. In the case of the Cu-Pd(25%) alloy, only dissociatively chemisorbed oxygen was seen at 500 K which desorbed at the same temperature. Oxygen spill-over from copper to palladium is suggested as the mechanism of oxygen desorption from the oxidised Cu-Pd alloy surfaces.

X-ray photoelectron spectra and Auger studies of the surface oxidation of cobalt

Surface oxidation of Co has been investigated at different temperatures in the 300–600 K range at oxygen exposures upto 106 L by XPES and AES techniques. In the XPES, both the valence band and core level bands have been employed to monitor the oxidation while in the AES, metal Auger intensity ratios as well as O(KLL)/Co(L23M45M45) ratios have been examined. Only CoO is formed on the surface at high oxygen exposures at and above 500 K.

1H and 13C nuclear magnetic resonance studies on X-537A (lasalocid-A)-calcium complexes: observation of a sandwich complex

Studies on the conformational and binding characteristics of the ionophoric antibiotic X-537A (lasalocid-A)�calcium ion complexes have been carried out in deuteriated acetonitrile (CD3 CN) using proton and carbon-13 nuclear magnetic resonance (1 H and 13C n.m.r.) spectroscopy. Detailed analysis of the salt-induced chemical shifts at various X-537A to calcium concentration ratios indicated that X-537A forms charged complexes with calcium with 2 : 1 and 1 : 1 stoicheiometries. The conformational model for the complex based on the n.m.r. data showed that the calcium ion is preferentially bound to one end of the molecule, which is binding to three oxygen atoms, the other end (the salicylic acid part) being relatively free. In the 2 : 1 (sandwich) complex, the calcium ion is sandwiched between two X-537A molecules with three oxygen atoms binding to it from each molecule.

Probing into the role of conserved N-glycosylation sites in the Tyrosinase glycoprotein family

N-linked glycosylation has a profound effect on the proper folding, oligomerization and stability of glycoproteins. These glycans impart many properties to proteins that may be important for their proper functioning, besides having a tendency to exert a chaperone-like effect on them. Certain glycosylation sites in a protein however, are more important than other sites for their function and stability. It has been observed that some N-glycosylation sites are conserved over families of glycoproteins over evolution, one such being the tyrosinase related protein family. The role of these conserved N-glycosylation sites in their trafficking, sorting, stability and activity has been examined here. By scrutinizing the different glycosylation sites on this family of glycoproteins it was inferred that different sites in the same family of polypeptides can perform distinct functions and conserved sites across the paralogues may perform diverse functions.

Ternary metal complexes of anionic and neutral pyridoxine (vitamin B6) with 2,2'-bipyridine. Syntheses and x-ray structures of (pyridoxinato)bis(2,2'-bipyridyl)cobalt(III) perchlorate and chloro(2,2'-bipyridyl)(pyridoxine)copper(II) perchlorate hydrate

Ternary metal complexes involving vitamin B6 with formulas [CO",(PN-H)](anCdI [OC)'(bpy)(PN)Cl]C10(.bpHy 0 = 2,2'-bipyridine, PN = neutral pyridoxine, PN-H = anionic pyridoxine) have been prepared for the first time and characterized by means of magnetic and spectroscopic measurements. The crystal structures of the compounds have also been determined. [CO(PN-H)](CcryIsOta,l)lize s in the space group P2,/c with a = 18.900 (3) A, b = 8.764 (1) A, c = 20.041 (2) A,p = 116.05 (l)', and Z = 4 and [Cu(bpy)(PN)C1]C104-H20in the space group Pi with a = 12.136 (5) A, b = 13.283 (4) A,c = 7.195 (2) A, a = 96.91 (Z)', 0 = 91.25 (3)', y = 71.63 (3)', and Z = 2. The structures were solved by the heavy-atom method and refined by least-squares techniques to R values of 0.080 and 0.042 for 3401 and 2094 independent reflections, respectively. Both structures consist of monomeric units. The geometry around Co(II1) is octahedral and around Cu(I1) is distorted square pyramidal. In [CO(PN-H)]t(wCo IoxOy~ge)n~s ,fro m phenolic and 4-(hydroxymethyl) groups of PN-H and two nitrogens from each of two bpy's form the coordination sphere. In [Cu(bpy)(PN)C1]C104.H20o ne PN and one bpy, with the same donor sites, act as bidentate chelates in the basal plane, with a chloride ion occupying the apical position. In both structures PN and PN-H exist in the tautomeric form wherein pyridine N is protonated and phenolic 0 is deprotonated. However, a novel feature of the cobalt compound is that PN-H is anionic due to the deprotonation of the 4-(hydroxymethyl) group. The packing in both structures is governed by hydrogen bonds, and in the copper compound partial stacking of bpy's at a distance of -3.55 also adds to the stability of the system. Infrared, NMR, and ligand field spectroscopic results and magnetic measurements are interpreted in light of the structures.