Disordered matter studied by x-ray Raman scattering

Spectroscopy can provide valuable information on the structure of disordered matter beyond that which is available through e.g. x-ray and neutron diffraction. X-ray Raman scattering is a non-resonant element-sensitive process which allows bulk-sensitive measurements of core-excited spectra from light-element samples. In this thesis, x-ray Raman scattering is used to study the local structure of hydrogen-bonded liquids and solids, including liquid water, a series of linear and branched alcohols, and high-pressure ice phases. Connecting the spectral features to the local atomic-scale structure involves theoretical references, and in the case of hydrogen-bonded systems the interpretation of the spectra is currently actively debated. The systematic studies of the intra- and intermolecular effects in alcohols, non-hydrogen-bonded neighbors in high-pressure ices, and the effect of temperature in liquid water are used to demonstrate different aspects of the local structure that can influence the near-edge spectra. Additionally, the determination of the extended x-ray absorption fine structure is addressed in a momentum-transfer dependent study. This work demonstrates the potential of x-ray Raman scattering for unique studies of the local structure of a variety of disordered light-element systems.

Nucleophilic attacks of 1,2-diaminoethane on MeCN ligands: synthesis, x-ray structure, and spectral and electrochemical properties of [Ru(.mu.-O)(.mu.-O2CAr)2[NH2CH2CH2NHC(Me)NH]2(PPh3)2](ClO4)2(Ar = C6H4-p-X; X = H, Me, OMe, Cl)

The diruthenium(III) complex [Ru2O(O2CAr)2(MeCN)4(PPh3)2](ClO4)2 (1), on reaction with 1,2-diaminoethane (en) in MeOH at 25-degrees-C, undergoes nucleophilic attacks at the carbon of two facial MeCN ligands to form [(Ru2O)-O-III(O2CAr)2-{NH2CH2CH2NHC(Me)NH}2(PPh3)2](ClO4)2 (2) (Ar = C6H4-p-X, X = H, Me, OMe, Cl) containing two seven-membered amino-amidine chelating ligands. The molecular structure of 2 with Ar = C6H4-p-OMe was determined by X-ray crystallography. Crystal data are as follows: triclinic, P1BAR, a = 13.942 (5) angstrom, b = 14.528 (2) angstrom, c = 21.758 (6) angstrom, alpha = 109.50 (2)-degrees, beta = 92.52 (3)-degrees, gamma = 112.61 (2)-degrees, V = 3759 (2) angstrom 3, and Z = 2. The complex has an {Ru2(mu-O)(mu-O2CAr2)2(2+)} core. The Ru-Ru and average Ru-O(oxo) distances and the Ru-O-Ru angle are 3.280 (2) angstrom, 1.887 [8] angstrom, and 120.7 (4)-degrees, respectively. The amino group of the chelating ligand is trans to the mu-oxo ligand. The nucleophilic attacks take place on the MeCN ligands cis to the mu-oxo ligand. The visible spectra of 2 in CHCl3 display an absorption band at 565 nm. The H-1 NMR spectra of 2 in CDCl3 are indicative of the formation of an amino-amidine ligand. Complex 2 exhibits metal-centered quasireversible one-electron oxidation and reduction processes in the potential ranges +0.9 to +1.0 V and -0.3 to -0.5 V (vs SCE), respectively, involving the Ru(III)2/Ru(III)Ru(IV) and Ru(III)2/Ru(II)Ru(III) redox couples in CH2Cl2 containing 0.1 M TBAP. The mechanistic aspects of the nucleophilic reaction are discussed.

Synthetic, spectroscopic, magnetic, and x-ray structural studies on a vitamin B6-amino acid Schiff base complex, aqua(5'-phosphopyridoxylidenetyrosinato)copper(II) tetrahydrate

A Schiff base metal complex, [Cu(II)(PLP-DL-tyrosinato)(H2O)].4H2O (PLP = pyridoxal phosphate), with the molecular formula CuC17O13N2H27P has been prepared and characterized by magnetic, spectral, and X-ray structural studies. The compound crystallizes in the triclinic space group P1BAR with a = 8.616 (2) angstrom, b = 11.843 (3) angstrom, c = 12.177 (3) angstrom, alpha = 103.40 (2)degrees, beta = 112.32 (2)degrees, gamma = 76.50 (1)degrees, and Z = 2. The structure was solved by the heavy-atom method and refined by least-squares techniques to a final R value of 0.057 for 3132 independent reflections. The coordination geometry around Cu(II) is distorted square pyramidal with phenolic oxygen, imino nitrogen, and carboxylate oxygen from the Schiff base ligand and water oxygen as basal donor atoms. The axial site is occupied by a phosphate oxygen from a neighboring molecule, thus resulting in a one-dimensional polymer. The structure reveals pi-pi interaction of the aromatic side chain of the amino acid with the pyridoxal pi system. A comparative study is made of this complex with similar Schiff base complexes. The variable-temperature magnetic behavior of this compound shows a weak antiferromagnetic interaction.

1, 2-Bis (diphenylphosphino) etane bridged dinuclear copper (I) complexes: Investigations of solid state and solution structures by CP/MAS31P NMR spectroscopy, X-ray crystallography, IR spectroscopy and solution 31P NMR and 63Cu NMR spectroscopy

Three different complexes of copper (I) with bridging 1, 2-bis(diphenylphosphino)ethane (dppe), namely [Cu2 (mu-dppe) (CH3CN)6] (ClO4)2 (1), [Cu2 (mu-dppe)2 (CH3 CN)2] (ClO4)2 (2), and [Cu2 (mu-dppe) (dppe)2 (CH3CN)2] (ClO4)2 (3) have been prepared. The structure of [Cu2 (mu-dppe) (dPPe)2 (CH3CH)2] (ClO4)2 has been determined by X-ray crystallography. It crystallizes in the space group PT with a=12.984(6) angstrom, b=13.180(6) angstrom, c=14.001(3) angstrom, alpha=105.23(3), beta=105.60(2), gamma=112.53 (4), V=1944 (3) angstrom3, and Z=1. The structure was refined by least-squares method with R=0.0365; R(w)=0.0451 for 6321 reflections with F0 greater-than-or-equal-to 3 sigma (F0). The CP/MAS P-31 and IR spectra of the complexes have been analysed in the light of available crystallographic data. IR spectroscopy is particularly helpful in identifying the presence of chelating dppe. P-31 chemical shifts observed in solid state are very different from those observed in solution, and change significantly with slight changes in structure. In solution, complex 1 remains undissociated but complexes 2 and 3 undergo extensive dissociation. With a combination of room temperature H-1, Cu-63, and variable temperature P-31 NMR spectra, it is possible to understand the various processes occurring in solution.

Magnetoresistance of FexNi80-xCr20 (50

The authors have measured longitudinal and transverse magnetoresistance (MR) of crystalline pseudo-binary alloys FexNi80-xCr20 (50

Critical exponent of the electrical conductivity in the paracoherence region of a thin film of YBa2Cu3O7?x

Critical exponent of the electrical conductivity in the paracoherence region (gamma) of the high temperature superconductor YBa2Cu3O7-x (YBCO) has been estimated for high quality thin film on ZrO2 substrate prepared by high pressure oxygen sputtering. High energy ion irradiation was carried out using 100 MeV O-16(7+) ions at liquid nitrogen to see the effects of disorder on the value of the exponent. The critical exponent from a value of about 2 to 1.62 upon irradiation. Studies were also carried film to see the effect of ageing and annealing.

Edge-sharing bioctahedral diruthenium(III) complexes containing methoxy and carboxylate bridges:x-ray structures, redox behavior, and core stability

Edge-sharing bioctahedral (ESBO) complexes [Ru-2(OMe)(O2CC6H4-p-X)3(1-MeIm)(4)](ClO4)2 (X = OMe (1a), Me (1b)) and [Ru-2(O2CC6H4-P-X)(4)(1-MeIm)(4)](ClO4)(2) (X = OMe (2a), Me (2b)) are prepared by reacting Ru2Cl(O(2)CR)(4) with 1-methylimidazole (1-MeIm) in methanol followed by treatment with NaClO4. Complex 2a and the PF6- salt (1a') of 1a have been structurally characterized. Crystal data for 1a.1.5MeCN. 0.5Et(2)O: triclinic, P (1) over bar, a = 13.125(2) Angstrom, b = 15.529(3) Angstrom, c 17.314(5) Angstrom, a; 67.03(2)degrees, beta 68.05(2)degrees, gamma = 81.38(1)degrees, V 3014(1) Angstrom(3), Z = 2. Crystal data for 2a: triclinic, P (1) over bar, a 8.950(1) Angstrom, b = 12.089(3) Angstrom, c = 13.735(3) Angstrom, alpha 81.09(2)degrees, beta = 72.27(1)degrees, gamma = 83.15(2)degrees, V = 1394(1) Angstrom(3), Z = 1. The complexes consist of a diruthenium(III) unit held by two monoatomic and two three-atom bridging ligands. The 1-MeIm ligands are at the terminal sites of the [Ru-2(mu-L)(eta(1):mu-O(2)CR)(eta(1):eta(1):mu-O(2)CR)(2)](2+) core having a Ru-Ru single bond (L = OMe or eta(1)-O(2)CR). The Ru-Ru distance and the Ru-O-Ru angle in the core of 1a' and 2a are 2.49 Angstrom and similar to 76 degrees. The complexes undergo one-electron oxidation and reduction processes in MeCN-0.1 M TBAP to form mixed-valence diruthenium species with Ru-Ru bonds of orders 1.5 and 0.5, respectively.

Crystallization and preliminary X-ray diffraction analysis of a galactose-specific lectin from the seeds of Butea monosperma

The galactose-specific lectin from the seeds of Butea monosperma has been crystallized by the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 78.45, b = 78.91, c = 101.85 A, alpha = 74.30, beta = 76.65, gamma = 86.88 degrees. X-ray diffraction data were collected to a resolution of 2.44 A under cryoconditions (100 K) using a MAR image-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the coordinates of several structures of legume lectins as search models indicate that the galactose-specific lectin from B. monosperma forms an octamer.

Crystallization and preliminary X-ray diffraction analysis of a galactose-specific lectin from the seeds of Butea monosperma

The galactose-specific lectin from the seeds of Butea monosperma has been crystallized by the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 78.45, b = 78.91, c = 101.85 A, alpha = 74.30, beta = 76.65, gamma = 86.88 degrees. X-ray diffraction data were collected to a resolution of 2.44 A under cryoconditions (100 K) using a MAR image-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the coordinates of several structures of legume lectins as search models indicate that the galactose-specific lectin from B. monosperma forms an octamer.

Crystallization and preliminary X-ray studies of a galactose-specific lectin from the seeds of Spatholobus parviflorus

A galactose-specific seed lectin was purified from the legume Spatholobus parviflorus and crystallized using the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 60.998, b = 60.792, c = 78.179 angstrom, alpha = 101.32, beta = 91.38, gamma = 104.32 degrees. X-ray diffraction data were collected under cryoconditions (100 K) to a resolution of 2.04 angstrom using a MAR image-plate detector system mounted on a rotating-anode X-ray (Cu K alpha) generator. Molecular replacement using legume-lectin coordinates as a search model gave a tetrameric structure.

Synthesis, X-ray structure and properties of (eta(6)-p-cymene)ruthenium(II) Schiff-base complexes of vinylpyridine and vinylimidazole ligands

Complexes of the formulation [(eta(6)-p-cymene)Ru(O-2-C6H4-CH=NC6H4-4-CH3)(L)](ClO4), where L is gamma-picoline, 4-vinylpyridine, 1-methylimidazole and 1-vinylimidazole have been prepared and characterised. The molecular structure of the vinylpyridine adduct has been determined by X-ray crystallography. The crystal belongs to the monoclinic space group P2(1) with the following cell dimensions for the C31H33CIN2O5Ru(M = 650.11): a = 10.890(2)Angstrom, b = 22.295(9)Angstrom, c = 12.930(2)Angstrom, beta = 109.30(2)degrees(3), V = 2964(l)Angstrom 3, Z = 4; D-c = 1.457g cm(-3), lambda(Mo-K alpha) = 0.7107 Angstrom; mu(Mo-K alpha)= 6.61 cm(-1); T = 293 K; R = 0.0359 (wR(2) = 0.0981) for 4819 reflections with I > 2 sigma(I). The structure shows the non-bonding nature of the double bond of the 4-vinylpyridine ligand in the complex in which the metal is bonded to the eta(6)-p-cymene, the N, O-bidentate chelating schiff-base and the unidentate N-donor pyridine ligands.

Synthesis of acicular hydrogoethite (alpha-FeOOH center dot xH(2)O; 0.1 < x < 0.22) particles using morphology controlling cationic additives and magnetic properties of maghemite derived from hydrogoethite

A method for the preparation of acicular hydrogoethite (alpha -FeOOH.xH(2)O, 0.1 < x < 0.22) particles of 0.3-1 mm length has been optimized by air oxidation of Fe( II) hydroxide gel precipitated from aqueous (NH4)(2)Fe(SO4)(2) solutions containing 0.005-0.02 atom% of cationic Pt, Pd or Rh additives as morphology controlling agents. Hydrogoethite particles are evolved from the amorphous ferrous hydroxide gel by heterogeneous nucleation and growth. Preferential adsorption of additives on certain crystallographic planes thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shapes with high aspect ratios of 8-15. Synthetic hydrogoethite showed a mass loss of about 14% at similar to 280 degreesC, revealing the presence of strongly coordinated water of hydration in the interior of the goethite crystallites. As evident from IR spectra, excess H2O molecules (0.1- 0.22 per formula unit) are located in the strands of channels formed in between the double ribbons of FeO6 octahedra running parallel to the c- axis. Hydrogoethite particles constituted of multicrystallites are formed with Pt as additive, whereas single crystallite particles are obtained with Pd (or Rh). For both dehydroxylation as well as H-2 reduction, a lower reaction temperature (similar to 220 degreesC) was observed for the former (Pt treated) compared to the latter (Pd or Rh) (similar to 260 degreesC). Acicular magnetite (Fe3O4) was prepared either by reducing hydrogoethite (magnetite route) or dehydroxylating hydrogoethite to hematite and then reducing it to magnetite (hematite- magnetite route). According to TEM studies, preferential dehydroxylation of hydrogoethite along < 010 > leads to microporous hematite. Maghemite (gamma -Fe2O3 (-) (delta), 0 < < 0.25) was obtained by reoxidation of magnetite. The micropores are retained during the topotactic transformation to magnetite and finally to maghemite, whereas cylindrical mesopores are formed due to rearrangement of the oxygen sublattice from hexagonal to cubic close packing during the conversion of hydrogoethite to magnetite and then to maghemite. Accordingly, three different types of maghemite particles are realized: strongly oriented multicrystalline particles, single crystalline acicular particles with micropores or crystallites having mesopores. Higher values of saturation magnetization ((s) = 74 emu g(-1)) and coercivity (H-c = 320 Oe) are obtained for single crystalline mesoporous particles. In the other cases, the smaller size of particles and larger distribution of micropores decreases sigma (s) considerably ( < 60 emu g(-1)) due to relaxation effects of spins on the surface atoms as revealed by Mossbauer spectroscopy.

Study of the CP property of the Higgs boson at a photon collider using gamma gamma -> t(t)over-bar -> lX

We study the possible effects of CP violation in the Higgs sector on t (t) over bar production at a gammagamma collider. These studies are performed in a model-independent way in terms of six form factors {R(S-gamma), J(S-gamma), R(P-gamma), J(P-gamma), S-t, P-t} which parametrize the CP mixing in the Higgs sector, and a strategy for their determination is developed. We observe that the angular distribution of the decay lepton from t/(t) over bar produced in this process is independent of any CP violation in the tbW vertex and hence best suited for studying CP mixing in the Higgs sector. Analytical expressions are obtained for the angular distribution of leptons in the c.m. frame of the two colliding photons for a general polarization state of the incoming photons. We construct combined asymmetries in the initial state lepton (photon) polarization and the final state lepton charge. They involve CP even (x's) and odd (y's) combinations of the mixing parameters. We study limits up to which the values of x and y, with only two of them allowed to vary at a time, can be probed by measurements of these asymmetries, using circularly polarized photons. We use the numerical values of the asymmetries predicted by various models to discriminate among them. We show that this method can be sensitive to the loop-induced CP violation in the Higgs sector in the minimal supersymmetric standard model.

Crystallization and preliminary X-ray diffraction studies of sortase A from Streptococcus pneumoniae

Sortases are cell-membrane-anchored cysteine transpeptidases that are essential for the assembly and anchoring of cell-surface adhesins in Gram-positive bacteria. Thus, they play critical roles in virulence, infection and colonization by pathogens. Sortases have been classified into four types based on their primary sequence and the target-protein motifs that they recognize. All Gram-positive bacteria express a class A housekeeping sortase (SrtA). Sortase A from Streptococcus pneumoniae (NP_358691) has been crystallized in two crystal forms. Diamond-shaped crystals of Delta N(59)SrtA diffracted to 4.0 angstrom resolution and belonged to a tetragonal system with unit-cell parameters a = b = 122.8, c = 86.5 angstrom, alpha = beta = gamma = 90 degrees, while rod-shaped crystals of Delta N(81)SrtA diffracted to 2.91 angstrom resolution and belonged to the monoclinic space group P2(1) with unit-cell parameters a = 66.8, b = 103.47, c = 74.79 angstrom, alpha = gamma = 90, beta = 115.65 degrees. The Matthews coefficient (V(M) = 2.77 angstrom(3) Da(-1)) with similar to 56% solvent content suggested the presence of four molecules in the asymmetric unit for Delta N(81)SrtA. Also, a multi-copy search using a monomer as a probe in the molecular-replacement method resulted in the successful location of four sortase molecules in the asymmetric unit, with statistics R = 41.61, R(free) = 46.44, correlation coefficient (CC) = 64.31, CC(free) = 57.67.

X-ray structure of a galactose-specific lectin from Spatholobous parviflorous

A galactose-specific seed lectin from Spatholobous parviflorus (SPL) has been purified, crystallized and its X-ray structure solved. It is the first lectin purified and crystallized from the genus Spatholobus (family: Fabaceae). The crystals belong to the space group P1, with a = 60.792 angstrom, b = 60.998 angstrom, c = 78.179 angstrom, alpha = 78.68 degrees, beta = 88.62 degrees, gamma = 104.32 degrees. The data were collected at 2.04 angstrom resolution under cryocondition, on a MAR image-plate detector system, mounted on a rotating anode X-ray generator. The coordinates of Dolichos biflorus lectin (1lu1) were successfully used for the structure solution by molecular replacement method. The primary structure of the SPL was not known earlier and it was unambiguously visible in the electron density. S. parviflorus lectin is a hetero-dimeric-tetramer with two alpha and two beta chains of 251 and 239 residues respectively. SPL has two metal ions, Ca(2+) and Mn(2+), bound to a loop region of each chain. The SPL monomers are in jelly roll form. (C) 2011 Elsevier B.V. All rights reserved.