Synthesis and crystal phase evaluation of hydroxylapatite using the rietveld-maximum entropy method

Bioceramic systems based on hydroxylapatite (HAP) are an important class of bioactive materials that may promote bone regeneration. The aim of this research was to evaluate how the stoichiometry of HAP influences its microstructural properties when diagnosed using the combined Rietveld method and Maximum entropy method (MEM). The Rietveld Method (RM) is recognizably a powerful tool used to obtain structural and microstructural information of polycrystalline samples analyzed by x-ray diffraction. Latterly have combined the RM with the maximum entropy method (MEM), with the goal of improve structural refinement results. The MEM provides high resolution maps of electron density and their analysis leave the accurate localization of atoms inside of unit cell. Like that, cycles Rietveld-MEM allow an excellent structural refinement In this work, a hydroxylapatite sample obtained by emulsion method had its structure refined using one cycle Rietveld-MEM with x-ray diffraction data. The indices obtained in initial refinement was Rwp = 7.50%, Re = 6.56%, S - 1.14% e RB = 1.03%. After MEM refinement and electron densities maps analysis to correction of atomics positions, the news indicators of Rietveld refinement quality was Rwp = 7.35%, Re = 6.56%, S = 1.12% and RB = 0.75%. The excellent result obtained to RB shows the efficiency of MEM as auxiliary in the refinement of structure of hydroxylapatite by RM.

An ellipsometric study of manganese oxide films: In situ characterization of the deposition and electroreduction of MnO2

The electrodeposition of manganese oxide films onto a platinum substrate was investigated by means of in situ ellipsometry. In the thickness range from 0 to 150 nm, the anodic oxide behaves as an Isotropic single layer with optical constants that are independent of thickness. Deviations at higher thickness are explained in terms of anisotropic properties of the film. The electroreduction of thin films (up to ca. 150 nm) in an alkaline electrolyte leads to a decrease in both the refractive index and the extinction coefficient and is accompanied by a thickness increase of ca. 10%. The Mn(IV) to Mn(III) conversion takes place from the oxide/electrolyte interface inwards. © 2004 The Electrochemical Society. All rights reserved.

Kinetics and crystal structure of human purine nucleoside phosphorylase in complex with 7-methyl-6-thio-guanosine

Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of nucleosides and deoxynucleosides, generating ribose 1-phosphate and the purine base, which is an important step of purine catabolism pathway. The lack of such an activity in humans, owing to a genetic disorder, causes T-cell impairment, and drugs that inhibit this enzyme may have the potential of being utilized as modulators of the immunological system to treat leukemia, autoimmune diseases, and rejection in organ transplantation. Here, we describe kinetics and crystal structure of human PNP in complex with 7-methyl-6-thio-guanosine, a synthetic substrate, which is largely used in activity assays. Analysis of the structure identifies different protein conformational changes upon ligand binding, and comparison of kinetic and structural data permits an understanding of the effects of atomic substitution on key positions of the synthetic substrate and their consequences to enzyme binding and catalysis. Such knowledge may be helpful in designing new PNP inhibitors. © 2005 Elsevier Inc. All rights reserved.

cDNA cloning and 1.75 Å crystal structure determination of PPL2, an endochitinase and N-acetylglucosamine-binding hemagglutinin from Parkia platycephala seeds

Parkia platycephala lectin 2 was purified from Parkia platycephala (Leguminosae, Mimosoideae) seeds by affinity chromatography and RP-HPLC. Equilibrium sedimentation and MS showed that Parkia platycephala lectin 2 is a nonglycosylated monomeric protein of molecular mass 29 407 ± 15 Da, which contains six cysteine residues engaged in the formation of three intramolecular disulfide bonds. Parkia platycephala lectin 2 agglutinated rabbit erythrocytes, and this activity was specifically inhibited by N-acetylglucosamine. In addition, Parkia platycephala lectin 2 hydrolyzed β(1-4) glycosidic bonds linking 2-acetoamido-2-deoxy-β-d-glucopyranose units in chitin. The full-length amino acid sequence of Parkia platycephala lectin 2, determined by N-terminal sequencing and cDNA cloning, and its three-dimensional structure, established by X-ray crystallography at 1.75 Å resolution, showed that Parkia platycephala lectin 2 is homologous to endochitinases of the glycosyl hydrolase family 18, which share the (βα) 8 barrel topology harboring the catalytic residues Asp125, Glu127, and Tyr182. © 2006 The Authors.

Crystal structure of potassium trifluoro[1,3-dithiano]borate, K(C 4S2H7BF3)

C4H7BF3KS2, monoclinic, P121/c1 (no. 14), a = 14.7374(3) Å, b = 9.0612(1) Å, c = 13.5805(2) Å, β = 98.964(4)°, V = 1791.4 Å3, Z = 8, Rgt(F) = 0.029, wRref(F2) = 0.010, T = 296 K. © by Oldenbourg Wissenschaftsverlag.

Defect-induced photoluminescence of powdered silica glass

Visible photoluminescence was generated in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The broad emission band maximum shows a linear dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. The photoluminescence was attributed to defect generation related to unsatisfied chemical bonds due to the high surface area. Raman scattering and ultraviolet-visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that the powder is composed by nanocrystallites with about 10-20 nanometers immersed in an amorphous media.

Crystal and supramolecular structures of dysprosium(III) 2-methoxybenzoate tetrahydrate

The compound dysprosium(III) 2-metoxybenzoate, {[Dy(2-MeO-Bz)2μ-(2-MeO-Bz)(H2O)2]2·4H2O}n (2-MeO-Bz = 2- methoxybenzoate), was synthesized from a reaction mixture containing DyCl3 and Na(2-MeO-Bz), and characterized by single-crystal X-ray diffraction. The molecular structure showed dinuclear units in which each Dy(III) ion is coordinated by nine oxygen atoms. The carboxylato groups are bound to the dysprosium centers in two modes: bidentate chelating and tridentate chelating-bridging. Besides this, the occurrence of hydrogen bonds involving a coordinated water molecule and carboxylato groups leads to the formation of helicoidal chains along the crystal lattice, resulting in a supramolecular one-dimensional polymer. 2008 © The Japan Society for Analytical Chemistry.

Hydrothermal synthesis and crystal structure of a copper(ii) coordination polymer with bridging dicarboxylate and diamine ligands

This work reports on the synthesis of a copper(II) coordination compound with 4,4-oxibis(benzoate) (obb) and trans-1,2- bis(4-pyridyl)ethene (bpe) ligands. The complex was characterized by single-crystal X-ray diffraction, which showed a 3D polymeric structure. Each copper center is surrounded by four oxygen atoms at the basal plane and one nitrogen atom and one copper atom at the axial positions, revealing a distorted octahedral geometry. Four carboxylic groups bridge two copper atoms, forming a cage-like structure, with the distance between the metallic centers being 2.656(1)Å. 2008 © The Japan Society for Analytical Chemistry.

Molecular and crystal structure of trans-(dicyanato)-bis(triphenylphosphine)palladium(II)

The triphenylphosphine (PPh3) displaces the acetonitrile from [PdCl2(CH3CN)2], and subsequent addition of the potassium cyanate causes substitution of the chloro ligand by NCO- to yield trans-[Pd(NCO)2(PPh3)2]. The complex was characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The title compound was crystallized in a triclinic system, space group P1 with a = 9.213(3)Å, b = 9.781(7)Å, c = 10.483(5)Å, α = 111.39(5)°, β = 93.49(3)°, γ = 103.81(4)°, V = 845.0(1)Å3, Z = 1. The coordination geometry around Pd(II) in this complex is nearly square-planar, with the ligands in a trans relationship. 2008 © The Japan Society for Analytical Chemistry.

Crystal and molecular structure of dinuclear palladium(II) complex containing nitrogen and phosphorus donor ligands, [Pd2(N3)4(PPh3)2(μ-ted)]

The dinuclear azido-palladium(II) complex [Pd2(N3)4(PPh3)2(μ-ted)], where PPh3 = triphenylphosphine and ted = triethylenediamine, was synthesized and characterized by single-crystal X-ray diffraction. The title compound was crystallized in a triclinic system, space group P1 with a = 11.5875(2)Å, b = 13.0817(3)Å, c = 15.2618(3)Å, α = 93.306(2)°, β =110.040(1)°, γ = 98.486(1)°, V = 2134.95(8)Å3, Z = 2. Each Pd(II) center displays a distorted squareplanar coordination environment formed by two N atoms from two trans terminally coordinated azido groups, one P atom from the phosphine and one N atom from the bridging ted ligand. 2008 © The Japan Society for Analytical Chemistry.

Molecular and crystal structure of Di(μ-N,S-thiocyanato)-bis[(N,N-dimethylbenzylamine-C2, N)palladium(II)]

The cyclopalladated complex [Pd(C2,N-dmba)(μ-SCN)]2, where dmba = N,N-dimethylbenzylamine, was structurally characterized by single-crystal X-ray diffraction. This compound crystallizes in the monoclinic system, space group P21/n with a = 9.578(1)Å, b = 12.323(2)Å, c = 10.279(2)Å, β = 117.03(1)°, V = 1080.7(3)Å3, Z = 2. Each Pd(II) center displays a distorted square-planar coordination environment, formed by the C and N atoms from the dmba ligand, and one set of N and S atoms from the bridging SCN groups. 2009 © The Japan Society for Analytical Chemistry.

Experimental observation of infrared spectral enlargement in As 2S3 suspended core microstructured fiber

The development of chalcogenide glasses fibers for application in the infrared wavelength region between 1 and 10 μm is a big opportunity. More particularly, the possibility to generate efficient non linear effects above 2 μm is a real challenge. We present in this work the elaboration and optical characterizations of suspended core microstructured optical fibers elaborated from the As2S3 chalcogenide glass. As an alternative to the stack and draw process a mechanical machining has been used to the elaboration of the preforms. The drawing of these preforms into fibers allows reaching a suspended core geometry, in which a 2.5 μm diameter core is linked to the fiber clad region by three supporting struts. The zero dispersion wavelength is thus shifted towards 2 μm. At 1.55 μm our fibers exhibit a dispersion around -250 ps/nm/km. Their background level of losses is below 0,5 dB/m. By pumping them at 1.55 μm with a ps source, we observe self phase modulation as well as Raman generation. Finally a strong spectral enlargement is obtained with an average output power of - 5 dbm. © 2010 SPIE.

Thermal tunability of photonic bandgaps in photonic crystal fibers selectively filled with nematic liquid crystal

We address the bandgap effect and the thermo-optical response of high-index liquid crystal (LC) infiltrated in photonic crystal fibers (PCF) and in hybrid photonic crystal fibers (HPCF). The PCF and HPCF consist of solid-core microstructured optical fibers with hexagonal lattice of air-holes or holes filled with LC. The HPCF is built from the PCF design by changing its cladding microstructure only in a horizontal central line by including large holes filled with high-index material. The HPCF supports propagating optical modes by two physical effects: the modified total internal reflection (mTIR) and the photonic bandgap (PBG). Nevertheless conventional PCF propagates light by the mTIR effect if holes are filled with low refractive index material or by the bandgap effect if the microstructure of holes is filled with high refractive-index material. The presence of a line of holes with high-index LC determines that low-loss optical propagation only occurs on the bandgap condition. The considered nematic liquid crystal E7 is an anisotropic uniaxial media with large thermo-optic coefficient; consequently temperature changes cause remarkable shifts in the transmission spectrums allowing thermal tunability of the bandgaps. Photonic bandgap guidance and thermally induced changes in the transmission spectrum were numerically investigated by using a computational program based on the beam propagation method. © 2010 SPIE.

Nonlinear effects generation in suspended core chalcogenide fibre

In this work we report our achievements in the elaboration and optical characterizations of low-losses suspended core optical fibers elaborated from As2S3 glass. For preforms elaboration, alternatively to other processes like the stack and draw or extrusion, we use a process based on mechanical drilling. The drawing of these drilled performs into fibers allows reaching a suspended core geometry, in which a 2 μm diameter core is linked to the fiber clad region by three supporting struts. The different fibers that have been drawn show losses close to 0.9 dB/m at 1.55 μm. The suspended core waveguide geometry has also an efficient influence on the chromatic dispersion and allows its management. Indeed, the zero dispersion wavelength, which is around 5 μm in the bulk glass, is calculated to be shifted towards around 2μm in our suspended core fibers. In order to qualify their nonlinearity we have pumped them at 1.995 μm with the help of a fibered ns source. We have observed a strong non linear response with evidence of spontaneous Raman scattering and strong spectral broadening. © 2011 SPIE.

Recent developments in chalcogenide photonic crystal fibres

Elaboration of low-losses highly non linear chalcogenide optical fibers for the generation of efficient non linear effects in the infrared remains a challenge. In recent years, much work has been devoted to the study of microstructured optical fibers (MOFs) with different designs and various elaboration processes. Their background losses were typically of several dB/m. © 2011 IEEE.