Search

The description of the inhomogeneity of the cosmic ray spectrum in the region of 10 TV, which is observed in experimental data, in terms of isotropic diffusion from a single close source is considered. It is shown that such a description is possible, and the area of possible localization of the source in space and time and its energy are found. The method of penalty functions is used to account for the data on the spectrum of all particles. [ABSTRACT FROM AUTHOR]

Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastructure. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy. Their assignment is supported by a combination of X-ray diffraction and DFT-normal modes calculations. We investigate the effect of heating on bone tissue and synthetic calcium-phosphates compounds with close structure and composition to bone mineral, including stoichiometric and non-stoichiometric hydroxyapatite (HA), tricalcium phosphate, calcium pyrophosphate and tetracalcium phosphate. We thus demonstrate that the narrow vibrational mode at 2.1 THz in bone samples exposed to thermal treatment above 750 °C arises from a lattice mode of stoichiometric HA. This feature is also observed in the other synthetic compounds, although weaker or broader, but is completely smeared out in the non-stoichiometric HA, close to natural bone mineral composition, or in synthetic poorly crystalline HA powder. The THz spectral range therefore provides a clear signature of the crystalline state of the investigated bone tissue and could, therefore be used to monitor or identify structural transitions occurring in bone upon heating. [ABSTRACT FROM AUTHOR]

MX2 is an in‐vacuum undulator‐based crystallography beamline at the 3 GeV Australian Synchrotron. The beamline delivers hard X‐rays in the energy range 4.8–21 keV to a focal spot of 22 × 12 µm FWHM (H × V). At 13 keV the flux at the sample is 3.4 × 1012 photons s−1. The beamline endstation allows robotic handling of cryogenic samples via an updated SSRL SAM robot. This beamline is ideal for weakly diffracting hard‐to‐crystallize proteins, virus particles, protein assemblies and nucleic acids as well as smaller molecules such as inorganic catalysts and organic drug molecules. The beamline is now mature and has enjoyed a full user program for the last nine years. This paper describes the beamline status, plans for its future and some recent scientific highlights. [ABSTRACT FROM AUTHOR]

Low temperature (<200 °C) crystallization of GeSn (substitutional Sn concentration: >8%) on insulating substrates is essential to realize next generation flexible electronics. To achieve this, a growth method of high quality GeSn films on insulating substrates by combination of laser irradiation and subsequent thermal annealing is developed. Here, the laser fluence is chosen as weak, which is below the critical fluence for crystallization of GeSn. It is clarified that for samples irradiated with weak laser fluence, complete crystallization of GeSn films is achieved by subsequent thermal annealing at ~170 °C without incubation time. In addition, the quality of GeSn films obtained by this method is higher compared with conventional growth techniques such as melting growth by pulsed laser annealing or solid-phase crystallization (SPC) without pre-laser irradiation. Substitutional Sn concentrations in the grown layers estimated by Raman spectroscopy measurements are 8-10%, which far exceed thermal equilibrium solid-solubility of Sn in Ge (~2%). These phenomena are explained by generation of a limited number of nuclei by weak laser irradiation and lateral SPC by subsequent thermal annealing. This method will facilitate realization of next-generation high performance devices on flexible insulating substrates. [ABSTRACT FROM AUTHOR]

Biphenyl-based compounds are clinically important for the treatments of hypertension and inflammatory, while many more are under development for pharmaceutical uses. In the present study, a series of 2-([1,1'-biphenyl]-4-yl)-2-oxoethyl benzoates, 2(a-q), and 2-([1,1'-biphenyl]-4-yl)-2-oxoethyl pyridinecarboxylate, 2(r-s) were synthesized by reacting 1-([1,1'-biphenyl]-4-yl)-2-bromoethan-1-one with various carboxylic acids using potassium carbonate in dimethylformamide at ambient temperature. Single-crystal X-ray diffraction studies revealed a more closely packed crystal structure can be produced by introduction of biphenyl moiety. Five of the compounds among the reported series exhibited significant anti-tyrosinase activities, in which 2p, 2r and 2s displayed good inhibitions which are comparable to standard inhibitor kojic acid at concentrations of 100 and 250 μg/mL. The inhibitory effects of these active compounds were further confirmed by computational molecular docking studies and the results revealed the primary binding site is active-site entrance instead of inner copper binding site which acted as the secondary binding site. [ABSTRACT FROM AUTHOR]

The application of diamond coatings for strengthening cemented tungsten carbide has been previously attempted, but suffers from delamination. Plasma enhanced chemical vapor deposition boriding improves the strength of cemented carbides by forming WCoB, W 2 CoB 2 , and/or CoB phases using controllable diborane stoichiometry; this research explores these borides as interlayers for nanostructured diamond coatings. Diamond deposition occurred between 600 °C and 1100 °C at 100 °C increments for 30 min to 4 h. Raman spectroscopy showed enhanced diamond growth compared to untreated WC-Co, however predominantly WCoB and CoB phase interlayers suffered from diamond film delamination. Examination by scanning electron microscopy and energy dispersive X-ray spectroscopy showed interfacial cobalt clusters on these interlayers. Predominantly W 2 CoB 2 phase interlayers showed improvement with a reduction in reactive cobalt, and improved adhesion of nanostructured diamond coatings. Diamond on W 2 CoB 2 was well adhered with deposition temperature dependent nanoindentation hardness ranging from 10 to 60 GPa and elastic modulus of 400 to 750 GPa. Scratch testing revealed cohesive and adhesive failure of the diamond coatings at 5 N ± 2 N and 8 N ± 2 N respectively and epoxy pull testing resulted in a surface adhesion tensile strength of 8.2 MPa ± 0.1 MPa. The W 2 CoB 2 phase is shown to be desirable as an interlayer for improved nanostructured diamond adhesion on cemented tungsten carbide. Prime novelty statement The scope of diamond deposition parameters used and the comparison of interlayer effect for CVD diamond coatings on ternary borides (WCoB, W 2 CoB 2 ) with a cemented tungsten carbide substrate has not been previously examined to this level. [ABSTRACT FROM AUTHOR]

Mineralogical, chemical, and spectroscopic properties of chrysoberyl crystals recovered from sapphire placer deposits, related to Tertiary volcanic rocks, in the New England gem fields in New South Wales (NSW), Australia, are presented. The samples appeared yellow, yellowish brown, or brown in transmitted light, and some crystals revealed a distinct sectorial zoning between brown i (011) and yellow o (111) growth areas. In reflected light, the i sectors showed a whitish appearance, and cabochon-cut samples with larger whitish i sectors displayed chatoyancy. On the basis of morphological properties, trace-element contents, and absorption spectra, the chrysoberyl samples were subdivided into four different groups, possibly originating from different host rocks. The largest such group, comprised of samples with distinct sectorial color zoning, also revealed a pronounced variation in trace-element levels of titanium, niobium, and tantalum between the different growth sectors. Smaller variations were found for boron, magnesium, and iron, and almost no variation was observed for gallium. [ABSTRACT FROM AUTHOR]

Raman and infrared spectra of twinned M(IO) (M = Mn, Ni, Co, and Zn) crystals are recorded and the observed bands are assigned in terms of vibrations of the IO octahedron. The IO octahedra in Mn(IO) and Zn(IO) are comparatively more distorted than those of Co(IO) and β-Ni(IO). The I/I ratio of Mn(IO) is higher compared to other compounds, and its linear polarizability is more than that of angular polarizability. The noncentrosymmetric space group of the title compounds is confirmed by the coincidence of the majority of IR and Raman bands, and the compounds giving intense Raman bands are expected to give better SHG efficiency. [ABSTRACT FROM AUTHOR]

The structure and photophysical properties of the Zn(II) complex with the novel fluorescent Schiff base ligand L: (E)- N ′-((2-hydroxynaphthalen-1-yl) ethylene)acetohydrazide have been investigated. X-ray crystallography has proved the neutral, mononuclear complex: [ZnL 2 ]·H 2 O·DMF, ZnL. The crystal packing proves intramolecular-interactions between the alternating naphthalene rings. Photophysical measurements of the complex in solvents of varying polarity (DCM, THF and DMSO) provide evidence for the formation of molecular aggregates in non-polar solvents that enhance the energy of the S 0 –S 1 level. In the solid states, the complex exhibits unusual blue-shifted emission with respect to the ligand, due to excited state intermolecular proton transfer (ESIPT) within the ZnL molecules in the lattice. The experimental measurements are also complimented by DFT and TD-DFT calculations in the gas-phase and solution states. [ABSTRACT FROM AUTHOR]

Monocycloplatinated complexes [Pt(HL n )(PPh 3 )] were synthesized using [Pt(dmso) 2 Cl 2 ], N ʹ-(arylidene)benzohydrazides (H 3 L n , arylidene = 1-naphthylidene or 9-phenanthrylidene), NaOAc·3H 2 O, and PPh 3 in 1:1:1:2 mol ratio. The same reagents in 2:1:1:2 mol ratio provided the dicycloplatinated complexes [Pt 2 ( μ -L n )(PPh 3 ) 2 Cl]. All the complexes have been characterized by elemental analysis, X-ray crystallographic and spectroscopic measurements. X-ray structures reveal that (HL n ) 2− acts as pincer-like CNO-donor in [Pt(HL n )(PPh 3 )], while the dinucleating (L n ) 3− behaves as pentadentate ligand and acts is CNO-donor to one metal centre and CN-donor to the second metal centre in [Pt 2 ( μ -L n )(PPh 3 ) 2 Cl]. The spectroscopic (IR, UV–Vis and NMR) features of both types of complexes are in agreement with their corresponding identities. [ABSTRACT FROM AUTHOR]

Inthe present work, geometric structures, electronic properties,and 4f → 5d transitions of γ-Ca2SiO4:Ce3ꘚⲦᨫ have been investigated by using first-principlescalculations. Four categories of typical substitutions (i.e., thedoping of the Ce3숫憢 the neighboring dopants/defectsand with the neighboring VO••,AlSi′, and VCa″) are taken intoaccount to simulate local environments of the Ce3隇᪵at two crystallographically different calcium sites in the γ-Ca2SiO4. Density functional theory (DFT) geometryoptimization calculations are first performed on the constructed supercellsto obtain the information about the local structures and preferredsites for the Ce3. On the basis of the optimized crystalstructures, the electronic properties of γ-Ca2SiO4:Ce3ꘚⲦᨫ are calculated with the Heyd–Scuseria–Ernzerhofscreened hybrid functional, and the energies and relative oscillatorstrengths of the 4f → 5d transitions of the Ce3檷 derived from the ab initioembedded clustercalculations at the CASSCF/CASPT2/RASSI-SO level. A satisfactory agreementwith the available experimental results is thus achieved. Moreover,the relationships between the dopants/defects and the electronic aswell as spectroscopic properties of γ-Ca2SiO4:Ce3ꘚⲦᨫ have been explored. Such informationis vital, not least for the design of Ce3+based phosphorsfor the white light-emitting diodes (w-LEDs) withexcellent performance. [ABSTRACT FROM AUTHOR]

Designing new functional materials with increasingly complex compositions is of current interest in science and technology. Complex rare-earth-based chalcogenides have specific thermal, electrical, magnetic and optical properties. Tetragadolinium bis[tetraoxidosilicate(IV)] oxide telluride, Gd4(SiO4)2OTe, was obtained accidentally while studying the Gd2Te3-Cu2Te system. The crystal structure was determined by means of single-crystal X-ray diffraction. The compound crystallizes in the space group Pnma. Three symmetry-independent gadolinium sites were determined. The excitation and emission spectra were collected at room temperature and at 10 K. Gd4(SiO4)2OTe appears to be a promising optical material when doped with rare-earth ions. [ABSTRACT FROM AUTHOR]

An experimental system for serial femtosecond crystallography using an X-ray free-electron laser (XFEL) has been developed. It basically consists of a sample chamber, fluid injectors and a two-dimensional detector. The chamber and the injectors are operated under helium atmosphere at 1 atm. The ambient pressure operation facilitates applications to fluid samples. Three kinds of injectors are employed to feed randomly oriented crystals in aqueous solution or highly viscous fluid. Experiments on lysozyme crystals were performed by using the 10 keV XFEL of the SPring-8 Angstrom Compact free-electron LAser (SACLA). The structure of model protein lysozyme from 1 µm crystals at a resolution of 2.4 Å was obtained. [ABSTRACT FROM AUTHOR]

Beamline 08B1-1 is a recently commissioned bending-magnet beamline at the Canadian Light Source. The beamline is designed for automation and remote access. Together with the undulator-based beamline 08ID-1, they constitute the Canadian Macromolecular Crystallography Facility. This paper describes the design, specifications, hardware and software of beamline 08B1-1. A few scientific results using data obtained at the beamline will be highlighted. [ABSTRACT FROM AUTHOR]

In this article the crystal structures of the starting material TZ-5 and the key intermediate TZ-6 of temozolomide (TZ-7), an anticancer therapeutic agent, are presented, together with their spectroscopic and thermal characteristics. Both compounds crystallize in the triclinic P-1 space group. X-ray crystallography studies proved that the compound TZ-6 exists as a monohydrate. A complete structural assignment was obtained for the signals in the 1H-, 13C- and 15N-nuclear magnetic resonance spectra and the structures were confirmed by Fourier-Transform infrared and Raman spectroscopy. The article describes the importance of the high purity of TZ-6 during the small-scale plant production of TZ-7 in a desired polymorphic form III with the purity higher than 99.50%, according to an HPLC method. [ABSTRACT FROM AUTHOR]

Thermal reactions in two Tyr-Ala-Phe(YAF) tripeptide crystalswith different molecular packing (monoclinic and hexagonal), distinctstereochemistry of central amino acid (D or L alanine) and specificarrangement of molecules in the crystal lattice (head-to-tail) wereinvestigated. Samples were heated up to 180 °C, while the meltingpoint for YAF crystals is above the 220 °C. Below the meltingtemperature, in both cases the chemical reactions leading to formationof cyclic dipeptides (YA diketopiperazine) and leaving of phenylalaninewere observed. Two possible mechanisms of chemical reaction in thecrystal lattice assuming intra- and/or intermolecular pathways wereconsidered. 13C and 15N enriched YAF sampleswere employed to study of mechanism of solid state reactivity usingmass spectrometry and advanced solid state NMR techniques (2D DARR(Dipolar Assisted Rotational Resonance) and 2D Double CP (Cross-Polarization)correlations). [ABSTRACT FROM AUTHOR]

Hemoglobin (Hb) is the heme-containing O2 transport protein essential for life in all vertebrates. The resting high-spin (S = 2) ferrous form, deoxy-Hb, combines with triplet O2, forming diamagnetic (S = 0) oxy-Hb. Understanding this electronic structure is the key first step in understanding transition metal-O2 interaction. However, despite intense spectroscopic and theoretical studies, the electronic structure description of oxy-Hb remains elusive, with at least three different descriptions proposed by Pauling, Weiss, and McClure-Goddard, based on theory, spectroscopy, and crystallography. Here, a combination of X-ray absorption spectroscopy and extended X-ray absorption fine structure, supported by density functional theory calculations, help resolve this debate. X-ray absorption spectroscopy data on solution and crystalline oxy-Hb indicate both geometric and electronic structure differences suggesting that two of the previous descriptions are correct for the Fe-O2 center in oxy-Hb. These results support the multiconfigurational nature of the ground state developed by theoretical results. Additionally, it is shown here that small differences in hydrogen bonding and solvation effects can tune the ground state, tipping it into one of the two probable configurations. These data underscore the importance of solution spectroscopy and show that the electronic structure in the crystalline form may not always reflect the true ground-state description in solution. [ABSTRACT FROM AUTHOR]

A new purification method of magnesium(II) and zinc(II) porphine complexes (MgP and ZnP, respectively) by crystallization of their respective pyridine adducts is described. Pure MgP and ZnP can be regenerated by removal of the coordinated pyridine ligands by heating at 200°C under vacuum. X-ray crystallographic structures of the pyridine adducts are presented for the first time. NMR analyses of the adducts reveal the coordination of two pyridine molecules. Electrochemical as well as UV-vis absorption spectroscopy analyses in DMF of MgP·(Py) 2 , ZnP·(Py) 2 , MgP and ZnP indicate that pyridine adducts are totally dissociated. Besides, oxidation peaks of these complexes are totally irreversible, revealing a high reactivity of the oxidized species. Electrolyses at the first oxidation potential lead to the formation of the meso-meso (ZnP) 2 and (MgP) 2 dimers, oligomers and polymers on the electrode surface, as attested by MALDI-TOF mass spectrometry and UV-vis absorption spectroscopy analyses of the crude solution. [ABSTRACT FROM AUTHOR]

An algorithm is presented which determines the equivalence of two settings of a (3 + d)-dimensional superspace group ( d = 1, 2, 3). The algorithm has been implemented as a web tool on , providing the transformation of any user-given superspace group to the standard setting of this superspace group in . It is shown how the standard setting of a superspace group can be directly obtained by an appropriate transformation of the external-space lattice vectors (the basic structure unit cell) and a transformation of the internal-space lattice vectors (new modulation wavevectors are linear combinations of old modulation wavevectors plus a three-dimensional reciprocal-lattice vector). The need for non-standard settings in some cases and the desirability of employing standard settings of superspace groups in other cases are illustrated by an analysis of the symmetries of a series of compounds, comparing published and standard settings and the transformations between them. A compilation is provided of standard settings of compounds with two- and three-dimensional modulations. The problem of settings of superspace groups is discussed for incommensurate composite crystals and for chiral superspace groups. [ABSTRACT FROM AUTHOR]

The focusing properties of cylindrically bent crystals in symmetric Laue geometry are discussed using the formalism of Fresnel diffraction and the analytical solution of the Takagi-Taupin equations for a point source on the entrance surface. The existence of a focal shift in the dynamical focusing effect is pointed out and discussed. The present theoretical framework is applied to experiments performed at the energy-dispersive X-ray absorption spectroscopy beamline of the European Synchrotron Radiation Facility concerning the position and the size of the focal spot obtained from a polychromatic source at a large distance from the bent crystal. [ABSTRACT FROM AUTHOR]

This paper explains how to take the counting precision available for XAFS (X-ray absorption fine structure) and attenuation measurements, of perhaps one part in 106 in special cases, to produce a local variance below 0.01% and an accuracy of attenuation of the order 0.01%, with an XAFS accuracy at a similar level leading to the determination of dynamical bond lengths to an accuracy similar to that obtained by standard and experienced crystallographic measurements. This includes the necessary corrections for the detector response to be linear, including a correction for dark current and air-path energy dependencies; a proper interpretation of the range of sample thicknesses for absorption experiments; developments of methods to measure and correct for harmonic contamination, especially at lower energies without mirrors; the significance of correcting for the actual bandwidth of the beam on target after monochromation, especially for the portability of results and edge structure from one beamline to another; definitions of precision, accuracy and XAFS accuracy suitable for theoretical model analysis; the role of additional and alternative high-accuracy procedures; and discusses some principles regarding data formats for XAFS and for the deposition of data sets with manuscripts or to a database. Increasingly, the insight of X-ray absorption and the standard of accuracy needed requires data with high intrinsic precision and therefore with allowance for a range of small but significant systematic effects. This is always crucial for absolute measurements of absorption, and is of equal importance but traditionally difficult for (usually relative) measurements of fluorescence XAFS or even absorption XAFS. Robust error analysis is crucial so that the significance of conclusions can be tested within the uncertainties of the measurements. Errors should not just include precision uncertainty but should attempt to include estimation of the most significant systematic error contributions to the results. This is essential if the results are to be subject to deposition in a central accessible reference database; it is also crucial for specifying a standard data format for portability and ease of use by depositors and users. In particular this will allow development of theoretical formulations to better serve the world-wide XAFS community, and a higher and more easily comparable standard of manuscripts. [ABSTRACT FROM AUTHOR]

Optical absorption spectroscopy and X-ray structural refinements were used to characterize short-range and long-range structures of 10 gem-quality, blue spinel single crystals synthesized on the (Mg1-xCox) Al2O4 solid solution (x = 0.07-1.00). The site distributions of Mg, Co2+, and Al show that the tetrahedrally coordinated site (T) is mainly populated by Mg and Co2+, with a marked preference of Co2+ for tetrahedral coordination with respect to Mg, while the octahedrally coordinated site (M) is dominated by Al. Crystals also show a certain degree of inversion, i.e., occurrence of Al at T counterbalanced by the occurrence of divalent cations at M, which decreases from 0.24 to 0.13 with increasing Co2+ content. Short-range information based on the crystal field splitting parameter Dq derived from single-crystal optical spectra suggests that the local Co2+-O bond length at the T-site may increase marginally at increasing Co2+ content. An almost constant value for the Racah B-parameter, also derived from optical spectra, for tetrahedrally coordinated Co2+ suggests that any influence of substitutional second nearest neighbor cations on the ionicity of Co2+-O bonds at the T-site is very small. Long-range information shows that variations in the unit-cell parameter from 8.084 to 8.105 Å along the solid-solution series are mainly related to the ordering of Al at the M site as a result of the replacement of Mg by Co2+. Therefore, the spinel structure responds to the chemical variation by ordering of Al in such a manner that M-O remains almost constant and T-O increases. In this way, the lengths of shared octahedral edges are reduced and the destabilization effect due to the increased octahedral cation-cation repulsion is minimized. In line with other studies, the importance of steric factors for controlling the cation distributions in the spinel structure has also been shown to be valid in the MgAl2O4-CoAl2O4 solid-solution series. [ABSTRACT FROM AUTHOR]

Abstract: A novel Y3Si3O10F:Eu3+ phosphor was synthesized under hydrothermal conditions. Luminescence properties and crystallographic sites for Eu3+ ions in Y3Si3O10F:Eu3+ are investigated by site-selective laser-excitation spectroscopy. The three Eu3+ centers are identified in the 7F0 → 5D0 excitation spectra. The luminescence due to the 5D0 → 7FJ (J =1, 2) transitions under excitation at each center exhibits its own spectral features and temporal behavior. The crystal-field splitting of the 7F1 and 7F2 multiplets and intensity ratio of the 5D0 → 7F2 to 5D0 → 7F1 emission depend strongly on the crystallographic sites in Y3Si3O10F. The decay time of the 5D0 level is shorter for the site with higher energy. The results are discussed in relation to the site symmetry and the crystal-field strength on Eu3+ in the Y3Si3O10F lattice. [Copyright &y& Elsevier]

Photoinduced electron transfer in biological systems, especially in proteins, is a highly intriguing matter. Its mechanistic details cannot be addressed by structural data obtained by crystallography alone because this provides only static information on a given redox system. In combination with transient spectroscopy and site-directed manipulation of the protein, however, a dynamic molecular picture of the ET process may be obtained. In BLUF (blue light sensors using FAD) photoreceptors, proton-coupled electron transfer between a tyrosine and the flavin cofactor is the key reaction to switch from a darkadapted to a light-adapted state, which corresponds to the biological signaling state. Particularly puzzling is the fact that, although the various naturally occurring BLUF domains show little difference in the amino acid composition of the flavin binding pocket, the reaction rates of the forward reaction differ quite largely from a few ps up to several hundred ps. In this study, we modified the redox potential of the flavin/tyrosine redox pair by site-directed mutagenesis close to the flavin C2 carbonyl and fluorination of the tyrosine, respectively. We provide information on how changes in the redox potential of either reaction partner significantly influence photoinduced protoncoupled electron transfer. The altered redox potentials allowed us furthermore to experimentally describe an excited state charge transfer intermediately prior to electron transfer in the BLUF photocycle. Additionally, we show that the electron transfer rate directly correlates with the quantum yield of signaling state formation. [ABSTRACT FROM AUTHOR]

A new analysis method for the short excited-state lifetime measurement of photosensitive species in crystals is described. Based on photocrystallographic techniques, this method is an alternative to spectroscopic methods and is also valid for non-luminescent excited species. Two different approaches are described depending on the magnitude of the lifetime τ. For very short lifetimes below the width of the synchrotron pulse, an estimated τ can be obtained from the occurrence of the maximal system response as a function of the pump-probe delay time Δ t. More precise estimates for both short and longer lifetimes can be achieved by a refinement of a model of the response as a function of the pump-probe delay time. The method also offers the possibility of the structure determination of excited species with lifetimes in the 40-100 ps range. [ABSTRACT FROM AUTHOR]

This paper reports the growth and spectral properties of Er3+-doped and Er3+/Yb3+-codoped Li3Ba2La3(WO4)8 crystals. The Er3+: Li3 Ba2La3(WO4)8 crystal with dimensions of 56 mm×28 mm×9 mm and Er3+/Yb3+: Li3Ba2La3(WO4)8 crystal with dimensions of 52 mm×24 mm×8 mm were obtained by the top-seeded solution growth (TSSG) method. Thermal expansion coefficients and thermal conductivity of both crystals were measured. The spectroscopic characterizations of both crystals were investigated. The spectroscopic analysis reveals that the Er3+/Yb3+: Li3Ba2La3(WO4)8 crystal has much better optical properties than the Er3+: Li3Ba2La3(WO4)8 crystal, thus it may become a potential candidate for solid-state laser gain medium material. [ABSTRACT FROM AUTHOR]

The present study describes about synthesis and characterization of Cadmium Sulphide nanoparticles. CdS nanostructured materials were synthesised by aqueous method and physically characterized by spectroscopic and microscopic studies. The results reveal that absorption band edge at 475 nm is due to position dependent quantum confinement and it was observed that both cubic and hexagonal crystallographic studies were found to be present at ambient temperature. The optical properties and effect of cationic micelles in this synthesis is described in this article. [ABSTRACT FROM AUTHOR]

Single crystals of 6-amino-8a-methoxy-5-methyl-4,7-dioxo-1,1a, 2,4,7,8,8a,8b-octahydroazireno[2',3':3,4]pyrrolo[1,2-a]indol-8-yl]methyl carbamate (Mitomycin), an organic marine dye material has been grown from solution by slow evaporation at ambient temperature. The growth of crystals has been carried out at various pH values and the growth was confirmed at pH 6. The chemical composition of the grown crystals was determined by the FTIR spectra. The crystalline nature and its various planes of reflections were observed by the powder XRD. The grain size is found to be 500 microns using SEM studies and the NLO activity of the grown crystal has been checked by second harmonic generation (SHG) test. [ABSTRACT FROM AUTHOR]

Four hosts (7-10) containing 2,6-bisamidopyridine- and 2,5-bisamidopyrrole-bearing pyridyl or 1,8-naphthyridyl groups have been prepared and their structures studied by a combination of multinuclear NMR spectroscopy and X-ray crystallography. Their behavior in molecular recognition of urea derivatives, including (+)-biotin methyl ester, has been approached by molecular modeling (Monte Carlo conformational search, AMBER force field). The minimum energy values for the complexes are correlated with the experimental binding energies determined by means of ¹H NMR titrations. [ABSTRACT FROM AUTHOR]

9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([l,2-a:2'-l'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents. Solution-phase (ensemble) time-resolved photoluminescence measurements show up to 4-fold decreases in fluorescence lifetime in acetonitrile compared to hexane. The combined results are consistent with photoinduced, transient intramolecular charge-transfer from the bis-anisylamine unit to the polyeyclic aromatic unit. Computational modeling is in accord with intramolecular transfer of electron density from the bis-anisylamino unit to the anthracene, based on in comparisons of HOMO and LUMO. [ABSTRACT FROM AUTHOR]

The crystal chemistry of Ti-rich phlogopite from deposits of the oldest activity (~740 ka) of Mt. Vulture, Potenza, Italy, was investigated to identify the substitution mechanisms in Ti-rich phlogopite and to determine its potential as a geohygrometer. Substitution mechanisms were determined by electron probe microanalysis (EPMA), single-crystal X-ray diffraction (SCXRD), Mössbauer spectroscopy, and micro-Fourier transform infrared (FTIR) spectroscopy. Magnetite and sanidine from the mica-rich host rocks were also analyzed. Use of the biotite-magnetite-sanidine geohygrometer in these volcanics (essentially trachytic-phonolitic ignimbrites) is exploited. All investigated phlogopite samples consist of the 1M polytype, with 5.3275(2) ≤ a ≤ 5.3635(4) Å, 9.2211(4) ≤ b ≤ 9.2958(8) Å, 10.1211(5) ≤ c ≤ 10.281(1) Å, and 99.980(3) ≤ β ≤ 100.097(2)°. Structure refinements in space group C2/m converged to 2.42 ≤ R1 ≤ 4.00% and 2.04 ≤ wR2 ≤ 4.50%. VIFe3+ /Fetot from Mössbauer analyses ranged from 34(1)-89(1)%. The main bands in the OH-stretching region are 3709, 3682, and 3658 cm-1, and were assigned to 3Mg-OH--K-OH , 3Mg-OH--K-O2-, and 2MgFe3+ - OH--K-O2- local configurations, respectively. The overall crystal chemical features are compatible with the M3+-Tschermak substitutions (VIM2+ + IVSi4 ↔ VIM3+ + IVAl, with M3+ = Al, Fe3+), M3+-oxy [VIM2+ + (OH)- ↔ M3+ + (O) 2- + 1/2H2↑ and Ti-oxy substitutions [VIM2+ + 2(OH)-1 → VITi4+ + 2(O)2- + H2↑]. The magnetite composition varies between Mt82Uv18 and Mt93Uv07, whereas the proportion of orthoclase with respect to albite plus anorthite is 0.77 ≤ XOr =≤ 0.82. A partly ionic model was used to estimate annite activity, starting from experimentally determined substitutions in phlogopite. The resulting water fugacity was an order of magnitude lower than that calculated using stoichiometry to determine the phlogopite formula. The results are consistent with the occurrence of a well-developed hydrothermal system that altered the magmatic oxygen fugacity conditions at Mt. Vulture. [ABSTRACT FROM AUTHOR]

The article focuses on the structure of a new noncentrosymmetric organic-inorganic hybrid material synthesized as single crystal at room temperature and characterized by X-ray diffraction and solid-state nuclear magnetic resonance (NMR) spectroscopy. Two 4-methylbenzylammonium cations and one anion connected by hydrogen bonds composed the novel structure. It describes the zinc (Zn)II metal centre as having a slightly distorted tetrahedral coordination geometry. It notes the agreement of carbon peaks with crystallographically independent sites.

Oriented single crystals of stibioellisite (Tl3SbS3), parapierrotite (TlSb5S8), weissbergite (TlSbS2), and lorandite (TlAsS2) were investigated by polarized Raman spectroscopy. Whereas stibioellsite shows isolated SbS3 groups, the rest of the minerals show interconnected pyramidal (As,Sb)S3 groups. Raman bands of the investigated minerals occur between 400 and 10 cm-1. The internal vibrations for stibioellsite occur between 350-100 cm-1. Those of the interconnected pyramidal groups occur between 350 and 10 cm-1 in parapierrotite, 350 and 90 cm-1 in weissbergite, and 420 and 130 cm-1 in lorandite. Approximate similarities in the spectral features are evident when comparing the spectra of minerals containing XS3 pyramids with the spectra of the minerals in the present study. A clear distinction between Raman spectra of separated and interconnected SbS3 groups is not observed. [ABSTRACT FROM AUTHOR]

Efficiency droop and green gap are terms that summarize performance limitations in GaInN/GaN high brightness light emitting diodes (LEDs). Here we summarize progress in the development of green LEDs and report on time resolved luminescence data of polar c-plane and non-polar m-plane material. We find that by rigorous reduction of structural defects in homoepitaxy on bulk GaN and V-defect suppression, higher efficiency at longer wavelengths becomes possible. We observe that the presence of donor acceptor pair recombination within the active region correlates with lower device performance. To evaluate the aspects of piezoelectric polarization we compare LED structures grown along polar and non-polar crystallographic axes. In contrast to the polar material we find single exponential luminescence decay and emission wavelengths that remain stable irrespective of the excitation density. Those findings render high prospects for overcoming green gap and droop in non-polar homoepitaxial growth. [ABSTRACT FROM AUTHOR]

The crystal structures of 4-(4-methylphenyl)-6-phenyl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazole (IIa) and 4-(4-methoxyphenyl)-6-phenyl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazole (IIb) were elucidated by single crystal X-ray diffraction. Compound (IIa), C28H25N, crystallizes in the triclinic system, space group P-1, with a = 8.936(2) Å, b = 10.490(1) Å, c = 11.801(1) Å, α = 102.69(5)º, β = 103.27(3)º, γ = 93.80(1)º, and Z = 2. The compound (IIb), C28H25NO, crystallizes in the monoclinic system, space group P21/a, with a = 11.376(5) Å, b = 14.139(3) Å, c = 13.237(4) Å, β = 97.41(3)º, and Z = 4. In both the structures, the pyrido ring adopts a twist boat conformation and the carbazole molecule has the twisted envelope structure with C3 and C13 at the flap. No classical hydrogen bonds are observed in the crystal structures. Details of the preparation, structures, and spectroscopic properties of the new compounds are discussed. [ABSTRACT FROM AUTHOR]

It is shown that the positron annihilation spectroscopy (PAS) method is one of the most effective ways of determining the sizes of nanoobjects (vacancies, vacancy clusters, free pore spaces, cavities, and voids) and their concentrations in the place of annihilation of positrons in porous systems and in a wide range of technically important materials and nanomaterials. The possibilities of the method are demonstrated by example of porous silicon and silicon irradiated with protons. [ABSTRACT FROM AUTHOR]

Abstract: A facile, one pot, high yield synthesis of α,β-vinylester (1–14) and alkoxy substituted γ-lactones (15–28) has been achieved by the photochemical reaction of terminal acetylene (ferrocenyl phenyl trimethylsillyl, hexyl and cyclohexyl) with alcohol (methanol, ethanol and isopropanol) and carbon monoxide in presence of iron pentacarbonyl as a catalyst. The selectivity of the compounds depends on the time of photolysis of the reaction as well as the solvent used. A stable reaction intermediate ferrole was isolated, and further photolysis with alcohols, resulted in the formation of α,β-vinylester. All the compounds were fully characterised by spectroscopic methods and the molecular structures of compounds 1, 16, 17 and 20 were established crystallographically. [ABSTRACT FROM AUTHOR]

Single crystals of InSe and CuInSe compounds and (InSe)·(CuInSe) solid solutions have been grown from the melt using the Bridgman method and their composition and structure determined. It is shown that the crystals have n-type conductivity. Their transmission spectra were studied in the self-absorption edge region at 80 and 295 K. Based on the spectral measurements, the band gap width (E) was determined and the band gap concentration dependences were plotted. It is found that E varies with the x composition nonlinearly. Using the dielectric model of Van Vechten-Bergstresser and the Hill-Richardson pseudo potential model, E(x) was calculated theoretically. [ABSTRACT FROM AUTHOR]

In this study, we report the results of an in situ X-ray absorption spectroscopy investigation of the La2O3–B2O3–GeO2 (LBG) glass compressed in a diamond anvil cell until 17 GPa at ambient temperature. A pressure-induced coordination change of germanium from fourfold to sixfold is shown here. The analysis of Ge K-edge X-ray absorption near-edge structure spectra supports a model of mixing of fourfold and sixfold coordinated Ge sites during the compression/decompression cycle. This transformation proves to be irreversible: about 25% of sixfold coordinated Ge still exists at ambient pressure. This phenomenon underlines a polymorphism property of the LBG glass, whose origin lies in the complexity of composition. [ABSTRACT FROM AUTHOR]

This work aims to study the crystal structure and spectral properties of the fluorescent dye, thiazole orange (TO) derivative. The single crystals with a size of 0.20x0.16x0.12 cm3 have been obtained by the slow evaporation of a methanol solution at room temperature and characterized by NMR, TG⁄DTA thermograms, IR spectroscopy and single crystal X–ray diffraction. The compound crystallizes in the Triclinic system and belongs to P–1 space group. The fluorescence spectra of the crystal in solutions have been measured. [ABSTRACT FROM AUTHOR]

Treatment of a precursor to the chelating Lewis acid 2,2′-diborabiphenyl with 2,6-bisalkynyl-substituted pyridazines, leads to elimination of 2 equiv. of ClSiMe3; subsequent treatment of the mixture with PtCl2 catalyzes the cyclization of observable intermediates to the title 5b,7b-diaza-3b,9b-diborabenzo[ghi]perylene compounds in low isolated yields. The compounds were characterized by NMR and UV–vis spectroscopies, and in one case, by X-ray crystallography. NICS(1) computations indicate that the inner ring is less aromatic than the outer rings. Le traitement d’un précurseur de l’acide de Lewis chélatant 2,2′-diborabiphényle avec des pyridazines substituées dans les positions 2,6 par des groupes bisalkynyles conduit à l’élimination de deux équivalents de ClSiMe3; le traitement subséquent du mélange avec du PtCl2 catalyse la cyclisation des intermédiaires observables et à la formation des composés 5b,7b-diaza-3b,9b-diborabenzo[ghi]pérylènes mentionnés dans le titre qui sont isolés avec de faibles rendements. Les composés ont été caractérisés par spectroscopies RMN et UV–vis et, dans un cas, par diffraction des rayons-X. Des calculs NICS(1) indiquent que le noyau interne est moins aromatique que les cycles externes. [ABSTRACT FROM AUTHOR]

We have used site-directed mutagenesis, EPR spectroscopy, redox potentiometry, and protein crystallography to monitor assembly of the FSO [4Fe-4S] cluster and molybdo-bis(pyranopterin guanine dinucleotide) cofactor (Mo-bisPGD) of the Escherichia coli nitrate reductase A (NarGHI) catalytic subunit (NarG). Cys and Ser mutants of NarG-His49 both lack catalytic activity, with only the former assembling FSO and Mo-bisPGD. Importantly, both prosthetic groups are absent in the NarGH49S mutant. EPR spectroscopy of the Cys mutant reveals that the Em value of the FSO cluster is decreased by at least 500 mV, preventing its participation in electron transfer to the MobisPGD cofactor. To demonstrate that decreasing the FSO cluster Em results in decreased enzyme activity, we mutated a critical Arg residue (NarG-Arg94) in the vicinity of FS0 to a Ser residue. In this case, the Em of FS0 is decreased by 115 mV, with a concomitant decrease in enzyme turnover to ∼30% of the wild type. Analysis of the structure of the NarG-H49S mutant reveals two important aspects of NarGHI maturation: (1) apomolybdoNarGHI is able to bind GDP moieties at their respective P and Q sites in the absence of the Mo-bisPGD cofactor, and (ii) a critical segment of residues in NarG, 49HGVNCTG55, must be correctly positioned to ensure holoenzyme maturation. [ABSTRACT FROM AUTHOR]

During synthetic studies on anti-elastase polycyclic β-lactams from conveniently substituted monolactams, we attempted to obtain an N-(1´-methoxycarbonyalkylidene)-β-lactam by α-selenoxide elimination. Although the desired alkenes 5 were obtained, the main products were the N-unsubstituted 2-azetidinone 2 and the bridged bicyclic pyrrolidinedione 7. The structure of compound 7 was established by spectroscopic methods and confirmed by X-ray crystallography. [ABSTRACT FROM AUTHOR]

First principles studies on periodic TS-1 models at Ti content corresponding to 1.35% and 2.7% in weight of TiO2are presented. The problem of Ti preferential siting is addressed by using realistic models corresponding to the TS-1 unit cell [TiSi95O192] and adopting for the first time a periodic DFT approach, thus providing an energy scale for Ti in the different crystallographic sites in nondefective TS-1. The structure with Ti in site T3 is the most stable, followed by T4 (+0.3 kcal/mol); the less stable structure, corresponding to Ti in T1, is 5.6 kcal/mol higher in energy. The work has been extended to investigate models with two Ti’s per unit cell [Ti2Si94O192] (2.7%). The possible existence of Ti−O−Ti bridges, formed by two corner-sharing TiO4tetrahedra, is discussed. By using cluster models cut from the optimized periodic DFT structures, both vibrational (DFT) and electronic excitation spectra (TDDFT) have been calculated and favorably compared with the experimental data available on TS-1. Interesting features emerged from excitation spectra: (i) Isolated tetrahedral Ti sites show a Beer−Lambert behavior, with absorption intensity proportional to concentration. Such a behavior is gradually lost when two Ti’s occupy sites close to each other. (ii) The UV−vis absorption in the 200−250 nm region can be associated with transitions from occupied states delocalized on the framework oxygens to empty d states localized on Ti. Such extended-states-to-local-states transitions may help the interpretation of the photovoltaic activity recently detected in Ti zeolites. [ABSTRACT FROM AUTHOR]

By refluxing a mixture of (NH4)2[MoCl5(H2O)] and KSCN in γ-picoline, crystalline trans- [(γ-pic)2H][Mo(NCS)4(γ-pic)2] (1) was prepared. After addition of P(C6H5)4Br to the solution of 1 in acetonitrile, trans-[P(C6H5)4][Mo(NCS)4(γ-pic)2] ∙ 2CH3CN (2) was isolated. Both compounds were characterized by IR spectroscopy, and their crystal structures were determined. X-ray structural analysis revealed the presence of trans-[Mo(NCS)4(γ-pic)2]- anions, with N-bonding of the NCS groups in both compounds. The positions of the v(CN) and δ(NCS) bands are in agreement with the crystal-structure results. The results of analyses were compared with the results of the related trans-py2H)[Mo(NCY)4py2] (Y = S, O) complexes. [ABSTRACT FROM AUTHOR]

Cr xHg1 − x crystals grown by solid-state recrystallization have been characterized by electron paramagnetic resonance spectroscopy, transport measurements, and X-ray microanalysis. The results demonstrate that the crystals contain rectangular HgCr2Se4 inclusions elongated along one of their axes and irregularly shaped Cr xHg1 − x and CrHg inclusions. In the range 77–400 K, the electrical properties of samples cut from different parts of the crystals are typical of semiconductors with a strongly degenerate electron gas. [ABSTRACT FROM AUTHOR]

We have studied the optical properties of gold- and silver-infiltrated opal photonic crystals composed of close-packed SiO2 spheres ∼200 nm in diameter. The reflectivity spectra obtained are used to assess the photonic band gap of the crystals in the visible range. We present the characteristics of the emission induced in the opal photonic crystals by monochromatic and broadband light sources and calculated reflectances of the synthetic opal samples. [ABSTRACT FROM AUTHOR]

We have studied the optical properties of opal photonic crystals infiltrated with the M0.35Zn0.65Fe2O4 (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO2 nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap and their refractive index. [ABSTRACT FROM AUTHOR]

Abstract: A systematic series of η5-monocyclopentadienylruthenium(II) complexes with substituted thiophene nitrile ligands of general formula [Ru(η5-C5H5)(P_P)(NC{SC4H2} n NO2)][PF6] (P_P=dppe, (+)-diop; n =1–3) has been synthesized and characterized. Spectroscopic and electrochemical data were used in order to get an insight on the molecular nonlinear optical properties of these complexes when compared to those found for the reported thiophene iron(II) and p-benzonitrile or 1,2-di-(2-thienyl)-ethene derived iron(II)/ruthenium(II) related complexes. The compound [Ru(η5-C5H5)(dppe)(NC{SC4H2}2NO2)][PF6] was also characterized by X-ray diffraction. The solid state nonlinear optical properties of the chiral compounds were also evaluated by Kurtz powder technique with a Nd:YAG laser emitting at 1064nm. [Copyright &y& Elsevier]