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PubMedDate not supplied

Lipase-catalyzed synthesis of a pure macrocyclic polyester from dimethyl terephthalate and diethylene glycol.

The polymerization of dimethyl terephthalate and diethylene glycol by enzymic catalysis in toluene is described. The potential pi-pi interactions of the aromatic rings together with the relative flexibility of the diol segment have been regarded as synergy factors responsible for the formation of a pure cyclic compound. The so-called C2 macrocycle was characterized by (1)H and (13)C NMR, size-exclusion chromatography, differential scanning calorimetry, mass spectrometry, and X-ray diffraction on powder. Structurally speaking, it is made of two repeating units. The substitution of the central oxygen atom of the diol by -CH(2)- or -S- as well as the presence of ortho-substituents (-NH(2) or -NO(2)) on the phthalate were expected to disrupt the stacking of the phenyl groups more or less.

Catalysis↗
PubMed2004

Speciation of PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc smelters.

The purpose of this study was to estimate the speciation of PM10 sources of airborne Pb, Zn, and Cd metals (PM10 is an aerosol standard of aerodynamic diameter less than 10 microm.) in the atmosphere of a 3 km zone surrounding lead/zinc facilities in operation for a century. Many powdered samples were collected in stacks of working units (grilling, furnace, and refinery), outdoor storages (ores, recycled materials), surrounding waste slag (4 Mt), and polluted topsoils (3 km). PM10 samples were generated from the raw powders by using artificial resuspension and collection devices. The bulk PM10 multielemental analyses were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The proportions in mass of Pb (50%), Zn (40%), and Cd (1%) contents and associated metals (traces) reach the proportions of corresponding raw powdered samples of ores, recycled materials, and fumesize emissions of plants without specific enrichment. In contrast, Pb (8%) and Zn (15%) contents of PM10 of slag deposit were found to be markedly higher than those of raw dust, Pb (4%), and Zn (9%), respectively. In the same way, Pb (0.18%), Zn (0.20%), and Cd (0.004%) were enriched by 1.7, 2.1, and 2.3 times, respectively, in PM10 as compared with raw top-soil corresponding values. X-ray wavelength dispersive electron-microprobe (EM-WDS) microanalysis did not indicate well-defined phases or simple stoichiometries of all the PM10 samples atthe level of the spatial resolution (1 microm3). X-ray photoelectron spectroscopy (XPS) indicated that minor elements such as Cd, Hg, and C are more concentrated on the particle surface than in the bulk of PM10 generated by the smelting processes. (XPS) provided also the average speciation of the surface of PM10; Pb is mainly represented as PbSO4, Zn as ZnS, and Cd as CdS or CdSO4, and small amounts of coke were also detected. The speciation of bulk PM10 crystallized compounds was deduced from XRD diffractograms with a raw estimation of the relative quantities. PbS and ZnS were found to be the major phases in PM10 generated by the smelting facilities with PbSO4, PbSO4 x PbO, PbSO4 x 4PbO, Pb metal, and ZnO as minor phases. The slag waste PM10 was found to contain some amounts of PbCO3, PbSO4 x PbO, and ZnFe2O4 phases. The large heterogeneity at the level of the individual particle generates severe overlap of chemical information even at the microm scale using electron microprobe (WDS) and Raman microprobe techniques. Fortunately, scanning Raman microspectrometry combined with SIMPle-to-use Interactive Self-modeling Mixture Analysis (SIMPLISMA) performed the PM10 speciation at the level of individual particles. The speciation of major Pb, Zn, and Cd compounds of PM10 stack emissions and wind blown dust of ores and recycled materials were found to be PbSO4, PbSO4 x PbO, PbSO4 x 4PbO, PbO, metallic Pb, ZnS, ZnO, and CdS. The PM10 dust of slag waste was found to contain PbCO3, Pb(OH)2 x 2PbCO3, PbSO4 x PbO, and ZnS, while PM10-bound Pb, Zn of the top-soils contain Pb5(PO4)3Cl, ZnFe2O4 as well as Pb(II) and Zn(II) compounds adsorbed on Fe(III) oxides and in association with clays.

Air Pollutants↗
PubMed2002

Construction of a functional layered solid using the tetrakis(imidazolyl)borate coordinating anion.

The coordination polymer Pb[B(Im)(4)](NO(3)), constructed by using tetrakis(imidazolyl)borate and lead(II) nitrate solutions, is a layered material with the metal centers facing the interlayer spacing. As in naturally occurring layered minerals, this compound can readily undergo anion exchange in the solid state with retention of crystallinity. We examined stoichiometric exchange of (15)N-nitrate for nitrate and iodide for nitrate by (15)N and (207)Pb SSNMR and confirmed retention of crystallinity by IR and powder XRD diffraction.

Journal Article↗
PubMed2005

Synthesis, structure, and magnetic properties of Sr2NiOsO6 and Ca2NiOsO6: two new osmium-containing double perovskites.

Two new double perovskite oxides, Ca(2)NiOsO(6) and Sr(2)NiOsO(6), have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca(2)NiOsO(6) was found to adopt a monoclinic structure (P2(1)/n), while Sr(2)NiOsO(6) was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca(2)NiOsO(6) orders in a canted antiferromagnetic state at about 175 K while Sr(2)NiOsO(6) orders antiferromagnetically at about 50 K.

Journal Article↗
PubMed1998

Crystal Structures of AuCN and AgCN and Vibrational Spectroscopic Studies of AuCN, AgCN, and CuCN.

The crystal structures of AuCN and AgCN have been determined by powder neutron diffraction measurements. The structure of AuCN consists of rows of linear AuCN chains parallel to [001] with alternating long Au-C = 2.06(2) and short Au-N = 1.82(2) Å. The Au atoms form sheets and are bonded to 6 other Au atoms at a distance of 3.396(2) Å, so that the local environment of each Au atom can be described as a compressed scalehedron. The Au- - -Au distance is within the range expected for an "aurophilic attraction" between these atoms. The AgCN structure is very similar to that for AuCN, in that it consists of rows of AgCN chains with alternating long Ag-C = 2.15(6) and short Ag-N = 1.86(8) Å. The major difference is that the Ag- - -Ag separation within the Ag sheets is noticeably longer, 3.881(5) Å, so that there are no significant Ag- - -Ag interactions. The IR spectra of MCN show nu(CN) at 2170, 2164, 2236; nu(MC,MN) at 591, 480, 598; delta(MCN) at 326, 272, 358; and delta(NMC) = 168, 112, 224 cm(-)(1) for M = Cu, Ag, and Au, respectively. This pattern of band positions strongly suggests that CuCN has the same infinite linear chain structure as AgCN and AuCN. Anomalies in the previously reported IR spectrum of CuCN are shown to be due to the formation of an unusual CuCN/KBr/H(2)O product in KBr disks, which is possibly an intercalation compound involving incorporation of KBr and H(2)O between the chains in the CuCN structure.

Journal Article↗
PubMed1998

Structure of LaMo(2)O(5) Containing Both Isolated Mo(6)O(18) Clusters and Sheets of Fused Triangular Mo(3) Clusters.

The structure of the disordered lanthanum molybdate, LaMo(2)O(5), has been solved and refined using powder neutron diffraction data collected at 300 K. The average structure is described in P6(3)/mmc, a = 8.373(1) Å, c = 19.1510(1) Å, Z = 12. The compound contains two types of Mo-Mo bonded units: isolated octahedral Mo(6)O(18) clusters, and infinite molybdenum oxide sheets, formed from condensed triangular Mo(3)O(13) clusters joined together to give a total of four Mo-Mo bonds for each molybdenum. The Mo(6)O(18) clusters have 16 electrons available for metal-metal bonding and the Mo-Mo distances within the unit are 2.643(4) Å x 6 and 2.695(5) Å x 6. In the infinite sheets the molybdenum-molybdenum distances are 2.612(9) Å within one equilateral triangular cluster and 2.621(8) Å within another. Each of the molybdenum atoms in the two different Mo(3) clusters has two molybdenum neighbors from the other cluster at a distance of 2.882(6) Å. Disorder in this layered structure occurs because of interchange of layers of Mo sheets with layers of lanthanum ions. The Bragg scattering is accounted for by including layers occupied with a 50% probability by each of these structural elements and their associated oxygen atoms. A model showing how ordered subunits are stacked together to produce the average structure is presented. Extended X-ray absorption fine structure spectroscopy (EXAFS) at the Mo K-edge was used to give information on the local structure around molybdenum and to confirm that the final structural model gives a good description of Mo-O and Mo-Mo bonding.

Journal Article↗
PubMed1999

Synthesis and Structure of NaZnSiO(3)OH, a New Chiral Zincosilicate Framework Material.

The structure of NaZnSiO(3)OH, synthesized hydrothermally by reaction of Na(2)ZnSiO(4) and NaOH, has been determined from single-crystal X-ray and powder neutron diffraction data (orthorhombic, space group P2(1)2(1)2(1,) a = 7.6872(2) Å, b = 9.3899(2) Å, c = 5.155(1) Å, Z = 4). The structure has a framework constructed from ZnO(4) and SiO(3)OH tetrahedra with bridging and trigonal oxygen atoms. Channels formed from eight-membered rings of tetrahedra house the sodium ions and are also partially blocked by moderately strongly hydrogen bonded OH groups.

Journal Article↗
PubMed1999

Structure, Chemical Bonding, and Nuclear Quadrupole Interactions of beta-Cd(OH)(2): Experiment and First Principles Calculations.

The structure of Cd(OH)(2) was determined by X-ray diffraction on powder crystals and by calculations using the full-potential linearized augmented plane wave method. Good agreement between the two results was found. The chemical bonding is characterized by the interactions of the OH(-) group with Cd(2+) which is not only electrostatic but shows some polarization or covalent admixtures and by the covalent bond in the OH(-) group. The electric field gradient (EFG) was calculated and compared with an experimental determination of the nuclear quadrupole interaction using perturbed angular correlation of gamma-rays. The calculated EFG agrees well with the EFG derived from experiment. The total electric field gradient was decomposed into contributions from different orbitals and energy regions showing that both the Cd 5p and 4d wave functions contribute significantly. Finally, the influence of spin-orbit coupling on the electric field gradient was investigated and found to be of little importance.

Journal Article↗
PubMed2002

Magnetic structure of the europium fulleride ferromagnet Eu(6)C(60).

The powder neutron diffraction technique has been used for the direct observation of magnetic scattering below a Curie temperature of approximately 14 K in the fullerene-based molecular ferromagnet Eu6C60. Europium is in the divalent state with a magnetic moment of 7.1(3) muB per atom, and the configurational symmetry of the magnetic structure is body-centered cubic. Close contacts between Eu2+ and neighboring C60 units provide the signature of orbital hybridization, which can evidently account for the conducting and magnetic properties of the material.

Journal Article↗
PubMed2005

One-pot synthesis of hollow superparamagnetic CoPt nanospheres.

Hollow metal nanospheres are of interest for a variety of academic and technological applications, including drug delivery, catalysis, plasmonics, and lightweight structural composites. Despite recent advances in synthesizing metal nanostructures with controlled morphologies, there are very few reports of hollow bimetallic nanospheres, although such systems promise to offer advantages over single-metal systems. Here, were report a one-pot synthetic strategy for accessing hollow CoPt nanospheres with a Co-Pt alloy structure. The approach utilizes an in situ Co template and exploits galvanic displacement reactions to selectively dissolve the Co core while depositing a Pt shell. The combination of reducing conditions and a polymer stabilizer appears to allow the Co and Pt to co-reduce and form a Co-Pt fcc alloy phase with a morphology that is templated by the sacrificial Co core. The hollow CoPt nanospheres, which show magnetic hysteresis at low temperatures, are thermally stable up to 300 degrees C. The approach, which adds to a growing toolbox of reactions that yield morphologically controlled magnetic CoPt and FePt nanomaterials, is likely to be general for a variety of alloy systems.

Alloys↗
PubMed2006

Demonstrating oxygen loss and associated structural reorganization in the lithium battery cathode Li[Ni0.2Li0.2Mn0.6]O2.

The cathode in rechargeable lithium-ion batteries operates by conventional intercalation; Li+ is extracted from LiCoO2 on charging accompanied by oxidation of Co3+ to Co4+; the process is reversed on discharge. In contrast, Li+ may be extracted from Mn4+-based solids, e.g., Li2MnO3, without oxidation of Mn4+. A mechanism involving simultaneous Li and O removal is often proposed. Here, we demonstrate directly, by in situ differential electrochemical mass spectrometry (DEMS), that O2 is evolved from such Mn4+ -containing compounds, Li[Ni(0.2)Li(0.2)Mn(0.6)]O2, on charging and using powder neutron diffraction show that O loss from the surface is accompanied by diffusion of transition metal ions from surface to bulk where they occupy vacancies created by Li removal. The composition of the compound moves toward MO(2). Understanding such unconventional Li extraction is important because Li-Mn-Ni-O compounds, irrespective of whether they contain Co, can, after O loss, store 200 mAhg(-1) of charge compared with 140 mAhg(-1) for LiCoO(2).

Journal Article↗
PubMed2006

La3Ni2O6: a new double T'-type nickelate with infinite Ni1+/2+O2 layers.

New mixed-valent, Ni1+/Ni2+, metastable nickelate, La3Ni2O6, was synthesized by low-temperature reduction of La3Ni2O7 with CaH2. The crystal structure of La3Ni2O6 (space group: I4/mmm, a = 3.9686(1) A and c = 19.3154(6) A) was determined from powder neutron diffraction data by Rietveld analysis. The structure can be described as an intergrowth of LaO2 fluorite and double infinite layer (LaNiO2)2 blocks and represents the n = 2 homologue of the T'-type series Lan+1NinO2n+2. Such double T'-type structural arrangement has never been observed before. The 3d9/3d8 electronic configuration of Ni1+/Ni2+ and the presence of NiO2 infinite layers resemble electronic and structural features of the superconducting cuprates. X-ray absorption spectroscopy supports the 1+/2+ oxidation state and planar coordination of Ni in agreement with the structure determination.

Journal Article↗
PubMed2005

Plastic and glassy crystal states of caffeine.

The present paper focuses on the high temperature form I of caffeine and on its low temperature metastable form. Structural, dynamic, and kinetic information has been obtained by X-ray, dielectric, and calorimetric investigations. This study shows the following features: (1) The high temperature phase (I) of caffeine is in a state of dynamically orientationally disordered crystalline state (so-called "plastic, or rotator, phase"). (2) This high-symmetry hexagonal phase can be maintained at low temperature in a metastable situation. (3) Under deep undercooling of form I a glass transition occurs in the disordered crystalline state near room temperature. It is associated with the orientational freezing in of the molecular motions. Otherwise stated, the metastable state I enters into a nonergodic unstable state, so-called "glassy crystal" state. These findings rationalize the difficulties seen with caffeine in pharmaceutical science.

Caffeine↗
PubMed2006

Growth of single-crystalline KNbO3 nanostructures.

This communication reports on the growth of highly uniform KNbO3 nanowires exhibiting a narrow diameter distribution around 60 nm and a length-to-width ratio up to 100. The nanowires were prepared by a hydrothermal route, which enables simple, gram-scale production. A systematic study of the synthesized nanowires in terms of the morphological and chemical characteristics was carried out by varying the temperature-pressure conditions and the composition of the starting mixture. The results indicate that highly uniform single-crystalline nanowires form within a narrow window of the ternary phase diagram of KOH-Nb2O5-H2O.

Crystallization↗
PubMed2006

Mechanochemical synthesis and crystal structure of alpha'-AlD3 and alpha-AlD3.

AlD3 AlD3 was synthesized by ball milling of 3LiAlD4 + AlCl3. Planetary ball milling at room temperature resulted in a mixture of AlD3 (alpha and alpha') and Al in addition to LiCl, whereas cryomilling at 77 K resulted in only AlD3 and LiCl. The AlD3 obtained was a mixture of about 2/3alpha and 1/3alpha'. Alpha' was determined by powder neutron diffraction to take the beta-AlF3 structure with space group Cmcm and a = 6.470(3), b = 11.117(5), and c = 6.562(2) A. It is built up of corner-sharing AlD6 octahedra in an open structure with hexagonal holes of radius 3.9 A. Alpha' slowly decomposes during storage at 40 degrees C. Alpha-AlD3 is also described by a corner-sharing AlD6 network but in a more dense ReO3-type arrangement. Both AlD3 modifications have slightly shorter Al-D distances compared to Na3AlD6, Na2LiAlD6, and K2NaAlH6.

Journal Article↗
PubMed2006

Formation of orientation-ordered superlattices of magnetite magnetic nanocrystals from shape-segregated self-assemblies.

Magnetic magnetite (Fe3O4) nanocrystals have been synthesized by combining nonhydrolytic reaction with seed-mediated growth. The shape of these magnetite nanocrystals can be controlled either as pure spheres or a mixture of mainly faceted nanocrystals. Faceted magnetite nanocrystals consist of truncated tetrahedral platelets (TTPs), truncated octahedrons (TOs), and octahedrons (OTs). Transmission electron microscopy analysis indicates that the faceted nanocrystal mixture tends to self-segregate based upon the shape in a self-assembly process, and each shape forms its own distinct crystallographic orientation-ordered superlattice assemblies. Self-assemblies of the Fe3O4 nanocrystals in the shapes of TTP, TO, and OT show hexagonal, primitive cubic, and distorted body-centered cubic (bcc) superlattice structures, respectively. The possible mechanism for the formation of different superstructures is attributed to van der Waals interactions. Nanocrystals with different shapes provide diverse building blocks for bottom-up approaches in building nano- and mesosystems. Furthermore, the self-segregation phenomenon of different shaped nanocrystals in self-assembly processes could be very important in envisioning efficient assembly strategies for nanoscience- and nanotechnology-based devices.

Crystallization↗
PubMed2006

Conversion between hexagonal GaN and beta-Ga(2)O(3) nanowires and their electrical transport properties.

We have observed that the hexagonal GaN nanowires grown from a simple chemical vapor deposition method using gallium metal and ammonia gas are usually gallium-doped. By annealing in air, the gallium-doped hexagonal GaN nanowires could be completely converted to beta-Ga(2)O(3) nanowires. Annealing the beta-Ga(2)O(3) nanowires in ammonia could convert them back to undoped hexagonal GaN nanowires. Field effect transistors based on these three kinds of nanowires were fabricated, and their performances were studied. Because of gallium doping, the as-grown GaN nanowires show a weak gating effect. Through the conversion process of GaN nanowires (gallium-doped) --> Ga(2)O(3) nanowires --> GaN nanowires (undoped) via annealing, the final undoped GaN nanowires display different electrical properties than the initial gallium-doped GaN nanowires, show a pronounced n-type gating effect, and can be completely turned off.

Gallium↗