Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE(3+) = Eu(3+), Gd(3+) and Tb(3+)) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H(2)O)(2)], [RE(TLA)(H(2)O)(4)] and [RE(TMA)(H(2)O)(G)], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd(3+)-(BTC) complexes showed that the triplet states (T) of the BTC(3-) anions have energy higher than the main emitting states of the Eu(3+) ((5)D(0)) and Tb(3+) ((5)D(4)), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Omega(2)) of Eu(3+)-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited (5)D(0) and (5)D(4) levels of the Eu(3+) and Tb(3+) ions is discussed. The emission quantum efficiencies (eta) of the (5)D(0) emitting level of the Eu(3+) ion have been also determined. In the case of the Tb(3+) ion, the photoluminescence data show the high emission intensity of the characteristic transitions (5)D(4) -> (7)F(J) (J=0-6), indicating that the BTC ligands are good sensitizers. The RE(3+)-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials. (C) 2009 Elsevier B.V. All rights reserved.

Effect of Eu(2)O(3) doping on Ta(2)O(5) crystal growth by the laser-heated pedestal technique

High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications To study the potential of Ta(2)O(5) as a host compound pure and Eu(2)O(3)-doped Ta(2)O(5) crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 pm and in lengths of up to 50 mm The axial temperature gradient at the solid/liquid interface of pure Ta(2)O(5) fibers revealed a critical diameter of 2200 gm above which the fiber cracks X-ray diffraction measurements of the pure Ta(2)O(5) single crystals showed a monoclinic symmetry and a growth direction of [1 (1) over bar 0] An analysis of the pulling rate as a function of the fiber diameter for Eu(2)O(3)-doped Ta(2)O(5) fibers indicated a well defined region in which constitutional supercooling is absent Photoluminescence measurements of pure Ta(2)O(5) crystals using excitation above the band gap (3 8 eV) were dominated by a broad unstructured green band that peaked at 500 nm Three Eu(3+)-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol% Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations The third one was visible in the presence of the triclinic phase (C) 2010 Elsevier B V All rights reserved

Tightened Lieb-Oxford Bound for Systems of Fixed Particle Number

The Lieb-Oxford bound is a constraint upon approximate exchange-correlation functionals. We explore a nonempirical tightening of that bound in both universal and electron number-dependent form. The test functional is PBE. Regarding both atomization energies (slightly worsened) and bond lengths (slightly improved), we find the PBE functional to be remarkably insensitive to the value of the Lieb-Oxford bound. This both rationalizes the use of the original Lieb-Oxford constant in PBE and suggests that enhancement factors more sensitive to sharpened constraints await discovery.

A theoretical study on the XeF(2) molecule

A relativistic four-component study was performed for the XeF(2) molecule by using the Dirac-Coulomb (DC) Hamiltonian and the relativistic adapted Gaussian basis sets (RAGBSs). The comparison of bond lengths obtained showed that relativistic effects on this property are small (increase of only 0.01 angstrom) while the contribution of electron correlation, obtained at CCSD(T) or CCSD-T levels, is more important (increase of 0.05 angstrom). Electron correlation is also dominant over relativistic effects for dissociation energies. Moreover, the correlation-relativity interaction is shown to be negligible for these properties. The electron affinity, the first ionization potential and the double ionization potential are obtained by means of the Fock-space coupled cluster (FSCC) method, resulting in DC-CCSD-T values of 0.3 eV, 12.5 eV and 32.3 eV, respectively. Vibrational frequencies and some anharmonicity constants were also calculated under the four-component formalism by means of standard perturbation equations. All these molecular properties are, in general, ill satisfactory agreement with available experimental results. Finally, a partition in terms of charge-charge flux-dipole flux (CCFDF) contributions derived by means of the quantum theory of atoms in molecules (QTAIM) in non-relativistic QCISD(FC)/3-21G* calculations was carried out for XeF(2) and KrF(2). This analysis showed that the most remarkable difference between both molecules lies on the charge flux contribution to the asymmetric stretching mode, which is negligible in KrF(2) but important in XeF(2). (c) 2008 Elsevier B.V. All rights reserved.

Analysis of the emissions of volatile organic compounds from the compression ignition engine fueled by diesel-biodiesel blend and diesel oil using gas chromatography

This paper describes the procedures of the analysis Of Pollutant gases, as volatile organic compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) emitted by engines, using high-resolution gas chromatography (HRGC). In a broad sense, CI engine burning diesel was compared with B10 and a drastic reduction was observed in the emissions of the aromatic compounds by using B10. Especially for benzene, the reduction of concentrations occurs on the level of about 19.5%. Although a concentration value below 1 mu g ml(-1) has been obtained, this reduction is extremely significant since benzene is a carcinogenic compound. (c) 2008 Elsevier Ltd. All rights reserved.

Validation of a manual headspace gas chromatography method for determining volatile compounds in biological fluids

Background: We report the validation of a method for the determination of acetaldehyde, acetone, methanol, and ethanol in biological fluids using manual headspace sample introduction and an acetonitrile internal standard. Method: This method uses a capillary column (I = 30 m, I.D. = 0.25 mm, dF = 0.25 mu m) installed in a gas chromatography-flame ionization detector (GC-FID) apparatus with a run time of 7.5 minutes. Results: Analysis of the retention times and the resolution of the analyte peaks demonstrated excellent separation without widening of the peaks. Precision and accuracy were good (interassay precision < 15% and recovery between 85% and 115%) in both blood and urine. Conclusion: The method was linear (r > 0.09) over the analytical measurement range (AMR) of each analyte.

Determination of volatile organic compounds in recycled polyethylene terephthalate and high-density polyethylene by headspace solid phase microextraction gas chromatography mass spectrometry to evaluate the efficiency of recycling processes

A method for the determination of volatile organic compounds (VOCs) in recycled polyethylene terephthalate and high-density polyethylene using headspace sampling by solid-phase microextraction and gas chromatography coupled to mass spectrometry detection is presented. This method was used to evaluate the efficiency of cleaning processes for VOC removal from recycled PET. In addition, the method was also employed to evaluate the level of VOC contamination in multilayer packaging material containing recycled HDPE material. The optimisation of the extraction procedure for volatile compounds was performed and the best extraction conditions were found using a 75 mu m carboxen-polydimethylsiloxane (CAR-PDMS) fibre for 20 min at 60 degrees C. The validation parameters for the established method were linear range, linearity, sensitivity, precision (repeatability), accuracy (recovery) and detection and quantification limits. The results indicated that the method could easily be used in quality control for the production of recycled PET and HDPE. (C) 2011 Elsevier B.V. All rights reserved.

Volatile compounds in the thermoplastic extrusion of bovine rumen

The volatile compounds of raw and extruded bovine rumen, extracted by dynamic headspace, were separated by gas chromatography and analyzed by GC-MS. Raw and extruded materials presented thirty-two volatile compounds. The following compounds were identified in raw bovine rumen: heptane, 1-heptene, 4-methyl-2-pentanone, toluene, hexanal, ethyl butyrate, o-xylene, m-xylene, p-xylene, heptanal, limonene, nonanal, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane and octadecane. The following compounds were identified in the extruded material: 1-heptene, 2,4-dimethylhexane, toluene, limonene, undecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane and nonadecane. Mass spectra of some unidentified compounds indicated the presence of hydrocarbons with branched chains or cyclic structure.

Polar organic marker compounds in atmospheric aerosols during the LBA-SMOCC 2002 biomass burning experiment in Rondonia, Brazil: sources and source processes, time series, diel variations and size distributions

Measurements of polar organic marker compounds were performed on aerosols that were collected at a pasture site in the Amazon basin (Rondonia, Brazil) using a high-volume dichotomous sampler (HVDS) and a Micro-Orifice Uniform Deposit Impactor (MOUDI) within the framework of the 2002 LBA-SMOCC (Large-Scale Biosphere Atmosphere Experiment in Amazonia - Smoke Aerosols, Clouds, Rainfall, and Climate: Aerosols From Biomass Burning Perturb Global and Regional Climate) campaign. The campaign spanned the late dry season (biomass burning), a transition period, and the onset of the wet season (clean conditions). In the present study a more detailed discussion is presented compared to previous reports on the behavior of selected polar marker compounds, including levoglucosan, malic acid, isoprene secondary organic aerosol (SOA) tracers and tracers for fungal spores. The tracer data are discussed taking into account new insights that recently became available into their stability and/or aerosol formation processes. During all three periods, levoglucosan was the most dominant identified organic species in the PM(2.5) size fraction of the HVDS samples. In the dry period levoglucosan reached concentrations of up to 7.5 mu g m(-3) and exhibited diel variations with a nighttime prevalence. It was closely associated with the PM mass in the size-segregated samples and was mainly present in the fine mode, except during the wet period where it peaked in the coarse mode. Isoprene SOA tracers showed an average concentration of 250 ng m(-3) during the dry period versus 157 ng m(-3) during the transition period and 52 ng m(-3) during the wet period. Malic acid and the 2-methyltetrols exhibited a different size distribution pattern, which is consistent with different aerosol formation processes (i.e., gas-to-particle partitioning in the case of malic acid and heterogeneous formation from gas-phase precursors in the case of the 2-methyltetrols). The 2-methyltetrols were mainly associated with the fine mode during all periods, while malic acid was prevalent in the fine mode only during the dry and transition periods, and dominant in the coarse mode during the wet period. The sum of the fungal spore tracers arabitol, mannitol, and erythritol in the PM(2.5) fraction of the HVDS samples during the dry, transition, and wet periods was, on average, 54 ng m(-3), 34 ng m(-3), and 27 ng m(-3), respectively, and revealed minor day/night variation. The mass size distributions of arabitol and mannitol during all periods showed similar patterns and an association with the coarse mode, consistent with their primary origin. The results show that even under the heavy smoke conditions of the dry period a natural background with contributions from bioaerosols and isoprene SOA can be revealed. The enhancement in isoprene SOA in the dry season is mainly attributed to an increased acidity of the aerosols, increased NO(x) concentrations and a decreased wet deposition.

A new approach for in vitro bioassay to measure tannin biological effects based on a gas production technique

The aim of this paper was to study a method based on gas production technique to measure the biological effects of tannins on rumen fermentation. Six feeds were used as fermentation substrates in a semi-automated gas method: feed A - aroeira (Astronium urundeuva); feed B - jurema preta (Mimosa hostilis), feed C - sorghum grains (Sorghum bicolor); feed D - Tifton-85 (Cynodon sp.); and two others prepared mixing 450 g sorghum leaves, 450 g concentrate (maize and soybean meal) and 100 g either of acacia (Acacia mearnsii) tannin extract (feed E) or quebracho (Schinopsis lorentzii) tannin extract (feed F) per kg (w:w). Three assays were carried out to standardize the bioassay for tannins. The first assay compared two binding agents (polyethylene glycol - PEG - and polyvinyl polypirrolidone - PVPP) to attenuate the tannin effects. The complex formed by PEG and tannins showed to be more stable than PVPP and tannins. Then, in the second assay, PEG was used as binding agent, and this assay was done to evaluate levels of PEG (0, 500, 750, 1000 and 1250 mg/g DM) to minimize the tannin effect. All the tested levels of PEG produced a response to evaluate tannin effects but the best response was for dose of 1000 mg/g DM. Using this dose of PEG, the final assay was carried out to test three compounds (tannic acid, quebracho extract and acacia extract) to establish a curve of biological equivalent effect of tannins. For this, five levels of each compound were added to I g of a standard feed (Lucerne hay). The equivalent effect showed not to be directly related to the chemical analysis for tannins. It was shown that different sources of tannins had different activities or reactivities. The curves of biological equivalence can provide information about tannin reactivity and its use seems to be important as an additional factor for chemical analysis. (C) 2007 Elsevier B.V. All rights reserved.

A Validated Reverse-phase HPLC Analytical Method for the Quantification of Phenolic Compounds in Baccharis dracunculifolia

Introduction - Baccharis dracunculifolia, which has great potential for the development of new phytotherapeutic medicines, is the most important botanical source of the southeastern Brazilian propolis, known as green propolis on account of its color. Objective - To develop a reliable reverse-phase HPLC chromatographic method for the analysis of phenolic compounds in both B. dracunculifolia raw material and its hydroalcoholic extracts. Methodology - The method utilised a C(18) CLC-ODS (M) (4.6 x 250 mm) column with nonlinear gradient elution and UV detection at 280 nm. A procedure for the extraction of phenolic compounds using aqueous ethanol 90%, with the addition of veratraldehyde as the internal standard, was developed allowing the quantification of 10 compounds: caffeic acid, coumaric acid, ferulic acid, cinnamic acid, aromadendrin-4`-methyl ether, isosakuranetin, drupanin, artepillin C, baccharin and 2,2-dimethyl-6-carboxyethenyl-2H-1-benzopyran acid. Results - The developed method gave a good detection response with linearity in the range 20.83-800 mu g/mL and recovery in the range 81.25-93.20%, allowing the quantification of the analysed standards. Conclusion - The method presented good results for the following parameters: selectivity, linearity, accuracy, precision, robustness, as well as limit of detection and limit of quantitation. Therefore, this method could be considered as an analytical tool for the quality control of B. dracunculifolia raw material and its products in both cosmetic and pharmaceutical companies. Copyright (C) 2008 John Wiley & Sons, Ltd.

Generation of Naphthoquinone Radical Anions by Electrospray Ionization: Solution, Gas-Phase, and Computational Chemistry Studies

Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(center dot-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q + 15](-) was described as being a reaction between the solvent system and the radical anion, Q(center dot-).The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses.

Gas-phase dissociation of 1,4-naphthoquinone derivative anions by electrospray ionization tandem mass spectrometry

Gas-phase dissociation pathways of deprotonated 1,4-naphthoquinone (NQ) derivatives have been investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The major decomposition routes have been elucidated on the basis of quantum chemical calculations at the B3LYP/6-31+G(d,p) level. Deprotonation sites have been indicated by analysis of natural charges and gas-phase acidity. NQ anions underwent an interesting reaction under collision-induced dissociation conditions, which resulted in the radical elimination of the lateral chain, in contrast with the even-electron rule. Possible pathways have been suggested, and their mechanisms have been elucidated on the basis of Gibbs energy and enthalpy values for the anions previously described at each pathway. Copyright (C) 2009 John Wiley & Sons, Ltd.

Supercritical fluid extracts from the Brazilian cherry (Eugenia uniflora L.): Relationship between the extracted compounds and the characteristic flavour intensity of the fruit

Supercritical carbon dioxide (SC-CO(2)) extractions of Brazilian cherry (Eugenia uniflora L.) were carried out under varied conditions of pressure and temperature, according to a central composite 2(2) experimental design, in order to produce flavour-rich extracts. The composition of the extracts was evaluated by gas chromatography coupled with mass spectrometry (GC/MS). The abundance of the extracted compounds was then related to sensory analysis results, assisted by principal component and factorial discriminant analysis (PCA and FDA, respectively). The identified sesquiterpenes and ketones were found to strongly contribute to the characteristic flavour of the Brazilian cherry. The extracts also contained a variety of other volatile compounds, and part of the fruit wax contained long-chain hydrocarbons that according to multivariate analysis, contributed to the yield of the extracts, but not the flavour. Volatile phenolic compounds, to which antioxidant properties are attributed, were also present in the extracts in high proportion, regardless of the extraction conditions. (C) 2010 Elsevier Ltd. All rights reserved.

Stereochemical transfer to atmospheric aerosol particles accompanying the oxidation of biogenic volatile organic compounds

Asymmetric emission profiles of the stereoisomers of plant-derived volatile organic compounds vary with season, geography, plant type, and stress factors. After oxidation of these compounds in the atmosphere, the low-vapor pressure products ultimately contribute strongly to the particle-phase material of the atmosphere. In order to explore the possibility of stereochemical transfer to atmospheric aerosol particles during the oxidation of biogenic volatile organic compounds, second-order coherent vibrational spectra were recorded of the particle-phase organic material produced by the oxidation of different stereoisomeric mixes of alpha-pinene. The spectra show that the stereochemical configurations are not scrambled but instead are transferred from the gas-phase molecular precursors to the particle-phase molecules. The spectra also show that oligomers formed in the particle phase have a handed superstructure that depends strongly and nonlinearly on the initial stereochemical composition of the precursors. Because the stereochemical mix of the precursors for a material can influence the physical and chemical properties of that material, our findings suggest that chirality is also important for such properties of plant-derived aerosol particles. Citation: Ebben, C. J., S. R. Zorn, S.-B. Lee, P. Artaxo, S. T. Martin, and F. M. Geiger (2011), Stereochemical transfer to atmospheric aerosol particles accompanying the oxidation of biogenic volatile organic compounds, Geophys. Res. Lett., 38, L16807, doi: 10.1029/2011GL048599.