bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hierarchical nanoporous anodic alumina templates by asymmetric two‐step anodization
Authors: Santos A. , Ferré‐Borrull J. , Pallarès J. , Marsal L. F. 
Published: December 2010

AbstractAn asymmetric two‐step anodization process is used to fabricate hierarchical nanoporous anodic alumina templates (HNAATs) with different geometric characteristics. This nanostructure consists of an outer hexagonal lattice of concavities in the interior of which pores grow. The anodization conditions (anodization voltage, and type and concentration of the acid electrolyte) between the first and the second step are considerably varied to obtain different types of templates. Two growth regimes (mild and hard), three types of acid electrolytes (phosphoric, oxalic and sulphuric) and three acid electrolyte concentrations (0.3, 0.2 and 0.1 M) are combined. In addition, the voltage ratio between the second and the first step of the anodization process is ranged from 0.11 to 0.71. By modifying these parameters, it is possible to control the fabrication process and obtain HNAATs with a wide range of morphologies.
Exciton polaritons in ZnO microcavities with different active layer thicknesses
Authors: Kawase Toshiki , Kim DaeGwi , Miyazaki Kenichi , Nakayama Masaaki 
Published: December 2010

AbstractWe have investigated the characteristics of exciton polaritons in ZnO microcavities with different active layer thicknesses. The microcavity was made from a bulk ZnO active layer and two distributed Bragg reflectors (DBRs) consisting of HfO2 and SiO2 layers. We adopted rf magnetron sputtering and pulsed laser deposition for the preparation of the DBR and ZnO active layer, respectively. Angle‐resolved reflectance spectra demonstrate the formation of cavity polaritons. From the analysis using a phenomenological Hamiltonian for the coupling between the cavity photon and three kinds of excitons labeled A, B, and C peculiar to ZnO, the vacuum Rabi‐splitting energies in the λ/2‐microcavity are estimated to be 30, 71, and 84 meV for the A, B, and C excitons, respectively. Moreover, we indicate the potential to control the Rabi‐splitting energy by changing the active layer thickness.
Circularly polarized photoluminescence of insulating InGaAs/GaAs heterostructures with a ferromagnetic Mn δ‐layer in the barrier
Authors: Zaitsev S. V. , Zvonkov B. N. 
Published: December 2010

AbstractThe photoluminescence (PL) of insulating heterostructures containing an InGaAs/GaAs quantum well (QW) and a tunneling close ferromagnetic (FM) Mn δ‐layer in the GaAs barrier has been investigated in detail. We found that a slow increase of a circular polarization degree and a Zeeman splitting of the QW emission band at high, normal to the QW plane, magnetic field B > 1 T, characteristic of non‐magnetic QWs, is preceded at low temperatures by a much faster increase at B < 1 T. The fast increase slows down with increasing temperature and disappears above a Curie temperature of the Mn δ‐layer, which evidences effective p–d exchange interaction of the QW holes with Mn ions in the FM δ‐layer.
Non‐standard anisotropy of the energy spectrum of a layered TlGaSe2 crystal
Authors: Bercha D. M. , Glukhov K. E. , Sznajder M. 
Published: December 2010

AbstractThe ab initio band structure calculations of the TlGaSe2 crystal in the framework of DFT, within LDA were performed using the relevant Brillouin zone for the base‐centered monoclinic lattice. It was shown that the main features of this structure can be obtained in the framework of the elementary energy bands concept, taking into account the existence of the Davydov splitting that is the consequence of structural properties of TlGaSe2.The obtained results confirm that TlGaSe2 is an indirect band‐gap material, however, an additional local minimum of the conduction band in the Γ point is located both in a near energetic and near k‐space distance from the absolute minimum. It was shown that TlGaSe2 is the next example of a layered semiconductor for which an universal anisotropy of the energy spectrum branches that coincide with its mechanical anisotropy cannot be established.
Photoluminescence and Raman studies on tin dioxide powder and tin dioxide/single‐walled carbon‐nanotube composites
Authors: Gontia I. I. , Baibarac M. , Baltog I. 
Published: December 2010

AbstractPhotoluminescence (PL) and Raman spectroscopy were used to characterize the tin dioxide (SnO2) powder and the SnO2/single‐walled carbon‐nanotube (SWCNT) composites. The SnO2 powder shows a strong PL broad band centered at 1.95 eV (635 nm) under excitation at 280 nm (4.43 eV) and four PL bands peaking at: 1.95 eV (635 nm), 2.67 eV (464 nm), 2.82 eV (439 nm), and 2.98 eV (416 nm) under excitation at 350 nm (3.54 eV). PL decay‐time measurements of the SnO2 powder indicates a PL lifetime of about 1.53 ns. In the SnO2/SWCNT composites, prepared mechanicochemically, a quenching of PL is observed as the concentration of SWCNT increases. The Raman spectra were recorded at two excitation wavelengths: 514.5 and 676.4 nm. At the excitation wavelength of 676.4 nm (1.83 eV), the Raman spectrum shows a narrowed asymmetric profile of the G band (∼1585 cm−1), which indicates that in the SnO2/SWCNT composite there is an interaction between SnO2 and metallic SWCNTs.
Examination of long‐wave radiative bias in general circulation models over North Africa during May–July
Authors: Allan Richard P. , Woodage Margaret J. , Milton Sean F. , Brooks Malcolm E. , Haywood James M. 
Published: December 2010

AbstractSatellite data are used to quantify and examine the bias in the outgoing long‐wave (LW) radiation over North Africa during May–July simulated by a range of climate models and the Met Office global numerical weather prediction (NWP) model. Simulations from an ensemble‐mean of multiple climate models overestimate outgoing clear‐sky long‐wave radiation (LWc) by more than 20 W m−2relative to observations from Clouds and the Earth's Radiant Energy System (CERES) for May–July 2000 over parts of the west Sahara, and by 9 W m−2for the North Africa region (20°W–30°E, 10–40°N). Experiments with the atmosphere‐only version of the High‐resolution Hadley Centre Global Environment Model (HiGEM), suggest that including mineral dust radiative effects removes this bias. Furthermore, only by reducing surface temperature and emissivity by unrealistic amounts is it possible to explain the magnitude of the bias.Comparing simulations from the Met Office NWP model with satellite observations from Geostationary Earth Radiation Budget (GERB) instruments suggests that the model overestimates the LW by 20–40 W m−2during North African summer. The bias declines over the period 2003–2008, although this is likely to relate to improvements in the model and inhomogeneity in the satellite time series. The bias in LWc coincides with high aerosol dust loading estimated from the Ozone Monitoring Instrument (OMI), including during the GERBILS field campaign (18–28 June 2007) where model overestimates in LWc greater than 20 W m−2and OMI‐estimated aerosol optical depth (AOD) greater than 0.8 are concurrent around 20°N, 0–20°W. A model‐minus‐GERB LW bias of around 30 W m−2coincides with high AOD during the period 18–21 June 2007, although differences in cloud cover also impact the model–GERB differences. Copyright © Royal Meteorological Society and Crown Copyright, 2010
Determination of distinctive carbohydrate signatures obtained from the Aeromonas hydrophila (chemotype II) core oligosaccharide pinpointing the presence of the 4‐O‐phosphorylated 5‐O‐linked Kdo reducing end group using electrospray ionization quadrupole orthogonal time‐of‐flight mass spectrometry and tandem mass spectrometry
Authors: Sioud Salim , Jahouh Farid , Nashed Mina , Joly Nicolas , Banoub Joseph H. 
Published: December 2010

AbstractThe electrospray quadrupole orthogonal time‐of‐flight mass spectrometric (ESI‐QqTOF‐MS) structural elucidation of the core oligosaccharide of Aeromonas hydrophila (chemotype II) lipopolysaccharide has been investigated and it was demonstrated that it contained an 4‐O‐phosphorylated Kdo reducing end group, which was glycosylated by the remaining outer core oligosaccharide through its O‐5 position. After releasing the core oligosaccharide from the native LPS with acid, the phosphorylated Kdo residue eliminated phosphoric acid, to produce a core oligosaccharide containing a mixture of diastereomeric 4,8‐ and 4,7‐anhydro‐α‐keto acids and an open‐chain olefinic Kdo residue. The characteristic glycone sequence was elucidated by collision‐induced dissociation tandem mass spectrometry (CID‐MS/MS) of the protonated molecule of the native core oligosaccharide.In addition, the analysis of the Hakomori permethylated core oligosaccharide was carried out by electrospray ionization quadrupole orthogonal time‐of‐flight mass spectrometry (ESI‐QqTOF‐MS) and matrix‐assisted laser desorption/ionization (MALDI)‐QqTOF‐MS analyses. The presence of more than nine isobaric isomers of this core was detected. The CID‐MS/MS analysis of the various protonated permethylated core oligosaccharide molecules showed a similar and diagnostic fragmentation pattern. The over‐methylation of the permethylated core oligosaccharide containing either the 4,7‐ or the 4,8‐anhydro‐α‐keto acid unit and the open‐chain olefinic Kdo unit was reported. It was realized that the extra minor satellite signals obtained in the ESI‐QqTOF‐MS and MALDI‐TOF‐MS analyses were dimethyl sulfoxide (DMSO) stable covalent addition products, which have occurred by a Michael addition on the 4,8‐Kdo exocyclic double bond. The occurrence of this series of covalent addition products during the MS analysis of a permethylated core oligosaccharide should be considered as ‘carbohydrate‐distinctive signatures’ establishing and confirming the presence of a 4‐O‐phosphorylated‐5‐O‐linked Kdo reducing end group. Copyright © 2010 John Wiley & Sons, Ltd.
δ15N of soil N and plants in a N‐saturated, subtropical forest of southern China
Authors: Koba K. , Isobe K. , Takebayashi Y. , Fang Y.T. , Sasaki Y. , Saito W. , Yoh M. , Mo J. , Liu L. , Lu X. , Zhang T. , Zhang W. , Senoo K. 
Published: December 2010

AbstractWe investigated the δ15N profile of N (extractable NH, NO, and organic N (EON)) in the soil of a N‐saturated subtropical forest. The order of δ15N in the soil was EON > NH > NO. Although the δ15N of EON had been expected to be similar to that of bulk soil N, it was higher than that of bulk soil N by 5‰. The difference in δ15N between bulk soil N and EON (Δ15Nbulk‐EON) was correlated significantly with the soil C/N ratio. This correlation implies that carbon availability, which determines the balance between N assimilation and dissimilation of soil microbes, is responsible for the high δ15N of EON, as in the case of soil microbial biomass δ15N. A thorough δ15N survey of available N (NH, NO, and EON) in the soil profiles from the organic layer to 100 cm depth revealed that the δ15N of the available N forms did not fully overlap with the δ15N of plants. This mismatch in δ15N between that of available N and that of plants reflects apparent isotopic fractionation during N uptake by plants, emphasizing the high N availability in this N‐saturated forest. Copyright © 2010 John Wiley & Sons, Ltd.
Limitations of mass spectrometric methods for the characterization of polydisperse materials
Authors: Herod Alan A. 
Published: December 2010

AbstractThis paper is a review of work on the characterization of coal liquids and petroleum residues and asphaltenes over several decades in which various mass spectrometric methods have been investigated. The limitations of mass spectrometric methods require exploration in order to understand what the different analytical methods can reveal about environmental pollution by these kinds of samples and, perhaps more importantly, what they cannot reveal.The application of mass spectrometry to environmental problems generally requires the detection and determination of the concentration of specific pollutants released into the environment by accident or design. The release of crude petroleum or coal liquids into the environment can be detected and tracked during biodegradation processes through specific chemicals such as alkanes or polyaromatic hydrocarbons (PAHs). However, petroleum asphaltenes are polydisperse materials of unknown mass range and chemical structures and, therefore, there are no individual chemicals to detect. It is necessary to determine methods of detection and the ranges of mass of such materials. This can only be achieved through fractionation to reduce the polydispersity of the initial sample. Comparison of mass spectrometric results with results from an independent analytical method such as size‐exclusion chromatography with a suitable eluent is advisable to confirm that all the sample has been detected and mass discrimination effects avoided. Copyright © 2010 John Wiley & Sons, Ltd.
Minimization of sample requirement for δ18O in benzoic acid
Authors: Hagopian William M. , Jahren A. Hope 
Published: December 2010

AbstractThe measurement of the oxygen stable isotope content in organic compounds has applications in many fields, ranging from paleoclimate reconstruction to forensics. Conventional High‐Temperature Conversion (HTC) techniques require >20 µg of O for a single δ18O measurement. Here we describe a system that converts the CO produced by HTC into CO2 via reduction within a Ni‐furnace. This CO2 is then concentrated cryogenically, and 'focused' into the isotope ratio mass spectrometry (IRMS) source using a low‐flow He carrier gas (6–8 mL/min). We report analyses of benzoic acid (C7H6O2) reference materials that yielded precise δ18O measurement down to 1.3 µg of O, suggesting that our system could be used to decrease sample requirement for δ18O by more than an order of magnitude. Copyright © 2010 John Wiley & Sons, Ltd.
Role of 2‐oxo and 2‐thioxo modifications on the proton affinity of histidine and fragmentation reactions of protonated histidine
Authors: Lam Adrian K. Y. , Hutton Craig A. , O'Hair Richard A. J. 
Published: December 2010

AbstractA combination of electrospray ionisation (ESI), multistage and high‐resolution mass spectrometry experiments was used to compare the gas‐phase chemistry of the amino acids histidine (1), 2‐oxo‐histidine (2), and 2‐thioxo‐histidine (3). Collision‐induced dissociation (CID) of all three different proton‐bound heterodimers of these amino acids led to the relative gas‐phase proton affinity order of: histidine >2‐thioxo‐histidine >2‐oxo‐histidine. Density functional theory (DFT) calculations confirm this order, with the lower proton affinities of the oxidised histidine derivatives arising from their ability to adopt the more stable keto/thioketo tautomeric forms. All protonated amino acids predominately fragment via the combined loss of H2O and CO to yield a1 ions. Protonated 2 and 3 also undergo other small molecule losses including NH3 and the imine HN=CHCO2H. The observed differences in the fragmentation pathways are rationalised through DFT calculations, which reveal that while modification of histidine via the introduction of the oxygen atom in 2 or the sulfur atom in 3 does not affect the barriers against the loss of H2O+CO, barriers against the losses of NH3 and HN=CHCO2H are lowered relative to protonated histidine. Copyright © 2010 John Wiley & Sons, Ltd.
Ionspray microchip
Authors: Pól Jaroslav , Kauppila Tiina J. , Franssila Sami , Kotiaho Tapio , Kostiainen Risto 
Published: December 2010

AbstractAn ionspray microchip is introduced. The chip is based on the earlier presented nebulizer microchip that consists of glass and silicon plates bonded together. A liquid inlet channel, nebulizer gas inlet, and nozzle are etched on the silicon plate and a platinum heater is integrated on the glass plate. The nebulizer microchip has been previously used in atmospheric pressure chemical ionization, atmospheric pressure photoionization, sonic spray ionization, and thermospray ionization modes. In this work we show that the microchip can be operated also in ionspray mode by introducing high voltage to the silicon plate of the microchip. The effects of operation parameters (voltage, nebulizer gas pressure, sample solution flow rate, solvent composition, and analyte concentration) on the performance of the ion spray microchip were studied. Under optimized conditions the microchip provides efficient ionization of small and large compounds and good quantitative performance. The feasibility of the ion spray microchip in liquid chromatography/mass spectrometry (LC/MS) was demonstrated by the analysis of tryptic peptides of bovine serum albumin. Copyright © 2010 John Wiley & Sons, Ltd.
Electron ionisation mass spectrometry of the pentafluoropropionate esters of trichothecene analogues and culmorin compounds from Fusarium species
Authors: Langseth Wenche , Rundberget Thomas , Uhlig Silvio 
Published: December 2010

AbstractThis paper reports the mass spectra, obtained after electron ionisation (EI) at 70 eV, of 34 trichothecenes and five culmorin compounds after acylation with pentafluoropropionic anhydride. The derivatised fungal metabolites were separated by gas chromatography, and the mass spectra were obtained by scanning of a single quadrupole mass filter in the scan range m/z 200‐900. The fragmentation pathways of three trichothecenes (triacetyl‐deoxynivalenol, 4,15‐diacetoxy‐scirpenol, T‐2 toxin) have been studied in more detail by linked scan – high‐resolution mass spectrometry. The most common trichothecenes are today more often routinely analysed using LC/MS‐based methodologies. However, EI‐MS may give complementary structural information, and the data that are summarised in this article may help to identify analogues of one of the largest class of mycotoxins, the tricothecenes, as well as culmorin compounds that are commonly co‐produced by Fusarium culmorum and F. graminearum in cultures or naturally contaminated samples. Copyright © 2010 John Wiley & Sons, Ltd.
Quantitation of a de‐fluorinated analogue of Casopitant Mesylate by normal‐phase liquid chromatography/mass spectrometry
Authors: Dams Riet , Bernabe Elena , Nicoletti Anna , Loda Claudio , Martini Luca , Papini Damiano 
Published: December 2010

AbstractThe introduction of Quality by Design (QbD) in Drug Development has resulted in a greater emphasis on chemical process understanding, in particular on the origin and fate of impurities. Therefore, the identification and quantitation of low level impurities in new Active Pharmaceutical Ingredients (APIs) play a crucial role in project progression and this has created a greater need for sensitive and selective analytical methodology. Consequently, scientists are constantly challenged to look for new applications of traditional analytical techniques. In this context a normal‐phase liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) method was developed to determine the amount of a de‐fluorinated analogue impurity in Casopitant Mesylate, a new API under development in GlaxoSmithKline, Verona. Normal‐phase LC provided the selectivity needed between our target analyte and Casopitant, while a single quadrupole mass spectrometer was used to ensure the sensitivity needed to detect the impurity at <0.05%w/w. Standard solutions and samples were prepared in heptane/ethanol (50:50, v/v) containing 1% of 2 M NH3 in ethanol; the mobile phase consisted of heptane/ethanol (95:5, v/v) with isocratic elution (flow rate: 1.0 mL/min, total run time: 23 min). To allow the formation of ions in solutions under normal‐phase (apolar) conditions, a post‐column infusion of a solution of 0.1% v/v of formic acid in methanol was applied (flow rate: 200 µL/min). The analysis was carried out in positive ion mode, monitoring the impurity by single ion monitoring (SIM). The method was fully validated and its applicability was demonstrated by the analysis of real‐life samples. This work is an example of the need for selective and accurate methodology during the development of a new chemical entity in order to develop an appropriate control strategy for impurities to ultimately ensure patient safety. Copyright © 2010 John Wiley & Sons, Ltd.
Analysis of epoxyeicosatrienoic acids by chiral liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry using [13C]‐analog internal standards
Authors: Mesaros Clementina , Lee Seon Hwa , Blair Ian A. 
Published: December 2010

AbstractThe metabolism of arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) is thought to be mediated primarily by the cytochromes P450 (P450s) from the 2 family (2C9, 2C19, 2D6, and 2J2). In contrast, P450s of the 4 family are primarily involved in omega oxidation of AA (4A11 and 4A22). The ability to determine enantioselective formation of the regioisomeric EETs is important in order to establish their potential biological activities and to asses which P450 isoforms are involved in their formation. It has been extremely difficult to analyze individual EET enantiomers in biological fluids because they are present in only trace amounts and they are extremely difficult to separate from each other. In addition, the deuterium‐labeled internal standards that are commonly used for stable isotope dilution liquid chromatography/mass spectrometry (LC/MS) analyses have different LC retention times when compared with the corresponding protium forms. Therefore, quantification by LC/MS‐based methodology can be compromised by differential suppression of ionization of the closely eluting isomers. We report the preparation of [13C20]‐EET analog internal standards and the use of a validated high‐sensitivity chiral LC/electron capture atmospheric pressure chemical ionization (ECAPCI)‐MS method for the trace analysis of endogenous EETs as their pentafluorobenzyl (PFB) ester derivatives. The assay was then used to show the exquisite enantioselectivity of P4502C19‐, P4502D6‐, P4501A1‐, and P4501B1‐mediated conversion of AA into EETs and to quantify the enantioselective formation of EETs produced by AA metabolism in a mouse epithelial hepatoma (Hepa) cell line. Copyright © 2010 John Wiley & Sons, Ltd.
Structural characterization and identification of oleanane‐type triterpene saponins in Glycyrrhiza uralensis Fischer by rapid‐resolution liquid chromatography coupled with time‐of‐flight mass spectrometry
Authors: Zheng Yun‐Feng , Qi Lian‐Wen , Zhou Jian‐Liang , Li Ping 
Published: December 2010

AbstractOleanane‐type triterpene saponins (OTS) are major active ingredients in Glycyrrhiza uralensis. In this work, a rapid‐resolution liquid chromatography with time‐of‐flight mass spectrometry (RRLC/TOF‐MS) method has been developed to characterize and identify OTS from G. uralensis. The major diagnostic ions and fragmentation pathways from thirteen OTS have been characterized for the first time. At a low fragmentor voltage of 120 V in positive ion mode, the precursor ion [M + H]+ or/and [M + Na]+ was obtained for accurate determination of molecular formula. When the fragmentor voltage was increased to 425 V, abundant characteristic fragment ions were observed for structural characterization. Neutral losses of sugar moieties, such as glucuronic acid (GlcA, 176 Da), glucose (Glc, 162 Da) and rhamnose (Rha, 146 Da), were commonly observed in the MS spectra for prediction of the sugar number and sequences. Other typical losses included AcOH (60 Da), CH2O (30 Da), 2 × H2O (2 × 18 Da) and HCOOH (46 Da) from [Aglycone + H–H2O]+ (named [B]+), corresponding to the presence of a C22‐acetyl group, C24‐hydroxyl group, C22‐hydroxyl group or C30‐carboxyl group on the aglycone moiety, respectively. In particular, characteristic ring cleavages of the aglycone moieties on A‐ and B‐rings were observed. Based on the fragmentation patterns of reference compounds, nineteen OTS have been identified in an extract of G. uralensis, thirteen of which were unambiguously identified and the other six were tentatively assigned. Copyright © 2010 John Wiley & Sons, Ltd.