bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and kinetics of graft polymerization of methyl methacrylate from the RAFT coordinated surface of nano‐TiO2
Authors: Hojjati Behnaz , Charpentier Paul A.
Published: May 2008

Polymer chains of PMMA were grown from nano titania (n‐TiO2) by the reversible addition‐fragmentation chain transfer polymerization process. The mechanism and kinetics of MMA polymerization from both solution and “grafted from” n‐TiO2 were studied. The RAFT agent, 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl) sulfanyl pentanoic acid, with an available carboxyl group was used to anchor onto the n‐TiO2 surface, with the SC(SC12H25) moiety used for subsequent RAFT polymerization of MMA to form n‐TiO2/PMMA nanocomposites. The functionalization of n‐TiO2 was determined by FTIR, XPS, partitioning studies, and thermal analysis. The livingness of the polymerization was verified using NMR and GPC, while the dispersion of the inorganic filler in the polymer was studied using electron microscopy, FTIR, and thermal analysis. The monomer conversion and molecular weight kinetics were explored for the living RAFT polymerization, both in solution and grafted from n‐TiO2, with first‐order kinetics being observed in both cases. Increased graft density on n‐TiO2 led to a lower rate of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3926–3937, 2008
Hydrophilic, cationic large‐core star polymers and polymer networks: Synthesis and physicochemical characterization
Authors: Kafouris Demetris , Gradzielski Michael , Patrickios Costas S.
Published: May 2008

Group transfer polymerization was used to prepare hydrophilic, cationic large‐core star polymers (LCSPs) and networks of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA) in a two‐step procedure involving the synthesis of linear DMAEMA arms, followed by their crosslinking using a mixture of DMAEMA monomer and EGDMA crosslinker. The degree of polymerization of the linear chains prepared in the first step was kept constant, while the composition of the crosslinking mixture was varied systematically at a constant amount of crosslinker. The monomer/crosslinker molar ratio determined whether LCSPs or polymer networks would be produced. In particular, a high monomer/crosslinker molar ratio led to the formation of networks, whereas LCSPs were formed when a low monomer/crosslinker molar ratio was used. The absolute weight‐average molecular weight of the LCSPs was determined using static light scattering, whereas their hydrodynamic radii and radii of gyration were determined using dynamic light scattering and small‐angle neutron scattering, respectively. The sol fraction extracted from the networks decreased as the monomer/crosslinker molar ratio increased. The degrees of swelling of all of the networks were measured as a function of pH and were found to increase below pH 7. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3958–3969, 2008
Synthesis and properties of polythiophene derivatives containing triphenylamine moiety and their photovoltaic applications
Authors: Li Yaowen , Xue Lili , Xia Haijian , Xu Bin , Wen Shanpeng , Tian Wenjing
Published: May 2008

A series of novel soluble polythiophene derivatives containing triphenylamine moiety were synthesized by Grignard metathesis (GRIM) method. The structures of the polymers were characterized and their physical properties were investigated. High molecular weight (Mn up to 25,800 g/mol) and thermostable polymers were obtained. The absorption spectra demonstrated that the absorption wavelength of the polymers could be tuned dramatically by introducing thiophene units in the main chain of the polymers. Photoluminescence spectra indicated that there was intramolecular energy transfer from the side chain to the main chain, and the maximum emission was red‐shifted gradually with the increase of thiophene units in the main chain. Cyclic voltammetry displayed that the polymers possessed relatively high oxidation potential, which promised good air stability and high open circuit voltage for photovoltaic cells application. Finally, bulk heterojunction photovoltaic devices were fabricated by using the polymers as donors and (6,6)‐phenyl C61‐butyric acid methyl ester (PCBM) as acceptor. The maximal open circuit voltage of the photovoltaic cells reached 0.71–0.87 V and the power conversion efficiencies of the devices were measured between 0.014% and 0.45% under white light at 100 mW/cm2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3970–3984, 2008
Synthesis and characterization of oligo(oxyethylene)/carbosilane copolymers for thermoset elastomers via ADMET
Authors: Matloka Piotr P. , Kean Zachary , Greenfield Meghan , Wagener Kenneth B.
Published: May 2008

Acyclic diene metathesis (ADMET) polymerization has been used to synthesize latent reactive processable elastomers constructed of carbosilane and polyether segments. Two types of latent modes have been introduced: “chain‐internal” and “chain‐end” sites through the use of labile silicon methoxy functionalities. These latent reactive groups are inert when exposed to metathesis conditions allowing formation of the linear copolymer; subsequently exposure to moisture triggers hydrolysis of the methoxy groups and formation of a chemically crosslinked thermoset. The thermoset's mechanical response can be potentially varied from plastic to elastic behavior, depending on the ratio of carbosilane and oligooxyethylene monomers employed. Different lengths of glycols and numbers of methylene groups between them in the polymer backbone have been investigated to explore structure/property relationship. Polymers composed of oligooxyethylenes with eight methylene groups in between them exhibited fully amorphous character, while the ones with up to 20 methylene groups between glycol units showed their semicrystalline nature. The concentration of “chain‐internal” and “chain‐end” crosslink sites enhances strength; modification to the run length and structure of the soft phase enhances elasticity. Resultant materials have been subjected to mechanical tests using Instron; generated stress/strain curves have shown plastic and elastic behavior. Depending on the composition obtained samples have shown moduli from 0.3 to 115 MPa, tensile strengths from 0.6 to 10 MPa and elongations from 20 to 700%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3992–4011, 2008
Understanding the role of Arg96 in structure and stability of green fluorescent protein
Authors: Stepanenko Olesya V. , Verkhusha Vladislav V. , Shavlovsky Michail M. , Kuznetsova Irina M. , Uversky Vladimir N. , Turoverov Konstantin K.
Published: May 2008

Arg96 is a highly conservative residue known to catalyze spontaneous green fluorescent protein (GFP) chromophore biosynthesis. To understand a role of Arg96 in conformational stability and structural behavior of EGFP, the properties of a series of the EGFP mutants bearing substitutions at this position were studied using circular dichroism, steady state fluorescence spectroscopy, fluorescence lifetime, kinetics and equilibrium unfolding analysis, and acrylamide‐induced fluorescence quenching. During the protein production and purification, high yield was achieved for EGFP/Arg96Cys variant, whereas EGFP/Arg96Ser and EGFP/Arg96Ala were characterized by essentially lower yields and no protein was produced when Arg96 was substituted by Gly. We have also shown that only EGFP/Arg96Cys possessed relatively fast chromophore maturation, whereas it took EGFP/Arg96Ser and EGFP/Arg96Ala about a year to develop a noticeable green fluorescence. The intensity of the characteristic green fluorescence measured for the EGFP/Arg96Cys and EGFP/Arg96Ser (or EGFP/Arg96Ala) was 5‐ and 50‐times lower than that of the nonmodified EGFP. Intriguingly, EGFP/Arg96Cys was shown to be more stable than EGFP toward the GdmCl‐induced unfolding both in kinetics and in the quasi‐equilibrium experiments. In comparison with EGFP, tryptophan residues of EGFP/Arg96Cys were more accessible to the solvent. These data taken together suggest that besides established earlier crucial catalytic role, Arg96 is important for the overall folding and conformational stability of GFP. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Lycotoxin‐1 insecticidal peptide optimized by amino acid scanning mutagenesis and expressed as a coproduct in an ethanologenic Saccharomyces cerevisiae strain
Authors: Hughes Stephen R. , Dowd Patrick F. , Hector Ronald E. , Panavas Tadas , Sterner David E. , Qureshi Nasib , Bischoff Kenneth M. , Bang Sookie S. , Mertens Jeffrey A. , Johnson Eric T. , Li Xin‐Liang , Jackson John S. , Caughey Robert J. , Riedmuller Steven B. , Bartolett Scott , Liu Siqing , Rich Joseph O. , Farrelly Philip J. , Butt Tauseef R. , Labaer Joshua , Cotta Michael A.
Published: May 2008

New methods of safe biological pest control are required as a result of evolution of insect resistance to current biopesticides. Yeast strains being developed for conversion of cellulosic biomass to ethanol are potential host systems for expression of commercially valuable peptides, such as bioinsecticides, to increase the cost‐effectiveness of the process. Spider venom is one of many potential sources of novel insect‐specific peptide toxins. Libraries of mutants of the small amphipathic peptide lycotoxin‐1 from the wolf spider were produced in high throughput using an automated integrated plasmid‐based functional proteomic platform and screened for ability to kill fall armyworms, a significant cause of damage to corn (maize) and other crops in the United States. Using amino acid scanning mutagenesis (AASM) we generated a library of mutagenized lycotoxin‐1 open reading frames (ORF) in a novel small ubiquitin‐like modifier (SUMO) yeast expression system. The SUMO technology enhanced expression and improved generation of active lycotoxins. The mutants were engineered to be expressed at high level inside the yeast and ingested by the insect before being cleaved to the active form (so‐called Trojan horse strategy). These yeast strains expressing mutant toxin ORFs were also carrying the xylose isomerase (XI) gene and were capable of aerobic growth on xylose. Yeast cultures expressing the peptide toxins were prepared and fed to armyworm larvae to identify the mutant toxins with greatest lethality. The most lethal mutations appeared to increase the ability of the toxin α‐helix to interact with insect cell membranes or to increase its pore‐forming ability, leading to cell lysis. The toxin peptides have potential as value‐added coproducts to increase the cost‐effectiveness of fuel ethanol bioproduction. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.
Microstructure and soft magnetic properties of nanocrystalline (Co0.77Si0.135B0.095)90Fe7Nb3 alloy
Authors: Iturriza N. , Zhukov A. , Val J. J. del , Murillo N. , González J.
Published: May 2008

Microstructure and magnetic hysteretic properties of (Co0.77Si0.135B0.095)90Fe7Nb3 amorphous ribbons submitted to current annealing (current density of 56 A/mm2 during 2 minutes), to develop the nanocrystallization state, are reported. Temperature dependencies of the saturation magnetization, remanence and coercivity are explained by considering the presence of two crystalline phases, namely: nanocrystals of bcc‐Fe,Co(Si) and fcc‐Co grains and the remaining amorphous matrix. A significant magnetic hardening is observed above the Curie point of the residual amorphous matrix, which could be ascribed to an exchange and a dipolar decoupling of the nanograins. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Confinement effect in CdTe nanocrystals embedded in silica thin films
Authors: Levichev S. , Rolo A. G. , Chahboun A. , Conde O. , Kovalev A. I. , Wainstein D. L. , Gomes M. J. M.
Published: May 2008

In this paper we report on the optical and structural properties of CdTe nanoparticles embedded in silica matrix grown by the radio‐frequency (RF) magnetron sputtering technique with subsequent annealing in vacuum. Optical transmittance, Raman scattering, X‐ray photoelectron spectroscopy (XPS), grazing incidence X‐ray diffraction (GIXRD) and photoluminescence (PL) were used to study the grown samples. GIXRD shows the presence of the cubic phase of CdTe nanocrystals (NCs) in the silica matrix, with size ranging from 2.5 nm to 10.5 nm. Raman spectroscopy illustrates features linked to LO phonons in the CdTe structure. The absorption spectra of annealed samples demonstrate shoulders on the absorption in the range 650–700 nm, in agreement with the PL emission observed at 650–725 nm. However, the blue shift observed in the NCs bandgap in relationship with their size was below the expected level. We attribute this feature to the graded interface between the NCs and the matrix, which causes a weak confinement of carriers in CdTe NCs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tailoring the diameter, density and number of walls of carbon nanotubes through predefined catalyst particles
Authors: Schäffel F. , Rümmeli M. H. , Kramberger C. , Queitsch U. , Mohn E. , Kaltofen R. , Pichler T. , Büchner B. , Rellinghaus B. , Schultz L.
Published: May 2008

We have explored the influence of predefined gas phase prepared catalyst particles on carbon nanotube (CNT) properties such as their diameter and number of walls. During the catalyst preparation particles are simultaneously deposited onto a substrate for chemical vapour deposition as well as on a witness grid for analysis in transmission electron microscopy. This allows us to obtain precise information on the starting catalyst material on one side and the CNT product on the other. Clear correlations between the catalyst's size and the CNT diameter and number of walls have been found. Our results indicate a dependence of the resultant CNT on the volume to surface area ratio of the catalyst particle and fit well with our understanding of cap formation at CNT nucleation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetocaloric effect in nanogranular glass coated microwires
Authors: Ilyn M. I. , Zhukova V. , Santos J. D. , Sánchez M. L. , Prida V. M. , Hernando B. , Larin V. , González J. , Tishin A. M. , Zhukov A.
Published: May 2008

Thermal dependences of the magnetic susceptibility of the glass‐coated microwires with compositions Fe3P and SnMn prepared by the Taylor–Ulitovski method have been determined. Direct measurements of the adiabatic temperature change revealed ΔTad of 0.04 K in the SnMn and ΔTad of 0.02 K in the Fe3P microwires on the field change of 12 kOe. Temperatures of the peak values of MCE were found to be of ∼215 K and ∼320 K respectively. The variation of magnetic properties of the Fe3P wires with the change of their diameters was observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band structure effects on the Be(0001) acoustic surface plasmon energy dispersion
Authors: Silkin V. M. , Pitarke J. M. , Chulkov E. V. , Diaconescu B. , Pohl K. , Vattuone L. , Savio L. , Hofmann Ph. , Farı’︁as D. , Rocca M. , Echenique P. M.
Published: May 2008

We report first‐principles calculations of acoustic surface plasmons on the (0001) surface of Be, as obtained in the random‐phase approximation of many‐body theory. The energy dispersion of these collective excitations has been obtained along two symmetry directions. Our results show a considerable anisotropy of acoustic surface plasmons, and underline the capability of experimental measurements of these plasmons to map the electron–hole excitation spectrum of the quasi two‐dimensional Shockley surface state band that is present on the Be(0001) surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grafting organic polymer films on surfaces of carbon nanotubes by surface electroinitiated emulsion polymerization
Authors: Tessier Lorraine , Chancolon Jérôme , Alet Pierre‐Jean , Trenggono Adhitya , Mayne‐L'Hermite Martine , Deniau Guy , Jégou Pascale , Palacin Serge
Published: May 2008

Diazonium salts coupled with vinylic monomers were able to functionalize carpets of carbon nanotubes by electro‐activation in aqueous media. Hence, nano‐sized carbon surfaces were shown to react with active radical species in solution through a new covalent grafting process called Surface Electroinitiated Emulsion Polymerization (SEEP), where diazonium salts are used both to initiate the polymerization of vinylic monomers in solution and to form a primer grafted polyphenylene‐like layer on the carbon surface. SEM and TEM analyses revealed that ultrathin polymer films are grafted on the sidewalls of carbon nanotubes. XPS spectroscopy further confirmed the functionalization of multi‐walled carbon nanotubes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unifying catalyst size dependencies in floating catalyst and supported catalyst carbon nanotube synthesis
Authors: Rümmeli M. H. , Schäffel F. , Löffler M. , Kramberger C. , Adebimpe D. , Gemming T. , Ayala P. , Rellinghaus B. , Schultz L. , Büchner B. , Pichler T.
Published: May 2008

Detailed studies with floating catalyst systems, namely, laser evaporation and laser assisted chemical vapour deposition (CVD), enabled the development of a catalyst volume to surface area model which dictates if a single walled carbon nanotube (SWCNT) can emerge or not. The model predicts differences in the case of supported catalysts. It predicts multi‐walled carbon nanotubes (MWCNT) will also emerge. This difference arises due to the catalyst/support interaction. Further, the model says that for supported catalysts the catalyst volume to surface area ratio also regulates the tube diameter and the number of walls the nanotube will have. In this contribution, experimental CVD data using predefined catalyst particles on a support are presented and compared with floating catalyst data. The findings for supported catalysts are in full agreement with those predicted by the catalyst surface area to volume model. The data show unified catalyst size dependencies for floating catalyst and supported catalyst carbon nanotube synthesis routes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large‐scale “atomistic” approach to discrete‐dopant‐induced characteristic fluctuations in silicon nanowire transistors
Authors: Li Yiming , Hwang Chih‐Hong , Huang Hsuan‐Ming
Published: May 2008

Nanowire fin‐typed field effect transistors (FinFETs) are ultimate structures and potential candidates for next generation nanoelectronic devices. Due to the limitation of manufacturability, nanowire transistors with a perfect gate structure (i.e., a surrounding gate with 100% gate‐coverage ratio) theoretically are not always guaranteed. Impact of the discrete dopants on device performance is crucial in determining the behaviour of nanoscale semiconductor devices. The immunity of nanowire transistor against random discrete‐dopant‐induced fluctuation may suffer from the variation of gate‐coverage‐ratio. Therefore, in this paper, we for the fist time study the impact of non‐ideal gate coverage on immunity against random‐dopant‐induced fluctuations for nanowire FinFETs. A 3D statistically sound “atomistic” approach for analyzing random‐dopant effect in nanodevice is presented. Discrete dopants are statistically positioned into the channel region to examine associated carrier transportation characteristics, concurrently capturing “dopant concentration variation” and “dopant position fluctuation”. Our results confirm that the influence of non‐ideal gate coverage disturbs the channel controllability of nanowire FinFETs and thus decreases the immunity against discrete‐dopant‐induced fluctuation. This study provides an insight into the problem of fluctuation in nanowire transistors and shows the importance of gate‐coverage ratio on device's immunity against discrete‐dopant‐induced fluctuation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lifetime fluctuations of a single emitter in a disordered nanoscopic system: The influence of the transition dipole orientation
Authors: Froufe‐Pérez L. S. , Carminati R.
Published: May 2008

We study the fluctuations of the fluorescence decay rate of a single emitter in a random cluster of nanoparticles, in a regime dominated by near‐field scattering. Configurational changes of the environment induce statistical changes of the decay rate. Two regimes are considered which differ in terms of transition dipole orientation. In one regime, the orientation of the transition dipole is assumed to remain constant while the configuration of the cluster changes randomly. In another regime, the orientation of the transition dipole is assumed unknown and continuously averaged over the three directions of space. Using exact numerical simulations and a simple analytical model, we show that the statistical distributions of the spontaneous decay rate are substantially different in both regimes. In both cases, the decay rate fluctuations are strongly dependent on the level of absorption at the nanoscale. We discuss the impact of this result in terms of imaging in complex media. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low energy properties of even‐legged d ‐dimensional quantum spin systems: a variational approach
Authors: Richert Jean , Gühne Otfried
Published: May 2008

We develop a variational formalism in order to study the gap structure in the spectrum of frustrated quantum spin systems. We introduce a trial wave function of a two‐leg ladder with one spin 1/2 on each site. The domains in which the wave function behaves realistically are determined. In these domains the spectra show a finite energy gap between the ground state and excited states. Under some approximations which are discussed the result can be extended to 2d and higher dimensional systems with an even number of rows. The gap vanishes for specific values of the coupling strengths which correspond to the location of phase transitions. In a second step we introduce quantitative estimates of the relevance of the variational ansatz which rest on the entanglement concept. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ab initio study of indium clusters on the Ge(5 × 5) wetting layer of Si(111)‐7 × 7
Authors: Psiachos D. , Stott M. J.
Published: May 2008

An ab initio study of In adsorbed on the Ge(111)‐5 × 5 wetting layer, which forms on top of a Si(111)‐7 × 7 substrate, is reported. A recent experiment showed that small In clusters form on this surface with some regularity but their exact size and structure are still unknown. Results are presented of a detailed investigation of the structural and electronic properties of a single adsorbed In atom and small candidate In clusters, carried out using density‐functional calculations. Using density difference plots and population analysis, the mechanisms of bonding for different In structures are explained. Comparison of total energies shows that for a single In atom the faulted half cell is marginally preferred to the unfaulted half, and little tendency for clustering of In is found for low coverages. Both of these conclusions seem to be at odds with the experimental results and possible explanations are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐phonon Umklapp process in silicon nanowires with square cross sections
Authors: Lü Xiang
Published: May 2008

We have evaluated the relaxation rate of silicon (Si) nanowires with square cross sections by considering the three‐phonon Umklapp process. The calculated model takes into account the energy gap between the phonon modes due to acoustic phonon confinement. It is found that the relaxation rate increases with increasing nanowire side length at small side length, and shows a peak behavior at about 5 nm before falling off at large side length. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability conditions for the coupled cluster equations
Authors: Szakács Péter , Surján Péter R.
Published: May 2008

The coupled cluster (CC) equations are studied from the point of view of the stability of their solution. The nonlinear nature of these equations may lead to undesired iteration properties including chaotic solutions. Iterations of various types (convergent, oscillatory, chaotic or divergent) are identified by the eigenvalues of the stability (Jacobi) matrix at the fixed points. Explicit (orbital) form of the stability matrix is obtained for the CCSD case, and the various iteration domains are investigated as a function of the control (damping) parameter of the CC iteration. The case of the BeH2 molecule at various nuclear arrangements is chosen as a numerical example. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Towards a universal product ion mass spectral library – reproducibility of product ion spectra across eleven different mass spectrometers
Authors: Hopley Chris , Bristow Tony , Lubben Anneke , Simpson Alec , Bull Elaine , Klagkou Katerina , Herniman Julie , Langley John
Published: May 2008

Product ion spectra produced by collision‐induced dissociation (CID) in tandem mass spectrometry experiments can differ markedly between instruments. There have been a number of attempts to standardise the production of product ion spectra; however, a consensus on the most appropriate approach to the reproducible production of spectra has yet to be reached. We have previously reported the comparison of product ion spectra on a number of different types of instruments – a triple quadrupole, two ion traps and a Fourier transform ion cyclotron resonance mass spectrometer (Bristow AWT, Webb KS, Lubben AT, Halket JM. Rapid Commun. Mass Spectrom. 2004; 18: 1). The study showed that a high degree of reproducibility was achievable. The goal of this study was to improve the comparability and reproducibility of CID product ion mass spectra produced in different laboratories and using different instruments. This was carried out experimentally by defining a spectral calibration point on each mass spectrometer for product ion formation. The long‐term goal is the development of a universal (instrument independent) product ion mass spectral library for the identification of unknowns.

The spectra of 48 compounds have been recorded on eleven mass spectrometers: six ion traps, two triple quadrupoles, a hybrid triple quadrupole, and two quadrupole time‐of‐flight instruments. Initially, 4371 spectral comparisons were carried out using the data from eleven instruments and the degree of reproducibility was evaluated. A blind trial has also been carried out to assess the reproducibility of spectra obtained during LC/MS/MS.

The results suggest a degree of reproducibility across all instrument types using the tuning point technique. The reproducibility of the product ion spectra is increased when comparing the tandem in time type instruments and the tandem in space instruments as two separate groups. This may allow the production of a more limited, yet useful, screening library for LC/MS/MS identification using instruments of the same type from different manufacturers. Copyright © 2008 John Wiley & Sons, Ltd.
Interactions of nucleosides with CrO and Cr3+ as studied by electrospray ionization mass spectrometry
Authors: Frańska Magdalena , Gierczyk Karolina
Published: May 2008

The interactions of CrO and Cr3+ with nucleosides studied by electrospray ionization mass spectrometry (ESI‐MS) are reported. In water, the nucleosides which do not contain the NH2 group form the unstable [M+HCrO4]− anion. In the presence of a reducing agent, namely methanol, chromate anion forms stable complexes with nucleosides, [M+CH3CrO4]− anions. The fragmentation of [M+CH3CrO4]− anions involve elimination of the methanol molecule. Chromium cation‐nucleoside complexes were not observed in water. In methanol solutions, adenosine and cytidine form [(M−H)+CrOCH3]+ and [(M−H)2+Cr]+ ions. Most probably, deprotonated imine tautomers form complexes in which a metal cation is simultaneously coordinated by two nitrogen atoms. Complexes containing chloride anions and a few methanol molecules were observed for other nucleosides. Guanosine and inosine form doubly charged ions of the type [M2+CrOCH3]2+ that probably contain a bond between the oxygen atom and the chromium cation, (HN(1)C(6)O)Cr3+). Copyright © 2008 John Wiley & Sons, Ltd.
Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size
Authors: Wiedemann‐Bidlack Felicitas B. , Colman Albert S. , Fogel Marilyn L.
Published: May 2008

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology‐based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.

We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag3PO4 crystals by using a strongly buffered, moderate‐temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as δ18O, V‐SMOW scale) is typically 0.2–0.3‰ (1 s.d.) on samples as small as 300 µg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen. Copyright © 2008 John Wiley & Sons, Ltd.
Characterization of metabolites of a novel histamine H2‐receptor antagonist, lafutidine, in human liver microsomes by liquid chromatography coupled with ion trap mass spectrometry
Authors: Wang Yuya , Chen Xiaoyan , Li Qiang , Zhong Dafang
Published: May 2008

The metabolism of lafutidine in human liver microsomes was studied using liquid chromatography/ion trap mass spectrometry with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources. A total of 14 metabolites were identified including hydroxylated lafutidine and sulfonyl lafutidine as the major metabolites. The chemical properties and the MSn behaviors of lafutidine and all of its identified metabolites were studied in detail. Lafutidine had a fragmentation pattern as a result of homolytic bond cleavage in the MS/MS spectrum. This cleavage can form an odd‐electron ion with the loss of furan‐2‐ylmethyl radical (−81 Da with a proton shift), which then sequentially loses neutral groups in the MS3 spectrum. This fragmentation sequence was also observed from the metabolites with the unchanged sulfinyl moiety. When the sulfinyl moiety was oxidized to the sulfonyl moiety, this fragmentation sequence did not exist, which could be used to identify S‐oxidation metabolites of lafutidine. In general, N‐oxides could produce distinct [M+H–O]+ ions under LC/APCI‐MS due to the thermal activation in the desolvation region of the API source, which could be used to identify N‐oxidation metabolites of lafutidine. In order to avoid the possibility of false positives, the MS/MS spectrum of the [M+H–O]+ ion was compared with that of the non‐N‐oxidation metabolites or parent drug in the APCI source. If they were consistent, the structure could be finally confirmed. The exact masses for lafutidine and lafutidine N‐oxide fragment ions were determined using an LTQ/Orbitrap mass spectrometer. Copyright © 2008 John Wiley & Sons, Ltd.
Characterization of compounds from the roots of Saposhnikovia divaricata by high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry
Authors: Kang Jie , Sun Jiang‐Hao , Zhou Lei , Ye Min , Han Jian , Wang Bao‐Rong , Guo De‐An
Published: May 2008

In this study, four types of compounds including coumarins, chromones, furoylmethyl amino acid derivative and benzofuran glycoside were isolated from the roots of Saposhnikovia divaricata. The electrospray ionization (ESI) mass spectral fragmentation pathways of these compounds were proposed. In particular, the ESI‐MSn fragmentation behavior of linear dihydrofurocoumarins, dihydrofuro‐ and dihydropyranochromones were deduced in detail. For the linear dihydrofurocoumarins, the fragmentation was triggered by the initial loss of the C‐4′ substituting group. Then, the characteristic ions were observed followed by the losses of 15, 18, 28 and 46 Da. It is noteworthy that the elimination of H2O (18 Da) from the cleavage of the dihydrofuran ring is reported for the first time. For the linear dihydrofurochromones, characteristic eliminations of 18, 48 and 72 Da were observed. The loss of 18 Da could arise from two different fragmentation pathways, and the observed ion was composed of a mixture of two different structural ions. For the linear dihydropyranochromones, it was found that the dihydropyran ring was converted into the pyran ring by the elimination of the C‐3′ substituting group. This fragmentation was followed by the diagnostic losses of 18, 28, 42 and 54 Da in tandem mass spectrometry. The above fragmentation rules were successfully applied for the analysis of the chemical constituents of the roots of Saposhnikovia divaricata. A total of 32 compounds were identified or tentatively characterized by HPLC/DAD/ESI‐MSn. Among them, eight compounds were new and seven compounds were reported from that genus for the first time. Copyright © 2008 John Wiley & Sons, Ltd.
New features on the fragmentation and differentiation of C‐glycosidic flavone isomers by positive electrospray ionization and triple quadrupole mass spectrometry
Authors: Abad‐García Beatriz , Garmón‐Lobato Sergio , Berrueta Luis A. , Gallo Blanca , Vicente Francisca
Published: May 2008

Six flavone mono‐C‐glucosides, four standards (β‐D‐glucopyranosyl‐(1 → C‐6)‐ and ‐(1 → C‐8)‐ apigenin and luteolin) and two others from lemon juice (β‐D‐glucopyranosyl‐(1 → C‐6)‐ and ‐(1 → C‐8)‐diosmetin) have been studied in order to analyze their fragmentation patterns. Initial separation was carried out using high‐performance liquid chromatography with diode‐array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface and a triple quadrupole mass spectrometer. Several systematic differences between collision‐induced dissociation tandem mass (CID‐MS/MS) spectra of C‐6‐ and C‐8‐isomers have been found and some general guidelines and two new diagnostic product ions have been proposed for the differentiation of C‐6‐ and C‐8‐flavonoid glycosides. These results have been successfully applied to the characterization of two flavone C‐glycosides found in lemon juice, and mass spectra of a flavone di‐C‐glycoside detected in lemon juice have been studied and interpreted. Copyright © 2008 John Wiley & Sons, Ltd.
A simple and universal method for the separation and identification of phospholipid molecular species
Authors: Retra Kim , Bleijerveld Onno B. , van Gestel Renske A. , Tielens Aloysius G.M. , van Hellemond Jaap J. , Brouwers Jos F.
Published: May 2008

One of the major challenges in lipidomics is to obtain as much information about the lipidome as possible. Here, we present a simple yet universal high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method to separate molecular species of all phospholipid classes in one single run. The method is sensitive, robust and allows lipid profiling using full scan mass spectrometry, as well as lipid class specific scanning in positive and negative ionisation mode. This allows high‐throughput processing of samples for lipidomics, even if different types of MS analysis are required. Excellent separation of isobaric and even isomeric species is achieved, and original levels of lyso‐lipids can be determined without interference from lyso‐lipids formed from diacyl species by source fragmentation. As examples of application of this method, more than 400 phospholipid species were identified and quantified in crude phospholipid extracts from rat liver and the parasitic helminth Schistosoma mansoni. Copyright © 2008 John Wiley & Sons, Ltd.
Rapid screening of clenbuterol in urine samples by desorption electrospray ionization tandem mass spectrometry
Authors: Lin Ziqing , Zhang Sichun , Zhao Mengxia , Yang Chengdui , Chen Depu , Zhang Xinrong
Published: May 2008

Rapid screening of clenbuterol in urine was performed by combining desorption electrospray ionization (DESI) and tandem mass spectrometry (MS/MS). Optimization experiments were carried out including the selection of substrates, spray solutions, nebulizing gas pressures, high‐voltage power supplies and flow rates of spray solution. The limit of detection (LOD), defined as the lowest quantity that can be detected, was 5.0 pg for the pure compound. Using DESI coupled with solid‐phase extraction (SPE), the linear response range was from 10 to 400 ng/mL (R2 = 0.993) and the concentration LOD for urine sample was 2.0 ng/mL. The analysis for one spiked urine sample was achieved within 4 min. In addition to the fast analysis speed, MS/MS provided structural information for the confirmation of clenbuterol. Urine samples from different people were investigated and the recoveries were within 100 ± 20%. The developed method can potentially be used for screening of clenbuterol in doping control. Copyright © 2008 John Wiley & Sons, Ltd.
Composition of the seed bank in drawdown areas of Navigation Pool 8 of the Upper Mississippi River
Authors: Kenow Kevin P. , Lyon James E.
Published: May 2008

In an effort to enhance aquatic plant production and habitat diversity on the Upper Mississippi River (UMR), resource managers considered water level reduction as a management tool to increase the area of emergent and submersed aquatic vegetation by natural seed germination. To quantify the availability of seed, we assessed the potential seed bank of selected areas of Navigation Pool 8 of the UMR from substrate samples collected in spring 2000. We tested these samples for viable seed content under four hydrologic conditions: dry, moist, shallow flooded and submerged. Forty‐seven species were identified in the seed bank, including 27 obligate wetland, 10 facultative wetland and 7 upland species. Dominant taxa within the seed bank included Sagittaria spp., Lindernia dubia, Zosterella dubia, Cyperus spp., Eragrostis spp. and Leersia oryzoides. Of the four hydrologic treatments, moist substrates had the greatest species diversity and were the most productive, yielding an average density of 1420 seedlings m−2. Emergent and submersed aquatic species were widely distributed, each type occurring in more than 90% of the samples. Timing of seedling germination varied among species and has implications for scheduling drawdowns to promote establishment of desired species. Seed bank results were correlated with the vegetation response on substrates exposed during a reduction of water levels of Pool 8 during summer 2001. Experimentally determining the composition and viability of seed banks from drawdown areas provides information useful in predicting the types of vegetation that may develop on exposed substrates. Further, these findings provide resource managers a better understanding of the potential for achieving desired vegetation response through water level reductions. Published in 2008 by John Wiley & Sons, Ltd.
Effects of water level fluctuations on Vallisneria nana in the Burnett River in Southeast Queensland, Australia
Authors: Duivenvoorden Leo J.
Published: May 2008

Changes in aquatic macrophyte populations in the Burnett River in southeast Queensland, Australia are described with respect to the effects of water level fluctuations and possible impact on the Queensland lungfish (Neoceratodus forsteri). This protected fish relies on macrophyte beds as spawning and nursery areas. Studies were conducted prior to, during and following construction of a new weir on the river. Comparative results of impounded and non‐impounded sites were conducted to investigate seasonal and inter‐annual changes in macrophytes and the effects of both a rapid rise in water level when the impoundment first filled and a decline, on new plants in shallow water. Macrophyte communities in newly inundated areas were studied to determine the time taken for seedlings to emerge and reach a cover sufficient to represent spawning habitats for the lungfish. Vallisneria nana dominated the macrophyte beds, which were scoured from the river by a large flow event in May 1998, the effects of which persisted for at least 1 year. Most newly emerging seedlings of Vallisneria perished following a small decline of 7 cm in water level. Decrease in plant biomass and death of established plants in highly turbid water resulted within 6–9 weeks following larger water level rises of 4.0–5.5 m in the new impoundment. In the period leading up to the lungfish‐spawning season at least 5 months is required for submerged plants to reach the 90% cover preferred for spawning. Implications of the results for water level management and lungfish populations are discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Forecasting backwater through bridge constrictions in Mississippi River Basin
Authors: Seckin Galip , Haktanir Tefaruk , Cobaner Murat , Selek Zeliha
Published: May 2008

Hydraulic data collected in the 1960s during 92 distinct floods at 35 different bridge sites in the Mississippi River Basin revealed that the water surface profiles of these real‐life cases were distinctly different from those observed in laboratory models of the comprehensive experimental studies of the 1950s by the U.S. Geological Survey (USGS) and by U.S. Bureau of Public Roads (USBPR). The laboratory‐developed methods of USGS and USBPR yielded only about half of the field backwaters when applied to the comprehensive field data. In the current work, using the same field data and accepting a profile like that observed in the field, a new regression‐based formula for estimating bridge backwater is proposed and compared with the methods of USGS and USBPR, which yields more accurate results than these two methods with the advantage of requiring a smaller load of arithmetic operations. Copyright © 2008 John Wiley & Sons, Ltd.
Substrate indices as indicators of interstitial pore space in gravel‐bed channels
Authors: Haschenburger Judith K. , Roest Paul
Published: May 2008

Streambed sediments that determine aquatic habitat quality are typically assessed using substrate indices. These indices are proxies for the amount of interstitial pore space that facilitates biological processes within the substrate. This study evaluates how well a suite of substrate indices characterize streambed porosity. Using the hybrid McNeil sampler, 37 cores were collected from six gravel‐bed rivers on the North Island of New Zealand. Central tendency indices correlate more strongly to porosity than critical size indices, but both types are imprecise indicators of the amount of interstitial pore space. Copyright © 2008 John Wiley & Sons, Ltd.
A novel mathematical approach for modelling time‐dependent musculoskeletal outcomes for office staff
Authors: Lu Xiaoshu , Takala Esa‐Pekka
Published: May 2008

Musculoskeletal disorders are common in prolonged computer use. The dynamics of the relationship between musculoskeletal outcomes and duration of computer use is not easy to model by common statistical methods due to the nonlinearity of the data. The use of inappropriate statistical models increases the likelihood of drawing wrong conclusions. In this paper we present a new mathematical methodology for modelling such a dynamic data set. Data on simultaneous direct measures of computer usage and questionnaire diaries of discomfort ratings were analysed using singular value decomposition as a means to track dominant dynamic trends, which presented the common characteristic of the relationship between computer‐related workload and musculoskeletal outcomes over time. The relationship was constructed explicitly as a dose–response functional relationship that was parametrized by body region parameters. Standard statistical software was employed to quantify the variability of the estimates due to the complicated feature involved in the data. A deterministic population model was then developed to simulate the dynamics of computer‐related workload and musculoskeletal outcomes. A stochastic model was also proposed to describe the stochastic nature of dynamics for individual subjects. The model was verified by comparison with real data for forecasting purposes. Possibilities for extending the model to accommodate more complicated medical data are discussed. The mathematical model can be served as both a deterministic population model that can project the demographic consequences and a stochastic model that can describe the whole quantity evolution of the study subjects. The proposed methodology is a flexible and broadly applicable one, which can be utilized by a variety of medical research. Copyright © 2008 John Wiley & Sons, Ltd.
A nonparametric likelihood test for detecting discordance between two measurements with application to censored viral load determinations
Authors: Hu Zonghui , Follmann Dean , Qin Jing , Dewar Robin L. , Sangweni Phumelele
Published: May 2008

Patient management frequently involves quantitative evaluation of a patient's attributes. For example, in HIV studies, a high viral load can be a trigger to initiate or modify an antiretroviral therapy. At times, a new method of evaluation may substitute for an established one, provided that the new method does not result in different clinical decisions compared with the old method. Traditional measures of agreement between the two methods are inadequate for deciding if a new method can replace the old. Especially, when the data are censored by a detection limit, estimates of agreement can be biased unless the distribution for the censored data is correctly specified; this is usually not feasible in practice. We propose a nonparametric likelihood test that seamlessly handles censored data. We further show that the proposed test is a generalization of the test on nominal measurement concordance to continuous measurement. An exact permutation procedure is proposed for implementing the test. Our application is an HIV study to determine whether one method of processing plasma samples can safely substitute for the other. The plasma samples are used to determine viral load and a large portion of data are left censored due to a lower detection limit. Copyright © 2008 John Wiley & Sons, Ltd.
Effective atomic numbers and electron densities of CuGaSe2 semiconductor in the energy range 6–511 keV
Authors: Çelik A. , Çevik U. , Bacaksiz E. , Çelik N.
Published: May 2008

The effective atomic numbers and electron densities of the CuGaSe2 semiconductor were calculated at 29 different energies from 6.9 to 511.0 keV by using the measured mass attenuation coefficients. Also, the mass attenuation coefficients for Cu, Ga, and Se elements were obtained at this energy range. The samples were irradiated using Cd‐109, Co‐57, Ba‐133, and Na‐22 radioactive sources. The x‐ray energies were obtained using secondary targets. The gamma and x‐rays were counted by an Ultra‐LEGe detector with a resolution of 0.55 at 122.0 keV. The mass attenuation coefficients were compared with theoretical ones obtained using the XCOM program. Copyright © 2008 John Wiley & Sons, Ltd.