bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses and signaling pathways in human optic nerve head astrocytes exposed to hydrostatic pressure in vitro
Authors: Salvador‐Silva Mercedes , Aoi Shun , Parker Amy , Yang Ping , Pecen Paula , Hernandez M. Rosario
Published: February 2004

In this study, we examined the effects of mechanical stress induced by elevated hydrostatic pressure (HP) on the migration of human optic nerve head (ONH) astrocytes, using an in vitro model that follows repopulation of a cell‐free area (CFA) created on a monolayer of cultured astrocytes. α‐Tubulin staining detected phenotypic changes in astrocytes exposed to HP. The influence of proliferation in closure of the CFA was determined by incorporation of BrdU under 1.5‐cm H2O, control pressure (CP), and 10‐cm H2O HP with or without 5‐fluorouracil. Under control and experimental conditions, closure of the CFA occurred mostly by migration and less by proliferation. Exposure to 10‐cm H2O HP induced faster closure of the CFA at 1, 3, and 5 days. The signaling pathways involved in responses to HP were determined using genistein, tyrphostin A25, AG1478, and AG1295, inhibitors of receptor tyrosine kinases; wortmannin and LY294002, inhibitors of phosphatidyl inositol 3‐kinase (PI‐3K); and SC58236, an inhibitor of inducible cyclooxygenase‐2 (COX2). Genistein and tyrphostin A25 blocked HP‐induced migration at 1, 3, and 5 days, but did not affect closure of the CFA under CP. AG1478 and AG1295 blocked HP‐induced migration and partially inhibit closure of the CFA under CP. LY294002 blocked HP‐induced migration. SC58236 markedly inhibited closure of the CFA under CP by inhibiting COX2 activity. Exposure to HP, a physical stress, induced faster closure of the CFA via activation of members of the epidermal growth factor receptor (EGFR) family and PI‐3K pathways. Under CP, closure of the CFA in response to denudation, a form of injury, is due to activation of COX2 in ONH astrocytes. © 2004 Wiley‐Liss, Inc.
Preparation and Analysis of Phenol‐Formaldehyde Resins by High‐Throughput Techniques
Authors: Pasch Harald , Schrod Matthias
Published: February 2004

Summary: Phenolic resin composition depends on monomer ratio, catalyst, reaction conditions, and residual free monomers. Using a simple device for parallel synthesis, large numbers of samples of different compositions were prepared. Residual free phenol and formaldehyde were determined by fast HPLC. Using this approach, combinatorial libraries for a huge variety of different experimental conditions can be developed. These libraries bear information on the effect of different experimental parameters on resin composition.

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Combinatorial Methods, Automated Synthesis and High‐Throughput Screening in Polymer Research: The Evolution Continues
Authors: Meier Michael A. R. , Hoogenboom Richard , Schubert Ulrich S.
Published: February 2004

Summary: For speeding‐up preparation as well as investigating new polymeric materials, combinatorial techniques, parallel experimentation, and high‐throughput screening methods represent a very promising approach in polymer chemistry: a large variety of parameters can be screened simultaneously resulting in new structure–property relationships. As previously described, polymer chemistry seems to be perfectly suited for combinatorial approaches since it is relatively easy to vary many parameters during the synthesis, processing, blending, or compounding. Moreover, the development and application of high‐throughput screening techniques for polymer properties can accelerate the development of new materials and can result in new structure–property relationships. Therefore, these screening tools, together with parallel preparation techniques, will significantly decrease the time to market of new products. Here we provide an update of our recent overview covering new developments in the field of combinatorial and parallel polymer synthesis and high‐throughput screening.

Development of high‐throughput screening techniques for polymer properties.

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Development of high‐throughput screening techniques for polymer properties.
High‐Throughput Chemical Vapor Deposition System and Thin‐Film Silicon Library
Authors: Wang Qi , Liu Fengzhen , Han Daxing
Published: February 2004

Summary: Thin‐film Si materials library were fabricated rapidly on glass substrates using the combinatorial hot‐wire CVD technique. We found that the films with high hydrogen dilution become microcrystalline Si, and the films with no and low hydrogen dilution remain in the amorphous Si structure. We also found that the ratio of hydrogen to silane (R) is a good measure of the structure change.

Schematics of a combinatorial HWCVD system.

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Schematics of a combinatorial HWCVD system.
High‐Throughput Synthesis of New Ni(II), Pd(II), and Co(II) Catalysts and Polymerization of Norbornene Utilizing the Self‐Made Parallel Polymerization Reactor System
Authors: Cho Hyun Yong , Hong Dae Sik , Jeong Dong Wook , Gong Young‐Dae , Woo Seong Ihl
Published: February 2004

Summary: We report the development of new Ni(II), Pd(II), and Co(II) catalysts containing ligands of pyrazolylpyridine derivatives by combinatorial and high‐throughput synthesis technology. Vinyl type polynorbornene was polymerized utilizing the self‐made parallel polymerization reactor system. The Ni(II) catalyst 1 has a polymerization activity of 266.7 kgpolymer · molcat−1 · h−1. We introduce a fast way to conduct catalyst synthesis and high‐throughput screening for polymerization.

The self‐made parallel polymerization reactor system.

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The self‐made parallel polymerization reactor system.
Software Solutions for Combinatorial and High‐Throughput Materials and Polymer Research
Authors: Adams Nico , Schubert Ulrich S.
Published: February 2004

Summary: Combinatorial and high‐throughput experimentation has, over the past few years, started to play an increasingly important role in the area of materials and polymer science. However, many of the informatics tools currently available to support combinatorial experimentation were developed with the needs of medicinal and biological chemistry in mind. Recently, companies specialising in cheminformatics software have begun to address the need for dedicated materials informatics tools and, although still in its infancy, the development of such tools is rapidly gathering pace. This short review provides a summary of the current state‐of‐the‐art.

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Applications of High Throughput Research at The Dow Chemical Company
Authors: Peil Kevin P. , Neithamer David R. , Patrick Don W. , Wilson Bruce E. , Tucker Chris J.
Published: February 2004

Summary: With high throughput research (HTR), a new research approach towards the development of catalysts and materials has been established at The Dow Chemical Company. While drawing on many of the same concepts as combinatorial chemistry, HTR introduced a new set of specific challenges. New workflows needed to be developed for catalyst and material preparation, activity screens, product and process analytical as well as the management of large amounts of data. Integration of the workflow is critical and requires appropriate skills from such fields as chemistry, engineering, materials, analytical, robotics and informatics. It is not simply having a HTR capability that matters, but what one does with the capability that counts the most. The paradigm shift that has occurred at Dow as a result of HTR will allow Dow to deliver solutions to customers faster than ever. This will be illustrated by several examples of how the HTR capability has had a major impact at Dow.

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Assembly of Nanoparticles using Surface‐Grafted Orthogonal Polymer Gradients
Authors: Bhat Rajendra R. , Tomlinson Michael R. , Genzer Jan
Published: February 2004

Summary: We report on preparing poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) gradient substrate, wherein molecular weight (MW) and grafting density (σ) of the surface‐anchored PDMAEMA chains vary continuously in two orthogonal directions. Such a specimen is used to control the assembly of charged gold nanoparticles. Increasing MW and σ of the grafted PDMAEMA cause an enhanced binding of the nanoparticles to PDMAEMA, thus leading to an orthogonal number density gradient of surface‐bound gold nanoparticles.

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A Screening Workflow for Synthesis and Testing of 10,000 Heterogeneous Catalysts per Day – Lessons Learned
Authors: Duff Daniel G. , Ohrenberg Arne , Voelkening Stephan , Boll Matthias
Published: February 2004

Summary: For some years now a trend toward the employment of high‐throughput technologies in the development of new catalysts has been apparent in academic and industrial research. One reason is the unmanageably large parameter space present in heterogeneous catalysis, which implies that an increase in throughput in the preparation and testing of candidate substances is necessary, in order to be able to identify a new catalyst in a practicable amount of time. We have tried to locate the current boundaries in achievable throughput. To this end, we developed a workflow in which 10,000 substances per day were synthesised and their activity tested in a heterogeneously catalysed gas phase reaction (alkene epoxidation). The substances were synthesised by dosing precursor solutions onto a single substrate, using ink‐jet printer technology and subsequent thermal treatment. For the activity testing, the product stream of each candidate was conducted through a detection layer, where the target product was converted into a fluorescent substance. By locally resolved fluorescence spectroscopy a rough assessment of each candidate was possible. Because a throughput of 10,000 substances per day is still not able to map the whole parameter space in a practicable amount of time, we used a combination of evolutionary optimisation and data mining as our experiment design strategy for the reduction of the experimental parameter space. It became apparent that a throughput of 10,000 substances per day was only possible at the cost of abstraction and simplification with a concomitant reduction in knowledge gain per individual experiment. Because not every reaction is suited to be simplified in such a manner, whether a high‐throughput screening approach is effective or not has to be considered on a case by case basis.

Methods of synthesis and testing to achieve a throughput of 10,000 catalysts per day.

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Methods of synthesis and testing to achieve a throughput of 10,000 catalysts per day.
High‐Throughput Screening of the Influence of Thermal Treatment on the Mechanical Properties of Semicrystalline Polymers: A Case Study for iPP
Authors: Schneider Konrad , Zafeiropoulos Nikolaos Evangelos , Häußler Liane , Stamm Manfred
Published: February 2004

Summary: High‐throughput screening is a convenient tool to determine the influence of parameters, such as composition or processing conditions on certain materials' properties. In the present study, iPP was used to construct a combinatorial library made from a processing temperature gradient requiring only a minimised amount of material. Clear changes in the crystalline modification and crystal morphology of the iPP, and their impact on mechanical properties have been identified.

The construction of a combinatorial library to study the effect of thermal history upon the properties of polymers.

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The construction of a combinatorial library to study the effect of thermal history upon the properties of polymers.
A Computational Model for High Speed Screening of Polymer Microstructures
Authors: Wang Kegang , Glicksman Martin E. , Rajan Krishna
Published: February 2004

Summary: In this paper we outline a computational strategy that permits the modeling of simultaneous interactions between very large numbers of polymer aggregates. Using a multiparticle diffusion method, we have simulated the dynamics of phase coarsening which can serve as the basis of conducting “virtual” combinatorial experiments and high‐throughput screening of pore size distributions for ultrafiltration membranes.

Particle size distributions for various volume fractions of aggregates calculated for two thousand polymer aggregates.

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Particle size distributions for various volume fractions of aggregates calculated for two thousand polymer aggregates.
On the Estimation of Flow Properties of Polyolefins Based on Fast and Conventional Size Exclusion Chromatography
Authors: Gabriel Claus , Lilge Dieter , Laun Hans Martin , Rüllmann Maximilian , Schulze Dirk , Friedrich Christian
Published: February 2004

Summary: The present article highlights the possible perdiction of flow properties of polyolefins by fast and conventional size exclusion chromatography measurements. By using a rheological model based on double reptation the viscosity function under shear can be predicted from the molecular mass distribution. The predicted flow curves for polyolefins of narrow molecular mass distributions agree fairly well with the measured data.

Comparison of predicted and measured complex viscosity functions of polyethylenes with narrow molecular mass distribution.

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Comparison of predicted and measured complex viscosity functions of polyethylenes with narrow molecular mass distribution.
The Combinatorial Approach: A Useful Tool for Studying Epitaxial Processes in Doped Magnetic Semiconductors
Authors: Tsui Frank , Chu Yong S.
Published: February 2004

Summary: We describe the recent discovery of promising new Ge‐based magnetic semiconductors and heterostructures using combinatorial molecular‐beam epitaxy for the science and applications of spintronics. We discuss key experimental considerations for implementing combinatorial synthesis and characterization, and highlight important findings in epitaxial films of (100) Ge doped by Co and Mn, specifically the ternary epitaxial phase‐diagram, and the novel magnetic and electrical‐transport phenomena. We illustrate the natural “marriage” between the controlled synthesis and combinatorial approach, and demonstrate the usefulness of the approach for studying complex epitaxial processes.

Epitaxial phase‐diagram of CoxMnyGe1 − x − y (100) films.

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Epitaxial phase‐diagram of CoxMnyGe1 − x − y (100) films.
Novel Method for the Synthesis of Molecularly Imprinted Polymer Bead Libraries
Authors: Kempe Henrik , Kempe Maria
Published: February 2004

Summary: A novel method for the synthesis of spherical molecularly imprinted polymer (MIP) beads by suspension polymerization in mineral oil is described. The usefulness of the method was demonstrated by the synthesis of a propranolol imprinted MIP library. The composition of the library was generated by statistical experimental design. Multivariate data analysis correlated the screening data, obtained by a radioligand binding assay, to the composition of the MIPs.

Light micrograph of MIP beads (MIP 4; size fraction 25–50 μm).

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Light micrograph of MIP beads (MIP 4; size fraction 25–50 μm).
Micro‐Flow Reaction Systems for Combinatorial Syntheses
Authors: Kikutani Yoshikuni , Kitamori Takehiko
Published: February 2004

Summary: Micro‐flow chemical processes, which are attracting great attention lately, offer more than the advantage of size. In microspaces, mass and heat transfer lengths are short, the specific interfacial area is large, and heat capacity is remarkably small compared with the situation in conventional scale reaction vessels. These characteristics make precise control of reaction conditions possible, and higher selectivity and conversion can be obtained. In some cases, reactions that are too dangerous to be carried out on a conventional scale can be safely done using micro‐flow reaction systems. Recently, some researchers have developed basic model systems for solution‐phase combinatorial synthesis by utilizing micro‐flow chemical processes. There are two types of combinatorial synthesis systems using micro‐flow chemical processes: parallel reaction systems and sequential reaction systems. In parallel reaction systems, components in starting libraries are simultaneously mixed in all possible combinations by using many micro reaction channels. In addition to needing as many pumps as the starting materials and as many reaction channels as members of the product library, complicated three‐dimensional piping is necessary to connect the pumps and the micro reaction channels. In sequential reaction systems, segments of starting materials are sequentially injected and reacted in a single micro reaction channel in all possible combinations. The latter systems are usually smaller than the former, however, relatively large fluid control devices are necessary in both of them, and improvement of micro‐fluid‐control devices is a critical issue for putting micro‐combinatorial‐synthesis systems to practical use.

Parallel micro‐flow reaction system made up of multiple micro chemical chips for combinatorial 2 × 2 synthesis.

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Parallel micro‐flow reaction system made up of multiple micro chemical chips for combinatorial 2 × 2 synthesis.
A Cold Plasma Generator and its Applications to Combinatorial Copolymerization of Carbon Dioxide with Organic Molecules
Authors: Terajima Takeshi , Koinuma Hideomi
Published: February 2004

Summary: As an energy minimum process for CO2 fixation, we propose the reaction of CO2 with a hydrocarbon excited by our originally designed plasma reactor. In this reactor, the CO2/hydrocarbon ratio and pulsed plasma mode can be changed combinatorially to produce plasma copolymers under sequentially controlled conditions. The presence of CO double bonds in the FT‐IR spectra of the insoluble films confirmed that CO2 has actually been incorporated into the plasma polymerized products.

FT‐IR spectra of products copolymerized from a CO2/C2H4 system (a), and relative intensities of the carbonyl absorbance (b).

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FT‐IR spectra of products copolymerized from a CO2/C2H4 system (a), and relative intensities of the carbonyl absorbance (b).
An Electrochemical Robotic System for the Optimization of Amperometric Glucose Biosensors Based on a Library of Cathodic Electrodeposition Paints
Authors: Reiter Sabine , Ruhlig Dirk , Ngounou Bertrand , Neugebauer Sebastian , Janiak Sandra , Vilkanauskyte Aiste , Erichsen Thomas , Schuhmann Wolfgang
Published: February 2004

Summary: A library of 148 cathodic electrodeposition paints was synthesized and the properties of related amperometric glucose biosensors were evaluated. For this a novel automatic electrochemical robotic system was designed. The automatic biosensor fabrication and characterization sequence involves the electrochemically induced precipitation of the cathodic paint on the electrode surface in the presence of glucose oxidase, the conditioning of the obtained polymer layer, the recording of a glucose calibration graph and the quantitative dissolution of the polymer film and cleaning of the electrode surface.

Schematic representation of the developed electrochemical robotic system for electrochemical screening in microtiter plates.

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Schematic representation of the developed electrochemical robotic system for electrochemical screening in microtiter plates.
Molecularly Imprinted Polymers via High‐Throughput and Combinatorial Techniques
Authors: Lanza Francesca , Sellergren Börje
Published: February 2004

Summary: Techniques allowing high‐throughput synthesis and evaluation of molecularly imprinted polymer sorbents at a reduced scale (mini‐MIPs) have been developed and used for the optimisation of MIPs for recognition of target molecules in various environments. The most recent technique incorporates a liquid‐handling robot for the rapid dispensing of monomers, templates, solvents and initiator into the reaction vessels of a 96‐well plate. A library of 96 polymers, each of about 50 mg, can thus be prepared within 24 hours and the binding properties assessed within one to two weeks by quantification of nonbound fractions in parallel. Examples of how mini‐MIPs have been used as a tool to find superior MIPs for various targets (e.g. hydantoins, dihydropyridines, pteridines, triazines, drug lead compounds) and how to optimise them for particular matrices will be given. Applications of the resulting materials encompass selective solid‐phase extraction for quantitative analysis, chemical sensors, sorbents for preparative separations, screening tools in drug discovery and enzyme‐like catalysis.

Semiautomated high‐throughput procedure for the synthesis of mini‐MIP libraries in microtiter plate format and evaluation of the library via serial (HPLC) or parallel (multifunctional plate reader) techniques.

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Semiautomated high‐throughput procedure for the synthesis of mini‐MIP libraries in microtiter plate format and evaluation of the library via serial (HPLC) or parallel (multifunctional plate reader) techniques.
Combinatorial Growth and Analysis of the Transparent Conducting Oxide ZnO/In (IZO)
Authors: Taylor Matthew P. , Readey Dennis W. , Teplin Charles W. , van Hest Maikel F. A. M. , Alleman Jeff L. , Dabney Matthew S. , Gedvilas Lynn M. , Keyes Brian M. , To Bobby , Parilla Philip A. , Perkins John D. , Ginley David S.
Published: February 2004

Summary: Compositionally graded, combinatorial libraries of indium‐doped zinc oxide (IZO) were grown by DC‐magnetron sputtering on glass at 100 °C. The In content ranged from 5 to 50 cation‐%. The highest conductivity, σ = 2 000 Ω−1 · cm−1 with μ = 25 cm2 · V−1 · s−1, was found at ≈50% In content with a visible transmittance greater than 80%. The (00l) layer spacing increased from ≈2.6 to 2.85 Å as the In content increased from 5 to 50%.

Conductivity as a function of indium content for the three In‐Zn‐O transparent conducting oxide libraries studied here.

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Conductivity as a function of indium content for the three In‐Zn‐O transparent conducting oxide libraries studied here.
The Effect of Temperature on the Living Cationic Polymerization of 2‐Phenyl‐2‐oxazoline Explored Utilizing an Automated Synthesizer
Authors: Hoogenboom Richard , Fijten Martin W. M. , Schubert Ulrich S.
Published: February 2004

Summary: The temperature dependency of the polymerization of 2‐phenyl‐2‐oxazoline was investigated utilizing a commercially available automated synthesizer equipped with individually heatable reactors. Kinetic investigations resulted in an optimal polymerization temperature and activation energy determination for the polymerizations initiated with methyl tosylate. Moreover, the in situ generation of benzyl iodide (more reactive initiator) from benzyl chloride and sodium iodide is described, whereby solid sodium iodide was automatically dosed into the reactors.

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High‐Throughput Evaluation of the Wettability of Polymer Libraries
Authors: Thaburet Jean‐François , Mizomoto Hitoshi , Bradley Mark
Published: February 2004

A high‐throughput method for assessing the wettability of polymer libraries has been developed. Droplets of water are dispensed by a liquid handler onto polymer films, and a digital camera mounted on the robotic arm records the spread of the droplets. The surface area of the droplet (related to the contact angle) was measured by image processing software. This method is fully automated and allows rapid wettability measurements of polymer libraries to be obtained.

Automated system for spreading area measurement of water droplets on polymer films.

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Automated system for spreading area measurement of water droplets on polymer films.
Combinatorial Investigation of the Vapor Deposition Polymerization of Aromatic Polyimides
Authors: Bäte Markus , Neuber Christian , Giesa Reiner , Schmidt Hans‐Werner
Published: February 2004

Summary: A combinatorial study on the synthesis and in situ orientation of polyimide thin films by vapor deposition polymerization was carried out. The combinatorial libraries consisted of sectors with different thicknesses, compositions, and with or without alignment layers. Monomers were selected to prepare rigid rodlike polyimides and to optimize their orientation during deposition and the imidization process. Vapor deposition of the monomers was performed sequentially or by coevaporation. By using this combinatorial approach the polymerization and the orientation behavior can be simultaneously studied and optimized by variation of film thickness, film composition, and deposition sequence.

The combinatorial substrate for sequential evaporation consists of sectors with three PTFE alignment layers (rows B, C, and E) on quartz glass for UV/Vis measurements.

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The combinatorial substrate for sequential evaporation consists of sectors with three PTFE alignment layers (rows B, C, and E) on quartz glass for UV/Vis measurements.
Materials Screening and Combinatorial Development of Thin Film Multilayer Electro‐Optical Devices
Authors: Thelakkat Mukundan , Schmitz Christoph , Neuber Christian , Schmidt Hans‐Werner
Published: February 2004

Summary: Rapid materials screening and combinatorial development of thin film multilayer electro‐optical devices is essential for fast research and development progress and the implementation of device structures into commercial products. A well‐established and reliable film preparation technique within the required nanometer film thickness range is vapor deposition. The combinatorial approach underlying this feature article is based on the preparation of linear or step gradient and the preparation of sectors of material combinations or device structures by using mask movements in combination with a rotation of the substrate. Both of the two principles are combined to obtain an infinite number of possible libraries with different complexity, which may differ in each sector by the layer thickness, the sequence of layers, and the material selection. In addition by simultaneous evaporation using two or more sources and varying the deposition rate, material compositions can also be created. In this feature article we review our work on combinatorial material screening and combinatorial optimization of multilayer thin film organic electro‐optical devices prepared by vapor deposition. This article covers results on organic light emitting devices (OLEDs), organic solar cells, the orientation behavior of formanisotropic functional molecules on alignment layers and the in situ preparation and orientation of rodlike and thermally stable aromatic polyimides.

Example of a combinatorial vapor deposition technique, which is a powerful tool to screen efficiently new materials and configurations in thin film multilayer electro‐optical devices.

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Example of a combinatorial vapor deposition technique, which is a powerful tool to screen efficiently new materials and configurations in thin film multilayer electro‐optical devices.
Individual quality of life of patients undergoing autologous peripheral blood stem cell transplantation
Authors: Frick E. , Borasio G.D. , Zehentner H. , Fischer N. , Bumeder I.
Published: February 2004

Background. Most quality‐of‐life (QoL) studies in autologous Peripheral Blood Stem Cell Transplantation (PBSCT) are descriptive and concentrate on symptom severity and functional deficits. The aim of this study is to compare individual QoL (iQoL) with health‐related QoL (hrQoL) and functional status of patients before high‐dosed therapy/PBSCT.

Patients and methods. Multiple Myeloma, non‐Hodgkin's Lymphoma and other tumor patients were asked to complete the following measures before high‐dosed therapy/PBSCT: the European Organization for Research and Treatment of Cancer (EORTC) Quality‐of‐life Questionnaire Core 30 (QLQ–C30), and the Schedule for the Evaluation of Individual QoL—Direct Weighting (SEIQoL–DW), a patient‐generated instrument which allows the patients to nominate the five most important domains (cues) for their present QoL. The SEIQoL‐DW assessment generates: (1) a global QoL score (SEIQoL‐INDEX), calculated as Σ(levels×weights); (2) the current overall QoL, rated on a visual analogue scale (VAS). Additional measures included demographic data, clinical disease status of remission and Karnofsky's index.

Results. Seventy‐nine patients completed both types of questionnaires. The QoL domains nominated by the patients were assigned to groups (aggregated cues), the most frequent of which were family (89%), hobbies/pastimes (74%), health (physical, including mobility) (70%), profession/occupation (51%), social life/friends (47%) and marriage/partnership (33%). There was no correlation between the SEIQoL‐DW total scores and the EORTC QLQ‐C30 scale or the Karnofsky index.

Conclusion. Individual QoL as assessed by the SEIQoL–DW is unrelated to standard health‐status measures such as the EORTC QLQ‐C30 or the Karnofsky index. Patient‐perceived iQoL in PBSCT seems to depend largely on areas others than health and physical functioning, with the family playing a prominent role. Copyright © 2003 John Wiley & Sons, Ltd.
First principles study of the structure, electronic state, and stability of CmN2 clusters
Authors: Jiang Zhen‐Yi , Xu Xiao‐Hong , Wu Hai‐Shun , Zhang Fu‐Qiang , Jin Zhi‐Hao
Published: February 2004

Geometric and electronic properties of CmN2 (m = 1–14) clusters have been investigated by density functional theory using the hybrid B3LYP functional and the 6‐311G(d) basis set. Harmonic frequencies for these clusters are given to aid in the characterization of the ground states. These results show that CmN2 (m = 1–14) clusters form linear structures with D∞h symmetry. Two N atoms favor to bond at ends in linear isomers. The chains with odd m have triplet ground states whereas the ones with even m have singlet ground states. The calculated HOMO–LUMO gaps and ionization potentials all show that the CmN2 (m = 1–14) clusters with even m are more stable than those with odd m, which is consistent with the observed even–odd alternation of the time‐of‐flight signal intensities. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Determination of Abacavir in maternal plasma, amniotic fluid, fetal and placental tissues by a polarity switching liquid chromatography/tandem mass spectrometry method
Authors: Clark T. Nicole , White Catherine A. , Bartlett Michael G.
Published: February 2004

A rapid and efficient high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method for the determination of concentrations of the carbocyclic nucleoside antiviral Abacavir in maternal rat plasma, amniotic fluid, placental and fetal tissue samples has been developed and validated. All tissue samples were homogenized in water prior to analysis and all samples were prepared by acetonitrile precipitation followed by dilution with HPLC‐grade water. Separation of the analyte and internal standard from the matrices was achieved on a C8 analytical column (2.1 × 150 mm, 5 μm particle size). The mobile phase consisted of 10 mM ammonium acetate/acetonitrile using a gradient method at a flow rate of 0.25 mL/min for all matrices. The method yields retention times of approximately 3.4 and 5.1 min for the internal standard (Azidouridine) and Abacavir, respectively. For all matrices the limit of detection was approximately 1 ng/ml. Recoveries from the different matrices ranged from 53–87% for Abacavir and from 69–84% for Azidouridine. Within‐ and between‐run precision (%RSD) and accuracy (%Error) were under 15% for all matrices. Copyright © 2004 John Wiley & Sons, Ltd.
Structural assignment of isomeric 2‐aminopyridine‐derivatized oligosaccharides using MSn spectral matching
Authors: Takegawa Yasuhiro , Ito Shinya , Yoshioka Shinji , Deguchi Kisaburo , Nakagawa Hiroaki , Monde Kenji , Nishimura Shin‐Ichiro
Published: February 2004

Two isomeric pairs of 2‐aminopyridine (PA)‐derivatized fucosylated and non‐fucosylated oligosaccharides (complex‐type N‐glycans of IgG) were analyzed using liquid chromatography/ion trap mass spectrometry (LC/ITMS) with a sonic spray ionization source and by varying the collision‐induced dissociation voltage. Reproducibility of MSn (n = 2) spectra obtained by LC/ITMS was tested considering both fragment ions (m/z) and intensities. A comparison of their MSn spectra and evaluation of similarities (or matching), based on correlation coefficients between MSn spectra, was investigated as a possibility for structural assignment of the isomers. It is shown that such MSn spectral matching is useful and applicable to the structural assignment of relatively large fucosylated and sialylated PA‐oligosaccharides released from IgG based on Bn‐ and Yn‐type fragmentations of the corresponding [M+H+Na]2+ ions. Copyright © 2004 John Wiley & Sons, Ltd.
Use of 13C to monitor soil organic matter transformations caused by a simulated forest fire
Authors: Fernandez Irene , Cabaneiro Ana , González‐Prieto Serafín J.
Published: February 2004

Soil organic matter (SOM) transformations caused by heating were analyzed using the stable carbon isotope 13C as a tracer to follow C mineralization dynamics and C transfers between different organic compartments. A 13C‐labelled soil, obtained by incorporation of 13C‐enriched Lolium perenne phytomass into a pine forest soil, was heated for 10 min at 385°C to reproduce conditions typical of a forest fire and changes in total C content, potential C mineralization activity and C distribution between the different soil organic fractions were determined. Changes caused by heating on the potential soil C mineralization, determined by laboratory aerobic incubation, reveal alterations to the SOM biodegradability; some stabilized SOM showed an increase in biodegradability, whereas less stabilized SOM became more resistant to microorganisms. Chemical fractionations of SOM allowed us to monitor changes in its composition. As a consequence of heating, the less polymerized humic fractions were the most strongly affected, with the total disappearance of fulvic acids. A significant increase in the quantity and degree of polymerization of the humic acids at the expense of other more 13C‐enriched substances was also found. Finally, a large decrease in humin was observed, its solubilizable part disappearing completely, probably as a consequence of the incorporation of the byproducts into the free organic matter fraction. Copyright © 2004 John Wiley & Sons, Ltd.
New fragmentation mechanisms in matrix‐assisted laser desorption/ionization time‐of‐flight/time‐of‐flight tandem mass spectrometry of carbohydrates
Authors: Spina Emanuela , Sturiale Luisa , Romeo Donatella , Impallomeni Giuseppe , Garozzo Domenico , Waidelich Dietmar , Glueckmann Matthias
Published: February 2004

The spectra recorded by matrix‐assisted laser desorption/ionization time‐of‐flight/time‐of‐flight tandem mass spectrometry (MALDI‐TOF/TOF‐MS/MS) of complex carbohydrates from human milk are presented. Besides ions originating from glycosidic cleavages and from sugar ring fragmentations, these spectra show intense peaks that may be assigned to ions produced by three new fragmentation pathways involving a six‐atom rearrangement. These ions, together with the A fragments from sugar ring fragmentations, open the possibility of obtaining a complete mapping of the linkage positions present in the carbohydrates investigated by MALDI‐TOF/TOF. Copyright © 2004 John Wiley & Sons, Ltd.
Diagnostic ions for the rapid analysis by nano‐electrospray ionization quadrupole time‐of‐flight mass spectrometry ofO‐glycans from human mucins
Authors: Robbe Catherine , Capon Calliope , Coddeville Bernadette , Michalski Jean‐Claude
Published: February 2004

Nano‐electrospray ionization quadrupole time‐of‐flight mass spectrometry (nanoESI‐Q‐TOFMS) was used for sensitive mapping and sequencing of underivatized oligosaccharide alditols obtained from human mucins. Using subnanomolar amounts of oligosaccharides previously analyzed by nuclear magnetic resonance (NMR), series of diagnostic ions relevant to the structural characterization ofO‐glycans were deduced. Determination of the core type as well as positions and partial linkages of fucose residues could be readily obtained from the dominant [M+Na]+ions. Differentiation of isomeric structures and glycosidic linkages were defined by the characteristic cross‐ring0,2A‐type cleavages in the negative ion mode. Tandem (MS/MS) mass spectra of [MH]−ions from sialylated or sulfatedO‐glycans revealed information concerning the position and linkage of such residues. These fragmentation rules were further applied in the structural determination of glycans from human colonic mucins. All these findings indicated the efficiency of ESI‐Q‐TOFMS for the determination of oligosaccharide composition, sequence, partial linkage and substitution, providing a wealth of structural information with sensitivity sufficient for the analysis of quantities as obtained from natural sources. Copyright © 2004 John Wiley & Sons, Ltd.
Mass spectral fingerprints of detergents in gasolines using electrospray ionization
Authors: Carraze B. , Delafoy J. , Bertin J. , Beziau J.‐F. , Lange C. M.
Published: February 2004

Mass spectral fingerprints of detergents in Austrian, Hungarian, Uruguayan, and Chilean gasolines have been obtained using electrospray ionization mass spectrometry. Polymers or copolymers were observed based on ether motifs (inter‐peak spacings of 44, 58 and 72 u) in all samples. Austrian gasoline was found to also contain polymers based on isobutene‐amine. Copyright © 2004 John Wiley & Sons, Ltd.
In vitro metabolism of ethoxidine by human CYP1A1 and rat microsomes: identification of metabolites by high‐performance liquid chromatography combined with electrospray tandem mass spectrometry and accurate mass measurements by time‐of‐flight mass spectrometry
Authors: Deroussent Alain , Ré Micheline , Hoellinger Henri , Vanquelef Enguerran , Duval Olivier , Sonnier Michèle , Cresteil Thierry
Published: February 2004

Ethoxidine (N‐methyl‐12‐ethoxy‐2,3,8,9‐tetramethoxybenzo[c]phenanthridinium methylsulfonate salt) is a synthetic 2‐methoxy‐12‐ethoxy derivative of the natural alkaloid fagaronine. This new inhibitor of DNA‐topoisomerase I is considered as a potential antitumor agent with higher in vitro activity than fagaronine. In order to further improve the efficiency of ethoxidine, its in vitro biotransformation by hepatic monooxygenases and the structures of its metabolites were investigated by high‐performance liquid chromatography (HPLC) combined with electrospray ionization tandem mass spectrometry (ESI‐MS/MS) and accurate mass measurement by time‐of‐flight mass spectrometry (TOFMS). When ethoxidine was incubated with BNF‐treated rat liver microsomes or with cells expressing different recombinant human cytochrome P450, the same four ethoxidine metabolites (m1–m4) were detected and were formed exclusively by CYP1A1. The structures of these metabolites were assigned from ESI‐MS/MS mass spectra and compared with those of ethoxidine derivatives. Accurate mass measurements of in‐source ESI‐TOFMS fragment ions exhibited successive neutral losses of C2H4 and CO for ethoxidine and its metabolites. Whereas a 15 Da loss (methyl radical) was observed for the metabolites m1–m4 containing a quaternary ammonium group, a 16 Da loss (methane) was observed for ethoxidine and could have resulted from the presence of two methoxy groups at adjacent positions (C‐2 and C‐3). The proposed oxidative modifications of ethoxidine were further confirmed by determination of the number of exchangeable hydrogen atoms and by the proposed elemental compositions of the metabolites based on accurate mass measurements by TOFMS. Two major metabolites resulted from O‐demethylation of ethoxidine; one was tentatively identified as 12‐ethoxyfagaronine (m3) and the second as an O‐demethylated ethoxidine isomer (m4). Two polar metabolites were shown to be O‐demethylated (m1) and hydroxylated (m2) derivatives of 12‐ethoxyfagaronine. When 12‐ethoxyfagaronine was incubated under the same conditions as ethoxidine, m2 was formed, thus supporting the proposal that 12‐ethoxyfagaronine is the primary oxidative product of ethoxidine. Copyright © 2004 John Wiley & Sons, Ltd.
Quantitation of human glutathione S‐transferases in complex matrices by liquid chromatography/tandem mass spectrometry with signature peptides
Authors: Zhang Fagen , Bartels Michael J. , Stott William T.
Published: February 2004

Direct quantitation of glutathione S‐transferase (GST) isoforms [α (GST‐A) and μ (GST‐M)] in human liver cytosol was achieved by liquid chromatography/tandem mass spectrometry (LC/ESI‐MS/MS) analysis of signature peptides of GST‐A and GST‐M and their corresponding stable isotopic peptide internal standards via multiple reaction monitoring (MRM). The selection of signature peptides was performed via trypsin digestion of commercially available cDNA‐expressed GST‐A1 and GST‐M1, followed by LC/ESI‐MS/MS with an ion trap mass spectrometer and sequencing with the TurboSEQUEST® application. Quantitative analysis of the selected signature peptides in the multi‐reaction monitoring (MRM) mode was performed using a triple‐quadruple mass spectrometer. A series of human cytosol samples was quantitatively analyzed for levels of GST‐A and GST‐M. The total level of GST‐A and GST‐M obtained from this LC/ESI‐MS/MS method was well correlated with the total level of GST determined by the 1‐chloro‐2,4‐dinitrobenzene (CDNB) method. Copyright © 2004 John Wiley & Sons, Ltd.
Comparison of analyses of urinary 8‐hydroxy‐2′‐deoxyguanosine by isotope‐dilution liquid chromatography with electrospray tandem mass spectrometry and by enzyme‐linked immunosorbent assay
Authors: Hu Chiung‐Wen , Wu Ming‐Tsang , Chao Mu‐Rong , Pan Chih‐Hong , Wang Chien‐Jen , Swenberg James A. , Wu Kuen‐Yuh
Published: February 2004

A highly sensitive and selective method, using isotope‐dilution liquid chromatography with tandem mass spectrometry (LC/MS/MS), for quantification of urinary 8‐hydroxy‐2′‐deoxyguanosine (8‐OHdG), an important biomarker of oxidative stress, was developed and compared with a method using an enzyme‐linked immunosorbent assay (ELISA). The synthesis of 15N5‐8‐OHdG is described. In this study, 140 urine samples were collected from workers in a coke oven plant, including samples from 49 control workers and 91 workers who had been occupationally exposed to polyaromatic hydrocarbons (PAHs). The major urinary metabolite of PAHs, 1‐hydroxypyrene (1‐OHP), was measured for the exposed workers. Results from the present study showed a significant correlation between these two measurements for determination of 8‐OHdG (p < 0.05, r2 = 0.70). However, only the LC/MS/MS measurements of urinary levels of 8‐OHdG showed a significant difference between the exposed and the control subjects (p < 0.05). The ELISA method failed to demonstrate this difference. Furthermore, only by using the LC/MS/MS method was a significant correlation observed between the urinary levels of 1‐OHP and 8‐OHdG. These findings suggest that a highly specific and sensitive analytical method such as isotope‐dilution LC/MS/MS is extremely important and necessary for accurate measurement and a comprehensive study of oxidative stress in human subjects. Copyright © 2004 John Wiley & Sons, Ltd.
A fully automated method for accurate mass determination using high‐performance liquid chromatography with a quadrupole/orthogonal acceleration time‐of‐flight mass spectrometer
Authors: Colombo Maristella , Sirtori Federico Riccardi , Rizzo Vincenzo
Published: February 2004

A generic LC/ESI(+)‐oaTOFMS method has been developed for routine automated high accuracy mass determinations of different classes of substances. The system makes use of micro‐high‐performance liquid chromatography and a hybrid quadrupole/orthogonal acceleration time‐of‐flight (Q‐oaTOF) mass spectrometer. Reproducible and accurate mass measurements were obtained using an electrospray dual sprayer with reserpine as reference compound, introduced into the mass spectrometer alternating with the samples. Experiments were performed to optimize analyte/reference response ratio, statistical algorithm correction setting, and analyte concentration. In these experiments, a clear dependence of the mass measurement error on the analyte/reference response ratio was observed. The dependence of average mass error versus different dead time correction algorithm settings (Np factors) was also explored. In the final automated procedure, verified for a statistically significant set of compounds (∼550) obtained from a medicinal chemistry department, about 70% of the analyzed samples satisfied the acceptance criteria fixed at a maximum error of ±5 ppm (mass range 150–800 Da). Copyright © 2004 John Wiley & Sons, Ltd.
Measuring myoelectric fatigue of the serratus anterior in healthy subjects and patients with long thoracic nerve palsy
Authors: Ebied Ayman M. , Kemp Graham J. , Frostick Simon P.
Published: February 2004

Proper function of serratus anterior plays a vital role in the movement and stability of the scapula, and thus of the glenohumeral joint and the upper limb. The unique anatomy of this muscle makes direct measurements of its fatigue properties impossible. Here we describe for the first time indirect measurements of the myoelectric manifestations of fatigue in the serratus anterior. Eight healthy volunteers (29–35 years) were tested, four of them on two different occasions, using two exercise protocols (60 s isometric maximum upward force in 120° arm flexion, and 60 s maximum forward force at 90° arm flexion) with simultaneous recording by surface and wire electrodes applied according to established methods. Signals were analysed to obtain the rate of fall of median EMG frequency and the rate of rise of amplitude. Both exercise protocols gave similar results. Frequency‐slope measurements (mean rate of fall 0.6 ± 0.1% initial value per second (% s−1) with both surface and wire electrodes) were more precise than those of amplitude (mean rate of rise 2.6 ± 0.3% s−1 with surface electrodes, only 1.3 ± 0.2% s−1 with wire electrodes). Surface electrodes gave much lower variation than fine wires, the coefficient of variation of slopes for surface electrodes being approximately 20–40% both between studies in a single subject and between subjects. In 5 patients (aged 22–59 years) recovering from long thoracic nerve palsy studied using surface electrodes the frequency slopes was normal (0.6 ± 0.1% s−1), while the amplitude slope was reduced (0.9 ± 0.4% s−1, P = 0.01). This shows abnormal fatigue properties of the reinnervated muscle and a dissociation between the frequency and amplitude manifestations of fatigue. Crown Copyright © 2003 Published by Elseiver Ltd. on behalf of Orthopaedic Research Society. All rights reserved.