bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactions of Silicon Atoms with Benzene: A Matrix‐Spectroscopic Study
Authors: Maier Günther , Reisenauer Hans Peter 
Published: May 2004

AbstractThe reaction of silicon atoms with benzene in argon at 10 K has been studied. The addition to the aromatic π‐system of benzene occurs in a [1,4]‐fashion. Upon irradiation the π‐adduct 7‐silabicyclo[2.2.1]heptadien‐7‐ylidene (2) rearranges to the formal C−C insertion product 1‐silacycloheptatrienylidene (3). The structural elucidation of the new species is based on comparison of the experimental observations with density functional calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
On the Mechanism of the Oxygen Transfer to Sulfoxides by (Peroxo)[tris(hydroxyalkyl)amine]TiIV Complexes − Evidence for a Metal‐Template‐Assisted Process
Authors: Bonchio Marcella , Bortolini Olga , Licini Giulia , Moro Stefano , Nugent William A. 
Published: May 2004

AbstractOxidation of p‐XC6H4SOMe (X = NC, F3C) by (alkylperoxo){tris[(2R)‐2‐hydroxy‐2‐phenylethyl]amine}titanium (2b) has been shown to follow Michaelis−Menten kinetics demonstrating the occurrence of an intramolecular nucleophilic oxygen transfer to the TiIV‐coordinated sulfoxide. The reaction of the titanium(IV) precursors 1 with sulfoxides has been studied by ESI‐MS techniques together with ab initio calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Oxidation of Benzylic Alcohols and Ethers to Carbonyl Derivatives by Nitric Acid in Dichloromethane
Authors: Strazzolini Paolo , Runcio Antonio 
Published: May 2004

AbstractNitric acid in dichloromethane may be successfully employed for the oxidation of benzylic alcohols and ethers to the corresponding carbonyl compounds. The proposed method proved to be of general applicability, affording very good yields of aldehydes and ketones and showing interesting chemoselectivity in many instances, allowing competitive aromatic nitration to be avoided, as well as − in the case of aldehydes − any further oxidation to carboxylic acids. The reaction probably proceeds by a radical mechanism, the active species in the oxidation process being NO2. Competitive formation of nitro esters was observed in some cases, whereas poor results were obtained with allylic and non‐benzylic substrates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Concise and Efficient Synthesis of seco‐Duocarmycin SA
Authors: Tietze Lutz F. , Haunert Frank , Feuerstein Tim , Herzig Tobias 
Published: May 2004

AbstractA short and efficient synthesis of seco‐duocarmycin SA (3), a highly potent cytostatic agent and direct precursor of the natural product duocarmycin SA (1), has been achieved. Starting from commercially available 2‐methoxy‐4‐nitroaniline (4) the synthetic protocol contains a Fischer indole synthesis to introduce the heterocyclic scaffold and a radical 5‐exo‐trig cyclization to furnish the (chloromethyl)indoline ring system as key reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Trend assessment in a long memory dependence model using the discrete wavelet transform
Authors: Craigmile Peter F. , Guttorp Peter , Percival Donald B. 
Published: May 2004

AbstractIn this article we consider trend to be smooth deterministic changes over long scales, and tackle the problem of trend estimation in the presence of long memory errors (slowly decaying autocorrelations). Using the fractionally differenced (FD) process as a motivating example of such a long memory process, we demonstrate how the discrete wavelet transform (DWT) is a natural choice at extracting a polynomial trend from such an error process. We investigate the statistical properties of the trend estimate obtained from the DWT, and provide pointwise and simultaneous confidence intervals for the estimate. Based on evaluating the power in the trend estimate relative to the estimated errors, we provide a test of nonzero trend. We finish by applying the methods to a climatological example. Copyright © 2004 John Wiley & Sons, Ltd.
PRDX4, a member of the peroxiredoxin family, is fused to AML1 (RUNX1) in an acute myeloid leukemia patient with a t(X;21)(p22;q22)
Authors: Zhang Yanming , Emmanuel Neelmini , Kamboj Ginny , Chen Jianjun , Shurafa Muhammad , Van Dyke Daniel L. , Wiktor Anne , Rowley Janet D. 
Published: May 2004

AbstractThe AML1 gene (also known as RUNX1) at 21q22 codes for core binding factor (CBF) α, which forms a heterodimer with CBF β that acts as a transcriptional activating factor. CBF is a critical regulator in the generation and differentiation of definitive hematopoietic stem cells and is frequently disrupted in leukemia through chromosome translocations. We cloned a novel AML1 partner gene, PRDX4, in an X;21 translocation in a 74‐year‐old male patient diagnosed with acute myeloid leukemia–M2. Chromosome analysis detected a t(X;21)(p22;q22) as the sole abnormality in bone marrow samples. The involvement of AML1 was confirmed by fluorescence in situ hybridization studies. Using 3′ RACE‐PCR, we cloned a fusion between exon 5 of AML1 and exon 2 of PRDX4. RT‐PCR confirmed the fusion and detected another fusion between exon 6 of AML1 and exon 2 of PRDX4, indicating alternative splicing of exon 6 of AML1 in the fusion transcripts. PRDX4 is one of six peroxiredoxin‐family genes that are highly conserved in eukaryotes and prokaryotes and are ubiquitously expressed. Peroxiredoxin genes exhibit thioredoxin‐dependent peroxidase activity and have been implicated in a number of other cellular functions such as cell proliferation and differentiation. PRDX4 plays a regulatory role in the activation of the transcription factor NF‐κB and is significantly down‐regulated in acute promyelocytic leukemia. This is the first example of antioxidant enzyme involvement in a chromosome translocation in leukemia. © 2004 Wiley‐Liss, Inc.
Microcell‐mediated chromosome transfer provides evidence that polysomy promotes structural instability in tumor cell chromosomes through asynchronous replication and breakage within late‐replicating regions
Authors: Kost‐Alimova Maria , Fedorova Ludmila , Yang Ying , Klein George , Imreh Stefan 
Published: May 2004

AbstractIt was reported earlier that normal chromosome 3 (chr3) transfer into tumor cells of different origin may suppress their ability to grow in SCID mice. Tumorigenicity may be restored by the loss of certain 3p regions. We transferred a normal cell‐derived chr3 into cells of a human renal cell carcinoma line and followed the chromosomal changes during in vivo and in vitro growth. In cells cultivated for 6 weeks or more and in the tumors grown in SCID mice, supernumerary chrs3 were always rearranged, accompanied by 3p losses. Unexpectedly, we found that the rearrangements affected not only the transferred exogenous chr3, but also the endogenous chrs3. Other chromosomes that were polysomic in the recipient cells were affected as well, suggesting that polysomy may be associated with structural chromosome instability. The dominant chromosomal aberrations were unbalanced translocations with preferentially pericentromeric breakpoints. The breakpoint distribution on chr3 preferentially affected the pericentromeric 3p11 (8 breaks) and 3p12–13 (5 breaks) regions. The regions 3p14 and 3q26–27 occasionally were involved as well (one break in each case). These four regions were the latest replicating, as shown by BrdU incorporation–based replication banding. Using fluorescence in situ hybridization–based replication timing, we detected asynchronous and incomplete centromere replication in cells with 3 or 4 copies of chr3, but not in cells with 2. We concluded that in tumor cells, asynchronous and incomplete replication of polysomic chromosomal parts is associated with aberrations that have breakpoints within the late‐replicating regions. This may explain the increased structural chromosome instability and preferential pericentromeric localization of breakpoints in hyperploid tumors. © 2004 Wiley‐Liss, Inc.
Nitrification by immobilized cells in a micro‐ecological life support system using packed‐bed bioreactors: an engineering study
Authors: Pérez J , Montesinos JL , Albiol J , Gòdia F 
Published: May 2004

AbstractThe nitrifying component of a micro‐ecological life support system alternative (MELISSA) based on microorganisms and higher plants was studied. The MELISSA system consists of an interconnected loop of bioreactors to allow the recycling of the organic wastes generated in a closed environment. Conversion of ammonia into nitrates in such a system was improved by selection of microorganisms, immobilization techniques, reactor type and operation conditions. An axenic mixed culture of Nitrosomonas europaea and Nitrobacter winogradskyi, immobilized by surface attachment on polystyrene beads, was used for nitrification in packed‐bed reactors at both bench and pilot scale. Hydrodynamics, mass transfer and nitrification capacity of the reactors were analysed. Mixing and mass transfer rate were enhanced by recirculation of the liquid phase and aeration flow‐rate, achieving a liquid flow distribution close to a well‐mixed tank and without oxygen limitation for standard operational conditions of the nitrifying unit. Ammonium conversion ranged from 95 to 100% when the oxygen concentration was maintained above 80% of saturation. The maximum surface removal rates were measured as 1.91 gN‐NH4+ m−2 day−1 at pilot scale and 1.77 gN‐NH4+ m−2 day−1 at bench scale. Successful scale‐up of a packed‐bed bioreactor has been carried out. Good stability and reproducibility were observed for more than 400 days. Copyright © 2004 Society of Chemical Industry
Anaerobic acidogenesis of dairy wastewater: the effects of variations in hydraulic retention time with no pH control
Authors: Demirel Burak , Yenigun Orhan 
Published: May 2004

AbstractThe performance of a laboratory‐scale mesophilic acidogenic reactor was evaluated in this study, in terms of volatile fatty acid production and distribution, with respect to variations in hydraulic retention time (HRT). The continuous flow‐completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated in a hydraulic retention time ranging between 24 and 12 h, and up to an organic loading rate of about 9.3 kg COD m−3 d−1, without pH control. The acid production gradually increased proportionally to the organic loading rate, with decrease in hydraulic retention time. The highest degree of acidification and the rate of acid production were 56% and 3.1 g dm−3 d−1 at 12 h of HRT. Variations in hydraulic retention time affected volatile fatty acid production and distribution substantially, for the range investigated. Acetic, propionic, butyric and valeric acids were commonly produced during acidogenesis of dairy wastewater. Copyright © 2004 Society of Chemical Industry
Ultra‐fast essential oil characterization by capillary GC on a 50 μm ID column
Authors: Mondello Luigi , Shellie Robert , Casilli Alessandro , Quinto Tranchida Peter , Marriott Philip , Dugo Giovanni 
Published: May 2004

AbstractA 5 m × 50 μm capillary column with 0.05 μm stationary phase film thickness, with a calculated efficiency of almost 20,000 plates per metre (under optimum conditions), was used for very fast high resolution GC analysis of lime essential oil. The total analysis time of this volatile essential oil was less than 90 s. Fast GC is shown to be appropriate for essential oil quality assurance analysis, and quantitative results of key components are comparable with those obtained by using conventional GC analysis. The fast GC analysis is approximately 33 times faster than the conventional GC method.
Analysis of sulfur‐containing compounds in crude oils by comprehensive two‐dimensional gas chromatography with sulfur chemiluminescence detection
Authors: Hua Ruixiang , Wang Jinghua , Kong Hongwei , Liu Jun , Lu Xin , Xu Guowang 
Published: May 2004

AbstractThis paper reports an analytical method for separating, identifying, and quantifying sulfur‐containing compounds in crude oil fraction (IBP‐360°C) samples based on comprehensive two‐dimensional gas chromatography coupled with a sulfur chemiluminescence detector. Various sulfur‐containing compounds and their groups were analyzed with one direct injection. 3620 peaks were detected including 1722 thiols/thioethers/disulfides/1‐ring thiophenes, 953 benzothiophenes, 704 dibenzothiophenes, and 241 benzonaphthothiophenes. The target sulfur compounds and their groups were identified based on the group separation feature and structured retention of comprehensive two‐dimensional gas chromatography as well as standard substances. The quantitative analysis of major sulfur‐containing compounds and total sulfur was based on the linear response of the sulfur chemiluminescence detector using the internal standard method. The sulfur contents of target sulfur compounds and their groups in 4 crude oil fractions were also determined. The recoveries for standard sulfur‐containing compounds were in the range of 90–102%. The quantitative result of total sulfur in the Oman crude oil fraction sample was compared with those from ASTM D 4294 standard method (total S by X‐ray fluorescence spectrometry), the relative deviation (RD%) was 4.2% and the precision of the method satisfactory.
Reduced‐bore monolithic silica column modified with C8‐TEOS for reversed‐phase electrochromatography
Authors: Qu Qishu , Qu Rongjun , Xu Qiang , Wang Yubao , Wang Xiaorong , He Youzhao 
Published: May 2004

AbstractMonolithic silica columns of 2.7 mm ID were prepared and derivatized with C8‐TEOS and TEOS by on‐column sol‐gel reaction. These C8 large diameter monolithic silica columns gave 21 000 theoretical plates for aromatic hydrocarbons in 60% acetonitrile and 40% Tris‐HCl buffer. The surface areas as well as the separation reproducibility were improved on coating by the sol‐gel approach. Joule heating was greatly reduced by using monolithic columns to which fine quartz sand had been added during column preparation. Since this is a preliminary investigation on a monolithic column with such a large inner diameter, the separation efficiency was not so high as that presently achieved in normal capillary electrochromatography (CEC). However, use of the columns improved sample loadability and concentration detectability of electrochromatography, and semi‐preparative separations could be performed.
Interfacial phenomena in polymer films and generation of maxwell displacement current
Authors: Iwamoto Mitsumasa 
Published: May 2004

AbstractInterfacial electrostatic phenomena in ultrathin polyimide films have been examined, and the space charge distribution and electronic density of states have been determined. The presence of excess negative charges at the film‐metal interface of nanometer thickness has been revealed and the alignment of the surface Fermi level of polymer films and Fermi level of metals have been elucidated. Taking into account the interfacial space charge, a step structure observed in the I‐V characteristic of metal‐polyimide‐rhodamine‐polyimide‐metal junction, very similar to Coulomb staircase, is well explained. Furthermore, the electrical breakdown mechanism of a nanometer‐thick polyimide film is found quite different from that of micrometer‐thick films, owing to the presence of this interfacial nanometric space charge. Finally, for a profound understanding of the behaviour of surface monolayer, the Maxwell displacement current measurement coupled with optical second harmonic generation measurement has been employed.
Traps for charge carriers in molecular materials formed by dipolar species: towards light‐driven molecular switch
Authors: Sworakowski Juliusz , Nešpůrek Stanislav 
Published: May 2004

AbstractThe influence of polar species on the transport and trapping of charge carriers is discussed. Calculations performed on a model molecular lattice demonstrate that polar dopants locally modify the polarization energy thus creating traps for charge carriers in the vicinity of the dipole. The presence of polar dopants in disordered solids gives rise to a broadening of the density‐of‐states function. A scheme of a molecular switch has been put forward, based on electrostatic interactions between photochromic moieties and charge carriers travelling on a molecular wire (conjugated polymer chain).
Correlation between large polarons in molecular chains
Authors: Brizhik Larissa , Eremko Alexander 
Published: May 2004

AbstractWe studied few extra electrons in a molecular chain with the account of electron‐phonon coupling in the adiabatic approximation. It is shown that the lowest state of two extra electrons in a chain corresponds to the singlet bisoliton state with one deformational potential well. Two electrons with parallel spins form a localised triplet state, which corresponds to the two‐hump charge distribution function. Three extra electrons form an almost independent nonlinear superposition of a soliton and bisoliton states. In the case of four electrons, the two almost independent bisolitons are formed. These two states tend to separate in the chain at the maximal distance due to the Fermi repulsion, accounted for in the zero‐order adiabatic approximation. This repulsion is partly compensated by the attraction between the solitons due to their exchange with virtual phonons, described by the non‐adiabatic part of the Hamiltonian. The formation of solitons is characterised by the appearance of the bound soliton and bisoliton levels in the forbidden energy band. This constitutes the qualitative difference of the large polaron (soliton) states from the almost free electron states and small polaron states.
Design of molecular magnets
Authors: Yakhmi J.V. 
Published: May 2004

AbstractThe conventional magnetic materials used in present‐day technology, such as Fe, Fe2O3, Cr2O3, SmCo5, Nd2Fe14B, etc. are all atom‐based, whose synthesis requires high‐temperature routes. Employing ambient‐temperature synthetic organic chemistry, it has become possible to engineer a bulk molecular material with long‐range magnetic order, primarily due to the weak nature of intermolecular interactions in it. Typical synthetic approach to design molecule‐based magnets consists of choosing molecular precursors, each bearing an unpaired spin, and assembling them in such a way that there is no compensation of spins at the scale of the crystal lattice. Magnetism being a co‐operative effect, the spin‐spin interaction must extend to all the three dimensions, either through space or through bonds. Specific occurrence of ‘spin delocalisation’ and ‘spin polarisation’ in molecular lattices is helpful in bringing about ferromagnetic interaction by facilitating necessary intermolecular exchange interactions. Since the first successful synthesis of molecular magnets in 1986, a large variety of them have been synthesized, which can be classified on the basis of the chemical nature of the magnetic units involved: organic systems, metal‐based systems, hetero‐bimetallic assemblies, or mixed organic‐inorganic systems. The design of molecular magnets has also opened the doors for the unique possibility of designing polyfunctional molecular materials, such as magnets exhibiting second‐order optical nonlinearity, liquid crystalline magnets, or chiral magnets. Solubility of molecular magnets, their low density and biocompatibility are attractive features. Being weakly colored, unlike the opaque classic magnets, possibilities of photomagnetic switching can be envisaged. Persistent efforts continue to design the ever‐elusive polymer magnets for applications in industry. While providing a brief overview of the field of molecular magnetism, we highlight some recent developments, with emphasis on a few studies from the author's own lab.
Optical rotatory power of biodegradable polylactic acid films
Authors: Tajitsu Yoshiro 
Published: May 2004

AbstractPolylactic acid (PLA) is a polymer material on which biodegradability research has been the most advanced. PLA is a chiral polymer in which molecules containing asymmetric carbon atoms have a helical structure. Two optical isomers of PLA exist, PLLA (poly(L‐lactic acid)) and PDLA (poly(D‐lactic acid)). In this study, using various physical processes, we fabricated various samples such as oriented PLLA film, PLLA fiber, rolled PLLA film and forged PLLA plate. We observed a large optical rotatory power ρ in the cylindrical plate fabricated using a forging process. ρ of forged PLLA plates is 7200°/mm which is approximately 300 times larger than that of α‐quartz.
Features of charge carrier concentration and mobility in π‐conjugated polymers
Authors: Juška Gytis , Genevičius Kristijonas , Arlauskas Kęstutis , Österbacka Ronald , Stubb Henrik 
Published: May 2004

AbstractWe show the possibilities of experimental investigation of charge carrier mobility and concentration features by extraction methods of equilibrium, photoexcited and injected charge carriers in π‐conjugated polymers, where, due to relatively high conductivity, the classic time‐of‐flight method is inappropriate.
Infrared and Raman studies of the charge ordering in the organic semiconductor κ‐[Et4N][Co(CN)6(ET)4]·3H2O
Authors: Świetlik Roman , Ouahab Lahcène , Guillevic Joseph , Yakushi Kyuya 
Published: May 2004

AbstractPolarised infrared reflectance and Raman spectra of the charge transfer salt κ‐[Et4N][Co(CN)6(ET)4]·3H2O were measured as a function of temperature. The salt undergoes a phase transition at 150 K, which is related to a charge ordering inside conducting ET layers. The charge ordering has a considerable influence on vibrational as well as electronic spectra. New vibrational bands related to ET+ cations are seen below 150 K. Moreover, formation of a new energy gap (charge gap) in electronic excitation spectrum is observed.
Ultraweak spectrally resolved thermoluminescence in polymers
Authors: Mandowska Ewa , Mandowski Arkadiusz , Świątek Józef 
Published: May 2004

AbstractSpectrally resolved thermoluminescence (TL) measurements provide a lot of information concerning trapping and recombination states in various dielectric materials. As long‐lived luminescence is typically weak, this technique requires a very sensitive apparatus. This paper describes the measurement system that is used for studying spectrally resolved TL and phosphorescence decay in polymers. Exemplary investigations are presented for poly(N‐vinylcarbazole) (PVK) thin films. The obtained spectra clearly indicate the influence of solvents (dioxane, chlorobenzene) and excitation wavelengths on TL in PVK samples.
Recombination in complex systems – an analytical approach
Authors: Mandowski Arkadiusz 
Published: May 2004

AbstractA new analytical model is proposed to describe the kinetics of trapping and recombination of charge carriers in complex systems with an arbitrary spatial distribution of traps and recombination centres. The structural properties of a material are described by two functions Γm and Γn irrespective of the thermal history of the sample. A simple method is proposed to determine the function Γm from simultaneous thermoluminescence (TL) and thermally stimulated conductivity (TSC) measurements.
Effect of spatial irregularities on the temperature and field dependence of the mobility in liquid‐crystalline conjugated polymer films
Authors: Martin Simon J. , Kambili Agapi , Walker Alison B. 
Published: May 2004

AbstractWe have performed simulations of time‐of‐flight measurements via the Monte Carlo approach for films made of conjugated polymers in the liquid‐crystalline phase. In spatially regular films with a distribution of on‐site energies the mobility is affected by the interplay between electrostatic and thermal energy. When the width of the on‐site energy distribution is comparable to the thermal energy, the mobility increases with temperature at low fields, but shows the opposite behaviour at larger fields. However, when spatial irregularities in the arrangement of the film are introduced, the mobility is enhanced at all temperatures, as the electrostatic energy plays less of a role in charge transport than thermal activation over energy barriers.