bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anionic Polymerization of Ethylene Oxide in the Presence of the Phosphazene Base ButP4 – Kinetic Investigations Using In‐Situ FT‐NIR Spectroscopy and MALDI‐ToF MS
Authors: Schmalz Holger , Lanzendörfer Michael G. , Abetz Volker , Müller Axel H. E. 
Published: May 2003

AbstractFourier‐transform near‐infrared (FT‐NIR) fiber‐optic spectroscopy was successfully used to monitor the anionic polymerization of ethylene oxide (EO). Kinetic data are provided for the polymerization of EO with the sec‐BuLi/ButP4 initiating system under different reaction conditions. In addition, the influence of different initiators and reaction conditions on the polymerization of EO is investigated. Online monitoring using NIR spectroscopy reveals an unexpected induction period present in EO homopolymerizations as well as in the synthesis of PEO containing block copolymers with [Li/ButP4]+ counterions. The resulting polymers are characterized by size exclusion chromatography (SEC). A low‐molecular‐weight polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) diblock copolymer was synthesized to gain more insight into the observed induction period by matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS) on samples taken during EO polymerization. The induction period is believed to be a result of different factors involved in the formation of active centers, for example, the break up of lithium alkoxide aggregates by the phosphazene base ButP4, and chain length effects. It depends on reaction temperature, concentration of the phosphazene base ButP4, as well as the structure of the initiator.SEC traces for EO homopolymerizations using different initiating systems at 50 °C.magnified imageSEC traces for EO homopolymerizations using different initiating systems at 50 °C.
Missions and Challenges of Polymer Science and Technology
Authors: Horie Kazuyuki 
Published: May 2003

AbstractThis section contains reports on topical conferences. Reports are usually written at the request of the editorial office, but unsolicited contributions are also welcome. Suggestions should be sent to the editorial office of the Macromolecular journals, preferably by E‐mail to macromol@wiley‐vch.de.
Solvent Effects, Diffusion Control and Mechanistic Aspects of Catalytic Chain Transfer Polymerization
Authors: Pierik Sebastiaan C. J. , Vollmerhaus Rainer , van Herk Alex M. 
Published: May 2003

AbstractIn the catalytic chain transfer polymerization of methyl methacrylate, butyl methacrylate and 2‐ethylhexyl methacrylate in toluene, it was found that the chain transfer constants (CT) were independent of solvent concentration and therefore of solution viscosity, and did not differ from the bulk polymerization values. For a diffusion controlled system, theoretical calculations predict an increase in CT when the solution viscosity is lowered. This points at a non‐diffusion controlled catalytic chain transfer step. These results were obtained when the solvent was thoroughly purified using a Grubbs‐type set‐up, whereas a large reduction in CT was found in unpurified solvent. Similar results were obtained for butyl acetate. Therefore it is concluded that the decrease of CT in non‐purified solvents is not related to the solvent itself, but to solvent impurities. Further we found that methyl methacrylate ended radicals do not covalently bind to the cobalt complex, in contrast to styrene and acrylate ended radicals.Chain transfer constant for the CCT polymerization of 2‐ethylhexyl methacrylate in toluene, and predictions for diffusion controlled systems.magnified imageChain transfer constant for the CCT polymerization of 2‐ethylhexyl methacrylate in toluene, and predictions for diffusion controlled systems.
Anionic Ring‐Opening Polymerization of Propylene Oxide in the Presence of Phosphonium Catalysts at Various Temperatures
Authors: Rexin Ornulf , Mülhaupt Rolf 
Published: May 2003

AbstractAnionic ring‐opening polymerization of propylene oxide in the presence of a potassium alkoxide initiator was accelerated by the addition of the bulky phosphonium salts tetrakis[cyclohexyl(methyl)amino]phosphonium‐, tetrakis[propyl(methyl)amino]phosphonium‐, and tetrakis[octyl(methyl)amino]phosphonium‐tetrafluoroborate. Dipropylene glycol (DPG) was partially deprotonated (5%) and used as initiator. The delocalization of the positive charge over five atoms promoted the formation of a separated ion‐pair, thus enhancing nucleophilicity and reactivity. The polymerization behavior of the counterions at varied temperatures was studied. Characterization of poly(propylene oxide)s by means of 1H NMR spectroscopy, size exclusion chromatography (SEC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) showed low polydispersities and the absence of by‐products and impurities. The degree of polymerization (DPn) for the polymers was in the range of 8–60 (Mn = 630–3 620 g · mol−1) and Mw/Mn obtained was 1.03–1.35 and 1.11–1.32 for MALDI‐TOF‐MS and SEC, respectively. Values calculated from the titration of hydroxyl groups (OHV) showed good agreement. Determination of the total degree of unsaturation in the range 13–60 mmol · kg−1 indicated larger amounts with decreasing polymerization rates and increasing polymerization temperatures.The phosphonium salts Cy4PBF, Pr4PBF, and Oc4PBF.magnified imageThe phosphonium salts Cy4PBF, Pr4PBF, and Oc4PBF.
Biospecific Properties of Random Copolymers, 1
Authors: Bouzou Bérengère , Pflüger Fernando 
Published: May 2003

AbstractThe kinetic study of copolymer synthesis is important to understand how a material is built and how it can get some particular properties. The radical copolymerization of one, two or more monomers can be simulated with classical analytic models, but can also be simulated by a Monte Carlo model that allows a bigger flexibility and is a lot easier to compute and use. We have shown that this Monte Carlo simulation gives the same results of the kinetic study of the terpolymerization as the analytic model, and it can create easily a bank of virtual copolymers for all the compositions needed to analyze the structure of the macromolecular chains in terms of sequences of monomers occurring as a function of the global composition. The search for the sequences is very simple to compute as it consists in a simple reading of the virtual chains previously simulated. This result can thus be applied to make appear a simple correlation between the distribution of functional groups and some specific observed biological activities of biospecific copolymers.Simplified schema of the numerical virtual terpolymerization.imageSimplified schema of the numerical virtual terpolymerization.
Adsorption Profiles of Long‐Chain Polymer in Semidilute Solutions Physisorbed to a Wall
Authors: Cifra Peter 
Published: May 2003

AbstractEquilibrium concentration profiles for long macromolecules in solution strongly adsorbed to a flat wall were estimated by a combination of persistent reptation and partial chain regrowth using a configurational bias lattice Monte Carlo method. The profiles were obtained for various concentrations in the semidilute regime and different chain lengths. A master curve exists in a plot of the profile reduced by the bulk concentration as a function of the distance to the wall reduced by the correlation length estimated for the bulk concentration. Near the wall, the master curve follows a power law with an exponent predicted in the scaling theory. Compared to depletion profiles at a repulsive wall that require a small penetration length, no correction of the distance to the wall is needed for the adsorption profiles.Reduced plot of ϕ(x)/ϕbulk vs. x/ξ for chain length N = 1 000 and five bulk concentrations above ϕ* indicated in legend. Slope with the exact exponent from scaling theory is shown for comparison.imageReduced plot of ϕ(x)/ϕbulk vs. x/ξ for chain length N = 1 000 and five bulk concentrations above ϕ* indicated in legend. Slope with the exact exponent from scaling theory is shown for comparison.
Diamagnetic and nonlinear Zeeman shifts in spatially separated electron and hole layers of semiconductor heterostructures with disorder
Authors: Desforges J. , Singh M. R. 
Published: May 2003

AbstractThe effect of the diamagnetic shift on the formation of excitons is investigated for double layer semiconductor systems in which electrons and holes are spatially separated. The effect of disorder due to interface roughness of the double layer structures is included in the calculation of exciton density. Numerical calculations are performed based on an effective lattice‐gas model where the electron–hole system is divided into unit cells. The exciton density is calculated by using the partition function method. The effect of the nonlinear Zeeman splitting is also included in the numerical calculations. It is found that the density of the optically allowed exciton states (excitons with Sz = 0) increases under the influence of either or both the diamagnetic and the nonlinear Zeeman shifts.
High‐pressure phase transitions in semimagnetic semiconductor I: Pb1–xMnxS
Authors: Srivastava Anurag , Singh R. K. , Ahuja R. , Johansson B. 
Published: May 2003

AbstractPressure‐induced structural phase transitions in Pb1–xMnxS (0 < x < 0.05), from the rocksalt (B1) to the CsCl (B2) type phase, have been calculated. The present study of the phase transition is based on the three‐body potential (TBP) approach, which includes long‐range as well as short‐range interactions. The long‐range part consists of a Coulomb and three‐body interactions, whereas the short‐range part includes the van der Waals and overlap repulsive interactions. In order to strengthen the significance of our results and verify the presence of intermediate orthorhombic phase during B1 to B2 structural transition in the host binary compound PbS we performed first principles full potential linear muffin tin orbital approach and provided a good support to our TBP results. Our first‐principles calculations, based on the full potential muffin tin orbital (FPLMTO) method, successfully predicts the TlI type phase and supports the TBP results.
Optical properties and concentration dependence of the luminescence of Pr3+ion in fluoroindate glass
Authors: Mazurak Z. , Pisarski W. A. , Gabryś‐Pisarska J. , Żelechower M. 
Published: May 2003

AbstractOptical absorption and emission spectra are presented for Pr3+and Pr3++ Cr3+ions in fluoroindate glass. Also, X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements are carried out in order to characterize investigated materials. The measured oscillator strengths and radiative rates for several transitions of the Pr3+ion are compared with calculated values. Radiative transition rates for the excited states are determined by using the Judd–Ofelt theory. Energy transfer effects account for the non‐radiative transitions. Although the Judd–Ofelt analysis does not yield the same excellent consistency for Pr3+as for Nd3+and Er3+, the experimental observations are consistent with Judd–Ofelt calculations. The linear concentration quenching and exponential decay times of the1D2level are explained assuming cross‐relaxation and energy transfer between the Pr3+ions. Energy level diagrams of Cr3+and Pr3+reveal that the1G4level of Pr3+lies close in energy to the4T2fluorescent level of Cr3+, and hence will expect a portion of excitation energy from Cr3+. Unfortunately, the mismatch in energy of this Pr3+level with the4T2level of Cr3+(∼3000 cm–1) cannot be compensated for by the phonons of the host, having an energy of about 500 cm–1.
Splitting of X‐ray photoelectron spectra in incommensurate ferroelectric TlInS2 crystals
Authors: Grigas J. , Talik E. 
Published: May 2003

AbstractThis paper presents the first observation of the resolved splitting of X‐ray photoelectron spectra (XPS) in the incommensurate phase of the ferroelectric semiconductor TlInS2 single crystal. The XPS were measured with monochromatised Al Kα radiation in the energy range 0–1400 eV and the temperature range 195–300 K. At room temperature, the valence band is located 1–9 eV below the Fermi level. The chemical shifts in the TlInS2 crystal for the Tl, In and S states are obtained. The mechanism of the XPS splitting in the incommensurate phase is discussed.
The semimetallic S = 1/2 antiferromagnetic chain Yb4As3: quantum transfer‐matrix simulations and experimental field‐dependent specific‐heat data
Authors: Matysiak R. , Kamieniarz G. , Gegenwart P. , Aoki H. , Ochiai A. , Steglich F. 
Published: May 2003

AbstractThe S=1/2 antiferromagnetic Heisenberg model with the Dzyaloshinsky–Moriya interaction is applied to Yb4As3. In this paper we calculate the specific heat of this model, mapped onto the isotropic Heisenberg model with both uniform field Bx and staggered field Bys, by the numerical quantum transfer‐matrix (QTM) method and we present new experimental results for the polydomain sample in the applied field.
Elastic relaxation of a truncated circular cylinder with uniform dilatational eigenstrain in a half space
Authors: Glas Frank 
Published: May 2003

AbstractWe give a fully analytical solution for the displacement and strain fields generated by the coherent elastic relaxation of a type of misfitting inclusions with uniform dilatational eigenstrain lying in a half space, assuming linear isotropic elasticity. The inclusion considered is an infinitely long circular cylinder having an axis parallel to the free surface and truncated by two arbitrarily positioned planes parallel to this surface. These calculations apply in particular to strained semiconductor quantum wires. The calculations are illustrated by examples showing quantitatively that, depending on the depth of the wire under the free surface, the latter may significantly affect the magnitude and the distribution of the various strain components inside the inclusion as well as in the surrounding matrix.
Elastic relaxation of a truncated circular cylinder with uniform dilatational eigenstrain in a half space
Authors: Glas Frank 
Published: May 2003

AbstractOur Editor's Choice [1] presents results of analytical calculations of the displacement and strain field induced by a linear inclusion such as a strained semiconductor quantum wire in an isotropically elastic half‐space solid. The cover picture shows the total dilatation distribution in the plane perpendicular to a crescent‐shape wire which is parallel to the free surface, marked by the straight red line, and, as thick curved red lines, the sections of the two truncated cylinders used to generate the wire.Frank Glas is currently in charge of the research group ‘Elaboration and Physics of Epitaxial Structures’ at the Laboratoire de Photonique et de Nanostructures, CNRS Marcoussis. His activities include experimental and theoretical studies of the structural, elastic and thermodynamical properties of III–V semiconductor alloys and epitaxial structures, analytical elasticity calculations as well as electron microscopy and microanalysis.
Duration of ruptured membranes and extended labor are risk factors for HIV transmission
Authors: Garcia‐Tejedor A. , Perales A. , Maiques V. 
Published: May 2003

AbstractObjectives: To determine the effects of duration of ruptured membranes (DRM) and duration of labor in HIV transmission. Methods: A retrospective cohort study of 366 HIV‐infected pregnant women and their infants analyzed the effects of these two variables; the cut‐off point for transmission increase was estimated using a ROC curve. A multivariate analysis was performed with the most important risk factors according to the literature: maternal age, lymphocyte count, use of invasive procedures during gestation, antiretroviral treatment during pregnancy and labor, mode of delivery, newborn weight, DRM, labor duration, and the interaction of these last two factors. Results: The cut‐off points were estimated at 6 h for DRM and at 5 h for labor duration. A lymphocyte count below 500 cells/ml, use of invasive procedures, use of antiretroviral treatment during pregnancy and interaction between DRM, and labor duration remained significant in perinatal HIV transmission (P<0.05). Conclusions: An increased DRM increased perinatal HIV transmission when it was associated with prolonged labor.
Hemodynamic and metabolic effects after nifedipine and ritodrine tocolysis
Authors: Papatsonis D.N.M. , van Geijn H.P. , Bleker O.P. , Adèr H.J. , Dekker G.A. 
Published: May 2003

AbstractObjectives: The purpose of this study is to compare the hemodynamic and metabolic changes after ritodrine and nifedipine tocolysis. Methods: For an open randomized study, patients with preterm labor (N=185) were allocated to groups to receive ritodrine intravenously (N=90) or nifedipine orally (N=95). Results: The mean diastolic blood pressure was significantly lower in the ritodrine group 24 h (65±12 vs. 70±8, P=0.001) and 48 h (65±12 vs. 71±8, P=0.004) after starting tocolysis compared with the nifedipine group. Mean maternal heart rate was significantly higher in the ritodrine group 24 h (105±17 vs. 86±13, P<0.0001) and 48 h (100±21 vs. 85±12, P<0.0001) after starting tocolysis compared with the nifedipine group. Mean fasting glucose levels were higher (6.68±2.53 vs. 4.93±1.23, P=0.0016), while mean potassium levels were lower (3.52±0.84 vs. 3.81±0.45, P=0.04) in the ritodrine group 48 h after starting tocolysis compared with the nifedipine group. Conclusions: Use of nifedipine for preterm labor is associated with a lower incidence of adverse hemodynamic and metabolic changes compared with ritodrine after 24 and 48 h of tocolysis. In our opinion nifedipine is the preferred drug of choice for the treatment of preterm labor.
Eukaryotic release factors (eRFs) history
Authors: Inge‐Vechtomov Sergei , Zhouravleva Galina , Philippe Michel 
Published: May 2003

AbstractIn the present review, we describe the history of the identification of the eukaryotic translation termination factors eRF1 and eRF3. As in the case of several proteins involved in general and essential processes in all cells (e.g., DNA replication, gene expression regulation…) the strategies and methodologies used to identify these release factors were first established in prokaryotes. The genetic investigations in Saccharomyces cerevisiae have made a major contribution in the field. A large amount of data have been produced, from which it was concluded that the SUP45 and SUP35 genes were controlling translation termination but were also involved in other functions important for the cell organization and the cell cycle accomplishment. This does not seem to be restricted to yeast but is also probably the case in eukaryotes in general. The biochemical studies of the proteins encoded by the higher eukaryote homologs of SUP45 and SUP35 were efficient and permitted the identification of eRF1 as being the key protein in the termination process, eRF3 having a stimulating role. Around 25 years were needed after the identification of sup45 and sup35 mutants for the characterization of their gene products as eRF1 and eRF3, respectively. It also has to be pointed out that if the results came first from bacteria, the identification of RF3 and eRF3 was made practically at the same time. Moreover, eRF1 was the first crystal structure obtained for a class‐1 release factor, the bacterial RF2 structure came later. The goal is now to understand at the molecular level the roles of both eRF1 and eRF3 in addition to their translation termination functions.
Placental Tissue Interleukin‐10 Receptor Distribution in Pre‐eclampsia
Authors: Hennessy A. , Painter D. M. , Orange S. , Horvath J. S. 
Published: May 2003

PROBLEM: Reduced placental (trophoblast) cytokine interleukin‐10 (IL‐10) occurs in human pre‐eclampsia. Along with an increase in inflammatory cytokines this may play an important role in the development of hypertension in pregnancy. It is not clear whether the changes in placental IL‐10 are due to a change in the placental cell production of IL‐10 or a result of changes in cytokine receptor status in adjacent tissues. This study is aimed at qualifying the presence and distribution of IL‐10 receptors in women with a pre‐eclamptic outcome compared to normal pregnancy and gestational hypertension.METHOD OF STUDY: Patients at the KGV Hospital, Sydney was selected for the study. Placentas were collected fresh and paraffin serial sections made. Sections were stained with IL‐10 receptor antibody (10 μg/mL) using avidin–biotin immunohistochemistry. Tissues of patients with pre‐eclampsia (n = 11) were compared with normal pregnancy (n = 12). Pre‐eclampsia was defined as a blood pressure >140/90 mmHg on two occasions and de novo proteinuria > 300 mg per day which resolved post‐partum. The fetal weights, gestational ages and maternal ages at delivery were compared (ANOVA) and the differences in staining of decidual and villous tissues were graded according to density. Statistical comparisons were made using the Kruskal–Wallis test.RESULTS: The groups were similar for maternal gestational age but delivered at earlier gestation and with lower fetal weight. There was significantly less villous cytotrophoblast staining for IL‐10 receptor in all groups (P = 0.012) compared to decidual trophoblast cells. There was equal intensity and density of extravillous staining observed in normal pregnancy (45 ± 12%) positive cells compared to pre‐eclampsia (27 ± 12%).CONCLUSION: IL‐10 receptors are present in greater concentration in the extravillous (decidual) trophoblast compared to villi. The decrease in IL‐10 produced by trophoblast cells in pre‐eclampsia is not explained by a difference in the IL‐10 receptor distribution compared to normal pregnancy.
Thymidine phosphorylase induces angiogenesis in vivo and in vitro: an evaluation of possible mechanisms
Authors: Sengupta Shiladitya , Sellers Lynda A , Matheson Hugh B , Fan Tai‐Ping D 
Published: May 2003

Thymidine phosphorylase (TP) is elevated in the plasma of cancer patients, and has been implicated in pathophysiological angiogenesis. However, the downstream signals underlying this implication remain obscure. The purpose of the present study was to examine the effects of TP on the neovascularisation response in vitro and in vivo.
Both TP and its catalytic product, 2‐deoxy‐D‐ribose‐1‐phosphate, and downstream 2‐deoxy‐D‐ribose (2‐DDR) promoted endothelial tubulogenesis in vitro, and the regeneration of a wounded monolayer of endothelial cells without exerting any mitogenic effect. In vivo, both TP and 2‐DDR promoted the development of functional vasculature into an avascular sponge. A TP inhibitor, 6‐amino‐5‐chlorouracil, was able to partially reverse the effects of TP, but had no effect on the 2‐DDR‐induced angiogenesis.
Enhanced monolayer regeneration was observed with TP‐cDNA‐transfected bladder carcinoma cells. The transfection of TP‐cDNA, however, did not confer any proliferative advantage. The regeneration of TP overexpressing cells was associated with a time‐dependent expression of the enzyme haeme‐oxygenase (HO‐1).
The present study demonstrates that both TP and its ribose‐sugar metabolites induce angiogenesis by mediating a cohesive interplay between carcinoma and endothelial cells. The induction of HO‐1 in TP‐transfected cells suggests that it could be a possible downstream signal for the angiogenic effects of TP. Furthermore, reducing sugars have been shown to induce oxidative stress, and ribose could be a possible cause for the upregulation of HO‐1, which has been implicated in the release of angiogenic factors. Therefore, we postulate that 2‐DDR could be mediating the angiogenic effects of TP possibly through an oxidative stress mechanism and additionally getting integrated in the endothelial metabolic machinery.

British Journal of Pharmacology (2003) 139, 219–231. doi:10.1038/sj.bjp.0705216