bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of silica‐supported late transition metal catalyst and ethylene polymerization
Authors: Ma Zhi , Sun Wen‐Hua , Zhu Ning , Li Zilong , Shao Changxing , Hu Youliang
Published: August 2002

A Correction has been published for this article in Polymer International 51(6) 2002, 561

The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming SiOAl bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst.

The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming SiOAl bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst.

© 2002 Society of Chemical Industry
Thermochemistry of cyclopentadienylidene (c‐C5H4, C2v, 3B1), cyclopentadienyl radical (c‐C5H5•, C2v, 2B1) and 1,3‐cyclopentadiene (c‐C5H6, C2v, 1A1): a theoretical study by the G2M(RCC,MP2) method
Authors: Nguyen Thanh Lam , Le Trung Ngoc , Mebel Alexander M.
Published: August 2002

The thermochemistry of c‐C5H4 (3B1), c‐C5H5• and c‐C5H6 was investigated at the G2M(RCC,MP2) level. The heat of formation (ΔHof,298), ionization potential (IP), electron affinity (EA) and proton affinity (PA) are respectively, 125.1, 204.4, 42.5 and 230.7 kcal mol−1 for c‐C5H4 (3B1), 63.5, 195.2, 44.9 and 197.2 kcal mol−1 for c‐C5H5• and 32.1, 199.9, 26.0 and 195.2 kcal mol−1 for c‐C5H6. The computed values for the last two molecules are in excellent agreement with available experimental data, with the errors of ±1 and ±2 kcal mol−1 for the heat of formation and the other parameters, respectively. In addition, the heat of formation of c‐C5H4•− is evaluated as 82.0 kcal mol−1, about 10 kcal mol−1 higher than the experimental value. This leads to the suggestion that the experimental ΔHof,298(c‐C5H4•−) value needs to be re‐examined. Copyright © 2001 John Wiley & Sons, Ltd.
AM1 and PM3 studies of some thio analogues of pyrimidine bases in the gas and aqueous phases
Authors: Civcir Pervin Ünal
Published: August 2002

Heats of formation, entropies, Gibbs free energies, relative tautomerization energies, dipole moments, and ionization potentials for the tautomers of 2‐thiocytosine, 2,4‐dithiouracil and 2,4‐dithiothymine and their 1‐methyl analogues were studied by using semiempirical AM1 and PM3 quantum‐chemical calculations at the SCF level both in the gas phase and in aqueous solution, with full geometry optimization. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the thiol‐amino tautomer of 2‐thiocytosine is the most stable in the gas phase whereas the thione‐amino tautomer is the most stable in the aqueous phase. For 2,4‐dithiouracil and 2,4‐dithiothymine, dithione tautomers are the most stable in both phases. The results are in good agreement with available experimental and theoretical results. The entropy effect on the Gibbs free energy of the thiopyrimidine bases is very small and has practically no significance for the tautomeric equilibria of thiopyrimidine bases. The enthalpic term is dominant in the determination of the equilibrium constant. Copyright © 2001 John Wiley & Sons, Ltd.
Synthesis and structural analysis of 1,4‐bis[n‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diynes and charge‐transfer complexes with TCNE
Authors: Gonzalo Rodríguez J. , Lafuente Antonio , Martín‐Villamil Rosa , Martínez‐Alcazar M. Paz
Published: August 2002

n‐(N,N‐Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n‐(N,N‐dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4‐bis[n‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diyne were obtained by oxidative dimerization with copper(I) chloride. X‐ray molecular structure analysis of the dimer 1,4‐bis[2‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diyne corroborated the resonance contribution of the o‐dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o‐ and p‐(N,N‐dimethylamino) conjugate dimers develop 1:1 charge‐transfer complexes with TCNE and their structure was identified by NMR, IR and UV–visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3‐diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd.
Particle formation under monomer‐starved conditions in the semibatch emulsion polymerization of styrene. I. Experimental
Authors: Sajjadi S.
Published: August 2002

Particle formation and particle growth compete in the course of an emulsion polymerization reaction. Any variation in the rate of particle growth, therefore, will result in an opposite effect on the rate of particle formation. The particle formation in a semibatch emulsion polymerization of styrene under monomer‐starved conditions was studied. The semibatch emulsion polymerization reactions were started by the monomer being fed at a low rate to a reaction vessel containing deionized water, an emulsifier, and an initiator. The number of polymer particles increased with a decreasing monomer feed rate. A much larger number of particles (within 1–2 orders of magnitude) than that generally expected from a conventional batch emulsion polymerization was obtained. The results showed a higher dependence of the number of polymer particles on the emulsifier and initiator concentrations compared with that for a batch emulsion polymerization. The size distribution of the particles was characterized by a positive skewness due to the declining rate of the growth of particles during the nucleation stage. A routine for monomer partitioning among the polymer phase, the aqueous phase, and micelles was developed. The results showed that particle formation most likely occurred under monomer‐starved conditions. A small average radical number was obtained because of the formation of a large number of polymer particles, so the kinetics of the system could be explained by a zero–one system. The particle size distribution of the latexes broadened with time as a result of stochastic broadening associated with zero–one systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3940–3952, 2001
Diblock copolymers, micelles, and shell‐crosslinked nanoparticles containing poly(4‐fluorostyrene): Tools for detailed analyses of nanostructured materials
Authors: Becker Matthew L. , Remsen Edward E. , Wooley Karen L.
Published: August 2002

Amphiphilic core–shell nanostructures containing 19F stable isotopic labels located regioselectively within the core domain were prepared by a combination of atom transfer radical polymerization (ATRP), supramolecular assembly, and condensation‐based crosslinking. Homopolymers and diblock copolymers containing 4‐fluorostyrene and methyl acrylate were prepared by ATRP, hydrolyzed, assembled into micelles, and converted into shell‐crosslinked nanoparticles (SCKs) by covalent stabilization of the acrylic acid residues in the shell. The ATRP‐based polymerizations, producing the homopolymers and diblock copolymers, were initiated by (1‐bromoethyl)benzene in the presence of CuBr metal and employed N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the coordinating ligand for controlled polymerizations at 75–90 °C for 1–3 h. Number‐average molecular weights ranged from 2000 to 60,000 Da, and molecular weight distributions, generally less than 1.1 and 1.2, were achieved for the homopolymers and diblock copolymers, respectively. Methyl acrylate conversions as high as 70% were possible, without observable chain–chain coupling reactions or molecular weight distribution broadening, when bromoalkyl‐terminated poly(4‐fluorostyrene) was used as the macroinitiator. Poly(4‐fluorostyrene), incorporated as the second segment in the diblock copolymer synthesis, was initiated from a bromoalkyl‐terminated poly(methyl acrylate) macroinitiator. After hydrolysis of the poly(methyl acrylate) block segments, micelles were formed from the resulting amphiphilic block copolymers in aqueous solutions and were then stabilized by covalent intramicellar crosslinking throughout the poly(acrylic acid) shells to yield SCKs. The SCK nanostructures on solid substrates were visualized by atomic force microscopy and transmission electron microscopy. Dynamic light scattering was used to probe the effects of crosslinking on the resulting hydrodynamic diameters of nanoparticles in aqueous and buffered solutions. The presence of fluorine atoms in the diblock copolymers and resulting SCK nanostructures allowed for characterization by 19F NMR in addition to 1H NMR, 13C NMR, and IR spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4152–4166, 2001
Formation of pore‐filled microfiltration membranes using a combination of modified interfacial polymerization and grafting
Authors: Childs Ronald F. , Weng Junfan , Kim Marcus , Dickson James M.
Published: August 2002

A novel method of fabricating pore‐filled membranes has been developed by coating a hydrophobic polyolefinic microfiltration membrane with polyethylenimine (PEI) to produce a chemically active surface. An evaporative coating technique was used to coat the internal surface of a polyolefinic membrane with PEI in chloroform (CHCl3). The coated PEI was then crosslinked by naphthalene‐1,4‐disulfonyl chloride in carbon tetrachloride (CCl4). The incorporation of the PEI coating changed the properties of the base membrane from hydrophobic to relatively hydrophilic; the nitrogens could be titrated, and the coating could not be washed out. 4,4′‐Azo‐bis(4‐cyanovaleryl chloride), a heat‐sensitive radical source, was incorporated into the coated membrane. The coated membrane, with incorporated azo compound, was heated to 75 °C in the presence of acrylic acid, 4‐(vinylpyridine), or styrene to give the corresponding grafted, pore‐filled membranes. The membranes exhibited hydraulic fluxes and pH valve effects consistent with molecular brushes grafted within the pores of the membranes. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 242–250, 2002
Rare‐earth‐catalyzed alternating copolymerization of carbon monoxide with styrene
Authors: Yao Fanglian , Xu Chunjian , Deng Liandong , Bai Yun , Zhang Jianhui , Sun Jingwu
Published: August 2002

Rare‐earth acetates were used to catalyze the copolymerization reaction of carbon monoxide and styrene. Cupric acetate, 1,10‐phenanthroline, p‐toluenesulfonic acid, and 1,4‐benzoquinone were also added to the catalyst system. The structures of the copolymers obtained were characterized with IR, 1H NMR, 13C NMR, wide‐angle X‐ray diffraction, and elemental analysis methods. The relationship between the catalytic activity and the catalyst composition was studied in detail. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 642–649, 2002; DOI 10.1002/pola.10147
Nylon–selected topics
Authors: Zimmerman Joseph , Kohan Melvin I.
Published: August 2002

Elements of the technology of nylon fibers and nylon plastics are reviewed. These include the development of equations to quantify the effects of end‐group imbalance and chain‐ending impurities, the kinetics of the polymerization of caprolactam, the solid‐state polymerization of nylon‐66, and the dependence of fiber tensile strength on molecular weight. This is followed by remarks that include comments on the significance of the amidation equilibrium for melt behavior and estimates of the activation energy of viscous flow, the pyrolysis of nylon, the use of the glass‐transition temperature (Tg) to predict the effect of moisture on properties, and the prospect for new nylons. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2565–2570, 2001
Synthesis and optical and electrochemical properties of novel polyethers containing isolated distyrylbenzene derivatives and side‐aromatic 1,3,4‐oxadiazole chromophores
Authors: Chen Yun , Lai Shiao‐Ping
Published: August 2002

New polyethers (P2, P4) with isolated emitting distyrylbenzene derivatives and pendant aromatic 1,3,4‐oxadiazole chromophores have been prepared by the Horner–Wadsworth–Emmons olefination reaction. Polyethers P1 and P3 without oxadiazole groups have also been synthesized for comparison. The reduced viscosities were about 0.20–0.33 dL/g, and the solubility in organic solvents increased with a number of side methoxy or ethoxy substituents in the distyrylbenzene section. Absorption spectra showed two peaks at 371–388 and 304 nm that corresponded to the π‐π* transition of the conjugated distyrylbenzene derivatives and aromatic oxadiazoles, respectively. The band gaps were at 2.76–2.85 eV, which were calculated from onset absorption in the film state. The photoluminescence (PL) maxima were at 459–469 nm, indicating that they are blue‐emitting materials, and the relative PL quantum efficiencies were 0.62–0.77 and 0.23–0.40 in solution and the film state, respectively. Cyclic voltammetric investigations demonstrated that oxadiazole moieties decrease the barrier of electron injection but also retard hole injection. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2571–2580, 2001
New cholesteric liquid‐crystal epoxy resins derived from 6‐hydroxy‐2‐naphthoic acid
Authors: Espinosa M. A. , Cádiz V. , Galià M.
Published: August 2002

Liquid‐crystalline epoxy resins were synthesized from 6‐hydroxy‐2‐naphthoic acid, which was used as a mesogenic component, with phenylhydroquinone or isosorbide and via a further reaction with (6‐bromo‐1‐hexyl)glycidylether, which was used as a flexible spacer. In this way, phenylhydroquinone‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly A) and isosorbide‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly B) were obtained. Nematic elastomers were obtained by the crosslinking of Gly A with 2,4‐diaminotoluene (DAT) and 1,10‐decanedicarboxylic acid (SA). The liquid‐crystalline behavior was investigated with differential scanning calorimetry, polarizing light microscopy, and X‐ray diffractometry. Cholesteric mesophases were produced by the blending of different ratios of Gly A and Gly B, and these blends were then crosslinked with SA to produce nematic mesophases. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2847–2858, 2001
Modeling of solute release from polymeric monoliths subject to linear structural relaxation
Authors: Papadokostaki K. G. , Polishchuk A. Ya. , Petrou J. K.
Published: August 2002

A previously developed model of solute release from a swellable polymeric matrix induced by solvent uptake that obeys Fickian kinetics is here extended to cover the case of non‐Fickian solvent uptake caused by slow structural relaxation of the swelling polymer. For this purpose, we have adopted a model description of the absorption process (also previously developed in our laboratory), which has been shown to be capable of realistically simulating a wide range of non‐Fickian kinetics (including the well‐known two‐stage sorption and case II regimes). The aforementioned structural relaxation phenomena constitute important characteristics of glassy polymeric matrices. Accordingly, the predictions of the resulting combined model have been investigated in some detail in this series of articles. This particular article is concerned with the simplest version of the model, involving constant uptake kinetic parameters (diffusion coefficient and relaxation frequency) for both osmotically inactive and osmotically active solutes. Emphasis is put on possibilities of achieving and sustaining nearly constant release rates, and it is shown that such possibilities are considerably more numerous here than under conditions of Fickian solvent uptake kinetics. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1171–1188, 2002
Formation of junction zones in thermoreversible methylcellulose gels
Authors: Takahashi Masae , Shimazaki Masako
Published: August 2002

To analyze the structure of junction zones formed in methylcellulose (MC) gel, the modified Eldridge–Ferry method was applied to phase diagrams for aqueous solutions of different molecular weight MCs derived from micro‐DSC, small‐angle X‐ray scattering, and visual inspection. The results suggested that junctions in MC gels took thin, rodlike fringed‐micellar crystallites. The junction multiplicity s decreased from 4.3 for low‐temperature melting gels to 2.0 for high‐temperature melting gels. With increasing molecular weight, the number ζ of statistical units in a junction along a single chain increased from 27 to 54. Because the number depends sensitively on the enthalpy of bonding per mole of the repeat units of MC, our estimate is considered to give an upper bound to the junction length. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 943–946, 2001
Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion
Authors: Nakamura Koh , Nagai Masayuki , Kanamoto Tetsuo , Takahashi Yoshiyuki , Furukawa Takeo
Published: August 2002

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (Tm). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the Tm. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization Pr of 100 mC/m2 and electromechanical coupling factor along the thickness direction kt of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001
Thermodynamic properties of dendrimers compared with linear polymers: General observations
Authors: Hay Grant , Mackay Michael E. , Hawker Craig J.
Published: August 2002

The pressure‐volume‐temperature and thermal properties of dendrimers based on benzyl ether were measured and compared with literature values for monodisperse, linear polystyrenes. In addition, property measurements are presented for an exact linear analogue to the fifth‐generation dendrimer. The thermodynamic properties' molecular weight behavior for the dendrimers is unique when compared with that of linear polystyrene. All of the evidence presented in this work suggests that some form of structural transition occurs in the bulk at a molecular mass near that for the fourth‐generation dendrimer. No such transition is seen for polystyrene. Dendrimers exhibit an increased packing efficiency as evidenced by a decreased specific volume (increased density) as compared with an exact linear analogue of the fifth‐generation dendrimer analogue, and the dendrimer highlights the entropic differences between the two molecules. In addition, differences in the change in heat capacity with temperature for the two systems further allude to their entropic differences. A crystalline state can be formed for the lower generation dendrimer and linear analogue. This crystalline state is not seen in dendrimers above the third generation. These behaviors compiled with the difference in the glass‐transition temperature for the linear analogue suggest that the dendrimers' microstructure has a significant influence on the bulk thermodynamic state of the material. The Tait equation was fitted to the volume data for comparative purposes; the Tait equation has known limitations but was selected because of its widespread application. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1766–1777, 2001
Preparation of polymer optical fibers doped with nonlinear optical active organic chromophores
Authors: Peng Gang‐Ding , Li Alexander D. Q.
Published: August 2002

We synthesized two novel organic nonlinear optical chromophores—chiral S(+)‐N‐[p‐(4‐nitrostyryl) phenyl] prolinol and non‐chiral [p‐(4‐nitrostyryl) phenyl] piperdine—as potential laser‐active dyes for photonic applications. Both materials show good optical transmittance in the telecommunication frequency region, desirable solubility in acrylic polymer optical fiber matrices, and attractive fluorescence properties that are advantageous for laser‐gain materials and devices. Subsequently, these two chromophores were incorporated into poly(methyl methacrylate) and poly(ethyl methacrylate) and drawn into polymer optical fibers. The relevant properties of these organic dye‐doped fibers have been studied, revealing essential attributes of laser‐active characteristics. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1794–1801, 2001
Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene
Authors: Opdahl A. , Somorjai G. A.
Published: August 2002

The surface structure and surface mechanical properties of low‐ and high‐density polyethylene were characterized by atomic force microscopy (AFM) as the polymers were stretched. The surfaces of both materials roughened as they were stretched. The roughening effect is attributed to deformation of nodular structures, related to bulk spherulites, at the surface. The surface‐roughening effect is completely reversible at tensile strains in the elastic regime and partially reversible at tensile strains in the plastic regime until the polymers are irreversibly drawn into fibers. AFM force versus distance interaction curves, used to measure changes in the stiffness of the surface and the surface elastic modulus as a function of elongation, show that the surfaces become softer as the polymers are drawn into fibers at high strains. At low elastic strains, however, the surface elastic modulus of HDPE increases—attributed to elastic energy stored by the amorphous regions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2263–2274, 2001
Considerations in using tumor markers: what the psycho‐oncologist needs to know
Authors: Fertig Debra L. , Hayes Daniel F.
Published: August 2002

Tumor markers are measures of biological features of a cancer. By revealing important biological aspects of the tumor, tumor markers can be useful in staging patients, predicting cancer outcomes, and guiding treatments. The psychological consequences of using tumor markers are virtually unknown. In this review article, we draw on clinical studies involving the psychological impact of risk information, screening, prognostic information and surveillance of cancer. Such studies may be helpful in considering possible psychological reactions to tumor marker information in clinical practice. Copyright © 2001 John Wiley & Sons, Ltd.
Pulmonary function in technology‐dependent children 2 years and older with bronchopulmonary dysplasia*
Authors: Talmaciu Isaac , Ren Clement L. , Kolb Susan M. , Hickey Eileen , Panitch Howard B.
Published: August 2002

Somatic and pulmonary growth coincide with resolution of hypoxemia by 2 years of age in most children with bronchopulmonary dysplasia (BPD). However, a distinct subgroup of children with BPD continue to require mechanical ventilation and/or supplemental oxygen beyond 2 years of age. This study tested the hypothesis that indices of pulmonary function would be significantly worse in children with BPD 2 years and older who remained technology‐dependent secondary to hypoxemia, compared to those of age‐matched children with BPD who were normoxemic. We measured pulmonary mechanics in 21 oxygen‐ or ventilator‐dependent children with BPD 2 years and older (BPDO2 group; mean age ± SD, 30.2 ± 6.5 months) and in 19 children with BPD who had been weaned off mechanical ventilation and supplemental oxygen for at least 6 months (control group; mean age, 30.1 ± 5.5 months). Respiratory rate and tidal volume were measured after sedation with chloral hydrate, and dynamic compliance and expiratory conductance were calculated using the esophageal catheter technique. Maximal flow at FRC (V′maxFRC) and ratio of forced‐to‐tidal flows at midtidal volume were obtained by the rapid thoracic compression technique. FRC was determined by nitrogen washout.

There were no statistically significant differences in most measured indices of pulmonary mechanics between the BPDO2 and control groups. However, V′maxFRC/FRC was higher in controls compared to subjects in the BPDO2 group (0.81 ± 0.40 sec−1 vs. 0.34 ± 0.21 sec−1, P < 0.003).

We conclude that most indices of pulmonary function in children with BPD 2 years and older do not reflect the need for mechanical ventilation or supplemental oxygen. We speculate that measurements of lung elastic recoil and tests of distribution of ventilation and pulmonary perfusion may be more sensitive in differentiating normoxemic and hypoxemic children with BPD 2 years and older. Pediatr Pulmonol. 2002; 33:181–188. © 2002 Wiley‐Liss, Inc.
Measurements of resistance by the interrupter technique and of transcutaneous partial pressure of oxygen in young children during methacholine challenge
Authors: Beydon Nicole , Trang‐Pham Ha , Bernard Agnès , Gaultier Claude
Published: August 2002

Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O2 (PtcO2) ≥ 20% (PD20PtcO2) in young children. Rint was calculated using the linear back‐extrapolation method (RintL) and the end‐interrupter method (RintEI). Twenty‐two children (mean age, 5.2 ± 1.1 years; range, 3.4 – 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. PtcO2, RintL, and RintEI were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation.

PtcO2 decreased significantly during M challenge, from 85 ± 6 mmHg (B) to 62 ± 9 mmHg (P < 0.05), and increased after BD inhalation, to 82 ± 8 mmHg. RintL and RintEI increased significantly during M challenge, from 0.94 ± 0.2 KPa/L/s and 1.11 ± 0.19 KPa/L/s (B) to 1.27 ± 0.35 KPa/L/s and 1.47 ± 0.37 KPa/L/s, respectively (P < 0.05), and decreased after BD inhalation to 0.80 ± 0.17 KPa/L/s and 0.95 ± 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD20PtcO2 at a dose of M ranging from 50–400 μg. At the PD20PtcO2, significant changes in RintL and RintEI (sensitivity index (SI) ≥ 2) were found in 79% and 63% of children, respectively.

We conclude that: 1) M challenge using PtcO2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge. Pediatr Pulmonol. 2001; 31:238–246. © 2001 Wiley‐Liss, Inc.
Albuterol delivery in a neonatal ventilated lung model: Nebulization versus chlorofluorocarbon‐ and hydrofluoroalkane‐pressurized metered dose inhalers*
Authors: Lugo Ralph A. , Kenney Julie K. , Keenan Jim , Salyer John W. , Ballard Julie , Ward Robert M.
Published: August 2002

The aim of this study was to compare albuterol delivery in a neonatal ventilated lung model, using three delivery methods: 1) jet nebulizer; 2) chlorofluorocarbon‐pressurized metered dose inhaler (CFC‐MDI) actuated into an ACE® spacer; and 3) hydrofluoroalkane‐pressurized MDI (HFA‐MDI) actuated into an ACE® spacer. The bench model consisted of a mechanically ventilated infant test lung with ventilator settings to simulate a very low birth weight neonate with moderate lung disease. Albuterol solution (0.5%) was nebulized at the humidifier and temperature port, 125 cm and 30 cm from the Y‐piece, respectively. Albuterol metered dose inhalers (MDIs) were actuated into an ACE® spacer that was tested in two positions: 1) inline between the endotracheal (ET) tube and the Y‐piece; and 2) attached to the ET tube and administered by manual ventilation. Albuterol was collected on a filter at the distal end of the ET tube and was quantitatively analyzed by high performance liquid chromatography.

Albuterol delivery by CFC‐MDI (position 1, 4.8 ± 1.0%, vs. position 2, 3.8 ± 1.6%, P > 0.05) and HFA‐MDI (position 1, 5.7 ± 1.6%, vs. position 2, 5.5 ± 2.4%, P > 0.05) were significantly greater than delivery by nebulization at 30 cm (0.16 ± 0.07%) and 125 cm (0.15 ± 0.03%) from the Y‐piece (P < 0.001). A single actuation of albuterol MDI delivered the equivalent of nebulizing 2.5–3.7 mg of albuterol solution.

We conclude that albuterol administered by MDI and ACE® spacer resulted in more efficient delivery than by nebulization in this mechanically ventilated neonatal lung model. There was no significant difference in drug delivery between CFC‐MDI and HFA‐MDI; nor did the placement of the spacer significantly affect drug delivery. Pediatr Pulmonol. 2001; 31:247–254. © 2001 Wiley‐Liss, Inc.
Physical effects of heliox versus oxygen on measurements of functional residual capacity by the nitrogen washout technique in small lung volumes: A model study
Authors: Hentschel Roland , Suska Andreas , Volbracht Andreas , Harms Erik , Haberland Hellmut , Jorch Gerhard
Published: August 2002

Measurements of functional residual capacity (FRC) by the nitrogen (N2) washout technique yield low N2 signals in neonates and preterm infants, especially when they are on high fractions of inspired oxygen (FiO2). Thus, recorded values often lie in the low range of detectability. We hypothesized that using heliox instead of oxygen as a washout gas would affect the electric discharge conditions of N2 molecules in a standard UV analyzer and thus yield higher N2 signals. We performed three laboratory experiments using conditions similar to those in neonates with pulmonary disease, reproducing different initial FiO2 values and very small lung volumes. Standard calibration procedures with physical models between 13.5–87 mL using a calibration syringe and purpose‐built small calibration cylinders were carried out, and washout gas was either pure oxygen (as is general practice) or heliox at different ratios.

We observed that the calibration line with heliox was shifted upwards and the slope was increased, depending on helium concentration and initial FiO2. Since this effect was dose‐dependent with respect to the proportion of helium in the washout gas, this strongly suggests a physical process elicited by the noble gas helium.

We conclude that the heliox wash‐out modification may help to increase the accuracy of FRC measurements and thus may enable studies of smaller patients or patients on high inspired FiO2. Pediatr Pulmonol. 2001; 31:255–260. © 2001 Wiley‐Liss, Inc.
Progressive lung and cardiac changes associated with pulmonary hypertension in the fetal rat
Authors: Fabris Viciany E. , Pato Mary D. , Belik Jaques
Published: August 2002

To determine the natural history of lung vascular remodeling and cardiac changes in the rat model of persistent pulmonary hypertension syndrome (PPHN) of the newborn, we studied fetal rats subjected to maternal indomethacin administration initiated on day 19 of gestation and continued for 2, 3, or 4 days. Animals receiving a similar volume of water or alcohol served as controls.

Significant pulmonary hypertension was noted in the experimental group, as evidenced by a significantly increased right to left ventricular wall ratio to 1.6 ± 0.1 in the 4‐day treatment group, as compared with 1.2 ± 0.4 in the control group (P < 0.01). The smooth muscle area for <25 μm external diameter arterial vessels was significantly increased (12.7 ± 0.6 vs. 10.0 ± 0.6 μm; P < 0.01) and the adventitial area of all diameters vessels was significantly greater (P < 0.01) following 3 days of indomethacin treatment, as compared with water controls. Associated with these changes, the 4‐day treatment group's lung/body weight ratio was 0.021 ± 0.001, and was significantly less (P < 0.01) than for the control group (0.035 ± 0.001). This reduction in lung weight was not associated with changes in lung protein content or wet/dry weight ratio, indicating that pulmonary hypertension in the fetal rat induced lung hypoplasia.

In conclusion, closure of the ductus arteriosus in the fetal rat results in early‐onset right ventricular hypertrophy, followed by pulmonary vascular remodeling and lung hypoplasia. We speculate that lung growth in late gestation is adversely affected by pulmonary hypertension. Pediatr Pulmonol. 2001; 31:344–353. © 2001 Wiley‐Liss, Inc.
Differential expression of interleukin‐15, a pro‐inflammatory cytokine and T‐cell growth factor, and its receptor in human prostate
Authors: Handisurya Alessandra , Steiner Georg E. , Stix Ursula , Ecker Rupert Ch. , Pfaffeneder‐Mantai Sabine , Langer Dina , Kramer Gero , Memaran‐Dadgar Nima , Marberger Michael
Published: August 2002

Background

Pro‐inflammatory interleukin (IL)‐15 plays a major role in host defense and chronic inflammation by stimulating T‐lymphocyte recruitment and growth. Expression of IL‐15 and IL‐15 receptor (IL‐15R) in human prostate was examined.

Methods

Normal and benign hyperplastic (BPH) prostate specimens (n = 23) were analyzed for IL‐15 and IL‐15Rα‐chain expression by immunohistochemistry and Real‐Time‐PCR/RT‐PCR. Regulation of prostatic stromal cell (PSC) IL‐15 mRNA and effect of IL‐15 on prostatic cell growth were analysed in vitro.

Results

In normal prostate, anti‐IL‐15 and anti‐IL‐15Rα‐chain reactivity were restricted to smooth muscle and stromal cells. However, in BPH, in addition epithelial cells frequently exhibited discrete anti‐IL‐15R and often intense, membranous anti‐IL‐15 reactivity. IL‐15/IL‐15R mRNA were detected in all prostatic cells types. In BPH tissues, IL‐15 mRNA content was variable (15‐fold). IL‐15 mRNA synthesis of PSC was significantly up‐regulated by IFN‐γ. Furthermore IL‐15 strongly stimulated the growth of BPH‐T‐lymphocytes and weakly that of carcinoma cell lines, but not of stromal cells.

Conclusions

Overexpression of IL‐15 and IL‐15Rα‐chain in BPH and massive proliferation of BPH‐T‐lymphocytes induced by IL‐15 suggest a role for IL‐15 in prostatic inflammation. Since IFN‐γ, a T‐lymphocyte product, stimulates prostatic IL‐15 production; chronic inflammation might be triggered by this paracrine loop. Prostate 49:251–262, 2001. © 2001 Wiley‐Liss, Inc.
Melatonin and prostate cancer cell proliferation: Interplay with castration, epidermal growth factor, and androgen sensitivity
Authors: Siu Stephanie W.F. , Lau Kai W. , Tam Po C. , Shiu Stephen Y.W.
Published: August 2002

BACKGROUND

Potential modulatory effects of melatonin on the proliferation of androgen‐sensitive LNCaP and androgen‐insensitive PC‐3 and DU 145 prostate cancer cells were reported recently. In this study, we investigated the effects of combined melatonin and castration on LNCaP tumor growth in vivo, the interactions between melatonin and epidermal growth factor (EGF) on LNCaP cell proliferation, and melatonin actions on the proliferation of PC‐3 and DU 145 cells.

METHODS

Tumor development and growth in castrated nude mice inoculated with LNCaP cells or in intact animals inoculated with DU 145 cells, with or without daily melatonin treatment, were monitored by observation and caliper measurement. MT1 receptor expression in native or transfected prostate cancer cell lines was examined by immunocytochemistry or 2‐[125I]iodomelatonin binding. Cyclin D1 expression in LNCaP cells was assessed by Western blotting, and cell proliferation was measured by thymidine incorporation and/or cell count.

RESULTS

Melatonin treatment was associated with further decreases in LNCaP tumor incidence and growth rate in castrated nude mice. Melatonin and 2‐iodomelatonin (a melatonin receptor agonist) attenuated EGF‐stimulated increases in LNCaP cell proliferation and cyclin D1 levels. Melatonin had no effect on the proliferation or growth of MT1 receptor‐expressing DU 145 cells, and of PC‐3 cells in which MT1 receptor protein was undetectable. The proliferation of transfected PC‐3 cells expressing MT1 receptor was unaffected by 2‐iodomelatonin.

CONCLUSION

Together with previous data, the present results indicate synergistic action of melatonin and castration in inhibiting the growth of androgen‐sensitive LNCaP tumor. Androgen‐sensitive prostate cancer cell proliferation may be modulated by opposite changes in cyclin D1 levels induced by activated MT1 and EGF receptors. In androgen‐insensitive prostate cancer cells, MT1 receptor‐mediated signal transduction may become defective not only through changes in membrane receptor protein expression and/or functions, but also by means of alterations in downstream postreceptor signaling events. Prostate 52:106–122, 2002. © 2002 Wiley‐Liss, Inc.
Using multiple cutpoints for the free‐to‐total prostate specific antigen ratio improves the accuracy of prostate cancer detection*
Authors: Hoffman Richard M. , Clanon David L. , Chavez Margarita , Peirce John C.
Published: August 2002

BACKGROUND

Using a single cutpoint for the free‐to‐total (F/T) prostate specific antigen (PSA) ratio loses important diagnostic information. We evaluated the performance of multiple F/T PSA cutpoints in detecting prostate cancer in men with nonspecific PSA values.

METHODS

We extracted sensitivity and specificity data from 12 studies reporting on ≥30 cancer patients with PSA values between 2.0 and 10.0 ng/mL. We calculated stratum‐specific likelihood ratios (LR) and areas under the receiver operating characteristic (ROC) curves.

RESULTS

Multiple cutpoints for the F/T PSA ratio significantly increased the area under the ROC (0.70) compared with the single investigator‐selected cutpoint (0.62), P < 0.004. The LR for the most positive cutpoint stratum (2.62) was significantly higher than the LR for a positive test from the single cutpoint (1.36), P < 0.004.

CONCLUSIONS

Using multiple cutpoints increased the discriminating power of the F/T PSA ratio and led to greater probability revisions in the most positive test‐result strata. Prostate 52:150–158, 2002. © 2002 Wiley‐Liss, Inc.
Reduction of human prostate tumor vascularity by the α1‐adrenoceptor antagonist terazosin
Authors: Keledjian Kaspar , Borkowski Andrew , Kim Grace , Isaacs John T. , Jacobs Stephen C. , Kyprianou Natasha
Published: August 2002

BACKGROUND

We previously demonstrated that the quinazoline‐derived a1‐adrenoceptor antagonists doxazosin and terazosin suppress prostate cancer growth via apoptosis induction. The aim of this study was to determine the potential effect of a1‐adrenoceptor antagonists on tumor vascularity of the human prostate.

METHODS

A total of 34 men with benign prostatic hyperplasia (BPH) who have been on terazosin treatment (for the obstructive symptoms) were pathologically diagnosed with prostate cancer following surgery. These patients were stratified according to the length of treatment periods with terazosin into two groups, 1 week–6 months, and 6–17 months. The control group consisted of prostatectomy specimens from 25 untreated prostate cancer patients undergoing surgery for localized disease. Formalin‐fixed, paraffin‐embedded prostate specimens were analyzed for apoptosis (TUNEL assay), cell proliferation (Ki‐67), microvessel density (MVD) (von Willebrand factor/Factor VIII), vascular endothelial growth factor (VEGF) expression, and prostate specific antigen (PSA) immunoreactivity.

RESULTS

A significant induction of apoptosis was observed among cancerous prostatic epithelial cells in the terazosin‐treated, as compared to the untreated prostate cancer specimens, while there was no significant change in the proliferative index of the same tumor cell populations after treatment. Furthermore, terazosin resulted in a significant decrease in prostate tissue MVD compared with the untreated group (P < 0.01), that correlated with the increased apoptotic index of the cancerous areas. Tissue PSA expression in the prostatic tumor foci was also markedly reduced after terazosin treatment, while no significant changes in VEGF expression were detected.

CONCLUSIONS

These findings provide the first evidence that terazosin, a quinazoline‐based a1‐blocker decreases prostate tumor vascularity. Our study has significant clinical implications in identifying selected α1‐adrenoceptor antagonists as potential anti‐tumor agents with apoptotic and anti‐angiogenic effects in the human prostate that can be exploited for the treatment of advanced prostate cancer. Prostate 48:71–78, 2001. © 2001 Wiley‐Liss, Inc.
Molecular dynamics simulations of the acyl‐enzyme and the tetrahedral intermediate in the deacylation step of serine proteases
Authors: Topf Maya , Várnai Péter , Schofield Christopher J. , Richards W. Graham
Published: August 2002

Despite the availability of many experimental data and some modeling studies, questions remain as to the precise mechanism of the serine proteases. Here we report molecular dynamics simulations on the acyl‐enzyme complex and the tetrahedral intermediate during the deacylation step in elastase catalyzed hydrolysis of a simple peptide. The models are based on recent crystallographic data for an acyl‐enzyme intermediate at pH 5 and a time‐resolved study on the deacylation step. Simulations were carried out on the acyl enzyme complex with His‐57 in protonated (as for the pH 5 crystallographic work) and deprotonated forms. In both cases, a water molecule that could provide the nucleophilic hydroxide ion to attack the ester carbonyl was located between the imidazole ring of His‐57 and the carbonyl carbon, close to the hydrolytic position assigned in the crystal structure. In the “neutral pH” simulations of the acyl‐enzyme complex, the hydrolytic water oxygen was hydrogen bonded to the imidazole ring and the side chain of Arg‐61. Alternative stable locations for water in the active site were also observed. Movement of the His‐57 side‐chain from that observed in the crystal structure allowed more solvent waters to enter the active site, suggesting that an alternative hydrolytic process directly involving two water molecules may be possible. At the acyl‐enzyme stage, the ester carbonyl was found to flip easily in and out of the oxyanion hole. In contrast, simulations on the tetrahedral intermediate showed no significant movement of His‐57 and the ester carbonyl was constantly located in the oxyanion hole. A comparison between the simulated tetrahedral intermediate and a time‐resolved crystallographic structure assigned as predominantly reflecting the tetrahedral intermediate suggests that the experimental structure may not precisely represent an optimal arrangement for catalysis in solution. Movement of loop residues 216–223 and P3 residue, seen both in the tetrahedral simulation and the experimental analysis, could be related to product release. Furthermore, an analysis of the geometric data obtained from the simulations and the pH 5 crystal structure of the acyl‐enzyme suggests that since His‐57 is protonated, in some aspects, this crystal structure resembles the tetrahedral intermediate. Proteins 2002;47:357–369. © 2002 Wiley‐Liss, Inc.
Substrate flow in catalases deduced from the crystal structures of active site variants of HPII from Escherichia coli
Authors: Melik‐Adamyan William , Bravo Jerónimo , Carpena Xavier , Switala Jack , Maté Maria J. , Fita Ignacio , Loewen Peter C.
Published: August 2002

The active site of heme catalases is buried deep inside a structurally highly conserved homotetramer. Channels leading to the active site have been identified as potential routes for substrate flow and product release, although evidence in support of this model is limited. To investigate further the role of protein structure and molecular channels in catalysis, the crystal structures of four active site variants of catalase HPII from Escherichia coli (His128Ala, His128Asn, Asn201Ala, and Asn201His) have been determined at ∼2.0‐Å resolution. The solvent organization shows major rearrangements with respect to native HPII, not only in the vicinity of the replaced residues but also in the main molecular channel leading to the heme distal pocket. In the two inactive His128 variants, continuous chains of hydrogen bonded water molecules extend from the molecular surface to the heme distal pocket filling the main channel. The differences in continuity of solvent molecules between the native and variant structures illustrate how sensitive the solvent matrix is to subtle changes in structure. It is hypothesized that the slightly larger H2O2 passing through the channel of the native enzyme will promote the formation of a continuous chain of solvent and peroxide. The structure of the His128Asn variant complexed with hydrogen peroxide has also been determined at 2.3‐Å resolution, revealing the existence of hydrogen peroxide binding sites both in the heme distal pocket and in the main channel. Unexpectedly, the largest changes in protein structure resulting from peroxide binding are clustered on the heme proximal side and mainly involve residues in only two subunits, leading to a departure from the 222‐point group symmetry of the native enzyme. An active role for channels in the selective flow of substrates through the catalase molecule is proposed as an integral feature of the catalytic mechanism. The Asn201His variant of HPII was found to contain unoxidized heme b in combination with the proximal side His–Tyr bond suggesting that the mechanistic pathways of the two reactions can be uncoupled. Proteins 2001;44:270–281. © 2001 Wiley‐Liss, Inc.