bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amphiphilic diblock, triblock, and star block copolymers by living radical polymerization: Synthesis and aggregation behavior
Authors: Narrainen Amilcar Pillay , Pascual Sagrario , Haddleton David M. 
Published: August 2002

AbstractCopper(I)‐mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n‐butyl methacrylate) [P(n‐BMA)] and poly[(2‐dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n‐BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2‐bromo‐2‐methylpropionic acid 4‐methoxyphenyl ester, 1,4‐(2′‐bromo‐2′‐methyl‐propionate)benzene, and 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow‐polydispersity polymers for which the number‐average molecular weight increased fairly linearly with time with good first‐order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2‐dimethylamino)ethyl methacrylate to obtain well‐defined [P(n‐BMA)x‐b‐PDMAEMAy]z diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22–7.13 × 10−3 g L−1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 439–450, 2002; DOI 10.1002/pola.10122
Polyterephthalamides with naphthoxy‐pendent groups
Authors: Liou Guey‐Sheng , Hsiao Sheng‐Huei 
Published: August 2002

AbstractA series of new aromatic polyamides having pendent naphthoxy groups were synthesized by the triphenyl phosphite‐activated polycondensation of (2‐naphthoxy)terephthalic acid (NOTPA) with various aromatic diamines in a medium consisting of N‐methyl‐2‐pyrrolidone (NMP), pyridine, and calcium chloride. The diacid monomer NOTPA was prepared from the nitro displacement of dimethyl 2‐nitroterephthalate with the potassium naphthoxide of β‐naphthol, followed by base‐induced ester hydrolysis. All the resulting polymers were noncrystalline and readily soluble in aprotic polar solvents such as NMP and N,N‐dimethylacetamide. Almost all the polymers could be solution‐cast to tough, creasable amorphous films with good mechanical properties, the values of tensile strengths ranging from 90 to 124 MPa with initial moduli ranging from 1.72 to 2.51 GPa. Except for two examples, all the other polyamides displayed discernible glass transitions between 189 and 248 °C in the differential scanning calorimetric traces. These polyamides showed insignificant decomposition below 400 °C in nitrogen or air. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1781–1789, 2002
Synthesis and characterization of rigid‐chain liquid–crystalline polymers containing laterally attached side rods
Authors: Zhao Lun , He Chaobin , Lu Zhihua , Chung T. S. 
Published: August 2002

AbstractA series of rigid‐chain polymers containing different concentrations of laterally attached side rods was synthesized. These polymers exhibited liquid crystallinity even up to a maximum side rod concentration of 20 mol %. The crystallinity of the polymers, however, decreased with an increase in the side‐rod concentration. These polymers had lower dielectric constants compared with their parent polymers, that is, similar polymers, but without laterally attached side rods. A dielectric constant of 2.6 can be achieved by incorporating 10 mol % of laterally attached side rods, which is 0.5 lower than that of its parent polymer. The reduction of dielectric constant may be attributed to low crystallinity as well as the less dense packing structure of the polymers induced by the incorporation of laterally attached side rods. This series of polymers also had good thermal stability. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1288–1294, 2001
Synthesis of high molecular weight trans‐poly(9,9‐di‐n‐octylfluorene‐2,7‐vinylene) by the acyclic diene metathesis polymerization using molybdenum catalysts
Authors: Nomura Kotohiro , Morimoto Hisao , Imanishi Yukio , Ramhani Zoubir , Geerts Yves 
Published: August 2002

AbstractHigh molecular weight trans‐poly(9,9‐di‐n‐octylfluorene‐2,7‐vinylene) was prepared under reduced pressure in the presence of a well‐defined Schrock‐type catalyst, Mo(CHCMe2Ph)(N‐2,6‐Me2C6H3)[OCMe(CF3)2]2, in toluene. The effect of initial monomer concentration was found to be an important factor for preparing high molecular weight polymers with unimodal molecular weight distributions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2463–2470, 2001
Synthesis of an amphiphilic styrenic block copolymer: Polycondensation of dichloromethane and low molecular weight poly(ethylene glycol) in the presence of hydroxypropylated polystyrene‐block‐polybutadiene
Authors: Shen Guang‐Min , Chen Chien‐Chih , Tsiang Raymond Chien‐Chao 
Published: August 2002

AbstractAn amphiphilic styrenic block copolymer, polystyrene‐block‐polybutadiene‐block‐poly[oxymethylene‐alt‐oligo(oxyethylene)] (PS‐b‐PB‐b‐POME), was synthesized through a polycondensation reaction of low molecular weight poly(ethylene glycol) and dichloromethane in the presence of hydroxypropylated polystyrene‐block‐polybutadiene (PS‐b‐PB‐OH) used as a monofunctional chain‐capping reagent. PS‐b‐PB‐OH was in turn prepared via an anionic synthesis of PS‐b‐PB followed by oxetane capping and methanol quenching. Although PS‐b‐PB‐OH has insignificant hydrophilicity, PS‐b‐PB‐b‐POME containing both the hydrophobic PS‐b‐PB segment and the hydrophilic POME segment had an improved emulsifying capability and effectively decreased the interfacial tension between water and toluene. The hydrophile–lipophile balance value of this amphiphilic PS‐b‐PB‐b‐POME copolymer, consisting of 86 wt % of the POME segment and 14 wt % of the PS‐b‐PB segment, was 17.2. The molecular weight of the copolymer molecule was determined by gel permeation chromatography–multi‐angle laser light scattering, and the microstructure was analyzed using 1H NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2625–2632, 2001
Hyperbranched polymers from propargyloxysilanes: New types of acetylenic resins
Authors: Xiao Yingxin , Son David Y. 
Published: August 2002

AbstractNew hyperbranched polymers (1P–3P) from propargyloxysilanes (1–3) are described. The propargyloxysilanes were prepared from readily available reagents in 53–61% yields. The polymerizations were clean, one‐pot hydrosilylation processes catalyzed by Pt/C that were typically complete within 3 h. The polymers contained pendant acetylenic groups that underwent thermally induced crosslinking reactions. Heating the polymers to 1300 °C in flowing nitrogen resulted in weight losses ranging from 33 to 66%. Methyl substitution resulted in lower thermal stability. Further modification of the polymers was demonstrated by the reaction of 1P and 2P with phenylethynyldimethylsilane in the presence of a Pt catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3383–3391, 2001
Mechanics of contact and adhesion between viscoelastic spheres: An analysis of hysteresis during loading and unloading
Authors: Lin Yu‐Yun , Hui C. Y. 
Published: August 2002

AbstractDetailed finite element simulations are carried out to study the adhesive contact of viscoelastic spheres. The spheres are brought into contact by a compressive force that increases at a constant rate. Upon reaching a maximum load, the spheres are unloaded until they separate. We studied in detail the effect of loading and unloading rates on hysteresis and on the pull‐off force for a standard viscoelastic solid. The surface interaction is modeled by the Dugdale–Barenblatt model. Numerical results are compared with analytical models for bonding and debonding, including a recent theory proposed by Johnson. There is excellent agreement between analytical and finite element results for the bonding phase. However, for the debonding phase, current analytical models break down unless the loading and unloading rates are slow in comparison with the material relaxation time. Based on the finite element results, a simple approximate analytical model is proposed to quantify adhesive contact in the debonding phase. We also examine the dependence of hysteresis on interfacial parameters such as the cohesive strength and the intrinsic work of adhesion. Our results show that viscoelastic adhesive contact depends on the details of the surface interaction and cannot be determined solely by the work of adhesion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 772–793, 2002
Polydispersity of ethylene sequence length in metallocene ethylene/α‐olefin copolymers. II. Influence on crystallization and melting behavior
Authors: Zhang Fajun , Liu Jieping , Xie Fengchao , Fu Qiang , He Tianbai 
Published: August 2002

AbstractIn this work, crystallization and melting behavior of metallocene ethylene/α‐olefin copolymers were investigated by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results indicated that the crystallization and melting temperatures for all the samples were directly related to the long ethylene sequences instead of the average sequence length (ASL), whereas the crystallization enthalpy and crystallinity were directly related to ASL, that is, both parameters decreased with a decreasing ASL. Multiple melting peaks were analyzed by thermal analysis. Three phenomena contributed to the multiple melting behaviors after isothermal crystallization, that is, the melting of crystals formed during quenching, the melting‐recrystallization process, and the coexistence of different crystal morphologies. Two types of crystal morphologies could coexist in samples having a high comonomer content after isothermal crystallization. They were the chain‐folded lamellae formed by long ethylene sequences and the bundlelike crystals formed by short ethylene sequences. The coexistence phenomenon was further proved by the AFM morphological observation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 822–830, 2002
Structural and dynamic study of chemically modified polyHIPE by solid‐state 13C NMR spectroscopy
Authors: Mercier A. , Kuroki S. , Ando I. , Deleuze H. , Mondain‐Monval O. 
Published: August 2002

AbstractThe structure of laboratory‐made polyHIPEs was successfully characterized by cross‐polarity/magic‐angle spinning, solid‐state 13C NMR experiments. The signals of vinyl groups appeared in the spectrum of the polyHIPE precursor PHCHCH2, which was prepared by the polymerization of the divinylbenzene continuous phase from a highly concentrated reverse emulsion. This material was chemically modified by the regioselective free‐radical addition of thiols to the pendant vinyl groups. Spectra of materials modified by the grafting of C8 and C12 alkyl chains, PHSC8 and PHSC12, respectively, were produced. The signals of the vinyl groups disappeared in favor of methylene groups. This experiment clearly established that the alkyl chains were covalently bound to the polymer. To elucidate the dynamic aspect of long chains in polyHIPE, we measured the 13C spin–lattice relaxation times (T1) of PHSC12 from 25 to 100 °C with variable‐temperature, solid‐state, high‐resolution 13C NMR spectroscopy, revealing a strong variation in T1 along the alkyl side chain. Furthermore, the crystallinity of a wide range of chemically modified polyHIPEs, including PHSC12, was studied with pulse 1H NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 956–963, 2001
Entanglement friction and dynamics in blends of starlike and linear polymer molecules
Authors: Lee Jung Hun , Archer Lynden A. 
Published: August 2002

AbstractWe investigate relaxation dynamics in a series of six‐arm star/linear 1,4‐polybutadiene blends with mechanical rheometry measurements. Blend systems are formulated to systematically probe constraint release and arm relaxation dynamics. Zero shear viscosity and terminal relaxation times of star/linear polymer blends with fixed star arm molecular weights (Ma) and compositions (ϕS) are found to follow nonmonotonic dependencies on the linear polymer molecular weight (ML). At low values of ϕS, at least two scaling regimes are apparent from the data (ξ0 ∼ M and ξ0 ∼ M), where ξ0 refers to the zero shear viscosity or terminal relaxation time of the blend. The two regimes are separated by a critical linear polymer molecular weight M* that is more than 20 times larger than the critical molecular weight for entanglements. When the linear polymer contribution to blend properties is removed, a clear transition from dilution dynamics, ξ0 ∼ M, to Rouse‐like constraint‐release dynamics, ξ0 ∼ M, is apparent at low values of ϕS. At higher ϕS values, a new activated constraint‐release dynamic regime is evident in which ξ0 ∼ M and ξ0 ∼ ϕ, where α changes continuously from approximately 2 to 0.5 as ϕS increases and β varies from 2.0 to 1.0 as ML increases. The experimental results are compared with theoretical predictions based on a drag coupling model for entangled polymer liquids. All features observed experimentally are captured by this model, including the value of M* for the transition from dilution to Rouse constraint‐release dynamics. Predictions of the drag coupling model are also compared with published data for the zero shear viscosity and terminal relaxation time in bidisperse linear polymer blends and pure entangled starlike molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2501–2518, 2001
Hypersensitivity to inhaled TOBI® following reaction to gentamicin
Authors: Spigarelli Michael G. , Hurwitz Martin E. , Nasr Samya Z. 
Published: August 2002

AbstractCystic fibrosis (CF) is the most common autosomal‐recessive disease in Caucasians. Colonization with Pseudomonas aeruginosa (P. aeruginosa) of the CF airways causes deterioration of pulmonary status. TOBI® (Tobramycin solution for inhalation) is an inhaled antibiotic that can improve the pulmonary disease.We report on a 9‐year old boy with CF who developed a rash following a course of IV gentamicin. The rash resolved after its discontinuation. However, the rash returned all over his body, with the start of inhalation of TOBI® therapy. We desensitized the patient using escalating doses of inhaled TOBI®. He tolerated the procedure well, and continues to be on TOBI® 9 months after desensitization on a once‐a‐day regimen. Pediatr Pulmonol. 2002; 33:311‐314. © 2002 Wiley‐Liss, Inc.
Expression profiles of voltage‐gated Na+ channel α‐subunit genes in rat and human prostate cancer cell lines
Authors: Diss James K.J. , Archer Simon N. , Hirano Joe , Fraser Scott P. , Djamgoz Mustafa B.A. 
Published: August 2002

AbstractBackgroundVoltage‐gated Na+ channel (VGSC) activity has been implicated in prostate cancer (PC) metastasis. Although VGSCs can occur as multiple‐subunit assemblies, the α‐subunits (VGSCαs) alone can encode functional channels. The VGSCα gene(s) responsible for the functional VGSCα expression in strongly metastatic PC cell lines is not known.MethodsTwo reverse transcription‐PCR (RT‐PCR) methods, degenerate primer screening and a novel semi quantitative PCR (SQT‐PCR) technique, were used. These methods enabled a detailed qualitative and quantitative investigation of VGSCα mRNA expression in rat (MAT‐LyLu/AT‐2) and human (PC‐3/LNCaP) PC cells of markedly different metastatic potential.ResultsExpression of eight different VGSCα genes (SCN1A‐4A, SCN7A‐9A, and SCN11A) was determined in the PC cell lines. Most were expressed as multiple splice variants. SQT‐PCR results were consistent with a basal level of VGSCα mRNA expression occurring in weakly metastatic (AT‐2/LNCaP) cells, and this being greatly elevated in cells of stronger metastatic potential (MAT‐LyLu/PC‐3), primarily due to the elevated expression of the SCN9A gene (also termed PN1/hNe‐Na).Conclusions(1) Several VGSCα genes and their splice variants are expressed similarly in both rat and human PC cell lines. (2) Expression levels are much higher in the strongly metastatic (MAT‐LyLu/PC‐3) cells. (3) Levels of SCN9A mRNA specifically are predominant in MAT‐LyLu and PC‐3 cells; thus, SCN9A is highly likely to be the main source of the functional VGSC detected. Prostate 48:165–178, 2001. © 2001 Wiley‐Liss, Inc.
Docking multiple conformations of a flexible ligand into a protein binding site using NMR restraints
Authors: Zabell Adam P.R. , Post Carol Beth 
Published: August 2002

AbstractA method is described for docking a large, flexible ligand using intra‐ligand conformational restraints from exchange‐transferred NOE (etNOE) data. Numerous conformations of the ligand are generated in isolation, and a subset of representative conformations is selected. A crude model of the protein–ligand complex is used as a template for overlaying the selected ligand structures, and each complex is conformationally relaxed by molecular mechanics to optimize the interaction. Finally, the complexes were assessed for structural quality. Alternative approaches are described for the three steps of the method: generation of the initial docking template; selection of a subset of ligand conformations; and conformational sampling of the complex. The template is generated either by manual docking using interactive graphics or by a computational grid‐based search of the binding site. A subset of conformations from the total number of peptides calculated in isolation is selected based on either low energy and satisfaction of the etNOE restraints, or a cluster analysis of the full set. To optimize the interactions in the complex, either a restrained Monte Carlo‐energy minimization (MCM) protocol or a restrained simulated annealing (SA) protocol were used. This work produced 53 initial complexes of which 8 were assessed in detail. With the etNOE conformational restraints, all of the approaches provide reasonable models. The grid‐based approach to generate an initial docking template allows a large volume to be sampled, and as a result, two distinct binding modes were identified for a fifteen‐residue peptide binding to an enzyme active site. Proteins 2002;46:295–307. © 2002 Wiley‐Liss, Inc.
Influence of rotational energy barriers to the conformational search of protein loops in molecular dynamics and ranking the conformations
Authors: Tappura Kirsi 
Published: August 2002

AbstractAn adjustable‐barrier dihedral angle potential was added as an extension to a novel, previously presented soft‐core potential to study its contribution to the effectivity of the search of the conformational space in molecular dynamics. As opposed to the conventional soft‐core potential functions, the leading principle in the design of the new soft‐core potential, as well as of its extension, the soft‐core and adjustable‐barrier dihedral angle (SCADA) potential (referred as the SCADA potential), was to maintain the main equilibrium properties of the original force field. This qualifies the methods for a variety of a priori modeling problems without need for additional restraints typically required with the conventional soft‐core potentials. In the present study, the different potential energy functions are applied to the problem of predicting loop conformations in proteins. Comparison of the performance of the soft‐core and SCADA potential showed that the main hurdles for the efficient sampling of the conformational space of (loops in) proteins are related to the high‐energy barriers caused by the Lennard–Jones and Coulombic energy terms, and not to the rotational barriers, although the conformational search can be further enhanced by lowering the rotational barriers of the dihedral angles. Finally, different evaluation methods were studied and a few promising criteria found to distinguish the near‐native loop conformations from the wrong ones. Proteins 2001;44:167–179. © 2001 Wiley‐Liss, Inc.
Model for the three‐dimensional structure of vitronectin: Predictions for the multi‐domain protein from threading and docking
Authors: Xu Dong , Baburaj Kunnumal , Peterson Cynthia B. , Xu Ying 
Published: August 2002

AbstractThe structure of vitronectin, an adhesive protein that circulates in high concentrations in human plasma, was predicted through a combination of computational methods and experimental approaches. Fold recognition and sequence–structure alignment were performed using the threading program PROSPECT for each of three structural domains, i.e., the N‐terminal somatomedin B domain (residues 1–53), the central region that folds into a four‐bladed β‐propeller domain (residues 131–342), and the C‐terminal heparin‐binding domain (residues 347–459). The atomic structure of each domain was generated using MODELLER, based on the alignment obtained from threading. Docking experiments between the central and C‐terminal domains were conducted using the program GRAMM, with limits on the degrees of freedom from a known inter‐domain disulfide bridge. The docked structure has a large inter‐domain contact surface and defines a putative heparin‐binding groove at the inter‐domain interface. We also docked heparin together with the combined structure of the central and C‐terminal domains, using GRAMM. The predictions from the threading and docking experiments are consistent with experimental data on purified plasma vitronectin pertaining to protease sensitivity, ligand‐binding sites, and buried cysteines. Proteins 2001;44:312–320. © 2001 Wiley‐Liss, Inc.
Analysis of the segmental stability of helical peptides by isotope‐edited infrared spectroscopy
Authors: Venyaminov S. Yu. , Hedstrom J.F. , Prendergast F.G. 
Published: August 2002

AbstractIsotope‐edited infrared spectroscopy has the ability to probe the segmental properties of long biopolymers. In this work, we have compared the infrared spectra of a model helical peptide (12C) Ac‐W‐(E‐A‐A‐A‐R)6‐A‐NH2, described originally by Merutka et al. (Biochemistry 1991;30:4245–4248) and three derivatives that are 13C labeled at the backbone carbonyl of alanines. The locations of six isotopically labeled alanines are at the N‐terminal, C‐terminal, and the middle two repeating units of the peptide. Variation in temperature from 1° to 91°C transformed the peptides from predominantly helical to predominantly disordered state. Amplitude and position of the infrared amide I′ absorption bands from 12C‐ and 13C‐labeled segments provided information about the helical content. Temperature dependence of infrared spectra was used to estimate segmental stability. As a control measure of overall peptide stability and helicity (independent of labeling), the temperature dependence of circular dichroism spectra in the far‐UV range at identical conditions (temperature and solvent) as infrared spectra was measured. The results indicate that the central quarter of the 32 amino acids helix has the maximal helicity and stability. The midpoint of the melting curve of the central quarter of the helix is 5.4 ± 0.8°C higher than that of the termini. The N‐terminal third of the helix is more helical and is 2.0 ± 1.4°C more stable than the C‐terminus. Proteins 2001;45:81–89. © 2001 Wiley‐Liss, Inc.