bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microwave‐assisted ring‐opening polymerization of trimethylene carbonate in the presence of ionic liquid
Authors: Liao Liqiong , Zhang Chao , Gong Shaoqin 
Published: November 2007

AbstractMicrowave‐assisted ring‐opening polymerization (MROP) of trimethylene carbonate in the presence of 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim]BF4) ionic liquid was investigated. In the presence of 5 wt % [bmim]BF4, poly (trimethylene carbonate) (PTMC) with a number‐average molar mass (Mn) of 36,400 g/mol was obtained at 5 W for only 60 min. The Mn of PTMC synthesized in the presence of [bmim]BF4 was much higher than that produced in bulk at the same reaction time. In addition, compared with those produced by conventional heating, the Mn of PTMC and monomer conversion by MROP with or without [bmim]BF4 were both higher. Thermal properties of the resulting PTMC were characterized by differential scanning calorimetry. Under microwave irradiation in the presence of ionic liquid, the polymerization could be carried out efficiently and effectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5857–5863, 2007
Small band gap conjugated polymers based on thiophene–thienopyrazine copolymers
Authors: Cheng Kai‐Fang , Liu Cheng‐Liang , Chen Wen‐Chang 
Published: November 2007

AbstractIn this study, five small band gap thiophene (TH)–thienopyrazine (TP) conjugated copolymers were synthesized by Stille‐coupling reaction. The polymer structures consisted of one to four thiophene rings with the TP of different side groups provided a systematical investigation on the structure–electronic property relationship. The absorption maxima of the polymer films decreased from 850 to 590 nm as the thiophene moieties increased from thiophene to quaterthiophene. The optical and electrochemical band gaps of the studied poly[2,3‐didodecyl‐5‐(thiophen‐2‐yl)thieno[3,4‐b]pyrazine] (PTHTP‐C12) were 0.97 and 0.78 eV, respectively, indicating a significant intramolecular charge transfer. The theoretical geometry and electronic properties of the TH‐TP copolymers by the density functional theory at the B3LYP level and 6‐31G(d) basis set suggested that the bond length alternation enlarged with enhancing the thiophene content and resulted in the variation on the polymer band gap. The relatively small theoretical effective mass of poly(TH‐alt‐TP) also indicated its potential applications for field transistor applications. Our study demonstrates the tunable electronic properties of small band gap copolymers by the thiophene content and the resulted geometry variation. Such polymers could be potentially used for near‐infrared electronic and optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5872–5883, 2007
Radiation‐induced fabrication of polymer nanoporous materials from microphase‐separated structure of diblock copolymers as a template
Authors: Sekine Ryojun , Sato Nobuhiro , Matsuyama Tomochika , Akasaka Satoshi , Hasegawa Hirokazu 
Published: November 2007

AbstractPolymer nanoporous materials with periodic cylindrical holes were fabricated from microphase‐separated structure of diblock copolymers consisting of a radiation‐crosslinking polymer and a radiation‐degrading polymer through simultaneous crosslinking and degradation by γ‐irradiation. A polybutadiene‐block‐poly(methyl methacrylate) (PB‐b‐PMMA) diblock copolymer film that self‐assembles into hexagonally packed poly(methyl methacrylate) cylinders in polybutadiene matrix was irradiated with γ‐rays. Solubility test, IR spectroscopy, and TEM and SEM observations for this copolymer film in comparison with a polystyrene‐block‐poly(methyl methacrylate) diblock copolymer film revealed that poly(methyl methacrylate) domains were removed by γ‐irradiation and succeeding solvent washing to form cylindrical holes within polybutadiene matrix, which was rigidified by radiation crosslinking. Thus, it was demonstrated that nanoporous materials can be prepared by γ‐irradiation, maintaining the original structure of PB‐b‐PMMA diblock copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5916–5922, 2007
Triarylamine N‐functionalized 3,6‐linked carbazole main chain polymers and copolymers: Preparation and physical properties
Authors: Kulasi Akbar , Yi Hunan , Iraqi Ahmed 
Published: November 2007

AbstractThe preparation of triarylamine N‐functionalized 3,6‐linked carbazole homopolymers as well as alternating copolymers with 2,5‐diphenyl‐[1,3,4]oxadiazole and benzo[1,2,5]thiadiazole was undertaken using Suzuki cross‐coupling polymerization procedures associating 3,6‐bis(4,4,5,5‐tetramethyl‐[1,3,2]dioxaborolan‐2‐yl)‐9‐(bis[4‐(2‐butyl‐octyloxy)‐phenyl]‐amino‐phen‐4‐yl)‐carbazole and, respectively, 3,6‐dibromo‐9‐(bis[4‐(2‐butyl‐octyloxy)‐phenyl]‐amino‐phen‐4‐yl)‐carbazole, 2,5‐bis(4‐bromo‐phenyl)‐[1, 3,4]oxadiazole, and 4,7‐dibromo‐benzo[1,2,5]thiadiazole. Both the carbazole homopolymer and alternating copolymer with 2,5‐diphenyl‐[1,3,4]oxadiazole were found as wideband gap materials emitting in the blue part of the electromagnetic spectrum while the carbazole alternating copolymer with 4,7‐benzo[1,2,5]thiadiazole had a narrower band gap and emitted in the orange part of the electromagnetic spectrum. The new polymers are thermally stable up to 300 °C. A discussion of the electrochemical and optical properties of the new polymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5957–5967, 2007.
Selective polymerization of functional monomers with Novozym 435
Authors: Veld Martijn A. J. , Palmans Anja R. A. , Meijer E. W. 
Published: November 2007

AbstractTwo novel monomers, ambrettolide epoxide and isopropyl aleuriteate, encompassing functional groups, were obtained in a single step from commercially available materials. Novozym 435 catalyzed ring opening polymerization of ambrettolide epoxide furnished a polymer of Mn = 9.7 kg/mol and PDI = 1.9 while the epoxide groups remained unaffected during the polymerization. Selective polymerization of the primary hydroxyl groups of isopropyl aleuriteate using Novozym 435 was feasible and a polymer with moderate molecular weight (Mn = 5.6 kg/mol, PDI = 3.2) was isolated in moderate yield (43%). Subsequently, copolymerization of isopropyl aleuriteate with ε‐CL in different ratios was performed, resulting in soluble, hydroxy functional polymers with good molecular weights (Mn = 10.4–27.2 kg/mol) in good yield (71–78%). The secondary hydroxy groups in the polymer reacted easily with hexyl isocyanate, showing the potential of isopropyl aleuriteate as a comonomer for the synthesis of functional polyesters. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5968–5978, 2007
Polymers from a levopimaric acid–acrylic acid Diels–Alder adduct: Synthesis and characterization
Authors: Bicu Ioan , Mustata Fanica 
Published: November 2007

AbstractThe Diels–Alder adduct of levopimaric acid with acrylic acid was efficiently prepared from resin acids. When the adduct was subjected to a dehydrodecarboxylation reaction, a ketone diacid derivative was obtained. New ketone type linear polymers were synthesized by the advanced dehyrodecarboxylation, a nonconventional polycondensation reaction, of both the above in presence of sulfonic catalysts. The polyketones turned out to be excellent tackifiers in adhesive formulae. The ketone polymers were condensed with diamines to give crosslinked polyazomethines. The structures of the monomers and polymers were established by means of elemental analysis, IR and NMR spectroscopy, and molecular weight determinations. Both the polyketones and polyazomethines were low‐molecular‐weight polymers, soluble in some polar and nonpolar solvents. The thermal behavior of the monomers and polymers was evaluated by thermogravimetric analysis. The thermal studies showed that the polymers were substances with good thermal stability, except the polyazomethine synthesized by the condensation of polyketone with an aromatic diamine, which appeared to be a substance with high thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5979–5990, 2007
The role of polydispersity in the lamellar mesophase of model diblock copolymers
Authors: Lynd Nathaniel A. , Hamilton Benjamin D. , Hillmyer Marc A. 
Published: November 2007

AbstractHigh‐resolution small angle X‐ray scattering (SAXS) measurements were performed on two series of poly(ethylene‐alt‐propylene)‐b‐poly(D,L‐lactide) (PEP‐PLA) diblock copolymer materials exhibiting differences in the widths of the poly(D,L‐lactide) block molecular mass distributions as measured by their polydispersity indices (PDIPLA). At symmetric compositions of PEP‐PLA (fPLA ≈ 0.5), all SAXS data were successfully fit to an established model describing the small angle scattering from lamellar mesostructures. According to this model, the increase in the PDIPLA negligibly affected the amount of lattice disorder. The apparent asymmetry of the poly(ethylene‐alt‐propylene)‐block lamellae (ϕ), also determined by the fitting procedure, were more substantially affected; increasing the PDIPLA resulted in a decrease in ϕ. At asymmetric compositions of PEP‐PLA (fPLA ≈ 0.67), only the data at the highest values of the PDIPLA could be reasonably fit to this model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3386–3393, 2007
Deformation and adhesive contact of elastomeric membranes
Authors: Flory Anny L. , Brass David A. , Shull Kenneth R. 
Published: November 2007

AbstractWe have developed a highly sensitive inflation technique for probing adhesive interactions between soft materials. In this method, an elastomeric membrane is placed across a cylindrical glass tube and is pressurized into contact with a substrate. The adhesive interaction between the membrane and the substrate is obtained from the angle of contact, which is determined indirectly from the measured contact radius and applied pressure. An analysis of the membrane profile based on the numerical solution of the axisymmetric Laplace equation is developed. In a nonadhesive situation, where the membrane contact angle is known to be zero, the analysis is used to obtain the relationship between the membrane deformation and the biaxial membrane strain. Linearization of the governing equations is used to develop an analytic solution for the contact angle and energy release rate, making a connection to existing, more restrictive analyses of this problem. Results from three different types of membranes are presented as illustrative applications of the method. The substrate in these experiments is the gold electrode surface of a quartz crystal resonator, and the effect of membrane contact on the crystal resonance is summarized briefly. Adhesive interactions between the membranes are minimized in most cases by adding a grafted polyethylene glycol brush to one or both of the contacting surfaces. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3361–3374, 2007
Shape instabilities in adsorbed polymer condensates
Authors: Pereira G. G. , Pattanayek S. K. 
Published: November 2007

AbstractA polymer chain in a poor solvent collapses to a spherical globule. If this globule is subsequently deformed, either by stretching it or if it has some non‐zero net electric charge, it will become unstable to sinusoidal perturbations leading to novel final states. When such globules are imaged by direct methods such as atomic force microscopy the substrate on which they adsorb can affect the final morphological state. We therefore investigate strongly adsorbed polymers in poor solvents. We demonstrate that the real‐space, Self‐Consistent Field method is an ideal numerical tool in predicting equilibrium morphologies. New structures are predicted, which support previous explicit free energy calculations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3327–3337, 2007
Phase behavior predictions for polymer blends containing reversibly associating endgroups
Authors: Anthamatten Mitchell 
Published: November 2007

AbstractA mean field model is developed to predict how polymer–polymer miscibility changes if polymers are functionalized with noncovalent, reversibly binding endgroups. The free‐energy model is based on the Flory–Huggins mixing theory and has been modified using Painter's association model to account for equilibrium self‐association of endgroups. Model input parameters include the length of polymer chains, a temperature‐dependent interaction parameter, and a temperature‐dependent equilibrium constant for each type of associating endgroup. The analysis is applied to 12 possible blend combinations involving self‐complementary interactions and seven combinations involving hetero‐complementary [i.e. donor–acceptor (DA)] interactions. Combinations involve both monofunctional and telechelic associating chains. Predicted phase diagrams illustrate how self‐complementary interactions can stabilize two‐phase regions and how DA interactions can stabilize single phase regions. The model is a useful tool in understanding the delicate balance between the combinatorial entropy of mixing polymer chains, the repulsive interactions between dissimilar polymers, and the additional enthalpic and entropic changes due to end‐group association of chain ends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3285–3299, 2007
Proteomics of traumatic brain injury and regeneration
Authors: Zupanc Günther K. H. 
Published: November 2007

AbstractDespite the enormous medical and economic consequences of traumatic brain injury (TBI), little is known about the proteins involved in the resulting pathology. Major advances in the identification of such proteins have been made in recent years through application of differential proteome analysis. Such an approach has revealed a number of novel proteins as potential regulators of the degenerative and regenerative processes that take place in the mammalian brain after a traumatic insult. Some of these proteins may serve as diagnostic and prognostic markers to assess the severity of the brain damage. Comparative proteome analysis of brain systems differing in their intrinsic regenerative potential are likely to provide new insights into the cellular signals that could be targeted for therapeutic intervention to increase the repair capacity of the human brain.
A finite element framework for computation of protein normal modes and mechanical response
Authors: Bathe Mark 
Published: November 2007

AbstractA computational framework based on the Finite Element Method is presented to calculate the normal modes and mechanical response of proteins and their supramolecular assemblies. Motivated by elastic network models, proteins are treated as continuum elastic solids with molecular volume defined by their solvent‐excluded surface. The discretized Finite Element representation is obtained using a surface simplification algorithm that facilitates the generation of models of arbitrary prescribed spatial resolution. The procedure is applied to a mutant of T4 phage lysozyme, G‐actin, syntenin, cytochrome‐c′, beta‐tubulin, and the supramolecular assembly filamentous actin (F‐actin). Equilibrium thermal fluctuations of alpha‐carbon atoms and their inter‐residue correlations compare favorably with all‐atom‐based results, the Rotational‐Translational Block procedure, and experiment. Additionally, the free vibration and compressive buckling responses of F‐actin are in quantitative agreement with experiment. The proposed methodology is applicable to any protein or protein assembly and facilitates the incorporation of specific atomic‐level interactions, including aqueous‐electrolyte‐mediated electrostatic effects and solvent damping. The procedure is equally applicable to proteins with known atomic coordinates as it is to electron density maps of proteins, protein complexes, and supramolecular assemblies of unknown atomic structure. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Thermodynamic and kinetic determinants of Thermotoga maritima cold shock protein stability: A structural and dynamic analysis
Authors: Motono Chie , Gromiha M. Michael , Kumar Sandeep 
Published: November 2007

AbstractThe cold shock protein (CSP) from hyperthermophile Thermotoga maritima (TmCSP) is only marginally stable (ΔG(Topt) = 0.3 kcal/mol) at 353 K, the optimum environmental temperature (Topt) for T. maritima. In comparison, homologous CSPs from E. coli (ΔG(Topt) = 2.2 kcal/mol) and B. subtilis (ΔG(Topt) = 1.5 kcal/mol) are at least five times more stable at 310 K, the Topt for the mesophiles. Yet at the room temperature, TmCSP is more stable (ΔG(TR) = 4.7 kcal/mol) than its homologues (ΔG(TR) = 3.0 kcal/mol for E. coli CSP and ΔG(TR) = 2.1 kcal/mol for B. subtilis CSP). This unique observation suggests that kinetic, rather than thermodynamic, barriers toward unfolding might help TmCSP native structure at high temperatures. Consistently, the unfolding rate of TmCSP is considerably slower than its homologues. High temperature (600 K) complete unfolding molecular dynamics (MD) simulations of TmCSP support our hypothesis and reveal an unfolding scheme unique to TmCSP. For all the studied homologues of TmCSP, the unfolding process first starts at the C‐terminal region and N‐terminal region unfolds in the end. But for TmCSP, both the terminals resist unfolding for consistently longer simulation times and, in the end, unfold simultaneously. In TmCSP, the C‐terminal region is better fortified and has better interactions with the N‐terminal region due to the charged residues, R2, E47, E49, H61, K63, and E66, being in spatial vicinity. The electrostatic interactions among these residues are unique to TmCSP. Consistently, the room temperature MD simulations show that TmCSP is more rigid at its N‐ and C‐termini as compared to its homologues from E. coli, B. subtilis, and B. caldolyticus. Proteins 2008. © 2007 Wiley‐Liss, Inc.
CLEMAPS: Multiple alignment of protein structures based on conformational letters
Authors: Liu Xin , Zhao Ya‐Pu , Zheng Wei‐Mou 
Published: November 2007

AbstractCLEMAPS is a tool for multiple alignment of protein structures. It distinguishes itself from other existing algorithms for multiple structure alignment by the use of conformational letters, which are discretized states of 3D segmental structural states. A letter corresponds to a cluster of combinations of three angles formed by Cα pseudobonds of four contiguous residues. A substitution matrix called CLESUM is available to measure the similarity between any two such letters. The input 3D structures are first converted to sequences of conformational letters. Each string of a fixed length is then taken as the center seed to search other sequences for neighbors of the seed, which are strings similar to the seed. A seed and its neighbors form a center‐star, which corresponds to a fragment set of local structural similarity shared by many proteins. The detection of center‐stars using CLESUM is extremely efficient. Local similarity is a necessary, but insufficient, condition for structural alignment. Once center‐stars are found, the spatial consistency between any two stars are examined to find consistent star duads using atomic coordinates. Consistent duads are later joined to create a core for multiple alignment, which is further polished to produce the final alignment. The utility of CLEMAPS is tested on various protein structure ensembles. Proteins 2008. © 2007 Wiley‐Liss, Inc.
The differences in the microenvironment of the two tryptophan residues of the glutamine‐binding protein from Escherichia coli shed light on the binding properties and the structural dynamics of the protein
Authors: D'Auria Sabato , Staiano Maria , Varriale Antonio , Gonnelli Margherita , Marabotti Anna , Rossi Mose' , Strambini Giovanni B. 
Published: November 2007

AbstractGlutamine‐binding protein (GlnBP) from Escherichia coli is a monomer (26 kDa) that is responsible for the first step in the active transport of L‐glutamine across the cytoplasmic membrane. GlnBP consists of two domains (termed large and small) linked by two antiparallel β‐strands. The large domain is similar to the small domain but it contains two additional α‐helices and three more short antiparallel β‐strands. The deep cleft formed between the two domains contains the ligand‐binding site. The binding of L‐glutamine leads to cleft closing and a significant structural change with the formation of the so‐called “closed form” structure. The protein contains two tryptophan residues (W32 and W220) and 10 tyrosine residues. We used phosphorescence spectroscopy measurements to characterize the role of the two tryptophan residues in the protein structure in the absence and the presence of glutamine. Our results pointed out that the phosphorescence of GlnBP is easily detected in fluid solutions where the emission of the two tryptophan residues is readily discriminated by the drastic difference in the phosphorescence lifetime allowing the assignments of the short lifetime to W220 and the long lifetime to W32. In addition, our results showed that the triplet lifetime of the superficial W220 is unusually short because of intramolecular quenching by the proximal Y163. On the contrary, the lifetime of W32 is several hundred milliseconds long, implicating a well‐ordered, compact fold of the surrounding polypeptide. The spectroscopic data were analyzed and discussed together with a detailed inspection of the 3D structure of GlnBP. Proteins 2008. © 2007 Wiley‐Liss, Inc.
Negative modulation of signal transduction via interleukin splice variation
Authors: Denessiouk Konstantin A. , Denesyuk Alexander I. , Johnson Mark S. 
Published: November 2007

AbstractInterleukin 6 (IL‐6) belongs to a large group of secreted proteins called cytokines functioning to mediate and regulate immunity, inflammation, and hematopoiesis with direct effects on cell proliferation, apoptosis, and differentiation. Along with the IL‐6 protein, two of its splice variants, IL‐6δ2 and IL‐6δ4, were reported to be transcribed or expressedin vivoin human, and the mRNAs of IL‐6δ3 and IL‐6δ5 had been observed in mouse. While the existence of different splice variants of IL‐6 has been shown, very little is known on how the structural modifications of IL‐6 resulting from the formation of the different splice variants may alter cytokine functions. We have analyzed the potential effects splicing would have on interactions with the cell surface receptor complex. We (1) constructed three‐dimensional structures of the IL‐6 splice variants, IL‐6δ2, IL‐6δ3, and IL‐6δ4, with the assumption that an interleukin splice variant as a folded protein should retain a functional hydrophobic core; (2) reconstructed the ternary structural complexes consisting of the modeled IL‐6 splice variants, the IL‐6 receptor molecule (IL‐6R) and the dimeric signal‐transducing protein, gp130, and (3) analyzed all complexes and made comparisons with the X‐ray structure of the wild‐type IL‐6 complex. We identified three separate sites on IL‐6 where interactions are made with IL‐6R and with each of the two copies of gp130. The structural consequences of losing an exon lead to a unique pattern of lost interaction with different components of the receptor complex. Thus, in IL‐6 and its splice variants, the exons appear to have compartmentalized roles contributing to the combined function of the cytokine. The modeled interactions suggest that splice variants could act as antagonists, and that IL‐6δ2, missing the signal peptide, would be a cytoplasmic protein and be released and interact with nearby cell‐surface receptors when cells are damaged. We argue that in the case of IL‐6, helix E may act as a “silent secondary structure,” which only has an active role when it substitutes for a part of the hydrophobic core, for example, replacing helix A in IL‐6δ2. Proteins 2008. © 2007 Wiley‐Liss, Inc.