bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraporous 3D polymer meshes by low‐temperature electrospinning: Use of ice crystals as a removable void template
Authors: Simonet Marc , Schneider Oliver D. , Neuenschwander Peter , Stark Wendelin J.
Published: November 2007

While electrospinning provides an excellent preparation method for the manufacturing of polymer fibers with defined diameter, controlling the overall porosity of the resulting fiber assemblies has remained elusive, particularly at higher porosities. In this study, the use of a low‐temperature fiber collection device in air with controlled humidity allowed the simultaneous deposition of polymer fibers and ice particles from condensing humidity. The ice particles were intimately embedded within the polymer fibers and served as a pore template thus defining the mesh porosity after drying of the collected fiber assemblies. The amount of water condensation therefore contributes to the control of the mean interfiber distance and the resulting porosity. This simple and well accessible use of ice crystals as void templates gives access to the preparation of biodegradable tissue engineering scaffolds with an up to four times higher porosity if compared to conventional fiber electrospinning. The successful application of low‐temperature electrospinning using polyesters or polyurethanes suggests a broad, material independent applicability of the process for the preparation of highly porous polymer structures. POLYM. ENG. SCI., 47:2020–2026, 2007. © 2007 Society of Plastics Engineers
Study on epoxy/thermoplastic blends based on the addition of a novel aromatic block copolymer
Authors: Cicala Gianluca , Mamo Antonino , Recca Giuseppe , Restuccia Carmelo Luca
Published: November 2007

In this article we present a study of the properties of some epoxy/thermoplastic blends based on the addition of a novel block copolymer of an ABA type. The block A was a commercial poly(2,6‐dimethyl‐1,4‐phenylene ether or oxide) (PPE or PPO) while block B was a random copolyethersulphone synthesized in our laboratory. The comparison with the epoxy blends modified only with the homopolymers A or B is also reported. The homopolymers were also mixed via solution blending and the resulting physical mixture was used as modifier for comparison purposes. The blends have been thoroughly characterized by parallel plate rheometry, dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy. Upon curing, the epoxy blends containing the physical mixture underwent phase separation showing a morphology which resembled the combination of those found for the blends modified with each of the homopolymers. On the contrary, the addition of the block copolymer resulted in a unique morphology. The viscoelastic properties of the blends both in the unreacted and cured state varied significantly when the block copolymer was added rather than the homopolymers or their physical mixture. POLYM. ENG. SCI., 47:2027–2033, 2007. © 2007 Society of Plastics Engineers
The effect of epoxy‐polyester hybrid resin on mechanical properties, rheological behavior, and water absorption of polypropylene wood flour composites
Authors: Jahani Yousef
Published: November 2007

The effect of epoxy resin on mechanical and Rheological properties, and moisture absorption of wood flour polypropylene composites (WPCs) were investigated. The reactive mixing of epoxy resin with 30, and 40 wt% wood flour and polypropylene (PP) was carried out in twin screw extruder with a special screw elements arrangement. PP grafted maleic anhydrides (MPP) were used as coupling agent to improve the interfacial interactions of wood flour, epoxy resin, and PP. The tensile strength of composites decreased, and elastic modulus and moisture absorption increased with increasing epoxy resin content. The complex viscosity η* increased with increasing epoxy resin content of composites, and a synergistic effect in increasing the η* was observed at 3 wt% resin. The epoxy resin modified wood‐PP composites that chemically coupled by MPP showed minimum water absorption with highest elastic modulus. The experimental oscillation rheologyical data were used to drive a model to predict the flow behavior of WPCs, in a wide range of frequencies. POLYM. ENG. SCI., 47:2041–2048, 2007. © 2007 Society of Plastics Engineers
Transport characteristics of carboxylic acids based chain extended PU membranes with n‐alkane penetrants
Authors: Siddaramaiah  , Manjula K.S.
Published: November 2007

Castor oil based chain extended polyurethanes (PUs) have been prepared using citric acid and maleic acid as chain extenders. Molecular transport of n‐alkanes into prepared carboxylic acid chain extended PUs has been studied at different temperatures, viz., 25, 40, and 60°C using a gravimetric sorption method. The sorption (S), the diffusion (D), and the permeation (P) coefficients for n‐alkane penetrants have been calculated. Transport data are affected by the nature of the interacting solvent molecules, molar volume, solubility parameters, temperature, and the structural variation of the chain extended PUs. The temperature dependence of the transport coefficient has been used to estimate the kinetic parameters for the processes of diffusion (ED) and permeation (EP) from the Arrhenius plots. The van't Hoff relation was used to obtain enthalpy (ΔH) and entropy (ΔS) of sorption process. POLYM. ENG. SCI., 47:2057–2064, 2007. © 2007 Society of Plastics Engineers
Through‐thickness embossing process for fabrication of three‐dimensional thermoplastic parts
Authors: Nagarajan Pratapkumar , Yao Donggang , Ellis Thomas S. , Azadegan Reza
Published: November 2007

The standard embossing process is limited to the fabrication of surface structures on relatively large polymer substrates. To overcome this limitation, a hybrid punching and embossing process was investigated for through‐thickness embossing of three‐dimensional parts. The embossing tool included a punching head and to‐be‐ replicated features in the socket behind the punching head. The built‐in punching head facilitated a through‐thickness action and provided a closed‐die environment for embossing pressure buildup. The method was used to emboss multichannel millimeter waveguides which requires uniform edges and accurate dimensions. With a tool temperature of 140°C, an embossing time of 3 min and a total cycle time of 7 min, discrete 4‐channel waveguides were successfully embossed from a room‐temperature ABS substrate. A computer model was established to study the flow behavior during through‐thickness embossing. It was found that nonisothermal embossing conditions help confine the polymer in the cavity and reduce the outflow into the surrounding region, thus achieving complete fill of the cavity. POLYM. ENG. SCI., 47:2075–2084, 2007. © 2007 Society of Plastics Engineers
Modeling of dynamic mechanical properties of vulcanized fluoroelastomer
Authors: Likozar Blaž , Šebenik Urška , Krajnc Matjaž
Published: November 2007

The dynamic mechanical properties of a vulcanized fluoroelastomer (FKM) were studied over a range of temperatures and shear frequencies. Dynamic mechanical analysis and differential scanning calorimetry were used for the purpose of the study. A model was developed in order to describe FKM's viscoelastic behavior at various temperatures. The model was fitted to experimental data using an algorithm, which was developed for this purpose. As a result the FKM discrete relaxation spectrum at two reference temperatures was obtained, as well as the Williams‐Landel‐Ferry (WLF) equation parameters or the activation energy equivalent. Further on, the model was applied on storage modulus and loss tangent values obtained from the experiments, during which the temperature increased linearly. It was observed that the WLF equation fits well with the results during the glass transition, while the Arrhenius‐type relationship predicted too rapid decrease of the storage modulus during the glass transition. The master curves were constructed using the previously calculated WLF parameters and the activation energy equivalent. The developed model may be readily applied for the prediction of the numerous FKM compounds' frequency–temperature behavior using the dynamic mechanical properties obtained from either isothermal or low linear heating rate program measurements. POLYM. ENG. SCI., 47:2085–2094, 2007. © 2007 Society of Plastics Engineers
Preparation and characterization of bis‐ortho‐diynylarene (BODA)‐derived submicrogratings
Authors: Zengin Huseyin , Zengin Gulay , Zhou Wensheng , Topping Chris M. , Smith Dennis W. , Foulger Stephen H.
Published: November 2007

The objective of this study was to illustrate how submicrogratings can be prepared from bis‐ortho‐diynylarene (BODA)‐derived polymers. BODA monomers undergo thermal step‐growth polymerization and careful control of this conversion, with respect to molecular weight and viscosity, can be used to produce reactive, processable branched polyarlyene intermediates. “Soft‐lithography” techniques were used to prepare submicrogratings from these intermediates, which were subsequently stabilized by further polymerization. The surface morphology and dimensions of the submicrogratings were examined using scanning electron microscopy techniques and crystallinity was studied. Reflectivity data was also obtained from linear submicrogratings. These BODA‐derived microstructures can be carbonized at 1000°C, or above, to obtain carbonized microstructures with potential for application in optical and electronic microdevices. POLYM. ENG. SCI., 47:2095–2099, 2007. © 2007 Society of Plastics Engineers
Influence of screw profile and extrusion conditions on the microstructure of polypropylene/organoclay nanocomposites
Authors: Lertwimolnun W. , Vergnes B.
Published: November 2007

Direct melt mixing in a twin screw extruder is a simple and classical technique for preparing nanocomposites by dispersing organoclay in a thermoplastic matrix. In this paper, we focus on organoclay/polypropylene nanocomposites, using maleated polypropylene as compatibilizer. The objective of the work is to characterize the influence of screw profile and processing conditions on the microstructure of the nanocomposite (intercalation and exfoliation). Different screw profiles, more or less severe in terms of mixing elements, have been investigated. For each profile, different processing conditions (feed rate, screw speed) have been tested. Samples were collected both at die exit and all along the screw profiles and analyzed (X‐ray diffraction and rheometry). Numerical simulations have been performed to quantify the thermomechanical treatment experienced by the material inside the extruder. For all profiles and operating conditions, a mixed intercalated/exfoliated structure has been observed. Exfoliation increases linearly with the ratio of screw speed to feed rate, but is more important for the less severe profile. Except at low feed rate, intercalation and exfoliation do not change a lot along the screw profile. In many cases, the final microstructure is already obtained after the melting zone of the extruder. POLYM. ENG. SCI., 47:2100–2109, 2007. © 2007 Society of Plastics Engineers
Stress–strain behavior as related to surface topography and thickness uniformity in uni‐ and biaxially stretched PVDF/PMMA blends
Authors: Zhou Xixian , Cakmak M.
Published: November 2007

The influence of blend composition and processing conditions on the surface roughness and thickness uniformity of PVDF/PMMA blends were investigated in uniaxial and biaxial deformation mode for PVDV and PVDF/PMMA blends 70/30, 55/45, and 40/60 wt%. The addition of PMMA retards the thermal crystallizability of the blends and this allows rapid solidification into films with little or no crystallinities. Such precursors with lowered crystallinity were found to be easily uni‐ and biaxially stretched into uniform and transparent films in the temperature range between the glass transition temperature and cold crystallization temperature where they exhibit strain hardening. Thus, these blends are suitable for processes such as tenter frame biaxial stretching, double bubble film blowing, and stretch blow molding where they will exhibit good transparency and thickness uniformity. POLYM. ENG. SCI., 47:2110–2117, 2007. © 2007 Society of Plastics Engineers
Nitroxide‐mediated controlled degradation of polypropylene
Authors: Psarreas Alexandros , Tzoganakis Costas , McManus Neil , Penlidis Alexander
Published: November 2007

The purpose of this work is to evaluate a new polypropylene (PP)‐based nitroxyl radical generator (NOR) and offer comparisons with a commonly used peroxide in the production of controlled‐rheology polypropylene (CRPP) resins. CRPP resins are produced by reactive processing in a batch mixer by using different amounts of either the NOR or a peroxide initiator at different temperatures. Molecular weight and rheological properties are determined for all CRPP produced and a comparison between the effectiveness of the NOR and the peroxide initiator is provided. POLYM. ENG. SCI., 47:2118–2123, 2007. © 2007 Society of Plastics Engineers
Nonisothermal finite‐element analysis of thermoforming of polyethylene terephthalate sheet: Incomplete effect of the forming stage
Authors: Erchiqui F. , Souli M. , Yedder R. Ben
Published: November 2007

In this work, we consider a nonisothermal finite‐element analysis approach using an explicit dynamic procedure for the forming of a polyethylene terephthalate (PET) sheet subjected to air‐flow loading. The dynamic pressure load is thus deduced from the van der Waals equation of state. The effect of the radiative‐conduction heat transfer during the reheating stage, the stress‐deformation behavior during the incomplete forming stage, and the solidification during the cooling stage are simulated. The viscohyperelastic behavior of the Christensen–Yang‐like model is considered. The Lagrangian formulation, together with the assumption of the membrane shell theory, is used. The viscohyperelastic model is validated with the equibiaxial stretching tests. Also, temperature validation is performed by comparing the computed, the theoretical, and the experimental temperature profiles obtained from measuring the inside and outside PET sheet surface. An example of thermoforming a PET part is presented. In this example, the influence of the air‐flow on the thickness and the stress distribution is presented. POLYM. ENG. SCI., 47:2129–2144, 2007. © 2007 Society of Plastics Engineers
Effects of interfacial morphology on the welding strength of injection‐molded polyamide
Authors: Qiu Jianhui , Tsuboi Atsushi , Izumi Kazuo , Wu Hong , Guo Shaoyun , Huang Yudong
Published: November 2007

The effect of interfacial morphology controlled by injection‐molding conditions on the welding strength of injection‐molded polyamide was investigated in this article. The experimental results showed that the first injection‐molding conditions had distinct influence on the welding strength at the low secondary injection‐molding temperature T2 (≤265°C), but the influence vanishes at T2 ≥ 285°C. On the other hand, no matter what the first injection‐molding conditions are, the welding strength increases with increasing T2, and when T2 ≥ 285°C, the highest welding strength reaches 45 MPa, due to the formation of trans‐crystals at the interface. Morphology studies showed that trans‐crystals grow along the perpendicular direction of the interface, and their nuclei are formed at the surface of the first injection‐molded specimens. For the specimens with high‐welding strength, the welding strength relies on the skin layer of the first injection‐molded specimens in which the fracture induced by shear stress happens. POLYM. ENG. SCI., 47:2164–2171, 2007. © 2007 Society of Plastics Engineers
Liver proteome analysis of adaptive response in rat immediately after partial hepatectomy
Authors: Sun Yanwei , Deng Xinyu , Li Wenrui , Yan Yujuan , Wei Handong , Jiang Ying , He Fuchu
Published: November 2007

The extraordinary ability of the liver to regenerate after resection continues to be an important fascination to mammalian liver researchers. However, at present, there are still several central questions regarding the process of liver regeneration that are not clear. In our study, we try to clarify how the liver is able to maintain its functions as well as to initiate liver regeneration after a significant loss of two‐thirds. Here differentially expressed proteins in rat livers at 1 h after partial hepatectomy (PHx) and sham operation were analyzed using 2‐DE combined with MALDI‐TOF/TOF MS. After the analysis, 24 significantly changed spots (ratio≥2, p<0.05) were identified. Those proteins are involved in important liver functions such as metabolism, detoxification, and inflammation. Based on the changes in the protein levels found in our data, we identified two aspects of remnant liver immediately after PHx, which focused on the hepatic adaptation and the inflammatory response associated with the initiation of liver regeneration after PHx. For the first time, the differential expression of pyruvate dehydrogenase complex (PDHX), paraoxonase 1 (PON1), thyroid hormone receptor β, GAP43 (where GAP stands for growth‐associated protein), and interleukin‐2 (IL2), after PHx, were validated by Western blot.
Analysis of DIGE data using a linear mixed model allowing for protein‐specific dye effects
Authors: Krogh Morten , Liu Yingchun , Waldemarson Sofia , Valastro Barbara , James Peter
Published: November 2007

Differential in‐gel electrophoresis (DIGE) experiments allow three protein samples to be run per gel. The three samples are labeled with the spectrally resolvable fluorescent dyes, Cy2, Cy3, and Cy5, respectively. Here, we show that protein‐specific dye effects exist, and we present a linear mixed model for analysis of DIGE data which takes dye effects into account. A Java implementation of the model, called DIGEanalyzer, is freely available at http://bioinfo.thep.lu.se/digeanalyzer.html. Three DIGE experiments from our laboratory, with 173, 64, and 24 gels, respectively, were used to quantify and verify the dye effects. DeCyder 5.0 and 6.5 were used for spot detection and matching. The fractions of proteins with a statistically significant (0.001 level) dye effect were 19, 34, and 23%, respectively. The fractions of proteins with a dye effect above 1.4‐fold change were 1, 4, and 6%, respectively. The median magnitude of the dye effect was 1.07‐fold change for Cy5 versus Cy3 and 1.16‐fold change for Cy3 versus Cy2. The maximal dye effect was a seven‐fold change. The dye effects of spots corresponding to the same protein tend to be similar within each of the three experiments, and to a smaller degree across experiments.
Quantitative proteomics of intracellular Porphyromonas gingivalis
Authors: Xia Qiangwei , Wang Tiansong , Taub Fred , Park Yoonsuk , Capestany Cindy A. , Lamont Richard J. , Hackett Murray
Published: November 2007

Whole‐cell quantitative proteomic analyses were conducted to investigate the change from an extracellular to intracellular lifestyle for Porphyromonas gingivalis, a Gram‐negative intracellular pathogen associated with periodontal disease. Global protein abundance data for P. gingivalis strain ATCC 33277 internalized for 18 h within human gingival epithelial cells and controls exposed to gingival cell culture medium were obtained at sufficient coverage to provide strong evidence that these changes are profound. A total of 385 proteins were overexpressed in internalized P. gingivalis relative to controls; 240 proteins were shown to be underexpressed. This represented in total about 28% of the protein encoding ORFs annotated for this organism, and slightly less than half of the proteins that were observed experimentally. Production of several proteases, including the classical virulence factors RgpA, RgpB, and Kgp, was decreased. A separate validation study was carried out in which a 16‐fold dilution of the P. gingivalis proteome was compared to the undiluted sample in order to assess the quantitative false negative rate (all ratios truly alternative). Truly null (no change) abundance ratios from technical replicates were used to assess the rate of quantitative false positives over the entire proteome. A global comparison between the direction of abundance change observed and previously published bioinformatic gene pair predictions for P. gingivalis will assist with future studies of P. gingivalis gene regulation and operon prediction.
Synthesis and characterization of arborescent (hyperbranched) polyisobutylenes from the 4‐(1,2‐oxirane‐isopropyl)styrene inimer
Authors: Foreman Elizabeth A. , Puskas Judit E. , Kaszas Gabor
Published: November 2007

The synthesis of the novel inimer (initiator‐monomer) 4‐(1,2‐oxirane‐isopropyl)styrene EPOIM and the copolymerization of this inimer with isobutylene (IB) to form arborescent polyisobutylene (PIB) is described. Polymerizations were accomplished by use of TiCl4 coinitiator and the effect of reaction conditions was investigated. Size exclusion chromatography (SEC) was used demonstrate EPOIM incorporation across the whole molecular weight distribution. The average number of branch points (B) per chain measured by use of selective link destruction increased with increasing EPOIM/IB ratio and decreased with [TiCl4]. Large scale polymerizations were carried out based on results from small scale polymerizations. Architecture analysis carried out through use of branching parameters based on the radii of gyration Rg and hydrodynamic radii Rh measured by multidetector SEC corroborated the proposed arborescent architecture. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5847–5856, 2007
Microwave‐assisted ring‐opening polymerization of trimethylene carbonate in the presence of ionic liquid
Authors: Liao Liqiong , Zhang Chao , Gong Shaoqin
Published: November 2007

Microwave‐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

In 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

Polymer 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

The 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

Two 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

The 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

High‐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

We 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

A 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

A 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

Despite 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

A 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

The 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

CLEMAPS 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

Glutamine‐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

Interleukin 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.
Analyzing the catalytic mechanism of MPtpA: A low molecular weight protein tyrosine phosphatase from Mycobacterium tuberculosis through site‐directed mutagenesis
Authors: Madhurantakam Chaithanya , Chavali Venkata Ramana Murthy , Das Amit Kumar
Published: November 2007

Mycobacterium tuberculosis adopts various measures to escape from the hostile environment of the host cells. A low molecular weight protein tyrosine phosphatase (LMWPTPase) MPtpA was found to be active in virulent mycobacterial forms during the phagocytosis process. To ascertain the importance of conserved residues Cys11, Arg17, and Asp126 in the catalytic mechanism of MPtpA, site‐directed mutagenesis was performed, namely C11S, R17A, D126A, and D126N. Kinetic characterization of wild‐type and the mutant MPtpAs using para‐nitrophenyl phosphate revealed the reaction mechanism followed by this LMWPTPase and it is similar to the other PTPases. All the LMWPTPases have a common signature motif, ‘C(X)5R(S/T)’ and an Asp as the general acid residue and the mechanism followed by MPtpA can be aptly attributed to other LMWPTPases as well, considering the similar three‐dimensional conformation. We have shown that the mutations caused major changes in the chemical environment surrounding the mutated residues and resulted in the decrease of catalytic activity significantly. Inhibition kinetics was performed with phosphate analogues: sodium molybdate, sodium orthovanadate, and sodium tungstate. Proteins 2008. © 2007 Wiley‐Liss, Inc.
The balance between the rates of incorporation and pyrophosphorolytic removal influences the HIV‐1 reverse transcriptase bypass of an abasic site with deoxy‐, dideoxy‐, and ribonucleotides
Authors: Sharma Bechan , Crespan Emmanuele , Villani Giuseppe , Maga Giovanni
Published: November 2007

Abasic (AP) sites pose a potential danger to HIV‐1 replication. HIV‐1 RT has been shown to preferentially incorporate purines opposite an AP site, and subsequently extend from the lesion. While it is clear that AP sites are bypassed inefficiently and are major sites of RT pausing, detailed kinetic analysis of the relative contributions of both the incorporation and the pyrophosphorolytic reactions in translesion synthesis by HIV‐RT is still lacking. Investigation of the molecular basis of these processes is important, in light of the fact that HIV‐1 RT is the major target for anti‐HIV chemotherapy, and its low fidelity is an essential determinant of the extraordinary genetic variability of HIV‐1, which is important for the appearance of mutant viruses resistant to chemotherapy. Here, we analyzed the effects of the presence of an AP site on the template strand on the catalytic properties of the DNA‐dependent polymerization reaction as well as on the phosphorolytic activity of HIV‐1 RT, in the presence of deoxy‐, dideoxy,‐ and ribonucleotides. We find that AP sites can substantially influence the substrate specificity of HIV‐1 RT and that pyrophosphorolysis plays a significant role in determining the ability of HIV‐1 RT to (mis)incorporate nucleotides Proteins 2008. © 2007 Wiley‐Liss, Inc.