bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and light emitting properties of polyacetylenes having pendent fluorene groups
Authors: Huang Chun‐Hao , Yang Sheng‐Hsiung , Chen Kuei‐Bai , Hsu Chain‐Shu
Published: November 2005

Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] (PFA1), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) (PFA2), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] (PFA3), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] (PFA4), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] (PFA5) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers (M1–M5), using WCl6, MoCl5, and TaCl5 as catalysts and n‐Bu4Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m2 at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m2 at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006
Synthesis of polyacrylonitrile via reverse atom transfer radical polymerization catalyzed by FeCl3/isophthalic acid
Authors: Hou Chen , Qu Rongjun , Ji Chunnuan , Wang Chunhua , Wang Chengguo
Published: November 2005

FeCl3 coordinated by isophthalic acid was first used as a catalyst in the azobisisobutyronitrile‐initiated reverse atom transfer radical polymerization of acrylonitrile. N,N‐Dimethylformamide was used as a solvent to improve the solubility of the ligand. An FeCl3‐to‐isophthalic acid ratio of 0.5 not only gave the best control of the molecular weight and its distribution but also provided rather a rapid reaction rate. The effects of different solvents on the polymerization of acrylonitrile were also investigated. The rate of the polymerization in N,N‐dimethylformamide was faster than that in propylene carbonate and toluene. The molecular weight of polyacrylonitrile agreed reasonably well with the theoretical molecular weight in N,N‐dimethylformamide. The rate of polymerization increased with increasing polymerization temperature, and the apparent activation energy was calculated to be 59.9 kJ mol−1. Reverse atom transfer radical polymerization was first used to successfully synthesize acrylonitrile polymers with a molecular weight higher than 80,000 and a narrow polydispersity as low as 1.22. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 219–225, 2006
New solvent for polyrotaxane. I. Dimethylacetamide/lithium chloride (DMAc/LiCl) system for modification of polyrotaxane
Authors: Araki Jun , Ito Kohzo
Published: November 2005

Dimethylacetamide (DMAc) containing 8–9% (w/w) of lithium chloride (LiCl) or lithium bromide (LiBr) was found to be a good solvent for a polyrotaxane consisting of poly (ethylene glycol) (PEG) and α‐cyclodextrin (CD). In the new DMAc/LiCl solvent system, various modification reactions such as acetylation, direct dansylation, and reaction with acid chloride could be performed, which was unattainable in the previously reported solvents, i.e., dimethylsulfoxide (DMSO) and aqueous sodium hydroxide solution. Acetylation with acetic anhydride and direct dansylation of the polyrotaxane were investigated in detail in comparison with reactions in DMSO. The dissolution of the polyrotaxane in DMAc/LiCl suggested that the solubility and insolubility of the polyrotaxane is strongly in relation to the inter‐ and intramolecular hydrogen bonding of the polyrotaxane. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 532–538, 2006
Influence of varying hard segments on the properties of chemically crosslinked moisture‐cured polyurethane‐urea
Authors: Chattopadhyay D. K. , Sreedhar B. , Raju K. V. S. N.
Published: November 2005

Polyurethane prepolymers are widely used in the reactive hot melt adhesives and moisture‐cured coatings. The chemically crosslinked moisture‐cured formulation based on PEG‐1000 and isophorone diisocyanate was prepared with NCO/OH ratio of 1.6:1.0. Trimethylol propane was used as a crosslinking agent. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols, and 4:1 with different aromatic diamines. The polymer network maturation during moisture cure was followed by dynamic mechanical thermal analyzer (DMTA) instrument. The thermal and dynamic mechanical properties of the crosslinked polymers were evaluated using thermogravimetric analysis, differential scanning calorimetric analysis and DMTA. Surface properties were evaluated through angle‐resolved X‐ray photoelectron spectroscopy.

The present article discusses the physical properties of moisture‐cured polyurethane‐urea (MCPU) containing chemical crosslinks in the hard segment. The complete moisture‐cured polymers showed amorous results toward room temperature modulus, tensile strength, hardness, thermal stability, and transparency. The surface properties showed the enrichment of soft segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 102–118, 2006
Synthesis and self‐assembly of highly incompatible polybutadiene–poly(hexafluoropropylene oxide) diblock copolymers
Authors: Zhu Shixiong , Edmonds William F. , Hillmyer Marc A. , Lodge Timothy P.
Published: November 2005

A versatile coupling reaction for the preparation of polybutadiene–poly‐(hexafluoropropylene oxide) (BF) diblock copolymers is described. Six diblock copolymers with different block lengths were characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography; all six had total molecular weights below 15,000. Microphase separation of the block copolymers in the bulk state was established by small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry. SAXS data suggest that the diblocks are characterized by an unusually large Flory‐Huggins interaction parameter, χ, on the order of 10. However, extraction of χ from the order–disorder transition gave large (order 1) but significantly different values, thereby suggesting that these copolymers are too small and too strongly interacting to be described by block copolymer mean‐field theory. Dynamic light scattering was used to analyze dilute solutions of the title block copolymers in four selective organic solvents; the sizes of the micelles formed were solvent dependent. The micellar aggregates were large and nonspherical, and this is also attributed to the high degree of incompatibility between the two immiscible blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3685–3694, 2005
Electrical and optical properties of a novel nonconjugated conductive polymer, poly(β‐pinene)
Authors: Vippa P. , Rajagopalan H. , Thakur M.
Published: November 2005

Electrical conductivity in a novel nonconjugated conductive polymer, poly(β‐pinene), has been measured as a function of molar concentration of iodine. The conductivity increases about 10 orders of magnitude to a maximum value ˜8 × 10−3 S/cm. The molar concentration of iodine, corresponding to saturation, is ˜0.85. The optical absorption measurements after light doping have shown two peaks: one at 4.0 eV and the other at 3.1 eV. The first peak is due to the radical cation, and the second due to the charge‐transfer between the double bond and the dopant. As observed in other nonconjugated conductive polymers, the second peak becomes broader and undergoes a red shift, upon higher doping. The FTIR spectroscopic studies have shown that the CC stretching vibration at 1610 cm−1 and the CH bending vibration band at 728 cm−1 decrease upon doping, because of decrease of double bonds. Photoluminescence studies of poly(β‐pinene) show a maximum value at 360 nm for excitation at 280 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3695–3698, 2005
Equilibrium thermal behavior and morphology of organophilic montmorillonite/poly(ε‐caprolactone) nanocomposites
Authors: Pucciariello Rachele , Villani Vincenzo , Guadagno Liberata , Vittoria Vittoria
Published: November 2005

With differential scanning calorimetry, we have demonstrated a peculiar behavior under equilibrium conditions of neat poly(ε‐caprolactone) and its organophilic montmorillonite nanocomposites. In particular, in the determination of the equilibrium melting temperature by the extrapolation of the data of the melting temperature (Tm) versus the crystallization temperature (Tc), a bimodal trend has been observed. At the lower Tc's, the data of Tm follow a constant trend, whereas at the higher ones, the usual increasing trend has been obtained. Morphological observations by atomic force microscopy (AFM) have provided evidence of two different crystalline morphologies for the lower and higher Tc ranges. Moreover, AFM has shown that the thermal treatments strongly influence the clay dispersion in the polymer matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 22–32, 2006
Zero‐order kinetics of the thermal degradation of polypropylene/clay nanocomposites
Authors: Qin Huaili , Zhang Shimin , Zhao Chungui , Yang Mingshu
Published: November 2005

The thermal degradation kinetics of polypropylene/clay microcomposites and nanocomposites were studied by thermogravimetric analysis. In comparison with pure polypropylene, the reaction order of the degradation of the composites became zero‐order, and the activation energy increased dramatically. The zero‐order kinetics were associated with the acidic sites (H+) created on the clay layers, whereas the increase in the activation energy was coupled with the shielding effect of clay. The kinetic analysis could provide additional mechanistic clues concerning the thermal stability and flammability of polymer/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3713–3719, 2005
Novel phthalocyanine crystals as a conductive filler in crosslinked epoxy materials: Fractal particle networks and low percolation thresholds
Authors: Chen Zhe , Brokken‐Zijp José C. M. , Michels M. A. J.
Published: November 2005

Novel nanosized crystals of aquocyanophthalocyaninatocobalt (III) (Phthalcon 11) were used as a conductive filler in crosslinked epoxy materials. The crosslinked composite materials had a very low percolation threshold (φc ≈ 0.9 vol %). The relationship between the volume conductivity and the filler fraction follows the scaling law of the percolation theory and suggests that the conducting particle networks were formed by random percolation of primary aggregates. The occurrence of the low φc can be explained by the presence of a fractal Phthalcon 11 particle network formed from fractal aggregates during crosslinking. The position of the percolation threshold and the volume conductivity of these crosslinked materials were found to depend heavily on the processing conditions applied. These dependencies are explained in terms of specific particle–matrix interactions and the particle–particle interactions and by taking into account different mechanisms of particle network formation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 33–47, 2006
Ultrafine electrospun polyamide‐6 fibers: Effect of emitting electrode polarity on morphology and average fiber diameter
Authors: Supaphol Pitt , Mit‐Uppatham Chidchanok , Nithitanakul Manit
Published: November 2005

Electrostatic spinning or electrospinning is now a well‐known process for fabricating ultrafine fibers with diameters in the submicrometer down to nanometer range from materials of diverse origins. The polarity of the emitting electrode (i.e., the one that is in contact with the polymer solution or melt) can be either positive or negative. In the present contribution, the effects of emitting electrode polarity and some processing parameters (i.e., polyamide‐6 (PA‐6) concentration, molecular weight of PA‐6, electrostatic field strength, solution temperature, solvent type, and addition of an inorganic salt) on morphological appearance and average size of the as‐spun PA‐6 fibers were investigated. Scanning electron micrographs showed obvious morphological difference between the fibers obtained under positive and negative polarity of the emitting electrode. The main differences were that the cross section of the as‐spun PA‐6 fibers obtained under the negative electrode polarity was flat, while that of those obtained under the positive one appeared to be round and that the average size of the fibers obtained under the negative electrode polarity was larger than that of those obtained under the positive one. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3699–3712, 2005
Crystalline structure of polyamide 12 as revealed by solid‐state 13C NMR and synchrotron WAXS and SAXS
Authors: Dencheva Nadya , Nunes Teresa G. , Oliveira M. Jovita , Denchev Zlatan
Published: November 2005

The crystalline structure of polyamide‐12 (PA12) was studied by solid‐state 13C nuclear magnetic resonance (NMR) as well as by synchrotron wide‐ and small‐angle X‐ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ‐ and γ′‐crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ‐form and the oriented γ′‐form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ‐PA12 partially transformed into α‐modification. No such transition was observed with the oriented γ′‐PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d‐spacings, the Bragg's long spacings, the average thicknesses of the crystalline (lc) and amorphous (la) phases, and the linear crystallinity xcl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005
Ruptured conjugated polymer thin films formed during spin coating
Authors: Luo Shyh‐Chyang , Douglas Elliot P.
Published: November 2005

The formation of ruptured poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenyl vinylene] (MEH–PPV) thin films coated from undried tetrahydrofuran (THF) solutions was investigated. Because of the incompatibility of water and MEH–PPV, the polymer films coated from THF/water solutions showed a ruptured film structure. In the photoluminescence (PL) spectra of the polymer thin films, the ruptured polymer films showed a redshifted emission in comparison with continuous polymer thin films. According to a comparison of the PL spectra of polymer solutions and films, MEH–PPV in THF showed a coil–cylinder transition during precipitation from solution. Because of the incompatibility of water and MEH–PPV, an increase in the water content could increase the ratio of polymer chains in the cylinder conformation, resulting in a redshifted emission for the films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 79–84, 2006
Thermal expansion of polymers submitted to supercritical CO2 as a function of pressure
Authors: Boyer Séverine A. E. , Randzio Stanislaw L. , Grolier Jean‐Pierre E.
Published: November 2005

Interactions of polymers with compressed supercritical CO2 has been studied by using pressure‐controlled scanning calorimetry (PCSC). Global cubic thermal expansion coefficients (αpol‐g‐int) for medium density polyethylene (MDPE) and poly(vinylidene fluoride) (PVDF) saturated with supercritical CO2 have been determined at 352.4 K over the pressure range from 0.1 MPa to 100 MPa. In both cases, the isotherms of global αpol‐g‐int exhibit minima near 20 MPa. At pressures below the minimum, αpol‐g‐int for the PVDF–CO2 system are higher than for the MDPE–CO2 system, while at pressures above the minimum the opposite was observed. This proves that incorporation of CO2 in PVDF is stronger than in MDPE. The appearance of the minimum is attributed to the action of compressed CO2 molecules, which at higher pressures are forced to enter deep inside the interstitial or other voids in the polymer and cause their mechanical distension, which must be associated with an endothermic effect. The measurements have been performed on polymers used for fabrication of pipelines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:185–194, 2006
Structure and properties of some novel fluoroelastomer/clay nanocomposites with special reference to their interaction
Authors: Maiti Madhuchhanda , Bhowmick Anil K.
Published: November 2005

In the present work, rubber/clay nanocomposites were prepared by a solution mixing process using fluoroelastomers and different nanoclays (namely, Cloisite NA+, Cloisite 10A, Cloisite 20A, and Cloisite 30B). Fluoroelastomers having different microstructure and viscosity (Viton B‐50, Viton B‐600, Viton A‐200, and VTR‐8550) were used. Characterization of the nanocomposites was done by using X‐ray diffraction and atomic force microscopy. The mechanical and dynamic mechanical properties were studied. The surface energy of the clays and the elastomer was also measured. Even with the addition of only 4 phr of clay in Viton B‐50, tensile strength and modulus improved by 30–96% and 80–134%, respectively, depending on the nature of the nanoclays. Exfoliation was observed with both the unmodified and the modified clays at low loading in all the fluoroelastomers. Best properties were observed with the unmodified clay. All the grades of fluororubber followed the same trend. The increment (19%) in storage modulus was also higher in the case of the unmodified clay filled Viton B‐50 system. The results were explained with the help of thermodynamics, surface energies, and swelling studies. The difference in surface energy, Δγ, between the rubber and the unmodified clay was lower. The work of adhesion (67.63 mJ/m2) between Viton B‐50 and Cloisite NA+ was also higher than that (51.42 mJ/m2) between Viton B‐50 and Cloisite 20A. Negative ΔHS value for the unmodified clay‐filled system thermodynamically favored the formation of the nanocomposite as compared to the modified clay filled samples where ΔHS is positive or zero. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 162‐176, 2006
Maximum tensile properties of oriented polyethylene, achieved by uniaxial drawing of solution‐grown crystal mats: Effects of molecular weight and molecular weight distribution
Authors: Sawai Daisuke , Nagai Kazuhiko , Kubota Minato , Ohama Toshio , Kanamoto Tetsuo
Published: November 2005

The effects of molecular weight (MW) and MW distribution on the maximum tensile properties of polyethylene (PE), achieved by the uniaxial drawing of solution‐grown crystal (SGC) mats, were studied. The linear‐PE samples used had wide ranges of weight‐average (Mw = 1.5–65 × 105) and number‐average MWs (Mn = 2.0–100 × 104), and MW distribution (Mw/Mn = 2.3–14). The SGC mats of these samples were drawn by a two‐stage draw technique, which consists of a first‐stage solid‐state coextrusion followed by a second‐stage tensile drawing, under controlled conditions. The optimum temperature for the second‐stage draw and the resulting maximum‐achieved total draw ratio (DRt) increased with the MW. For a given PE, both the tensile modulus and strength increased steadily with the DRt and reached constant values that are characteristic for the sample MW. The tensile modulus at a given DRt was not significantly affected by the MW in the lower DRt range (DRt < 50). However, both the maximum achieved tensile modulus (80–225 GPa) and strength (1.0–5.6 GPa), as well as those at higher DRts > 50, were significantly higher for a higher MW. Although the maximum modulus reached 225 ± 5 for Mn ≥ 4 × 105, the maximum strength continued to increase with Mn even for Mn > 4 × 105, showing that strength is more strongly dependent on the Mn, even at higher Mn. Furthermore, it was found that each of the maximum tensile modulus and strength achieved could be expressed by a unique function of the Mn, independently of the wide variations of the sample MW and MW distribution. These results provide an experimental evidence that the Mn has a crucial effect on the tensile properties of extremely drawn and chain‐extended PE fibers, because the structural continuity along the fiber axis increases with the chain length, and hence with the Mn. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 153–161, 2006
Role of phosphorylated Thr160 for the activation of the CDK2/Cyclin A complex
Authors: De Vivo Marco , Cavalli Andrea , Bottegoni Giovanni , Carloni Paolo , Recanatini Maurizio
Published: November 2005

The enzymatic activity of the CDK2/Cyclin A complex increases upon the specific phosphorylation of Thr160@CDK2. In the present study, we have performed a comparative molecular dynamics (MD) study of models of the complex CDK2/Cyclin A/Substrate, which differ for the presence or absence of the phosphate group bound to Thr160. The models are based on two X‐ray structures available for CDK2/CyclinA and pCDK2/CyclinA/Substrate complexes. In this way, we analyze the influence of the phosphorylated Thr160 (pThr160) on both the flexibility of CDK2 activation loop (AL) and substrate binding in CDK2. Our calculations point to a decreased flexibility of the AL in the phosphorylated model, in fairly good agreement with experimental data, and to a key role of pThr160 for substrate recognition and stability. Multiple alignments of the CDKs sequences point to the very high conservation of the AL sequence among the CDKs, thus extending our results to all CDKs. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Structure, conformational stability, and enzymatic properties of acylphosphatase from the hyperthermophile Sulfolobus solfataricus
Authors: Corazza Alessandra , Rosano Camillo , Pagano Katiuscia , Alverdi Vera , Esposito Gennaro , Capanni Cristina , Bemporad Francesco , Plakoutsi Georgia , Stefani Massimo , Chiti Fabrizio , Zuccotti Simone , Bolognesi Martino , Viglino Paolo
Published: November 2005

The structure of AcP from the hyperthermophilic archaeon Sulfolobus solfataricus has been determined by 1H‐NMR spectroscopy and X‐ray crystallography. Solution and crystal structures (1.27 Å resolution, R‐factor 13.7%) were obtained on the full‐length protein and on an N‐truncated form lacking the first 12 residues, respectively. The overall Sso AcP fold, starting at residue 13, displays the same βαββαβ topology previously described for other members of the AcP family from mesophilic sources. The unstructured N‐terminal tail may be crucial for the unusual aggregation mechanism of Sso AcP previously reported. Sso AcP catalytic activity is reduced at room temperature but rises at its working temperature to values comparable to those displayed by its mesophilic counterparts at 25–37°C. Such a reduced activity can result from protein rigidity and from the active site stiffening due the presence of a salt bridge between the C‐terminal carboxylate and the active site arginine. Sso AcP is characterized by a melting temperature, Tm, of 100.8°C and an unfolding free energy, ΔG, at 28°C and 81°C of 48.7 and 20.6 kJ mol−1, respectively. The kinetic and structural data indicate that mesophilic and hyperthermophilic AcP's display similar enzymatic activities and conformational stabilities at their working conditions. Structural analysis of the factor responsible for Sso AcP thermostability with respect to mesophilic AcP's revealed the importance of a ion pair network stabilizing particularly the β‐sheet and the loop connecting the fourth and fifth strands, together with increased density packing, loop shortening and a higher α‐helical propensity. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Are structural biases at protein termini a signature of vectorial folding?
Authors: Laio Alessandro , Micheletti Cristian
Published: November 2005

Experimental investigations of the biosynthesis of a number of proteins have pointed out that part of the native structure may be acquired already during translation. We carried out a comprehensive statistical analysis of some average structural properties of proteins that have been put forward as possible signatures of this progressive buildup process. Contrary to a widespread belief, we found that there is no major propensity of the amino acids to form contacts with residues that are closer to the N‐terminus. Moreover, we found that the C‐terminus is significantly more compact and locally organized than the N‐terminus. This bias, though, is unlikely to be related to vectorial effects, since it correlates with subtle differences in the primary sequence. These findings indicate that even if proteins acquire their structure vectorially, no signature of this seems to be detectable in their average structural properties. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Preparation of amino‐acid‐type selective isotope labeling of protein expressed in Pichia pastoris
Authors: Chen Chiu‐Yueh , Cheng Chun‐Ho , Chen Yi‐Chun , Lee Jenq‐Chang , Chou Shan‐Ho , Huang Wenya , Chuang Woei‐Jer
Published: November 2005

We report the culture conditions for successful amino‐acid‐type selective (AATS) isotope labeling of protein expressed in Pichia pastoris (P. pastoris). Rhodostomin (Rho), a six disulfide‐bonded protein expressed in P. pastoris with the correct fold, was used to optimize the culture conditions. The concentrations of [α‐15N] selective amino acid, nonlabeled amino acids, and ammonium chloride, as well as induction time, were optimized to avoid scrambling and to increase the incorporation rate and protein yield. The optimized protocol was successfully applied to produce AATS isotope‐labeled Rho. The labeling of [α‐15N]Cys has a 50% incorporation rate, and all 12 cysteine resonances were observed in HSQC spectrum. The labeling of [α‐15N]Leu, ‐Lys, and ‐Met amino acids has an incorporation rate greater than 65%, and the expected number of resonances in the HSQC spectra were observed. In contrast, the labeling of [α‐15N]Asp and ‐Gly amino acids has a low incorporation rate and the scrambling problem. In addition, the culture condition was successfully applied to label dendroaspin (Den), a four disulfide‐bonded protein expressed in P. pastoris. Therefore, the described condition should be generally applicable to other proteins produced in the P. pastoris expression system. This is the first report to present a protocol for AATS isotope labeling of protein expressed in P. pastoris for NMR study. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Thermal denaturation of a recombinant mouse amelogenin: Circular dichroism and differential scanning calorimetric studies
Authors: Oobatake Motohisa , Yamasaki Tomoko , Simmer James P. , Renugopalakrishnan V.
Published: November 2005

Conformational analyses of a recombinant mouse tooth enamel amelogenin (rM179) were performed using circular dichroism (CD), fluorescence, differential scanning calorimetry, and sedimentation equilibrium studies. The results show that the far‐UV CD spectra of rM179 at acidic pH and 10°C are different from the spectra of random coil in 6 M GdnHCl. A near‐UV CD spectrum of rM179 at 10°C is similar to that of rM179 in 6 M GdnHCl, which indicates that aromatic residues of native structure are exposed to solvent and rotate freely. Far‐UV CD values of rM179 at 80°C are different from that of random‐coil structure in 6 M GdnHCl, which suggests that rM179 at 80°C has specific secondary structures. A gradual thermal transition was observed by far‐UV CD, which is interpreted as a weak cooperative transition from specific secondary structures to other specific secondary structures. The fluorescence emission maximum for the spectrum due to Trp residues in rM179 at 10°C shows the same fluorescence emission maximum as rM179 in 6 M GdnHCl and amino acid Trp, which indicates that the three Trp in rM179 are exposed to solvent. Deconvolution of differential scanning calorimetry curve gives the population of three states (A, I, and C states). These results indicate that three states (A, I, and C) have specific secondary structures, in which hydrophobic and Trp residues are exposed to the solvent. The thermodynamic characteristics of rM179 are unique and different from a typical globular protein, proline‐rich peptides, and a molten globule state. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Functional role of a protein foldon—An Ω‐loop foldon controls the alkaline transition in ferricytochrome c
Authors: Maity Haripada , Rumbley Jon N. , Englander S. Walter
Published: November 2005

Hydrogen exchange results for cytochrome c and several other proteins show that they are composed of a number of foldon units which continually unfold and refold and account for some functional properties. Previous work showed that one Ω‐loop foldon controls the rate of the structural switching and ligand exchange behavior of cytochrome c known as the alkaline transition. The present work tests the role of foldons in the alkaline transition equilibrium. We measured the effects of denaturant and 14 destabilizing mutations. The results show that the ligand exchange equilibrium is controlled by the stability of the same foldon unit implicated before. In addition, the results obtained confirm the ε‐amino group of Lys79 and Lys73 as the alkaline replacement ligands and bear on the search for a triggering group. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Managing and mining protein crystallization data
Authors: Amin Abdullah A. , Faux Noel G. , Fenalti Gustavo , Williams Geoffrey , Bernadou Adam , Daglish Ben , Keefe Karen , Middleton Shayne , Rae Joseph , Tetis Kosmas , Law Ruby H.P. , Fulton Kate F. , Rossjohn Jamie , Whisstock James C. , Buckle Ashley M.
Published: November 2005

The crystallization of macromolecules remains a major bottleneck in structural biology. The routine screening of more than one thousand crystallization conditions and subsequent optimization by fine screening presents a challenge to conventional laboratory notebook keeping. In addition, the development of high‐throughput robotic crystallization and imaging systems presents a pressing need for low‐cost laboratory information management system (LIMS). Here we describe CLIMS2, a crystallization LIMS that features a simple, user‐friendly graphical interface, allowing the storage, management, retrieval and mining of crystallization data. The CLIMS2 executable and documentation is freely available at http://clims.med.monash.edu.au. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Experimental determination and estimation of closed cup flash points of mixtures of flammable solvents
Authors: Catoire Laurent , Paulmier Stéphanie , Naudet Valérie
Published: November 2005

Flash points, in air at atmospheric pressure, of some binary and ternary mixtures are experimentally determined in this study. All the components of these mixtures are flammable. These data are used to further validate a simple and accurate method proposed for the estimation of flash points for both pure compounds and multicomponent mixtures. This method does not depend on experimental flash point or flammability limit data and requires only the normal boiling point temperature, the heat of vaporization, and the number of carbon atoms for the pure components, as well as vapor–liquid equilibrium data on the mixture. This method can be used to predict hazards resulting from minimum flash point behavior and probably the effects of small concentrations of volatile flammable contaminants on the flash point value of a mixture. It may therefore help to develop products (lubricants, fuels, etc.) that meet safety standards. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2006
A study of dislocation contribution from the temperature dependence of zero‐bias resistance‐area product of long‐wavelength n‐on‐p mercury cadmium telluride diodes
Authors: Gopal Vishnu , Gupta Sudha
Published: November 2005

A study of the contribution of dislocations to the zero‐bias resistance–area product (R0A) of long‐wavelength infrared n‐on‐p mercury cadmium telluride (HgCdTe) diodes has been carried out from the modelling of the temperature dependence of R0A product of diodes fabricated in a material of known dislocation density. The capture probabilities of electrons and holes relevant to the modelling of the effect of dislocations in p‐type HgCdTe have been thus evaluated. The general applicability of these parameters has been further verified by using them to model the temperature variation of the R0A of the diodes reported by other groups. Results of the present study show that dislocations degrade the impedance of HgCdTe diodes at low temperatures on account of their shunt‐resistance behavior rather than the commonly accepted dislocation‐assisted tunnelling mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From electronic grade to solar grade silicon: chances and challenges in photovoltaics
Authors: Pizzini S. , Acciarri M. , Binetti S.
Published: November 2005

Photovoltaics is a promising but challenging opportunity for the environmentally clean production of electric energy, as the cost of the produced energy is still too high to compete with conventional thermal and nuclear sources, in spite of the scientific and technological progress occurred in this field after the first oil crisis of 1973. Among the problems which should be solved to make photovoltaics fully competitive, a breakthrough concerning the cost reduction of the base material is compulsory. Aim of this paper is to discuss the scientific and technological problems encountered in the development of solar silicon for its use in high efficiency and low cost solar cells, and to give some firm experimental evidences about its potentialities. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wet‐oxidation effect on p‐type transparent conducting CuAlO2 thin film
Authors: Kim Dae‐Sung , Choi Se‐Young
Published: November 2005

The wet‐oxidation effect on optical and electrical properties of CuAlO2 thin films was investigated with different water vapor pressures. Preferential (006) oriented films were ob‐tained after wet‐oxidation. The transmittance was 50–85% for the visible range and the optical band gap was estimated to be 3.96–4.20 eV. The p‐type nature of the films was confirmed by Hall effect measurements. The resistivity and transmittance were increased as water vapor pressure, and these phenomena were caused by the decrease of lower oxides with higher oxygen pressure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray synchrotron diffraction studies of III–V semiconductor compounds implanted with hydrogen
Authors: Wieteska K. , Wierzchowski W. , Graeff W. , Gawlik G.
Published: November 2005

GaAs crystals and Al0.43Ga0.57As epitaxial layers of low dislocation density were implanted with 146 keV, 100 keV and 60 keV H+ ions and studied by recording of rocking curves, reciprocal space mapping and Bragg‐type section topography. The X‐ray investigation were performed also in the case of GaAs double implanted with 146 keV and 60 keV protons with doses of 6 × 1015 cm–2 and 4.2 × 1015 cm–2, with penetration ranges differing by a factor 2. The rocking curves and Bragg‐type section patterns for single implantation were readily explainable by approximating the strain profiles by the point‐defect distribution calculated with the TRIM95 program. In the case of double implantation with hydrogen ions the rocking curve contained much narrower interference maxima than the curves for single implantation. The experimental curve was well approximated by the theoretical one obtained by numerical integration of the Takagi–Taupin equations. The strain profile in this calculation was a sum of strain profiles of single implantations. The narrow interference maxima were most probably caused by beating of the radiation, reflected by two strain maxima located at different depths in the implanted crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct evidence of self‐aligned Si nanocrystals formed by ion irradiation of Si/SiO2 interfaces
Authors: Röntzsch Lars , Heinig Karl‐Heinz , Schmidt Bernd , Mücklich Arndt , Möller Wolfhard , Thomas Jürgen , Gemming Thomas
Published: November 2005

Energy‐filtered transmission electron microscopy proves directly that ion irradiation and post‐irradiation annealing of a Si/SiO2 interface results in the formation of a narrow layer of monodisperse Si nanocrystals in the oxide at a tunnel distance from the interface. Position and size of the Si nanocrystals are in agreement with predictive atomistic computer simulations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bogoliubov theory of Bose‐condensates of spinor exciton‐polaritons
Authors: Shelykh I. A. , Malpuech G. , Kavokin A. V.
Published: November 2005

In the present work, we present the formalism allowing to calculate the energy spectrum of polariton spinor Bose condensates. We investigate the dispersion of the elementary excitations of the weakly depleted polariton condensate within the framework of the Bogoliubov approach. We show that for linearly polarized condensates the anisotropy of the polariton‐polariton interactions leads to important differences in polariton dispersion in linear co‐ and cross‐linear polarizations. Surprisingly, we find that contrary to the standard Bogoliubov model (which does not take into account the spin of the condensate) the dispersion is not necessary linear at k  = 0, but can be parabolic. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultrafast nonlinear response of AlGaAs/InAlGaAs MQW photonic crystal waveguides
Authors: Murzyn P. , Garcia‐Déniz A. Z. , Fox A. M. , Wells J.‐P. R. , Whittaker D. M. , Skolnick M. S. , Krauss T. F. , Roberts J. S.
Published: November 2005

We report ultrafast optical tuning of the reflection properties of MQW AlGaAs/InAlGaAs 1D photonic crystal waveguides using a reflection geometry, pump‐probe technique. Very fast pump‐induced shifts of photonic resonances between 800–900 nm by up to 18 nm nanometers are demonstrated. This is followed by a fast decay which varies from 5 to 30 ps depending on the sample dimensions. Together with the maximum reflectivity change of ΔR /R  > 30%, this demonstrates excellent potential for application of photonic crystals as ultrafast nonlinear switches with decay times depending on the structure period. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dark exciton decay dynamics of a semiconductor quantum dot
Authors: Dalgarno Paul A. , Smith Jason M. , Gerardot Brian D. , Govorov Alexander O. , Karrai Khaled , Petroff Pierre M. , Warburton Richard J.
Published: November 2005

We report measurements of the exciton decay dynamics of a single self‐assembled quantum dot following non‐resonant excitation. The singly charged exciton, the trion, exhibits a simple one component exponential decay corresponding to radiative recombination. Conversely, the neutral exciton exhibits a two component exponential decay. We argue that the secondary component arises from dark exciton creation and subsequent conversion to a bright exciton through a spin flip. The spin flip time is a strong function of the bias applied between a Fermi reservoir close to the dot and a Schottky gate electrode as a result of a Kondo‐like spin swap process. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarisation properties of optical parametric oscillator emission in a semiconductor microcavity
Authors: Krizhanovskii D. N. , Sanvitto D. , Ceccarelli S. , Skolnick M. S. , Roberts J. S.
Published: November 2005

Polarisation properties of the light emitted by a semiconductor microcavity are studied in the regime of stimulated parametric scattering for one and two beam continuous wave excitation. For linearly polarized excitation with one beam we observe strongly linearly polarized signal emission with the plane of polarization rotated by 60°–120° relative to that of the pump. Moreover, a degree of circular polarisation is found for certain orientations of the plane of polarisation of the pump. These effects arise from the splitting between linearly and circularly polarized polariton states, as well as from the anisotropy of polariton‐polariton scattering. Resonantly exciting the lower polariton branch simultaneously with two independent cross circularly polarised pumps with opposite k‐vectors, we observe an enhancement of the total signal emission at k  = 0 by 3–5 times, accompanied by a new idler state located at k  = 0. The effect indicates efficient scattering of two pump polaritons, involving a biexciton intermediate state. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First‐principles study of BNxSb1–x, BPxSb1–x and BAsxSb1–x alloys
Authors: El Haj Hassan F.
Published: November 2005

The first ab initio calculations were carried out for the electronic, structural and thermodynamic properties of BNxSb1–x, BPxSb1–x and BAsxSb1–x boron ternary alloys. The full potential linearized augmented plane wave (FP‐LAPW) method was employed within density functional theory (DFT). The local density approximation was used with generalized gradient correction (GGA) as well as the Engel–Vosko GGA formalism to calculate the band gap. The effect of composition on lattice constants, bulk modulus and band gap was investigated. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the three alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co‐workers. In addition, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric and calorimetric studies of ferroelectric phase transitions in Li(2–x)NaxGe4O9 crystals
Authors: Cebula I. , Cach R.
Published: November 2005

The ferroelectric phase transitions of LiNaGe4O9, Li1.1Na0.9Ge4O9, Li1.2Na0.8Ge4O9 and Li1.7Na0.3Ge4O9 crystals were studied. Experiments were carried out by means of classical dielectric measurements and using an AC calorimetric specific‐heat measuring system. Critical behaviour is explained within Landau theory. The expansion coefficients of the state equation are determined. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of dielectric function inhomogeneities on spectral width of Er3+ ion luminescence in structures of Si nanocrystals
Authors: Teterukov S. A. , Lisachenko M. G. , Zhigunov D. M. , Shalygina O. A. , Kashkarov P. K. , Timoshenko V. Yu.
Published: November 2005

Calculations of the Stark‐effect splitting of the energy levels of Er3+ ions in SiO2 layers alternating with layers of quasi‐ordered Si‐nanocrystals have been performed. The splitting is caused by the electric field of image charges at the interface between the layers having different dielectric constants. It has been established, that the splitting increases with increasing difference between the dielectric constants of SiO2 and nanocrystalline layers, and as the ions approach the interface. The results obtained allow us to explain the experimental data on an additional spectral broadening of the Er3+ photoluminescence line at 0.8 eV with increasing thickness of nanocrystalline Si layers. Moreover, a modeling of the spectral line shape has been performed, assuming that it consists of six components, properties of which depend on the additional electric field induced by dielectric function inhomogeneity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thinking inside the box: Novel linear scaling algorithm for Coulomb potential evaluation
Authors: Thompson David C. , Ayers Paul W.
Published: November 2005

Beginning with the Poisson equation, and expanding the electronic potential in terms of sine functions, the natural orbitals for describing the particle‐in‐a‐box problem, we find that simple analytic forms can be found for the evaluation of the Coulomb energy for both the interacting and non‐interacting system of N‐electrons in a box. This method is reminiscent of fast‐Fourier transform and scales linearly. To improve the usefulness of this result, we generalize the idea by considering a molecular system, embedded in a box, within which we determine the electrostatic potential, in the same manner as that described for our model systems. Within this general formalism, we consider both periodic and aperiodic recipes with specific application to systems described using Gaussian orbitals; although in principle the method is seen to be completely general. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Are the hydrogen bonds involving sulfur bases inverse or anomalous?
Authors: Vila Antonio , Mosquera Ricardo A.
Published: November 2005

The hydrogen‐bonded complexes (HBCs) of H2S, CH2S, and CH4S with H–F (hydrogen fluoride) were studied within the framework of the quantum theory of atoms in molecules at several theoretical levels (HF, B3LYP, MP2, and QCISD) with a wide range of basis sets. According to the integrated atomic populations obtained at correlated levels, the interacting hydrogen of the acid gains charge upon complexation, in sharp contrast to the conventional picture of hydrogen bonding, whereas the HF method yields a small loss of charge. The study of several HnA…HmD HBCs of hydrides, where A is the hydrogen‐acceptor atom and D is the atom bonded to the hydrogen donor, reveals this behavior is followed when the electronegativity of D significantly exceeds that of A. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Dispersion treatment for NDDO‐based semiempirical MO techniques
Authors: Martin Bodo , Clark Timothy
Published: November 2005

We introduce an additional term to treat dispersion in NDDO‐based semiempirical molecular orbital techniques. The dispersion energy is calculated using additive “atomic orbital” polarizability tensors determined with our modified version of Rivail's variational technique. Frequency‐dependent polarizabilities can be obtained using Padé approximants, which proved more reliable than the Unsöld approximation or a Taylor‐series approach. Dispersion energies are best calculated using the Slater–Kirkwood modification of the London formula, although they can also be obtained using the Casimir–Polder approach with frequency‐dependent polarizabilities. A test parameterization using MNDO as the semiempirical technique indicated that weak interactions can be reproduced satisfactorily. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Mass spectrometric investigation of Maltacines E1a and E1b—two members of the Maltacine family of peptide antibiotics
Authors: Hagelin Gunnar
Published: November 2005

We have recently described the discovery of the Maltacines—a new family of cyclic peptide antibiotics from Bacillus subtilis. In this paper the mass spectrometric characterisation of two of the members is reported. A chemoselective ring opening with base to give the linear peptides was necessary before mass spectrometric characterisation could be performed. MSn of the singly and doubly charged protonated molecules gave uninterrupted series of Bn and Y″n ions that allowed determination of the amino acid sequence. By using a combination of derivatisation with phenylisothiocyanate (PITC), high‐resolution mass spectrometry and H/D exchange, the identities of three unknown residues were determined. The nature and position of the cyclic structure were disclosed by a chemoselective ring opening with Na18OH and it was found to be a lactone formed between a hydroxyl of residue number 4 and the C‐terminal amino acid number 12. Peptides with different combinations of P/Q and P/K at the N‐terminus were synthesised to verify the sequence of the N‐terminal B2 ion. The structure of the two peptides is proposed to be: E1a: cyclo‐4,12(P‐Q‐Y‐Adip‐V‐E‐T‐Y‐Orn‐S‐Y‐I‐OH) and E1b: cyclo‐4,12(P‐Q‐Y‐Adip‐V‐E‐T‐Y‐K‐S‐Y‐I‐OH). Adip = (2‐amino‐4,5‐dihydroxypentanoic acid). Copyright © 2005 John Wiley & Sons, Ltd.