bluuebunny/crossref_metadata_2025 huggingface dataset:
pH‐induced Micelle Formation of Poly(histidine‐co‐phenylalanine)‐block‐Poly(ethylene glycol) in Aqueous Media
Authors: Kim Goo Myun , Bae You Han , Jo Won Ho
Published: October 2005

Summary:Poly[(L‐histidine)‐co‐(L‐phenylalanine)]‐block‐poly(ethylene glycol) (HF‐b‐PEG) diblock copolymers were synthesized to be used for preparation of pH‐sensitive polymeric micelles. First, HF block was synthesized by ring opening copolymerization ofL‐histidine andL‐phenylalanineN‐carboxyanhydride, and then the resulting copolymer was coupled with PEG. The pKavalue of diblock copolymer can be controlled by adjusting the histidine/phenylalanine ratio in HF block. It is observed that the block copolymers form micelles in aqueous media and that the micelles are spherical in shape with a unimodal distribution. The micelle is formed at pH higher than pKaof block copolymer while it is not formed at lower pH. This is because the protonation of histidine residue in the HF block converts the hydrophobic core into hydrophilic one at lower pH.

Acid‐Base titration profile of HF41(5600)‐b‐PEG, HF56(5500)‐b‐PEG, H(5100)‐b‐PEG and 0.1 N NaCl.

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Acid‐Base titration profile of HF41(5600)‐b‐PEG, HF56(5500)‐b‐PEG, H(5100)‐b‐PEG and 0.1 N NaCl.
Correlation between Solid‐State Structures and Enzymatic Degradability of Cocrystallized Blends
Authors: Hirota Yuuki , Yoshie Naoko , Ishii Nariaki , Kasuya Ken‐ichi , Inoue Yoshio
Published: October 2005

Summary: Solid‐state structures and enzymatic degradability have been investigated for cocrystallized blends between poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [PHBV] and poly(3‐hydroxybutyrate‐co‐3‐hydroxypropionate) [PHBP]. From wide‐angle X‐ray diffraction patterns, small‐angle X‐ray scattering data, and the comparison of the enzymatic degradability of these blends, the solid‐state structures of PHBV/PHBP blend samples, in which the PHBV component has higher isothermal crystal growth rate (G) value than the PHBP one, might be similar to those of the component PHBVs; while those of the PHBP/PHBV blend samples, in which PHBP component has higher G value, were similar to the component PHBPs.

Normalized one‐dimensional correlation functions γ(x) of PHBV/PHBP binary blends crystallized at 90 °C.

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Normalized one‐dimensional correlation functions γ(x) of PHBV/PHBP binary blends crystallized at 90 °C.
Synthesis and Antioxidant Efficiency of a New Copolymer Containing Phosphorylated Myo‐Inositol
Authors: Iemma Francesca , Trombino Sonia , Puoci Francesco , Cirillo Giuseppe , Spizzirri Umile Gianfranco , Muzzalupo Rita , Picci Nevio
Published: October 2005

Summary: New data are constantly gathered to show the role of oxidative stress and the involvement of reactive oxygen species in the pathogenesis of degenerative diseases. InsP6 is able to coordinate iron metal in order to prevent iron‐catalyzed free radical formation. The aim of the present paper is to describe a new synthetic strategy in order to prepare a polymeric structure containing chemical functions able to coordinate iron ions. Here, we report the synthesis of a copolymer containing phosphorylated myo‐inositol groups and we evaluate its antioxidant efficiency. Such a system was synthesized by binding chemical groups susceptible of radical polymerization to myo‐inositol. The synthesized monomer was copolymerized with N,N‐dimethylacrylamide (DMAA) (molar ratio 1:3) and submitted to exhaustive phosphorylation. The reaction was proved by an assay specific for phosphate groups. Finally, we evaluated the copolymer's ability in inhibiting lipid peroxidation in rat liver microsomal membranes. This study showed that the designed macromolecular system is particularly effective as antioxidant.

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Intrinsic Adhesion Properties of Poly(vinyl pyrrolidone) to Pharmaceutical Materials: Humidity Effect
Authors: Lee Jonghwi
Published: October 2005

Summary: Poly(vinyl pyrrolidone) (PVP) is widely used for bioengineering and pharmaceutical applications, and its adhesion characteristics are critical. When used as a binder in pharmaceutical granulation, it covers the resultant granules and governs their surface properties. The intrinsic adhesion forces of PVP toward common hydrophobic (magnesium stearate) and hydrophilic (lactose) pharmaceutical materials have been studied as a function of relative humidity (RH). The effect of RH on adhesion force was more significant for the PVP/hydrophilic material than the PVP/hydrophobic material. Adhesion was lowest between 20 and 40% RH, and it increased at RH above 40% and below 20%. This is likely to be due to the development of capillary and triboelectrification forces, respectively. In a nano‐indentation experiment using a silicon tip at room temperature, the PVP surface underwent a glass transition at 70% RH. This result suggests that surface softening contributes to the increased PVP adhesion at RH above 70%. To adjust the adhesion properties of PVP, humidity control should be an essential part of research and development.

Effect of humidity on the adhesion forces between PVP and lactose (LT) or magnesium stearate (MS).

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Effect of humidity on the adhesion forces between PVP and lactose (LT) or magnesium stearate (MS).
Reactive Compatibilization of Melt Mixed PA6/SWNT Composites: Mechanical Properties and Morphology
Authors: Bhattacharyya Arup R. , Pötschke Petra , Häußler Liane , Fischer Dieter
Published: October 2005

Summary: Styrene maleic anhydride copolymer (SMA) encapsulated single wall carbon nanotubes (SWNT) were melt mixed with polyamide 6 (PA6) utilizing an interfacial reaction in order to disperse SWNT homogeneously and to enhance interfacial adhesion. The intended reactive coupling between PA6 and SMA was evident from IR spectroscopy. Raman spectroscopy was used to characterize the SWNT and the nanocomposites. Studies on crystallization behavior showed the nucleating behavior of SWNT in the composites, as found using DSC and WAXD. The encapsulation of SWNT by SMA copolymer leads to increased elongation at break in the composites, which can be attributed to the enhanced interfacial adhesion between PA6 and SMA modified SWNT as observed from the SEM investigation of tensile fractured surfaces of PA6/SWNT+SMA composites. The glass transition temperature of PA6 increased significantly in the composites.

Tensile fractured surface of SMA encapsulated PA6/SWNT composites.

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Tensile fractured surface of SMA encapsulated PA6/SWNT composites.
Photopolymerization of Reactive Mesogens
Authors: Thiem Heiko , Strohriegl Peter , Shkunov Maxim , McCulloch Iain
Published: October 2005

Summary: The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4‐phenylene‐bis{4‐[6‐(acryloyloxy)hexyloxy]benzoate} 1 and acrylic acid 6‐{4‐[6‐(6‐acryloyloxyhexyloxy)naphthalen‐2‐yl]‐phenoxy}hexyl ester 2 has been investigated using Photo‐DSC measurements. Photocrosslinking of 1 in the nematic phase at 100 °C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100 °C compared to the isotropic phase at 120 °C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.

Photopolymerization of reactive mesogens.

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Photopolymerization of reactive mesogens.
A Facile One‐Pot Synthesis to Dextran‐Based Nanoparticles with Carboxy Functional Groups
Authors: Dou Hongjing , Tang Minhua , Sun Kang
Published: October 2005

Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.

Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.

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Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.
Reactively Modified Poly(lactic acid): Properties and Foam Processing
Authors: Di Yingwei , Iannace Salvatore , Di Maio Ernesto , Nicolais Luigi
Published: October 2005

Summary: In order to produce modified poly(lactic acid) (PLA) resins for applications requiring high melt viscosity and elasticity (e.g., low‐density foaming, thermoforming), a commercial PLA product has been reactively modified in melt by sequentially adding 1,4‐butanediol and 1,4‐butane diisocyanate as low‐molecular‐weight chain extenders. By varying amounts of the two chain extenders associated to the end group contents of PLA, three resulted samples were obtained. They were then structurally characterized by FTIR spectroscopy and molecular structure analysis. Their thermal, dynamic mechanical thermal properties and melt viscoelastic properties were investigated and compared along with unmodified PLA. The results indicated that chemical modification may be characterized as chain scission, extension, crosslinking, or any combination of the three depending on the chain extender amounts. The increase of PLA molecular weight could be obtained by properly controlling amounts of two chain extenders. The samples with increased molecular weights showed enhanced melt viscosity and elasticity. Such property improvements promised a successful application for modified PLA in a batch foam processing by producing foams with reduced cell size, increased cell density and lowered bulk foam density in comparison with plain PLA foam.

Cellular morphology of a modified PLA foam.

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Cellular morphology of a modified PLA foam.
Mechanical Response of Thermoset Polymers under High Compressive Loads, 1
Authors: Ståhlberg Daniel , Nordin Lars‐Olof , Varna Janis , Johansson Mats
Published: October 2005

Summary: The present study describes the mechanical response of thermoset polymers under high compressive loads. A well‐defined free radically cured vinyl ester resin has been used and studied in six different geometries in order to determine the dependence of apparent mechanical properties on the particular size and shape of a sample. The mechanical response in compression has also been compared to the response in tensile tests. Variation of the film thickness, boundary conditions and loading conditions reveal that there is a significant effect on the mechanical performance (apparent properties) of the polymer. When the thickness‐to‐width ratio of the sample is reduced in a compression test, the friction between the sample and the compression plates proves to be of great importance. The yield stress increases dramatically when the thickness of the sample is reduced, whereas it decreases when the friction between sample and the compression plate is reduced. The creep decreases when the thickness of the material is reduced and it decreases even more due to reaction of the material surrounding the compressed part of the sample. The described test conditions and observed phenomena will be subject to simulation in Part 2 of this study.

Mechanical performance of a thermoset polymer under high compressive loads.

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Mechanical performance of a thermoset polymer under high compressive loads.
Conducting Shape Memory Polyurethane‐Polypyrrole Composites for an Electroactive Actuator
Authors: Sahoo Nanda Gopal , Jung Yong Chae , Goo Nam Seo , Cho Jae Whan
Published: October 2005

Summary: Electroactive shape memory composites were prepared using polyurethane block copolymer and conducting polypyrrole by chemical oxidative polymerization. The electrical conductivity, thermal and mechanical properties, and morphology of the composites were investigated, and a voltage‐triggered shape memory effect was demonstrated. The polyurethane synthesized had a transition temperature near 46 °C. The presence of polypyrrole increased the conductivity of the composites, and a high conductivity of the order of 10−2 S/cm was obtained at 6–20 wt.‐% polypyrrole. Such a conductivity of composites was enough to show electroactive shape recovery by heating above the transition temperature of 40–45 °C due to melting of the polycaprolactone soft segment domain. Thus a good shape recovery of 85–90% could be obtained in the shape recovery test with bending mode when an electric field of 40 V was applied.

Electroactive shape recovery behavior of PU/PPy composite.

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Electroactive shape recovery behavior of PU/PPy composite.
The Use of the Indentation Test for Studying the Solidification Behaviour of Different Semicrystalline Polymers during Injection Molding
Authors: La Carrubba Vincenzo , Gabriëlse Wouter , Piccarolo Stefano
Published: October 2005

Summary: An in‐line method for monitoring the solidification process during injection molding of semicrystalline polymers (demonstrated previously in J. Appl. Polym. Sci. 2003, 89, 3713) is based on a simple device, where an additional ejector pin is pushed on the injection molded part at different times during the solidification phase. The ‘indentation depth profile’, i.e., residual deformation as a function of time, was obtained and allowed to determine the evolution of the solidification front in the mold as a function of the cooling time. The present work shows the reliability and the powerfulness of the aforementioned method for a large variety of different semicrystalline polymers (PET, PBT, polyamide‐6 PA6, isotactic poly(propylene) iPP) characterized also by different molecular weight and/or nucleating agents. The results show that the indentation test may be considered as a ‘predictive’ tool to qualitatively and quantitatively compare the solidification process of different polymers and polymer grades during injection molding.

Comparison of the solid front propagation during injection molding of different materials.

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Comparison of the solid front propagation during injection molding of different materials.
Solvent Controlled Multi‐Morphological Self‐Assembly of Amphiphilic Graft Copolymers
Authors: Zhang Jian Xiang , Qiu Li Yan , Zhu Kang Jie
Published: October 2005

Summary: Amphiphilic graft polyphosphazenes (EtTrp/PNIPAm‐PPP) with different mole ratios of hydrophobic groups to hydrophilic segments were synthesized by ring‐opening polymerization and subsequent substitution reactions. The self‐assembly behavior of these graft copolymers was studied in detail by TEM, SEM, CLSM, and AFM. Depending on the copolymer composition and common organic solvent employed in dialysis process, supramolecular aggregates ranging from network, nanospheres, high‐genus particles to macrophage‐like aggregates were produced with graft copolymers.

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Synthesis, Optical, and Electrochemical Properties of the High‐Molecular‐Weight Conjugated Polycarbazoles
Authors: Fu Yaqin , Bo Zhishan
Published: October 2005

Summary: A kind of novel dibromocarbazole monomer bearing three alkyl chains was prepared. Two strategies were developed to improve the solubility and molecular weight of carbazole polymers. One was the polymerization of N‐octyl‐2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)carbazole with the alkylated dibromocarbazole. Another one was the polymerization of N‐octyl‐2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)carbazole with N‐octyl‐3,6‐dibromocarbazole. All the polymerizations were carried out under palladium‐catalyzed Suzuki polycondensation (SPC) conditions. Through using carbazole monomer bearing three alkyl chains to polymerize, we have successfully boosted the number‐average molecular weight of 2,7‐linked carbazole polymers from not more than 5 to 67 kDa. The high‐molecular‐weight polymers were obtained in high yields and displayed good solubility in common organic solvents. Their optical, electrochemical, and thermal properties were also reported.

Preparation of carbazole polymers by Suzuki polycondensation.

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Preparation of carbazole polymers by Suzuki polycondensation.
Effects of Catalyst Isoquinoline in Polymerization Process on the Aggregation Structures of Polyimide in Solution
Authors: Liu Xiangyang , Yang Jin , Guo Linghong , Gu Yi
Published: October 2005

Summary: A thermoreversible gel or a dendritic crystal has been obtained in a novel polyimide solution at low temperature, depending on the approach taken to add the isoquinoline catalyst during the polymerization process. By adding the isoquinoline at the beginning of polymerization, two kinds of layer structures in the gel are developed. However, by adding the isoquinoline after the polymerization has been carried out for one hour, a perfect dendritic crystalline structure is gradually developed in the polymerization solution.

PLM photographs of the obtained polyimide crystals.

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PLM photographs of the obtained polyimide crystals.
Electrostatically Dissipative Polystyrene Nanocomposites containing Copper Nanowires
Authors: Gelves Genaro A. , Sundararaj Uttandaraman , Haber Joel A.
Published: October 2005

Summary: A scalable synthesis of copper nanowires by alternating current electrodeposition into porous aluminium oxide was used to produce multigram quantities of 16 nm diameter by >2 µm long nanowires. Polystyrene nanocomposites were prepared by solution processing. The composites containing unpassivated nanowires were non‐uniformly dispersed and showed electrical percolation at ≈2 vol.‐% Cu loading, while the composites containing HSC18H37‐passivated nanowires were uniformly dispersed, but remained resistive up to at least 10 vol.‐% Cu loading.

Copper nanowires prepared by alternating current electrodeposition into porous aluminium oxide templates.

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Copper nanowires prepared by alternating current electrodeposition into porous aluminium oxide templates.
Crosslinkable Vesicles Self‐Assembled by Amphiphilic Hyperbranched Polyester
Authors: Zou Jianhua , Ye Xiaodong , Shi Wenfang
Published: October 2005

Summary: Amphiphilic hyperbranched polyester (H20‐AM) with methacrylate end groups was synthesized based on hyperbranched aliphatic polyester (Boltorn™ H20). Narrow‐dispersed crosslinkable vesicles were obtained by dissolving H20‐AM in water, and characterized by laser light scattering and TEM. The hollow structural vesicle is composed of around 350 H20‐AM molecules, having a radius of around 40 nm and $\overline M _{\rm w}$ of 1.9 × 106 g · mL−1. The vesicles were fixed by crosslinking of methacrylate groups to form shape‐persistent structures.

TEM images of the crosslinked vesicles at lower magnification.

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TEM images of the crosslinked vesicles at lower magnification.
Novel Polymer Electrolyte Membrane, Based on Pyridine Containing Poly(ether sulfone), for Application in High‐Temperature Fuel Cells
Authors: Pefkianakis Elefterios K. , Deimede Valadoula , Daletou Maria K. , Gourdoupi Nora , Kallitsis Joannis K.
Published: October 2005

Summary: Novel poly(aryl ether sulfone) copolymers containing 2,5‐biphenylpyridine and tetramethyl biphenyl moieties were synthesized by polycondensation of 4‐fluorophenyl sulfone with 2,5‐(4′,4″ dihydroxy biphenyl)pyridine and tetramethyl biphenyl diol. Copolymers with different molecular weights and different monomer compositions were obtained. These copolymers exhibit excellent film‐forming properties, mechanical integrity, and high modulus up to 250 °C, high glass transition temperatures (above 280 °C) as well as high thermal stability up to 400 °C. In addition to the above properties required for PEMFC application, this novel material shows high oxidative stability and acid doping ability, enabling proton conductivity in the range of 10−2 S · cm−1 above 130 °C.

Synthesis of copolymers with high acid uptake and ionic conductivity.

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Synthesis of copolymers with high acid uptake and ionic conductivity.
The impact of institutions on entrepreneurial activity
Authors: Stephen Frank H. , Urbano David , van Hemmen Stefan
Published: October 2005

This paper presents an empirical analysis of the factors which promote entrepreneurial activity across a number of transition, developing and developed countries. It produces results which highlight the importance of institutions in promoting entrepreneurial activity. This work is part of an on‐going research project on the relationship between the legal system and factors which influence economic development. In particular, it has been shown that legal rules protecting creditors and investors influence the size of financial markets which in turn influence economic development. Our paper thus extends the analysis of the impact of institutions beyond that previously established to demonstrate its influence on another driver of economic development. Copyright © 2005 John Wiley & Sons, Ltd.
Enron, corporate governance and deterrence
Authors: Dnes Antony W.
Published: October 2005

In this paper, I investigate the lessons from the financial scandals surrounding companies like Enron and WorldCom. These companies have generated concerns leading to the legal reform of corporate governance in America, and to the revision of voluntary, self‐regulatory codes in Europe. The passage of time since the Enron debacle shows that critics were too quick to criticize, since the required adjustments have more the nature of minor adjustments to regulations. Copyright © 2005 John Wiley & Sons, Ltd.
Disclosure level and cost of equity capital: evidence from the banking industry
Authors: Poshakwale Sunil , Courtis John K.
Published: October 2005

The impact of voluntary disclosures on cost of equity capital is of significant interest to investors and managers. Using a disclosure scoring model this association is examined for 135 banks from Europe, North America and Australia. After controlling for the cross‐sectional variation in beta, firm size, price to book value and price to earnings ratios, the study found that higher disclosure levels are associated with a reduction in cost of equity capital. Disclosures about risk management practices seem to most influence the reduction in the cost of equity capital. European banks show greater reduction in the cost of equity capital from improved disclosures compared to their non‐European counterparts. Copyright © 2005 John Wiley & Sons, Ltd.
Corporate governance and development: the case of China
Authors: Liu Sean
Published: October 2005

There has been a growing interest in corporate governance in China in recent years. This article assesses some of the key moves by the Chinese authorities aimed at developing corporate governance in China. Many problems persist that are typical of systems that fail to protect shareholder interests, and we can detect political influence in the two‐tiered board system. Privatization has focused attention on the rules governing enterprise operations. The new legal framework of company law still leaves much scope for developing corporate governance at the level of the enterprise. Copyright © 2005 John Wiley & Sons, Ltd.
Corporate governance, ownership structure and corporate efficiency: the case of Ukraine
Authors: Zheka Vitaliy
Published: October 2005

The goal of this paper is to examine the effects of different ownership structures and of the quality of corporate governance on the Farrell measure of efficiency. Data Envelopment Analysis and Limited Dependent Variable Estimations are applied to the set of Ukrainian joint‐stock companies listed on the main Ukrainian stock exchange, First Securities Trading System. Domestic ownership of the organization is found to enhance efficiency the most, whereas managerial ownership has a detrimental effect on efficiency. Foreign owned firms are relatively inefficient; however foreign ownership is found to have a positive and significant effect on corporate governance quality. Concentrated ownership rights (including state ownership) improve efficiency, possibly reflecting country‐specific factors. The quality of corporate governance is found to have a positive impact on the efficiency of domestically owned firms. Copyright © 2005 John Wiley & Sons, Ltd.
The existence of positive solutions to a non‐local singular boundary value problem
Authors: O'Regan Donal , Staněk Svatoslav
Published: October 2005

We consider the non‐local singular boundary value problem

where q ∈ C0([0,1]) and f, h ∈ C0((0,∞)), limf(x)=−∞, limh(x)=∞. We present conditions guaranteeing the existence of a solution x ∈ C1([0,1]) ∩ C2((0,1]) which is positive on (0,1]. The proof of the existence result is based on regularization and sequential techniques and on a non‐linear alternative of Leray–Schauder type. Copyright © 2005 John Wiley & Sons, Ltd.
Dispersive estimate for the Schrödinger equation with point interactions
Authors: D'Ancona Piero , Pierfelice Vittoria , Teta Alessandro
Published: October 2005

We consider the Schrödinger operator in ℝ3 with N point interactions placed at Y=(y1,…,yN), yj ∈ ℝ3, of strength α=(α1,…,αN), αj ∈ ℝ. Exploiting the spectral theorem and the rather explicit expression for the resolvent we prove the (weighted) dispersive estimate for the corresponding Schrödinger flow.

In the special case N=1 the proof is directly obtained from the unitary group which is known in closed form. Copyright © 2005 John Wiley & Sons, Ltd.
An existence result for a two‐phase Stefan problem arising in metal casting
Authors: Bermúdez A. , Otero M. V.
Published: October 2005

We present a model arising from the thermal modelling of two metal casting processes. We consider an enthalpy formulation for this two‐phase Stefan problem in a time varying three‐dimensional domain and consider convective heat transfer in the liquid phase. Then, we introduce a weak formulation in a fixed domain, by means of a suitable transformation. Existence of solution is obtained by applying an abstract theorem. The proof of this theorem is done by taking an implicit discretization in time together with a regularization. By passing to the limit in the regularization parameter and in the time step, we obtain the existence of solution of the continuous problem. Copyright © 2005 John Wiley & Sons, Ltd.
Approximate source conditions in Tikhonov–Phillips regularization and consequences for inverse problems with multiplication operators
Authors: Hofmann Bernd
Published: October 2005

The object of this paper is threefold. First, we investigate in a Hilbert space setting the utility of approximate source conditions in the method of Tikhonov–Phillips regularization for linear ill‐posed operator equations. We introduce distance functions measuring the violation of canonical source conditions and derive convergence rates for regularized solutions based on those functions. Moreover, such distance functions are verified for simple multiplication operators inL2(0, 1). The second aim of this paper is to emphasize that multiplication operators play some interesting role in inverse problem theory. In this context, we give examples of non‐linear inverse problems in natural sciences and stochastic finance that can be written as non‐linear operator equations inL2(0, 1), for which the forward operator is a composition of a linear integration operator and a non‐linear superposition operator. The Fréchet derivative of such a forward operator is a composition of a compact integration and a non‐compact multiplication operator. If the multiplier function defining the multiplication operator has zeros, then for the linearization an additional ill‐posedness factor arises. By considering the structure of canonical source conditions for the linearized problem it could be expected that different decay rates of multiplier functions near a zero, for example the decay as a power or as an exponential function, would lead to completely different ill‐posedness situations. As third we apply the results on approximate source conditions to such composite linear problems inL2(0, 1) and indicate that only integrals of multiplier functions and not the specific character of the decay of multiplier functions in a neighbourhood of a zero determine the convergence behaviour of regularized solutions. Copyright © 2005 John Wiley & Sons, Ltd.
Novel organic–inorganic hybrid materials from renewable resources: Hydrosilylation of fatty acid derivatives
Authors: Lligadas G. , Callau L. , Ronda J. C. , Galià M. , Cádiz V.
Published: October 2005

Novel hybrid organic–inorganic materials were prepared from 10‐undecenoyl triglyceride and methyl 3,4,5‐tris(10‐undecenoyloxy)benzoate via hydrosilylation. 1,4‐Bis(dimethylsilyl)benzene, tetrakis(dimethylsilyloxy)silane, and 2,4,6,8‐tetramethylcyclotetrasiloxane were used as crosslinkers. The hydrosilylation reaction was catalyzed by Karstedt's catalyst [Pt(0)–divinyltetramethyldisiloxane complex]. The networks were structurally characterized by Fourier transform infrared spectroscopy, 13C NMR, and 29Si magic‐angle‐spinning NMR. The thermal properties of these hybrids were studied with differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The obtained materials showed good transparency and promising properties for optical applications. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6295–6307, 2005
Polymers from a levopimaric acid–acrylonitrile Diels–Alder adduct: Synthesis and characterization
Authors: Bicu Ioan , Mustata Fanica
Published: October 2005

The Diels–Alder adduct of levopimaric acid with acrylonitrile was efficiently prepared from resin acids. Excellent addition reaction yields (ca. 95%) were obtained. The adduct was converted into polyamides by polycondensation with diamines. When the same adduct was subjected to a dehydrodecarboxylation reaction, a novel ketone dinitrile derivative was obtained. This trifunctional product was also converted into polyamides by polycondensation with diamines. When the ketone dinitrile was hydrolyzed in the presence of alkalies and the reaction product was chlorinated, a ketone diacid chloride was obtained. A polyester was synthesized by the polycondensation of the diacid chloride with a diol. The structures of the Diels–Alder adduct, ketone dinitrile derivative, ketone diacid chloride, and polymers were established by means of elemental analysis, IR and NMR spectroscopy, and molecular weight determinations. Both the polyamides and the polyester were low‐molecular‐weight polymers soluble in polar solvents. The thermal behavior of the monomers and polymers was evaluated by thermogravimetric analysis. The thermal studies showed that the polymers were fairly thermostable substances, except the polyester, which appeared to be a substance with good thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6308–6322, 2005
Preparation of new π‐conjugated polypyrroles by organometallic polycondensations. Synthesis of N‐BOC (t‐butoxycarbonyl) and N‐phenylethynyl polymers, thermal deprotection of the BOC Group, and packing structure of the N‐phenylethynyl polymer
Authors: Yamamoto Takakazu , Yoshizawa Masataka , Mahmut Abla , Abe Masahiro , Kuroda Shin‐ichi , Imase Tatsuya , Sasaki Shintaro
Published: October 2005

New π–conjugated polypyrroles such as poly(3‐heptyl‐N‐(t‐butoxycarbonyl)pyrrole‐2,5‐diyl), PPr(3‐Hep; N‐BOC), and poly(N‐(phenylethynyl)pyrrole‐2,5‐diyl‐alt‐thiophene‐2,5‐diyl), Copoly‐2, were prepared by organometallic polycondensations using the corresponding 2.5‐dihalopyrroles as the starting materials. Deprotection of the BOC group of PPr(3‐Hep; N‐BOC) proceeded at 185 °C to give poly(3‐heptylpyrrole). XRD (X‐ray diffraction) data of Copoly‐2 indicated that Copoly‐2 assumed a stacked structure in the solid. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6223–6232, 2005
Synthesis of cyclic methacrylic acid oligomers by atom transfer radical polymerization
Authors: Saito Reiko , Yamaguchi Kazutaka
Published: October 2005

Poly(methacrylic acid) (PMAA) oligomers were synthesized by combining template polymerization and copper‐mediated atom transfer polymerization with multivinyl monomer of β‐cyclodextrin (CD) having 20.4 methacryloyl groups on both primary and secondary hydroxyl group sides of CD scaffold, with 1,3‐dibromobutane as an initiator. The initiation and propagation sites of polymerized sequence of β‐CD were connected by postpolymerization of polymerized products with CuBr and tris[(2‐dimethylamino)ethyl]amine (Me6TREN) in a methanol/water mixture of 10 wt % of water. Polymerized and cyclized sequences, PMAA oligomers formed on the primary and the secondary hydroxyl group sides, were detached from β‐CD scaffold by hydrolysis. Molecular weights of PMAA oligomers were measured by GPC and matrix assisted laser desorption ionization time‐of‐flight mass measurement. By 1H NMR measurements, it was found that three types of cyclic PMAA were obtained by postpolymerization. The cyclization preferentially occurred on the secondary hydroxyl group side than on the primary hydroxyl group side. From the structures of cyclic PMAA, two reaction positions were proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6262–6271, 2005
Highly selective oxidative cross‐coupling polymerization with copper(I)‐bisoxazoline catalysts
Authors: Temma Tomohisa , Habaue Shigeki
Published: October 2005

The asymmetric oxidative coupling polymerization of methyl 6,6′‐dihydroxy‐2,2′‐binaphthalene‐7‐carboxylate with the copper‐diamine catalysts under an O2 atmosphere was carried out. As is the case with the CuCl‐2,2′‐(S)‐isopropylidenbis(4‐phenyl‐2‐oxazoline) [(S)IPhO] catalyst, a polymer with a high cross‐coupling selectivity of 96% was obtained in 71% yield, whose THF‐soluble part had a number‐average molecular weight of 4.5 × 103. To estimate the enantioselectivity with respect to the cross‐coupling linkage in the obtained polymer, the model asymmetric oxidative cross‐coupling reaction with CuCl‐(S)IPhO was also conducted, and the products showed a 94% cross‐coupling selectivity and enantioselectivity of 31% ee (S). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6287–6294, 2005
Glycogen phosphorylase inhibitors: A free energy perturbation analysis of glucopyranose spirohydantoin analogues
Authors: Archontis G. , Watson K. A. , Xie Q. , Andreou G. , Chrysina E. D. , Zographos S. E. , Oikonomakos N. G. , Karplus M.
Published: October 2005

GP catalyzes the phosphorylation of glycogen to Glc‐1‐P. Because of its fundamental role in the metabolism of glycogen, GP has been the target for a systematic structure‐assisted design of inhibitory compounds, which could be of value in the therapeutic treatment of type 2 diabetes mellitus. The most potent catalytic‐site inhibitor of GP identified to date is spirohydantoin of glucopyranose (hydan). In this work, we employ MD free energy simulations to calculate the relative binding affinities for GP of hydan and two spirohydantoin analogues, methyl‐hydan and n‐hydan, in which a hydrogen atom is replaced by a methyl‐ or amino group, respectively. The results are compared with the experimental relative affinities of these ligands, estimated by kinetic measurements of the ligand inhibition constants. The calculated binding affinity for methyl‐hydan (relative to hydan) is 3.75 ± 1.4 kcal/mol, in excellent agreement with the experimental value (3.6 ± 0.2 kcal/mol). For n‐hydan, the calculated value is 1.0 ± 1.1 kcal/mol, somewhat smaller than the experimental result (2.3 ± 0.1 kcal/mol). A free energy decomposition analysis shows that hydan makes optimum interactions with protein residues and specific water molecules in the catalytic site. In the other two ligands, structural perturbations of the active site by the additional methyl‐ or amino group reduce the corresponding binding affinities. The computed binding free energies are sensitive to the preference of a specific water molecule for two well‐defined positions in the catalytic site. The behavior of this water is analyzed in detail, and the free energy profile for the translocation of the water between the two positions is evaluated. The results provide insights into the role of water molecules in modulating ligand binding affinities. A comparison of the interactions between a set of ligands and their surrounding groups in X‐ray structures is often used in the interpretation of binding free energy differences and in guiding the design of new ligands. For the systems in this work, such an approach fails to estimate the order of relative binding strengths, in contrast to the rigorous free energy treatment. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Structural characterization of proteins using residue environments
Authors: Mooney Sean D. , Liang Mike Hsin‐Ping , DeConde Rob , Altman Russ B.
Published: October 2005

A primary challenge for structural genomics is the automated functional characterization of protein structures. We have developed a sequence‐independent method called S‐BLEST (Structure‐Based Local Environment Search Tool) for the annotation of previously uncharacterized protein structures. S‐BLEST encodes the local environment of an amino acid as a vector of structural property values. It has been applied to all amino acids in a nonredundant database of protein structures to generate a searchable structural resource. Given a query amino acid from an experimentally determined or modeled structure, S‐BLEST quickly identifies similar amino acid environments using a K‐nearest neighbor search. In addition, the method gives an estimation of the statistical significance of each result. We validated S‐BLEST on X‐ray crystal structures from the ASTRAL 40 nonredundant dataset. We then applied it to 86 crystallographically determined proteins in the protein data bank (PDB) with unknown function and with no significant sequence neighbors in the PDB. S‐BLEST was able to associate 20 proteins with at least one local structural neighbor and identify the amino acid environments that are most similar between those neighbors. Proteins 2005. © 2005 Wiley‐Liss, Inc.
The Protein Circular Dichroism Data Bank (PCDDB): A bioinformatics and spectroscopic resource
Authors: Wallace B. A. , Whitmore Lee , Janes Robert W.
Published: October 2005

This article describes the development and creation of the Protein Circular Dichroism Data Bank (PCDDB), a deposition and searchable data bank for validated circular dichroism spectra located at http://pcddb.cryst.bbk.ac.uk/. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Molecular docking of balanol to dynamics snapshots of protein kinase A
Authors: Wong Chung F. , Kua Jeremy , Zhang Yingkai , Straatsma T.P. , McCammon J. Andrew
Published: October 2005

Even if the structure of a receptor has been determined experimentally, it may not be a conformation to which a ligand would bind when induced fit effects are significant. Molecular docking using such a receptor structure may thus fail to recognize a ligand to which the receptor can bind with reasonable affinity. Here, we examine one way to alleviate this problem by using an ensemble of receptor conformations generated from a molecular dynamics simulation for molecular docking. Two molecular dynamics simulations were conducted to generate snapshots for protein kinase A: one with the ligand bound, the other without. The ligand, balanol, was then docked to conformations of the receptors presented by these trajectories. The Lamarckian genetic algorithm in Autodock [Goodsell et al. J Mol Recognit 1996;9(1):1–5; Morris et al. J Comput Chem 1998;19(14):1639–1662] was used in the docking. Three ligand models were used: rigid, flexible, and flexible with torsional potentials. When the snapshots were taken from the molecular dynamics simulation of the protein–ligand complex, the correct docking structure could be recovered easily by the docking algorithm in all cases. This was an easier case for challenging the docking algorithm because, by using the structure of the protein in a protein–ligand complex, one essentially assumed that the protein already had a pocket to which the ligand can fit well. However, when the snapshots were taken from the ligand‐free protein simulation, which is more useful for a practical application when the structure of the protein–ligand complex is not known, several clusters of structures were found. Of the 10 docking runs for each snapshot, at least one structure was close to the correctly docked structure when the flexible‐ligand models were used. We found that a useful way to identify the correctly docked structure was to locate the structure that appeared most frequently as the lowest energy structure in the docking experiments to different snapshots. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Binding energy analysis for wild‐type and Y181C mutant HIV‐1 RT/8‐Cl TIBO complex structures: Quantum chemical calculations based on the ONIOM method
Authors: Saen‐oon Suwipa , Kuno Mayuso , Hannongbua Supa
Published: October 2005

Two‐layered and three‐layered ONIOM calculations were performed to compare the binding energies of 8‐Cl TIBO inhibitor when bound into the human immunodeficiency virus reverse transcriptase binding pocket and a Y181C variant. Both consisted of 20 residues within a radius of 15 Å. A combination of different methods [MP2/6‐31G(d), B3LYP/6‐31G(d,p), and PM3] were performed to take advantage of ONIOM's layering strategy analysis. The obtained results clearly indicate that the Y181C mutation reduces the binding affinity and stability of the inhibitor by approximately 8–9 kcal/mol as obtained from different combined MO:MO methods. Analyses regarding the energetic components of the interaction and deformation energies for 8‐Cl TIBO inhibitor upon binding were also examined extensively. Additional calculations involving the interaction energies between 8‐Cl TIBO with individual residues surrounding the binding pocket were performed at MP2/6‐31G(d,p) and B3LYP/6‐31G(d,p) levels of theory to gain more insight into the energetic differences of wild‐type and Y181C mutant type at the atomistic level. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Nonlinear excitations in self‐assembled one‐dimensional quantum dot arrays
Authors: Amuda Rajamani , Krishnan Ramya
Published: October 2005

Self‐assembled quantum dot arrays are modeled by one‐dimensional Heisenberg ferromagnetic spin chains. The interdot interaction is responsible for the ferromagnetic ordering. Starting from the Heisenberg Hamiltonian, using Bosonic operators coupled with Glauber's coherent state ansatz, the equation of motion is derived. In the lower order of the expansion parameters the dynamics is found to be governed by the nonlinear Schrödinger equation which admits soliton solution. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic behavior in Ce1–xTbxMn2Si2 silicides by XRD, DSC and AC susceptibility measurements
Authors: Kervan S. , Kılıç A. , Aksu E. , Gencer A.
Published: October 2005

The structural and magnetic properties the polycrystalline Ce1–xTbxMn2Si2 (0 ≤ x ≤ 1) compounds were studied by means of X‐ray powder diffraction, AC susceptibility and differential scanning calorimetry (DSC). All compounds investigated crystallize in the body‐centred tetragonal ThCr2Si2‐type structure with the space group I4/mmm. Substitution of Tb for Ce leads to a linear decrease of the lattice constants and the unit cell volume. The lattice constants and the unit cell volume obey Vegard's law. At low temperatures, the rare earth sublattice orders and reconfigures the ordering in the Mn sublattice for x ≥ 0.2. The Néel temperature TN(Mn) determined by DSC technique increases linearly with increasing Tb content x. The results are collected in the x–T magnetic phase diagram. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Disruption of LRG1 inhibits mother–daughter separation in Saccharomyces cerevisiae
Authors: Svarovsky Michael J. , Palecek Sean P.
Published: October 2005

LRG1, previously characterized as a Rho‐GAP that regulates β‐1,3‐glucan synthesis, was identified using a filtration screen designed to isolate genes that promote cell aggregation in Σ1278b Saccharomyces cerevisiae. Disruption of LRG1 in haploid cells resulted in enhanced invasive growth and a strain‐specific ‘clustered’ phenotype that is a consequence of failed separation of mother and daughter cells. Genetic analysis revealed that clustering required functional ROM2, FKS1 and STE12 but not FLO8 or FLO11. Additionally, this phenotype required sufficient nitrogen. β‐1,3‐Glucan content was elevated in lrg1 haploids and these cells possessed a thicker cell wall and septum than wild‐type strains. Additional glucan at the bud site inhibited separation of lrg1 mutants as the clustered phenotype was repressed by expression of the glucanases ENG1 or EGT2. Copyright © 2005 John Wiley & Sons, Ltd.
Genetic/genomic evidence for a key role of polarized endocytosis in filamentous differentiation of S. cerevisiae
Authors: Wu Xiaofeng , Jiang Yi Wei
Published: October 2005

Unicellular S. cerevisiae cells switch from the yeast form to pseudohyphal or filamentous form in response to environmental cues. We report that wild‐type BY diploids (in which yeast ORFs have been systematically deleted) undergo normal HU‐induced filamentous growth and discernable nitrogen starvation‐induced filamentous growth, despite their perceived filamentation‐deficient S288C genetic background. This finding allowed us to perform a genome‐wide survey for non‐essential genes that are required for filamentous growth with the homozygous deletion strains. We report that genes involved in endocytosis are required for both HU‐induced and nitrogen starvation‐induced filamentous growth. Surprisingly, no known genes involved in exocytosis are required. Despite the fact that polarized growth involves transport of vesicles to the site of growth, we failed to obtain genetic/genomic evidence that exocytosis plays an essential role in filamentous growth. A possible key role of polarized endocytosis (from the growth tip) is consistent with the proposed biological function of filamentous growth as a foraging behaviour. In addition, BUD8 that encodes the distal landmark in yeast‐form bipolar budding is required for nitrogen starvation‐induced but not HU‐induced filamentous growth. Moreover, BUD5, SPA2, PEA2 and BUD6 that regulate bipolar bud site selection do not regulate the unipolar distal budding pattern in HU‐induced filamentous growth. Copyright © 2005 John Wiley & Sons, Ltd.
Global metabolite analysis of yeast: evaluation of sample preparation methods
Authors: Villas‐Bôas Silas G. , Højer‐Pedersen Jesper , Åkesson Mats , Smedsgaard Jørn , Nielsen Jens
Published: October 2005

Sample preparation is considered one of the limiting steps in microbial metabolome analysis. Eukaryotes and prokaryotes behave very differently during the several steps of classical sample preparation methods for analysis of metabolites. Even within the eukaryote kingdom there is a vast diversity of cell structures that make it imprudent to blindly adopt protocols that were designed for a specific group of microorganisms. We have therefore reviewed and evaluated the whole sample preparation procedures for analysis of yeast metabolites. Our focus has been on the current needs in metabolome analysis, which is the analysis of a large number of metabolites with very diverse chemical and physical properties. This work reports the leakage of intracellular metabolites observed during quenching yeast cells with cold methanol solution, the efficacy of six different methods for the extraction of intracellular metabolites, and the losses noticed during sample concentration by lyophilization and solvent evaporation. A more reliable procedure is suggested for quenching yeast cells with cold methanol solution, followed by extraction of intracellular metabolites by pure methanol. The method can be combined with reduced pressure solvent evaporation and therefore represents an attractive sample preparation procedure for high‐throughput metabolome analysis of yeasts. Copyright © 2005 John Wiley & Sons, Ltd.