bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of chiral polyacetylenes carrying amino acids and azobenzenes and transformation of the higher order structure by photoirradiation
Authors: Sanda Fumio , Teraura Takayuki , Masuda Toshio 
Published: August 2004

AbstractThis study examined the synthesis of copolymers of an alanine‐derived chiral N‐propargylamide [N‐(tert‐butoxycarbonyl)‐L‐alanine N′‐propargylamide] with an azobenzene‐containing N‐propargylamide [N‐4‐(phenylazo)benzoyl‐L‐alanine N′‐propargylamide] and the transformation of the higher order structure of the copolymers by photoirradiation. The trans‐azobenzene moiety of the copolymers isomerized into the cis one, which was accompanied by the transformation of the helical structure into a random state by UV irradiation. Visible‐light irradiation induced the reisomerization of cis‐azobenzene into the trans one, but it did not induce the recovery of the higher order structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4641–4647, 2004
Stereological simulations of asymmetric polymerization in channels of bile acid inclusion compounds: A detailed analysis of the monomer arrangements in the channels
Authors: Inoue Katsunari , Kato Kazuaki , Tohnai Norimitsu , Miyata Mikiji 
Published: August 2004

AbstractWe studied simulations by computer graphics to estimate the steric mechanism of the asymmetric polymerization of prochiral diene monomers in channels of inclusion compounds of steroidal bile acids, such as deoxycholic acid (DCA) and cholic acid. We applied a hierarchization method to interpret the crystal structures of bile acids, clarifying that the chiral host molecules associated to form characteristic 21‐helical assemblies with uneven surfaces. A detailed analysis of the uneven channels in a close‐packing state indicated that there were many possible arrangements of the monomers in the channels. The plausible arrangements in the channel could explain a previous study, which showed that the polymerization in the DCA channel yielded chiral polymers with a predominant configuration from prochiral diene monomers, such as 2‐methyl‐trans‐1,3‐pentadiene. On the basis of such simulation studies of the arrangements of guest monomers in the channel, we examined a plausible steric mechanism for asymmetric inclusion polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4648–4655, 2004
Syntheses of helical polymers through the combination of axially dissymmetric segments
Authors: Temma Tomohisa , Kobayashi Motoyasu , Agata Yuya , Yamane Tomoya , Miura Jun , Takeishi Makoto 
Published: August 2004

AbstractWholly aromatic polymers with various helical structures were prepared through the combination of two axially dissymmetric bifunctional compounds. The palladium‐catalyzed condensation of (R)‐2,2‐diethoxy‐6,6′‐dibromo‐1,1′‐binaphthyl with (R)‐1,1′‐binaphthyl‐2,2′‐diamine and the reaction of (S)‐2,2‐diethoxy‐6,6′‐dibromo‐1,1′‐binaphthyl with (S)‐1,1′‐binaphthyl‐2,2′‐diamine produced helical polyamines, and the chiral conformation was confirmed by their circular dichroism spectra and large specific rotations. The combination of (R)‐2,2‐diethoxy‐6,6′‐dibromo‐1,1′‐binaphthyl and (S)‐1,1′‐binaphthyl‐2,2′‐diamine afforded polyamines with a zigzag conformation. The condensation of (R)‐2,2′‐dimethylbiphenyl‐6,6′‐dicarbonyl chloride with (R)‐2,2′‐diamino‐6,6′‐dimethylbiphenyl and the reaction of (S)‐2,2′‐dimethylbiphenyl‐6,6′‐dicarbonyl chloride with (S)‐2,2′‐diamino‐6,6′‐dimethylbiphenyl predominantly yielded cyclic dimers and tetramers because of the steric proximity of the reactive groups of the propagating species. The experimental results indicated that the structures of the obtained polymers depended on the combination of the chirality of the bifunctional atropisomeric compounds and the position of the functional groups on the aromatic rings. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4607–4620, 2004
Convenient synthesis of fully and partially deuterated stereoregular poly(phenylacetylene)s bearing a carboxy pendant and helicity induction on the polymers with chiral amines and its memory
Authors: Morino Kazuhide , Asari Takeshi , Maeda Katsuhiro , Yashima Eiji 
Published: August 2004

AbstractPoly[(4‐carboxyphenyl)acetylene] and its derivatives deuterated in the main chain and/or on the phenyl group (poly‐1's) were conveniently synthesized by the polymerization of 4‐ethynylbenzoic acid or its derivative deuterated on the phenyl group in the presence of bases with a water‐soluble rhodium complex in water or deuterium oxide. The obtained polymers possesses highly cis–transoidal stereoregular structures according to NMR and Raman spectroscopy. Possible deuterium isotope effects of these partially and fully deuterated poly‐1's during the helicity induction with chiral amines and its memory assisted by achiral amines were investigated. The thermal cis–trans isomerization of the methyl esters of poly‐1's was also studied with 1H NMR spectroscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4711–4722, 2004
Characterization of the benzene‐insoluble fraction of the hydrolyzate of phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide
Authors: Pakjamsai Chitsakon , Kobayashi Noritomo , Koyano Mikio , Sasaki Shintaro , Kawakami Yusuke 
Published: August 2004

AbstractThe insoluble fraction obtained from the hydrolysis and condensation of (4‐dimethylamino‐, 2‐methyl‐, and nonsubstituted)phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide in benzene was characterized. IR, 1H NMR, and 29Si NMR suggested that the insoluble fraction was composed of RSi(O)3, that is, a T3 structure. X‐ray diffraction indicated the presence of a long‐range ordered structure composed of a mixture of crystals. Raman spectroscopy strongly suggested a cage structure by the presence of a ring‐opening vibration assignable to a cubic structure at 475–482 cm−1. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4587–4597, 2004
Synthesis of a polyester macromonomer via the cobalt‐catalyzed alternating copolymerization of propylene oxide and carbon monoxide
Authors: Nakano Koji , Fumitaka Kondo , Nozaki Kyoko 
Published: August 2004

AbstractThe alternating copolymerization of propylene oxide and carbon monoxide was investigated with cobalt complexes. The NaCo(CO)4/amine catalyst system selectively yielded oligo(3‐hydroxybutyrate)s bearing a polymerizable crotonate end group, whereas the use of Co2(CO)8 as a cobalt source resulted in a smaller concentration of the crotonate end group and a high degree of polymerization. The high selectivity for the oligoesters with the crotonate end group with the NaCo(CO)4/amine system was attributed to its more basic reaction condition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4666–4670, 2004
Chemoenzymatic synthesis of glycoconjugate polymers starting from nonreducing disaccharides
Authors: Miura Yoshiko , Wada Natsuko , Nishida Yoshihiro , Mori Hiroshi , Kobayashi Kazukiyo 
Published: August 2004

AbstractHere we report the chemoenzymatic synthesis and recognition function of glycoconjugate polymers carrying nonreducing disaccharides [α‐D‐glucopyranosyl‐(1‐1)‐α‐D‐glucopyranoside (trehalose) and α‐D‐galactopyranosyl‐(1‐1)‐α‐D‐glucopyranoside (Gal‐type trehalose)]. The lipase‐catalyzed esterification of the disaccharides with divinyl sebacate is completely selective at the primary Glc 6‐OH position of trehalose and at the Gal 6‐OH position of Gal‐type trehalose. The resultant vinyl esters can be polymerized to yield glycoconjugate polymers with poly(vinyl alcohol) backbones. The interactions of the glycoconjugate polymers with lectins (concanavalin A and Bandeiraera simplicifolia) are amplified because of the glycocluster effect. The polymer carrying pendant α‐D‐galactopyranosyl‐(1‐1)‐α‐D‐glucopyranoside shows inhibition activity against Shiga toxin‐1 based on a stereochemical structure similar to that of globosyl Gb2 disaccharide. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4598–4606, 2004
Design and synthesis of chiral poly(binaphthyl salen zinc complex) and application of the asymmetric field based on its helical conformation to a catalytic asymmetric reaction
Authors: Maeda Takeshi , Takeuchi Takeshi , Furusho Yoshio , Takata Toshikazu 
Published: August 2004

AbstractAccording to a rational design of helices (i.e., fusing C2 chiral binaphthyl units and metallosalen complexes inevitably results in the formation of helical polymers), chiral poly(binaphthyl salen zinc complex)es (3‐Zn) were synthesized from an (R)‐3,3′‐diformylbinaphthol derivative, α,ω‐diamines, and zinc acetate or diethylzinc. Their helical structures were well supported by their infrared, ultraviolet, and circular dichroism spectra, in addition to MM calculations and a CPK model study. The catalysis of 3‐Zn during the asymmetric addition of diethylzinc to aldehydes was investigated. In the presence of 5 unit mol % 3‐Zn, diethylzinc reacted with benzaldehyde to yield 1‐phenyl‐1‐propanol in high yields (∼100%) and with high enantioselectivity (∼95%). The asymmetric yield of 1‐phenyl‐1‐propanol increased significantly as the temperature was lowered, whereas both the asymmetric yield and the absolute configuration were drastically changed as the structure of the diamine unit of 3‐Zn was varied. Several aromatic aldehydes were converted into their corresponding alcohols with high enantioselectivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4693–4703, 2004
Crystallization of propylene–ethylene random copolymers
Authors: Weng J. , Olley R. H. , Bassett D. C. , Jääskeläinen P. 
Published: August 2004

AbstractOf the three melting peaks typical of a propylene–ethylene random copolymer (with 5.1 wt % ethylene) crystallized between 110 and 140 °C, the two higher peaks result from primary and secondary isothermal crystallization, whereas the material crystallized on cooling gives the lowest peak. In contrast to polypropylene homopolymers, which show strong morphological changes developing from the center of a spherulite, copolymer specimens are uniformly crosshatched. The highest melting peak is related to an open crosshatched framework of primary lamellae, and the next lower peak is related to later forming subsidiary lamellae filling the intervening space. The origin and nature of these double peaks are discussed in terms of the fractional crystallization and the ensuing constraints placed on isothermal lamellar thickening as a result of the exclusion of the comonomer from the polypropylene lattice. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3318–3332, 2004
Structure, morphology, and crystallization process of isotactic polypropylene/hydrogenated hydrocarbon resin blends
Authors: Silvestre C. , Cimmino S. , Lin J. S. 
Published: August 2004

AbstractThe structure, morphology, and isothermal and nonisothermal crystallization of isotactic polypropylene/low‐molecular‐mass hydrocarbon resin blends (iPP/HR) (up to 20% in weight of HR) have been studied, using optical and electron microscopy, wide‐ and small‐angle X‐ray and differential scanning calorimetry. New structures and morphologies can be activated, using appropriate preparation and crystallization conditions and blend composition. For every composition and crystallization condition, iPP crystallizes in α‐form, with a spherulitic morphology. The size of iPP spherulites increases with resin content, whereas the long period decreases. In the range of crystallization temperatures investigated, HR modifies the birefringence of iPP spherulites, favoring the formation of radial lamellae and changing the ratio between tangential and radial lamellae. Spherulitic radial growth rates, overall crystallization rates, and melting temperatures are strongly affected by resin, monotonically decreasing with resin content. This confirms miscibility in the melt between the two components of the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3368–3379, 2004
Charge renormalization of cylinders and spheres: Ion size effects
Authors: Borukhov Itamar 
Published: August 2004

AbstractThe effect of the counterion size on the degree of counterion condensation onto a cylindrical macroion and a spherical one in the absence of salt is studied theoretically within a modified Poisson–Boltzmann approach. We find that excluded volume interactions reduce the degree of condensation. Using a simple variational free energy we show that this reduction can be attributed to an effective increase in the macroion size due to the contribution of the condensed counterions. We also find that for a charged cylinder, the reduction in charge renormalization vanishes at infinite dilution because of the extended nature of the condensed layer. In contrast, excluded volume interactions can reduce the degree of charge renormalization of a sphere even at high dilutions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3598–3615, 2004
Exploring peptide energy landscapes: A test of force fields and implicit solvent models
Authors: Steinbach Peter J. 
Published: August 2004

AbstractA biased Monte Carlo‐minimization/annealing conformational search was used to characterize five descriptions of the energy landscape for each of three model systems: the 20‐residue “trp‐cage” miniprotein, the 20‐residue “BS1” peptide, and the 17‐residue “U(1‐17)T9D” peptide. The EEF1 and SASA energy landscapes were studied as well as those defined by using the GB/ACE implicit water model with one of three protein force fields: CHARMM19, CHARMM22, and CHARMM22/CMAP. The lowest‐energy structures of the trp‐cage and BS1 peptides found for the EEF1 landscape have main‐chain root‐mean‐square deviations (rmsds) from the respective NMR structures of less than 2 Å; for U(1‐17)T9D, the deviation is less than 3 Å using EEF1. The main‐chain rmsd of the minimum‐energy trp‐cage conformation obtained for the GB/ACE/CHARMM22/CMAP landscape is less than 1 Å. However, this energy function strongly favored helical structures for the two peptides shown by NMR to form beta‐sheet structures. Brief annealing of the system following main‐chain conformational changes was found to enhance the exploration of low‐energy states. The thousands of simulations reported here suggest that the prediction of protein structure might be improved by the simultaneous use of a CMAP‐like description of the main chain and an EEF1‐like description of the solvent. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Conformational sampling and dynamics of membrane proteins from 10‐nanosecond computer simulations
Authors: Faraldo‐Gómez José D. , Forrest Lucy R. , Baaden Marc , Bond Peter J. , Domene Carmen , Patargias George , Cuthbertson Jonathan , Sansom Mark S.P. 
Published: August 2004

AbstractIn the current report, we provide a quantitative analysis of the convergence of the sampling of conformational space accomplished in molecular dynamics simulations of membrane proteins of duration in the order of 10 nanoseconds. A set of proteins of diverse size and topology is considered, ranging from helical pores such as gramicidin and small β‐barrels such as OmpT, to larger and more complex structures such as rhodopsin and FepA. Principal component analysis of the Cα‐atom trajectories was employed to assess the convergence of the conformational sampling in both the transmembrane domains and the whole proteins, while the time‐dependence of the average structure was analyzed to obtain single‐domain information. The membrane‐embedded regions, particularly those of small or structurally simple proteins, were found to achieve reasonable convergence. By contrast, extra‐membranous domains lacking secondary structure are often markedly under‐sampled, exhibiting a continuous structural drift. This drift results in a significant imprecision in the calculated B‐factors, which detracts from any quantitative comparison to experimental data. In view of such limitations, we suggest that similar analyses may be valuable in simulation studies of membrane protein dynamics, in order to attach a level of confidence to any biologically relevant observations. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Structural and dynamic effects of α‐Helix deletion in Sso7d: Implications for protein thermal stability
Authors: Merlino Antonello , Graziano Giuseppe , Mazzarella Lelio 
Published: August 2004

AbstractSso7d is a 62‐residue protein from the hyperthemophilic archaeon Sulfolobus solfataricus with a denaturation temperature close to 100°C around neutral pH. An engineered form of Sso7d truncated at leucine 54 (L54Δ) is significantly less stable, with a denaturation temperature of 53°C. Molecular dynamics (MD) studies of Sso7d and its truncated form at two different temperatures have been performed. The results of the MD simulations at 300 K indicate that: (1) the flexibility of Sso7d chain at 300 K agrees with that detected from X‐ray and NMR structural studies; (2) L54Δ remains stable in the native folded conformation and possesses an overall dynamic behavior similar to that of the parent protein. MD simulations performed at 500 K, 10 ns long, indicate that, while Sso7d is in‐silico resistant to high temperature, the truncated variant partially unfolds, revealing the early phases of the thermal unfolding pathway of the protein. Analysis of the trajectories of L54Δ suggests that the unzipping of the N‐terminal and C‐terminal β‐strands should be the first event of the unfolding pathway, and points out the regions more resistant to thermal unfolding. These findings allow one to understand the role played by specific interactions connecting the two ends of the chain for the high thermal stability of Sso7d, and support recent hypotheses on its folding mechanism emerged from site‐directed mutagenesis studies. Proteins 2004. © 2004 Wiley‐Liss, Inc.
A computational study of a fluorescent photoinduced electron transfer (PET) sensor for cations
Authors: De Silva S. A. , Kasner M. L. , Whitener M. A. , Pathirana S. L. 
Published: August 2004

AbstractAb initio molecular orbital theory and density functional theory with the 6‐31G(d,p) basis set have been used to calculate the structural parameters of a fluorescent photoinduced electron transfer (PET) sensor for cations and its zinc complex. The optimized geometries are compared with the X‐ray crystal structures of N‐(9‐anthracenylmethyl)–N‐[(2‐pyridinyl)methyl]‐2‐pyridinemethanamine and [N‐(9‐anthracenylmethyl)‐N‐[(2‐pyridinyl‐κN)methyl]‐2‐pyridinemethanamine‐κN1, κN2]dichlorozinc. Although the X‐ray studies are based on solid‐phase structures and the computational studies are based on gas‐phase structures, comparisons of the data show significant agreement between the two sets of geometric parameters. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Theoretical study of adsorption of methyltert‐butyl ether on the substituted tetrahedral surface of dickite
Authors: Michalkova A. , Gorb L. , Zhikol O. A. , Leszczynski J. 
Published: August 2004

AbstractThe adsorption of methyltert‐butyl ether (MTBE) on the substituted tetrahedral surface of dickite has been studied using the n‐layered integrated molecular orbital and molecular mechanics (ONIOM) approach and Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP)/6‐31G(d):PM3 approximation. Two Si atoms of the tetrahedral side were substituted by Al atoms in three different mutual arrangements (1,2‐, 1,3‐, and 1,4‐substitution). The negative charge of the layer originating from the substitution was compensated by the exchangeable Mg2+cation. Initially the Mg2+cation was placed above the center of the six‐member ring with the tetrahedral structure of the mineral fragment. The Mg2+cation plays a crucial role in the adsorption of MTBE on the substituted surface of dickite. Methyl tert‐butyl ether is adsorbed due to the formation of a chemical bond between the oxygen atom of MTBE and the Mg2+cation and due to the formation of multiple weak C‐H…O hydrogen bonds between the C–H groups of MTBE and the surface oxygen atoms. The adsorption results in changes in the structural parameters of MTBE that are the most significant in the case of the 1,3‐substituted system. The interaction energies of MTBE adsorbed on the substituted surface of dickite corrected by basis set superposition error were predicted. The values of adsorption energies range from −42.8 kcal/mol (1,2‐substitution) to −45.9 kcal/mol (1,3‐substitution) to −47.2 kcal/mol (1,4‐substitution). © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Elemental distributions around the oxide scales/alloy interfaces by SIMS and GDOES analyses
Authors: Horita Teruhisa , Xiong Yueping , Yamaji Katsuhiko , Kishimoto Haruo , Sakai Natsuko , Yokokawa Harumi 
Published: August 2004

AbstractThe oxide scales formed on FeCr alloys in CH4H2O gas mixtures (at 1073 K for 3–1050 h) were precisely analysed by SIMS and GDOES. Depth profiles were compared between SIMS and GDOES. They were almost consistent with each other with some differences in minor elements. In depth profiles, the following three zones were identified from surface to internal oxides: Mn and Fe rich layer, Cr‐rich layer, and Si‐rich layer. The elemental distributions at different depths were investigated by the SIMS imaging technique. Concentration differences of some elements at grain and grain boundaries were imaged at the resolution of µms. The grain boundary diffusion of cations in the alloys was clearly visualized, and the grain boundary diffusion plays an important role in the formation of oxide scales. Copyright © 2004 John Wiley & Sons, Ltd.
Surface characterization of the oxide layer grown on TiNbZr and TiNbAl alloys
Authors: Gutiérrez A. , López M. F. , Jiménez J. A. , Morant C. , Paszti F. , Climent A. 
Published: August 2004

AbstractThe surface of the oxide layers formed after oxidation in air at 750°C of three titanium alloys has been characterized by several techniques. The investigated alloys were Ti7Nb6Al, Ti13Nb13Zr and Ti15Zr4Nb, with potential applications as biomaterials. XPS experiments showed that, after 24 h exposure, the surface of the Ti7Nb6Al alloy is mainly formed of Al2O3, with a minor presence of TiO2, and absence of Nb oxide. On the other hand, the surface of both TiNbZr alloys is mainly composed of TiO2, with some amount of ZrO2 and Nb2O5. An enrichment of the Nb signal is observed in both samples with respect to the bulk composition. The topography and surface morphology of the oxidized alloys were investigated by atomic force microscopy. A more regular surface topography was observed for the Ti7Nb6Al alloy than for the TiNbZr alloys and, consequently, a higher potentiality in biomedical applications. Finally, in order to get in‐depth information of the oxide scale, Rutherford backscattering spectroscopy experiments were also performed. The results obtained with this technique confirm those obtained by XPS, and can help to understand the mechanism and kinetics of the oxide film formation. Copyright © 2004 John Wiley & Sons, Ltd.