bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulfur Composite Cathode Materials for Rechargeable Lithium Batteries
Authors: Wang J. , Yang J. , Wan C. , Du K. , Xie J. , Xu N. 
Published: June 2003

AbstractConductive polymer/sulfur composite materials were prepared by heating the mixture of polyacrylonitrile (PAN) and sublimed sulfur. During the heating process, PAN was dehydrogenated by sulfur, forming a conductive main chain similar to polyacetylene. At the same time, the high‐polarity functional group –CN cyclized at the melt state, forming a thermally stable heterocyclic compound in which sulfur was embedded. The nanodispersed composites showed excellent electrochemical properties. Tested as cathode material in a non‐aqueous lithium cell based on poly(vinylidene fluoride) (PVDF) gel electrolyte at room temperature, the composite exhibited a specific capacity up to 850 mA h g–1 in the initial cycle. Its specific capacity remained above 600 mA h g–1 after 50 cycles, about five times that of LiCoO2, and recovered partly after replacement of the anode with a fresh lithium sheet. The utilization of the electrochemically active sulfur was about 90 % assuming a complete reaction to the product, Li2S.
Layer‐Structured Photoconducting Polymers: A New Class of Photorefractive Materials
Authors: Kwon O‐P. , Lee S.‐H. , Montemezzani G. , Günter P. 
Published: June 2003

AbstractWe study the photorefractive (PR) properties of a new kind of low glass‐transition temperature (Tg) polymer composite based on layered photoconductive polymers, poly(p‐phenylene terephthalate) carbazoles (PPT‐CZs). These photoconductors consist of the rigid backbone of PPT with pendant oxyalkyl CZ groups. The compounds are doped with the photosensitizer C60 and nonlinear optical chromophores diethylaminodicyanostyrene (DDCST), and no plasticizers are added. When the host polymers are mixed with various PR ingredients, the layers are preserved and their layer distance increases, indicating that all the guest molecules are confined to the nanoscale interlayer space. These composites showed very low Tg values (< ϕ °C). Despite the absence of a plasticizer and the lower concentration of the carbazole photoconductive moieties as compared to poly(N‐vinylcarbazole) systems, these materials show excellent PR properties, i.e., a PR gain of Γ = 250 cm–1 under an external electric field of 60 V μm–1, and diffraction efficiency and PR sensitivity of 93 % and 24 ± 7 cm2 kJ–1 at E = 100 V μm–1, respectively.
Metastable Hexagonal In2O3 Nanofibers Templated from InOOH Nanofibers under Ambient Pressure
Authors: Yu D. , Yu S.‐H. , Zhang S. , Zuo J. , Wang D. , Qian Y.T. 
Published: June 2003

AbstractSingle‐crystal, metastable, hexagonal In2O3 (H‐In2O3) nanofibers with an average diameter of 80 nm and length of up to several micrometers were synthesized on a large scale, for the first time under ambient pressure, by annealing InOOH nanofibers at 490 °C. The InOOH nanofibers were prepared by a controlled hydrolysis solvothermal reaction, using InCl3·4H2O as the starting material and ether as the solvent, in the temperature range of 190–240 °C. The solvent has significant effects on the formation of the metastable phase and the morphology of the In2O3 nanocrystals during the synthesis of the precursor InOOH. Room‐temperature optical absorption spectra of the hexagonal In2O3 nanofibers showed strong absorption peak located at 325 nm (3.83 eV) with a slight blue‐shift compared with that of bulk In2O3 (3.75 eV). The H‐In2O3 nanofibers photoluminesce at room temperature with emission peaks at 378 nm, 398 nm, and 420 nm. The successful production of metastable hexagonal In2O3 nanofibers in large scale under mild conditions could be of interest both for applications and fundamental studies.
High‐Tg Carbazole Derivatives as Blue‐Emitting Hole‐Transporting Materials for Electroluminescent Devices
Authors: Kundu P. , Justin Thomas K.R. , Lin J.T. , Tao Y.‐T. , Chien C.‐H. 
Published: June 2003

AbstractA series of dicarbazolyl derivatives bridged by various aromatic spacers and decorated with peripheral diarylamines were synthesized using Ullmann and Pd‐catalyzed C–N coupling procedures. These derivatives emit blue light in solution. In general, they possess high glass‐transition temperatures (Tg > 125 °C) which vary with the bridging segment and methyl substitution on the peripheral amine. Double‐layer organic light‐emitting devices were successfully fabricated using these molecules as hole‐transporting and emitting materials. Devices of the configuration ITO/HTL/TPBI/Mg:Ag (ITO: indium tin oxide; HTL: hole‐transporting layer; TPBI: 1,3,5‐tris(N‐phenylbenzimidazol‐2‐yl)benzene) display blue emission from the HTL layer. The EL spectra of these devices appear slightly distorted due to the exciplex formation at the interfaces. However, for the devices of the configuration ITO/HTL/Alq3/Mg:Ag (Alq3 = tris(8‐hydroxyquinoline)aluminum) a bright green light from the Alq3 layer was observed. This clearly demonstrates the facile hole‐transporting property of the materials described here.
Electroactivity of Polyaniline Multilayer Films in Neutral Solution and Their Electrocatalyzed Oxidation of β‐Nicotinamide Adenine Dinucleotide
Authors: Tian S. , Baba A. , Liu J. , Wang Z. , Knoll W. , Park M.‐K. , Advincula R. 
Published: June 2003

AbstractIn this paper, we report an alternative simple method to shift the electroactivity of polyaniline (PANI) films to neutral pH conditions by forming multilayer assemblies with poly(anions) using the layer‐by‐layer (LBL) deposition method. A series of self‐assembled PANI multilayer films with poly(anions), such as sulfonated polyaniline (SPANI), poly(acrylic acid) (PAA), poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS), were prepared by the LBL method. Their electrochemical behavior and catalytic ability for the oxidation of β‐nicotinamide adenine dinucleotide (NADH) in neutral solution were investigated by electrochemistry (EC) combined with surface plasmon spectroscopy (SPS) and the quartz crystal microbalance (QCM) technique. Results indicated that all the films showed very good stability, reversibility, and electroactivity in neutral solution. All the multilayer films can electrocatalyze the oxidation of NADH, with the catalytic ability of PANI/SPANI being higher than that of the other assemblies under the same conditions. The catalytic abilities of the films with the same thickness prepared by the copolymerization method and the LBL method were also compared.
Laser‐Ablation Growth and Optical Properties of Wide and Long Single‐Crystal SnO2 Ribbons
Authors: Hu J.Q. , Bando Y. , Liu Q.L. , Golberg D. 
Published: June 2003

AbstractWide and long ribbons of single‐crystalline SnO2 have been achieved via laser ablation of a SnO2 target. Transmission electron microscopy (TEM) shows the as‐grown SnO2 ribbons are structurally perfect and uniform, with widths of 300–500 nm, thicknesses of 30–50 nm (width‐to‐thickness ratio of ∼ 10), and lengths ranging from several hundreds of micrometers to the order of millimeters. X‐ray diffraction (XRD) pattern and energy‐dispersive X‐ray spectroscopy (EDS) spectral analysis indicate that the ribbons have the phase structure and chemical composition of the rutile form of SnO2. Selected‐area electron diffraction (SAED) patterns and high‐resolution TEM images reveal that the ribbons are single crystals and grow along the [100] crystal direction. Photoluminescence measurements show that the synthesized SnO2 ribbons have one strong emission band at ∼ 605 nm and a red‐shift of ∼ 30 nm, as compared to standard SnO2 powder, which may be attributed to crystal defects and residual strains accommodated during the growth of the ribbons.
Electrophosphorescence from a Polymer Guest–Host System with an Iridium Complex as Guest: Förster Energy Transfer and Charge Trapping
Authors: Gong X. , Ostrowski J.C. , Moses D. , Bazan G.C. , Heeger A.J. 
Published: June 2003

AbstractWe report high‐efficiency green electrophosphorescent light‐emitting diodes obtained by using tris[9,9‐dihexyl‐2‐(phenyl‐4′‐(‐pyridin‐2″‐yl))fluorene]iridium(III) (Ir(DPPF)3) as the guest, and a blend of poly(vinylcarbazole) (PVK) with 2‐tert‐butylphenyl‐5‐biphenyl‐1,3,4‐oxadiazol (PBD) as the host. The electrophosphorescent emission is characteristic of Ir(DPPF)3, with its maximum at 550 nm. An external quantum efficiency of 8 % photons per electron and luminous efficiency of 29 cd A–1, with maximum brightness of 3500 cd m–2, were achieved at 1 wt.‐% concentration of Ir(DPPF)3. The devices exhibited no emission from PVK or PBD, even at the lowest concentration of Ir(DPPF)3 (0.1 wt.‐%). The results indicate that Förster energy transfer plays a minor role in achieving high efficiencies in these devices. Direct charge trapping appears to be the main operating mechanism.
From Hybrid Microgels to Photonic Crystals
Authors: Xu S. , Zhang J. , Paquet C. , Lin Y. , Kumacheva E. 
Published: June 2003

AbstractWe have synthesized semiconductor and metal nanoparticles (NPs) in the constrained geometry of polymer microgels. We used electrostatically driven attraction between the ionic groups of the microgels and the precursor cations in the bulk liquid medium to introduce the cations in the interior of the microgel. In the second step, the cations in the microgel interior reacted with the anion (to obtain semiconductor NPs) or they were treated with a reducing agent (to obtain metal NPs). Good control over the size and the concentration of the NPs in the microgel particles was achieved by changing the composition of the corresponding microgel. The doped microgel spheres were heated at pH 4 above the volume‐transition temperature of the polymer to expel the water from the microsphere interior; then the polymer was encapsulated with a hydrophobic polymeric shell. Hybrid core–shell particles were used as the building blocks of the nanostructured material with properties of a photonic crystal.
Size‐Specific Interactions Between Single‐ and Double‐Stranded Oligonucleotides and Cationic Water‐Soluble Oligofluorenes
Authors: Wang S. , Liu B. , Gaylord B.S. , Bazan G.C. 
Published: June 2003

AbstractAn improved synthetic approach was developed for the synthesis of 1,4‐bis[9′,9′‐bis(6″‐(N,N,N‐trimethylammonium)‐hexyl)‐fluoren‐2′‐yl]benzene tetrabromide (1a), 1,4‐bis[9′,9′;9″,9″‐tetra(6″′‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″‐bisfluoren‐2′‐yl] benzene octabromide (1b) and 1,4‐bis[9′,9′;9″,9″;9″′,9″′‐hexakis(6″″‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″,7″,2″′‐trifluoren‐2′‐yl] benzene dodecabromide (1c). These molecules provide a size‐specific series of water‐soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy‐transfer measurements were performed with 1a–c and single‐stranded (ss) DNA and double‐stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per‐negative‐charge basis, ssDNA quenches the emission of 1a–c more effectively than dsDNA. Furthermore, we show that the energy‐transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a–c.
Glycosyltransferase Microarray Displayed on the Glycolipid LB Membrane
Authors: Nagahori Noriko , Niikura Kenichi , Sadamoto Reiko , Taniguchi Masahiro , Yamagishi Akihiko , Monde Kenji , Nishimura Shin‐Ichiro 
Published: June 2003

Abstractβ(1→4) Galactosyltransferase expressed as a fusion protein with maltose binding protein (MBP‐GalT) was displayed specifically on a Langmuir–Blodgett (LB) membrane prepared by photopolymerization of maltotriose‐carrying glycolipid (1) with 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine (2). The catalytic activity of MBP‐GalT on the LB film was directly monitored by the surface plasmon resonance (SPR) method using a GlcNAc‐carrying water‐soluble polymer (3) as an acceptor substrate. Highly sensitive sigmoidal‐type signals were obtained upon the addition of the acceptor substrate in the presence of the donor substrate, UDP‐galactose (UDP‐Gal), while the binding of 3 was not detected in the absence of UDP‐Gal. The intensities of the signals were dependent on the amount of immobilized MBP‐GalT on the LB film, which was estimated from the images obtained by atomic force microscope (AFM).
Glutaryl Acylases: One‐Reaction Enzymes or Versatile Enantioselective Biocatalysts?
Authors: Raimondi Stefano , Monti Daniela , Pagnoni Ugo Maria , Riva Sergio 
Published: June 2003

AbstractA significant broad substrate specificity, that crosses over the usual β‐lactam derivatives, has been observed with an industrial glutaryl‐7‐aminocephalosporanic acid acylase (GA). This enzyme possesses significant enantioselective amidase and even esterase activity, with a stereopreference for the S‐enantiomer. The easy separation of products from unreacted reagents, possessing different physical‐chemical properties, is achieved by solvent extraction, avoiding chromatography or distillation during reaction work‐up.
Baeyer–Villiger Monooxygenases, an Emerging Family of Flavin‐Dependent Biocatalysts
Authors: Kamerbeek Nanne M. , Janssen Dick B. , van Berkel Willem J. H. , Fraaije Marco W. 
Published: June 2003

AbstractBaeyer–Villiger monooxygenases (BVMOs) are flavoenzymes that catalyze a remarkably wide variety of oxidative reactions such as regio‐ and enantioselective Baeyer–Villiger oxidations and sulfoxidations. Several of these conversions are difficult to achieve using chemical approaches. Due to their selectivity and catalytic efficiency, BVMOs are highly valuable biocatalysts for the synthesis of a broad range of fine chemicals. For a long time, only one member of this class of flavin‐containing biocatalysts had been cloned and overexpressed which has limited their application for synthetic processes. Recently a number of new genes that encode BVMOs have been sequenced and overexpressed. In this paper the biocatalytic properties of recently cloned BVMOs are reviewed. Furthermore, the potential for obtaining novel BVMOs from sequenced genomes will be discussed.
Chemo‐ and Enantioselective Acyl Transfers by Lipases and Acylase I: Preparative Applications in Hydroxymethylpiperidine Chemistry
Authors: Lundell Katri , Lehtinen Petka , Kanerva Liisa T. 
Published: June 2003

AbstractThe lipase‐ and acylase I‐catalysed acylation of bifunctional 2‐ and 3‐hydroxymethylpiperidines (1 and 2) and the alcoholysis of the corresponding diacylated counterparts 7 and 8 have been studied. Lipase AK from Pseudomonas fluorescens allowed the preparative‐scale resolution of 7 in neat butanol at 50% conversion whereas the 3‐regioisomer 8 reacted with negligible enantioselectivity (E=7). The lipase‐ and acylase I‐catalysed acylations of 1 and 2 in organic solvents proceeded with low enantioselectivity. On the other hand, more than 90% of 1 and 2 were transformed to amino esters 3 and 4, respectively, in a highly chemoselective O‐acylation with 2,2,2‐trifluoroethyl butanoate in the presence of Candida antarctica lipase A in TBME. The O‐protected product 3 in the reaction mixture was readily available to another transformation at the piperidine nitrogen although 3 was not separated due to intramolecular O→N acyl migration. The tendency for acyl migration was much less significant in the case of 4.
High Throughput Discovery of Alcohol Dehydrogenases for Industrial Biocatalysis
Authors: Ravot Gilles , Wahler Denis , Favre‐Bulle Olivier , Cilia Valérie , Lefevre Fabrice 
Published: June 2003

AbstractTo speed up the discovery of novel biocatalysts for industrial synthesis, an efficient screening approach has been set up. The huge potential of natural biodiversity has been taken advantage of in a discovery protocol using bioinformatics analysis, polymerase chain reaction (PCR) techniques and direct in vitro expression of enzymes. This approach led to the direct characterization of 19 novel thermoactive alcohol dehydrogenases with a broad substrate range, that set up a useful enzymatic “toolbox” for fine chemistry synthesis.
Immobilisation of P450 BM‐3 and an NADP+ Cofactor Recycling System: Towards a Technical Application of Heme‐Containing Monooxygenases in Fine Chemical Synthesis
Authors: Maurer Steffen C. , Schulze Holger , Schmid Rolf D. , Urlacher Vlada 
Published: June 2003

AbstractAbstract: Cytochrome P450 monooxygenases are potentially a very useful class of hydroxylation catalysts; they are able to introduce oxygen at activated and non‐activated carbon‐hydrogen bonds and thus lead to regio‐ and/or stereochemically pure compounds. However, this potential is lowered by their intrinsic low activity and inherent instability. P450‐catalysed biotransformations require a constant supply of NAD(P)H, making the process an expensive one. To render these catalysts more suitable for industrial biocatalysis, the immobilisation of P450 BM‐3 (CYP 102A1) from Bacillus megaterium in a sol‐gel matrix was combined with a cofactor recycling system based on NADP+‐dependent formate dehydrogenase (EC 1.2.1.2) from Pseudomonas sp. 101 and tested for practical applicability. This approach was used for the conversion of β‐ionone, octane and naphthalene to the respective hydroxy compounds with DMSO as cosolvent using sol‐gel immobilised P450 BM‐3 mutants.
Enantioselective Enzymatic Cleavage of N‐Benzyloxycarbonyl Groups
Authors: Patel Ramesh N. , Nanduri Venkata , Brzozowski David , McNamee Clyde , Banerjee Amit 
Published: June 2003

AbstractA new enzymatic process for the enantioselective cleavage of N‐benzyloxycarbonyl (Cbz) groups from protected amino acids and related compounds has been developed. The Cbz‐deprotecting enzyme was isolated from cell extracts of Sphingomonas paucimobilis SC 16113 and purified to homogeneity. The purified protein has a molecular weight of 155,000 daltons and a subunit size of 44,000 daltons.
Cofactor Regeneration of both NAD+ from NADH and NADP+ from NADPH:NADH Oxidase from Lactobacillus sanfranciscensis
Authors: Riebel Bettina R. , Gibbs Phillip R. , Wellborn William B. , Bommarius Andreas S. 
Published: June 2003

AbstractA possible solution for the regeneration of NAD+ from NADH is the oxidation of NADH with concomitant reduction of oxygen catalyzed by NADH oxidase (E. C. 1.6.‐.‐). We employ NADH oxidase from Lactobacillus sanfranciscensis, which reduces O2 to innocuous H2O, and (R)‐alcohol dehydrogenase [(R)‐ADH] from Lactobacillus brevis to perform enantioselective oxidation of racemic phenylethanol to acetophenone and (S)‐phenylethanol with regeneration of either NADH or NADPH to their respective oxidized precursors. NADH oxidase from L. sanfranciscensis accepts both NADH and NADPH; in contrast, the wild‐type (R)‐ADH only accepts NADP(+)(H) whereas its G37D mutant strongly prefers NAD(+)(H). Highly purified. NADH oxidase (221 U/mg, two‐step protocol) was coupled with wild‐type ADH from L. brevis on NADP(H) and mutant ADH from L. brevis on NAD(H) to achieve 50% conversion of racemic phenylethanol to (S)‐phenylethanol and acetophenone. Depending on the relative concentration of alcohol to cofactor, up to more than 100 turnovers were observed. We believe that this is the first demonstration of a regeneration scheme for both NAD+ from NADH and NADP+ from NADPH with the same enzyme.
Modulation von Protein‐Protein‐Wechselwirkungen mit niedermolekularen organischen Molekülen
Authors: Berg Thorsten 
Published: June 2003

AbstractViele Proteine üben ihre biologische Funktion als Bestandteile von Komplexen aus, und die Funktionen von Proteinen werden oft durch die spezifischen Wechselwirkungen mit anderen Proteinen bestimmt. Wegen der zentralen Bedeutung von Protein‐Protein‐Wechselwirkungen für zelluläre Prozesse kann die Modulation dieser Wechselwirkungen Funktionen bestimmter Proteine innerhalb der Zelle wirksam beeinflussen. Zellpermeable organische Modulatoren von Protein‐Protein‐Wechselwirkungen sind daher interessante Verbindungen sowohl für die Untersuchung physiologischer zellulärer Prozesse als auch für die Behandlung zahlreicher Krankheiten. Hier werden einige Protein‐Protein‐Wechselwirkungen vorgestellt, die weithin als pharmazeutische Angriffspunkte gelten, und der Leser wird mit erfolgreichen Strategien zur Identifizierung niedermolekularer Modulatoren dieser Wechselwirkungen vertraut gemacht. Diese Beispiele lassen erwarten, dass die interdisziplinäre Forschung in der funktionellen Proteomik, der Assay‐Entwicklung und der organischen Synthese neuartige Wege und Möglichkeiten für die zukünftige Behandlung von Humankrankheiten eröffnen wird.
Modulation of Protein–Protein Interactions with Small Organic Molecules
Authors: Berg Thorsten 
Published: June 2003

AbstractMany proteins exert their biological roles as components of complexes, and the functions of proteins are often determined by their specific interactions with other proteins. Because of the central importance of protein–protein interactions for cellular processes, the ability to interfere with specific protein–protein interactions provides a powerful means of influencing the function of selected proteins within the cell. Cell‐permeable small organic modulators of protein–protein interactions are thus highly desirable tools both for the study of physiological cellular processes and for the treatment of numerous diseased states. Herein a number of protein–protein interactions that are considered to be pharmaceutical targets are presented, which will familiarize the reader with the strategies that have been employed for the successful identification of small molecule modulators of these protein–protein interactions. These encouraging examples suggest that combined research efforts in the areas of functional proteomics, assay development, and organic synthesis will open up novel possibilities for the treatment of human diseases in the future.
Reductive Electron Transfer and Transport of Excess Electrons in DNA
Authors: Wagenknecht Hans‐Achim 
Published: June 2003

AbstractIn principle, DNA‐mediated charge transfer processes can be categorized as either oxidative hole transfer or reductive electron transfer. In research on DNA damage, major efforts have focused on the investigation of oxidative hole transfer or transport, resulting in insights on the mechanisms. On the other hand, the transport or transfer of excess electrons has a large potential for biomedical applications, mainly for DNA chip technology. Yet the mechanistic details of this type of charge transfer chemistry were unclear. In the last two years this mechanism has been addressed in γ‐pulse radiolysis studies with randomly DNA‐bound electron acceptors or traps. The major disadvantage of this experimental setup is that the electron injection and trapping is not site‐selective. More recently, new photochemical assays for the chemical and spectroscopic investigation of reductive electron transfer and electron migration in DNA have been published which give new insights into these processes. Based on these results, an electron‐hopping mechanism is proposed which involves pyrimidine radical anions as intermediate electron carriers.
Small Sample Correction for the Variance of GEE Estimators
Authors: Morel J.G. , Bokossa M.C. , Neerchal N.K. 
Published: June 2003

AbstractWhen clustered multinomial responses are fit using the generalized logistic link, Morel (1989) introduced a small sample correction in the Taylor series based estimator of the covariance matrix of the parameter estimates. The correction reduces the bias of the Type I error rates in small samples and guarantees positive definiteness of the estimated variance‐covariance matrix. It is well known that small sample bias in the use of the Delta method persists in any application of the Generalized Estimating Equations (GEE) methodology. In this article, we extend the correction originally suggested for the generalized logistic link, to other link functions and distributions, when parameters are estimated by GEE. In a Monte Carlo study with correlated data generated under different sampling schemes, the small sample correction has been shown to be effective in reducing the Type I error rates when the number of clusters is relatively small.