bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nickel‐Mediated Surface Grafting From Polymerization of α‐Amino Acid‐N‐Carboxyanhydrides
Authors: Witte Peter , Menzel Henning 
Published: August 2004

AbstractSummary: The feasibility of a living grafting from polymerization of α‐amino acid‐N‐carboxyanhydrides (NCA) from a surface using nickel initiators was shown. The polymerization has been carried out on commercially available polystyrene resins as spherical substrates in two different ways. Firstly L‐glutamic acid was bound to the surface as γ‐ester via a UV‐labile linker and transferred into the NCA by treatment with triphosgene. The grafting from polymerization was then carried out as a “block copolymerization” by reaction of the surface bound NCA with an excess of the Ni amido‐amidate complex initiator and subsequent addition of free NCA to grow the polymer chain. By this procedure polymer was formed at the surface and can be isolated after photolysis of the linker. The characterization of the polymer by size exclusion chromatography indicates a living polymerization at the surface. The second approach employs N‐alloc‐amides at the surface to prepare an initiating Ni amido‐amidate complex directly at the surface. It can be shown that the latter approach is much more straightforward and gives smaller quantities of non‐tethered polypeptide.Surface bound polypeptides were obtained by ring opening polymerization of α‐amino acid‐N‐carboxyanhydrides initiated by nickel amido‐amidate complexes installed at surfaces of commercially available polystyrene resins.magnified imageSurface bound polypeptides were obtained by ring opening polymerization of α‐amino acid‐N‐carboxyanhydrides initiated by nickel amido‐amidate complexes installed at surfaces of commercially available polystyrene resins.
Xanthate‐Mediated Controlled/Living Free‐Radical Polymerization under 60Co γ‐Ray Irradiation: Structure Effect of O‐Group
Authors: Hua Daoben , Xiao Junpeng , Bai Ruke , Lu Weiqi , Pan Caiyuan 
Published: August 2004

AbstractSummary: The free‐radical polymerizations of vinyl monomers have been studied under 60Co γ‐ray irradiation in the presence of S‐benzyl O‐ethyl dithiocarbonate (X1), S‐benzyl O‐phenyl dithiocarbonate (X2), S‐benzyl O‐2‐naphthyl dithiocarbonate (X3), S‐benzyl O‐(4‐methoxyphenyl) dithiocarbonate (X4), and methyl 4‐{[(benzylthio)carbonothioyl]oxy}benzoate (X5), respectively. The results indicate that the polymerizations of methyl acrylate (MA) reveal good living characteristics in the presence of X2, X3, X4, and X5 with O‐aryl groups, which play an important role in polymerization behavior; large aryl groups lead to slow polymerization. In contrast, the polymerizations with X1 couldn't be controlled and the obtained polymers had a broad‐molecular‐weight distribution or were even cross‐linked. In addition, it was observed that the polymerization of styrene with X2 was a controlled process though it was very slow, and the uncontrolled polymerization of methyl methacrylate (MMA) occurred under γ‐ray irradiation. To the best of our knowledge, this is the first report of xanthates being used as control agents in controlled/living free radical polymerization under γ‐ray irradiation.The structures of the xanthates used here.magnified imageThe structures of the xanthates used here.
Synthetic Uniform Polymers and Their Use for Understanding Fundamental Problems in Polymer Chemistry
Authors: Hatada Koichi , Kitayama Tatsuki , Ute Koichi , Nishiura Takafumi 
Published: August 2004

AbstractSummary: A uniform polymer is a polymer composed of molecules that are uniform with respect to molecular weight and constitution. Besides natural uniform polymers such as nucleic acids and polypeptide, synthetic uniform polymers have been obtained by a variety of approaches. In particular, a combination of living polymerization and supercritical fluid chromatography (SFC) separation is one of the promising ways for the preparation of uniform polymers. End‐functionalized uniform polymers enabled us to prepare uniform polymer architectures such as block, graft, comb, and star polymers. Their use for understanding the fundamental problems in polymer chemistry is discussed; topics include crystallization of polymers, chain conformation in solution, and association of stereoregular polymers in solution.SFC traces of isotactic PMMA containing an authentic sample of the 45‐mer (a) and of the isolated uniform PMMA of 100‐mer (b).imageSFC traces of isotactic PMMA containing an authentic sample of the 45‐mer (a) and of the isolated uniform PMMA of 100‐mer (b).
Silica/Poly(1,5‐dioxepan‐2‐one) Hybrid Nanoparticles by “Direct” Surface‐Initiated Polymerization
Authors: Yoon Kuk Ro , Lee Yong‐Won , Lee Jungkyu K. , Choi Insung S. 
Published: August 2004

AbstractSummary: Biodegradable poly(1,5‐dioxepan‐2‐one) (PDXO) was grown directly from SiOH groups of a silica nanoparticle by surface‐initiated, ring‐opening polymerization (SI‐ROP) of 1,5‐dioxepan‐2‐one (DXO). The direct SI‐ROP of DXO was achieved by heating a mixture of Sn(Oct)2, DXO, and the silica nanoparticles (316 nm in diameter) in anhydrous toluene. The resulting silica/PDXO hybrid nanoparticles were characterized by means of 1H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, and field‐emission scanning electron microscopy.The procedure for the surface‐initiated, ring‐opening polymerization of 1,5‐dioxepan‐2‐one on silica nanoparticles reported here.imageThe procedure for the surface‐initiated, ring‐opening polymerization of 1,5‐dioxepan‐2‐one on silica nanoparticles reported here.
Machado–Joseph shoe
Authors: Liu Chin San , Hsieh Mingli , Chen Yi Yun , Lo Man Chi 
Published: August 2004

AbstractMachado–Joseph shoe (MJS), defined as a shoe/slipper with a deep hallux imprint at its base, and hyperostosis/osteoma toe were two early ataxic signs in 17 of 31 patients (55%) and 24 of 31 patients (77%) with Machado–Joseph disease (MJD), respectively. The MJS plus hyperostosis/osteoma toes may be helpful in the diagnosis of MJD in a patient during early truncal ataxia. © 2004 Movement Disorder Society
1H, 13C and 15N NMR spectra of ciprofloxacin
Authors: Ziȩba Andrzej , Maślankiewicz Andrzej , Sitkowski Jerzy 
Published: August 2004

Abstract1H NMR assignment, including the values of δH and J(H,H) for the cyclopropane moiety, and 13C NMR and 15N NMR spectral data for ciprofloxacin are presented. Copyright © 2004 John Wiley & Sons, Ltd.
Gene expression profiling of colorectal cancer and metastases divides tumours according to their clinicopathological stage
Authors: Koehler Astrid , Bataille Frauke , Schmid Cornelia , Ruemmele Petra , Waldeck Annette , Blaszyk Hagen , Hartmann Arndt , Hofstaedter Ferdinand , Dietmaier Wolfgang 
Published: August 2004

AbstractGene expression profiling of matched colorectal carcinomas and metastases could reveal key molecular events involved in tumour progression and metastasis. Expression profiles have been created from 25 colorectal carcinomas (CRCs, pT1–4), corresponding normal colonic mucosa, and 14 liver metastases using cDNA arrays containing 1176 cancer‐related genes (Clontech). Hierarchical clustering clearly distinguished carcinomas from non‐cancerous tissues, separated tumours into high‐stage (pT4 and extensive lymph node or distant metastases) and low‐stage (≤pT3) groups, and correlated with the histopathological classification in 87% (33/38 cases). Most primary tumours and matched liver metastases clustered on terminal branches of the dendrogram. Statistical analysis (Mann–Whitney U‐test) revealed 40 tumour‐specific genes (29 up‐regulated, 11 down‐regulated) which allowed identification of malignant tissue samples by cluster analysis. A specific expression signature in matching metastases was not found, but a set of 23 classifier genes with statistically significant expression patterns in high‐ and low‐stage tumours was identified. These genes may represent important targets in colorectal carcinogenesis and might provide useful clinicopathological tools in the management of colorectal cancer. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Segmental and secondary dynamics in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) blends
Authors: Zhang Shihai , Runt James 
Published: August 2004

AbstractBroadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20–80% and at temperatures from −30 to approximately glass‐transition temperature (Tg) + 80 °C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry Tg and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher Tg. This leads to well‐defined α and β relaxations in the blends above the corresponding Tg, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above Tg, but with an activation energy larger than that observed below Tg because of increased relaxation amplitude. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3405–3415, 2004
Structure of polypropylene crystallized in confined nanolayers
Authors: Jin Y. , Rogunova M. , Hiltner A. , Baer E. , Nowacki R. , Galeski A. , Piorkowska E. 
Published: August 2004

AbstractFilms with a thousand alternating layers of isotactic polypropylene (PP) and polystyrene (PS) were prepared by layer‐multiplying coextrusion. The crystal structure of extremely thin PP layers confined between PS layers was studied by optical light microscopy (OM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray scattering (WAXS). Changes in structure were observed as the PP layer thickness decreased to the nanoscale. The thin PP discoids were largely composed of edge‐on lamellae with (040) planes lying flat on the interface. In layers 65 and 10‐nm thick, compressed d‐spacings in the directions perpendicular to the chains and loss of registry along the chain axis were suggestive of smectic packing of conformationally distorted chains. Even so, crystalline lamellae were distinguishable in the AFM images. In addition to the crystal population with (040) planes parallel to the interface, the WAXS from layers 65‐nm thick revealed another crystal fraction with (110) planes parallel to the interface and (040) planes perpendicular to the interface. This fraction was more evident in layers 10‐nm thick, where it accounted for approximately 10–20% of the crystallinity. Decreasing layer thickness resulted in a change of the crystal growth plane from the usual (110) to the more rare (010). The new crystal structure possibly served to fill‐in the radial structure of the dendritic discoids when a limitation to the thickness of the layer left only a little space for secondary nucleation of the crosshatched lamella. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3380–3396, 2004
The β‐crystalline form of isotactic polypropylene in blends of isotactic polypropylene and polyamide‐6/clay nanocomposites
Authors: Feng Meng , Gong Fangling , Zhao Chungui , Chen Guangming , Zhang Shimin , Yang Mingshu , Han Charles C. 
Published: August 2004

AbstractBlends of isotactic polypropylene and polyamide‐6/clay nanocomposites (iPP/NPA6) were prepared with an internal batch mixer. A high content of the β‐crystalline form of isotactic polypropylene (β‐iPP) was observed in the injection‐molded samples of the iPP/NPA6 blends, whereas the content of β‐iPP in the iPP/PA6 blends and the iPP/clay composite was low and similar to that of neat iPP. Quiescent melt crystallization was studied by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy. We found that the significant β‐iPP is not formed during quiescent melt crystallization regardless of whether the sample used was the iPP/NPA6 blend or an NPA6 fiber/iPP composite. Further characterization of the injection‐molded iPP/NPA6 revealed a shear‐induced skin–core distribution of β‐iPP and the formation of β‐iPP in the iPP/NPA6 blends is related to the shear flow field during cavity‐filling. In the presence of clay, the deformation ability of the NPA6 domain is decreased, as evidenced by rheological and morphological studies. It is reasonable that the enhanced relative shear, caused by low deformability of the NPA6 domain in the iPP matrix, is responsible for β‐iPP formation in the iPP/NPA6 blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3428–3438, 2004
Modeling the swelling pressure of degrading hydroxyethylmethacrylate‐grafted dextran hydrogels
Authors: Amsden B. G. , Stubbe B. G. , Horkay F. , De Smedt S. C. , Demeester J. 
Published: August 2004

AbstractDegrading hydroxyethylmethacrylate‐grafted dextran (dex‐HEMA) hydrogels generate a relatively sudden increase in osmotic pressure upon degradation into dextran solutions. This phenomenon is currently being examined as a possible means of developing a pulsatile drug‐delivery system. Here a mathematical model based on scaling concepts is presented to describe this sudden increase in swelling pressure and to provide a framework for the rational design of pulsatile delivery systems based on this phenomena. The model provides a good fit to the swelling pressures measured for dex‐HEMA gel/free dextran mixtures that simulate degrading dex‐HEMA gels. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3397–3404, 2004
Psychological and educational factors: Better predictors of work status than FEV1 in adults with cystic fibrosis
Authors: Burker Eileen J. , Sedway Jan , Carone Stacia 
Published: August 2004

AbstractNow that more individuals with cystic fibrosis (CF) are living into adulthood, vocational attainment is an increasingly important consideration. Work is a key factor in quality of life. The purpose of the present paper was to evaluate the factors that are associated with work status in 183 adults with CF. Approximately half of the participants were working at the time of evaluation, an impressive figure given that the mean forced expired volume in 1 sec (FEV1) was 31.9%. The average number of hours worked was 32.7 hr/week. The majority of individuals were employed in professional, technical, or managerial occupations (accounting, teaching, law, or social work). A third were employed in clerical and sales occupations, and the remaining individuals were employed in a wide range of other occupations (hotel manager, undercover shopper, artist, or dental technician). Interestingly, FEV1 and age did not differentiate between subjects who were working and those who were not. Individuals who were working had significantly lower depression scores and a higher educational level than those who were not working. Future research is needed to determine whether it is the increased socialization and the resulting social support that may come from a work environment, or a reduction in financial stress because of better income and health benefits that helps to explain this difference. Alternatively, work may serve as a distraction from the symptoms of CF. It is likely that those with higher educational levels had more professional jobs that were more easily modified as health declined. Future research needs to assess how career choices are made, and what factors into a patient's decision to keep working. © 2004 Wiley‐Liss, Inc.
Comparative evaluation of eight docking tools for docking and virtual screening accuracy
Authors: Kellenberger Esther , Rodrigo Jordi , Muller Pascal , Rognan Didier 
Published: August 2004

AbstractEight docking programs (DOCK, FLEXX, FRED, GLIDE, GOLD, SLIDE, SURFLEX, and QXP) that can be used for either single‐ligand docking or database screening have been compared for their propensity to recover the X‐ray pose of 100 small‐molecular‐weight ligands, and for their capacity to discriminate known inhibitors of an enzyme (thymidine kinase) from randomly chosen “drug‐like” molecules. Interestingly, both properties are found to be correlated, since the tools showing the best docking accuracy (GLIDE, GOLD, and SURFLEX) are also the most successful in ranking known inhibitors in a virtual screening experiment. Moreover, the current study pinpoints some physicochemical descriptors of either the ligand or its cognate protein‐binding site that generally lead to docking/scoring inaccuracies. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Three‐dimensional model of a substrate‐bound SARS chymotrypsin‐like cysteine proteinase predicted by multiple molecular dynamics simulations: Catalytic efficiency regulated by substrate binding
Authors: Pang Yuan‐Ping 
Published: August 2004

AbstractSevere acute respiratory syndrome (SARS) is a contagious and deadly disease caused by a new coronavirus. The protein sequence of the chymotrypsin‐like cysteine proteinase (CCP) responsible for SARS viral replication has been identified as a target for developing anti‐SARS drugs. Here, I report the ATVRLQp1Ap1'‐bound CCP 3D model predicted by 420 different molecular dynamics simulations (2.0 ns for each simulation with a 1.0‐fs time step). This theoretical model was released at the Protein Data Bank (PDB; code: 1P76) before the release of the first X‐ray structure of CCP (PDB code: 1Q2W). In contrast to the catalytic dyad observed in X‐ray structures of CCP and other coronavirus cysteine proteinases, a catalytic triad comprising Asp187, His41, and Cys145 is found in the theoretical model of the substrate‐bound CCP. The simulations of the CCP complex suggest that substrate binding leads to the displacement of a water molecule entrapped by Asp187 and His41, thus converting the dyad to a more efficient catalytic triad. The CCP complex structure has an expanded active‐site pocket that is useful for anti‐SARS drug design. In addition, this work demonstrates that multiple molecular dynamics simulations are effective in correcting errors that result from low‐sequence‐identity homology modeling. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Theoretical study of the ground‐state gas‐phase unimolecular decomposition channels of propynoic acid
Authors: Ndip Edmund Moses N. , Shukla Manoj K. , Leszczynski Jerzy , Redington Richard L. 
Published: August 2004

AbstractTheoretical studies have been carried out to elucidate the ground‐state unimolecular decomposition channels for propynoic acid (PA) in the gas phase. In this paper we present details of mechanisms for the decarboxylation and decarbonylation channels of PA. The transformations of PA result in the formation of carbon dioxide and acetylene from the decarboxylation channel while carbon monoxide and hydroxyacetylene, ultimately the ketene, are formed from the decarbonylation pathway. Equilibrium structures and the principal transition states (TSs) for each pathway have been identified and characterized. The Gaussian 98 suite of programs and MOLDEN were used for computation and visualization. All computations of equilibrium and TS structures relevant to the two competing unimolecular decomposition channels (decarboxylation and decarbonylation) were performed with second‐order Møller–Plesset (MP2) and Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP) levels using the 6‐31G(d,p), 6‐311++G (d, p) and Dunning's correlation‐consistent polarized valence basis set (aug‐cc‐pVDZ). The geometries were fully optimized and characterized as minima (0 imaginary frequencies) or first‐order saddle points (1 imaginary frequency) by harmonic vibrational analysis at the MP2/6‐311++G(d,p) and B3LYP/6‐311++G(d,p) levels. All the calculations indicate that the lowest energy decomposition pathway for PA is decarboxylation. Decarboxylation of PA occurs most easily through a three‐step mechanism: conversion of s‐cis‐HCCCO2H to s‐trans‐HCCCO2H, followed by a 1, 3‐hydrogen migration of hydroxyl hydrogen, resulting in a four‐center TS that decays easily to acetylene and carbon dioxide, with an activation barrier of 61.3–79.9 kcal/mol (average 65.67 kcal/mol). Decarbonylation, leading to hydroxyacetylene (and subsequently the ketene) and carbon monoxide, occurs easily via a direct (one‐step) three‐center TS. The direct (one‐step) elimination of carbon monoxide from propynoic acid has a calculated average activation barrier of 67.9–81.7 kcal/mol (average, 74.1 kcal/mol). The decarboxylation pathway is shown to occur with a maximum exothermicity of 28 kcal/mol. On the contrary, the decarbonylation of PA is predicted to occur with an overall endothermicity of ≈29.2 kcal/mol for formation of hydroxyacetylene and carbon monoxide and an average exothermicity of −7.69 kcal/mol for formation of the ketene and carbon monoxide. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Quantitative determination of trace concentrations of tetracycline and sulfonamide antibiotics in surface water using solid‐phase extraction and liquid chromatography/ion trap tandem mass spectrometry
Authors: Yang Shinwoo , Cha Jongmun , Carlson Kenneth 
Published: August 2004

AbstractThe occurrence of human and veterinary pharmaceutical compounds in surface waters (e.g. streams, lakes and reservoirs) is an important emerging environmental issue. There is a need for robust, sensitive and reliable analytical methods for measuring these compounds in a variety of natural water and wastewater matrices. This paper describes a method for the determination of seven tetracycline (TC) and six sulfonamide (SA) compounds in pristine and wastewater‐influenced surface water using solid‐phase extraction, and LCQ Duo ion trap liquid chromatography/tandem mass spectrometry (LC/MS/MS) with positive electrospray ionization (ESI(+)) and selected reaction monitoring (SRM). The seven TCs and six SAs analyzed using this method include oxytetracycline (OTC), chlortetracycline (CTC), tetracycline (TC), democlocycline (DMC), doxycycline (DXC), meclocycline (MCC), minocycline (MNC), sulfathiazole (STZ), sulfamerazine (SMR), sulfamethazine (SMT), sulfachloropyridazine (SCP), sulfamethoxazole (SMX), and sulfadimethoxane (SDM). This study discusses the effects of flow rate, LC column diameter and LC column temperature on UV and/or mass peak quality of the different analytes. Several product ions for MS/MS detection have been identified and compared for ion trap and triple quadrupole LC/MS/MS instruments. Statistical analysis for determination of the method detection limit (MDL), accuracy and precision of the method is described. Matrix effects are evaluated in deionized, pristine and wastewater‐influenced river water. The method is applied to evaluate the occurrence of these compounds in a small watershed in northern Colorado. Copyright © 2004 John Wiley & Sons, Ltd.