bluuebunny/crossref_metadata_2025_split huggingface dataset:
Addition of Organochromium Reagents to Carbonyl Compounds
Authors: Takai Kazuhiko 
Published: November 2004

AbstractOrganochromium compounds can be prepared by two methods: (1) transmetallation from the corresponding organolithium, ‐magnesium, or –zinc compounds with chromium(III) halides, and (2) reduction of organic substrates, such as halides and unsaturated compounds with chromium(II) salts. The second method is usually the one ised because the first method suffers from low solubility of chromium(III) salts in ethereal solvents and from the difficulty of preparing organolithium compounds. Low‐valent chromium species are reducing agents. Reduction of various types of organic halides and compounds having unsaturated hetero‐hetero bonds with the chromium (II) species is discussed. Also described are the transmetallation to organochromium compounds from other organometallics, the nature of the carbon‐chromium bonds, and the X‐ray structure of chromium compounds. Reactions of organochromium reagents with carbonyl compounds and their scope and limitations are described. Included in this discussion are the geminal chromium reagents. Other reagents discussed are the chromium‐nickel compounds and alkylchromium and other organochromium reagents.
Effect of ion exchange of glazed dental glass ceramics on strength parameters
Authors: Fischer H. , Brehme M. , Telle R. , Marx R. 
Published: November 2004

AbstractIon exchange treatments can significantly increase the strength of dental glass ceramic core materials by induced compressive residual stresses. However, the core materials of dental restorations need to be veneered or at least to be stained and glazed for esthetic and functional reasons. The objective of this study was to determine the effect of different ion exchange treatments on the strength parameters of stained and glazed glass ceramics. Batches of specimens made of a leucite reinforced dental glass with and without staining and glazing layer, untreated, single ion exchanged (KNO3), and dual ion exchanged (1. KNO3/27, 2. 30 mol% NaNO3/70 mol% KNO3) were tested. The strength of the core material was increased from 117 to 213 MPa by single ion exchange. Staining and glazing increased the strength up to 165 MPa. Single ion exchange of the stained and glazed core caused only a slight additional strength increase up to 173 MPa. The dual ion exchanged stained and glazed core exhibit a strength of 195 MPa and decreased the large strength scatter because of a well‐designed residual stress profile. We conclude that dual ion exchange treatments could significantly increase the mechanical reliability of stained and glazed glass ceramic restorations. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 72A: 175–179, 2005
The agnoprotein of polyomaviruses: A multifunctional auxiliary protein
Authors: Khalili Kamel , White Martyn K. , Sawa Hirofumi , Nagashima Kazuo , Safak Mahmut 
Published: November 2004

AbstractThe late region of the three primate polyomaviruses (JCV, BKV, and SV40) encodes a small, highly basic protein known as agnoprotein. While much attention during the last two decades has focused on the transforming proteins encoded by the early region (small and large T‐antigens), it has become increasingly evident that agnoprotein has a critical role in the regulation of viral gene expression and replication, and in the modulation of certain important host cell functions including cell cycle progression and DNA repair. The importance of agnoprotein is underscored by its expression during lytic infection of glial cells by JCV that occurs in progressive multifocal leukoencephalopathy (PML), and also in some JCV‐associated human neural tumors particularly medulloblastoma. In this review, we will discuss the structure and function of agnoprotein in the viral life cycle during the course of lytic infection and the consequences of agnoprotein expression for the host cell. © 2004 Wiley‐Liss, Inc.
Peroxide detoxification by brain cells
Authors: Dringen Ralf , Pawlowski Petra G. , Hirrlinger Johannes 
Published: November 2004

AbstractPeroxides are generated continuously in cells that consume oxygen. Among the different peroxides, hydrogen peroxide is the molecule that is formed in highest quantities. In addition, organic hydroperoxides are synthesized as products of cellular metabolism. Generation and disposal of peroxides is a very important process in the human brain, because cells of this organ consume 20% of the oxygen used by the body. To prevent cellular accumulation of peroxides and damage generated by peroxide‐derived radicals, brain cells contain efficient antioxidative defense mechanisms that dispose of peroxides and protect against oxidative damage. Cultured brain cells have been used frequently to investigate peroxide metabolism of neural cells. Efficient disposal of exogenous hydrogen peroxide was found for cultured astrocytes, oligodendrocytes, microglial cells, and neurons. Comparison of specific peroxide clearance rates revealed that cultured oligodendrocytes dispose of the peroxide quicker than the other neural cell cultures. Both catalase and the glutathione system contribute to the clearance of hydrogen peroxide by brain cells. For efficient glutathione‐dependent reduction of peroxides, neural cells contain glutathione in high concentration and have substantial activity of glutathione peroxidase, glutathione reductase, and enzymes that supply the NADPH required for the glutathione reductase reaction. This article gives an overview on the mechanisms involved in peroxide detoxification in brain cells and on the capacity of the different types of neural cells to dispose of peroxides. © 2004 Wiley‐Liss, Inc.
Mitochondrial permeability transition in CNS trauma: Cause or effect of neuronal cell death?
Authors: Sullivan P.G. , Rabchevsky A.G. , Waldmeier P.C. , Springer J.E. 
Published: November 2004

AbstractExperimental traumatic brain injury (TBI) and spinal cord injury (SCI) result in a rapid and significant necrosis of neuronal tissue at the site of injury. In the ensuing hours and days, secondary injury exacerbates the primary damage, resulting in significant neurologic dysfunction. It is believed that alterations in excitatory amino acids (EAA), increased reactive oxygen species (ROS), and the disruption of Ca2+ homeostasis are major factors contributing to the ensuing neuropathology. Mitochondria serve as the powerhouse of the cell by maintaining ratios of ATP:ADP that thermodynamically favor the hydrolysis of ATP to ADP + Pi, yet a byproduct of this process is the generation of ROS. Proton‐pumping by components of the electron transport system (ETS) generates a membrane potential (ΔΨ) that can then be used to phosphorylate ADP or sequester Ca2+ out of the cytosol into the mitochondrial matrix. This allows mitochondria to act as cellular Ca2+ sinks and to be in phase with changes in cytosolic Ca2+ levels. Under extreme loads of Ca2+, however, opening of the mitochondrial permeability transition pore (mPTP) results in the extrusion of mitochondrial Ca2+ and other high‐ and low‐molecular weight components. This catastrophic event discharges ΔΨ and uncouples the ETS from ATP production. Cyclosporin A (CsA), a potent immunosuppressive drug, inhibits mitochondrial permeability transition (mPT) by binding to matrix cyclophilin D and blocking its binding to the adenine nucleotide translocator. Peripherally administered CsA attenuates mitochondrial dysfunction and neuronal damage in an experimental rodent model of TBI, in a dose‐dependent manner. The underlying mechanism of neuroprotection afforded by CsA is most likely via interaction with the mPTP because the immunosuppressant FK506, which has no effect on the mPT, was not neuroprotective. When CsA was administrated after experimental SCI at the same dosage and regimen used TBI paradigms, however, it had no beneficial neuroprotective effects. This review takes a comprehensive and critical look at the evidence supporting the role for mPT in central nervous system (CNS) trauma and highlights the differential responses of CNS mitochondria to mPT induction and the implications this has for therapeutically targeting the mPT in TBI and SCI. © 2004 Wiley‐Liss, Inc.
Molecular and cellular mechanisms of neuroprotection by vascular endothelial growth factor
Authors: Sun Feng‐Yan , Guo Xin 
Published: November 2004

AbstractThe present view of the neuroprotective functions and mechanisms of action of vascular endothelial growth factor (VEGF) is based on studies of neuronal ischemic/hypoxic models in vivo and in vitro. Endogenous neuronal VEGF increases in the ischemic brain and plays a neuroprotective role in the pathophysiologic processes that follow stroke. Exogenous VEGF, directly administered or overexpressed by gene delivery into rat brains, reduces ischemic brain infarct and decreases hypoxic neuronal death. The main neuroprotective mechanisms of VEGF include: (1) modulation of the phosphatidylinositol 3′‐kinase (PI3K)/Akt/nuclear factor‐κB signaling pathway, inhibition of caspase‐3 activity, and reduction of ischemic neuronal apoptosis; (2) inhibition of outward delayed rectifier potassium channel currents and increase of ischemia‐induced tyrosine phosphorylation of Kv1.2 potassium channel proteins via activation of the PI3K pathway; and (3) enhancement of proliferation and migration of neural progenitors in the subventricular zone and improvement of striatal neurogenesis and maturation of newborn neurons in adult rat brains after stroke. © 2004 Wiley‐Liss, Inc.
Developing metropolitan tourism on the fringe of central London
Authors: Maitland Robert , Newman Peter 
Published: November 2004

AbstractThe paper examines the growth of a ‘new tourism area’ in Islington, north London — a locality that lacks a large attraction, acknowledged distinctive heritage and has not been planned as a destination. We review supply side changes and link them to the recent literature on economic and spatial trends in cities, particularly the role of amenity. We report on a survey of Islington visitors that shows they are drawn by distinctive qualities of place rather than particular attractions. The visitors have characteristics that distinguish them from visitors to London as a whole, but we speculate that they have similarities to Islington workers and residents in their search for amenity, entertainment and high‐level consumption services. In the final section of the paper we explore the consequences of our findings for understanding the growth of urban tourism. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and Characterization of a Highly Soluble Poly[3‐(10‐hydroxydecyl)thiophene]
Authors: Paganin Luisa , Lanzi Massimiliano , Costa‐Bizzarri Paolo , Bertinelli Franco , Masi Corrado 
Published: November 2004

AbstractThe preparation of a regioregular HH‐TT linked poly[3‐(10‐hexanoyloxy)decyl]thiophene and its conversion to the corresponding hydroxy‐functionalized polymer is described and discussed. The hydroxydecyl polymer, highly soluble in common organic solvents, has been characterized via NMR, FT‐IR, DSC and X‐ray diffractometry.
New Copoly(bisphenol‐A)carbonates, Having Hydrophilic Porphyrin Units as End‐Groups, Synthesized by Melt‐Reacting Processes
Authors: Scamporrino Emilio , Alicata Rossana , Bazzano Sebastiano , Vitalini Daniele , Mineo Placido 
Published: November 2004

AbstractThe synthesis of some poly(bisphenol‐A)carbonates (PCs) containing hydrophilic porphyrin units as end groups, by thermal treatment of commercial PC and 5,10,15‐tri{p[ω‐methoxy‐poly(oxyethylene)]phenyl}20(p‐hydroxy phenyl)porphyrin (I) blends, is reported. A suitable choice of reaction temperature, molar composition and reaction time, allowing the extent of the outer‐inner transesterification reactions, leads to a gradual insertion of porphyrin units in the polymer chains. The composition of the obtained materials was inferred by GPC and MALDI‐TOF mass spectrometric analysis.
Propene‐Norbornene Copolymers: Synthesis and Microstructure
Authors: Boggioni L. , Tritto I. , Ragazzi M. , Carbone P. , Ferro D.R. 
Published: November 2004

AbstractSeries of propene(norbornene (P–N) copolymers were synthesized in the presence of two C2 symmetric zirconocenes, rac‐Et(Indenyl)2ZrCl2 (1) and rac‐Me2Si(Indenyl)2ZrCl2 (2), and of the Cs symmetric zirconocene Me2C(Cp)(Fluorenyl)ZrCl2 (3) with MAO as cocatalyst. P–N copolymers were characterized by 13C NMR spectroscopy, SEC, and DSC. A first assignment of the main 13C NMR signals of P–N copolymers obtained with 1 and 2 containing isolated N units was obtained on the basis of DEPT experiments and by comparison with isotactic polypropene (i‐PP) and E–N copolymer spectra. Ab initio theoretical 13C NMR chemical shifts, combined with R.I.S. statistics of the P–N chain, gave important detailed indications for the assignment of the complex 13C spectra of these copolymers. Such assignments were used to estimate the N copolymer content. The comparison of N content values obtained from the areas of different regions of the spectra reveals that 1,3 propene misinsertions are formed in greater amount as the [N]/[P] ratio of the feed increases. This may be due to the steric hindrance of the Mt–tertiary carbon bond when N is the last inserted unit, which makes difficult the next propene insertion and causes the low polymerization activities, molecular masses and Tg. The spectra of P–N copolymers obtained with 3 revealed to be even more complex. A limited assignment of the spectrum has been achieved. This allowed us to evaluate the N content in the copolymers and to evidence the low tendency of the Cs symmetric 3 to give 1,3 propene misinsertions in P–N copolymers. This is in agreement with the results observed with this catalyst in propene homopolymerization.
Recent Advances in MALDI Mass Spectrometry of Polymers
Authors: Montaudo Giorgio , Carroccio Sabrina , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo 
Published: November 2004

AbstractMatrix‐Assisted Laser Desorption/Ionization (MALDI) allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers, and the estimate of composition and sequence for copolymers. MALDI has also been applied to the measurement of molar mass distributions in polymers and to the study of thermal and oxidative processes in polymers. This paper illustrates the detection of self‐association in macromolecules made by coupling MALDI and Size Exclusion Chromatography (SEC), the investigation of polymer oxidation phenomena, and the characterization of copolymers formed in the processing of reactive polymer blends.
Functionalization of Styrene‐Olefin Block Copolymers by Melt Radical Grafting of Glycidyl Methacrylate and Reactive Blending with PET
Authors: Pracella Mariano , Chionna Donatella 
Published: November 2004

AbstractBlocks copolymers styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) and styrene‐b‐(ethylene‐co‐propylene) (SEP, SEPSEP), with different styrene content and number of blocks in the chain, were functionalized with glycidyl methacrylate (GMA) by melt radical grafting. The influence of monomer concentration, radical initiator and copolymer structure on the grafting degree was examined. The grafted copolymers were characterised by DSC and capillary rheometry. Blends of PET with functionalized SEBS and SEPSEP showed a marked improvement of phase morphology and elongation at break when compared to blends with unfunctionalized copolymers.
Physical‐Mechanical and Thermal Properties of Polyethylene Toughened with Submicron BaSO4 Particles
Authors: Bianchi Francesca , Lazzeri Andrea , Pracella Mariano , D'Aquino Arianna , Ligeri Giorgio 
Published: November 2004

AbstractThe mechanical and thermal behaviour and the morphology of High‐Density Polyethylene (HDPE), filled with different types of Barium Sulfate (BaSO4) submicron particles have been examined. Composites with a filler content in the range 5‐15 vol% were obtained with a twin screw mixer‐single screw extruder and then analyzed by means of DSC, SEM and tensile and Charpy impact tests. The effect of different surface treatments of filler particles on the composite properties has been studied. The results indicate that the addition of BaSO4 particles leads to slight increase in Young's modulus and to a decrease in the yield stress independently of surface treatment. The fracture resistance tests demonstrated a strong influence of filler content and surface agents on impact parameters. The use of BaSO4 filler appears to induce a good toughening of HDPE, especially at low volume content, while surface agents reduce particle agglomeration and decrease the adhesion between filler and polymer matrix.
Properties/Structure Relationships in Innovative PCL‐SiO2 Nanocomposites
Authors: Avella Maurizio , Bondioli Federica , Cannello Valeria , Cosco Simona , Errico Maria Emanuela , Ferrari Anna Maria , Focher Bonaventura , Malinconico Mario 
Published: November 2004

AbstractPoly(caprolactone) (PCL) based nanocomposites filled with silica (SiO2) nanoparticles were prepared and the relationships between their structure and properties were investigated.Silica nanoparticles were synthesized by Stöber method. Surface of silica nanoparticles were successively functionalized in order to promote matrix/filler compatibilization and to improve interfacial adhesion. Morphological analysis performed on the fractured surface of samples revealed that the compatibilization process permitted to obtain an homogeneous and discrete distribution of the nanoparticles into polymeric matrix. Mechanical test showed that in the presence of a strong interphase, the elastic modulus increases of about 25% than the neat polymeric matrix value. Preliminary modelling analysis was also performed in order to assess the correlation existing between a computational model and experimental data.
Polyimide‐Silica Hybrids: Spectroscopy, Morphology and Mechanical Properties
Authors: Abbate Mario , Musto Pellegrino , Ragosta Giuseppe , Scarinzi Gennaro , Mascia Leno 
Published: November 2004

AbstractPolyimide/silica hybrids were prepared by a sol‐gel process and were evaluated in terms of curing behaviour, morphology and mechanical properties. The spectroscopic examination showed that the presence of the inorganic phase accelerates the imidization of the polyamic acid. Two types of morphology for the silica phase were obtained by tailoring the composition of the precursor solution mixture. The mechanical properties were found to be strongly dependent on the system morphology. The largest increase in rigidity and strength properties were achieved when the two phases were co‐continuous.
Organic‐Inorganic Hybrid Materials with the Ability to Bind Metal Ions: Calorimetric Properties and Thermostability
Authors: Sartore Luciana , Penco Maurizio , Bigotti Fabio , Pedrotti Cristian , D'Antone Salvatore 
Published: November 2004

AbstractOrganic‐inorganic hybrid materials with excellent heavy metal ions chelating properties were synthesized by covalent bonding of multifunctional polymers of polyamidoamine (PAA) type onto silica. Two series of polyamidoamine‐silica hybrid materials differing in the PAA chemical structure were prepared and their thermal properties were investigated. Differential Scanning Calorimetry was used to study the effects of chain immobilization and ion chelation on the glass‐transition temperature (Tg) of the polymers. The Tg of PAA‐hybrid materials was elevated with respect to ungrafted PAAs. Complex formation with metal ions such as Cu++ or Co++ caused total suppression of Tg for both linear polymers as well as the corresponding hybrid materials. Finally, the silica particles slightly influenced the decomposition temperatures of linear polymers increasing their thermal stability.
Thermal Behavior of Composites Based on Poly(vinyl alcohol) and Sugar Cane Bagasse
Authors: Grillo Fernandes Elizabeth , Cinelli Patrizia , Chiellini Emo 
Published: November 2004

AbstractPoly(vinyl alcohol) (PVA) and sugar cane bagasse (SCB) mixtures have been formulated as aimed at the production of hydro‐mulching composites and melt processed biobased composite items. Glycerol and urea have been proposed as suitable plasticizers and eventually, in the case of urea, for the realization also of slow release fertilizing hydro‐mulching. The investigation of thermal stability of raw components and relevant mixture is an important parameter to be assessed in view of processing and ultimate applications. PVA/SCB composites appeared suitable for melt processing up to 200°C. The urea containing PVA/SCB composites while resulted particularly suited for hydro‐mulching applications did not appear processable from the melt, due to urea thermal instability.
Alginate/Polyvinylalcohol Blends for Agricultural Applications: Structure‐Properties Correlation, Mechanical Properties and Greenhouse Effect Evaluation
Authors: Russo Roberto , Giuliani Anna , Immirzi Barbara , Malinconico Mario , Romano Gennaro 
Published: November 2004

AbstractBiodegradable blend films containing sodium alginate, polyvinyl alcohol and glycerol, for agricultural applications, were prepared by casting of aqueous solutions. Since the mechanical properties of alginate are not suitable for agricultural applications, the addition of polyvinyl alcohol and glycerol was necessary in order to improve some mechanical parameters like the strain at break. The interaction between different components was studied by thermogravimetric analysis and DSC, while mechanical parameters and the transmittance in the IR region were investigated in order to identify the compositions with suitable properties for application in agriculture.
Segmented Polyurethanes for Medical Applications: Synthesis, Characterization and in vitro Enzymatic Degradation Studies
Authors: Ciardelli Gianluca , Rechichi Alfonsina , Cerrai Piero , Tricoli Mario , Barbani Niccoletta , Giusti Paolo 
Published: November 2004

AbstractDegradable segmented poly(ether‐ester‐urethanes) of variable segment chemistry and content were synthesized and characterized. Polycaprolactone diol, a series of poly(ether‐ester) block copolymers, and a diisocyanate giving non toxic degradation products were used to form the prepolymer. Cyclohexane dimethanol and a L–phenylalanine–based diester (Phe diester) were used as chain extenders. The influence of α‐chimotrypsin on the degradation was investigated by exposing the polymers to buffer and enzyme solutions for 12 days. The SEM, SEC, and gravimetric results showed that a significant erosion of the Phe diester containing polymer compared with the control polyurethane occurred in the presence of the enzyme but not in a normal buffer solution.
Polyurethane Based Materials for the Production of Biomedical Materials
Authors: Covolan Vera L. , Di Ponzio Roberta , Chiellini Federica , Grillo Fernandes Elizabeth , Solaro Roberto , Chiellini Emo 
Published: November 2004

AbstractPolyurethanes (PUs) composed by hard and soft segments have been extensively used in the manufacturing of biocompatible prosthesis and medical devices. A broad variety of PUs can be obtained by modifying the balance between both segments. In the present work, different basically‐flexible PUs have been prepared by employing different combinations of aliphatic hexamethylene diisocyanate, poly(ethylene glycol) (Mw 400 Da), poly(ϵ‐caprolactone) diol (Mw 530 Da), and 1,4‐butanediol. Thermal analysis of the synthesized PUs demonstrated high thermal stability and the assumption of glassy state well below room temperature, in agreement with their marked flexibility. Morphological characterization of PUs films indicated that films prepared by spin coating were smoother and more homogeneous than those obtained by casting. Biological assays performed by using 3T3/BALB‐C mouse embryo fibroblast cell line confirmed the absence of toxicity and hence the biocompatibility of PU‐films.