bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of water absorption and hygrothermal aging rubber toughened poly(butylene terephthalate) with and without short glass fiber reinforcement
Authors: Yow B. N. , Ishiaku U. S. , Ishak Z. A. Mohd , Karger‐Kocsis J. 
Published: February 2004

AbstractThe objectives of this paper were to investigate the water absorption and hygrothermal aging behavior of rubber‐toughened poly(butylenes terephthalate) (RT‐PBT) with and without short glass fiber (SGF) reinforcement. The rubbers used in the study were AX8900 and EXL2314, both of which are acrylate‐based terpolymer. The effect of the hygrothermal aging on its fracture properties was also studied. The kinetics of the water absorption study were carried out on the injection‐molded samples of the RT‐PBTs and the SGF‐reinforced rubber‐toughened PBT (SGF‐RT‐PBT) at three immersion temperatures, 30, 60 and 90°C, for a total of 450 h. The study of the deterioration caused by the hygrothermal aging was conducted by investigating the fracture parameters and flexural properties of all the materials as both hygrothermally aged (HA) and redried state (RD). The modes of the failure of HA and RD samples were studied using the scanning electron microscopy (SEM) technique. It was found that all the samples conformed to Fickian behavior and the kinetics of absorption exhibited a strong dependency on the rubber types, presence of SGF, as well as the immersion temperature. Generally, SGF‐RT‐PBT showed a better resistance to hygrothermal aging than that of RT‐PBT and PBT, though a declining trend was observed in the fracture parameters, Kc and Gc. However, an opposite observation was exhibited in the flexural properties in some, but not all cases. Finally, the results obtained from SEM micrographs showed that permanent damage occurred in the materials and the hygrothermal aging had suppressed the plastic deformation ability of the PBT matrix and both types of impact modifiers where brittle failure was observed. Fiber pull‐out was apparently the failure mode of the SGF‐reinforced materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 506–516, 2004
A visco‐hyperelastic constitutive model to characterize both tensile and compressive behavior of rubber
Authors: Shim V. P. W. , Yang L. M. , Lim C. T. , Law P. H. 
Published: February 2004

AbstractThe strain rate–dependent finite deformation behavior of three types of rubber under tension and compression are experimentally characterized using a Hopkinson bar. Based on the measured data, a frame‐independent incompressible visco‐hyperelastic constitutive equation is proposed to describe the tensile and compressive responses of rubber under high strain rates. The equation comprises two parts: a three‐parameter component based on an elastic strain energy potential, to characterize static hyperelastic behavior, and another with four parameters, developed from the BKZ model, to define rate sensitivity and strain history dependence. Established static and dynamic experimental techniques are employed to determine the seven parameters in the constitutive relationship. Comparison of predictions based on the proposed model with experiments shows that it is able to describe the visco‐hyperelastic behavior of rubber‐like materials under high strain rates. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 523–531, 2004
PVC/montmorillonite nanocomposites based on a thermally stable, rigid‐rod aromatic amine modifier
Authors: Liang Zhu‐Mei , Wan Chao‐Ying , Zhang Yong , Wei Ping , Yin Jie 
Published: February 2004

AbstractTwo kinds of polyvinyl chloride (PVC)/montmorillonite (MMT) nanocomposites were prepared by the melt intercalation method based on a thermally stable, rigid‐rod aromatic amine modifier and a commonly used 1‐hexadecylamine. The information on morphological structure of PVC/MMT nanocomposites was obtained using XRD and TEM. The mechanical, thermal, and flame retardant properties of the nanocomposites were characterized by universal tester, DMA, TGA, and cone calorimeter. The degree of degradation of PVC was studied by 1H‐NMR. MMT treated by the aromatic amine exhibited better dispersibility than that treated by 1‐hexadecylamine. The nanocomposites, based on this MMT, consequently exhibited better mechanical, thermal, and flame retardant properties and lower degradation degree than those based on 1‐hexadecylamine‐treated MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 567–575, 2004
Preparation of asymmetric PEEKWC flat membranes with different microstructures by wet phase inversion
Authors: Buonomenna M. G. , Figoli A. , Jansen J. C. , Drioli E. 
Published: February 2004

AbstractMembranes with controlled morphology were prepared by wet phase inversion from PEEKWC, a modified polyetheretherketone. Different membrane structures were obtained by using different nonsolvent/solvent pairs. The influence of several parameters, such as the composition of the polymer solution (concentration, type of solvent), the composition of the coagulation bath, and the exposure time before immersion in the coagulation bath, on the membrane morphology was studied. The PEEKWC/solvent/nonsolvent phase diagrams, with various solvent/nonsolvent combinations, were determined and correlated to the process of phase separation during membrane formation. Using solvent/nonsolvent pairs with a high mutual affinity (DMF/water, DMA/water), porous membranes for possible application in microfiltration were obtained. The THF/water combination allowed the formation of asymmetric membranes with a dense skin layer, suitable for gas separation applications. Nitrogen permeance of all porous membranes was measured as function of pressure. Application of the Dusty Gas model permitted a qualitative description of the pore size and membrane morphology in relation to the membrane preparation conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 576–591, 2004
Positive temperature coefficient behavior of polymer composites having a high melting temperature
Authors: Kim Jung‐il , Kang Phil Hyun , Nho Young Chang 
Published: February 2004

AbstractThe positive temperature coefficient (PTC) behavior of polymers having a high melting temperature, such as nylon, polyvinylidene fluoride, polyester, and polyacetal, was investigated. Carbon black and nickel powder were used to investigate the influence of their conductive fillers on PTC intensity. The polymer/filler composite was irradiated with gamma rays at dosages of 50, 100, and 150 kGy for the purpose of reducing the negative temperature coefficient (NTC) of a conductive composite. It was found that the PTC temperature depended on the melting point of the polymer matrix. The crosslinking structure enhanced the electrical stability and decreased the NTC effect of the composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 394–401, 2004
Vanishing Flora – Lost Chemistry: The Scents of Endangered Plants around the World
Authors: Kaiser Roman 
Published: February 2004

AbstractAs part of our broad and ongoing evaluation of the olfactory components of fragrant plants and flowers during the past 25 years, we have encountered an astounding number of interestingly scented, but endangered plant species. In appreciation of nature's marvels in these species, we are compiling a report on their scent compositions and complementary information in an upcoming book ‘Vanishing Flora – Lost Chemistry’. In this paper, a few examples of endangered plant species and their scent components are presented as a brief introduction to the concept of the book project.
Non‐Nucleoside Reverse Transcriptase Inhibitors (NNRTIs): Past, Present, and Future
Authors: De Clercq Erik 
Published: February 2004

AbstractNon‐nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) have become an inherent ingredient of the drug combination schemes that are currently used in the treatment of human immunodeficiency virus type 1 (HIV‐1) infections. Starting from the 1‐[(2‐hydroxyethoxy)methyl]‐6‐(phenylsulfanyl)thymine (HEPT) and 4,5,6,7‐tetrahydroimidazo[4,5,1‐jk][1,4]benzodiazepin‐2(1H)‐one and ‐thione (TIBO) derivatives, numerous classes of compounds have been described as NNRTIs. Only three compounds have so far been approved for clinical use: nevirapine, delavirdine, and efavirenz. NNRTIs are notorious for rapidly leading to virus‐drug resistance development, primarily based on the emergence of the K103N and Y181C mutations in the HIV‐1 RT. Newer NNRTIs, such as capravirine, dapivirine (TMC 125), and DPC 083, are resilient to these ‘NNRTI’ mutations, and, therefore, offer considerable promise as future anti‐HIV‐1 drugs. NNRTIs are targeted at a specific ‘pocket’ binding site within the HIV‐1 RT, that is distinct from, but both spatially and functionally related to, the catalytic site, where the nucleoside RT inhibitors (NRTIs) and nucleotide RT inhibitors (NtRTIs) interact. NNRTIs have acquired a definitive position, as part of a combination regimen with NRTIs and NtRTIs, in the first‐line treatment of HIV‐1 infections.
The Importance of Being Exhaustive. Optimization of Bridging Structural Water Molecules and Water Networks in Models of Biological Systems
Authors: Kellogg Glen E. , Chen Deliang L. 
Published: February 2004

AbstractAlgorithms and protocols are described for the optimization for H‐bonding of isolated singular H2O molecules and entire networks of H2O molecules. Unlike other approaches that are prone to being trapped in local energy minima, these methods rely on exhaustive searches of orientation space for the H2O molecules. The results are scored with the HINT hydropathic interaction model, but the algorithms should be general for any energy‐scoring computation. Two examples are provided: 1) the tightly‐bound H2O molecule 301 of HIV‐1 protease is shown to be more reasonably oriented in terms of forming H‐bonds with this method than with a molecular mechanics energy minimization method; and 2) the H2O network surrounding carbonmonoxymyoglobin is constructed and analyzed for a 1.80‐Å neutron‐diffraction structure. The H‐atom positions calculated with this method show a somewhat better agreement with the experimental results than do the H‐atom positions calculated with molecular mechanics, and both are considerably better than random.
Quadricyclane Radical Cation Rearrangements: A Computational Study of the Transformations to 1,3,5‐Cycloheptatriene and Norbornadiene
Authors: Larsson Per‐Erik , Salhi‐Benachenhou Nessima , Lunell Sten 
Published: February 2004

AbstractAn alternative skeletal rearrangement of the quadricyclane radical cation (Q.+) explains the side products formed in the one‐electron oxidation to norbornadiene. First, the bicyclo[2.2.1]hepta‐2‐ene‐5‐yl‐7‐ylium radical cation, with an activation energy of 14.9 kcal mol−1, is formed. Second, this species can further rearrange to 1,3,5‐cycloheptatriene through two plausible paths, that is, a multistep mechanism with two shallow intermediates and a stepwise path in which the bicyclo[3.2.0]hepta‐2,6‐diene radical cation is an intermediate. The multistep rearrangement has a rate‐limiting step with an estimated activation energy of 16.5 kcal mol−1, which is 2.8 kcal mol−1 lower in energy than the stepwise mechanism. However, the lowest activation energy is found for the Q.+ cycloreversion to norbornadiene that has a transition structure, in close correspondence with earlier studies, and an activation energy of 10.1 kcal mol−1, which agrees well with the experimental estimate of 9.3 kcal mol−1. The computational estimates of activation energies were done using the CCSD(T)/6–311+G(d,p) method with geometries optimized on the B3LYP/6–311+G(d,p) level, combined with B3LYP/6–311+G(d,p) frequencies.
First Investigation of Non‐Classical Dihydrogen Bonding between an Early Transition‐Metal Hydride and Alcohols: IR, NMR, and DFT Approach
Authors: Bakhmutova Ekaterina V. , Bakhmutov Vladimir I. , Belkova Natalia V. , Besora Maria , Epstein Lina M. , Lledós Agustí , Nikonov Georgii I. , Shubina Elena S. , Tomàs Jaume , Vorontsov Eugenii V. 
Published: February 2004

AbstractThe interaction of [NbCp2H3] with fluorinated alcohols to give dihydrogen‐bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200–295 K, affording a clear picture of dihydrogen‐bond formation when [NbCp2H3]/HORf mixtures (HORf = hexafluoroisopropanol (HFIP) or perfluoro‐tert‐butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen‐bond energetics were determined to be 4.5±0.3 kcal mol−1 for TFE (TFE = trifluoroethanol) and 5.7±0.3 kcal mol−1 for HFIP. 1H NMR studies of solutions of [NbCp2H${{{\rm B}\hfill \atop 2\hfill}}$HA] and HFIP in [D8]toluene revealed high‐field shifts of the hydrides HA and HB, characteristic of dihydrogen‐bond formation, upon addition of alcohol. The magnitude of signal shifts and T1 relaxation time measurements show preferential coordination of the alcohol to the central hydride HA, but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride–proton distances based on T1 data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp2H3] with a series of non‐fluorinated (MeOH, CH3COOH) and fluorinated (CF3OH, TFE, HFIP, PFTB and CF3COOH) proton donors of different strengths showed dihydrogen‐bond formation, with binding energies ranging from −5.7 to −12.3 kcal mol−1, depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp2H3], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H3O+, the proton transfer occurs without any barrier, and no dihydrogen‐bonded intermediates are found. Proton transfer to [NbCp2H3] gives bis(dihydrogen) [NbCp2(η2‐H2)2]+ and dihydride(dihydrogen) complexes [NbCp2(H)2(η2‐H2)]+ (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen‐bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp2(η2‐H2)2]+ and the homoconjugated anion pair (CF3COO⋅⋅⋅ H⋅⋅⋅OOCCF3)− was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies.
Supramolecular Control of Charge‐Transfer Dynamics on Dye‐sensitized Nanocrystalline TiO2 Films
Authors: Hirata Narukuni , Lagref Jean‐Jacques , Palomares Emilio J. , Durrant James R. , Nazeeruddin M. Khaja , Gratzel Michael , Di Censo Davide 
Published: February 2004

AbstractA [Ru(dcbpy)2(NCS)2] dye has been chemically modified by the addition of a secondary electron donor moiety, N,N‐(di‐p‐anisylamino)phenoxymethyl. Optical excitation of the modified dye adsorbed to nanocrystalline TiO2 films shows a remarkably long‐lived charge‐separated state, with a decay half time of 0.7 s. Semiempirical calculations confirm that the HOMO of the modified dye molecule is localised on the electron donor group. The retardation of the recombination dynamics relative to the unmodified control dye is caused by the increase in the spatial separation of the HOMO orbital from the TiO2 surface. The magnitude of the retardation is shown to be in agreement with that predicted from the non‐adiabatic electron‐tunnelling theory.
A New Family of Dinuclear Rhodium Complexes Containing Tertiary Phosphanes in a Semibridging or Doubly Bridging Bonding Mode
Authors: Pechmann Thomas , Brandt Carsten D. , Werner Helmut 
Published: February 2004

AbstractThe reactions of [Rh2Cl(κ2‐acac)(μ‐CPh2)2(μ‐SbiPr3)] (3) and [Rh2(κ2‐acac)2(μ‐CPh2)2(μ‐SbiPr3)] (4) with PMe3 lead to exchange of the bridging ligand and afford the novel PMe3‐bridged counterparts 5 and 6, in which the phosphane occupies a semibridging (5) or a doubly bridging (6) position. In both cases, the bonding mode was confirmed crystallographically. Treatment of 6 with CO causes a shift of PMe3 from a bridging to a terminal position and gives the unsymmetrical complex [(κ2‐acac)Rh(μ‐CPh2)2(μ‐CO)Rh(PMe3)(κ2‐acac)] (7). Similarly to 5 and 6, the related compounds 10 and 11 with one or two acac‐f3 ligands were prepared. While both PEt3 and PnBu3 react with 3 by exchange of the bridging stibane for phosphane to give compounds 12 and 13, the reactions of 4 with PMePh2 and PnBu3 afford the mixed‐valent Rh0RhII complexes [(PR3)Rh(μ‐CPh2)2Rh(κ2‐acac)2] (17, 18) in high yields. In contrast, treatment of 4 with PEt3 and PMe2Ph generates the phosphane‐bridged compounds [Rh2(κ2‐acac)2(μ‐CPh2)2(μ‐PR3)] (14, 15) exclusively. Stirring a solution of 14 (R=Et) in benzene for 15 h at room temperature leads to complete conversion to the mixed‐valent isomer 16. The reaction of 6 with an equimolar amount of CR3CO2H (R=F, H) or phenol in the molar ratio of 1:10 results in substitution of one acac by one trifluoracetate, acetate, or phenolate ligand without disturbing the [Rh2(μ‐CPh2)2(μ‐PR3)] core. From 6 and an excess of CR3CO2H, the symmetrical bis(trifluoracetato) and bis(acetate) derivatives [Rh2(κ2‐O2CCR3)2(μ‐CPh2)2(μ‐PMe3)] (21, 22) were obtained.
Exacerbated Th2‐mediated airway inflammation and hyperresponsiveness in autoimmune diabetes‐prone NOD mice: a critical role for CD1d‐dependent NKT cells
Authors: Araujo Luiza M. , Lefort Jean , Nahori Marie‐Anne , Diem Séverine , Zhu Ren , Dy Michel , Leite‐de‐Moraes Maria C. , Bach J. F. , Vargaftig B. Boris , Herbelin André 
Published: February 2004

AbstractThe NOD mouse has proved to be a relevant model of insulin‐dependent diabetes mellitus, closely resembling the human disease. However, it is unknown whether this strain presents a general biastoward Th1‐mediated autoimmunity or remains capable of mounting complete Th2‐mediated responses. Here, we show that NOD mice have the capacity to develop a typical Th2‐mediated disease, namely experimental allergic asthma. In contrast to what might have been expected, they even developed a stronger Th2‐mediated pulmonary inflammatory response than BALB/c mice, a strain that shows a typical Th2 bias in this model. Thus, after allergen sensitization and intra‐nasal challenge, the typical features of experimental asthma were exacerbated in NOD mice, including enhanced bronchopulmonary responsiveness, mucus production and eosinophilic inflammation in the lungs as well as specific IgE titers in serum. These hallmarks of allergic asthma were associated with increased IL‐4, IL‐5, IL‐13 and eotaxin production in the lungs, as compared with BALB/c mice. Notwithstanding their quantitative and functional defect in NOD mice, CD1d‐dependent NKT cells contribute to aggravate the disease, since in OVA‐immunized CD1d–/– NOD mice, which are deficient in this particular T cell subset, airway eosinophilia was clearly diminished relative to NOD littermates. This is the first evidence that autoimmune diabetes‐prone NOD mice can also give rise to enhanced Th2‐mediated responses and might thus provide a useful model for the study of common genetic and cellular components, including NKT cells that contribute to both asthma and type 1 diabetes.
Alloreactive CD4 T lymphocytes responsible for acute and chronic graft‐versus‐host disease are contained within the CD45RChigh but not the CD45RClow subset
Authors: Xystrakis Emmanuel , Bernard Isabelle , Dejean Anne S. , Alsaati Talal , Druet Philippe , Saoudi Abdelhadi 
Published: February 2004

AbstractGraft‐versus‐host disease (GvHD) is a major complication of allogeneic bone marrow transplantation and occurs when donor T cells react with histo‐incompatible recipient's antigens. In thepresent study, we analyzed the contribution of CD4 T cell subsets, defined according to their CD45RC expression level, in the development of acute and chronic GvHD. For this purpose, we used the model of GvHD induced in rats when parental lymphocytes are transferred to irradiated (LEW×BN) F1 hybrid recipients. We showed that parental CD45RChigh (naive cells) CD4 T cells induced both acute and chronic GvHD while CD45RClow (memory cells) subset did not. In vitro, only CD45RChigh CD4 T cells proliferated and produced cytokines in response to alloantigen stimulation. LEW and BN CD45RChigh CD4 T cells produced different cytokine profiles in response to in vitro allostimulation, which could explain their ability to induce different forms of GvHD. Finally, we showed that memory CD45RClow CD4 T cells, known to contain regulatory T cells, were unable to prevent GvHD induction. Together these data show that memory CD45RClow CD4 T cells do not contain functional alloreactive T cells and suggest that selective transfusion of donor memory cells could greatly improve post‐transplant immune reconstitution without riskof GvHD induction.
Regulation of autoimmune diabetes by non‐islet‐specific T cells — a role for the glucocorticoid‐induced TNF receptor
Authors: Suri Anish , Shimizu Jun , Katz Jonathan D. , Sakaguchi Shimon , Unanue Emil R. , Kanagawa Osami 
Published: February 2004

AbstractDiabetogenic BDC2.5 CD4 T cells induce diabetes when injected into NOD.scid mice. However, when co‐transferred with the OVA‐specific DO11.10 CD4 T cells, BDC2.5 T cells failed to cause diabetes. This inhibition depended upon the stimulation of DO11.10 T cells only with soluble OVA, which skewed their differentiation to a Th2‐type pattern of cytokine secretion in vivo. However, in vivo neutralization of IL‐4, IL‐10 or TGF‐β using monoclonal antibodies did not prevent the inhibition whereas treatment with an antibody against the glucocorticoid‐induced TNF receptor abrogated the protection from disease. In the protected mice, the diabetogenic T cells could be isolated from their spleens and shown to transfer diabetes when injected into new NOD.scid recipients. Thus, the inhibition took place without the physical or functional elimination of the diabetogenic T cells.
Solvent‐Dependent Competitive Rearrangements of Cyclic Tertiary Propargylamine N‐Oxides
Authors: Szabó Anna , Galambos‐Faragó Ágnes , Mucsi Zoltán , Timári Géza , Vasvári‐Debreczy Lelle , Hermecz István 
Published: February 2004

AbstractIn protic media, cyclic propargylamine N‐oxides 1 undergo solvent‐dependent competitive rearrangements leading to enamino aldehydes 5, acrylamides 3, and secondary amines 4. The ratios of the products are evaluated and the possible mechanism of the competing reactions is interpreted by reaction kinetics studies and ab initio calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Sunfish Amphiphiles: Conceptually New Carriers for DNA Delivery
Authors: Hulst Ron , Muizebelt Inouk , Oosting Peter , van der Pol Cornelia , Wagenaar Anno , Šmisterová Jarmila , Bulten Erna , Driessen Cecile , Hoekstra Dick , Engberts Jan B. F. N. 
Published: February 2004

AbstractA conceptually new class of cationic amphiphiles, Sunfish amphiphiles, designed for the delivery of genes into cells is introduced. Sunfish amphiphiles have two hydrophobic tails, connected at the 4‐ and the N‐position to the cationic pyridinium headgroup. Two extreme morphologies visualised by backfolding and combining of both tails at one site (matching situation) or unfolding of the tails at distinct interaction sites at biological membranes will lead to considerable differences in morphological behaviour. The underlying rationale allows controlled release by using this morphological alteration of the Sunfish/helper‐lipid/DNA complex (lipoplex). The often‐excellent transfection efficiencies are probably related to these morphological changes. In addition, the Sunfish amphiphiles possess low toxicities, resulting in high cell survival after internalisation. The underlying rationale, design, synthesis and in vitro transfection potential are discussed in detail. Moreover, some physico‐chemical characteristics of the Sunfish amphiphiles have been studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)