bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Theoretical Study of the Photophysics and Structures of Europium Cryptates Incorporating 3,3′‐Bi‐isoquinoline‐2,2′‐dioxide
Authors: Gawryszewska Paula , Malta Oscar L. , Longo Ricardo L. , Goncalves e Silva Fabiana R. , Alves Severino , Mierzwicki Krzysztof , Latajka Zbigniew , Pietraszkiewicz Marek , Legendziewicz Janina 
Published: October 2004

AbstractA detailed photophysical study of [Eu⊂(biqO2.2.2)(CF3SO3)](CF3SO3)2⋅CH3CN⋅H2O (Eu⊂1) and two other types of cryptates incorporating three 3,3′‐biisoquinoline‐2,2′‐dioxide units has been performed. Structural crystallographic data of Eu⊂1, electronic structure calculations and theoretical models were used to obtain the intramolecular energy transfer rates and the appropriate set of rate equations, which was solved numerically. Quantum yields and decay lifetimes were obtained from these results and compared to the experimental data. The role of the ligand‐to‐metal charge transfer (LMCT) states was ascertained. A theoretical ligand field and intensity analysis was carried out and the results agree very well with the emission spectra. The molecular structures of the lanthanide cryptates were successfully modelled by the YIII ion using the restricted Hartree–Fock (RHF) method, with the advantage of dealing with closed‐shell systems. These molecular structures were used to explain the drastic differences in the photophysics of the three EuIII cryptates.
Azulene‐to‐Naphthalene Rearrangement: The Car–Parrinello Metadynamics Method Explores Various Reaction Mechanisms
Authors: Stirling András , Iannuzzi Marcella , Laio Alessandro , Parrinello Michele 
Published: October 2004

AbstractWe studied the thermal intramolecular and radical rearrangement of azulene to naphthalene by employing a novel metadynamics method based on Car–Parrinello molecular dynamics. We demonstrate that relatively short simulations can provide us with several possible reaction mechanisms for the rearrangement. We show that different choices of the collective coordinates can steer the reaction along different pathways, thus offering the possibility of choosing the most probable mechanism. We consider herein three intramolecular mechanisms and two radical pathways. We found the norcaradiene pathway to be the preferable intramolecular mechanism, whereas the spiran mechanism is the favored radical route. We obtained high activation energies for all the intramolecular pathways (81.5–98.6 kcal mol−1), whereas the radical routes have activation energies of 24–39 kcal mol−1. The calculations have also resulted in elementary steps and intermediates not yet considered. A few attractive features of the metadynamics method in studying chemical reactions are pointed out.
Pulsed‐Laser Production and Detection of Spin‐Polarized Hydrogen Atoms
Authors: Rakitzis* T. Peter 
Published: October 2004

AbstractSpin‐polarized hydrogen (SPH) atoms have traditionally been produced and detected using complex experimental methods with poor time resolution. Recently, SPH has been produced by pulsed‐laser photodissociation of HCl using circularly polarized light. In combination with the proposed detection of SPH via polarized fluorescence, this approach should allow the production and spatially resolved detection of SPH with a higher sensitivity than that currently available, and with a time resolution in the nanosecond regime. This represents an improvement of several orders of magnitude over the existing methods.
Visual Observation of Contact‐Induced Intercrystalline Migration of Aromatic Species Adsorbed in Zeolites by Fluorescence Microscopy
Authors: Hashimoto Shuichi , Yamashita Shinji 
Published: October 2004

AbstractIntercrystalline migration and a migration‐assisted chemical reaction of adsorbed aromatic species between zeolite particles in physical contact were visualized by fluorescence microscopy coupled with a particle manipulation technique. The luminescence color characteristics of particular zeolite particles originating from the specific photochemistry of adsorbed species was exploited to follow the migration of the molecules. Two examples are shown that are relevant to the visualization of the time‐dependent migration process: A one guest–two sets of zeolite crystals system: chrysene (Chry)‐loaded zeolite Na+‐X (the sodium form of zeolite X) crystals were placed in contact with unloaded Tl+‐X (thallium‐exchanged X) crystals and allowed to stand at room temperature. Initially, the blue fluorescence of Chry was detected only from the Na+‐X particles, but later, the development of green phosphorescence emission was discernible from the Tl+‐X, which suggests that Chry migrated from the Na+‐X to the Tl+‐X crystals. A two guest‐species systems: Electron‐donating Chry‐loaded Na+‐X crystals were placed in contact with electron‐accepting 1,2,4,5‐tetracyanobenzene (TCNB)‐loaded Na+‐X or Na+‐Y crystals. With time, the former system (Chry/Na+‐X and TCNB/Na+‐X) gave rise to the emission of Chry‐TCNB charge‐transfer complexes resulting mainly from the migration of Chry while the latter system (Chry/Na+‐X and TCNB/Na+‐Y) afforded the same emission resulting largely from the migration of TCNB. The present investigation reveals that there is a certain direction for guest migration depending on the zeolite host and the nature of host–guest or guest–guest interaction.
Accurate pKa Determination for a Heterogeneous Group of Organic Molecules
Authors: Schmidt am Busch Marcel , Knapp Ernst‐Walter 
Published: October 2004

AbstractSingle‐molecule studies that allow to compute pKa values, proton affinities (gas‐phase acidity/basicity) and the electrostatic energy of solvation have been performed for a heterogeneous set of 26 organic compounds. Quantum mechanical density functional theory (DFT) using the Becke‐half&half and B3 LYP functionals on optimized molecular geometries have been carried out to investigate the energetics of gas‐phase protonation. The electrostatic contribution to the solvation energies of protonated and deprotonated compounds were calculated by solving the Poisson equation using atomic charges generated by fitting the electrostatic potential derived from the molecular wave functions in vacuum. The combination of gas‐phase and electrostatic solvation energies by means of the thermodynamic cycle enabled us to compute pKa values for the 26 compounds, which cover six distinct chemical groups (carboxylic acids, benzoic acids, phenols, imides, pyridines and imidazoles). The computational procedure for determining pKa values is accurate and transferable with a root‐mean‐square deviation of 0.53 and 0.57 pKa units and a maximum error of 1.0 pKa and 1.3 pKa units for Becke‐half&half and B3 LYP DFT functionals, respectively.
Photon Counting Histogram: One‐Photon Excitation
Authors: Huang Bo , Perroud Thomas D. , Zare Richard N. 
Published: October 2004

AbstractThe photon counting histogram (PCH) analysis is a fluorescence fluctuation method that is able to characterize the brightness and concentration of different fluorescent species present in a liquid sample. We find that the PCH model using a three‐dimensional Gaussian observation volume profile is inadequate for fitting experimental data obtained from a confocal setup with one‐photon excitation. We propose an improved model, which is based on the correction to the observation volume profile for the out‐of‐focus emission. We demonstrate that this model is able to resolve different species present under a wide range of conditions. Attention is given to how this model allows the examination of the effects of different instrumental setups on the resolvability.
On the Quantum Nature of an Excess Proton in Liquid Hydrogen Fluoride
Authors: Raugei Simone , Klein Michael L. 
Published: October 2004

AbstractLiquid hydrogen fluoride consists of chains of hydrogen‐bonded molecules. The nature of an excess proton in liquid HF, which is of interest not only for its own sake, but also in relation to superacid chemistry and to its behavior in water, has been studied using computer simulations. The methodology employed is the density‐functional‐theory‐based path‐integral Car–Parrinello ab initio molecular dynamics. The excess proton, which formally exists as a H2F+ or a H2F2+ defect in an HF chain, is found to strongly perturb the chain to which it is attached. Moreover, due to large zero‐point energy, the charge defect is largely delocalized over several HF molecules.
Suppressive properties of human CD4+CD25+ regulatory T cells are dependent on CTLA‐4 expression
Authors: Birebent Brigitte , Lorho Richard , Lechartier Hélène , de Guibert Sophie , Alizadeh Mehdi , Vu Nicolas , Beauplet Alain , Robillard Nelly , Semana Gilbert 
Published: October 2004

AbstractIt has been demonstrated that T cells with regulatory properties are present within the peripheral blood CD4+CD25+ T cell compartment. Here, we describe an original method to purify human CD4+CD25+CD152+ T lymphocytes as living cells by forcing the exportation of CTLA‐4 molecules stored in intracellular vesicules at the cell surface. By doing so, we demonstrate that CD4+CD25+ T cells contain a smaller and more homogeneous population enriched in cells with in vitro regulatory activity. Moreover, we show that this enrichment in regulatory T cells is associated with an increased expression of Foxp3 and that CD4+CD25+CD152+ T lymphocytes display a much stronger suppressive activity in controlling in vitro proliferation of alloantigen‐specific T cells than CD4+CD25+CD152– T lymphocytes purified in parallel. Lastly, by purifying such cells expressing CTLA‐4, we demonstrate that indeed CTLA‐4 is involved in CD4+CD25+CD152+ T cell regulatory activity, while suppressive cytokines are not.
Paradoxical role of programmed death‐1 ligand 2 in Th2 immune responses in vitro and in a mouse asthma model in vivo
Authors: Oflazoglu Ezogelin , Swart David A. , Anders‐Bartholo Penny , Jessup Heidi K. , Norment Anne M. , Lawrence William A. , Brasel Kenneth , Tocker Joel E. , Horan Tom , Welcher Andrew A. , Fitzpatrick David R. 
Published: October 2004

AbstractProgrammed death‐1 ligand 2 (PD‐L2) is a ligand for programmed death‐1 (PD‐1), a receptor that plays an inhibitory role in T cell activation. Since previous studies have shown up‐regulation of PD‐L2 expression by Th2 cytokines, and asthma is driven by a Th2 response, we hypothesized that PD‐L2 might be involved in regulation of the immune response in this disease. We have found that lungs from asthmatic mice had sustained up‐regulation of PD‐1 and PD‐L2, with PD‐L2 primarily on dendritic cells. Although addition of PD‐L2‐Fc in vitro led to decreased T cell proliferation and cytokine production, administration of PD‐L2‐Fc in vivo in a mouse asthma model resulted in elevated serum IgE levels, increased eosinophilic and lymphocytic infiltration into bronchoalveolar lavage fluid, higher number of cells in the draining lymph nodes, and production of IL‐5 and IL‐13 from these cells. Although PD‐1 was expressed on regulatory T cells, PD‐L2‐Fc did not affect regulatory T cell activity in vitro. This study provides in vivo evidence of an exacerbated inflammatory response following PD‐L2‐Fc administration and indicates a potential role for this molecule in Th2‐mediated diseases such as asthma.
Prostaglandin E2 modulates the functional responsiveness of human monocytes to chemokines
Authors: Panzer Ulf , Uguccioni Mariagrazia 
Published: October 2004

AbstractProstaglandin E2 (PGE2) plays an important role in the immune response by modulating the complex interactions between leukocytes and tissue cells under inflammatory conditions. PGE2 may possibly influence pro‐inflammatory effects of chemokines and chemokine receptors that are among the main regulators of directional leukocyte migration. We analyzed whether PGE2 affects chemokine receptor expression on human monocytes and their functional responsiveness to inflammatory chemokines. Expression of CCR5 on monocytes was significantly reduced, whereas CCR2 and CXCR4 expression were not affected by PGE2. However, PGE2 treatment significantly increased the chemotactic response of monocytes to monocyte‐chemoattractant protein‐1 (MCP‐1), RANTES and stromal cell‐derived factor‐1 (SDF‐1). In addition, PGE2 induced a higher calcium mobilization and actin polymerization upon chemokine stimulation. To better characterize PGE2 effects, we used specific agonists for the PGE2 receptors (EP1 – EP4) characterized so far. The 11‐deoxy PGE1, an EP2 /EP4 ligand, could mimic the effects observed using PGE2. In contrast, the EP1 agonist, sulprostone, had not effects on monocytes, indicating that the effects of PGE2 are mediated by EP2/EP4 receptors. Monocytes acquire a higher functional responsiveness to MCP‐1, RANTES and SDF‐1 after exposure to PGE2, independently of the level of chemokine receptor expression. This mechanism might enhance the local monocyte recruitment under inflammatory conditions, and suggests specific PGE2 receptor EP2/EP4 antagonists as novel agents for the treatment of inflammatory diseases.
Frontline: Peripheral priming of alloreactive T cells by the direct pathway of allorecognition
Authors: Baratin Myriam , Bonin Karina , Daniel Claude 
Published: October 2004

AbstractRecent studies, though controversial, have suggested that secondary lymphoid organs may not constitute an essential site for the initiation of immune responses to transplant antigens. However, this issue has never been examined in the context of direct and indirect allorecognition. Here, we characterized immune responses arising in draining lymph nodes and skin allografts, in a murine model based on a single T cell clonotype where these two pathways can be independently studied. In this model, graft rejection by the direct or the indirect pathway occurred with similar kinetics, although initiation of the alloreactive responses was clearly different. During indirect responses, expansion and activation of alloreactive T cells were first observed in draining lymph nodes, at day 7 post‐transplant, and graft‐infiltrating T cells were observed later, at day 11. In striking contrast, directly activated alloreactive T cells were detected at an early stage inside the graft, and only later in the draining lymph nodes, after skin allograft rejection was almost completed. These results suggest that sensitization of naive T cells through the direct pathway could take place outside secondary lymphoid organs.See accompanying Commentary: http://dx.doi.org/10.1002/eji.200425506
Phenotypic heterogeneity of antigen‐specific CD4 T cells under different conditions of antigen persistence and antigen load
Authors: Harari Alexandre , Vallelian Florence , Pantaleo Giuseppe 
Published: October 2004

AbstractThe factors responsible for the phenotypic heterogeneity of memory CD4 T cells are unclear. In the present study, we have identified a third population of memory CD4 T cells characterized as CD45RA+CCR7– that, based on its replication history and the homeostatic proliferative capacity, was at an advanced stage of differentiation. Three different phenotypic patterns of memory CD4 T cell responses were delineated under different conditions of antigen (Ag) persistence and load using CD45RA and CCR7 as markers of memory T cells. Mono‐phenotypic CD45RA–CCR7+ or CD45RA–CCR7– CD4 T cell responses were associated with conditions of Ag clearance (tetanus toxoid‐specific CD4 T cell response) or Ag persistence and high load (chronic HIV‐1 and primary CMV infections), respectively. Multi‐phenotypic CD45RA–CCR7+, CD45RA–CCR7– and CD45RA+CCR7– CD4 T cell responses were associated with protracted Ag exposure and low load (chronic CMV, EBV and HSV infections and HIV‐1 infection in long‐term nonprogressors). The mono‐phenotypic CD45RA–CCR7+ response was typical of central memory (TCM) IL‐2‐secreting CD4 T cells, the mono‐phenotypic CD45RA–CCR7– response of effector memory (TEM) IFN‐γ‐secreting CD4 T cells and the multi‐phenotypic response of both IL‐2‐ and IFN‐γ‐secreting cells. The present results indicate that the heterogeneity of different Ag‐specific CD4 T cell responses is regulated by Ag exposure and Ag load.
Nuclear repositioning marks the selective exclusion of lineage‐inappropriate transcription factor loci during T helper cell differentiation
Authors: Hewitt Susannah L. , High Frances A. , Reiner Steven L. , Fisher Amanda G. , Merkenschlager Matthias 
Published: October 2004

AbstractTo address how heritable patterns of gene expression are acquired during the differentiation of Th1 and Th2 cells, we analyzed the nuclear position of lineage‐restricted cytokine genes and their upstream regulators by 3‐dimensional fluorescence in situ hybridization. During Th1 differentiation, GATA‐3 and c‐maf loci, which encode upstream regulators of Th2 cytokines, were progressively repositioned to centromeric heterochromatin as defined by a γ‐satellite repeat probe and/or the nuclear periphery, compartments that have been associated with transcriptional repression. A third transcription factor locus, T‐bet, which controls Th1‐specific programs, was subject to de novo CpG methylation in a Th2 cell clone. In contrast, we did not find repositioning of the cytokine gene loci IL‐2, IL‐3, IL‐4 or IFN‐γ during T helper cell differentiation. Instead, IFN‐γ was constitutively associated with the nuclear periphery, even when primed for expression in Th1 cells. Our results suggest that Th1/Th2 lineage commitment and differentiation involve repositioning of the regulators of cytokine expression, rather than the cytokine genes themselves.
Commentary: Priming of alloreactive T cells – where does it happen?
Authors: Golshayan Dela , Lechler Robert 
Published: October 2004

AbstractHost lymphocytes can recognize alloantigens directly on transplanted donor tissue or indirectly after these antigens are processed and presented on host APC. Here, we outline the features of alloresponses that distinguish them from responses to conventional antigens, then we discuss various study systems that have examined where the priming of alloreactive CD4+ and CD8+ T cells occurs. Finally, we discuss the implications of recent data which suggest that direct responses originate in the graft itself whereas indirect responses are initiated in the draining lymph nodes.See accompanying article: http://dx.doi.org/10.1002/eji.200425309
Synthesis, Molecular Structure, and Olefin Polymerisation Activity of an Oxovanadium(V) Alkoxide with Unprecedented Chloride Bridging Ligands
Authors: Rosenthal Esther C. E. , Cui Huiling , Lange Katharina C. H. , Dechert Sebastian 
Published: October 2004

AbstractThe reaction of 2‐methoxyethanol or (2‐methoxyethanolato)lithium with VOCl3 yields the chloro‐bridged dinuclear complex [VOCl2(OCH2CH2OCH3)]2, which has been characterised spectroscopically and structurally by single‐crystal X‐ray diffraction analysis. This is the first reported structure of a neutral dinuclear oxovanadium complex connected by bridging chloro ligands. The orange complex is a precatalyst for the polymerisation of ethene and the oligomerisation of styrene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Fluorescent Self‐Assembled Monolayers of Bis(salicylaldiminato)zinc(II) Schiff‐Base Complexes
Authors: Di Bella Santo , Leonardi Nicoletta , Consiglio Giuseppe , Sortino Salvatore , Fragalà Ignazio 
Published: October 2004

AbstractThe synthesis and fluorescence properties of novel bis(salicylaldiminato)zinc(II) Schiff‐base complexes is reported. Selfassembled monolayers (SAMs) of these complexes are obtained by reaction of coupling layers, functionalized quartz substrates and a derivatized precursor complex. A comparison between the integrated emission intensity of the SAM films and that of a suitable model compound in solution indicates molecular fluorescence retention of the ZnII Schiff bases on going from the solution phase to the monolayer. This is consistent with the absence of significant self‐quenching processes, as expected on the basis of the relatively high estimated surface coverage. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Acid‐Base Self‐Assembly Chemistry and Hydrogen Bonding Interactions Resulting in the Formation of a Tetranuclear Aggregate Containing Four Crystallographically Non‐Equivalent FeIII Centers
Authors: Tanase Stefania , Bouwman Elisabeth , Long Gary J. , Shahin Ahmed M. , Mills Allison M. , Spek Anthony L. , Reedijk Jan 
Published: October 2004

AbstractThe synthesis and characterization of a mononuclear iron(III) complex [Fe(Hphpz)Cl(CH3OH)] (1) and a tetranuclear assembly of a bis(μ‐hydroxo)‐bridged dinuclear iron(III) complex [{Fe(Hphpz)2(OH)}2][Fe(Hphpz)3]2 (2) with the ligand 3(5)‐methyl‐5(3)‐(2‐hydroxyphenyl)pyrazole (H2phpz) is reported. Compound 1 is converted into 2 in a methanol solution and in the presence of a base. The asymmetric unit of 2 consists of two independent [Fe(Hphpz)3] molecules and one dinuclear complex [Fe(Hphpz)2(OH)]2 containing two crystallographically non‐equivalent iron(III) ions; the three units are linked by N−H···O and O−H···O hydrogen bonding and stacking interactions to form a cluster with an approximate C2‐symmetry. The Mössbauer spectra of [{Fe(Hphpz)2(OH)}2][Fe(phpz)3]2 have been measured at 295 and 78 K and indicate the presence of four crystallographically distinct, but chemically similar iron(III) sites. The magnetic properties of this compound originate from the weak antiferromagnetic interaction between the FeIII ions of the [Fe(phpz)2(OH)]2 dimer (J = −2.8 cm−1). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The General Rule of Power Converted from Chemical Energy to Electrical Energy
Authors: Shen M. , Zhang J. , Scott K. 
Published: October 2004

AbstractElectrochemical power sources are widely used to convert chemical energy to electrical energy. Here we report an equation to describe the electrical power characteristics i.e., potential vs. the current performance curves, namely polarization curves of electrochemical power sources. From this basic equation, we describe the performance curve of general electrochemical power sources with three power source parameters: E0: equilibrium potential; R: internal resistance; and K: power conversion coefficient. The calculated values from this equation agree with the performance curves of power sources such as different type of fuel cells and batteries. The concept of the power convert coefficient is a new criterion to evaluate and compare the characteristics and capacity of different electrochemical power sources.
Activation of Colloidal PtRu Fuel Cell Catalysts via a Thermal “Conditioning Process”
Authors: Bönnemann H. , Endruschat U. , Hormes J. , Köhl G. , Kruse S. , Modrow H. , Mörtel R. , Nagabhushana K. S. 
Published: October 2004

AbstractThe activation of platinum‐ruthenium (Pt‐Ru) fuel cell catalysts, which were made by supporting nanoscopic colloidal precursors on conductive carbon (Vulcan XC72) is brought about by reactive annealing (“conditioning process”) at 250–300 °C, in a particular set‐up. The tetraalkylammonium (A) or triorganoaluminium (B) protecting shell is cleaved from the Pt‐Ru metal surface in three mandatory steps under flowing argon, oxygen, and hydrogen (30 min each). Ex‐situ TEM micrographs were used to monitor changes in particle size during this conditioning process. Additionally, in‐situ X‐ray absorption spectroscopic measurements on the Pt LIII‐edge provided insight into the processes occurring in the metallic core of the particles. While a small increase in size is found with conditioning, the dominant structural change in both catalyst types (A and B) is a reduction in the disorder inside the metallic particles, particularly in those having organoaluminium‐protected nanoparticles (B). During oxidation under flowing oxygen, platinum atoms only undergo oxidation in the bimetallic Pt‐Ru catalyst type (B) while the platinum atoms in the bimetallic Pt‐Ru catalyst (A) remain strictly zerovalent. This difference may be attributed to differences in the internal structure of the as prepared colloidal particles (A and B) as evidenced from Pt LIII EXAFS‐data and XANES spectra.