bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential effects of equiaxial and uniaxial strain on mesenchymal stem cells
Authors: Park Jennifer S. , Chu Julia S.F. , Cheng Catherine , Chen Fanqing , Chen David , Li Song 
Published: October 2004

AbstractBone marrow mesenchymal stem cells (MSCs) can differentiate into a variety of cell types, including vascular smooth muscle cells (SMCs), and have tremendous potential as a cell source for cardiovascular regeneration. We postulate that specific vascular environmental factors will promote MSC differentiation into SMCs. However, the effects of the vascular mechanical environment on MSCs have not been characterized. Here we show that mechanical strain regulated the expression of SMC markers in MSCs. Cyclic equiaxial strain downregulated SM α‐actin and SM‐22α in MSCs on collagen‐ or elastin‐coated membranes after 1 day, and decreased α‐actin in stress fibers. In contrast, cyclic uniaxial strain transiently increased the expression of SM α‐actin and SM‐22α after 1 day, which subsequently returned to basal levels after the cells aligned in the direction perpendicular to the strain direction. In addition, uniaxial but not equiaxial strain induced a transient increase of collagen I expression. DNA microarray experiments showed that uniaxial strain increased SMC markers and regulated the expression of matrix molecules without significantly changing the expression of the differentiation markers (e.g., alkaline phosphatase and collagen II) of other cell types. Our results suggest that uniaxial strain, which better mimics the type of mechanical strain experienced by SMCs, may promote MSC differentiation into SMCs if cell orientation can be controlled. This study demonstrates the differential effects of equiaxial and uniaxial strain, advances our understanding of the mechanical regulation of stem cells, and provides a rational basis for engineering MSCs for vascular tissue engineering and regeneration. © 2004 Wiley Periodicals, Inc.
Microfabricated platform for studying stem cell fates
Authors: Chin Vicki I. , Taupin Philippe , Sanga Sandeep , Scheel John , Gage Fred H. , Bhatia Sangeeta N. 
Published: October 2004

AbstractPlatforms that allow parallel, quantitative analysis of single cells will be integral to realizing the potential of postgenomic biology. In stem cell biology, the study of clonal stem cells in multiwell formats is currently both inefficient and time‐consuming. Thus, to investigate low‐frequency events of interest, large sample sizes must be interrogated. We report a simple, versatile, and efficient micropatterned arraying system conducive to the culture and dynamic monitoring of stem cell proliferation. This platform enables: 1) parallel, automated, long‐term (∼days to weeks), live‐cell microscopy of single cells in culture; 2) tracking of individual cell fates over time (proliferation, apoptosis); and 3) correlation of differentiated progeny with founder clones. To achieve these goals, we used microfabrication techniques to create an array of ∼10,000 microwells on a glass coverslip. The dimensions of the wells are tunable, ranging from 20 to >500 μm in diameter and 10–500 μm in height. The microarray can be coated with adhesive proteins and is integrated into a culture chamber that permits rapid (∼min), addressable monitoring of each well using a standard programmable microscope stage. All cells share the same media (including paracrine survival signals), as opposed to cells in multiwell formats. The incorporation of a coverslip as a substrate also renders the platform compatible with conventional, high‐magnification light and fluorescent microscopy. We validated this approach by analyzing the proliferation dynamics of a heterogeneous adult rat neural stem cell population. Using this platform, one can further interrogate the response of distinct stem cell subpopulations to microenvironmental cues (mitogens, cell–cell interactions, and cell–extracellular matrix interactions) that govern their behavior. In the future, the platform may also be adapted for the study of other cell types by tailoring the surface coatings, microwell dimensions, and culture environment, thereby enabling parallel investigation of many distinct cellular responses. © 2004 Wiley Periodicals, Inc.
Catalytic Photooxidation of 4‐Methoxybenzyl Alcohol with a Flavin–Zinc(II)‐Cyclen Complex
Authors: Cibulka Radek , Vasold Rudolf , König Burkhard 
Published: October 2004

AbstractFlavin–zinc(II)‐cyclen 10 contains a covalently linked substrate binding site (zinc(II)–cyclen) and a chromophore unit (flavin). Upon irradiation, compound 10 effectively oxidizes 4‐methoxybenzyl alcohol (11‐OCH3) to the corresponding benzaldehyde both in water and in acetonitrile. In the presence of air, the reduced flavin 10‐H2 is reoxidized, and so catalytic amounts of 10 are sufficient for alcohol conversion. The mechanism of oxidation is based on photoinduced electron transfer from the coordinated benzyl alcohol to the flavin chromophore. This intramolecular process provides a much higher photooxidation efficiency, with quantum yields 30 times those of the comparable intermolecular process with a flavin chromophore without a binding site. For the reaction in buffered aqueous solution a quantum yield of Φ = 0.4 is observed. The turnover number in acetonitrile is increased (up to 20) by high benzyl alcohol concentrations. The results show that the covalent combination of a chromophore and a suitable binding site may lead to photomediators more efficient than classical sensitizer molecules.
In Search of Ultrastrong Brønsted Neutral Organic Superacids: A DFT Study on Some Cyclopentadiene Derivatives
Authors: Vianello Robert , Liebman Joel F. , Maksić Zvonimir B. 
Published: October 2004

AbstractAn efficient but reasonably accurate B3LYP/6‐311+G(d,p)//B3LYP/6‐31G(d) computational procedure showed that pentasubstituted cyclopentadienes such as (CN)5C5H, (NO2)5C5H, and (NC)5C5H containing strongly electron‐withdrawing groups are neutral organic superacids of unprecedented strength. The boldface denotes the atom attached to the cyclopentadiene framework. All of them exhibit prototropic tautomerism by forming somewhat more stable structures with CNH, NO2H, and NCH exocyclic fragments, respectively. The acidity (ΔHacid) of these is lower, but only to a rather small extent. The ΔHacid enthalpies of these last three tautomers are estimated to be 271, 276, and 282 kcal mol−1, respectively. Hence, the most stable tautomers of (CN)5C5H and (NC)5C5H represent a legitimate target for synthetic chemists. On the other hand, (NO2)5C5H is less suitable for practical applications, because of its high energy density. The origin of the highly pronounced acidity of these compounds was analyzed by using the recently developed triadic formula. It is found that very high Koopmans' ionization energy (IE)${{{{\rm Koop}\hfill \atop n\hfill}}}$ of conjugate bases exerts a decisive influence on acidity. It follows as a corollary that the overwhelming effect leading to very high acidity is due to the properties of the final state. An alternative picture is offered by homodesmotic reactions, wherein the cyclic systems are compared with their linear counterparts. It is found that the acidity of cyclopentadiene (CP) is a consequence of aromatic stabilization in the CP− anion. The extreme acidity of pentacyanocyclopentadiene (CN)5C5H is due to aromatization of the five‐membered ring and a strong anionic resonance effect in the resultant conjugate base. The neutral organic superacids predicted by the present calculations may help to bridge the gap between existing very strong acids and bases.
Theoretical Studies of Aluminoxane Chains, Rings, Cages, and Nanostructures
Authors: Linnolahti Mikko , Luhtanen Tommi N. P. , Pakkanen Tapani A. 
Published: October 2004

AbstractAlumina nanostructures and three families of aluminoxanes, linear, cyclic, and cagelike structures, have structures that resemble their isovalent electronic hydrocarbon analogues. Specific examples of each family are the counterparts of fullerene, allene, benzene, and cubane, respectively. The aluminoxanes and alumina nanostructures are related to each other; the latter can be regarded as a hydrogen‐ or alkyl‐free form of aluminoxane. By exploiting this relationship, the relative stabilities of the three families of aluminoxanes, alumina nanostructures, and alumina crystal lattices have been estimated. According to ab initio calculations, aluminoxane cages, which take the form of a truncated octahedron and related polyhedra, are favored. The stability of the preferred cage, T‐symmetric Al28O28H28, is practically equal to that of the α‐alumina crystal lattice.
Characterization of Isolated Ga2 Molecules by Resonance Raman Spectroscopy and Variations of GaGa Bonding
Authors: Himmel Hans‐Jörg , Gaertner Benjamin 
Published: October 2004

AbstractIsolated Ga2 dimers were characterized in an argon matrix with the aid of resonance Raman and UV/Vis spectroscopy. The resonance Raman spectra gave evidence of not only the ν(GaGa) fundamental, but also four overtones. Each of the signals exhibits 69Ga/71Ga isotopic splitting leading to the triplet pattern characteristic of two equivalent Ga atoms. On the basis of the experimental data, a harmonic frequency and anharmonicity constant have been determined for Ga2. An estimate of the dissociation energy on the assumption of a Morse‐type potential energy curve results in a De value (upper limit) of about 145 kJ mol−1. The force constant (64.8±0.3 N m−1) and dissociation energy of Ga2 are compared with those of other diatomics and those of molecules featuring GaGa bonds.
Revision of the Dissociation Energies of Mercury Chalcogenides—Unusual Types of Mercury Bonding
Authors: Filatov Michael , Cremer Dieter 
Published: October 2004

AbstractMercury chalcogenides HgE (E=O, S, Se, etc.) are described in the literature to possess rather stable bonds with bond dissociation energies between 53 and 30 kcal mol−1, which is actually difficult to understand in view of the closed‐shell electron configuration of the Hg atom in its ground state (…︁4f145d106s2). Based on relativistically corrected many body perturbation theory and coupled‐cluster theory [IORAmm/MP4, Feenberg‐scaled IORAmm/MP4, IORAmm/CCSD(T)] in connection with IORAmm/B3LYP theory and a [17s14p9d5f]/aug‐cc‐pVTZ basis set, it is shown that the covalent HgE bond is rather weak (2–7 kcal mol−1), the ground state of HgE is a triplet rather than a singlet state, and that the experimental bond dissociation energies have been obtained for dimers (or mixtures of monomers, dimers, and even trimers) Hg2E2 rather than true monomers. The dimers possess association energies of more than 100 kcal mol−1 due to electrostatic forces between the monomer units. The covalent bond between Hg and E is in so far peculiar as it requires a charge transfer from Hg to E (depending on the electronegativity of E) for the creation of a single bond, which is supported by electrostatic forces. However, σ bonding between Hg and E is reduced by strong lone pair–lone pair repulsion to a couple of kcal mol−1. Since a triplet configuration possesses somewhat lower destabilizing lone pair energies, the triplet state is more stable. In the dimer, there is a HgHg π bond of bond order 0.66 without any σ support. Weak covalent Hg–O interactions are supported by electrostatic bonding. The results for the mercury chalcogenides suggests that all experimental dissociation energies for group‐12 chalcogenides have to be revised because of erroneous measurements.
The Jahn–Teller Effect of the TiIII Ion in Aqueous Solution: Extended Ab Initio QM/MM Molecular Dynamics Simulations
Authors: Kritayakornupong Chinapong , Plankensteiner Kristof , Rode Bernd M. 
Published: October 2004

AbstractCombined ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations, including only the first and the first and second hydration shells in the QM region, were performed for TiIII in aqueous solution. The hydration structure of TiIII is discussed in terms of radial distribution functions, coordination‐number distributions and several angle distributions. Dynamical properties, such as librational and vibrational motions and TiIIIO vibrations, were evaluated. A fast dynamical Jahn–Teller effect of TiIII(aq) was observed in the QM/MM simulations, in particular when the second hydration shell was included into the QM region. The results justify the computational effort required for the inclusion of the second hydration shell into the QM region and show the importance of this effort for obtaining accurate hydration‐shell geometries, dynamical properties, and details of the Jahn–Teller effect.
Two‐Photon Dissociation Spectroscopy of State‐Selected HCl+ and DCl+ Ions
Authors: Michel Michael , Weitzel Karl‐Michael 
Published: October 2004

AbstractHCl+ and DCl+ ions were formed via the R(1) pump line of the f3Δ2(v′=0)←1∑+(v′′=0) REMPI process. For these ions, the two‐photon dissociation spectroscopy, resonance‐enhanced via the A2∑+(v′)←2Π3/2(v′′=0) transition, was investigated for various intermediate states of HCl+ (v′=4,5,6) and DCl+ (v′=6, 7, 8, 9). From the analysis of the data, spectroscopic parameters of the X and the A states were derived (including the Λ‐doubling in the X state and the spin–rotation coupling in the A state). Some of the parameters deviate considerably from literature data. The spectra provide clear evidence that the REMPI process employed for forming the ions has a very high rotational selectivity.
Functional involvement of P‐selectin and MAdCAM‐1 in the recruitment of α4β7‐integrin‐expressing monocyte‐like cells to the pregnant mouse uterus
Authors: Fernekorn Uta , Butcher Eugene C. , Behrends Jochen , Hartz Sylvia , Kruse Andrea 
Published: October 2004

AbstractLeukocyte recruitment to the pregnant mouse uterus has been suggested to be associated with highly regulated expression of distinct patterns of vascular adhesion receptors. One of the most striking observations is the combined expression of mucosal addressin cell adhesion molecule‐1 (MAdCAM‐1) and P‐selectin by maternal vessels of the vascular zone during the critical period of initial placenta development. The predominant cell population within these vessels is of the monocyte/macrophage lineage and expresses the mucosal integrin α4β7, which represents the ligand for MAdCAM‐1; neutrophils and lymphocytes are rare. To directly assess the importance of identified adhesion receptors, we undertook long‐term in vivo inhibition studies using monoclonal antibodies to inhibit the contribution of MAdCAM‐1 in leukocyte trafficking to the decidua or to deplete α4β7+ leukocytes. In addition, implantation sites of mouse strains genetically deficient in specific adhesion receptors were investigated. Our results underline the importance of predicted adhesion pathways in the recruitment of monocyte‐like cells, especially those expressing α4β7. Interestingly, maternal/fetal units with inhibited recruitment of α4β7+ leukocytes or the absence of these cells are characterized by reduced size and frequency of uterine NK cells.
Homing of immature thymocytes to the subcapsular microenvironment within the thymus is not an absolute requirement for T cell development
Authors: Benz Claudia , Heinzel Kornelia , Bleul Conrad C. 
Published: October 2004

AbstractT cell development is thought to occur in distinct microenvironments within the thymus. Namely, the subcapsular zone, the cortex and the medulla have been described to support expansion of the immature thymocyte pool, positive selection of useful specificities and elimination of potentially self‐reactive specificities, respectively. Consistent with this model, thymocytes show a highly ordered migration pattern and move into these niches in the expected sequence. Here we show that the chemokine receptor CCR9 plays a nonredundant role in the homing of immature thymocytes to the subcapsular zone. In CCR9‐deficient mice, T cells in early stages of development do not accumulate in their physiological microenvironment underneath the thymic capsule and are instead homogeneously distributed across the thymic cortex. Remarkably, this abnormality does not result in a detectable defect in T cell development in CCR9‐deficient mice, suggesting that the transit of immature thymocytes through the subcapsular microenvironment is not an absolute requirement for proper T cell development.
Backbone Flexibility and Counterion Effects on the Structure and Thermal Properties of Di(thiourea)zinc Dicarboxylate Coordination Polymers
Authors: Burrows Andrew D. , Donovan Adele S. , Harrington Ross W. , Mahon Mary F. 
Published: October 2004

AbstractThe reaction between [Zn(tu)4]Cl2 and the appropriate sodium dicarboxylate has been shown to give the coordination polymers [Zn(tu)2(μ‐succinate)]n (7), [Zn(tu)2(μ‐itaconate)]n (8), [Zn(tu)2(μ‐ethylmalonate)]n (9), [Zn(tu)2(μ‐1,3‐phenylenediacetate)]n (10) and {[Zn(tu)2(μ‐mesaconate)]·2H2O}n (11), all of which have been crystallographically characterised. The crystal structures of 7−9 demonstrate that these compounds form helical structures in which the dicarboxylates adopt conformations with the relative positions of the carboxylate groups similar to those in constrained anions such as phthalate. The role of the chloride counterion in the starting material has been explored by investigating the reactions of [Zn(tu)4](NO3)2 with a range of dicarboxylates. Although in the majority of cases the counterion was shown to have no effect, in the case of fumarate, a hydrated coordination polymer {[Zn(tu)2(μ‐fumarate)]·2H2O}n (12) was observed in addition to the anhydrous product [Zn(tu)2(μ‐fumarate)]n (1), which was formed as the sole product from [Zn(tu)4]Cl2. Thermogravimetric analyses are reported for compounds 1−12. The compounds {[Zn(tu)2(μ‐isophthalate)]·H2O}n 3 and 12 lose their included water before 140 °C, whereas the compounds {[Zn(tu)2(μ‐maleate)]·H2O}n 6 and 11 only lose their water molecules at higher temperatures with the onset of decomposition. This difference in behaviour can be related to the structural role of the water molecules. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Supercritical fluid extraction–Oxidation technology to remediate PCB‐contaminated soils/sediments: An economic analysis
Authors: Zhou W. , Anitescu G. , Rice P.A. , Tavlarides L.L. 
Published: October 2004

AbstractThe remediation of PCB polluted soils/sediments, left to classical technologies such as incineration and bioremediation, is an overwhelming problem, given that vast amounts of spilled PCBs still exist in the environment after nearly three decades of PCB production ban. Other innovative, alternative cleanup technologies demonstrated that a better solution might exist. A two‐step remediation process proposed for real‐world PCB‐contaminated soils/sediments, based on supercritical fluid extraction (SCFE) and supercritical water oxidation (SCWO), is economically analyzed in this paper. The base case of the process consists of three 2.5‐m3 extractors operated in a 30‐min cycle and a 29‐m‐long SCWO tubular reactor (0.385 m i.d.), which can treat yearly 36,000 m3 of contaminated materials. To assess the commercial potential and the economic feasibility of the proposed process, capital and operational costs are analyzed and the results show total costs of the process in the range of $142–174/m3 sediment. Comparison with other alternative technologies suggests that the SCFE/SCWO process is economically feasible and attractive for the remediation of real‐world PCB highly contaminated soils/sediments. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 222–231, 2004
Selective catalytic reduction performance in steam–Methane reformer service: The chromium problem
Authors: O'Leary J.R. , Kunz R.G. , von Alten T.R. 
Published: October 2004

AbstractSelective catalytic reduction (SCR) performance has been seen to deteriorate with catalyst age at a greater than expected rate in steam–methane reformers (SMRs) and ethylene plants. Loss of catalyst activity has been attributed to deposition of chromium oxide species from alloy furnace tubes and coils on the catalyst surface, thereby masking active catalyst sites. This deposit is visible to the naked eye as a brown or iridescent black discoloration along the passages of a flow‐through honeycomb catalyst, darkest at the entrance face, and gradually becoming lighter as one proceeds downstream. The color becomes more intense with increased exposure to flue gas. It is important for proper design and catalyst‐replacement strategy to understand the governing phenomena at a fundamental level, especially at a time when SCR is increasingly being turned to as best available control technology (BACT), to comply with the more stringent nitrogen oxides (NOx) regulations. This paper describes a correlation of previously unpublished experimental data from catalyst test sections (logs) exposed in the field over a period of several years at multiple SMR plant locations. Consistent with the observed color change, chromium pickup increases with time and varies with operating conditions from plant to plant. Any given log, at any given time, shows an exponential, or semilogarithmic, decrease in chromium concentration over its length. Activity decay of the catalyst has been correlated with the chromium concentration. This single correlation holds true for all of the different plants investigated and can be used to predict remaining catalyst life and optimize future catalyst designs. Scanning electron microscopy (SEM) results and surface analyses from the SCR catalyst and SMR reformer tubes are also discussed, along with suggested countermeasures to mitigate the effects of chromium oxide deposition. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 194–205, 2004
Biological treatment of condensate from aerobic digestion of biodegradable waste: A German example
Authors: Czermak Peter , Han Binbing , Jaganjac Azra , Grüneklee C. Eberhard , Wickramasinghe S. Ranil 
Published: October 2004

AbstractSeparation of household waste into recyclable, biodegradable, and nonbiodegradable components is required in Germany. Aerobic digestion of the biodegradable component can further minimize the waste volume. During aerobic digestion a hot humid exhaust stream, containing volatile organic and other low molecular weight compounds, is produced. Cooling this stream produces up to 350 L of condensate per ton of biodegradable feed material. Efficient treatment of this condensate is essential for a practical aerobic digestion process. Reuse of the condensate could lead to improved process economics. In this paper, condensate treatment by biological degradation using intermittent sparging has been investigated. An inorganic ultrafiltration membrane was used to separate the biomass from the treated water. It is shown that this one‐step intermittent nitrification/denitrification process may be used to reduce COD, total nitrogen, and ammonia nitrogen concentrations to acceptable values for direct discharge of the treated water into rivers. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 215–221, 2004