361 research outputs found
Interpretation of comprehensive two-dimensional gas chromatography data using advanced chemometrics
The power of comprehensive two-dimensional gas chromatography (GC × GC) for the study of complex mixtures has been indisputably proved in the past several decades. This review encompasses the whole of GC × GC-related data processing and summarizes relevant applications. We include theoretical introduction to some specific methods and studies to aid readers' understanding of chemometrics strategies for advanced data interpretation
ZrCl4-catalyzed C-O bond to C-N bond formation: synthesis of 1,2,3-triazoles and their biological evaluation
A simple and efficient protocol was developed for the synthesis of aryl azides directly from aryl carbinols using ZrCl4as a Lewis acid catalyst. The azides were converted to novel triazoles under click reaction conditions, which were evaluated for their antimicrobial activity against various strains
A Quantitative Theory of Mechanical Unfolding of a Homopolymer Globule
We propose the quantitative mean-field theory of mechanical unfolding of a
globule formed by long flexible homopolymer chain collapsed in poor solvent and
subjected to extensional deformation. We demonstrate that depending on the
degree of polymerization and solvent quality (quantified by the Flory-Huggins
parameter) the mechanical unfolding of the collapsed chain may either
occur continuously (by passing a sequence of uniformly elongated
configurations) or involves intra-molecular micro-phase coexistence of a
collapsed and a stretched segment followed by an abrupt unraveling transition.
The force-extension curves are obtained and quantitatively compared to our
recent results of numerical self-consistent field (SCF) simulations. The phase
diagrams for extended homopolymer chains in poor solvent comprising one- and
two-phase regions are calculated for different chain length or/and solvent
quality.Comment: 24 pages, 18 figure
Implementation of the Projector Augmented Wave LDA+U Method: Application to the Electronic Structure of NiO
The so-called local density approximation plus the multi-orbital mean-field
Hubbard model (LDA+U) has been implemented within the all-electron projector
augmented-wave method (PAW), and then used to compute the insulating
antiferromagnetic ground state of NiO and its optical properties. The
electronic and optical properties have been investigated as a function of the
Coulomb repulsion parameter U. We find that the value obtained from constrained
LDA (U=8 eV) is not the best possible choice, whereas an intermediate value
(U=5 eV) reproduces the experimental magnetic moment and optical properties
satisfactorily. At intermediate U, the nature of the band gap is a mixture of
charge transfer and Mott-Hubbard type, and becomes almost purely of the
charge-transfer type at higher values of U. This is due to the enhancement of
the oxygen 2p states near the top of the valence states with increasing U
value.Comment: 23 pages, 6 figures, submitted to Phys. Rev.
Microparticles from patients with metabolic syndrome induce vascular hypo-reactivity via Fas/Fas-ligand pathway in mice
Peer reviewedPublisher PD
Structural, Electronic, and Magnetic Properties of MnO
We calculate the structural, electronic, and magnetic properties of MnO from
first principles, using the full-potential linearized augmented planewave
method, with both local-density and generalized-gradient approximations to
exchange and correlation. We find the ground state to be of rhombohedrally
distorted B1 structure with compression along the [111] direction,
antiferromagnetic with type-II ordering, and insulating, consistent with
experiment. We show that the distortion can be understood in terms of a
Heisenberg model with distance dependent nearest-neighbor and
next-nearest-neighbor couplings determined from first principles. Finally, we
show that magnetic ordering can induce significant charge anisotropy, and give
predictions for electric field gradients in the ground-state rhombohedrally
distorted structure.Comment: Submitted to Physical Review B. Replaced: regenerated figures to
resolve font problems in automatically generated pd
X-ray-Induced Reversible Switching of an Azobenzene Derivative Adsorbed on Bi(111)
We report on the adsorption of a submonolayer of di-m-cyanoazobenzene (DMC) on
Bi(111) and on the reversible switching of these molecules induced by resonant
X-ray illumination. DMC adsorbs in at least two configurations, the flat trans
and the nonflat cis isomer. We find that in 0.8 monolayers at least 26% of the
molecules change their configuration at 110 K by excitation of the N1s → LUMO
transition at the azo group, and by a thermally induced back reaction at 120
K. Nonresonant excitation with X-ray light does not induce any reversible
changes
Self-assembly of polysaccharides gives rise to distinct mechanical signatures in marine gels
Marine-gel biopolymers were recently visualized at the molecular level using atomic force microscopy (AFM) to reveal fine fibril-forming networks with low to high degrees of cross-linking. In this work, we use force spectroscopy to quantify the intra- and intermolecular forces within the marine-gel network. Combining force measurements, AFM imaging, and the known chemical composition of marine gels allows us to identify the microscopic origins of distinct mechanical responses. At the single-fibril level, we uncover force-extension curves that resemble those of individual polysaccharide fibrils. They exhibit entropic elasticity followed by extensions associated with chair-to-boat transitions specific to the type of polysaccharide at high forces. Surprisingly, a low degree of cross-linking leads to sawtooth patterns that we attribute to the unraveling of polysaccharide entanglements. At a high degree of cross-linking, we observe force plateaus that arise from unzipping, as well as unwinding, of helical bundles. Finally, the complex 3D network structure gives rise to force staircases of increasing height that correspond to the hierarchical peeling of fibrils away from the junction zones. In addition, we show that these diverse mechanical responses also arise in reconstituted polysaccharide gels, which highlights their dominant role in the mechanical architecture of marine gels
Tumor-Derived Microvesicles Induce, Expand and Up-Regulate Biological Activities of Human Regulatory T Cells (Treg)
Background: Tumor-derived microvesicles (TMV) or exosomes are present in body fluids of patients with cancer and might be involved in tumor progression. The frequency and suppressor functions of peripheral blood CD4 + CD25 high FOXP3 + Treg are higher in patients with cancer than normal controls. The hypothesis is tested that TMV contribute to induction/ expansion/and activation of human Treg. Methodology/Principal Findings: TMV isolated from supernatants of tumor cells but not normal cells induced the generation and enhanced expansion of human Treg. TMV also mediated conversion of CD4 + CD25 neg T cells into CD4 + CD25 high FOXP3 + Treg. Upon co-incubation with TMV, Treg showed an increased FasL, IL-10, TGF-b1, CTLA-4, granzyme B and perforin expression (p,0.05) and mediated stronger suppression of responder cell (RC) proliferation (p,0.01). Purified Treg were resistant to TMV-mediated apoptosis relative to other T cells. TMV also increased phospho-SMAD2/3 and phospho-STAT3 expression in Treg. Neutralizing Abs specific for TGF-b1 and/or IL-10 significantly inhibited TMV ability to expand Treg. Conclusions/Significance: This study suggests that TMV have immunoregulatory properties. They induce Treg, promote Treg expansion, up-regulate Treg suppressor function and enhance Treg resistance to apoptosis. Interactions of TMV wit
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