4,564 research outputs found
Optimization of polystyrene-supported triphenylphosphine catalysts for aza-Morita–Baylis–Hillman reactions
A series of polar group functionalized polystyrene-supported phosphine reagents were examined as catalysts in the aza-Morita–Baylis–Hillman reactions of N-tosyl arylimines and a variety of Michael acceptors with the aim of identifying the optimal polymer/solvent combination. For these reactions JandaJel-PPh3 (1 mmol PPh3/g loading) resin containing methoxy groups (JJ-OMe-PPh3) on the polystyrene backbone in THF solvent provided the highest yield of all the catalyst/solvent combinations examined. The methyl ether groups were incorporated into JJ-OMe-PPh3 using commercially available 4-methoxystyrene, and thus such polar polystyrene resins are easily accessible and should find utility as nucleophilic catalyst supports.postprin
Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors
MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV–vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate
H_2 emission arises outside photodissociation regions in ultra-luminous infrared galaxies
Ultra-luminous infrared galaxies are among the most luminous objects in the
local universe and are thought to be powered by intense star formation. It has
been shown that in these objects the rotational spectral lines of molecular
hydrogen observed at mid-infrared wavelengths are not affected by dust
obscuration, leaving unresolved the source of excitation of this emission. Here
I report an analysis of archival Spitzer Space Telescope data on ultra-luminous
infrared galaxies and demonstrate that star formation regions are buried inside
optically thick clouds of gas and dust, so that dust obscuration affects
star-formation indicators but not molecular hydrogen. I thereby establish that
the emission of H_2 is not co-spatial with the buried starburst activity and
originates outside the obscured regions. This is rather surprising in light of
the standard view that H_2 emission is directly associated with star-formation
activity. Instead, I propose that H_2 emission in these objects traces shocks
in the surrounding material, which are in turn excited by interactions with
nearby galaxies, and that powerful large-scale shocks cooling by means of H_2
emission may be much more common than previously thought. In the early
universe, a boost in H_2 emission by this process may speed up the cooling of
matter as it collapsed to form the first stars and galaxies and would make
these first structures more readily observable.Comment: Main text and supplemental information, 21 pages including 6 figures,
2 table
Mesenchymal Stem Cell-Mediated Functional Tooth Regeneration in Swine
Mesenchymal stem cell-mediated tissue regeneration is a promising approach for regenerative medicine for a wide range of applications. Here we report a new population of stem cells isolated from the root apical papilla of human teeth (SCAP, stem cells from apical papilla). Using a minipig model, we transplanted both human SCAP and periodontal ligament stem cells (PDLSCs) to generate a root/periodontal complex capable of supporting a porcelain crown, resulting in normal tooth function. This work integrates a stem cell-mediated tissue regeneration strategy, engineered materials for structure, and current dental crown technologies. This hybridized tissue engineering approach led to recovery of tooth strength and appearance
Cumulin, an Oocyte-secreted Heterodimer of the Transforming Growth Factor-β Family, Is a Potent Activator of Granulosa Cells and Improves Oocyte Quality
Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are oocyte-specific growth factors with central roles in mammalian reproduction, regulating species-specific fecundity, ovarian follicular somatic cell differentiation, and oocyte quality. In the human, GDF9 is produced in a latent form, the mechanism of activation being an open question. Here, we produced a range of recombinant GDF9 and BMP15 variants, examined their in silico and physical interactions and their effects on ovarian granulosa cells (GC) and oocytes. We found that the potent synergistic actions of GDF9 and BMP15 on GC can be attributed to the formation of a heterodimer, which we have termed cumulin. Structural modeling of cumulin revealed a dimerization interface identical to homodimeric GDF9 and BMP15, indicating likely formation of a stable complex. This was confirmed by generation of recombinant heterodimeric complexes of pro/mature domains (pro-cumulin) and covalent mature domains (cumulin). Both pro-cumulin and cumulin exhibited highly potent bioactivity on GC, activating both SMAD2/3 and SMAD1/5/8 signaling pathways and promoting proliferation and expression of a set of genes associated with oocyte-regulated GC differentiation. Cumulin was more potent than pro-cumulin, pro-GDF9, pro-BMP15, or the two combined on GC. However, on cumulus-oocyte complexes, pro-cumulin was more effective than all other growth factors at notably improving oocyte quality as assessed by subsequent day 7 embryo development. Our results support a model of activation for human GDF9 dependent on cumulin formation through heterodimerization with BMP15. Oocyte-secreted cumulin is likely to be a central regulator of fertility in mono-ovular mammals
Demon-like Algorithmic Quantum Cooling and its Realization with Quantum Optics
The simulation of low-temperature properties of many-body systems remains one
of the major challenges in theoretical and experimental quantum information
science. We present, and demonstrate experimentally, a universal cooling method
which is applicable to any physical system that can be simulated by a quantum
computer. This method allows us to distill and eliminate hot components of
quantum states, i.e., a quantum Maxwell's demon. The experimental
implementation is realized with a quantum-optical network, and the results are
in full agreement with theoretical predictions (with fidelity higher than
0.978). These results open a new path for simulating low-temperature properties
of physical and chemical systems that are intractable with classical methods.Comment: 7 pages, 5 figures, plus supplementarity material
Controlling Cherenkov angles with resonance transition radiation
Cherenkov radiation provides a valuable way to identify high energy particles
in a wide momentum range, through the relation between the particle velocity
and the Cherenkov angle. However, since the Cherenkov angle depends only on
material's permittivity, the material unavoidably sets a fundamental limit to
the momentum coverage and sensitivity of Cherenkov detectors. For example, Ring
Imaging Cherenkov detectors must employ materials transparent to the frequency
of interest as well as possessing permittivities close to unity to identify
particles in the multi GeV range, and thus are often limited to large gas
chambers. It would be extremely important albeit challenging to lift this
fundamental limit and control Cherenkov angles as preferred. Here we propose a
new mechanism that uses constructive interference of resonance transition
radiation from photonic crystals to generate both forward and backward
Cherenkov radiation. This mechanism can control Cherenkov angles in a flexible
way with high sensitivity to any desired range of velocities. Photonic crystals
thus overcome the severe material limit for Cherenkov detectors, enabling the
use of transparent materials with arbitrary values of permittivity, and provide
a promising option suited for identification of particles at high energy with
enhanced sensitivity.Comment: There are 16 pages and 4 figures for the manuscript. Supplementary
information with 18 pages and 5 figures, appended at the end of the file with
the manuscript. Source files in Word format converted to PDF. Submitted to
Nature Physic
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