146 research outputs found
On the relevance of polyynyl-substituted PAHs to astrophysics
We report on the absorption spectra of the polycyclic aromatic hydrocarbon
(PAH) molecules anthracene, phenanthrene, and pyrene carrying either an ethynyl
(-C2H) or a butadiynyl (-C4H) group. Measurements were carried out in the mid
infrared at room temperature on grains embedded in CsI pellets and in the near
ultraviolet at cryogenic temperature on molecules isolated in Ne matrices. The
infrared measurements show that interstellar populations of
polyynyl-substituted PAHs would give rise to collective features in the same
way non-substituted PAHs give rise to the aromatic infrared bands. The main
features characteristic of the substituted molecules correspond to the
acetylenic CH stretching mode near 3.05 mum and to the almost isoenergetic
acetylenic CCH in- and out-of-plane bending modes near 15.9 mum.
Sub-populations defined by the length of the polyynyl side group cause
collective features which correspond to the various acetylenic CC stretching
modes. The ultraviolet spectra reveal that the addition of an ethynyl group to
a non-substituted PAH molecule results in all its electronic transitions being
redshifted. Due to fast internal energy conversion, the bands at shorter
wavelengths are significantly broadened. Those at longer wavelengths are only
barely affected in this respect. As a consequence, their relative peak
absorption increases. The substitution with the longer butadiynyl chain causes
the same effects with a larger magnitude, resulting in the spectra to show a
prominent if not dominating pi-pi* transition at long wavelength. After
discussing the relevance of polyynyl-substituted PAHs to astrophysics, we
conclude that this class of highly conjugated, unsaturated molecules are valid
candidates for the carriers of the diffuse interstellar bands.Comment: 29 pages, 9 figures, accepted for publication in ApJ 2 April 201
Mechanism and specificity of pentachloropseudilin-mediated inhibition of myosin motor activity.
Here, we report that the natural compound pentachloropseudilin (PClP) acts as a reversible and allosteric inhibitor of myosin ATPase and motor activity. IC(50) values are in the range from 1 to 5 μm for mammalian class-1 myosins and greater than 90 μm for class-2 and class-5 myosins, and no inhibition was observed with class-6 and class-7 myosins. We show that in mammalian cells, PClP selectively inhibits myosin-1c function. To elucidate the structural basis for PClP-induced allosteric coupling and isoform-specific differences in the inhibitory potency of the compound, we used a multifaceted approach combining direct functional, crystallographic, and in silico modeling studies. Our results indicate that allosteric inhibition by PClP is mediated by the combined effects of global changes in protein dynamics and direct communication between the catalytic and allosteric sites via a cascade of small conformational changes along a conserved communication pathway
Power spectrum of turbulent convection in the solar photosphere
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport vary rapidly
and a strongly superadiabatic region lies very closely to a subadiabatic layer.
Our tools for probing the turbulence are high-resolution spectropolarimetric
observations such as have recently been obtained with the two sunrise missions,
and numerical simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations and
simulations. We also attempt to explain some properties of the photospheric
overshooting flow with the help of its governing equations and simulations. We
find that quiet-Sun observations and smeared simulations exhibit a power-law
behavior in the subgranular range of their Doppler velocity power spectra with
an index of. The unsmeared simulations exhibit a power-law index
of. The smearing considerably reduces the extent of the
power-law-like portion of the spectra. Therefore, the limited spatial
resolution in some observations might eventually result in larger uncertainties
in the estimation of the power-law indices.
The simulated vertical velocity power spectra as a function of height show a
rapid change in the power-law index from the solar surface to ~km above
it. A scale-dependent transport of the vertical momentum occurs. At smaller
scales, the vertical momentum is more efficiently transported sideways than at
larger scales. This results in less vertical velocity power transported upward
at small scales than at larger scales and produces a progressively steeper
vertical velocity power law below km. Above this height, the gravity work
progressively gains importance at all scales, making the atmosphere
progressively more hydrostatic and resulting in a gradually less steep power
law.Comment: 10 pages, 7 figures, Accepted in A and
Small-scale solar magnetic fields
As we resolve ever smaller structures in the solar atmosphere, it has become
clear that magnetism is an important component of those small structures.
Small-scale magnetism holds the key to many poorly understood facets of solar
magnetism on all scales, such as the existence of a local dynamo, chromospheric
heating, and flux emergence, to name a few. Here, we review our knowledge of
small-scale photospheric fields, with particular emphasis on quiet-sun field,
and discuss the implications of several results obtained recently using new
instruments, as well as future prospects in this field of research.Comment: 43 pages, 18 figure
DAF-12 Regulates a Connected Network of Genes to Ensure Robust Developmental Decisions
The nuclear receptor DAF-12 has roles in normal development, the decision to pursue dauer development in unfavorable conditions, and the modulation of adult aging. Despite the biologic importance of DAF-12, target genes for this receptor are largely unknown. To identify DAF-12 targets, we performed chromatin immunoprecipitation followed by hybridization to whole-genome tiling arrays. We identified 1,175 genomic regions to be bound in vivo by DAF-12, and these regions are enriched in known DAF-12 binding motifs and act as DAF-12 response elements in transfected cells and in transgenic worms. The DAF-12 target genes near these binding sites include an extensive network of interconnected heterochronic and microRNA genes. We also identify the genes encoding components of the miRISC, which is required for the control of target genes by microRNA, as a target of DAF-12 regulation. During reproductive development, many of these target genes are misregulated in daf-12(0) mutants, but this only infrequently results in developmental phenotypes. In contrast, we and others have found that null daf-12 mutations enhance the phenotypes of many miRISC and heterochronic target genes. We also find that environmental fluctuations significantly strengthen the weak heterochronic phenotypes of null daf-12 alleles. During diapause, DAF-12 represses the expression of many heterochronic and miRISC target genes, and prior work has demonstrated that dauer formation can suppress the heterochronic phenotypes of many of these target genes in post-dauer development. Together these data are consistent with daf-12 acting to ensure developmental robustness by committing the animal to adult or dauer developmental programs despite variable internal or external conditions
A Versatile Approach to Ullmann C–N Couplings at Room Temperature: New Families of Nucleophiles and Electrophiles for Photoinduced, Copper-Catalyzed Processes
Total Synthesis of Carbazoquinocin C: Application of the ortho-Benzannulation of Fischer Carbene Complexes to Carbazole-3, 4-quinone Alkaloids.
Iodo-Cycloisomerization of Aryl(indol-3-yl)methane-Tethered Propargyl Alcohols to 3Iodocarbazoles via Selective 1,2-Alkyl Migration
Iron(0) Tricarbonyl Complexes of Microbially Derived Cyclohexadiene Ligands Containing Quaternary Stereocenters
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