847 research outputs found
The chemical diversity of comets
A fundamental question in cometary science is whether the different dynamical
classes of comets have different chemical compositions, which would reflect
different initial conditions. From the ground or Earth orbit, radio and
infrared spectroscopic observations of a now significant sample of comets
indeed reveal deep differences in the relative abundances of cometary ices.
However, no obvious correlation with dynamical classes is found. Further
results come, or are expected, from space exploration. Such investigations, by
nature limited to a small number of objects, are unfortunately focussed on
short-period comets (mainly Jupiter-family). But these in situ studies provide
"ground truth" for remote sensing. We discuss the chemical differences in
comets from our database of spectroscopic radio observations, which has been
recently enriched by several Jupiter-family and Halley-type comets.Comment: In press in Earth, Moon and Planets (proceedings of the workshop
"Future Ground-based Solar System Research: Synergies with Space Probes and
Space Telescopes", Portoferraio, Isola d'Elba, Livorno (Italy), 8-12
September 2008). 6 pages with 2 figure
Hydrogen Isocyanide in Comet 73P/Schwassmann-Wachmann (Fragment B)
We present a sensitive 3-sigma upper limit of 1.1% for the HNC/HCN abundance
ratio in comet 73P/Schwassmann-Wachmann (Fragment B), obtained on May 10-11,
2006 using Caltech Submillimeter Observatory (CSO). This limit is a factor of
~7 lower than the values measured previously in moderately active comets at 1
AU from the Sun. Comet 73P/Schwassmann-Wachmann was depleted in most volatile
species, except of HCN. The low HNC/HCN ratio thus argues against HNC
production from polymers produced from HCN. However, thermal degradation of
macromolecules, or polymers, produced from ammonia and carbon compounds, such
as acetylene, methane, or ethane appears a plausible explanation for the
observed variations of the HNC/HCN ratio in moderately active comets, including
the very low ratio in comet 73P/Schwassmann-Wachmann reported here. Similar
polymers have been invoked previously to explain anomalous 14N/15N ratios
measured in cometary CN.Comment: 6 pages, 5 figures, 2 table
Antifreeze in the hot core of Orion - First detection of ethylene glycol in Orion-KL
Comparison of their chemical compositions shows, to first order, a good
agreement between the cometary and interstellar abundances. However, a complex
O-bearing organic molecule, ethylene glycol (CHOH), seems to depart
from this correlation because it was not easily detected in the interstellar
medium although it proved to be rather abundant with respect to other O-bearing
species in comet Hale-Bopp. Ethylene glycol thus appears, together with the
related molecules glycolaldehyde CHOHCHO and ethanol CHCHOH,
as a key species in the comparison of interstellar and cometary ices as well as
in any discussion on the formation of cometary matter. We focus here on the
analysis of ethylene glycol in the nearest and best studied hot core-like
region, Orion-KL. We use ALMA interferometric data because high spatial
resolution observations allow us to reduce the line confusion problem with
respect to single-dish observations since different molecules are expected to
exhibit different spatial distributions. Furthermore, a large spectral
bandwidth is needed because many individual transitions are required to
securely detect large organic molecules. Confusion and continuum subtraction
are major issues and have been handled with care. We have detected the aGg'
conformer of ethylene glycol in Orion-KL. The emission is compact and peaks
towards the Hot Core close to the main continuum peak, about 2" to the
south-west; this distribution is notably different from other O-bearing
species. Assuming optically thin lines and local thermodynamic equilibrium, we
derive a rotational temperature of 145 K and a column density of 4.6 10
cm. The limit on the column density of the gGg' conformer is five times
lower.Comment: 19 pages, 10 figures, A&A accepte
Mechanistic aspects of thioflavin-T self-aggregation and DNA binding: evidence for dimer attack on DNA grooves
Thioflavin-T (TFT) is a fluorescent marker widely employed in biomedical research but the mechanism of
its binding to polynucleotides has been poorly understood. This paper presents a study of the mechanisms
of TFT self-aggregation and binding to DNA. Relaxation kinetics of TFT solutions show that the cyanine
undergoes dimerization followed by dimer isomerisation. The interaction of TFT with DNA has been
investigated using static methods, such as spectrophotometric and spectrofluorometric titrations under
different conditions (salt content, temperature), fluorescence quenching, viscometric experiments and the
T-jump relaxation method. The combined use of these techniques enabled us to show that the TFT
monomer undergoes intercalation between the DNA base pairs and external binding according to a
branched mechanism. Moreover, it has also been observed that, under dye excess conditions, the TFT
dimer binds to the DNA grooves. The molecular structures of intercalated TFT and the groove-bound
TFT dimer are obtained by performing QM/MM MD simulations
Complex organic molecules in comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy): detection of ethylene glycol and formamide
A spectral survey in the 1 mm wavelength range was undertaken in the
long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m
telescope of the Institut de radioastronomie millim\'etrique (IRAM) in April
and November-December 2013. We report the detection of ethylene glycol
(CHOH) (aGg' conformer) and formamide (NHCHO) in the two comets.
The abundances relative to water of ethylene glycol and formamide are 0.2-0.3%
and 0.02% in the two comets, similar to the values measured in comet C/1995 O1
(Hale-Bopp). We also report the detection of HCOOH and CHCHO in comet
C/2013 R1 (Lovejoy), and a search for other complex species (methyl formate,
glycolaldehyde).Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
Intercalation of Zn(II) and Cu(II) complexes of the cyclic polyamine Neotrien into DNA: equilibria and kinetics
The equilibria and kinetics of the interaction of the Zn(II) and Cu(II) complexes of the macrocyclic polyamine 2,5,8,11-tetraaza[12]-[12](2,9)[1,10]-phenanthrolinophane (Neotrien) with calf thymus DNA have been investigated at pH = 7.0 and T = 25 degreesC by spectrophotometry, spectrofluorimetry and stopped-flow method. At low dye/polymer ratios both complexes bind to DNA according to the excluded site model. At high dye/polymer ratios the binding displays cooperative features. The logarithm of the binding constant depends linearly on - log[NaCl]. The kinetic results suggest the D + S reversible arrow D, S reversible arrow DS mechanism where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D, S) which, in turn, is converted into internally bound complex (DS) by intercalation. The binding constants, evaluated as ratios of rate constants, agree with those obtained from equilibrium binding experiments, thus confirming the validity of the proposed model. Fluorescence titrations, where the metal-Neotrien complexes were added to DNA previously saturated with ethidium bromide (EB), show that both complexes displace EB from the DNA cavities. The reverse process, i.e. the addition of excess ethidium to the DNA/metal Neotrien systems, leads to fluorescence recovery for DNA/ZnNeotrien but not for DNA/CuNeotrien. This observation suggests that the binding of CuNeotrien induces deep alterations in the DNA structure. Experiments with Poly(dA-dT) . Poly(dA-dT) and Poly(dG-dC) . Poly(dG-dC) reveal that CuNeotrien mainly affects the structure of the latter polynucleotide. (C) 2004 Elsevier Inc. All rights reserved
An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
176P/LINEAR is a member of the new cometary class known as main-belt comets
(MBCs). It displayed cometary activity shortly during its 2005 perihelion
passage that may be driven by the sublimation of sub-surface ices. We have
therefore searched for emission of the H2O 110-101 ground state rotational line
at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory on UT 8.78 August 2011,
about 40 days after its most recent perihelion passage, when the object was at
a heliocentric distance of 2.58 AU. No H2O line emission was detected in our
observations, from which we derive sensitive 3-sigma upper limits for the water
production rate and column density of < 4e25 molec/s and of < 3e10 cm^{-2},
respectively. From the peak brightness measured during the object's active
period in 2005, this upper limit is lower than predicted by the relation
between production rates and visual magnitudes observed for a sample of comets
by Jorda et al. (2008) at this heliocentric distance. Thus, 176P/LINEAR was
likely less active at the time of our observation than during its previous
perihelion passage. The retrieved upper limit is lower than most values derived
for the H2O production rate from the spectroscopic search for CN emission in
MBCs.Comment: 5 pages, 2 figures. Minor changes to match published versio
Radio observations of comet 9P/Tempel 1 with the Australia Telescope facilities during the Deep Impact encounter
We present radio observations of comet 9P/Tempel 1 associated with the Deep
Impact spacecraft collision of 2005 July 4. Weak 18-cm OH emission was detected
with the Parkes 64-m telescope, in data averaged over July 4 to 6, at a level
of 12 +/- 3 mJy km/s, corresponding to OH production rate 2.8 x 10^{28}
molecules/second (Despois et al. inversion model, or 1.0 x 10^{28} /s for the
Schleicher & A'Hearn model). We did not detect the HCN 1-0 line with the Mopra
22-m telescope over the period July 2 to 6. The 3 sigma limit of 0.06 K km/s
for HCN on July 4 after the impact gives the limit to the HCN production rate
of < 1.8 x 10^{25} /s. We did not detect the HCN 1-0 line, 6.7 GHz CH_3OH line
or 3.4-mm continuum with the Australia Telescope Compact Array (ATCA) on July
4, giving further limits on any small-scale structure due to an outburst. The 3
sigma limit on HCN emission of 2.5 K km/s from the ATCA around impact
corresponds to limit < 4 x 10^{29} HCN molecules released by the impact.Comment: 7 pages, 1 figure, accepted by MNRA
Role of the P2Y(13) Receptor in the Differentiation of Bone Marrow Stromal Cells into Osteoblasts and Adipocytes
Accumulating evidence indicates that extracellular nucleotides, signaling through purinergic receptors, play a significant role in bone remodeling. Mesenchymal stem cells (MSCs) express functional P2Y receptors whose expression level is regulated during osteoblast or adipocyte differentiation. P2Y13-deficient mice were previously shown to exhibit a decreased bone turnover associated with a reduction in the number of both osteoblasts and osteoclasts on the bone surfaces. We therefore examined whether P2Y13R activation was involved in the osteogenic differentiation of MSC. Our study demonstrated that ADP stimulation of P2Y13R+/+ (but not P2Y13R-/-) adherent bone marrow stromal cells (BMSCs) increased significantly the formation of alkaline phosphatase-colony-forming units (CFU-ALP) as well as the expression of osteoblastic markers (osterix, alkaline phosphatase, and collagen I) involved in the maturation of preosteoblasts into osteoblasts. The number of CFU-ALP obtained from P2Y13R-/- BMSC and the level of osteoblastic gene expression after osteogenic stimulation were strongly reduced compared to those obtained in wild-type cell cultures. In contrast, when P2Y13R-/- BMSCs were incubated in an adipogenic medium, the number of adipocytes generated and the level of adipogenic gene expression (PPARγ2 and Adipsin) were higher than those obtained in P2Y13R+/+ MSC. Interestingly, we observed a significant increase of the number of bone marrow adipocytes in tibia of P2Y13R-/- mice. In conclusion, our findings indicate that the P2Y13R plays an important role in the balance of osteoblast and adipocyte terminal differentiation of bone marrow progenitors. Therefore, the P2Y13 receptor can be considered as a new pharmacological target for the treatment of bone diseases like osteoporosis
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