520 research outputs found
Synthesis of urea on the surface of interstellar water ice clusters. A quantum chemical study
Urea is a prebiotic molecule that has been detected in few sources of the
interstellar medium (ISM) and in Murchison meteorite. Being stable against
ultraviolet radiation and high-energy electron bombardment, urea is expected to
be present in interstellar ices. Theoretical and experimental studies suggest
that isocyanic acid (HNCO) and formamide (NHCHO) are possible precursors of
urea. However, uncertainties still exist regarding its formation routes.
Previous computational works characterised urea formation in the gas phase or
in presence of few water molecules by reaction of formamide with
nitrogen-bearing species. In this work, we investigated the reaction of HNCO +
NH on an 18 water molecules ice cluster model mimicking interstellar ice
mantles by means of quantum chemical computations. We characterised different
mechanisms involving both closed-shell and open-shell species at
B3LYP-D3(BJ)/ma-def2-TZVP level of theory, in which the radical-radical
HNCO + NH coupling has been found to be the most favourable one due to
being almost barrierless. In this path, the presence of the icy surfaces is
crucial for acting as reactant concentrators/suppliers, as well as third bodies
able to dissipate the energy liberated during the urea formation.Comment: 12 pages, 7 figures. Accepted for pubication in Icaru
COMPUTATIONAL STUDY OF INTERSTELLAR GLYCINE FORMATION OCCURRING AT RADICAL SURFACES OF WATER-ICE DUST PARTICLES
First-Principles Modeling of Protein/Surface Interactions. Polyglycine Secondary Structure Adsorption on the TiO2(101) Anatase Surface Adopting a Full Periodic Approach
Quantum Mechanical Investigations on the Formation of Complex Organic Molecules on Interstellar Ice Mantles. Review and Perspectives
Does Fe2+ in olivine-based interstellar grains play any role in the formation of H2? Atomistic insights from DFT periodic simulations
Orbital characterization of superbolides observed from space: dynamical association with near-Earth objects, meteoroid streams and identification of hyperbolic meteoroids
There is an unceasing incoming flux of extraterrestrial materials reaching
the Earth's atmosphere. Some of these objects produce luminous columns when
they ablate during the hypersonic encounter with air molecules. A few fireballs
occur each year bright enough to be detected from space. The source of these
events is still a matter of debate, but it is generally accepted that they are
of sporadic origin. We studied the NASA-JPL Center for NEOs Studies (CNEOS)
fireball database to infer the dynamic origin of large bolides produced by
meter-sized projectiles that impacted our planet. These likely
meteorite-dropping events were recorded by the US Government satellite sensors.
We estimated the false-positive rate and analyzed the time evolution of
multiple orbit dissimilarity criteria concerning potential associations with
near-Earth objects and meteoroid streams. We found that at least 16% of the
large bolides could be associated with meteoroid streams, about 4% are likely
associated with near-Earth asteroids, and 4% may be linked to near-Earth
comets. This implies that a significant fraction of meter-sized impactors
producing large bolides may have an asteroidal or cometary origin. In addition,
we found at least three bolides having hyperbolic orbits with high tensile
strength values. Meter-sized meteoroids of interstellar origin could be more
common than previously thought, representing about 1% of the flux of large
bolides. The inferred bulk physical properties suggest that the interstellar
medium could bias these projectiles towards high strength rocks with the
ability to survive prolonged exposure to the harsh interstellar space
conditions.Comment: Accepted for publication in The Astronomical Journal (AAS38905R1
Hypoxia inducible factor-1α accumulation in steatotic liver preservation: Role of nitric oxide
Open-Acces journal.-- et al.[Aim]: To examine the relevance of hypoxia inducible factor (HIF-1) and nitric oxide (NO) on the preservation of fatty liver against cold ischemia-reperfusion injury (IRI).
Methods]: We used an isolated perfused rat liver model and we evaluated HIF-1α in steatotic and non-steatotic livers preserved for 24 h at 4°C in University of Wisconsin and IGL-1 solutions, and then subjected to 2 h of normothermic reperfusion. After normoxic reperfusion, liver enzymes, bile production, bromosulfophthalein clearance, as well as HIF-1α and NO [endothelial NO synthase (eNOS) activity and nitrites/nitrates] were also measured. Other factors associated with the higher susceptibility of steatotic livers to IRI, such as mitochondrial damage and vascular resistance were evaluated. [Results]: A significant increase in HIF-1α was found in steatotic and non-steatotic livers preserved in IGL-1 after cold storage. Livers preserved in IGL-1 showed a significant attenuation of liver injury and improvement in liver function parameters. These benefits were enhanced by the addition of trimetazidine (an antiischemic drug), which induces NO and eNOS activation, to IGL-1 solution. In normoxic reperfusion, the presence of NO favors HIF-1α accumulation, promoting also the activation of other cytoprotective genes, such as hemeoxygenase- 1.
[Concluison]: We found evidence for the role of the HIF-1α/NO system in fatty liver preservation, especially when IGL-1 solution is used. © 2010 Baishideng.Supported by The Ministerio de de Sanidad y Consumo (PI 081988), CIBER-EHD, Instituto Carlos III, Madrid and Ministerio de Asuntos Exteriores y de Cooperación Internacionales (A/020255/08 and A/02987/09), MadridPeer Reviewe
Recent advances in clinical practice: advances in cross-sectional imaging in inflammatory bowel disease
Endoscopy remains the reference standard for the diagnosis and assessment of patients with inflammatory bowel disease (IBD), but it has several important limitations. Cross-sectional imaging techniques such as magnetic resonance enterography (MRE) and intestinal ultrasound (IUS) are better tolerated and safer. Moreover, they can examine the entire bowel, even in patients with stenoses and/or severe inflammation. A variety of cross-sectional imaging activity scores strongly correlate with endoscopic measures of mucosal inflammation in the colon and terminal ileum. Unlike endoscopy, cross-sectional techniques allow complete visualisation of the small-bowel and assess for extraintestinal disease, which occurs in nearly half of patients with IBD. Extramural findings may predict outcomes better than endoscopic mucosal assessment, so cross-sectional techniques might help identify more relevant therapeutic targets. Coupled with their high sensitivity, these advantages have made MRE and IUS the primary non-invasive options for diagnosing and monitoring Crohn’s disease; they are appropriate first-line investigations, and have become viable alternatives to colonoscopy. This review discusses cross-sectional imaging in IBD in current clinical practice as well as research lines that will define the future role of these techniques
The first joint ESGAR/ ESPR consensus statement on the technical performance of cross-sectional small bowel and colonic imaging
Objectives: To develop guidelines describing a standardised approach to patient preparation and acquisition protocols for magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US) of the small bowel and colon, with an emphasis on imaging inflammatory bowel disease. Methods: An expert consensus committee of 13 members from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) and European Society of Paediatric Radiology (ESPR) undertook a six-stage modified Delphi process, including a detailed literature review, to create a series of consensus statements concerning patient preparation, imaging hardware and image acquisition protocols. Results: One hundred and fifty-seven statements were scored for agreement by the panel of which 129 statements (82 %) achieved immediate consensus with a further 19 (12 %) achieving consensus after appropriate modification. Nine (6 %) statements were rejected as consensus could not be reached. Conclusions: These expert consensus recommendations can be used to help guide cross-sectional radiological practice for imaging the small bowel and colon. Key points: • Cross-sectional imaging is increasingly used to evaluate the bowel • Image quality is paramount to achieving high diagnostic accuracy • Guidelines concerning patient preparation and image acquisition protocols are provided
Acetaldehyde binding energies: a coupled experimental and theoretical study
Acetaldehyde is one of the most common and abundant gaseous interstellar
complex organic molecules, found in cold and hot regions of the molecular
interstellar medium. Its presence in the gas-phase depends on the chemical
formation and destruction routes, and its binding energy (BE) governs whether
acetaldehyde remains frozen onto the interstellar dust grains or not. In this
work, we report a combined study of the acetaldehyde BE obtained via laboratory
TPD (Temperature Programmed Desorption) experiments and theoretical quantum
chemical computations. BEs have been measured and computed as a pure
acetaldehyde ice and as mixed with both polycrystalline and amorphous water
ice. Both calculations and experiments found a BE distribution on amorphous
solid water that covers the 4000--6000 K range, when a pre-exponential factor
of is used for the interpretation of the experiments.
We discuss in detail the importance of using a consistent couple of BE and
pre-exponential factor values when comparing experiments and computations, as
well as when introducing them in astrochemical models. Based on the comparison
of the acetaldehyde BEs measured and computed in the present work with those of
other species, we predict that acetaldehyde is less volatile than formaldehyde,
but much more than water, methanol, ethanol, and formamide. We discuss the
astrochemical implications of our findings and how recent astronomical high
spatial resolution observations show a chemical differentiation involving
acetaldehyde, which can easily explained as due to the different BEs of the
observed molecules.Comment: 12 pages, 6 figure
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