1,945 research outputs found
Laser-light scattering approach to peptideâmembrane interaction
© International University Line, 2010Membrane-active peptides are becoming widely used, mainly due to their high therapeutic potential. Although the therapeutic action is characterized, the mechanisms of interaction are often unclear or controversial. In biophysical studies, non-invasive techniques are overlooked when studying the effect of peptides on membranes. Light scattering techniques, such as dynamic light scattering and static light scattering, can be used as tools to determine whether promotion of membrane aggregation in the presence of peptides and of self-peptide aggregation in solution occurs. More recently, light scattering has been used for evaluating the alteration on membrane surface charge (ζ-potential) promoted by membraneâpeptide interactions. The data obtained by these techniques (either by themselves or combined with complementary experimental approaches) therefore yield valuable elucidations of membrane-active peptidesâ mechanisms of action at the molecular level.This work was partially supported by the Fundação para a CiĂȘncia e Tecnologia (FCT) of the Portuguese Ministry of Science, Technology and Higher Education. M.M.D. acknowledges the grant SFRH/BD/41750/2007 from FCT
A "diamond-ring" star: the unusual morphologic structure of a young (multiple?) object
We have observed IRAS06468-0325 obtaining optical and infrared images through
IJHKs and L' filters, K-band low-resolution spectroscopy, together with
millimetre line observations of CO and CS. IRAS06468-0325 has a very unusual
and enigmatic morphology with two components: a bright, close to point-like
source (the diamond) and a sharp-edge ring-like structure (the ring). The
source is not detected in the optical, at wavelengths shorter than the I-band.
The diamond is seen in all the imaging bands observed. The ring-like structure
in IRAS06468-0325 is clearly seen in the I, J, H, and Ks. It is not detected in
the L'-band image. Infrared colours of the diamond are compatible with excess
circumstellar emission and a young stellar nature. A strongly non-gaussian and
moderately bright CO(1-0) and {13}CO(2-1) lines are seen towards
IRAS06468-0325, at v_{LSR} of 30.5 km s{-1} (corresponding to a kinematic
distance of 3 kpc). Very weak C{18}O(2-1) and CS(2-1) lines were detected.
K-band spectra of the diamond and of the ring are similar both in the slope of
the continuum and in the presence of lines supporting the idea that the ring is
reflected light from the diamond. With the current data, a few different
scenarios are possible to explain the morphology of this object. However, the
available data seem to favour that the morphology of IRAS06468-0325 correspond
to a young stellar multiple system in a transient stage where a binary
co-exists with a circumbinary disc, similar to the case of GG Tau. In this
case, the sharpness of the well-defined ring may be due to tidal truncation
from dynamic interactions between components in a binary or multiple stellar
system. IRAS06468-0325 may be an important rare case that illustrates a
short-lived stage of the process of binary or multiple star formation.Comment: 7 pages, 6 figure
Spectroscopic direct detection of reflected light from extra-solar planets
At optical wavelengths, an exoplanet's signature is essentially reflected
light from the host star - several orders of magnitude fainter. Since it is
superimposed on the star spectrum its detection has been a difficult
observational challenge. However, the development of a new generation of
instruments like ESPRESSO and next generation telescopes like the E-ELT put us
in a privileged position to detect these planets' reflected light as we will
have access to extremely high signal-to-noise ratio spectra. With this work, we
propose an alternative approach for the direct detection of the reflected light
of an exoplanet. We simulated observations with ESPRESSO@VLT and HIRES@E-ELT of
several star+planet systems, encompassing 10h of the most favourable orbital
phases. To the simulated spectra we applied the Cross Correlation Function to
operate in a much higher signal-to-noise ratio domain than when compared with
the spectra. The use of the Cross-Correlation Function permitted us to recover
the simulated the planet signals at a level above 3 \sigma_{noise} significance
on several prototypical (e.g., Neptune type planet with a 2 days orbit with the
VLT at 4.4 \sigma_{noise} significance) and real planetary systems (e.g., 55
Cnc e with the E-ELT at 4.9 \sigma_{noise} significance). Even by using a more
pessimistic approach to the noise level estimation, where systematics in the
spectra increase the noise 2-3 times, the detection of the reflected light from
large close-orbit planets is possible. We have also shown that this kind of
study is currently within reach of current instruments and telescopes (e.g., 51
Peg b with the VLT at 5.2 \sigma_{noise} significance), although at the limit
of their capabilities.Comment: Accepted for Publication on MNRAS: 2013 August 29; Online Article:
http://mnras.oxfordjournals.org/content/early/2013/09/27/mnras.stt1642; 5
Figures, 11 page
Detailed theoretical models for extra-solar planet-host stars: The "red stragglers" HD37124 and HD46375
In this paper we analyse and discuss the HR Diagram position of two
extra-solar planet-host stars - HD37124 and HD46375 - by means of theoretical
stellar evolution models. This work was triggered by the results obtained by
Laws et al. (2003) who found that these stars were in contradiction to the
expectation based on their high metallicity. Fixing the age of both stars with
the value based on their chromospheric activity levels and computing our own
evolutionary models using the CESAM code, we are able to reproduce the observed
luminosity, effective temperature and metallicity of both stars for a set of
stellar parameters that are astrophysically reliable even if it is non-trivial
to interpret the absolute values for these parameters. Our results are
discussed in the context of the stellar properties of low mass stars.Comment: 6 pages, 2 figures, A&A, in pres
Environmental typology of rivers from the Brazilian semiarid as a first step for the application of the index of biotic integrity: The case of the Chapada Diamantina
Defining environmental river types is an essential step in the development of accurate fishâbased methods (IBI, Index of Biotic Integrity) to assess the environmental quality of aquatic ecosystems. In this study, the environmental typology of the rivers and streams in the region of Chapada Diamantina was developed. Thirtyâfive sampling sites representative of the upper Paraguaçu River and its main tributaries were characterized to characterize the fish assemblages and abiotic environmental descriptors. A cluster analysis based on fish species CPUE was performed to define a first biological typology. Then, a discriminant analysis model was developed to select the environmental descriptors that explained the fishâbased river types. The model selected 11 environmental variables and classified 91% of the cases. The river typology defined in this study will be used for the development of an IBI to assess the ecological status of the Chapada Diamantina rivers. It is expected that both the typology developed here and the future IBI will provide important and useful tools to develop and apply nature conservationâoriented management schemes in the Chapada Diamantina aquatic ecosystems.info:eu-repo/semantics/acceptedVersio
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CO2 conversion to phenyl isocyanates by uranium(vi) bis(imido) complexes.
Uranium(vi) trans-bis(imido) complexes [U(Îș4-{(tBu2ArO)2Me2-cyclam})(NPh)(NPhR)] react with CO2 to eliminate phenyl isocyanates and afford uranium(vi) trans-[O[double bond, length as m-dash]U[double bond, length as m-dash]NR]2+ complexes, including [U(Îș4-{(tBu2ArO)2Me2-cyclam})(NPh)(O)] that was crystallographically characterized. DFT studies indicate that the reaction proceeds by endergonic formation of a cycloaddition intermediate; the secondary reaction to form a dioxo uranyl complex is both thermodynamically and kinetically hindered
Dengue and Zika viruses : epidemiological history, potential therapies, and promising vaccines
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Dengue virus (DENV), which can lead to fatal hemorrhagic fever, affects 390 million people worldwide. The closely related Zika virus (ZIKV) causes microcephaly in newborns and Guillain-BarrĂ© syndrome in adults. Both viruses are mostly transmitted by Aedes albopictus and Aedes aegypti mosquitoes, which, due to globalization of trade and travel alongside climate change, are spreading worldwide, paving the way to DENV and ZIKV transmission and the occurrence of new epidemics. Local outbreaks have already occurred in temperate climates, even in Europe. As there are no specific treatments, these viruses are an international public health concern. Here, we analyze and discuss DENV and ZIKV outbreaks history, clinical and pathogenesis features, and modes of transmission, supplementing with information on advances on potential therapies and restraining measures. Taking advantage of the knowledge of the structure and biological function of the capsid (C) protein, a relatively conserved protein among flaviviruses, within a genus that includes DENV and ZIKV, we designed and patented a new drug lead, pep14-23 (WO2008/028939A1). It was demonstrated that it inhibits the interaction of DENV C protein with the host lipid system, a process essential for viral replication. Such an approach can be used to develop new therapies for related viruses, such as ZIKV.This research was supported by Fundação para a CiĂȘncia e a Tecnologia â MinistĂ©rio da CiĂȘncia, Tecnologia e Ensino Superior (FCT-MCTES, Portugal), and Calouste Gulbenkian Foundation (FCG, Portugal) project Science Frontiers Research Prize 2010. N.M.S. acknowledges FCT-MCTES fellowship SFRH/BD/144585/2019. I.C.M. acknowledges FCT-MCTES program âConcurso de EstĂmulo ao Emprego CientĂficoâ (CEECIND/01670/2017).info:eu-repo/semantics/publishedVersio
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