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•Chitosan thermoresponsivity is induced by glycerophosphate binding.•Binding stimulates formation of highly ordered hydrate structure of chitosan.•Hydrate structure melting triggers ...phase separation of the system.•Restoration of chitin-like structures after phase separation results in gelation.
Thermoresponsivity of chitosan induced by β-glycerophosphate (GP) in diluted aqueous solutions has been first studied by high-sensitivity differential scanning calorimetry. It has been found that the GP solutions of chitosan undergo a first-order phase transition upon heating. The onset of this transition coincides with the cloud point of the system. This allows one to identify the thermoresponsivity of chitosan as a macroscopic demonstration of the phase separation transition. The transition temperature, enthalpy, heat capacity increment, and width were determined as functions of GP and chitosan concentrations, and the dielectric constant of the solvent. Based on this data, we suggested that GP binds cooperatively to the chitosan matrix at low temperatures. The standard free energy of GP binding (Δbgint= −6 ± 1 kJ mol−1) was estimated from the DSC data. It was shown that the Okada–Tanaka model of cooperative hydration of polymers adequately describes the thermogram of the GP induced phase transition of chitosan.
High mass X-ray binaries hold the promise of allowing us to understand the structure of the winds of their supermassive companion stars by using the emission from the compact object as a backlight to ...evaluate the variable absorption in the structured stellar wind. The wind along the line of sight can change on timescales as short as minutes and below. However, such short timescales are not available for the direct measurement of absorption through X-ray spectroscopy with the current generation of X-ray telescopes. In this paper, we demonstrate the usability of color–color diagrams for assessing the variable absorption in wind accreting high mass X-ray binary systems. We employ partial covering models to describe the spectral shape of high mass X-ray binaries and assess the implication of different absorbers and their variability on the shape of color–color tracks. We show that in taking into account, the ionization of the absorber, and in particular accounting for the variation of ionization with absorption depth, is crucial to describe the observed behavior well.
Because of their inherently high flux allowing the detection of clear signals, black hole x-ray binaries are interesting candidates for polarization studies, even if no polarization signals have been ...observed from them before. Such measurements would provide further detailed insight into these sources' emission mechanisms. We measured the polarization of the gamma-ray emission from the black hole binary system Cygnus X-1 with the International Gamma-Ray Astrophysics Laboratory Imager on Board the Integral Satellite (INTEGRAL/IBIS) telescope. Spectral modeling of the data reveals two emission mechanisms: The 250- to 400-keV (kilo-electron volt) data are consistent with emission dominated by Compton scattering on thermal electrons and are weakly polarized. The second spectral component seen in the 400-keV to 2-MeV band is by contrast strongly polarized, revealing that the MeV emission is probably related to the jet first detected in the radio band.
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•Transition energetics of NIPAM-co-VSA microgels reveals their core-corona structure.•The mechanism of thermal transition in NIPAM microgels is a microphase separation.•IPN PNIPAM-PAA ...microgels reveal physiologically relevant pH- and thermoresponsivity.
Nano- and micro-sized stimuli-responsive polymer containers capable of an effective controlled binding and release of ionic amphiphilic drugs are highly demanded in drug delivery. Thermoresponsive cross-linked microgels based on N-isopropylacrylamide (NIPAM) were synthesized by precipitation polymerization in aqueous media. The microgels were functionalized by the introduction of an ionic component (acrylic acid, AA, or vinyl sulfonate, VSA) either as a comonomer (NIPAM-co-AA and NIPAM-co-VSA microgels) or interpenetrating polymer network (PNIPAM-PAA microgel). The thermoresponsive behavior of the microgels was investigated by high-sensitivity differential scanning calorimetry. Thermodynamic parameters of the phase transitions (the transition temperature, enthalpy, and width) for the copolymer and interpenetrating microgels were determined. The copolymer microgels involving weak and strong ionogenic groups differ drastically by the transition energetics. This implies different types of their primary structures provided by either comonomer affinity or segregation in the reaction mixture under the polymerization conditions. The microgel functionalization via interpenetrating networks does not affect notably the transition temperature typical of the reference parent PNIPAM microgel but reduces the transition cooperativity. An analysis of the heat capacity profile of the microgel phase transition reveals some features of the mechanism of the thermoresponsivity in the microgels.
Context.
The X-ray spectra of X-ray binaries are dominated by emission of either soft or hard X-rays which defines their soft and hard spectral states. While the generic picture is relatively well ...understood, little is known about the interplay of the various media at work, or about the reasons why some sources do not follow common behavior. Cygnus X-3 is amongst the list of X-ray binaries that show quite complex behavior, with various distinct spectral states not seen in other sources. These states have been characterized in many studies. Because of its softness and intrinsic low flux above typically 50 keV, very little is known about the hard X/soft gamma-ray (100–1000 keV) emission in Cygnus X-3.
Aims.
Using the whole INTEGRAL data base, we aim to explore the 3–1000 keV spectra of Cygnus X-3. This allows to probe this region with the highest sensitivity ever, and search for the potential signature of a high-energy non-thermal component as sometimes seen in other sources.
Methods.
Our work is based on state classification carried out in previous studies with data from the
Rossi
X-Ray Timing Explorer. We extend this classification to the whole INTEGRAL data set in order to perform a long-term state-resolved spectral analysis. Six stacked spectra were obtained using 16 years of data from JEM-X (3–25 keV), ISGRI (25–300 keV), and SPI (20–400 keV).
Results.
We extract stacked images in three different energy bands, and detect the source up to 200 keV. In the hardest states, our purely phenomenological approach clearly reveals the presence of an additonnal component > 50 keV in addition to the component usually interpreted as thermal Comptonization. We apply a more physical model of hybrid thermal/nonthermal corona (
EQPAIR
) to characterize this nonthermal component and compare our results with those of previous studies and analyses. Our modeling indicates a more efficient acceleration of electrons in states where major ejections are observed. We also evaluate and find a dependence of the photon index of the power law as a function of the strong orbital modulation of the source in the Flaring InterMediate state. This dependence could be due to a higher absorption when Cygnus X-3 is behind its companion. However, the uncertainties on the density column prevent us from drawing any firm conclusions.
ABSTRACT We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR). Despite the basic similarity ...of the observed spectra, there is clear spectral variability between epochs. To investigate this variability, we construct a model incorporating both the standard disk-corona continuum and relativistic reflection from the accretion disk, based on prior work on Cygnus X-1, and apply this model to each epoch independently. We find excellent consistency for the black hole spin and the iron abundance of the accretion disk, which are expected to remain constant on observational timescales. In particular, we confirm that Cygnus X-1 hosts a rapidly rotating black hole, , in broad agreement with the majority of prior studies of the relativistic disk reflection and constraints on the spin obtained through studies of the thermal accretion disk continuum. Our work also confirms the apparent misalignment between the inner disk and the orbital plane of the binary system reported previously, finding the magnitude of this warp to be ∼10°-15°. This level of misalignment does not significantly change (and may even improve) the agreement between our reflection results and the thermal continuum results regarding the black hole spin. The spectral variability observed by NuSTAR is dominated by the primary continuum, implying variability in the temperature of the scattering electron plasma. Finally, we consistently observe absorption from ionized iron at ∼6.7 keV, which varies in strength as a function of orbital phase in a manner consistent with the absorbing material being an ionized phase of the focused stellar wind from the supergiant companion star.
ABSTRACT
Since the discovery of cosmic rays (CRs) over a century ago, their origin remains an open question. Galactic CRs with energy up to the knee (1015 eV) are considered to originate from ...supernova remnants, but this scenario has recently been questioned due to lack of TeV γ-ray counterparts in many cases. Extragalactic CRs, on the other hand, are thought to be associated with accelerated particles in the relativistic jets launched by supermassive accreting black holes at the centre of galaxies. Scaled down versions of such jets have been detected in X-ray binaries hosting a stellar black hole (BHXBs). In this work, we investigate the possibility that the smaller scale jets in transient outbursts of low-mass BHXBs could be sources of Galactic CRs. To better test this scenario, we model the entire electromagnetic spectrum of such sources focusing on the potential TeV regime, using the ‘canonical’ low-mass BHXB GX 339–4 as a benchmark. Taking into account both the leptonic radiative processes and the γ-rays produced via neutral pion decay from inelastic hadronic interactions, we predict the GeV and TeV γ-ray spectrum of GX 339–4 using lower frequency emission as constraints. Based on this test-case of GX 339–4, we investigate whether other, nearby low-mass BHXBs could be detected by the next-generation very-high-energy γ-ray facility the Cherenkov Telescope Array, which would establish them as additional and numerous potential sources of CRs in the Galaxy.
Context. 0.1–10 MeV observations of the black hole microquasar Cygnus X-1 have shown the presence of a spectral feature in the
form of a power law in addition to the standard black body (0.1–10 keV) ...and Comptonization (10–200 keV) components observed
by INTEGRAL in several black-hole X-ray binaries. This so-called “high-energy tail” was recently shown to be strong in the hard
spectral state of Cygnus X-1, and, in this system, has been interpreted as the high-energy part of the emission from a compact jet.
Aims. This result was nevertheless obtained from a data set largely dominated by hard state observations. In the soft state, only upper
limits on the presence and hence the potential parameters of a high-energy tail could be derived. Using an extended data set, we aim
to obtain better constraints on the properties of this spectral component in both states.
Methods. We make use of data obtained from about 15 years of observations with the INTEGRAL satellite. The data set is separated
into the different states and we analyze stacked state-resolved spectra obtained from the X-ray monitors, the gamma-ray imager, and
the gamma-ray spectrometer (SPI) onboard.
Results. A high-energy component is detected in both states, confirming its earlier detection in the hard state and its suspected
presence in the soft state with INTEGRAL, as seen in a much smaller SPI data set. We first characterize the high-energy tail components in the two states through a model-independent, phenomenological analysis. We then apply physical models based on hybrid Comptonization (eqpair and belm). The spectra are well modeled in all cases, with a similar goodness of the fits. While in the
semi-phenomenological approach the high-energy tail has similar indices in both states, the fits with the physical models seem to
indicate slightly different properties. Based on this approach, we discuss the potential origins of the high-energy components in both
the soft and hard states, and favor an interpretation where the high-energy component is due to a compact jet in the hard state and
hybrid Comptonization in either a magnetized or nonmagnetized corona in the soft state.
Activin receptor-like kinase 1 (ALK1), an endothelial cell-specific type I receptor of the TGF-β superfamily, is an important regulator of normal blood vessel development as well as pathological ...tumor angiogenesis. As such, ALK1 is an important therapeutic target. Thus, several ALK1-directed agents are currently in clinical trials as anti-angiogenic cancer therapeutics. Given the biological and clinical importance of the ALK1 signaling pathway, we sought to elucidate the biophysical and structural basis underlying ALK1 signaling. The TGF-β family ligands BMP9 and BMP10 as well as the three type II TGF-β family receptors ActRIIA, ActRIIB, and BMPRII have been implicated in ALK1 signaling. Here, we provide a kinetic and thermodynamic analysis of BMP9 and BMP10 interactions with ALK1 and type II receptors. Our data show that BMP9 displays a significant discrimination in type II receptor binding, whereas BMP10 does not. We also report the crystal structure of a fully assembled ternary complex of BMP9 with the extracellular domains of ALK1 and ActRIIB. The structure reveals that the high specificity of ALK1 for BMP9/10 is determined by a novel orientation of ALK1 with respect to BMP9, which leads to a unique set of receptor-ligand interactions. In addition, the structure explains how BMP9 discriminates between low and high affinity type II receptors. Taken together, our findings provide structural and mechanistic insights into ALK1 signaling that could serve as a basis for novel anti-angiogenic therapies.
Background: Activin receptor-like kinase 1 (ALK1) is an important regulator of normal blood vessel formation and pathological tumor angiogenesis.
Results: Crystal structure of ALK1-BMP9-ACTRIIB signaling complex and kinetic and thermodynamic properties of receptor-ligand interactions are described.
Conclusions: ALK1 achieves high specificity for BMP9/10 through unusual receptor positioning and unique receptor-ligand interface.
Significance: Structural and mechanistic insights into ALK1 signaling provide a framework for novel anti-angiogenic therapies.
Endoglin (CD105), a transmembrane protein of the transforming growth factor β superfamily, plays a crucial role in angiogenesis. Mutations in endoglin result in the vascular defect known as ...hereditary hemorrhagic telangiectasia (HHT1). The soluble form of endoglin was suggested to contribute to the pathogenesis of preeclampsia. To obtain further insight into its function, we cloned, expressed, purified, and characterized the extracellular domain (ECD) of mouse and human endoglin fused to an immunoglobulin Fc domain. We found that mouse and human endoglin ECD-Fc bound directly, specifically, and with high affinity to bone morphogenetic proteins 9 and 10 (BMP9 and BMP10) in surface plasmon resonance (Biacore) and cell-based assays. We performed a function mapping analysis of the different domains of endoglin by examining their contributions to the selectivity and biological activity of the protein. The BMP9/BMP10 binding site was localized to the orphan domain of human endoglin composed of the amino acid sequence 26–359. We established that endoglin and type II receptors bind to overlapping sites on BMP9. In the in vivo chick chorioallantoic membrane assay, the mouse and the truncated human endoglin ECD-Fc both significantly reduced VEGF-induced vessel formation. Finally, murine endoglin ECD-Fc acted as an anti-angiogenic factor that decreased blood vessel sprouting in VEGF/FGF-induced angiogenesis in in vivo angioreactors and reduced the tumor burden in the colon-26 mouse tumor model. Together our findings indicate an important role of soluble endoglin ECD in the regulation of angiogenesis and highlight efficacy of endoglin-Fc as a potential anti-angiogenesis therapeutic agent.
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