In biological fluids, proteins may associate with nanoparticles (NPs), leading to the formation of a so-called “protein corona” largely defining the biological identity of the particle. Here, we ...present a novel approach to assess apparent binding affinities for the adsorption/desorption of proteins to silver NPs based on the impact of the corona formation on the agglomeration kinetics of the colloid. Affinities derived from circular dichroism measurements complement these results, simultaneously elucidating structural changes in the adsorbed protein. Employing human serum albumin as a model, apparent affinities in the nanomolar regime resulted from both approaches. Collectively, our findings now allow discrimination between the formation of protein mono- and multilayers on NP surfaces.
All over the world, different types of nanomaterials with a diversified spectrum of applications are designed and developed, especially in the field of nanomedicine. The great variety of ...nanoparticles (NPs), in vitro test systems and cell lines led to a vast amount of publications with conflicting data. To identify the decisive principles of these variabilities, we conducted an intercomparison study of collaborating laboratories within the German DFG Priority Program SPP1313, using well-defined experimental parameters and well-characterized NPs. The participants analyzed the in vitro biocompatibility of silica and polymer NPs on human hepatoma HepG2 cells. Nanoparticle mediated effects on cell metabolism, internalization, and inflammation were measured. All laboratories showed that both nanoparticle formulations were internalized and had a low cytotoxicity profile. Interestingly, small variations in nanoparticle preparation, cell handling and the type of culture slide influenced the nanoparticle stability and the outcomes of cell assays. The round robin test demonstrated the importance of the use of clearly defined and characterized NPs and parameters for reproducible results across laboratories. Comparative analyses of in vitro screening methods performed in multiple laboratories are absolutely essential to establish robust standard operation procedure as a prerequisite for sound hazard assessment of nanomaterials.
Size distributions of silver NPs are determined (left) and the influence of individual ionic components on the agglomeration behavior (middle) and the H-bonding structure of water (right) studied.
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► Individual ionic contribution to the destabilization of colloidal silver nanoparticles. ► Determination of elemental charges on colloidal NPs. ► Concentration-dependent determination of ion-induced agglomeration rates. ► Ionic influence on the water near structure.
The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee–Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs.
This work presents theoretical studies that combine aspects of combustion and explosion theory with exoplanetary atmospheric science. Super-Earths could possess a large amount of molecular hydrogen ...depending on disk, planetary, and stellar properties. Super-Earths orbiting pre-main-sequence M-dwarf stars have been suggested to possess large amounts of O2(g) produced abiotically via water photolysis followed by hydrogen escape. If these two constituents were present simultaneously, such large amounts of H2(g) and O2(g) can react via photochemistry to form up to ∼10 Earth oceans. In cases where photochemical removal is slow, hence O2(g) can indeed build up abiotically, the atmosphere could reach the combustion-explosion limit. Then, H2(g) and O2(g) react extremely quickly to release energy and form liquid water together with modest amounts of hydrogen peroxide. These processes set constraints for H2(g) and O2(g) atmospheric compositions in Super-Earth atmospheres. Our initial study of the gas-phase oxidation pathways for modest conditions (Earth's insolation and ∼10th of a percent of H2(g)) suggests that H2(g) is oxidized by O2(g) into H2O(g) mostly via HOx and mixed HOx-NOx catalyzed cycles. Regarding other pairs of atmospheric species, we find that CO-O2 could attain explosive-combustive levels on mini gas planets for midrange C/O in the equilibrium chemistry regime (p > ∼1 bar). Regarding (CH4-O2), a small number of modeled rocky planets assuming Earth-like atmospheres orbiting cooler stars could have compositions at or near the explosive-combustive level although more work is required to investigate this issue.
Atmospheric temperature and mixing ratio profiles of terrestrial planets vary with the spectral energy flux distribution for different types of M-dwarf stars and the planetary gravity. We investigate ...the resulting effects on the spectral appearance of molecular absorption bands, that are relevant as indicators for potential planetary habitability during primary and secondary eclipse for transiting terrestrial planets with Earth-like biomass emissions. Atmospheric profiles are computed using a plane-parallel, 1D climate model coupled with a chemistry model. We then calculate simulated spectra using a line-by-line radiative transfer model. We find that emission spectra during secondary eclipse show increasing absorption of methane, water and ozone for planets orbiting quiet M0-M3 dwarfs and the active M-type star AD Leo compared to solar type central stars. However, for planets orbiting very cool and quiet M dwarfs (M4 to M7), increasing temperatures in the mid-atmosphere lead to reduced absorption signals, making the detection of molecules more difficult in such scenarios. Transmission spectra during primary eclipse show strong absorption features of CH4, N2O and H2O for planets orbiting quiet M0-M7 stars and AD Leo. The N2O absorption of an Earth-sized planet orbiting a quiet M7 star can even be as strong as the CO2 signal. However, ozone absorption decreases for planets orbiting such cool central stars due to chemical effects in the atmosphere. To investigate the effect on the spectroscopic detection of absorption bands with potential future satellite missions, we compute signal-to-noise-ratios (SNR) for a James Webb Space Telescope (JWST)-like aperture telescope.
Abstract
The field of systematics is experiencing a new molecular revolution driven by the increased availability of high-throughput sequencing technologies. As these techniques become more ...affordable, the increased genomic resources have increasingly far-reaching implications for our understanding of the Tree of Life. With c. 2000 species, Carex (Cyperaceae) is one of the five largest genera of angiosperms and one of the two largest among monocots, but the phylogenetic relationships between the main lineages are still poorly understood. We designed a Cyperaceae-specific HybSeq bait kit using transcriptomic data of Carex siderosticta and Cyperus papyrus. We identified 554 low-copy nuclear orthologous loci, targeting a total length of c. 1 Mbp. Our Cyperaceae-specific kit shared loci with a recently published angiosperm-specific Anchored Hybrid Enrichment kit, which enabled us to include and compile data from different sources. We used our Cyperaceae kit to sequence 88 Carex spp., including samples of all the five major clades in the genus. For the first time, we present a phylogenetic tree of Carex based on hundreds of loci (308 nuclear exon matrices, 543 nuclear intron matrices and 66 plastid exon matrices), demonstrating that there are six strongly supported main lineages in Carex: the Siderostictae, Schoenoxiphium, Unispicate, Uncinia, Vignea and Core Carex clades. Based on our results, we suggest a revised subgeneric treatment and provide lists of the species belonging to each of the subgenera. Our results will inform future biogeographic, taxonomic, molecular dating and evolutionary studies in Carex and provide the step towards a revised classification that seems likely to stand the test of time.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We find that variations in the UV emissions of cool M-dwarf stars have a potentially large impact upon atmospheric biosignatures in simulations of Earth-like exoplanets i.e. planets with Earth's ...development, and biomass and a molecular nitrogen–oxygen dominated atmosphere. Starting with an assumed black-body stellar emission for an M7 class dwarf star, the stellar UV irradiation was increased stepwise and the resulting climate-photochemical response of the planetary atmosphere was calculated. Results suggest a “Goldilocks” effect with respect to the spectral detection of ozone. At weak UV levels, the ozone column was weak (due to weaker production from the Chapman mechanism) hence its spectral detection was challenging. At strong UV levels, ozone formation is stronger but its associated stratospheric heating leads to a weakening in temperature gradients between the stratosphere and troposphere, which results in weakened spectral bands. Also, increased UV levels can lead to enhanced abundances of hydrogen oxides which oppose the ozone formation effect. At intermediate UV (i.e. with ×10 the stellar UV radiative flux of black body Planck curves corresponding to spectral class M7) the conditions are “just right” for spectral detection. Results suggest that the planetary ozone profile is sensitive to the UV output of the star from ~200–350nm.We also investigated the effect of increasing the top-of-atmosphere incoming Lyman-α radiation but this had only a minimal effect on the biosignatures since it was efficiently absorbed in the uppermost planetary atmospheric layer, mainly by abundant methane. Earlier studies have suggested that the planetary methane is an important stratospheric heater which critically affects the vertical temperature gradient, hence the strength of spectral emission bands. We therefore varied methane and nitrous oxide biomass emissions, finding e.g. that a lowering in methane emissions by ×100 compared with the Earth can influence temperature hence have a significant effect on biosignature spectral bands such as those of nitrous oxide. Our work emphasises the need for future missions to characterise the UV of cool M-dwarf stars in order to understand potential biosignature signals.
•Planetary biosignatures such as ozone and nitrous oxide sensitive to UV from cool red dwarfs.•Planetary methane abundance affected by chemistry-climate feedbacks.•Need red-dwarf spectra in UV region to improve planetary biosignature understanding.
Context. In recent years, more and more transiting terrestrial extrasolar planets have been found. Spectroscopy already yielded the detection of molecular absorption bands in the atmospheres of ...Jupiter and Neptune-sized exoplanets. Detecting spectral features in the atmosphere of terrestrial planets is the next great challenge for exoplanet characterization. Aims. We investigate the spectral appearance of Earth-like exoplanets in the habitable zone (HZ) of different main sequence (F, G, and K-type) stars at different orbital distances. We furthermore discuss for which of these scenarios biomarker absorption bands and related compounds may be detected during primary or secondary transit with near-future telescopes and instruments. Methods. Atmospheric profiles from a 1D cloud-free atmospheric climate-photochemistry model were used to compute primary and secondary eclipse infrared spectra. The spectra were analyzed taking into account different filter bandpasses of two photometric instruments planned to be mounted to the James Webb Space Telescope (JWST). We analyzed in which filters and for which scenarios molecular absorption bands are detectable when using the space-borne JWST or the ground-based European Extremely Large Telescope (E-ELT). Results. Absorption bands of carbon dioxide (CO2), water (H2O), methane (CH4) and ozone (O3) are clearly visible in both high-resolution spectra as well as in the filters of photometric instruments. However, only during primary eclipse absorption bands of CO2, H2O and O3 are detectable for all scenarios when using photometric instruments and an E-ELT-like telescope setup. CH4 is only detectable at the outer HZ of the K-type star since here the atmospheric modeling results in very high abundances. Since the detectable CO2 and H2O absorption bands overlap, separate bands need to be observed to prove their existence in the planetary atmosphere. In order to detect H2O in a separate band, a ratio S/N > 7 needs to be achieved for E-ELT observations, e.g. by co-adding at least 10 transit observations. Using a space-borne telescope like the JWST enables the detection of CO2 at 4.3 μm, which is not possible for ground-based observations due to the Earth’s atmospheric absorption. Hence combining observations of space-borne and ground-based telescopes might allow to detect the presence of the biomarker molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere. Other absorption bands using the JWST can only be detected for much higher S/Ns, which is not achievable by just co-adding transit observations since this would be far beyond the planned mission time of JWST.
Earth-like planets orbiting M dwarfs are prominent targets when searching for life outside the Solar System. We apply our Coupled Atmosphere Biogeochemical model to investigate the coupling between ...the biosphere, geosphere, and atmosphere in order to gain insight into the atmospheric evolution of Earth-like planets orbiting M dwarfs and to understand the processes affecting biosignatures and climate on such worlds. This is the first study applying an automated chemical pathway analysis quantifying the production and destruction pathways of molecular oxygen (O
) for an Earth-like planet with an Archean O
concentration orbiting in the habitable zone of the M dwarf star AD Leonis, which we take as a type-case of an active M dwarf. The main production arises in the upper atmosphere from carbon dioxide photolysis followed by catalytic hydrogen oxide radical (HO
) reactions. The strongest destruction does not take place in the troposphere, as was the case in Gebauer et al. ( 2017 ) for an early Earth analog planet around the Sun, but instead in the middle atmosphere where water photolysis is the strongest. Results further suggest that these atmospheres are in absolute terms less destructive for O
than for early Earth analog planets around the Sun despite higher concentrations of reduced gases such as molecular hydrogen, methane, and carbon monoxide. Hence smaller amounts of net primary productivity are required to oxygenate the atmosphere due to a change in the atmospheric oxidative capacity, driven by the input stellar spectrum resulting in shifts in the intrafamily HO
partitioning. Under the assumption that an atmosphere of an Earth-like planet survived and evolved during the early high-activity phase of an M dwarf to an Archean-type composition, a possible "Great Oxidation Event," analogous to that on Early Earth, would have occurred earlier in time after the atmospheric composition was reached, assuming the same atmospheric O
sources and sinks as on early Earth. Key Words: Earth-like-Oxygen-M dwarf stars-Atmosphere-Biogeochemistry-Photochemistry-Biosignatures-Earth-like planets. Astrobiology 18, 856-872.
Understanding the evolution of Earth and potentially habitable Earth-like worlds is essential to fathom our origin in the Universe. The search for Earth-like planets in the habitable zone and ...investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of Earth as a reference for Earth-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on early Earth. The Great Oxidation Event in Earth's history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O
concentrations are fixed to values inferred by geological evidence. Applying a unique tool (Pathway Analysis Program), ours is the first quantitative analysis of catalytic cycles that governed O
in early Earth's atmosphere near the Great Oxidation Event. Complicated oxidation pathways play a key role in destroying O
, whereas in the upper atmosphere, most O
is formed abiotically via CO
photolysis. The O
bistability found by Goldblatt et al. ( 2006 ) is not observed in our calculations likely due to our detailed CH
oxidation scheme. We calculate increased CH
with increasing O
during the Great Oxidation Event. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity of the biosphere that produces O
is unique. Mixing, CH
fluxes, ocean solubility, and mantle/crust properties strongly affect net primary productivity and surface O
fluxes. Regarding exoplanets, different "states" of O
could exist for similar biomass output. Strong geological activity could lead to false negatives for life (since our analysis suggests that reducing gases remove O
that masks its biosphere over a wide range of conditions). Key Words: Early Earth-Proterozoic-Archean-Oxygen-Atmosphere-Biogeochemistry-Photochemistry-Biosignatures-Earth-like planets. Astrobiology 16, 27-54.
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