Large polycyclic aromatic hydrocarbons (PAHs) are an important component of the interstellar medium. PAHs have been identified in the soluble and insoluble matter of carbonaceous chondrites (CCs). ...Here, we study the evolution of PAHs under conditions relevant to the interiors of asteroids and compare our results to PAHs observed in CCs. We have performed long‐term and short‐term hydrothermal experiments, in which we exposed PAH‐mineral mixture analogs of meteorites to temperature conditions representative of those predicted for asteroids interiors. Our results show that small PAHs with melting points within the aqueous alteration temperature of CCs form carbonaceous spherules in the presence of water. In this work, we describe the microstructure and morphology of these spherules. We discuss the similarities and differences compared to globules isolated from CCs.
Metal sulphides constitute cheap, naturally abundant, and environmentally friendly materials for energy storage applications and chemistry. In particular, iron (II) monosulphide (FeS, mackinawite) is ...a material of relevance in theories of the origin of life and for heterogenous catalytic applications in the conversion of carbon dioxide (CO2) towards small organic molecules. In natural mackinawite, Fe is often substituted by other metals, however, little is known about how such substitutions alter the chemical activity of the material. Herein, the effect of Ni doping on the structural, electronic, and catalytic properties of FeS surfaces is explored via dispersion-corrected density functional theory simulations. Substitutional Ni dopants, introduced on the Fe site, are readily incorporated into the pristine matrix of FeS, in good agreement with experimental measurements. The CO2 molecule was found to undergo deactivation and partial desorption from the doped surfaces, mainly at the Ni site when compared to undoped FeS surfaces. This behaviour is attributed to the energetically lowered d-band centre position of the doped surface, as a consequence of the increased number of paired electrons originating from the Ni dopant. The reaction and activation energies of CO2 dissociation atop the doped surfaces were found to be increased when compared to pristine surfaces, thus helping to further elucidate the role Ni could have played in the reactivity of FeS. It is expected that Ni doping in other Fe-sulphides may have a similar effect, limiting the catalytic activity of these phases when this dopant is present at their surfaces.
Magnesite growth in chloride and sulfate-rich solutions has been examined at 90 °C in situ using phase-shift interferometry (PSI) and ex situ using atomic force microscopy (AFM) to evaluate the ...feasibility of cosequestering SO2 and CO2 in Mg-rich rocks. Although sulfate may assist desolvation at the magnesite surface, evidence for enhanced growth was only found at specific surface sites. The overall growth rates fit with those observed for chloride experiments in similarly saturated solutions. Thus, the formation of Mg-SO4 ion pairs in solution, which lowers the supersaturation with respect to magnesite, will have the dominant effect during sequestration. Lowering the activity of Mg(2+) ions in solution also inhibited the nucleation of other hydrated Mg-carbonate phases. As no evidence was found for sulfate incorporation into the growing magnesite, the presence of sulfate in solution will be detrimental to CO2 sequestration and is not expected to be cosequestered. The PSI data also emphasize the variability of reactivity over the surface and how this changes as a function of solution saturation and composition.
In situ observations during atomic force microscopy experiments and ex situ observations after static and flow-through experiments were used to explore the effect of three different electrolytes on ...magnesite (MgCO3) dissolution at pH 2. The experiments showed that the magnesite dissolution rate varied in the order NO3->Cl->SO42- when these anions were present in solution. Under the experimental conditions magnesite dissolution occurred via the removal of successive single surface layers, where changes in magnesite reactivity in the presence of different electrolytes could be observed as variations in the cycle length for the removal of one unit cell layer. The cycles began with the formation of sporadically distributed etch pits followed by the nucleation of homogeneously distributed etch pits. Coalescence of the etch pits formed isolated sections of the remnant surface, which then dissolved away. The timing of sporadic and homogeneous etch pit nucleation was constant despite the presence of different anions. However, the cycles in surface roughness and etch pit spreading rates indicate that the different anions affect step retreat rates and hence dissolution rates. Differences in magnesite reactivity can be attributed to the direct interaction of sulphate with the magnesite surface and the indirect effects of chloride and nitrate on the magnesite surface hydration and hydration of the Mg2+ ion in solution. In all experiments during the dissolution process evidence for the precipitation of a new phase was observed, either directly as precipitates forming on the magnesite surface in the AFM and after the experiments, seen in SEM analysis, or as changes in the Mg outlet concentration during flow-through experiments. EDX and Raman spectroscopy were used to analyse the composition of the precipitate and although it could not be definitively identified, considering previous observations the precipitate is most likely a hydrated Mg-carbonate phase with a MgCO3·xH2O composition. Thus, the formation of a precipitate can facilitate further magnesite dissolution by increasing the undersaturation of the interfacial solution.
Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation and ...serpentinization are spatio-temporally decoupled, we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched (
= 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted (
= 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe
2+
Mg
−1
exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium. This is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients
between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries.
Despite intensive high-dose multimodal therapy, high-risk neuroblastoma (NB) confers a less than 50% survival rate. This study investigates the role of replication stress in sensitivity to inhibition ...of Ataxia telangiectasia and Rad3-related (ATR) in pre-clinical models of high-risk NB. Amplification of the oncogene
always imparts high-risk disease and occurs in 25% of all NB. Here, we show that MYCN-induced replication stress directly increases sensitivity to the ATR inhibitors VE-821 and AZD6738. PARP inhibition with Olaparib also results in replication stress and ATR activation, and sensitises NB cells to ATR inhibition independently of
status, with synergistic levels of cell death seen in MYCN expressing ATR- and PARP-inhibited cells. Mechanistically, we demonstrate that ATR inhibition increases the number of persistent stalled and collapsed replication forks, exacerbating replication stress. It also abrogates S and G2 cell cycle checkpoints leading to death during mitosis in cells treated with an ATR inhibitor combined with PARP inhibition. In summary, increased replication stress through high MYCN expression, PARP inhibition or chemotherapeutic agents results in sensitivity to ATR inhibition. Our findings provide a mechanistic rationale for the inclusion of ATR and PARP inhibitors as a potential treatment strategy for high-risk NB.
Bacteria have developed resistance to antibiotics by various mechanisms, notable amongst these is the use of permeation barriers and the expulsion of antibiotics via efflux pumps. The ...resistance-nodulation-division (RND) family of efflux pumps is found in Gram-negative bacteria and a major contributor to multidrug resistance (MDR). In particular,
Salmonella
encodes five RND efflux pump systems: AcrAB, AcrAD, AcrEF, MdsAB and MdtAB which have different substrate ranges including many antibiotics. We produce a spatial partial differential equation (PDE) model governing the diffusion and efflux of antibiotic in
Salmonella
, via these RND efflux pumps. Using parameter fitting techniques on experimental data, we are able to establish the behaviour of multiple wild-type and efflux mutant
Salmonella
strains, which enables us to produce efflux profiles for each individual efflux pump system. By combining the model with a gene regulatory network (GRN) model of efflux regulation, we simulate how the bacteria respond to their environment. Finally, performing a parameter sensitivity analysis, we look into various different targets to inhibit the efflux pumps. The model provides an
in silico
framework with which to test these potential adjuvants to counter MDR.
Horse-related injuries account for one quarter of all paediatric sports fatalities. It is not known whether the pattern of injury spectrum and severity differ between children injured whilst mounted, ...compared with those injured unmounted around horses. We aimed to identify any distinctions between the demographic features, spectrum and severity of injuries for mounted versus unmounted patients.
Trauma registry data were reviewed for 505 consecutive paediatric patients (aged<16years) admitted to a large paediatric trauma centre with horse-related injuries over a 16-year period. Patients were classified into mounted and unmounted groups, and demographics, injury spectrum, injury severity, and helmet usage compared using odds ratios and Wilcoxon rank-sum tests.
More patients (56%) were injured in a private setting than in a sporting or supervised context (23%). Overall, head injuries were the most common horse-related injury. Mounted patients comprised 77% of the cohort. Mounted patients were more likely to sustain upper limb fractures or spinal injuries, and more likely to wear helmets. Unmounted were more likely to be younger males, and more likely to sustain facial or abdominal injuries. Strikingly, unmounted children had significantly more severe and critical Injury Severity Scores (OR 2.6; 95% CI 1.5, 4.6) and longer hospital stay (2.0days vs 1.1days; p<0.001). Unmounted patients were twice as likely to require intensive care or surgery, and eight times more likely to sustain a severe head injury.
Horse-related injuries in children are serious. Unmounted patients are distinct from mounted patients in terms of gender, age, likelihood of personal protective equipment use, severity of injuries, and requirement for intensive or invasive care. This study highlights the importance of vigilance and other safety behaviours when unmounted and around horses, and proposes specific targets for future injury prevention campaigns, both in setting of organised and private equestrian activity.
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