Uranium migration through the Swiss Opalinus Clay varies on the metre scale in response to differences of the stability constant of the aqueous, ternary uranyl complex Ca₂UO₂(CO₃)₃

The simulation of uranium migration through the Swiss Opalinus Clay is used as an example to quantify the influence of varying values of a stability constant in the underlying thermodynamic database on the migration lengths for the repository scale. Values for the stability constant of the neutral, ternary uranyl complex Ca2UO2(CO3)3 differ in literature by up to one order of magnitude. Within the studied geochemical system, either the neutral or the anionic complex CaUO2(CO3)32- is the predominant one, depending on the chosen value for the neutral complex. This leads to a changed interaction with the diffuse double layers (DDL) enveloping the clay minerals and thus can potentially influence the diffusive transport of uranium. Hence, two identical scenarios only differing in the value for the stability constant of the Ca2UO2(CO3)3 complex were applied in order to quantify and compare the migration lengths of uranium on the host rock scale (50 m) after a simulation time of one million years. We ran multi-component diffusion simulations for the shaly and sandy facies in the Opalinus Clay. A difference in the stability constant of 1.33 log units changes the migration lengths by 5 to 7 m for the sandy and shaly facies, respectively. The deviation is caused by the anion exclusion effect. However, with a maximum diffusion distance of 22 m, the influence of the stability constant of the Ca2UO2(CO3)3 complex on uranium migration in the Opalinus Clay is negligible on the host rock scale.

Influence of Electrolyte Concentration on Single-Molecule Sensing of Perfluorocarboxylic Acids

Perfluorocarboxylic acids (PFCAs) are an emerging class of persistent organic pollutants. During the fabrication process, it is unavoidable to form PFCA homologs or isomers which exhibit distinct occurrence, bioaccumulation, and toxicity. The precision measurement of PFCAs is therefore of significant importance. However, the existing characterization techniques, such as LC-MS/MS, cannot fully meet the requirement of isomer-specific analysis, largely due to the lack of authentic standards. Single-molecule sensors (SMSs) based on nanopore electrochemistry may be a feasible solution for PFCAs determination, thanks to their ultra-high spatiotemporal resolutions. Hence, as a first step, this work was to elucidate the influence of electrolyte concentration on the four most critical indicators of nanopore measurements, and furthermore, performance of nanopore SMSs. More specifically, three of the most representative short-chain PFCAs, perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA) and perfluoroheptanoic acid (PFHpA), were adopted as the target analytes, aerolysin nanopore was employed as the sensing interface, and 2, 3 and 4 M KCl solutions were used as electrolytes. It was found that, when the concentration of KCl solution increased from 2 to 4 M, the conductance of aerolysin nanopore increased almost linearly at a rate of 0.5 nS per molar KCl within the whole voltage range, the current blockade of PFPeA at −50 mV increased from 61.74 to 66.57% owing to the enhanced steric exclusion effect, the maximum dwell time was more than doubled from 14.5 to 31.5 ms, and the barrier limited capture rate increased by 8.3 times from 0.46 to 3.85 Hz. As a result, when using 4 M KCl as the electrolyte, over 90% of the PFPeA, PFHxA and PFHpA were accurately identified from a mixed sample, and the calculated limit of detection of PFPeA reached 320 nM, more than 24 times lower than in 2 M KCl. It was thus clear that tuning the electrolyte concentration was a simple but very effective approach to improve the performance of nanopore SMSs for PFCAs determination.

The role of host cell glycans on virus infectivity: The SARS-CoV-2 case

Long and complex chains of sugars, called glycans, often coat both the cell and protein surface. Glycans both modulate specific interactions and protect cells. On the cell surface, these sugars form a cushion known as the glycocalyx. Here, we show that Heparan Sulfate (HS) chains - part of the glycocalyx - and other glycans - expressed on the surface of both host and virus proteins - have a critical role in modulating both attractive and repulsive potentials during viral infection. We analyse the SARS-CoV-2 virus, modelling its spike proteins binding to HS chains and two key entry receptors, ACE2 and TMPRSS2. We include the volume exclusion effect imposed on the HS chains impose during virus insertion into glycocalyx and the steric repulsion caused by changes in the conformation of the ACE2 glycans involved in binding to the spike. We then combine all these interactions, showing that the interplay of all these components is critical to the behaviour of the virus. We show that the virus tropism depends on the combinatorial expression of both HS chains and receptors. Finally, we demonstrate that when both HS chains and entry receptors express at high density, steric effects dominate the interaction, preventing infection.

Intra- and Inter-Specific Crosses among Centaurea aspera L. (Asteraceae) Polyploid Relatives—Influences on Distribution and Polyploid Establishment

How polyploids become established is a long-debated question, especially for autopolyploids that seem to have no evolutionary advantage over their progenitors. The Centaurea aspera polyploid complex includes diploid C. aspera and two related tetraploids C. seridis and C. gentilii. Our purpose was to study the mating system among these three taxa and to analyze its influence on polyploid establishment. The distribution and ploidy level of the Moroccan populations, and forced intra- and inter-specific crosses were assessed. Allotetraploid C. seridis produced more cypselae per capitulum in the intra-specific crosses. It is a bigger plant and autogamous, and previous studies indicated that selfing forces the asymmetric formation of sterile hybrids. All these characteristics help C. seridis to avoid the minority-cytotype-exclusion effect and become established. Inter-specific hybridization was possible between C. aspera and C. gentilii, and with the symmetric formation of hybrids. However, 49% of the hybrid cypselae were empty, which probably reveals postzygotic barriers. Autotetraploid C. gentilii produced the same number of cypselae per capitulum as those of the diploid parental, has an indistinguishable field phenotype, is allogamous, and symmetrically produces hybrids. Therefore, C. gentilii does not seem to have the same competitive advantages as those of C. seridis.

Molecular Packaging of Biocatalysts Using a Robust Protein Cage

In this paper, we report on the discovery of a novel, robust protein cage (encapsulin) that we could use for packaging various biocatalysts. We have elucidated the structure of the stable encapsulin by electron microscopy and X-ray diffraction. Furthermore, we developed an effective expression system for the encapsulin and a facile protocol for preparing encapsulated enzymes. By packaging and testing various enzymes (varying in size, oligomeric structure, and cofactor type) we demonstrate that, through encapsulation, the enzymes become significantly more stable. We also provide evidence that the pores of the encapsulin, through a size-exclusion effect, can modulate the substrate acceptance profile of an encapsulated enzyme.

Molecular Packaging of Biocatalysts Using a Robust Protein Cage

In this paper, we report on the discovery of a novel, robust protein cage (encapsulin) that we could use for packaging various biocatalysts. We have elucidated the structure of the stable encapsulin by electron microscopy and X-ray diffraction. Furthermore, we developed an effective expression system for the encapsulin and a facile protocol for preparing encapsulated enzymes. By packaging and testing various enzymes (varying in size, oligomeric structure, and cofactor type) we demonstrate that, through encapsulation, the enzymes become significantly more stable. We also provide evidence that the pores of the encapsulin, through a size-exclusion effect, can modulate the substrate acceptance profile of an encapsulated enzyme.

How Does Environmental Regulation Affect the Location of New Polluting Firms? Exploring the Agglomeration Threshold of Effective Environmental Regulation

Some scholars have already proved the important role of agglomeration in studying how environmental regulation (ER) affects the location of polluting firms. However, further research is needed on both the mechanism and the empirical evidence. This paper reports the construction of a location database of new chemical plants in China’s Yangtze River Economic Belt (YREB), where a fixed-effects panel threshold regression model was used to explore the agglomeration threshold of effective ER. We found a single agglomeration threshold for the whole YREB region that represented the turning point of ER from excluding to attracting new chemical enterprises. Additionally, there were two agglomeration thresholds in the lower reaches. If agglomeration reached the lower threshold, the effect of ER changed from repulsion to nonsignificant attraction. Once above the upper threshold, the attraction effect became large and significant. The results for this region were consistent with the Porter hypothesis. Furthermore, there was a single agglomeration threshold in the middle reaches. When agglomeration level exceeded the threshold, the repellant effect of ER was no longer significant. In the upper reaches, we found no valid threshold and ER always exhibited a small and nonsignificant exclusion effect. The pollution haven hypothesis was more explanatory in the middle and upper reaches. In the end, some suggestions are provided to support the government to formulate differentiated environmental policies.