Assembly of Tight Junction Strands: Claudin-10b and Claudin-3 Form Homo-Tetrameric Building Blocks that Polymerise in a Channel-Independent Manner.

Tight junctions regulate paracellular permeability size and charge selectively. Models have been proposed for the molecular architecture of tight junction strands and paracellular channels. However, they are not fully consistent with experimental and structural data. Here, we analysed the architecture of claudin-based tight junction strands and channels by cellular reconstitution of strands, structure-guided mutagenesis, in silico protein docking and oligomer modelling. Prototypic channel- (Cldn10b) and barrier-forming (Cldn3) claudins were analysed. Förster resonance energy transfer (FRET) assays indicated multistep claudin polymerisation, starting with cis-oligomerization specific to the claudin subtype, followed by trans-interaction-triggered cis-polymerisation. Alternative protomer interfaces were modelled in silico and tested by cysteine-mediated crosslinking, confocal- and freeze fracture EM-based analysis of strand formation. The analysed claudin mutants included also mutations causing the HELIX syndrome. The results indicated that protomers in Cldn10b and Cldn3 strands form similar antiparallel double rows, as has been suggested for Cldn15. Mutually stabilising -hydrophilic and hydrophobic - cis- and trans-interfaces were identified that contained novel key residues of extracellular segments ECS1 and ECS2. Hydrophobic clustering of the flexible ECS1 ß1ß2 loops together with ECS2-ECS2 trans-interaction is suggested to be the driving force for conjunction of tetrameric building blocks into claudin polymers. Cldn10b and Cldn3 are indicated to share this polymerisation mechanism. However, in the paracellular centre of tetramers, electrostatic repulsion may lead to formation of pores (Cldn10b) and electrostatic attraction to barriers (Cldn3). Combining in vitro data and in silico modelling, this study improves mechanistic understanding of paracellular permeability regulation by elucidating claudin assembly and its pathologic alteration as in HELIX syndrome.

Concentrations of iodine isotopes ((129)I and (127)I) and their isotopic ratios in aerosol samples from Northern Germany.

New data about (129)I, (127)I concentrations and their isotopic ratios in aerosol samples from the trace survey station of the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Northern Germany, are presented and discussed in this paper. The investigated samples were collected on a weekly basis during the years 2011 to 2013. Iodine was extracted from aerosol filters using a strong basic solution and was separated from the matrix elements with chloroform and was analysed by accelerator mass spectrometry (AMS) for (129)I and by inductively coupled plasma mass spectrometry (ICP-MS) for (127)I. The concentrations of (127)I and (129)I in aerosol filters ranged from 0.31 to 3.71 ng m(-3) and from 0.06 to 0.75 fg m(-3), respectively. The results of (129)I/(127)I isotopic ratios were in the order 10(-8) to 10(-7). The (129)I originated directly from gaseous emissions and indirectly from liquid emissions (via sea spray) from the reprocessing plants in Sellafield and La Hague. In comparison with the results of (131)I after the Fukushima accident, no contribution of (129)I from this accident was detectable in Central Europe due to the high background originating from the (129)I releases of the European reprocessing plants. (129)I atmospheric activity concentrations were compared with those of an anthropogenic radionuclide ((85)Kr). We did not find any correlation between (129)I and (85)Kr, both having nuclear reprocessing plant as the main source.

Impact of former uranium mining activities on the floodplains of the Mulde River, Saxony, Germany.

The Mulde River drains the former uranium mining areas in Saxony (Germany), which has led to a large-scale contamination of the river and the adjacent floodplain soils with radionuclides of the uranium decay series. The objective of the investigation is to quantify the long-term effect of former uranium mining activities on a river system. All of the investigated environmental compartments (water, sediment, soil) still reveal an impact from the former uranium mining and milling activities. The contamination of water has decreased considerably during the last 20 years due to the operation of water treatment facilities. The uranium content of the sediments decreased as well (on average by a factor of 5.6), most likely caused by displacement of contaminated material during flood events. Currently, the impact of the mining activities is most obvious in soils. For some of the plots activity concentrations of >200 Bq/kg of soil were detected for uranium-238. Alluvial soils used as grassland were found to be contaminated to a higher degree than those used as cropland.

Remediation of TENORM residues: risk communication in practice.

Despite several decades of studies on the risk assessment and risk perception of ionising radiation, risk management of radioactive materials remains a challenging issue. This is also true for wastes containing technologically enhanced naturally occurring radioactive materials. The present work focuses on the underlying reasons for communication problems between experts and affected members of the public. Exploring the case of a German remediation site with residual radioactive contamination in a residential area, the experts' as well as the residents' perspectives were studied by conducting qualitative interviews. Our results indicate a variety of reasons for communication problems on different levels of risk management and risk communication: the regulatory, the communicative and the moral levels. In the observed case, four salient causes for problems in risk communication and risk management emerged: the mismatch in understanding the residents' values, the issue of risk communication in an unforeseen situation, the problem of the regulatory gap between radiation protection and soil protection in regard to legacies with naturally occurring radioactive material in Germany, and the challenge of communicating a highly complex scientific issue to non-scientists. Moreover, one (at least partial) solution could be seen: the introduction of an external mediator. The results indicate that coordination of different health and environment protection disciplines-in this case radiation protection relating to soil protection-is possible and urgently needed. The opportunity to put, at least natural, radioactive material in line with other conventional industrial materials should be taken.

Thermal stability of organoclays: effects of duration and atmosphere of isothermal heating on iodide sorption.

Heating periods necessary to destroy iodide sorption capacity of the quaternary (alkyl) ammonium and phosphonium modified bentonites were determined using iodide sorption batches. For this purpose, prior to the batches the studied organoclays were isothermally heated in air in the temperature ranges of 110-180 °C and 160-300 °C, respectively. The temperature dependence of the heating periods was found to follow the Arrhenius relationship, which allowed a determination of Arrhenius parameters for the reaction leading to the loss of the iodide sorption capacity of a bentonite modified by CP(+) (cetylpyridinium), BE(+) (benzethonium), CTMA(+) (cetyltrimethylammonium), or TPP(+) (tetraphenylphosphonium) surfactant. At 160 °C, the thermal stability of the iodide sorption capacity of TPP(+)-bentonite is much higher than that of the second most stable CTMA(+)-bentonite (80 days vs 5 days). However, the obtained Arrhenius parameters predict that CTMA(+)-bentonite becomes the most stable one as the heating temperature decreases to 40 °C with iodide sorption still available for ∼12000 years as compared to ∼8000 years for TPP(+)-bentonite. Heating of the organoclays in a N(2)-atmosphere (<70 ppm O(2)) at 160 °C revealed that the strong deficit of molecular oxygen in the contacting atmosphere resulted in a strong increase of their thermal stability. For CTMA(+)-bentonite, this increase is equivalent to the stability increase due to a decrease of the heating temperature by ∼20 °C (from 160 °C to ∼140 °C). Accordingly, the iodide sorption capacity of CTMA(+)-bentonite at a heating temperature of 40 °C is predicted to be retained for ∼350,000 years in the absence of molecular oxygen.

Influence of (calcium-)uranyl-carbonate complexation on U(VI) sorption on Ca- and Na-bentonites.

The influence of uranyl-carbonate and calcium-uranyl-carbonate complexations on the kinetics of U(VI) (approximately 3.4 x 10(-3) mol L(-1)) sorption from NaNO3 and Ca(NO3)2 solutions on Na- and Ca-bentonites at circumneutral ambient conditions was investigated. Complexation of U(VI) in Ca2UO2(CO3)3(aq) aqueous species, dominating the U(VI) speciation in Ca(NO3)2 solution, reduces its adsorption on bentonite by a factor of 2-3 in comparison with that in (UO2)2CO3(OH)3- species, dominating in NaNO3 solution, within the studied period of time (21 days). As a result of the dissolution of accessory calcite, Ca2UO2(CO3)3(aq) can be formed in the initially Ca-free solution in contact with either Na- or Ca-bentonite. U(VI) adsorption on Na-bentonite is a factor of approximately 2 higher than that on Ca-bentonite for solutions with the Ca2UO2(CO3)3(aq) complex dominating aqueous U(VI) speciation. This favors use of Na-bentonite over that of Ca-bentonite in final disposal of radioactive waste. Furthermore, the observed strong correlation between U(VI) adsorption and Mg release as a result of montmorillonite dissolution indicates in agreement with previous findings that under the applied conditions U(VI) is adsorbed on the edge surface of montmorillonite, which is a major mineral phase of the studied clays.

Classical swine fever (CSF): a historical review of research and vaccine production on the Isle of Riems.

A review on classical swine fever (CSF) research and vaccine production is given about four historical periods (1924-1948, 1949-1969, 1970-1991, since 1992). Similar as to research on foot and mouth disease, applied topics as diagnosis, pathogenesis, epidemiology and control represented the CSF research over many years. The development of vaccines and application procedures, e.g. oral and aerogenic immunisation and combined vaccines for large pig farms were the prominent investigations between 1950 and the middle of 1980s. After being reduced in the first years after affiliation to the Federal Research Centre for Virus Diseases of Animals, CSF is one of the main topics of the research on the Isle of Riems, not at least because nowadays the German National Reference Laboratory for CSF was established on the Island.

Retardation capacity of organophilic bentonite for anionic fission products.

Sorption and diffusivity of iodide and pertechnetate (I- and TcO4-) on MX-80 bentonite with different hexadecylpyridinium (HDPy+) loadings were studied using equilibrium solutions of different ionic strengths. In HDPy(+)-modified bentonite, iodide and pertechnetate ions exhibited increasing sorption (characterized by the distribution ratio, Rd), while Cs+ and Sr2+ showed decreasing sorption with increasing organophilicity. In case of medium-loading levels, the simultaneous sorption of anions (I- and TcO4-) and cations (Cs+ and Sr2+) was observed. Sorption of ions was influenced by the composition of the electrolytes employed. It decreased gradually with increasing ionic strength of the electrolyte solutions. The experiments revealed the general tendency that the diffusivity (Da [cm2.s-1]) for iodide and pertechnetate decreases with increasing organophilicity and increases with increasing ionic strength of the equilibrium solutions, confirming the results of the sorption experiments. Additionally, some mineralogical and chemical investigations, like IR spectral analysis of the organo-bentonite samples and exchange behavior of HDPy+, were performed. On the basis of these analyses, it was concluded that the alkylammonium ions are sorbed as (1) HDPy+ cations, (2) HDPyCl molecules and (3) micelles with decreasing binding intensities in this order.