Third international challenge to model the medium- to long-range transport of radioxenon to four Comprehensive Nuclear-Test-Ban Treaty monitoring stations.

In 2015 and 2016, atmospheric transport modeling challenges were conducted in the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification, however, with a more limited scope with respect to emission inventories, simulation period and number of relevant samples (i.e., those above the Minimum Detectable Concentration (MDC)) involved. Therefore, a more comprehensive atmospheric transport modeling challenge was organized in 2019. Stack release data of Xe-133 were provided by the Institut National des Radioéléments/IRE (Belgium) and the Canadian Nuclear Laboratories/CNL (Canada) and accounted for in the simulations over a three (mandatory) or six (optional) months period. Best estimate emissions of additional facilities (radiopharmaceutical production and nuclear research facilities, commercial reactors or relevant research reactors) of the Northern Hemisphere were included as well. Model results were compared with observed atmospheric activity concentrations at four International Monitoring System (IMS) stations located in Europe and North America with overall considerable influence of IRE and/or CNL emissions for evaluation of the participants' runs. Participants were prompted to work with controlled and harmonized model set-ups to make runs more comparable, but also to increase diversity. It was found that using the stack emissions of IRE and CNL with daily resolution does not lead to better results than disaggregating annual emissions of these two facilities taken from the literature if an overall score for all stations covering all valid observed samples is considered. A moderate benefit of roughly 10% is visible in statistical scores for samples influenced by IRE and/or CNL to at least 50% and there can be considerable benefit for individual samples. Effects of transport errors, not properly characterized remaining emitters and long IMS sampling times (12-24 h) undoubtedly are in contrast to and reduce the benefit of high-quality IRE and CNL stack data. Complementary best estimates for remaining emitters push the scores up by 18% compared to just considering IRE and CNL emissions alone. Despite the efforts undertaken the full multi-model ensemble built is highly redundant. An ensemble based on a few arbitrary runs is sufficient to model the Xe-133 background at the stations investigated. The effective ensemble size is below five. An optimized ensemble at each station has on average slightly higher skill compared to the full ensemble. However, the improvement (maximum of 20% and minimum of 3% in RMSE) in skill is likely being too small for being exploited for an independent period.

Toward sensitive immuno-based detection of tau protein by surface plasmon resonance coupled to carbon nanostructures as signal amplifiers.

Interest on Tau protein is fast increasing in Alzheimer's disease (AD) diagnosis. There is the urgent need of highly sensitive and specific diagnostic platforms for its quantification, also in combination with the other AD hallmarks. Up to now, SPR has been poorly exploited for tau detection by immunosensing, due to sensitivity limits at nanomolar level, whereas the clinical requirement is in the picomolar range. Molecular architectures built in a layer-by-layer fashion, biomolecules and nanostructures (metallic or not) may amplify the SPR signal and improve the limit of detection to the desired sensitivity. Mostly gold nanostructures are widely employed to this aim, but great interest is also emerging in Multi Walled Carbon Nanotubes (MWCNTs). Here MWCNTs are modified and then decorated with the secondary antibody for tau protein. Eventually we took advantage from MWCNTs-antibody conjugate to obtain a sandwich-based bioassay with the capability to increase the SPR signal of about 102 folds compared to direct detection and conventional unconjugated sandwich. With respect to these results, we hope to give a strong impulse for further investigation on studying possible roles of carbon nanotubes in optical-based biosensing.

Preparation of small size palladium nanoparticles by picosecond laser ablation and control of metal concentration in the colloid.

We assessed a method for the preparation of small, highly stable and unprotected Pd nanoparticles by picosecond laser ablation in 2-propanol. The nanoparticles can be extracted from 2-propanol by centrifugation and redispersed in water, where a strongly negative ζ-potential assures long term stability. The proposed procedure permits reduction of particle size down to 1.6nm and optimization of the Pd(0):Pd(II) ratio which, in the best cases, was of the order of 6:1. The increase of this ratio with ablation times has been correlated to the high temperature conversion of PdO to metallic Pd by a simple theoretical model. A study of the relationship between colloid absorption at 400nm and Pd concentration permitted the role of PdO in the determination of the UV-vis spectra to be clarified and the limits of the Mie theory for the evaluation of colloid concentration to be established. The absorption at 400nm can be used as a fast method to estimate the Pd content in the colloids, provided that a calibration of the ablation process is preliminarily performed.

Chiral/ring closed vs. achiral/open chain triazine-based organogelators: induction and amplification of supramolecular chirality in organic gels.

The purpose of this study is to compare the gelling behavior of two molecules: a chiral compound and its achiral counterpart. The chiral partner is characterized by a rigid, chiral pyrrolidine nucleus, while the achiral one contains a flexible diethanolamine moiety. The chiral compound is an already known good organogelator, but also the achiral compound shows remarkable gelling properties. Very interestingly, a small fraction of the chiral compound induces chirality and strong CD effects in its aggregates with the achiral one. The observed chirality amplification corresponds to a peculiar sergeant-and-soldier effect. Molecular modelling and CD calculations suggested a model for the supramolecular assembly of hetero-aggregates that fits the experimental data.

One-pot synthesis of cyclic nitrones and their conversion to pyrrolizidines: 7a-epi-crotanecine inhibits alpha-mannosidases.

[reaction: see text] A new straightforward and inexpensive one-pot procedure is described for the preparation of enantiopure five-membered cyclic nitrones starting from the corresponding lactols. Its efficiency relies on the condensation of unprotected hydroxylamine with readily available lactols and on the chemoselectivity of the subsequent esterification with methanesulfonyl chloride. The targeted enantiomerically pure pyrroline N-oxides are versatile synthetic intermediates: one of the nitrones so-obtained has been converted into new polyhydroxypyrrolizidines, analogues of the alkaloids rosmarinecine and crotanecine, which were assayed for their inhibitory activities toward 22 commercially available glycosidase enzymes. One of them ((-)-7a-epi-crotanecine) is a potent and selective inhibitor of alpha-mannosidases from jack beans and almonds.