Sels d'aziridinium stables c-fonctionnalisés II: Stéréochimie de la quaternisation,synthèses stérèodirigées de composés n-trideutériométhylés et attribution de leurs configurations relatives par el'fet overhauser nucléaire

Aziridines bearing a functionality on a ring carbon and an alkyl or deuteriomethyal group on nitrogen have been quaternized at different temperatures. The configurations of the resulting, stable, diastereomeric aziridinium ions have been assigned by Nuclear Overhauser effect. The stereoselectivity in quaternization is discussed.     

Self-organized criticality in the olami-feder-christensen model

A system is in a self-organized critical state if the distribution of some measured events obeys a power law. The finite-size scaling of this distribution with the lattice size is usually enough to assume that the system displays self-organized criticality. This approach, however, can be misleading. In this paper we analyze the behavior of the branching rate sigma of the events to establish whether a system is in a critical state. We apply this method to the Olami-Feder-Christensen model to obtain evidence that, in contrast to previous results, the model is critical in the conservative regime only.     

Evolution of the modulated antiferromagnetic structure of CeAl2 in the presence of nonmagnetic impurities

Neutron diffraction studies show that the alloy system Ce_1-xLa_xAl₂ with x = 0.1 and 0.2 orders in the same incommensurate modulated antiferromagnetic structure as the pure compound CeAl₂. The existence and concentration dependence of a commensurate extra reflection ($\text{5}\text{2}$$\text{3}\text{2}$$\text{1}\text{2}$) is interpreted as being due to a modulation quenching of the CeAl₂ structure. This is in contrast to the suggestion that the magnetic order of CeAl₂ can be described by a triple-q structure.     

Polarized neutron study of the RA12 compound: I. Magnetization density in NdA12

The magnetization density of the ferromagnet NdA1₂ has been studied by diffraction of polarized neutrons on single crystals. The data have been treated as well in direct space using Fourier transformation techniques as in reciprocal space with the tensor operator method. The two treatments give the same result: besides the localized magnetization due to the 4f electrons of Nd, and corresponding to 2.61 μ_B, there exist another magnetization, opposite to the first one, which fluctuates throughout the cell with a pronounced extremum around the Nd atoms. Its integrated value is -0.14 μ_B/ND. The 4f electron wave function corresponding to the localized magnetization has been determined.     

Could we expect new praziquantel derivatives? A meta pharmacometrics/pharmacoinformatics analysis of all antischistosomal praziquantel derivatives found in the literature

Praziquantel (PZQ) is the first line drug for the treatment of human Schistosoma spp. worm infections. However, it suffers from low activity towards immature stages of the worm, and its prolonged use induces resistance/tolerance. During the last 40 years, 263 PZQ analogues have been synthesized and tested against Schistosoma spp. worms, but less than 10% of them showed significant activity. Here, we propose a rationalization of the chemical space of the PZQ derivatives by a ligand-based approach. First, we constructed an in-house database with all PZQ derivatives available in the literature. This analysis shows a high heterogeneity in the data. Fortunately, all studies include PZQ as a reference, permitting the classification of compounds into three classes according to their activities. Models involving ligand-based pharmacophore and logistic regression were performed. Five physicochemical parameters were identified as the best to explain the biological activity. In the end, we proposed new PZQ derivatives with modifications at positions 1 and 7, we analysed them with our models, and we observed that they can be more active than the previously synthesized derivatives. The main goal of this work was to conduct the most valuable meta-pharmacometrics/pharmacoinformatics analysis with all Praziquantel medicinal chemistry data available in the literature.     

Magnetic behavior of HoAl2 single crystal

Heat capacity measurements recently reported on the compound HoAl₂ show an unexplained peak at 20 K. Magnetic measurements on a single crystal of HoAl₂ reveal the existence, at this temperature, of a first order reorientation of the holmium moment.     

Magnetic structure of the compound CeIn3

Neutron diffraction measurements on the CeIn₃ compound show that the magnetic ordered phase is an antiferromagnetic one with a propagation vector ($\text{1}\text{2}$, $\text{1}\text{2}$, $\text{1}\text{2}$) and a weak value of the magnetic moment 0.48±0.08 μ_B. Comparison are made with the CeAl₂ and CeSn₃ cases.     

Quasi-TEM mode propagation in twin-wire THz waveguides

We numerically investigate the trade-offs between the dispersion properties,coupling efficiency,and geometrical constraints in dual-wire (twin-lead) terahertz (THz) waveguides.In particular,we show that their inherent linearly polarized quasi-transverse electromagnetic (TEM) modes exist for waveguide transverse dimensions comparable with the wavelength,enabling significant end-fire coupling (>10%) for numericalaperture limited Gaussian beams while supporting a relatively low-dispersion propagation of below 0.5 ps 2 /m,as desired for short-pulse time-domain spectroscopy applications.Starting from the dual-wire structure,we also demonstrate that low-dispersion tapers can be designed to improve coupling efficiency.     

On the magnetic ordering of CeAl2

The magnetic behaviour of CeAl₂ at low temperature is not apparent : contradictory experiments have assumed either an antiferromagnetic ordering or a moment reduction of the Ce³⁺ ion. Using the multidetector D1B at the I.L.L. high flux reactor, we have measured neutron diffraction diagrams, above and below the transition temperature of 3.8 K. At 1.9 K, we have found very weak magnetic reflections corresponding to an antiferromagnetic structure sinusoǐdally modulated, according to the propagation vector (0.612, 0.388, 0.5). The moment reduction in such a modulated structure at 1.9 K can hardly be explained by a thermal partial disordering of the moments. It is rather due to the existence of a singlet ground state resulting from the negative exchange between the 4f electron of Ce³⁺ and the conduction electrons.