Synthesis and Properties of Higher Nuclearity Polyazanes

Polyazanes (i.e., higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5), including the first pentazane ever described, were prepared by the addition of lower-order polyazanes to diazo reagents. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement persists in solution. Although the polyazanes are all reducing agents, they become less so as the number of nitrogens increases.     

(E)‐3‐(4‐Methylphenyl)‐2‐(2‐thienyl)acrylonitrile has Z′ = 0.75 in the space group C2/m: fourfold disordered molecules lie in channels enclosed by fully ordered molecules

The title compound, C₁₄H₁₁NS, crystallizes with Z′ = 0.75 in the space group C2/m. Two independent molecules are present, one of which lies with all the non‐H atoms on a mirror plane, while the other is fourfold disordered across a site of 2/m symmetry. The ordered molecules are stacked such that they enclose continuous channels running along twofold rotation axes, and the disordered molecules are positioned within these channels.     

Development of an analytical approach for determination of total arsenic and arsenic (III) in airborne particulate matter by slurry sampling and HG-FAAS

Slurry sampling (SS) with hydride generation atomic absorption spectrometry (HG-AAS) was used to analyze 3 particulate matter samples collected in the Bananeira Village, Brazil, in 2005. The relative standard deviation (RSD), used to assess the precision, was lower than 4.8%. The accuracy of this method was confirmed by the analysis of certified atmospheric particulate matter urban dust reference material SRM 1649a. This method (SS/HG-AAS) was used to determine total arsenic and arsenic (III) in three particulate matter samples. In these samples, the total arsenic concentrations varied from 3.8 to 20.0 ng m^− 3, while As (III) concentrations varied from 2.7 to 10.5 ng m^− 3. All samples were also analyzed using acid digestion in digest block with cold finger and detection for HG-AAS. A paired t-test demonstrated no significant difference (95% CL) between the results obtained using these two sample preparation procedures. The limit of quantification, calculated considering the mass of particulate matter collected on every filter, was 0.6 ng m^− 3 for As total and 1.0 ng m^− 3 for As (III).     

Light scattering and cryo-transmission electron microscopy investigation of the self-assembling behavior of Di-C12P-nucleosides in solution

Aggregates formed from freshly prepared and annealed samples of dilauroyl-phosphatidyl-adenosine, dilauroyl-phosphatidyl-uridine, and their 1:1 mixture have been investigated by dynamic light scattering, cryo-transmission electron microscopy (cryo-TEM) observations, and circular dichroism. The two surfactants differ only for the nucleoside at the phospholipid polar headgroup and self-assemble in solution to form supramolecular structures that behave dissimilarly. The uridine derivative forms long wormlike aggregates that are invariant with the aging of the solution, while the wormlike aggregate of the adenosine derivative undergoes, as the sample ages, a subsequent self-assembling process forming giant helicoidal aggregates that coexist with the smaller wormlike aggregates. Dynamic light scattering and cryo-TEM show that the large helicoidal structures are formed at the expense of the small wormlike micelles. The 1:1 mixture behaves as the adenosine derivative and evolves to form giant superstructures for all the lipid concentrations investigated. Circular dichroism measurements suggest that the formation of the supramolecular helicoidal structure might not be driven by a purely chiral effect, but rather stacking and hydrogen bonding, present at the phospholipid headgroups of the self-assembled nucleosides, contribute to the final supramolecular structure.     

3D printed honeycomb bilayer structures based on polylactic acid as lightweight microwave absorbing materials

3D printed honeycomb structures constituted by neat polylactic acid (PLA) and conductive PLA (PLAc) with different cell sizes and thicknesses were manufactured through 3D printing technology based on material extrusion (MEX). These structures were arranged into bi-layer honeycomb structures (BHS) for evaluation of the microwave absorbing properties at the X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz) frequency ranges. The effects of cell size, sample thickness, layer thickness ratio and the nature of the top layer on the electromagnetic attenuation performance of BHS samples were investigated in terms of reflection loss (RL). The components geometric characteristics and the arrangement of the layers exerted great influence on the RL values and effective absorption bandwidth (EAB). Overall the bilayer structures with 5 mm total thickness presented the best EM response in terms of EAB and minimum RL, where the component with the larger cell size (7.7 mm), PLAc (1 mm) as the top layer and PLA (4 mm) as the bottom layer exhibited the best results with RL values of −41 dB and EAB of 9.5 GHz. The BHS system with 7.7 mm cell size was more efficient in Ku band frequency range, whereas that with 3.5 mm cell size gave better response in the X-band frequency range. Therefore, RL values and EAB can be adjustable by modifying the building strategy of the printed parts, such as thickness of the sample, cell size and thickness distribution of the conductive and non-conductive layers. The findings in this work show the importance of the building strategy to fabricate components with controllable BHS and improved properties for microwave absorption application.     

Silica-supported metallocenes: stereochemical comparison between homogeneous and heterogeneous catalysis

Propylene was polymerized in the presence of the isospecific Et(Ind)₂ZrCl₂ (Et: ethylene, Ind: indenyl) and the aspecific (Ind)₂ZrCl₂ complexes in solution and anchored to SiO₂ and SiO₂/MAO (MAO: methylaluminoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that (i) the same active species is formed when a metallocene is in solution and when it is anchored to the SiO₂/MAO support and (ii) a completely different active species is formed when the metallocene is anchored to the silica. The fact that both systems Et(Ind)₂ZrCl₂ SiO₂ and (Ind)₂ZrCl₂ SiO₂ produce the same prevailingly isospecific polymer suggests that only isospecific centers are formed in this case, independently of the metallocene stereochemical structure.     

Tools for the eigenvalue distribution in a non-Hermitian setting

Under mild trace norm assumptions on the perturbing sequence, we extend a recent perturbation result based on a theorem by Mirsky. The analysis concerns the eigenvalue distribution and localization of a generic (non-Hermitian) complex perturbation of a bounded Hermitian sequence of matrices. Some examples of application are considered, ranging from the product of Toeplitz sequences to the approximation of PDEs with given boundary conditions. A final discussion on open questions and further lines of research ends the note.