2,3,4,5,6‐Penta­nitro­aniline 1,2‐dichloro­ethane disolvate: `push–pull' deformation of aromatic rings by intra­molecular charge transfer

The title compound, C₆H₂N₆O₁₀·2C₂H₄Cl₂, forms layered stacks of penta­nitro­aniline mol­ecules, which possess twofold symmetry. The voids between these stacks are occupied by dichloro­ethane mol­ecules, which reside near a 2/m symmetry element and display pseudo‐inversion symmetry. The C atoms in one of the two solvent mol­ecules are threefold disordered. In the penta­nitro­aniline mol­ecule, considerable distortion of the benzenoid ring, coupled with the short C—N(H₂) bond and out‐of‐plane NO₂ twistings, point to significant intra­molecular `push–pull' charge transfer at the amino‐ and nitro‐substituted (ortho and para) positions, as theoretically quantified by natural bond orbital analysis of the π‐electron density.     

TeSe3]2- and [TeSe2]2- as synthons

The [Au2(TeSe2)2]2- anion has been prepared from the reaction of [TeSe3]2- with AuCN in DMF in the presence of PEt3 and from the reaction of [TeSe2]2- with AuCN in DMF. Reaction of [TeSe2]2- with AuCN in DMF in the presence of PEt3 leads ultimately to the [Au2(Te2)2]2- anion.     

Layer-by-layer adsorption of polyelectrolyte and surfactant and adsorption of their complexes on solid surface

The capillary electrokinetics method (measurement of streaming potential and current in a capillary with a radius of 5–7 μm made of fused quartz) is employed to study the structure formation at interfaces between quartz and solutions containing a cationic polyelectrolyte (poly(diallyldimethylammonium chloride) with molecular mass M = 100000−200000) and an anionic surfactant (sodium dodecyl sulfate). The kinetics of surface layer formation is studied upon the layer-by-layer adsorption of the components and the adsorption of their complexes at the same component ratios. It is established that the formation time and the electrokinetic potentials of the surface layers are almost independent of the procedure of their formation. In the case of the layer-by-layer adsorption, the first layers of the polyelectrolyte appear to be virtually undeformed, thus indicating that molecules with a planar conformation prevail in the adsorption layer. Surfactant adsorption enhances the deformation (layer loosening), which decreases with time (layer aging). Layers formed from the complexes have a denser (less deformable) structure. Variations in the electrokinetic potentials of the layers during the long-term pumping of a background electrolyte solution through a capillary witnesses the prevailing desorption of the anionic surfactant, with the desorption being noticeably more pronounced for the layers resultant from the adsorption of the complexes.     

Experimental Study of Zirconium(IV) Extraction from Fluoride-Containing Acid Solutions

Zirconium(IV) extraction from acid solutions was studied, and the optimal parameters of the process were found. Extractants for zirconium(IV) recovery from nitric and sulfuric acid solutions in the presence of fluoride ions were selected. The distribution coefficients of zirconium(IV) and fluoride ion were determined.     

Crystal‐Structure‐Guided Design of Self‐Assembling RNA Nanotriangles

RNA nanotechnology uses RNA structural motifs to build nanosized architectures that assemble through selective base‐pair interactions. Herein, we report the crystal‐structure‐guided design of highly stable RNA nanotriangles that self‐assemble cooperatively from short oligonucleotides. The crystal structure of an 81 nucleotide nanotriangle determined at 2.6 Å resolution reveals the so‐far smallest circularly closed nanoobject made entirely of double‐stranded RNA. The assembly of the nanotriangle architecture involved RNA corner motifs that were derived from ligand‐responsive RNA switches, which offer the opportunity to control self‐assembly and dissociation.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.