Microwave-enhanced synthesis of new (-)-steganacin and (-)-steganone aza analogues

[reaction: see text]. A novel, microwave-enhanced, highly efficient protocol for the synthesis of hitherto unknown (-)-steganacin and (-)-steganone 7-aza analogues containing a 1,2,3-triazole ring has been presented. Microwave irradiation was found to be highly beneficial in promoting the Suzuki reaction and the 1,3-dipolar cycloaddition reaction to generate the highly strained medium-sized ring system of the title molecules.     

Properties of poly(vinyl alcohol)-graft-polyacrylamide copolymers depending on the graft length. 3. Benzene solubilization by solutions of the copolymer

The peculiarities of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), which are characterized by the equal average number (N=9), but various molecular weight (or length) of graft chains, in comparison with individual PAA and PVA, were investigated in aqueous medium. Sharp rise in benzene solubilization in PVA-g-PAA solutions at M_PAA higher than 4.3·10⁵ has been established. It was shown that such effect is stipulated by the destruction of intramolecular polymer-polymer complex in the copolymer and increasing the benzene binding to separate PVA-g-PAA groups by means of hydrogen bonds. The changes in the PVA-g-PAA solubilizing ability as the function of temperature were also investigated. The obtained results are discussed from the point of view of conformational transitions of intramolecular polymer-polymer complexes (intraPPC), which exist in copolymers, in dependence on the length of graft chains.     

Palladium‐Catalyzed Chain‐Growth Polycondensation of AB‐type Monomers: High Catalyst Turnover and Polymerization Rates

Chain‐growth catalyst‐transfer polycondensations of AB‐type monomers is a new and rapidly developing tool for the preparation of well‐defined π‐conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu₃‐catalyzed Negishi chain‐growth polycondensation of AB‐type monomers, which proceeds with unprecedented TONs of above 100 000 and TOFs of up to 280 s^?1. In contrast, related AA/BB‐type step‐growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki‐type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst‐transfer process on both polymerization kinetics and catalyst lifetime has been revealed.     

A square‐planar NiII complex with an asymmetric coordination of a novel polynucleative 2,6‐diacetylpyridine bis{[2‐(hydroxyimino)propanoyl]hydrazone} ligand

The title compound, (2,6‐diacetylpyridine bis{[2‐(hydroxyimino)propanoyl]hydrazone}(2−))nickel(II) dimethyl sulfoxide solvate monohydrate, [Ni(C₁₅H₁₇N₇O₄)]·C₂H₆OS·H₂O, represents the first example of square‐planar N₄ coordination via N atoms with four different functions, namely amide, azomethine, hydroxyimino and pyridine. The coordination polyhedron of the central Ni atom has a slightly distorted square‐planar geometry. The 2,6‐diacetylpyridine bis{[2‐(hydroxyimino)propanoyl]hydrazone} ligand forms one six‐ and two five‐membered chelate rings, and a pseudo‐chelate ring through an intramolecular hydrogen bond with an amide group as donor and a deprotonated hydroxyimino group as acceptor, resulting in a pseudomacrocyclic arrangement.     

Equilibrium density of states and thermodynamic properties of a model glass former

This paper presents an analysis of the thermodynamics of a model glass former. We have performed equilibrium sampling of a popular binary Lennard-Jones model, employing parallel tempering Monte Carlo to cover the crystalline, amorphous, and liquid regions of configuration space. Disconnectivity graphs are used to visualize the potential energy landscape in the vicinity of a crystalline geometry and in an amorphous region of configuration space. The crystalline global minimum is separated from the bulk of the minima by a large potential energy gap, leading to broken ergodicity in conventional simulations. Our sampling reveals crystalline global minima that are lower in potential energy than some of the previous candidates. We present equilibrium thermodynamic properties based on parallel tempering simulations, including heat capacities and free energy profiles, which depend explicitly on the crystal structure. We also report equilibrium melting temperatures.     

Luminescent Analysis of Blood Serum for Diagnostics of Pathological and Pre-Pathological States of Cancer Patients

Journal of Fluorescence - This study is devoted to the development of a methodological approach to mathematical analysis and data interpretation of blood serum phosphorescence intensity in cancer...     

A martensitic phase transition in nanocrystalline 3Y-TZP powders under hydrostatic pressure conditions

The aim of this study was to produce yttria-stabilized zirconia nanopowders from zirconium oxychloride and zirconium oxynitrate salts using a co-precipitation technique, and to investigate the influence of hydrostatic pressure on the phase transition in these powders. It is shown that synthesis conditions and calcination temperature have a strong influence on the nanopowder's agglomeration, as well as on the stability of the tetragonal phase to phase transition under pressure conditions. Doped zirconia nanopowders synthesized from oxynitrate salts are more agglomerated and more stable than the oxychloride-based powders. Increasing the role of interfacial energy in agglomerated nanopowders leads to an increase in the stability of the tetragonal phase in doped zirconia nanopowders systems obtained at low and high calcination temperatures. Formation of separated nanoparticles at middle calcination temperature leads to a decrease in the stability of the tetragonal phase to phase transition under hydrostatic pressure conditions.