Highly accurate radiochemical neutron activation analysis of arsenic in biological materials involving selective isolation of arsenic by hybrid and conventional ion exchange

A highly accurate (definitive) radiochemical neutron activation analysis (RNAA) method was developed for the determination of traces of arsenic (As) in biological materials. It consists of the following steps: (a) irradiation in the nuclear reactor; (b) microwave-assisted sample digestion; (c) quantitative and selective radiochemical separation of arsenates on hydrated ferric oxide nanoparticles dispersed in a macroporous cation exchanger, preceded by a conventional strongly acidic cation exchanger column, and (d) gamma-ray spectrometric measurement of ⁷⁶As. The suitability and accuracy of the method was demonstrated by analysing several certified reference materials. The detection limit is 8 ng g^?1. The standard uncertainty in the determination of As in oriental tobacco leaves is around 3.4%. This, together with its compliance with several other formal requirements, makes the method comparable to primary methods based on isotope dilution mass spectrometry.     

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes

The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,β′-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6 , bispalladium(II) dioxo-di-p-pyrirubyrin 9 , and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting ( 9 ) the wavelength of Yb-based fiber lasers. The incorporation of an α,β′-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules.     

Porous Molecular Capsules as Non-Polymeric Transducers of Mechanical Forces to Mechanophores

Mechanical grinding/milling can be regarded as historically the first technology for changing the properties of matter. Mechanically activated molecular units (mechanophores) can be present in various structures: polymers, macromolecules, or small molecules. However, only polymers have been reported to effectively transduce energy to mechanophores, which induces breakage of covalent bonds. In this paper, a second possibility is presented—molecular capsules as stress-sensitive units. Mechanochemical encapsulation of fullerenes in cystine-based covalent capsules indicates that complexation takes place in the solid state, despite the fact that the capsules do not possess large enough entrance portals. By using a set of solvent-free MALDI (sf-MALDI) and solid-state NMR (ss-NMR) experiments, it has been proven that encapsulation proceeds during milling and in this process hydrazones and disulfides get activated for breakage, exchange, and re-forming. The capsules are porous and therefore prone to collapse under solvent-free conditions and their conformational rigidity promotes the collapse by the breaking of covalent bonds.     

Physical and Sensory Properties of Japanese Quince Chips Obtained by Osmotic Dehydration in Fruit Juice Concentrates and Hybrid Drying

Japanese quince has high health value, but due to its taste and texture, it is difficult to eat raw. The use of innovative drying methods to produce dried snack foods from these fruits may be of interest to producers and consumers. The physicochemical and sensory properties of 3 mm slices of Japanese quince fruit (with skin, without seeds) obtained by osmotic pre-treatment in chokeberry and apple juice concentrates, and with the use of convection (convective drying, C-D), freeze-drying (F-D), and convection-microwave-vacuum drying (hybrid) are assessed. The methods of drying osmo-dehydrated slices do not affect the dry matter content. In most dried quince, the water activity is 0.40 or lower. Pre-osmotic dehydration and drying have a significant impact on the mechanical and acoustic properties of quince chips. Sensory attractive chips emit loud acoustic emission (AE) during the breaking test. Chips that are osmo-dehydrated in a mixture of chokeberry juice concentrate and sucrose and dried by a hybrid method are attractive. They have a dark red color given by chokeberry concentrate and a slight sweet (with a slight sour-bitter) taste. The sensory evaluation was useful for determining the quality of the chips in terms of their texture (crispness) tested by mechanical methods. Their sensory ratings (overall desirability as weight of color, taste, crispness, and flavor) are high and similar (from 3.8 to 4.1). The use of innovative drying methods with pre-osmotic treatment allows obtaining dried material with properties comparable to those obtained by the F-D method, but in a much shorter time, i.e., with lower energy and using a simple method.     

Singular limit of a Navier–Stokes system leading to a free/congested zones two-phase model

The aim of this work is to justify mathematically the derivation of a viscous free/congested zones two-phase model from the isentropic compressible Navier–Stokes equations with a singular pressure playing the role of a barrier.     

Crystal structure and mesogenic behaviour of a new fluorene derivative: 9,9‐dimethyl‐2,7‐bis(4‐pentylphenyl)‐9H‐fluorene

The title compound, C₃₇H₄₂, is a new mesogenic compound containing the fluorene moiety. It exhibits enantiotropic nematic liquid crystalline behaviour with melting at 125 °C and isotropization at 175 °C. The crystallographically independent unit contains two molecules oriented face‐to‐edge with respect to each other. The two molecules have nearly the same conformation of the bis‐phenyl fluorene moiety. The molecular packing in the crystal phase is nematic‐like.     

A new method for the synthesis of mixed orthoesters from O-allyl acetals

Two new methods for the synthesis of orthoesters and compounds containing an orthoester moiety (dihydroisoxazoles) are presented. Mixed orthoesters of general formulas RC(OR¹)(OR²)₂ and RC(OR¹)(OR²)(OR³) were prepared via addition of ROH (R = Bu or m-methylphenyl) to O-allyl acetals (acrolein acetals: diethyl or cyclic, i.e., 2-vinyl-1,3-dioxanes or dioxolanes). The catalytic systems for these reactions were generated from [RuCl₂(PPh₃)₃] and Na₂CO₃; {[RuCl₂(COD)]_x} or {[OsCl₂(1,5-COD)]_x}, PPh₃, and Na₂CO₃. Compounds containing an orthoester moiety (dihydroisoxazoles) were prepared via tandem isomerization of O-allyl acetals (to O-vinyl acetals) catalyzed by ruthenium complexes followed by cycloaddition to in situ-generated 2,6-dichlorophenylnitrile oxide.     

Methylacrylate polymers with photochromic side chains containing heterocyclic sulfonamide substituted azobenzene

Methylacrylate monomers containing azobenzene groups with heterocyclic sulfonamide: sulfisomidyne (4-amino-N-[2,6-dimethylpyrimidyn-4-yl]benzenesulfonamide) and sulfamethoxazole (4-amino-N-[5-methylisoxazol-3-yl]benzenesulfonamide) substituents were synthesized. The monomers were used for preparation of homopolymers and copolymers with butyl 2-methylacrylate and 2-ethylhexyl acrylate. The materials obtained showed photochromic properties manifested by trans-cis isomerization of the side chain azobenzene fragments induced by illumination with unpolarized and polarized light. The decrease of the absorbance of the E(trans) form at ≈450 nm was observed and the materials tested were in form of thin films deposited onto glass.The isomerization of the polymers carried out during ellipsometric measurements showed the reversibility of the process in repeated illumination cycles with green laser light. The change of refractive index caused by illumination was in the range ≈0.005-0.008 as determined by ellipsometry.