Chemical synthesis of polyaniline in the presence of poly(amidosulfonic acids) with different rigidity of the polymer chain

Conducting polyaniline (PANI) was chemically synthesized in the presence of water-soluble aromatic polyamides containing sulfonic groups: poly-(p,p’-(2,2′-disulfonic acid)-diphenylene-tere-phthalamide) (t-PASA, rigid backbone), poly-(p,p’-(2,2′-disulfonic acid)-diphenylene-iso-phthalamide) (i-PASA, semi-rigid backbone) and their copolymer (co-PASA) with the monomers ratio 1:1, as well as in the presence of flexible-backbone polyacids: poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) and poly(styrene sulfonic acid) (PSSA). In these conditions the matrix polymerization of aniline results in the formation of water-soluble interpolymer complexes of PANI with the above cited polyacids. The character of spectral changes in the UV, visible and near IR (UV-Vis-NIR) range during the synthesis and the polymerization rates depend strictly on the structure of polyacid matrix. Higher flexibility of the polyacid backbone (PAMPSA, PSSA) contributes to higher relative absorption of localized polarons (750 nm), while in the spectrum of interpolymer complexes with rigid-chain polyacid (t-PASA) the absorption of delocalized polarons (1300-1500 nm) prevails. The complexes with semi-flexible i-PASA and co-PASA exhibit intermediate behavior. The results are interpreted in terms of differences in the inter-chain interactions in the interpolymer complexes of different structure. Fourier transform infrared (FTIR) spectroscopy data support the assumption of the incorporation of the polyacids in the PANI through an interaction between sulfonic groups of the polyacids and nitrogen atoms of PANI. Spectroelectrochemical and electrochemical (cyclic voltammetry) studies of the films cast from the obtained solutions showed that the formation of quinoid units at high oxidation level is retarded in the interpolymer complexes of PANI with rigid- and semi-rigid-chain polyacids. Atomic force microscopy (AFM) and direct current (DC)-conductivity data are also presented.     

A comparison of bismuth nanoforms obtained in vacuum and air by microwave heating of bismuth powder

The synthesis of bismuth nanotubes in the conditions of microwave (MW) heating is reported as a lower-cost and simple technique in comparison with the traditional methods. The nanotubes were prepared by heating the Bi powder (a) in air for 15, 30, 60, and 90 min and (b) in vacuum for 5, 10, and 15 min in a domestic MW-oven (2.45 GHz, 1300 W). The products were characterized by TEM and AFM. A mechanism of formation for bismuth nanotubes in different conditions (air and vacuum) is presented.     

Mullite formation from highly homogeneous mixtures of Al2O3 and SiO2

Mullite, 3A1₂O₃ · 2SiO₂, was synthesized by heat-treating homogeneous sol-gel-derived mixtures of A1₂O₃ and SiO₂ taken in stoichiometric amounts. To reduce the mullitization temperature, sols containing γ-AlOOH and SiO₂ nanoparticles (2 to 20 nm) were used in the preparation of the mullite precursors. A few samples were made using the products of hydrolysis of aluminum salts instead of the γ-AlOOH sol. The process parameters determining the homogeneity of the precursor mixtures were revealed. The preparation conditions ensuring mullite crystallization at temperatures between 1200 and 1250°C were found. The results are discussed in terms of the reaction between A1₂O₃ and SiO₂ during mullitization.     

Performance assessment of proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) for analysis of isobaric compounds in food-flavour applications

Characterisation of food-flavour release using quadrupole-based on-line mass spectrometers such as proton-transfer-reaction mass spectrometry (PTR-MS, or PTR-QMS) can be complicated when nominally isobaric aroma compounds are present in complex food matrices. The recent combination of PTR-MS with time-of-flight mass spectrometry (PTR-TOF-MS) offers an analytical tool potentially capable of overcoming this problem because of its enhanced mass resolution. In this context, four pairs of isobaric compounds (cis-3-hexenol and 2,3-pentanedione, benzaldehyde and m-xylene, ethyl butanoate and 2-methylbutanol, and isobutyl isopentanoate and 1-hexanol) were investigated by PTR-TOF-MS to assess its mass-resolving power for food-flavour applications. Headspace analyses of aqueous solutions containing nominally isobaric aroma compounds that are unresolvable by PTR-QMS demonstrated that the PTR-TOF-MS mass-resolving power, which is m/z-dependent, enabled discrimination between isobaric peaks at a centre of mass separation down to at least 0.030 Da. Visual discrimination between these isobaric compound peaks in the headspace of aqueous solutions down to a concentration range of a few tens of ng mL⁻¹ was also possible, enabling an empirical method for determining the limit of quantitation in solution for single compounds. PTR-TOF-MS offers distinct advantages over conventional PTR-MS for certain flavour release applications.     

Potato Expressing Beetle-Specific Bacillus thuringiensis Cry3Aa Toxin Reduces Performance of a Moth

Expression of the Bacillus thuringiensis beetle-specific toxin Cry3Aa, which renders a genetically modified potato cultivar resistant to the Colorado potato beetle Leptinotarsa decemlineata, exerts a deleterious effect on the polyphagous moth Spodoptera littoralis. The caterpillars of S. littoralis feed less and produce smaller pupae on the genetically modified cultivar (NewLeaf Superior) than on the parental nontransgenic cultivar (Superior). The conversion efficiencies of total dry matter, combustion heat, carbon, and nitrogen from leaves to insect biomass are similar on both cultivars. In spite of similar food utilization and a relatively small difference in the body mass at pupation, female adults that developed from caterpillars fed on NewLeaf Superior lay a mean of 309 eggs compared to a mean of 713 eggs deposited by females that developed from caterpillars fed on Superior. Because of this difference and a simultaneous reduction in fertility (egg hatchability) from 78 to 48%, a pair of adults that fed as larvae on NewLeaf Superior produces only 148 larvae, whereas a pair of adults that fed as larvae on Superior produces 556 larvae. We suggest that small amounts of Cry3Aa that accumulate in insect tissue and persist until the adult stage are responsible for the decline in reproduction.     

Features of low-temperature oxidation of hydrogen in the medium of nitrogen,carbon dioxide,and water vapor at elevated pressures

The article discusses novel research results on combustion features of high-density Н₂/О₂ mixtures (ρ_H2 = 0.70–1.89 mol/dm³, ρ_O2 = 0.32–0.81 mol/dm³) diluted with nitrogen, carbon dioxide, or water vapor (from 46 to 76% mol.) at the uniform heating (1 K/min) of tubular reactor. Based on time dependencies of temperature increment in the reaction mixtures caused by the heat release during oxidation of H₂, it is found that the self-ignition temperature of Н₂/О₂/N₂ and Н₂/О₂/H₂O mixtures is by ≈ 30 K lower than that of the Н₂/О₂/СО₂ mixture. Unlike combustion of H₂ in the N₂ medium, in the CO₂ and H₂O media a chain-thermal explosion is observed at a certain concentration of reagents. The influencing mechanisms of diluents on the H₂ oxidation dynamics, as well as the contribution of homogeneous and heterogeneous reactions in the heat release are revealed. It is established that high heat capacity of H₂/O₂/CO₂ mixture, chemical interaction between its components, and presence of CO₂ molecules adsorbed on the reactor inner surface, are the factors determining the H₂ oxidation dynamics in CO₂ medium. At oxidation of H₂ in the H₂O medium, the process takes place against the background of water evaporation and, as a consequence, is characterized by increased heat capacity and thermal conductivity of the H₂/O₂/H₂O reaction mixture.