The synthesis and structural study of two benzothiazolyl azo dyes: X-ray crystallographic and computational study of azo–hydrazone tautomerism

The synthesis, FT-IR, ¹H and ¹³C NMR characterisation, as well as crystal and molecular structure determined by single-crystal X-ray diffraction data, of two azo dyes derived from 6-aminobenzothiazole: 6-[(4-N,N-dimethylaminophenyl)diazenyl]benzothiazole and 6-[(2-hydroxy-1-naphthyl)diazenyl]benzothiazole are reported. Both dyes are essentially planar with the exclusion of methyl groups in 6-[(4-N,N-dimethylaminophenyl)diazenyl]benzothiazole, which exibits 100% E-configuration in terms of orientation of the substituents about the central azo linkage. Single-crystal X-ray study of 6-[(2-hydroxy-1-naphthyl)diazenyl]benzothiazole was undertaken to established whether the hydrazone or azo tautomer was present in the solid state as well as any potential shift in tautomeric equilibrium imparted by temperature variation (296 and 100 K). Density functional theory calculations revealed that the hydrazone tautomer was more stable than the azo tautomer and that the tautomeric equilibrium was shifted towards the hydrazone form at lower temperature.     

Poly(ether-ester)s modified with different amounts of fumaric moieties

A series of novel poly(ether-ester)s modified with fumaric moieties is synthesized by transesterification in the melt of dimethyl terephthalate (DMT), dimethyl fumarate (DMF), 1,4-butanediol (BD) and poly(tetramethylene oxide) (PTMO, M?_n=1000 g/mol). The effect of the introduction of double bonds into both the hard and soft segments and their content on the structure and the thermal and rheological properties of the synthesized polymers are investigated. The introduction of double bonds into the polymer main chains increases the molecular weight of the copolyesters, but reduces the crystallinity of the hard segments and related properties such as modulus and hardness. The presence of double bonds improves the high temperature properties and thermal stability, especially the thermo-oxidative one, lowers the melting and crystallization temperature and increases the glass transition temperature. The incorporation of fumaric moieties into the macrochains improves the adhesive strength of the polymer to a metal surface.     

Photoinduced electron transfer reactions: from the elucidation of old problems in bulk solutions towards the exploration of interfaces

The activities of our research group in the field of photoinduced electron transfer reactions are discussed and illustrated by several examples.     

Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.     

A parametric method for non-stationary interference suppression in direct sequence spread-spectrum systems

The problem of non-stationary interference suppression in direct sequence spread-spectrum (DS-SS) systems is considered. The phase of interference is approximated by a polynomial within the considered interval. According to the local polynomial Fourier transform (LPFT) principle, the received signal is dechirped by using the obtained phase approximation and the interference is, in turn, suppressed by excising the corrupted low-pass frequency band. For the estimation of polynomial coefficients, we use the product high-order ambiguity function (PHAF), known for its capability to successfully resolve components of a multicomponent polynomial-phase signal (PPS). The proposed method can suppress interferences with both polynomial and non-polynomial phase. In addition, it can suppress both monocomponent and multicomponent interferences. The simulations show that the proposed method outperforms time-frequency (TF) methods, that successfully deal with multicomponent interferences, in terms of the error probability and computational complexity.     

The effect of the mass ratio of hard and soft segments on some properties of thermoplastic poly(ester‐siloxane)s

A series of thermoplastic elastomers based on soft polydimethylsiloxane (PDMS) and hard poly(butylene terephthalate) (PBT) segments was synthesized using a two‐step transesterification reaction in the melt. The molar mass of the soft PDMS component was constant (M?_nPDMS = 1056 g mol^?1) while the starting reaction mixture compositions were varied to obtained copolymers with a mass ratio of hard to soft segments in the range from 70/30 to 40/60. The structure and composition of the copolymers was verified by ¹H NMR spectroscopy. It appeared that there was a pronounced molar mass maximum when the PBT content of the copolymers was approximately 60 mass%, whereas all samples were considerably inhomogeneous with respect to the distribution of the lengths of the hard segments. Differential scanning calorimetry (DSC) thermograms showed that the melting and crystallization temperature increased with increasing PBT content, as did the total degree of crystallinity, which was confirmed by wide‐angle X‐ray scattering (WAXS) analysis. Thermogravimetric analysis (TGA) performed in nitrogen gave subtle differences for samples of different composition, including that of the PBT homopolymer, whereas in oxygen these differences were more pronounced in the way the thermo‐oxidative stability of the obtained copolymers decreased with decreasing PBT content. Finally, it was shown that the hardness depended directly on the PBT content, ie the higher the PBT content, the greater the hardness of the corresponding copolymer. Copyright © 2004 Society of Chemical Industry     

Investigations on the Applicability of some Commercial Polyethylene Films to Permeation-type Passive Samplers for Organic Vapours

The paper presents the results of preliminary investigations on the applicability of commercial polyethylene films to permeation-type passive samplers for the preconcentration of organic indoor air pollutants. The samplers were calibrated in exposure chambers in the atmosphere of standard gaseous mixtures containing vapours of m-xylene, styrene, m-dichhobenzene and cyclohexanone – volatile organics often encountered in indoor atmospheres. The permeation rates remained constant for all the film in the entire investigation period (9 months). Of the materials examined, the most suitable proved to be Cryovac EFDX 003 (28 μm), ensuring the highest permeation rates.     

Uncertainty of Trypsin Inhibitor Activity Measurement of Legume Crops Using Microtiter Plate Method

Trypsin inhibitors could limit utilization of legumes in human nutrition, but they could also have beneficial health effects. The objective of this study was to measure trypsin inhibitor activity (TIA) of different legumes using microtiter plate method and to identify factors that contribute to uncertainty of TIA measurement. TIA measurements were performed on seeds of faba bean, pea, common vetch, soybean, and common bean cultivars. The significant effect of legume crop on TIA measurement uncertainty was confirmed with P = 0.045. Certain sources of measurement uncertainty were related with the content of trypsin inhibitors (Tis) in legume seeds. In respect to that, significant effect of level of sample dilution (P ? 0.001) was confirmed. Significant influence of the repeated absorbance measurement of sample reaction mixture on uncertainty of TIA measurement was identified (P ? 0.001), and it took 60% of overall TIA measurement uncertainty for soybean cultivars. TIA of soybean cultivars exceeded 90 TUI/mg. Repeated absorbance measurement of positive control reaction mixture took 70% of TIA measurement uncertainty of cultivars with TIA lesser than 4.5 TUI/mg. Graduated cylinder used for preparation of the final sample solutions took the range from 45 to 90% of overall TIA measurement uncertainty of the cultivars whose TIA were in the middle of previously mentioned. The uncertainty of TIA measurement of legume crops was not studied before; thus, this study pointed out that acquiring insight into factors contributing to uncertainty of TIA measurement could give directions for improvement of TIA testing if microtiter plate method is used.