Effect of ferroelectric liquid crystalline quaterphenyl structure and handedness on helical pitch length in bicomponent mixtures

The aim of this paper is characterisation of mesomorphic properties and helical structure parameters: handedness and helical pitch, of two laterally substituted ferroelectric compounds and mixtures based on them. These compounds have the same quaterphenyl rigid core and the same length of non-chiral chain – eight carbon atoms, as well as the absolute configuration of chiral centre (‘R’). Base compounds differ in the kind of a substituent in a rigid core (–Cl, –CH₃). Both of them have rather low melting temperature in comparison to most of quaterphenyls, and it affects the lowering of this temperature in binary mixtures. Thus they can be used for preparation of multicomponent ferroelectric mixtures useful for application.     

Preliminary thermal characterization of natural resins from different botanical sources and geological environments

The preliminary studies on thermal behavior of differently aged natural resins from Russia (Khatanga), Dominican Republic (El Valle), Colombia and Poland (Jantar) were performed. Thermal stability and behavior under elevated temperature were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), while the differences in the structure and composition by FT-IR spectroscopy. Analyzed resins show different thermal effects during heating suggesting that possible post-reactions and structural changes occurred. TG results indicated that Dominican, Russian and Colombian resins present relatively high thermal stability under air conditions in the range of 228–300 °C, whereas the mass loss of 5mass% at about 217 °C was observed for Baltic amber. During DSC experiments, the analyzed resins expose thermal events which make impossible determination of glass transition temperature in a raw sample. The results indicate that both TG and DSC cannot be considered as methods for age dating of natural resins and more advanced techniques should be applied. Careful analysis of FT-IR data in the carbonyl region may provide additional information about the composition and history of the natural resin.

     

Radiolytic decomposition of pesticide carbendazim in waters and wastes for environmental protection

The radiolytic degradation of widely used fungicide, carbendazim, in synthetic aqueous solutions and industrial wastewater was investigated employing γ-irradiation. The effect of the absorbed dose, initial concentration and pH of irradiated solution on the effectiveness of carbendazim decomposition were investigated. Decomposition of carbendazim in 100 μM concentration in synthetic aqueous solutions required irradiation with 600 Gy dose. The aqueous solutions of carbendazim have been irradiated in different conditions, where particular active radical species from water radiolysis predominate. The obtained data have been compared with the kinetic modeling. The reversed-phase high-performance liquid chromatography was used for the determination of carbendazim and its radiolytic decomposition products in irradiated solutions. The changes of toxicity of irradiated solutions were examined with different test organisms and human leukemia cells.     

Degradation of a model naphthenic acid, cyclohexanoic acid, by vacuum UV (172 nm) and UV (254 nm)/H2O2

The mechanism of hydroxyl radical initiated degradation of a typical oil sands process water (OSPW) alicyclic carboxylic acid was studied using cyclohexanoic acid (CHA) as a model compound. By use of vacuum ultraviolet irradiation (VUV, 172 nm) and ultraviolet irradiation in the presence of hydrogen peroxide UV(254 nm)/H(2)O(2), it was established that CHA undergoes degradation through a peroxyl radical. In both processes the decay of the peroxyl radical leads predominantly to the formation of 4-oxo-CHA, and minor amounts of hydroxy-CHA (detected only in UV/H(2)O(2)). In UV/H(2)O(2), additional 4-oxo-CHA may also have been formed by direct reaction of the oxyl radical with H(2)O(2). The oxyl radical can be formed during decay of the peroxyl-CHA radical or reaction of hydroxy-CHA with hydroxyl radical. Oxo- and hydroxy-CHA further degraded to various dihydroxy-CHAs. Scission of the cyclohexane ring was also observed, on the basis of the observation of acyclic byproducts including heptadioic acid and various short-chain carboxylic acids. Overall, the hydroxyl radical induced degradation of CHA proceeded through several steps, involving more than one hydroxyl radical reaction, thus efficiency of the UV/H(2)O(2) reaction will depend on the rate of generation of hydroxyl radical throughout the process. In real applications to OSPW, concentrations of H(2)O(2) will need to be carefully optimized and the environmental fate and effects of the various degradation products of naphthenic acids considered.     

Effect of selected scavengers on radiolytic degradation of 2,4-dichlorophenol for environmental purposes

The effect of pH of irradiated aerated solutions and the presence of various concentrations of bicarbonate and nitrate on radiolytic degradation of 2,4-dichlorophenol in aqueous solutions with γ-irradiation was examined using reversed phase HPLC and ion chromatography. The obtaining complete decomposition and dehalogenation of 2,4-dichlorophenol in the presence of naturally occurring inorganic scavengers may require to increase the irradiation dose in batch conditions up to 10 kGy. The presence of scavengers at different doses affects both efficiency of radiolytic degradation and its mechanism.     

Radiolytic degradation of pesticide 4-chloro-2-methylphenoxyacetic acid (MCPA)—Experimental data and kinetic modelling

The aqueous solutions of MCPA have been γ-irradiated in different conditions, where particular active radical species from water radiolysis predominate. The obtained data confirmed that largest yield of radiolytic decomposition is obtained in oxidation processes, where oxidation is carried out with hydroxyl radicals. The obtained data have been compared with kinetic modelling. A fair agreement was obtained for degradation of MCPA in different experimental conditions, including also irradiation in the presence of hydrogen peroxide, that in optimised conditions can be used to enhance the yield of decomposition. The obtained data have also shown a strong effect of the presence of large amount of chloride on yield of MCPA decomposition, which can be attributed to strong oxidation properties of chlorine radicals formed. It is also shown that MCPA can be completely decomposed in industrial wastes from various stages of MCPA production, although this is not accompanied by satisfactory reduction of toxicity of examined wastes.     

Impact of molecular structure of smectogenic chiral esters (3FmX1X2r) on vibrational dynamics as seen by IR and Raman spectroscopy

Smectogenic chiral esters with three-ring rigid core were examined by infrared and Raman spectroscopy. These compounds differ in the type of chiral centre, length of non-chiral chain and substitution of phenyl ring by fluorine atoms. The influence of molecular structure on the type of handedness of helical structure, as well as the shift and split of absorption bands on IR and Raman spectra were determined. The change of the length of non-chiral terminal chain has the most significant influence on the type of helical twist sense. All considered structural elements of tested compounds have the biggest influence on the value of wavelength of vibrational bands related to the carbonyl group located in the rigid core.