RESUMO
This paper reports unique and unusual formations of columnar liquid crystals and organogels by self-assembling discotic molecules, which are composed of an aromatic hexaazatriphenylene (HAT) core and six flexible aromatic side chains. In HAT derivatives 3a, with 4'-(N,N-diphenylamino)biphenyl-4-yl chains, 3b, with 4'-[N-(2-naphthyl)-N-phenylamino]biphenyl-4-yl chains, and 3c, with 4'-phenoxybiphenyl-4-yl chains, the two-dimensional hexagonal packings can be created by their self-assembling in the liquid crystalline phase, which were characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In certain solvents, HAT molecules 3a-c can form the viscoelastic fluid organogels, in which one-dimensional aggregates composed of the HAT molecules are self-assembled and entangled into three-dimensional network structures. The organogel structures were analyzed by scanning electron microscopy observation, (1)H NMR, UV-vis, and circular dichroism spectroscopy. In contrast to 3a-c, none of the liquid crystalline and organogel phases could be formed from 3d and 3e with short aromatic side chains including a phenylene spacer, and 3f (except a few specific solutions) and 3g without terminal diarylamino and phenoxy groups. In 3a-c, the aromatic side chains with terminal flexible groups make up soft regions that cooperatively stabilize the liquid crystalline and organogel supramolecular structures together with the hard regions of the hexaazatriphenylene core.
RESUMO
Environmental problems arise from the pollution of ground water and soil by propyzamide, 3,5-dichloro-N-(3-methyl-1-butyn-3-yl) benzamide, which is a popular herbicide. To decompose propyzamide, aqueous solutions containing propyzamide and TiO2 particles was irradiated by light. The photocatalytic decomposition was accelerated when the solution temperature and pH were high. The temperature dependence was due to the adsorption processes of propyzamide on the TiO2 particles. The decomposition was further promoted by addition of H2O2 because of its effective electron-trapping and generated *OH which was available to decompose propyzamide. Although no propyzamide was detected in the solution after the irradiation time of about 20 min, the decomposed intermediate compounds still remained. In order to mineralize completely propyzamide, simultaneous irradiation by light and ultrasonic waves was carried out. The hybrid effect of the irradiation by light and ultrasonic waves in conjunction with H2O2 was first confirmed to achieve the complete mineralization of propyzamide.
RESUMO
A method for the potentiometric determination of bromate by circulatory flow injection analysis (CFIA) is described. The procedure involves the use of an Fe(III)-Fe(II) potential buffer solution, which is recycled via a reservoir. The analytical method is based on a linear relationship between the concentration of bromate and a very transient potential change in the electrode potential due to the generation of intermediate bromine during the reaction of bromate with the Fe(III)-Fe(II) potential buffer solution, which also contains NaBr, (NH4)6Mo7O24 and H2SO4. An aliquot (5 microl) of a bromate sample solution was injected into the stream of the potential buffer solution, 100 ml of which was circulated at a flow rate of 1 ml/min; the potential buffer solution stream was then returned to the reservoir after passing through a flow-through redox electrode detector. A potential change due to the reaction of the injected sample with the potential buffer in a reaction coil was measured with the detector in the form of a peak signal. The effects of the bromide, sulfuric acid and Fe(III)-Fe(II) concentrations in the potential buffer, and length of the reaction coil on the peak heights were examined in order to optimize the proposed CFIA method. The analytical sensitivities to bromate were 5.6 mV/microM for 1 x 10(-2) M and 30.9 mV/microM for 1 x 10(-3) M in the concentration of Fe(III)-Fe(II) in a potential buffer solution containing 0.35 M NaBr, 0.2% (NH4)6Mo7O24 and 1 M H2SO4. The detection limit of bromate obtained by a 1 x 10(-3) M Fe(III)-Fe(II) potential buffer solution was 0.02 microM (2.5 ppb). The numbers of repetitive determinations in which the relative sensitivities within 5% were regarded as being tolerated were ca. 4000 and 2000 for the use of only 100 ml of 1 x 10(-2) M and 1 x 10(-3) M Fe(III)-Fe(II) potential buffer solution, respectively.
RESUMO
A highly sensitive potentiometric flow injection analysis method for the determination of manganese(II), utilizing a redox reaction with hexacyanoferrate(III) in near neutral media containing ammonium citrate is described. The analytical method is based on the detection of the change in potential of a flow-through type redox electrode detector, resulting from the composition change of an [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer solution. A linear relationship between the potential change (peak height) and the concentration of manganese(II) was found. Manganese(II) in a wide concentration range from 10(-4) to 10(-7) M could be determined by appropriately altering the concentration of the potential buffer from 10(-3) to 10(-5) M. The lower detection limit of manganese(II) was determined to be 1x10(-7) M. The sampling rate and relative standard deviation were 20 h(-1) and 1.9% (n=8) for 6x10(-6) M manganese(II), respectively. The proposed method was successfully applied to the determination of manganese(II) in actual soil samples obtained from tea fields. Analytical results obtained by the proposed method were in good agreement with those obtained by an atomic absorption spectrophotometric method.
