Three new aromatic diester–dicarboxylic acids containing furan rings, namely, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-4,4′-dicarboxylic acid, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-3,3′-dicarboxylic acid and benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-naphthyl ester-2,2′-dicarboxylic acid were synthesized by the reaction of benzofuro[2,3-b]benzofuran-2,9-dicarbonyl chloride with 4-hydroxybenzoic acid, 3-hydroxybenzoic acid and 3-hydroxy-naphthalene-2-carboxylic acid, respectively. Diester–dicarboxylic acids were characterized by FT-IR and NMR spectroscopy and elemental analyses. Then, these monomers were converted to aromatic copoly(ester–amide)s by their reaction with various aromatic diamines via the direct polycondensation. These polymers were characterized by viscosity measurements, solubility tests, FT-IR, Ultraviolet and 1H-NMR spectroscopy and thermogravimetry. The polymers with inherent viscosities in the range of 0.16–0.37 dl/g in dimethyl sulfoxide at 30 °C were obtained in high yield. Most of them dissolved readily at room temperature in polar solvents. The synthesized copoly(ester–amide)s possessed glass-transition temperatures from 210–255 °C. The copoly(ester–amide)s exhibited excellent thermal stabilities and had 10% weight loss at temperature above 295 °C under nitrogen atmosphere. 相似文献
Chrome azurol S immobilised on XAD-2 has been used in this study as a reagent phase for the development of an optical fibre Al(III) sensor. Using a kinetic approach, this sensor was able to give a linear response in the Al(III) concentration range of 1.3 x 10(-5)-2.0 x 10(-4) M with a limit of detection of 1.0 x 10(-4) M. The optimum responses were obtained at pH 6.0 and when the solution was stirred. The sensor response was found to have a repeatability and reproducibility of 1.6% and 5.8%, respectively. The results obtained for Al(III) determination in aqueous sample were in good agreement with those obtained using graphite furnace-atomic absorption spectrometry. 相似文献
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the Tg value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
A new electrochemical sensor, based on NdFeO3 nanoparticles as electrocatalytic material, was proposed here for the detection of dopamine (DA). NdFeO3 nanoparticles were first synthesized by a simple thermal treatment method and subsequent annealing at high temperature (700 °C). The prepared electrocatalytic material has been characterized in detail by SEM-EDX, XRD, and Raman techniques. Characterization results display its sheet-like morphology, constituted by a porous network of very small orthorhombic NdFeO3 nanoparticles. NdFeO3 electrocatalytic material was then used to modify the working electrode of screen-printed carbon electrodes (SPCEs). Electrochemical tests demonstrated that NdFeO3– modified screen-printed carbon electrode (NdFeO3/SPCE) exhibited a remarkable enhancement of the dopamine electrooxidation, compared to the bare SPCE one. The analytical performance of the developed sensor has been evaluated for the detection of this analyte by means of the square-wave voltammetry (SWV) technique. The modified electrode showed two linear concentration ranges, from 0.5 to 100 μM and 150 to 400 μM, respectively, a limit of detection (LOD) of 0.27 μM (at S/N = 3), and good reproducibility, stability, and selectivity. Additionally, we also report an attempt made to propose the modified sensor for the simultaneous detection of dopamine and uric acid (UA). The procedure was also applied for the determination of dopamine in spiked real samples. So, this paper reports for the first time the use of a modified NdFeO3 screen-printed electrode for developing an electrochemical sensor for the quantification of important biomolecules.
Characteristic fragment ions obtained in Fast atom bombardment (FAB) mass spectroscopy of ribose alkylated Uridine 5'-monophosphate (5'-UMP) derivatives in negative ion mode are described. All the compounds examined exhibited either [M]- or quasimolecular ion [M - H]- the fragmentations can be used to characterize these nucleotides. 相似文献
Fluorescence quenching by molecular oxygen has been employed to estimate dynamic parameters and solubility characteristics of molecular oxygen in micelle forming detergent solutions. A kinetic model which assumes that oxygen quenching occurs only in the micellar phase is employed to analyze the data. 相似文献
The photodegradation reactions of riboflavin (RF) in the presence of 0.05-2.00 M phosphate (pH 7.0) have been studied using a specific multicomponent spectrophotometric method. The reactions involve simultaneous photolysis (intramolecular photoreduction) and photoaddition (intramolecular photoaddition) leading to lumichrome (LC) and cyclodehydroriboflavin (CDRF), respectively, as major products. The contribution of each reaction in the overall photodegradation depends upon the phosphate concentration, i.e., higher the phosphate concentration higher the extent of photoaddition. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF at 0.25-2.00 M phosphate concentration range from 0.65 to 3.03 x 10(-2), and from 0.41 to 0.99 x 10(-2) and 0.12 to 1.63 x 10(-2) min(-1), respectively. The second-order rate constants for the phosphate catalysed photodegradation of RF and for the formation of LC and CDRF are 2.12 x 10(-4) and 0.61 x 10(-4) and 1.41 x 10(-4) M(-1)s (-1), respectively. Since the formation of CDRF by photoaddition is catalysed by HPO(4)(2-) ions, it is suggested that H(2)PO(4)(-) ions may be involved in the formation of LC by photolysis. Thus, both H(2)PO(4)(-) and HPO(4)(2-) ions may catalyse the two major reaction pathways of riboflavin photodegradation, respectively. 相似文献
The reaction of Cα,O-Dilithiooximes 2 and α-chloroketones afforded 5-(hydroxymethyl)-Δ2-soxazolines 4 . α,β-Unsaturated aldehydes and ketones reacted with 2 to give the corresponding acyclic 1,2-addition products 5 . The latter were cyclized with phosphorus pentoxide to 5-vinyl-Δ2-isoxazolines 6 . 相似文献
Effects of relative humidity conditions in the irradiation chamber and of temperature of the chamber on the response of 3 mm thick light blue poly (methyl methacrylate) sheets have been studied. The response was measured spectrophotometrically at 402, 450, 596 and 612 nm. The response of the dosimeter is independent of the relative humidity (12–97%) during irradiation if the response is measured within 24 h of irradiation. If the response is measured after longer storage time, the absorbance at 402 and 450 nm increases significantly. At these two wavelengths the response of the dosimeter is also independent of the temperature of the irradiation chamber in the range of 0 to 40 °C. However, at higher temperatures (60, 80 °C), the response is not uniform. 相似文献
An instrumental neutron activation analytical (INAA) technique is described for the determination of 26 toxic and other trace elements in Eastern Coal (NBS SRM-1632a), local coal and its ash. The coal ash was produced by heating coal at 750°C in a muffled furnace. The transfer of these elements to the environment on the complete compustion of coal is estimated from the difference between the elemental concentration of coal and its ash. 相似文献