Topics in calixarene chemistry

Several facets of calixarene chemistry have been investigated including the mechanism of their formation by the base-induced condensation of phenols and formaldehyde, procedures for introducing functional groups onto the upper rim and lower rim of calixarenes, the conformational behavior of calixarene oxyanions, the formation of complexes in aqueous and nonaqueous systems, and the application of calixarenes as catalysts.     

OH reactions with aliphatic alcohols: evaluation of kinetics by direct optical absorption measurement. A pulse radiolysis study

The kinetics of the reactions of hydroxyl radicals with aliphatic alcohols in aqueous solution were studied using pulse radiolysis. Based on the optical absorption observed in the UV region, the rate constants for the reaction of hydroxyl radicals with methanol, ethanol, 2-propanol and tert-butyl alcohol were determined to be 9.0×10⁸, 2.2×10⁹, 2.0×10⁹ and 6.2×10⁸ dm³ mol⁻¹ s⁻¹, respectively. The values obtained here by direct observation of the alcohol radicals basically confirm the values which were earlier determined indirectly by competition.     

Transformations of bicyclic systems containing an isothiazole ring

Isothiazolium salts, which are readily hydrolyzed to heterocyclic o-formyl disulfides, were obtained by alkylating bicyclic systems containing an isothiazole ring. The initial isothiazole-containing systems are stable in water and react with nucleophiles such as the hydroxyl ion with opening of the isothiazole ring and formation of o-cyanodisulfides.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 223–226, February, 1985.     

Concentration of radionuclides in building and ceramic materials of Bangladesh and evaluation of radiation hazard

The concentration of radioactive²²⁶Ra,²³²Th and⁴⁰K in building and ceramic materials of Bangladesh was investigated by γ-spectrometry with two HPGe detectors. Radium equivalent activities, representative level index values, criterion formula, emanation coefficients and²²²Rn mass exhalation rates were estimated for the radiation hazard of the natural radioactivity in the materials. The activity concentrations of the natural radionuclides, radium equivalent activities, emanation coefficients and²²²Rn mass exhalation rates are compared with the corresponding values for building and ceramic materials of different countries. The radium equivalent activities in the samples varied between 30.9 (mosaic stone) and 328.0 Bq·kg⁻¹ (gypsum). The emanation coefficient of the materials ranged from 7.83 (cement) to 33.0% (soil) and the²²²Rn mass exhalation rate ranged from 2.31 (stone chips) to 118.0 μBq·kg⁻¹·s⁻¹ (gypsum).     

Use of nonionic poly(ethylene glycol) p-isooctyl-phenyl ether (Triton X-1 00) surfactant mobile phases in the thin-layer chromatography of heavy-metal cations

The analytical potential of poly(ethylene glycol) p-isooctyl-phenyl ether (Triton X-100), a nonionic surfactant, is used as a mobile phase in the thin-layer chromatographic separation of heavy-metal cations. The surfactant concentration below its critical micellar concentration (CMC) as well as above the CMC value is used to investigate the migrational behavior of some heavy-metal ions on silica gel layers. The mobility of the metal ions is found to change marginally with the increase of surfactant concentration from 0.001M (below CMC) to 0.1M (above CMC). The influence of the pH of the medium, nonelectrolyte organic (urea and alkanols), and inorganic electrolyte (NaCI) additives in the surfactant containing mobile phase on the mobility of heavy metals on the silica gel layer is examined. For separating metal ions, surfactant must be used in the presence of buffers. Triton X-100 (0.02M) at pH 2.3 is found to be the best mobile phase for the separation of heavy-metal cations. In general, the presence of alcohol in aqueous surfactant solutions results in a decrease in the mobility of metal ions. Besides Cu2+ and Fe3+, all of the metal ions show a trend of increasing the retardation factor beyond a minima at 0.1 or 0.3M of added urea or NaCl. The proposed method is successfully applied for the simultaneous detection of Zn2+ and Cd2+ from a spiked human blood sample.     

EFFECT OF GAMMA RAYS IN THE PREPARATION OF POLYMER AND HYDROGEL FROM ACRYLAMIDE MONOMER

The formation of polymer and hydrogel from aqueous solutions having 20, 30 and 40% concentrations ofacrylamide monomer by γ-ray irradiation processing in the dose range 0.06-30 kGy using a Co-60 source and theircharacterization have been observed. Polymer conversion and gel fraction are found to depend on radiation doses. Polymerconversion increases with the increase of dose, depending on the solution concentration, where maximum conversion isachieved at 0.18, 0.16 and 0.10 kGy for 20%, 30% and 40% concentrations, respectively. On the other hand, gel fractionincreases with dose from the gel point (0.12 kGy) for all concentrations, where 100% conversion of gel occurs at doses≥5 kGy. Tensile strength, viscosity and molecular weight (M_w) of polymer samples increase with both the dose and theconcentration, showing a high value of M_w up to≈10~8. Swelling of hydrogels under water with respect to time varies due tothe variation of cross-linking density formed in the gels and the maximum swelling mainly occurs within 24 h. A remarkable change of surface morphology reveals characteristic features of monomer, polymer and hydrogel films.