Relative performance of immunochemical (enzyme-linked immunosorbent assay) and gas chromatography-electron-capture detection techniques to quantify polychlorinated biphenyls in mussel tissues

Results from polychlorinated biphenyls (PCB) analyses of mussel tissue extracts by immunoassay (PCB RaPID Assay^®) and conventional gas chromatography-electron-capture detection (GC-ECD) are described and compared. Mussels from natural populations with diverse concentrations of PCBs, mussel tissue fortified with technical Aroclor^® 1254 and a certified reference material are included.A strong correlation is reported between “total” PCBs quantified by both techniques (r²=0.95, n=27). Immunoassay results, however, exhibited lower values compared to GC-ECD, particularly when GC results are corrected for procedural recovery. A reduced antibody response, due to differences in the congener composition between the mussel extracts and Aroclor^® 1254 (used to raise and calibrate the ELISA), provides the most likely explanation for this difference. Non-parametric statistical analyses confirmed that, although differing from Aroclor^® 1254, PCB congener compositions in the mussel extracts most closely resemble that of Aroclor^® 1254. At very high PCB concentrations (>30 μg g⁻¹ dry weight), however, ELISA results are statistically different (P<0.01) from GC-ECD results, which is likely to be related to the solvation capacity of ELISA diluent. Similarity analysis showed high correlations between the most prominent congeners in Aroclor^® 1254 and immunoassay results. This analysis did not, however, identify a specific chlorine substitution pattern to which the immunoassay preferentially responded.Whilst GC-ECD affords the capability to quantify individual congeners of different reactivity and toxicity, the data reported do indicate that immunoassay offers a rapid and inexpensive alternative method for estimation of “total” PCBs at environmentally significant levels. It is, however, necessary to remove extraneous lipids to reduce matrix effects in the immunoassay.     

Complex dynamical behavior in the oxidation of hydroxylamine by bromate

Complex dynamical behavior has been observed in the oxidation of hydroxylamine by bromate in acidic sulfate medium. The reaction shows clock type kinetics in closed conditions and an aperiodic oscillations if gaseous products are removed from the system with a constant flow-rate. The reduction kinetics of bromate ions with excess hydroxylamine has been studied in the presence of allyl alcohol. The observed pseudo-first-order rate constant k_obs has been found to follow the expression where [hydroxylamine] is total initial hydroxylamine concentration, K₁ = 0.5 M^?1, K₂ = 10⁶ M^?1, and k = 2.57 × 10³ M^?1 s^?1 at 298.15 K and I = 2.0 M. The rate constant for the bromine oxidation of hydroxylamine in sulfuric aqueous solution has been determined. © 1994 John Wiley & Sons, Inc.     

Selectivity of calix[4]arene-bis(benzocrown-6) in the complexation and transport of francium ion

It is shown for the first time that a representative member of the "cesium-selective" calix[4]arene-crown-6 family exhibits a high affinity for Fr+ ion. In the investigation, the transport of 221Fr+ and Cs+ ions by calix[4]arene-bis(benzocrown-6) from an aqueous sodium nitrate solution into the water-immiscible diluent 1,2-dichloroethane was measured and compared to address the question of selectivity of the calix-crown-6 cavity toward alkali metal ions of increasing size. Selective separation of 221Fr+ from its parent 225Ac and from the matrix Na+ ions was demonstrated. Higher distribution ratios were obtained than those for the Cs+ ion. The extraction equilibria were determined for the case of the Cs+ ion, and the same equilibria were shown to be applicable to the case of Fr+ with inclusion of additional competitive effects.     

Effect of temperature on the structure of adsorption layers formed by adsorption of polymers in the transition region from dilute to semidilute solutions

The measurements of adsorption from solutions of polymers (poly(butyl methacrylate) and polystyrene) and their mixtures at various temperatures in the wide concentration region from dilute to semidilute solution have been made. The adsorption isotherms and fraction of bound segments confirm the existence of the transition concentration region near the critical concentration of the chain overlapping when the change of adsorption mechanisms take place. The effect of temperature on adsorption from the mixtures is different for both the polymers depending on the concentration regime. For PBMA, which adsorbs from the mixtures preferentially, the adsorption isotherms are of the same shape as for adsorption from binary solutions and are characterized by the presence of a small forepart in the transition region and by increasing adsorption with temperature. For less adsorbing PS by transition from dilute to semidilute regime the inversion of the temperature effect on adsorption is observed. These results are confirmed by the estimations of the parameters of preferential adsorption at various temperatures. The data on the fraction of bound segments for dilute regime corresponds to the extended conformation of chains at the surface. The transition to semidilute regime leads to the diminishing of the fraction of bound segments as a result of simultaneous adsorption of macromolecular aggregates. Values of adsorption layer thickness have been calculated for various solution regimes and concentration. The dependence of the adsorption layer thickness on the temperature and on the solution regime at which adsorption occurs was established.     

Hydride-alkenylcarbyne to alkenylcarbene transformation in bisphosphine-osmium complexes

The elongated dihydrogen complex [formula: see text](1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-pi-alkynol derivatives [OsH{=C=CHC(OH)R2}{eta2-HC(triple bond)CC(OH)R2}(PiPr3)2]BF4 (R = Ph (2), Me (3)), where the pi-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF(4) and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH((triple bond)CCH=CR2)S2(PiPr3)2][BF4]2 (R = Ph, S = H(2)O (4), CH(3)CN (5); R = Me, S = CH(3)CN (6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(=CHCH=CR2)(CH3CN)3(PiPr3)2][BF4](2) (R = Ph (7), Me (8)) by means of a concerted 1,2-hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2((triple bond)CCH=CPh2)(PiPr3)2 (10), which reacts with AgBF(4) and acetonitrile to give [OsHCl((triple bond)CCH=CPh2)(CH3CN)(PiPr3)2]BF(4) (11). In this solvent complex 11 is converted to [OsCl(=CHCH=CPh2)(CH3CN)2(PiPr3)2]BF(4) (12). Complex 5 reacts with CO to give [Os(=CHCH=CPh2)(CO)(CH3CN)2(PiPr3)2][BF(4)](2) (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as eta(2)-carbene species [formula: see text] increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported.     

Modeling of adsorption and ultrasonic desorption of cadmium(II) and zinc(II) on local bentonite

The adsorption and ultrasonic desorption of toxic heavy metal cations (i.e., Cd(II) and Zn(II)) on natural bentonite have been modeled with the aid of a factorial design approach. The ability of untreated bentonite to remove Cd(II) and Zn(II) from aqueous and acidic solutions at different pH values has been studied for different metal concentrations by varying the amount of adsorbent, temperature, stirring speed, and contact time. The same factors, except stirring speed and metal concentration, were applied in desorption study. Ultrasound power was used for desorption instead of stirring speed. A flame atomic absorption spectrometer was used to measure the cadmium and zinc concentration before and after both experimental study. The highest adsorption for Zn and Cd was 99.85 and 96.84%, respectively, and the highest desorption for Zn and Cd obtained was 66.57 and 51.37%, respectively. It is believed that the models obtained for adsorption and desorption may provide a background for detailed mechanism searches and pilot and industrial scale applications.     

Student Interest in Engineering Design‐Based Science

Current reform efforts in science education around the world call on teachers to use integrated approaches to teach science. As a part of such reform efforts in the United States, engineering practices and engineering design have been identified in K–12 science education standards. However, there is relatively little is known about effective ways of teaching science through engineering design. The study explores the approaches or strategies used by a sixth grade science teacher to teach science and engineering in an integrative manner. Classroom observations, teacher interview, and student surveys were used to study the features of engineering integration implemented by the teacher and the changes in student interest in science and engineering by participating in an engineering design‐based science unit. Findings suggest that the teacher explicitly included practices and core ideas from engineering and science; used an engaging, motivating engineering challenge; and provided students with opportunities to be autonomous. Students engaged in the activities in the engineering unit and their interest level slightly increased. The results suggest that the three strategies that the teacher used to teach engineering and science are important foundations of integrated science and engineering education.     

Small-molecule fluorophores to detect cell-state switching in the context of high-throughput screening

A small molecule capable of distinguishing the distinct states resulting from cellular differentiation would be of enormous value, for example, in efforts aimed at regenerative medicine. We screened a collection of fluorescent small molecules for the ability to distinguish the differentiated state of a mouse skeletal muscle cell line. High-throughput fluorescence-based screening of C2C12 myoblasts and myotubes resulted in the identification of six compounds with the desired selectivity, which was confirmed by high-content screening in the same cell states. The compound that resulted in the greatest fluorescence intensity difference between the cell states was used as the screening agent in a pilot screen of 84 kinase inhibitors, each present in four doses, for inhibition of myogenesis. Of the kinase inhibitors, 17 resulted in reduction of fluorescence at one or more concentrations; among the "hits" included known inhibitors of myogenesis, confirming that this compound is capable of detecting the differentiated myotube state. We suggest that the strategy of screening for screening agents reported here may be extended more broadly in the future.     

Experimental device for study of the thermal stimulated direct current in the composite materials

Journal of Thermal Analysis and Calorimetry - Presents the device for analysis the thermally stimulated electrical conductivity of composites in the wide temperature range. The main advantage of...     

Synthesis of new fluorogenic cyanine dyes and incorporation into RNA fluoromodules

A new fluorogenic cyanine dye was synthesized and found to have low fluorescence quantum yield in fluid solution and in the presence of double-stranded DNA but 80-fold enhanced fluorescence in viscous glycerol solution. An RNA aptamer selected for binding to the new dye exhibits K(d) = 87 nM and 60-fold fluorescence enhancement. The dye-aptamer pair is a fluoromodule that can be incorporated into fluorescent sensors and labels.