Comparative measures of single-wall carbon nanotube dispersion

Model composites of DNA-wrapped single-wall carbon nanotubes in poly(acrylic acid) are used to evaluate metrics of nanotube dispersion. By varying the pH of the precursor solutions, we introduce a controlled deviation from ideal behavior. On the basis of small-angle neutron scattering, changes in near-infrared fluorescence intensity are strongly correlated with dispersion, while optical absorption spectroscopy and resonant Raman scattering are less definitive. Our results represent the first systematic comparison of currently accepted measures of nanotube dispersion.     

MOLECULAR EVOLUTION OF THE Ca2+-BINDING PHOTOPROTEINS OF THE HYDROZOA

Abstract— Alignment of the primary structures of the hydrozoan photoproteins, aequorin, mitrocomin, clytin and obelin showed very strong amino acid sequence identities. The Ca²⁺-binding sites of the proteins were found to be highly conserved. The Ca²⁺-binding sites were also homologous to the Ca²⁺-binding sites of other Ca²⁺-binding proteins. However, aequorin, mitrocomin, clytin and obelin differed from other Ca²⁺-binding proteins in that they contained a relatively large number of cysteine, tryptophan, histidine, proline and tyrosine residues, suggesting that these residues may have evolved as part of the light-emitting mechanism. Construction of a phylogenetic tree showed that aequorin, mitrocomin, clytin and obelin form a closely related group of proteins.     

Vertical motion of a charged colloidal particle near an AC polarized electrode with a nonuniform potential distribution: theory and experimental evidence

Electroosmotic flow in the vicinity of a colloidal particle suspended over an electrode accounts for observed changes in the average height of the particle when the electrode passes alternating current at 100 Hz. The main findings are (1) electroosmotic flow provides sufficient force to move the particle and (2) a phase shift between the purely electrical force on the particle and the particle's motion provides evidence of an E2 force acting on the particle. The electroosmotic force in this case arises from the boundary condition applied when faradaic reactions occur on the electrode. The presence of a potential-dependent electrode reaction moves the likely distribution of electrical current at the electrode surface toward uniform current density around the particle. In the presence of a particle the uniform current density is associated with a nonuniform potential; thus, the electric field around the particle has a nonzero radial component along the electrode surface, which interacts with unbalanced charge in the diffuse double layer on the electrode to create a flow pattern and impose an electroosmotic-flow-based force on the particle. Numerical solutions are presented for these additional height-dependent forces on the particle as a function of the current distribution on the electrode and for the time-dependent probability density of a charged colloidal particle near a planar electrode with a nonuniform electrical potential boundary condition. The electrical potential distribution on the electrode, combined with a phase difference between the electric field in solution and the electrode potential, can account for the experimentally observed motion of particles in ac electric fields in the frequency range from approximately 10 to 200 Hz.     

Rapid isolation of omega‐3 long‐chain polyunsaturated fatty acids using monolithic high performance liquid chromatography columns

Eicosapentaenoic and docosahexaenoic acids are important bio‐active fatty acids in fish oils. Monolithic HPLC columns both in the polymeric cation exchange (silver‐ion) and RP formats were compared with corresponding packed columns for the isolation of these acids from tuna oil ethyl esters. Monolithic columns in both formats enabled rapid (typically 5–10 min) separations compared with packed columns (30 min). Polymeric monolithic silver‐ion disc column rapidly furnished mixtures of eicosapentaenoic and docosahexaenoic esters (90% purity) within 5–10 min, but was unable to resolve individual esters. A preparative version of the same column (80 mL bed volume) enabled isolation (>88% purity) of 100 mg quantities of eicosapentaenoic and docosahexaenoic esters from esterified tuna oil within 6 min. Baseline separation of eicosapentaenoic and docosahexaenoic esters was achieved on all RP columns. The results show that there is potential to use polymeric monolithic cation exchange columns for scaled‐up preparation of eicosapentaenoic and docosahexaenoic ester concentrates from fish oils.     

IUPAC collaborative trial study of a method to detect genetically modified soy beans and maize in dried powder.

This paper presents results of a collaborative trial study (IUPAC project No. 650/93/97) involving 29 laboratories in 13 countries applying a method for detecting genetically modified organisms (GMOs) in food. The method is based on using the polymerase chain reaction to determine the 35S promotor and the NOS terminator for detection of GMOs. reference materials were produced that were derived from genetically modified soy beans and maize. Correct identification of samples containing 2% GMOs is achievable for both soy beans and maize. For samples containing 0.5% genetically modified soy beans, analysis of the 35S promotor resulted also in a 100% correct classification. However, 3 false-negative results (out of 105 samples analyzed) were reported for analysis of the NOS terminator, which is due to the lower sensitivity of this method. Because of the bigger genomic DNA of maize, the probability of encountering false-negative results for samples containing 0.5% GMOs is greater for maize than for soy beans. For blank samples (0% GMO), only 2 false-positive results for soy beans and one for maize were reported. These results appeared as very weak signals and were most probably due to contamination of laboratory equipment.     

Comparison of three cyclodextrins to optimize bisphenol A extraction from source water: Computational,spectroscopic, and analytical studies

Computationally and spectroscopically assisted analytical comparative investigation into the extraction of bisphenol A using three cyclodextrins, that is, α, β, and γ respectively, were performed. A simple, self-tailored μ-solid-phase extraction podium was used to extract bisphenol A from water samples, and high-performance liquid chromatography-ultraviolet was used for the qualitative and quantitative analysis of bisphenol A. Density functional theory first principle calculations, attenuated total reflectance Fourier-transform infrared spectroscopy and Fourier-transform Raman spectroscopy data supports the analytical selection of β-cyclodextrin as the adsorbent for bisphenol A extraction. Analytical optimization of various parameters including sample volume, sample pH, eluting solvent and its volume was performed to discover the most proper conditions for maximum extraction. Under the optimized conditions, a limit of detection value of 0.70 ng/ml and a limit of quantification value of 2.31 ng/ml was achieved with β-cyclodextrin, with recovery (%) values over 98.40–102.50 in real source water samples. Overall, well assisted by comprehensive computational and spectroscopic studies, a novel, simple, sensitive and economic analytical method was developed for the extraction of bisphenol A from source water using cyclodextrin.