Synthesis,characterization, and toxicity of hollow gold nanoshells

Hollow gold nanoshells (HGN) with a diameter of 50–70 nm and tunable optical properties within the near-infrared region were synthesized from a substitution reaction using a sacrificial template, in which the morphological properties of the HGN were affected by the synthesis conditions. Using EDX line scan, the composition of the structure was determined to verify if the sacrificial template is completely consumed or residues remain after the chemical synthesis, obtaining that the final HGN structure contains about 11% of the remaining silver that showed no significant effect on the cell viability of a hNS1 cell line, but resulted as toxic on a C6 glioma cell line at high concentrations. The photothermal properties were evaluated using a NIR laser, which despite its low power showed the conversion of light into heat. This study was conducted to evaluate the potential of these nanostructures as therapeutic agents with an emphasis on toxicity.     

Enantioselective separation of all-E-astaxanthin and its determination in microbial sources

A method for the enantioselective separation of all-E-astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione), an important colorant in the feed industry, was developed. Different chiral stationary phases (CSPs) such as Pirkle phases (R,R Ulmo and l-leucine), modified polysaccharides and a beta-cyclodextrin have been investigated on their separation performance of astaxanthin enantiomers. Direct resolution was only achieved employing the Chiralcel OD-RH (cellulose-tris-3,5-dimethylphenyl-carbamate) under reversed phase conditions. The chiral separation of the enantiomeric forms of astaxanthin produced in microalgae and yeasts was reported. The yeast Xanthophyllomyces sp. produces astaxanthin predominantly in the R,R configuration, whereas in the green microalgae Scenedesmus sp. astaxanthin is built primarily in the S,S form. The separation method for the identification of astaxanthin enantiomers is of great interest since astaxanthin is used as functional food additive in human nutrition. Moreover the method may be used as a food chain indicator in farmed salmon.     

Silver as acrolein hydrogenation catalyst: intricate effects of catalyst nature and reactant partial pressures

The hydrogenation of acrolein over pure and supported silver has been investigated with a focus on the influence of catalyst structure and reaction pressure (mbar to 20 bar range) on activity and selectivity. An onset of formation of allyl alcohol beyond 100 mbar reaction pressure (at 250 degrees C) is ascribed to a change in adsorption geometry upon increasing coverage. Smaller silver particles (in the nanometer range), the proximity of a reducible oxide component as well as high pressure lead to enhanced allyl alcohol formation; the selectivity to the other main product propionaldehyde is reduced. The silver dispersion changed depending on the reaction pressure. Moreover, the presence of oxygen, most likely as subsurface oxygen, and the presence of defects are of paramount importance for the catalytic behaviour. The considerable changes of the silver catalysts under reaction conditions and the pressure dependence call for in situ measurements to establish true structure-activity/selectivity relationships for this system.