Asymmetric allylic alkylation of acyclic allylic ethers with organolithium reagents

A highly efficient, regio- and enantioselective Cu(I) /phosphoramidite-catalyzed asymmetric allylic alkylation of allyl ethers with organolithium reagents is reported. The use of organolithium reagents is essential for this catalytic C?C bond formation due to their compatibility with different Lewis acids. The versatility of allylic ethers under the copper-catalyzed reaction conditions with organolithium reagents is demonstrated in the shortest synthesis of (S)-Arundic acid.     

Growth behavior and kinetics of self-assembled silica-carbonate biomorphs

Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates--previously supposed to be involved in the growth mechanism--originate from secondary precipitation after growth is already terminated.     

Nucleic acid templated uncaging of fluorophores using Ru-catalyzed photoreduction with visible light

Hybridization-based reactions have attracted significant attention. The nucleic acid templated photocatalyzed azide reduction using catalytic amounts of a [Ru(bpy)(2)phen](2+) conjugate is reported. The reaction could be performed with as little as 2% of the Ru nucleic acid probe and was shown to productively unquench 7-azido-coumarin as well as uncage a small molecule.     

HF-LPME as a green alternative for the preconcentration of nickel in natural waters

In the last years, some analytical methodologies have been identified as a source of pollution, receiving increasing attention to decrease their impact on the environment. In this sense, the so-called solvent-less methodologies appear as a green alternative to reduce the volume of solvents used in many sample treatment procedures and, consequently, the volume of toxic wastes produced. Among these techniques, analytical methodologies based on liquid-phase microextraction are being continuously developed, although most applications are focused on organic compounds. In this work, a three-phase hollow-fibre liquid-phase microextraction (HF-LPME) system has been developed for the preconcentration of nickel in natural waters, prior to the analysis by atomic absorption spectrometry. Under optimum conditions, the new system allowed an enrichment factor of 29.80 to be obtained after 60 min of experiment, and it was successfully applied to the determination of nickel in both saline and non-saline water samples, at ppb and ppt levels. The results were compared with those obtained using a well-established methodology based on liquid solvent extraction showing no significant differences (α = 0.05) between both values. In addition, the new HF-LPME presents the advantages of a green analytical technique, as its greenness profile shows, with the additional reduction of sample manipulation and time cost.     

Ultrasound-assisted emulsification microextraction coupled with gas chromatography–mass spectrometry using the Taguchi design method for bisphenol migration studies from thermal printer paper, toys and baby utensils

The optimization of a clean procedure based on ultrasound-assisted emulsification liquid-liquid microextraction for the sensitive determination of four bisphenols is presented. The miniaturized technique was coupled with gas chromatography-mass spectrometry after derivatization by in situ acetylation. The Taguchi experimental method, an orthogonal array design, was applied to find the optimal combination of seven factors (each factor at three levels) influencing the emulsification, extraction and collection efficiency, namely acetic anhydride volume, sodium phosphate concentration, carbon tetrachloride volume, aqueous sample volume, sodium chloride concentration and ultrasound power and application time. A second factorial design was applied with four factors and five levels for each factor, 25 experiments being performed in this instance. The matrix effect was evaluated, and it was concluded that sample quantification can be done by calibration with aqueous standards. The detection limits ranged from 0.01 to 0.03 ng mL(-1) depending on the compound. The environmentally friendly sample pretreatment procedure was applied to study the migration of the bisphenols from different types of samples: thermal printer paper, compact discs, digital versatile discs, small tight-fitting waistcoats, baby's bottles, baby bottle nipples of different materials and children's toys.     

A quantum chemical study on the free radical scavenging activity of tyrosol and hydroxytyrosol

The free radical scavenging activity of hydroxytyrosol (HTyr) and tyrosol (Tyr) has been studied in aqueous and lipid solutions, using the density functional theory. Four mechanisms of reaction have been considered: single electron transfer (SET), sequential electron proton transfer (SEPT), hydrogen transfer (HT), and radical adduct formation. It was found that while SET and SEPT do not contribute to the overall reactivity of HTyr and Tyr toward ^·OOH and ^·OCH₃ radicals, they can be important for their reactions with ^·OH, ^·OCCl₃, and ^·OOCCl₃. The ^·OOH-scavenging activity of HTyr and Tyr was found to take place exclusively by HT, and it is also predicted to be the main mechanism for their reactions with ^·OCH₃. HT is proposed as the main mechanism for the scavenging activity of HTyr and Tyr when reacting with other ^·OR and ^·OOR radicals, provided that R is an alkyl or an alkenyl group. The major products of reaction are predicted to be the phenoxyl radicals. In addition, Tyr was found to be less efficient than HTyr as free radical scavenger. Moreover, while HTyr is predicted to be a good peroxyl scavenger, Tyr is predicted to be only moderately for that purpose.     

Photo-controlled release of zinc metal ions by spiropyran receptors anchored to single-walled carbon nanotubes

Light controllable release of antinflammatory zinc ions by a smart multifunctional material composed of spiropyrans and single walled carbon nanotubes (SWNTs) is demonstrated. The exploitation of a number of complementary characterization techniques allows the investigation of both composition and performance of the multifunctional SP/SWNT nanomaterial developed. Moreover, its suitability for potential applications in bio-systems is suggested by the effective removal of the metal catalyst and the introduction of biocompatible linkers into the SP/SWNT material. The realization of potential photo controllable SP/SWNTs based drug delivery systems (DDSs) is envisaged, where nanotubes act as intracellular carriers of light modulated receptors for bioactive agents.