Analysis of polybrominated diphenyl ethers in atmospheric deposition and snow samples by solid-phase disk extraction

An extraction method for the quantitative analysis of polybrominated diphenyl ethers (PBDEs) in aqueous samples has been evaluated. The analytical methodology includes the sample filtration through glass fiber filter and subsequent extraction of dissolved phase compounds by C18 solid-phase disk extraction. Dependence of extraction efficiency on factors such as pollutant concentrations, sample volume, and stability during storage has been investigated. Mean extraction efficiencies of 97% for total PBDEs (13 tri- to heptabrominated congeners at spiking levels in the range of 15-90pg) with a RSD between 9 and 20% were achieved. Higher recoveries were observed for the more volatile PBDEs (112%) in relation to more brominated congeners (88%). The developed methodology was successfully applied to the analysis of these compounds in atmospheric deposition and snow samples from remote sites in Europe with method detection and quantitation limits in the range of 2.1-10pgL(-1) for almost all congeners, which allow the determination of PBDEs in remote areas with levels in the range of low to medium pgL(-1) for SigmaPBDEs.     

Luminescent nanocrystals in phospholipid micelles for bioconjugation: an optical and structural investigation

Organic capped luminescent CdSe@ZnS nanocrystals (NCs) have been incorporated in block copolymer micelles, formed by polyethylene glycol modified phospholipids (PEG lipids). The obtained water soluble NC including PEG lipid micelles have been conjugated with bovine serum albumine (BSA). The entire process has been investigated by using optical, structural and electrophoretic complementary techniques. Such an integrated approach has allowed to elucidate critical issues, such as the time and temperature effects on the phase behavior of the PEG lipid/NC aggregate structures, the emitting properties of the NCs before and after micelle formation and bio-conjugation and the effect of conjugation on the biological moiety. The overall results provide relevant insight on the fabrication of the bio-conjugates, on their stability and on preparative procedure reproducibility, in view of the use of the resulting protein decorated NCs as multifunctional hybrid building blocks for the fabrication of a variety of supramolecular assemblies to exploit in biological sensing and diagnostic applications.     

Determination of aflatoxins in hazelnuts by various sample preparation methods and liquid chromatography-tandem mass spectrometry

A sensitive and reliable liquid chromatography-tandem mass spectrometric with electrospray ionization method for determining aflatoxins in hazelnuts has been developed. Three different extraction techniques, such as homogenization, ultrasonic extraction, and matrix solid phase dispersion have been tested and compared in terms of recovery, matrix effect, accuracy and precision. Ultrasound extraction was the most performing sample preparation method. Absolute recoveries for analytes and I.S. ranged from 93 to 101%. Accuracy and precision were calculated using matrix matched calibration, and ranged 91-102% and 2-11%, respectively. CC alpha and CC beta for aflatoxin B1 (EU limit=2 microg/kg) were 2.15 and 2.33 microg/kg, respectively. A ruggedness test performed on three other matrices demonstrated that sonication time was critical and a matrix matched calibration must be constructed for every sort of matrix.     

L-tryptophan transport through a hydrophobic liquid membrane using AOT micelles: dynamics of the process as revealed by small angle X-ray scattering

Hydrophobic liquid membranes have a high technological potential in many fields of separation science. The dynamics of these systems is very complex and still not fully understood. In this work we studied the effect of the incorporation of cationic and anionic L-tryptophan at pH 1.8 and 10.0, respectively, in Aerosol-OT reverse micelles performing small angle X-ray scattering experiments. The use of a synchrotron radiation source allowed efficient in situ data acquisition. Several insights on L-tryptophan transport dynamics through hydrophobic membranes containing AOT could be obtained from these SAXS experiments, such as amino acid site localization and changes in the reverse micelle sizes.     

Addition of allyltrichlorostannanes to aldehydes: application in the synthesis of 4-N-Boc-amino-3-hydroxy ketones

We wish to describe here the diastereoselective reaction between chiral N-Boc-α-amino aldehydes and achiral allyltrichlorostannanes leading to 1,2-syn-N-Boc-α-amino alcohols, which are treated with catalytic amounts of OsO₄ in the presence of NaIO₄ to provide the corresponding 4-N-Boc-amino-3-hydroxy ketones.     

How deeply are core electrons perturbed when valence electrons are spin polarized? The case study of transition metal compounds

The ferromagnetic and antiferromagnetic wave functions of the KMnF₃ perovskite have been evaluated quantum-mechanically by using an all electron approach and, for comparison, pseudopotentials on the transition metal and the fluorine ions. It is shown that the different number of α and β electrons in the d shell of Mn perturbs the inner shells, with shifts between the α and β eigenvalues that can be as large as 6 eV for the 3s level, and is far from negligible also for the 2s and 2p states. The valence electrons of F are polarized by the majority spin electrons of Mn, and in turn, spin polarize their 1s electrons. When a pseudopotential is used, such a spin polarization of the core functions of Mn and F can obviously not take place. The importance of such a spin polarization can be appreciated by comparing (i) the spin density at the Mn and F nuclear position, and then the Fermi contact constant, a crucial quantity for the hyperfine coupling, and (ii) the ferromagnetic–antiferromagnetic energy difference, when obtained with an all electron or a pseudopotential scheme, and exploring how the latter varies with pressure. This difference is as large as 50% of the all electron datum, and is mainly due to the rigid treatment of the F ion core. The effect of five different functionals on the core spin polarization is documented.     

Host-guest Assembly Based on γ-Cyclodextrin-functionalized Multiwalled Carbon Nanotubes for Rutin Electrochemical Sensing

Here, we report multiwalled carbon nanotubes (MWCNTs) functionalized with γ-cyclodextrins (γCD) as a novel electrochemical strategy for Rutin determination, showing superior performance than β-cyclodextrins (βCD) modified MWCNTs, suggesting an adequate environment for host-guest interactions. Under optimized conditions, the sensor showed a linear range of 39–975 nmol L⁻¹ and a limit of detection of 7 nmol L⁻¹. When tested with quercetin, catechin, and caffeine, the platform presented high selectivity with an interference response <10 %. The method was employed to quantify Rutin in spiked pharmaceutical and herbal extracts, providing recovery of 93–98.4 %. Also, HPLC-PDA confirmed the method‘s accuracy.     

Combining Imine Condensation Chemistry with [3,3] Diaza-Cope Rearrangement for One-Step Formation of Hydrolytically Stable Chiral Architectures

Dynamic covalent chemistry (DCC) has, in recent years, provided valuable tools to synthesize molecular architectures of increasing complexity. We have also taken advantage of imine DCC chemistry to prepare TPMA -based supramolecular cages for molecular recognition applications. However, the versatility of this approach has as a major drawback the intrinsic hydrolytic lability of imines, which hampers some applications. We present herein a synthetic strategy that combines the advantages of a thermodynamic-driven formation of a supramolecular structure using imine chemistry, together with the possibility to synthetize chiral hydrolytically stable structures through a [3,3]-sigmatropic rearrangement. A preliminary mechanistic analysis of this one-pot synthesis and the scope of the reaction are also discussed.