Chiral organoselenium-transition-metal catalysts in asymmetric transformations

In recent years, there has been an increasing application of chiral selenium compounds as ligands in metal-catalyzed enantioselective transformations. One of the most important challenges in this field is the development of new chiral complexes (catalyst) generated from the reaction between a metal and appropriate chiral selenium-containing compounds (ligand). The vast majority of these ligands are easily synthesized in a few high-yielding synthetic steps, starting from readily available chiral amino alcohols. In this context, the advantages of using these compounds will be discussed, mainly with regard to their easy accessibility, modular nature and the formation of strong bonds with soft or, more rarely, hard metals. Important selective contributions within the field of chiral selenium complexes are examined, according to their applications. As final remarks, future developments and perspectives of the field are discussed.     

Jacobson–Bourbaki Theory with Parameters

In this paper we generalize the classical Jacobson–Bourbaki correspondence for field extensions to K-vector space extensions (K a field). Namely, for such extensions, we state and prove a correspondence theorem – the Jacobson–Bourbaki correspondence with parameters. Some examples are provided.     

Metal-Free Intermolecular C−H Borylation of N-Heterocycles at B−B Multiple Bonds

Carbene-stabilized diborynes of the form LBBL (L=N-heterocyclic carbene (NHC) or cyclic alkyl(amino)carbene (CAAC)) induce rapid, high yielding, intermolecular ortho-C−H borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process.     

Rocket (Eruca vesicaria (L.) Cav.) vs. Copper: The Dose Makes the Poison?

The effects of copper addition, from various adsorbents, on the accumulation ability and glucosinolate content of cultivated rocket were studied. Different adsorbents (zeolite NaX, egg shells, substrate, fly ash) were treated with copper(II) solution with an adsorption efficiency of 98.36, 96.67, 51.82 and 39.13%, respectively. The lowest copper content and the highest total glucosinolate content (44.37 μg/g DW and 4269.31 µg/g DW, respectively) were detected in the rocket grown in the substrate with the addition of a substrate spiked with copper(II) ions. Rocket grown in the fly ash-substrate mixture showed an increase in copper content (84.98 μg/g DW) and the lowest total glucosinolate content (2545.71 µg/g DW). On the other hand, when using the egg shells-substrate mixture, the rocket copper content increased (113.34 μg/g DW) along with the total GSLs content (3780.03 µg/g DW), indicating the influence of an adsorbent type in addition to the copper uptake. The highest copper content of 498.56 μg/g DW was detected in the rocket watered with copper(II) solution with a notable decrease in the glucosinolate content, i.e., 2699.29 µg/g DW. According to these results rocket can be considered as a copper accumulator plant.     

Laser-induced breakdown spectroscopy and chemometrics for classification of toys relying on toxic elements

Quality control of toys for avoiding children exposure to potentially toxic elements is of utmost relevance and it is a common requirement in national and/or international norms for health and safety reasons. Laser-induced breakdown spectroscopy (LIBS) was recently evaluated at authors' laboratory for direct analysis of plastic toys and one of the main difficulties for the determination of Cd, Cr and Pb was the variety of mixtures and types of polymers. As most norms rely on migration (lixiviation) protocols, chemometric classification models from LIBS spectra were tested for sampling toys that present potential risk of Cd, Cr and Pb contamination. The classification models were generated from the emission spectra of 51 polymeric toys and by using Partial Least Squares - Discriminant Analysis (PLS-DA), Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN). The classification models and validations were carried out with 40 and 11 test samples, respectively. Best results were obtained when KNN was used, with corrected predictions varying from 95% for Cd to 100% for Cr and Pb.     

Hydrogenation of carbon dioxide: From waste to value

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Coalescence of metastable states in chemical reactions: double poles of the scattering matrix and exceptional points

Accidental degeneracy of two scattering resonances in chemical reactions is discussed. A novel analytical parameterization for the scattering matrix elements valid in the presence of two interacting resonances is derived and applied to investigate the coalescence of metastable states leading to double poles in the partial-wave amplitude. We show how double poles can manifest themselves in reaction cross-sections and discuss their relationship with exceptional points. The presence of two degenerate resonances interacting with each other can create a peculiar double-peak structure in the reaction probability. At the energy where the two decaying states coalesce the scattering matrix has a double pole and correspondingly the reaction probability reaches its minimum value. This novel formula has been tested with the well-established data obtained for the F + H₂ reaction, for which previous studies have revealed the existence of two interfering resonance pathways. The good agreement of model predictions and quantum scattering calculations shows that the present approach is reliable. Hence, we claim that it provides a way for the observation of interacting resonances in molecular collisions. Resonance positions and partial widths can be obtained by fitting the numerically calculated state-to-state reaction probabilities to the square modulus of the novel expression for the scattering matrix elements derived in the paper.     

Peptides trapping cocaine: docking simulation and experimental screening by solid phase extraction followed by liquid chromatography mass spectrometry in plasma samples

Two different hexapeptides were computationally designed and tested as selective SPE sorbent for cocaine. The amino acid residues used for designing the two hexapeptides, tested in SPE experiments, were, according to chemical function and interatomic distances, the most (QHWWDW) and the lowest (ESSIDH) preserved sequences in 4 proteins binding cocaine. The hexapeptide–cocaine complex was docked with different scoring functions combinations and resulting binding scores were compared with the SPE results. The extraction procedure for SPE was optimized considering volume loading, pH effect, and human plasma matrix interferences. Cocaine was loaded onto the modified resin cartridge at 10 ng mL⁻¹ and the peptide QHWWDW was found to have the highest recovery with the best retention at pH 7.5, in agreement with docking simulation. Retention experiments were carried out also on cocaine metabolites nor-cocaine, benzoylecgonine and ecgonine methyl ester. Except for nor-cocaine the retention of metabolites on resin modified with peptide QHWWDW decreased drastically confirming the peptide selectivity, and validating the simulation data. Compared to standard solutions, only a slight decrease in cocaine recovery was observed loading human plasma samples after a partial protein precipitation.