Beyond Acid Strength in Zeolites: Soft Framework Counteranions for Stabilization of Carbocations on Zeolites and Its Implication in Organic Synthesis

The generation of a carbocation with an acid depends not only on the acid strength but also on the ability of the counteranion to stabilize the positive charge left behind. Here we report that despite their relatively weak acidity, zeolites are able to generate and stabilize medium‐size (molecular weight ≈300 Da) delocalized carbocations on their surface under mild reaction conditions, as it can be done by strong Brønsted or Lewis acids in solution. The zeolite thus acts as a soft macroanion, prolonging the lifetime of the carbocation sufficiently to perform multifunctionalization reactions with amides, thioamides, and phenols, with high yield and selectivity. Biological studies show that some of the products obtained here present significant inhibition activity against colon cancer cells, illustrating the new possibilities of zeolites to prepare complex organic molecules.     

Chemoenzymatic Syntheses of Sialylated Oligosaccharides Containing C5‐Modified Neuraminic Acids for Dual Inhibition of Hemagglutinins and Neuraminidases

A fast chemoenzymatic synthesis of sialylated oligosaccharides containing C5‐modified neuraminic acids is reported. Analogues of GM₃ and GM₂ ganglioside saccharidic portions where the acetyl group of NeuNAc has been replaced by a phenylacetyl (PhAc) or a propanoyl (Prop) moiety have been efficiently prepared with metabolically engineered E. coli bacteria. GM₃ analogues were either obtained by chemoselective modification of biosynthetic N‐acetyl‐sialyllactoside (GM₃NAc) or by direct bacterial synthesis using C5‐modified neuraminic acid precursors. The latter strategy proved to be very versatile as it led to an efficient synthesis of GM₂ analogues. These glycomimetics were assessed against hemagglutinins and sialidases. In particular, the GM₃NPhAc displayed a binding affinity for Maackia amurensis agglutinin (MAA) similar to that of GM₃NAc, while being resistant to hydrolysis by Vibrio cholerae (VC) neuraminidase. A preliminary study with influenza viruses also confirmed a selective inhibition of N1 neuraminidase by GM₃NPhAc, suggesting potential developments for the detection of flu viruses and for fighting them.     

Comparison between polyethylenglycol and imidazolium ionic liquids as solvents for developing a homogeneous and reusable palladium catalytic system for the Suzuki and Sonogashira coupling

The carbapalladacycle complex of 4-hydroxyacetophenone oxime is a highly active palladium catalyst to effect the Suzuki coupling of aryl chlorides and other C-C forming reactions in water. In an attempt to develop a reusable, homogeneous system based on this complex, its stability against prolonged heating in different ionic liquids and polyethylenglycol (PEG) has been studied. It was found that the palladium complex decomposes in water, 1-butyl-1-methylimidazolium hexafluorophosphate and 1-butyl-1-methylimidazolium chloride to form palladium nanoparticles in the first two cases and PdCl₄²⁻ in the third case. In contrast, this cyclic palladium complex was stable upon extended heating in 1-butyl-2,3-dimethylimidazolium hexafluorophosphate and in PEG. The activity of this complex for the Suzuki and Sonogashira correlates with the stability of the complex, the activity in PEG being higher than any of the ionic liquids tested. Although the carbapalladacycle complex also decomposes in PEG upon reaction, the resulting Pd nanoparticles (2-5 nm size) are stabilized by PEG acting as ligand. In this way, a reusable, homogeneous system in PEG has been developed that is able to effect the Suzuki and Sonogashira couplings without the need of copper and phosphorous ligands, working at the open air.     

Structural and electrical characterisation of La0.5Ca0.5MnO3 thin films grown by pulsed laser deposition

Thin films of perovskite manganite, with nominal composition La_0.5Ca_0.5MnO₃, have been prepared by pulsed laser deposition on (1 0 0) SrTiO₃, (1 0 0) LaAlO₃, (1 0 0) Si and YSZ/CeO₂-buffered (1 0 0) Si substrates. Structural and electrical characterisation was performed on the films. The magneto-transport properties of all the thin films depart from the bulk behaviour. The LCMO film grown on buffered Si shows an insulator–metallic transition around 130–150 K while the one deposited directly on Si displayed a similar behaviour under a melting field of 1 T. However, that transition is absent in the films grown on LAO and STO. We suggest that appropriate stress values induced by the substrate favour the formation of metallic percolative paths.     

A new synthesis of (−)-epipyriculol: a phytotoxic metabolite

A convenient synthesis of the phytotoxic natural product epipyriculol has been accomplished in 17 steps from methyl l-tartrate. The synthetic strategy is based upon the use of a butanediacetal-protected scaffold as central core from which the alkenyl side chains were assembled.     

Quantification of Monoclonal Antibodies from Bioreactor Supernatants Using Protein-G Sepharose Chromatography

A protein-G sepharose affinity chromatography was validated to quantify antibodies from cell culture supernatants. The calibration curve linear range was 30–480 μg immunoglobulin (IgG). Between-run study demonstrated a coefficient of variation 5.73–9.02% in 20 purification cycles and sample dilution with protein-free medium (>3 mL) showed a marked IgG amount over estimation. Sensitivity was 30 μg, and bovine serum albumin addition to columns did not affect IgG recovery (?90%). CB.Ifn-2.4 antibody quantification in MiniPERM^® bioreactor supernatant reached 1.5 mg mL^?1, coinciding with concentration measured by ELISA and thus demonstrating the protein-G sepharose column accuracy used to quantify IgG under these experimental conditions.     

Study of Chlorambucil and Chlorambucil–Trimethyl-β-cyclodextrin Inclusion Complex by CE

The results of CE studies of solid inclusion complexes of chlorambucil (CHL) and trimethyl-β-cyclodextrin (TM-β-CD) are presented. Chlorambucil has low stability in aqueous solution, so the formation of complexes with β-CD is a good way to improve its stability and dissolution. The experimental results confirm the existence of inclusion complexes. CE can differentiate free CHL from CHL–TM-β-CD complexes due to their different electrophoretic mobilities.