Catalytic asymmetric hydrosilylation of acetophenone with new chiral thiourea ligands containing the (S)-α-phenylethyl group

New chiral thioureas 1–8 containing 1,2-ethylendiamine or trans-1,2-diaminocyclohexane as the carbon skeleton, and containing an (S)-α-phenylethyl group have been prepared (79–98% yield). Thioureas 1–8 were used as ligands for the zinc-based catalyzed asymmetric hydrosilylation of acetophenone with polymethylhydrosiloxane (PMHS). The best result was achieved with monothiourea 1 (up to 75% ee), in toluene and a catalyst load of 5 mol %.     

Solution structures of fluorescent Zn(II) complexes with bis(naphthyl amide)-EDTA

Two EDTA-based bichromophoric isomers form Zn(II) complexes that exhibit distinct fluorescent behaviors; the ligands are abbreviated as (edta1nap)H₂ and (edta2nap)H₂, each of which consists of an EDTA chain linked to two 1-naphthyl or 2-naphthyl groups. The coordination chemistry of these complexes was studied by UV-Vis, fluorescence and ¹H NMR. The formation constants and the inherent emission intensities were determined by the pH dependence of the emission spectra; the species of the most intense emission is ML(OH) for L = (edta1nap)²⁻, and ML for (edta2nap)²⁻. The ¹H NMR of Zn-(edta1nap)²⁻ exhibits two sets of signals due to a slow exchange between two equivalent coordination geometries, whereas Zn-(edta2nap)²⁻ undergoes a fast exchange to show a single set of NMR signals. The spin-lattice relaxation time T₁ determined for the isostructural Mn(II) complexes shows that the naphthyl proton closest to the metal ion is H(8) in the (edta1nap)²⁻ complex, and H(3) in the (edta2nap)²⁻ complex. The two ligands differ only in the substitution position of the naphthyl group, but this apparently small difference leads to the notable difference in structural, dynamic, and consequent emission-spectral properties of their metal complexes as a result of the steric and size effects of the aromatic rings.     

Size separations of starch of different botanical origin studied by asymmetrical-flow field-flow fractionation and multiangle light scattering

Asymmetrical-flow field-flow fractionation combined with multiangle light scattering and refractive index detection has been revealed to be a powerful tool for starch characterization. It is based on size separation according to the hydrodynamic diameter of the starch components. Starch from a wide range of different botanical sources were studied, including normal starch and high-amylose and high-amylopectin starch. The starch was dissolved by heat treatment at elevated pressure in a laboratory autoclave. This gave clear solutions with no granular residues. Amylose retrogradation was prevented by using freshly dissolved samples. Programmed cross flow starting at 1.0 mL min(-1) and decreasing exponentially with a half-life of 4 min was utilised. The starches showed two size populations representing mainly amylose and mainly amylopectin with an overlapping region where amylose and amylopectin were possibly co-eluted. Most of the first population had molar masses below 10(6) g mol(-1), and most of the second size population had molar masses above 10(7) g mol(-1). Large differences were found in the relative amounts of the two populations, the molar mass, and hydrodynamic diameters, depending on the plant source and its varieties.     

Hydrogen‐bonded sheets in benzylmethylammonium hydrogen maleate

In the title compound, C₈H₁₂N⁺·C₄H₃O₄⁻, there is a short and almost linear but asymmetric O—H...O hydrogen bond in the anion. The ions are linked into C₂²(6) chains by two short and nearly linear N—H...O hydrogen bonds and the chains are further weakly linked into sheets by a single C—H...O hydrogen bond.     

A constant-momentum/energy-selector time-of-flight mass spectrometer

A matrix assisted laser desorption/ionization time-of-flight mass spectrometer has been built with an ion source that can be operated in either constant-energy or constant-momentum acceleration modes. A decreasing electric field distribution in the ion-accelerating region makes it possible to direct ions onto a space-focal plane in either modes of operation. Ions produced in the constant-momentum mode have velocities and, thus, flight times that are linearly dependent on mass and kinetic energies that are inversely dependent on mass. The linear mass dispersion doubles mass resolving power of ions accelerated with space-focusing conditions in constant-momentum mode. The mass-dependent kinetic energy is exploited to disperse ions according to mass in a simple kinetic energy filter constructed from two closely spaced, oblique ion reflectors. Focusing velocity of ions of the same mass can substantially improve ion selection for subsequent post source decay or tandem time-of-flight analyses.     

Characterization of <Emphasis Type="Italic">Anemopsis californica</Emphasis> essential oil–β-cyclodextrin inclusion complex as antioxidant prolonged-release system

Antioxidant activity is a property of Anemopsis californica essential oil (ACO). However, ACO possesses volatile compounds that provide strong flavors and that are susceptible to degradation, complicating its application. An alternative is its encapsulation in a β-cyclodextrin (β-CD) matrix. Therefore, the characterization of β-CD–ACO inclusion complexes as an antioxidant prolonged-release system was the objective of this work. The ACO yield was 8.26 mg/g of dry sample. Elemicin (EL) (68.9%) and methyleugenol (ME) (11.7%) comprised the majority compounds identified by gas chromatography (GC). The β-CD–ACO inclusion complex, with a 90:10 ratio based on the precipitation technique, exhibited best percentage of recovery, greater ACO retention, and major antioxidant capacity determined by DPPH [2,2-diphenyl-1-picrylhydrazyl] and ABTS [2,2′-azino-bis-(3 ethylbenzothiazoline-6-sulfonic acid)] assays. Antioxidant activity was maintained during encapsulation. Free β-CD and β-CD:ACO presented the hysteresis phenomenon according to water sorption isotherms. A prolonged-release system was studied using different relative humidities (0, 33, 66, 96 and 100%). EL demonstrated 93.75% of release in highest relative humidity, while ME released completely. These results suggest application of the β-CD–ACO complex in systems in which it can be passively released and in controlled form, as in active food or drug packaging.     

Titania–Silica Materials for Enhanced Photocatalysis

Mesoporous titania–organosilica nanoparticles comprised of anatase nanocrystals crosslinked with organosilica moieties have been prepared by direct co‐condensation of a titania precursor, tetrabuthylortotitanate (TBOT), with two organosilica precursors, 1,4‐bis(triethoxysilyl) benzene (BTEB) and 1,2‐bis(triethoxysilyl) ethane (BTEE), in mild conditions and in the absence of surfactant. These hybrid materials show both high surface areas (200–360 m² g^?1) and pore volumes (0.3 cm³ g^?1) even after calcination, and excellent photoactivity in the degradation of rhodamine 6G and in the partial oxidation of propene under UV irradiation, especially after the calcination of the samples. During calcination, there is a change in the Ti^IV coordination and an increase in the content of Si?O?Ti moieties in comparison with the uncalcined materials, which seems to be responsible for the enhanced photocatalytic activity of hybrid titania–silica materials as compared to both uncalcined samples and the control TiO₂.     

Production and purification of bacterial membrane vesicles for biotechnology applications: Challenges and opportunities

Bacterial membrane vesicles (BMVs) are bi-layered nanostructures derived from Gram-negative and Gram-positive bacteria. Among other pathophysiological roles, BMVs are critical messengers in intercellular communication. As a result, BMVs are emerging as a promising technology for the development of numerous therapeutic applications. Despite the remarkable progress in unveiling BMV biology and functions in recent years, their successful isolation and purification have been limited. Several challenges related to vesicle purity, yield, and scalability severely hamper the further development of BMVs for biotechnology and clinical applications. This review focuses on the current technologies and methodologies used in BMV production and purification, such as ultracentrifugation, density-gradient centrifugation, size-exclusion chromatography, ultrafiltration, and precipitation. We also discuss the current challenges related to BMV isolation, large-scale production, storage, and stability that limit their application. More importantly, the present work explains the most recent strategies proposed for overcoming those challenges. Finally, we summarize the ongoing applications of BMVs in the biotechnological field.