Oxidation of benzoins to benzils in the presence of porphyrin sensitizers by air and sunlight or visible light

In this work, two new aerobic routes are introduced for the oxidation of a variety of benzoins to benzils by using molecular oxygen in the presence of porphyrins as sensitizers, using white light or sunlight in acetonitrile under mild conditions. The methods have a wide range of applications, do not involve cumbersome work-up, exhibit chemoselectivity and proceed under mild reaction conditions. The resulting products are obtained in good yields in a reasonable time.     

A new sample holder for excitation of transverse sound waves

A simple non-resonant sample holder with inclined electrodes is described by means of which transverse sound waves in the GHz range are easily generated by an evaporated piezoelectric layer. Because of its small size it is especially well suited for cryostat applications.     

60Co retention by Mexican montmorillonites

Radioactive elements may be retained by clays. The ability of natural Mexican clays to retain radioactive Co from aqueous solutions, is discussed. Experiments were performed with solutions containing labeled cobalt. The effect of contact time on Co²⁺ retention was studied. It was found that the Co²⁺ uptake value in dehydrated montmorillonites is between 0.30 and 0.70 meq g^–1 of clay. A sorption sequence was obtained for the various clays. The samples were characterized, before and after cobalt exchange, by X-ray diffraction.     

Acetic Acid Based Sol-Gel PLZT Thin Films: Processing and Characterization

PLZT 4/65/35 thin films were prepared by the acetic acid based sol-gel route. The choice of lanthanum precursor, i.e., acetate or nitrate, influences the functional group content of formamide modified sols and the microstructure of the thin films. The lanthanum nitrate based PLZT thin film deposited on Si/SiO2/TiO2 /Pt/TiO2 substrate has a columnar perovskite grain structure, while the lanthanum acetate based one is characterized by a lead-silicon containing reaction layer beneath the platinum electrode. Although lead is depleted from the PLZT thin film the perovskite structure is retained by the use of the top layer with a large excess of PbO.     

X-Ray Diffraction and Mössbauer Characterization of Raney Fe-Ni Catalysts

Rancy type catalysts were prepared by means of a two step procedure: (1) Mechanical alloying of the metals and, (2) alkaline aluminum leaching. Mechanical alloying is a novel atlernative related to the synthesis of skeletal Ni catalysts. X-ray diffraction, and Mössbauer spectroscopies were performed for catalysts characterization. Binary Al-Ni and ternary Al-Ni-Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic -(AlNi) phase was formed with a fine microstructure as a non-equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the -(AlNi) phase was transformed into the more stable nickel fee structure.     

In vivo neutron activation analysis of rats

A method of estimating total body calcium and sodium in rats by in vivo neutron activation analysis is described. The subjects were exposed to an integrated flux of about 1.6·10¹¹ thermal neutrons and activity was determined by counting with a 3″×3″ NaI(Tl) detector. The growth of the subjects was followed for about 75 days. The values of total body concentrations obtained are 0.83–0.90% for Ca and 0.128% for Na. Consideration is given to the accuracy attainable and to the effects on the blood and the hematopoietic tissues of the radiation doses imparted.     

Palladium-catalyzed tandem reactions to form 1-vinyl-1h-isochromene derivatives

The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the allylic system. The use of a lithium diamide base appears to be essential for success. The tert-butyldimethylsilyl protecting group is also an essential choice as it furnishes the appropriate reactivity to promote allylic substitution after the aryl coupling process. The use of more effective leaving groups, such as acetate, results in reaction of the allylic group, and no aryl coupling is observed. Through the appropriate selection of phosphine ligand and solvent, either the cyclized isochromene product or the noncyclized intermediate may be formed selectively. A short combinatorial study of the scope and limitations of the reaction, involving 24 ketones, is described.     

Host–Guest Interaction Study of Resveratrol With Natural and Modified Cyclodextrins

The aim of this work is to increase the stability and water solubility of resveratrol by complexation with different cyclodextrins. Furthermore, physical–chemical properties of each inclusion compound were investigated. Complexes of resveratrol with cyclodextrins both native (α, β, γ) and modified (2-hydroxypropyl-β-cyclodextrin, dimethyl-β-cyclodextrin) were obtained by using the suspension method. An inclusion complex with β-cyclodextrin was also prepared by using the microwave. Solid state characterization of the products was carried out using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (DRX); solution studies were performed by UV–Vis spectrophotometry and ¹H-NMR spectroscopy. Phase solubility profiles with all cyclodextrins employed were classified as A_N type, indicating the formation of 1:1 stoichiometric inclusion complexes. Stability constants (K _c) from the phase solubility diagrams were calculated. Stability studies in the solid state and in solution were performed; the photodegradation by UV–Vis spectrophotometry was monitored. The isomerization rate trans to cis, in ethanol solution, decreased with inclusion. The dissolution studies revealed that resveratrol dissolution rate was improved by the formation of inclusion complexes.     

Surface and bulk cation distribution of the spinel system ZnxMg1−xFe2O4

Zn_xMg_1-xFe₂O₄ mixed oxide spinels (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by conventional solid state reaction method. Bulk and surface characterization of these ferrites were carried out by different techniques. The ratios Zn/Fe and Mg/Fe determined by PIXE and AAS were nearly as expected from the synthesis mixture, i.e. following the substitution model. XRD shows only a spinel structure (fcc) with increasing lattice parameter as x increases from 0 to 1. The bulk ratios of tetrahedral to octahedral sites occupied by Fe cations measured by NGR are in good agreement with the theoretical bulk stoichiometry. LEIS results indicate a Mg substitution by Fe cations at the surface. Only octahedral sites are proposed at the surface. The transition from inverse to normal spinel was follow through NGR-spectra occurring at x=0.4.