Tetrahydroquinazoline-substituted chromones from Diels–Alder reaction of (E)-2-styrylchromones and pyrimidine ortho-quinodimethane

The Diels–Alder reaction of (E)-2-styrylchromones with a pyrimidine ortho-quinodimethane is reported for the first time. These cycloaddition reactions afford mixtures of two regioisomeric tetrahydroquinazoline-substituted chromones in moderate to excellent global yields. Irrespective of the substituents on the 2-styrylchromones, the 2-(7-aryl-4-methoxy-2-methyl-5,6,7,8-tetrahydroquinazolin-6-yl)chromone derivatives are always the major isomers.     

Sensitive coating for water vapors detection based on thermally sputtered calcein thin films

In this paper the adsorption properties of thermally sputtered calcein thin films towards water and other polar molecules vapors are studied by different characterization techniques: quartz crystal microbalance, surface plasmon resonance and visible spectroscopy. Sensitivity of calcein thin films to water vapors resulted much higher as compared with those of a number of dyes whose structure was close to that of calcein. All types of sensors with calcein coatings have demonstrated linear concentration dependences in the wide range of water vapor pressure from low concentrations up to 27,000 ppm (close to saturation). At higher concentrations of water vapor all sensors demonstrate the abrupt increase of the response (up to two orders). A theoretical model is advanced explaining the adsorption properties of calcein thin films taking into account their chemical structure and peculiarities of molecular packing. The possibility of application of thermally sputtered calcein films in sensing technique is discussed.     

Catalysis by rhodium complexes bearing pyridine ligands: Mechanistic aspects

The present review describes several examples of the use of soluble and immobilized complexes of rhodium with pyridine ligands as catalysts. Examples include the water-gas shift reaction, the carbonylation of methanol, the reduction of nitroarenes, the hydrocarboxylation and oligomerization of CO/ethylene, the hydrocarbonylation of 1-hexene, the hydroesterification and hydroformylation–acetalization of 1-hexene, the hydrodechlorination of dichloroethane, the carbonylation of naphtha and the hydrogenation and hydroformylation of alkenes.     

The dependence of α-tocopheroxyl radical reduction by hydroxy-2,3-diarylxanthones on structure and micro-environment

The flavonoid quercetin is known to reduce the α-tocopheroxyl radical (˙TocO) and reconstitute α-tocopherol (TocOH). Structurally related polyphenolic compounds, hydroxy-2,3-diarylxanthones (XH), exhibit antioxidant activity which exceeds that of quercetin in biological systems. In the present study repair of ˙TocO by a series of these XH has been evaluated using pulse radiolysis. It has been shown that, among the studied XH, only 2,3-bis(3,4-dihydroxyphenyl)-9H-xanthen-9-one (XH9) reduces ˙TocO, though repair depends strongly on the micro-environment. In cationic cetyltrimethylammonium bromide (CTAB) micelles, 30% of ˙TocO radicals are repaired at a rate constant of ~7.4 × 10(6) M(-1) s(-1) by XH9 compared to 1.7 × 10(7) M(-1) s(-1) by ascorbate. Water-soluble Trolox (TrOH) radicals (˙TrO) are restored by XH9 in CTAB (rate constant ~3 × 10(4) M(-1) s(-1)) but not in neutral TX100 micelles where only 15% of ˙TocO are repaired (rate constant ~4.5 × 10(5) M(-1) s(-1)). In basic aqueous solutions ˙TrO is readily reduced by deprotonated XH9 species leading to ionized XH9 radical species (radical pK(a) ~10). An equilibrium is observed (K = 130) yielding an estimate of 130 mV for the reduction potential of the [˙X9,H(+)/XH9] couple at pH 11, lower than the 250 mV for the [˙TrO,H(+)/TrOH] couple. A comparable value (100 mV) has been determined by cyclic voltammetry measurements.     

Modified RP-LC of Phenylthiocarbamyl Amino Acid Adducts in Plasma Acetonitrile Extracts Using Multiple Internal Standards and Photo-Diode UV Detection

Among the techniques available for quantitative analysis of physiological amino acids, systems using optical detection are of low specificity because of possible interference at the analytical wavelength. Another disadvantage is problems of sample extraction from complex biological matrices, for example plasma. This paper describes reversed-phase LC of phenylthiocarbamyl (PTC) amino acids in plasma deproteinated by addition of acetonitrile. Specificity was monitored by photo-diode UV detection and accuracy was assessed by a plasma spiking procedure with more than one internal standard. Dual-wavelength spectrophotometry (254 and 283 nm) was also used for separate measurement of co-eluting adducts of tryptophan and ornithine. This method enables the quantification, with high reproducibility, of a total of twenty-three plasma amino acids from fasting healthy subjects. LOQ values are satisfactory for all the amino acids (average 6 μmol L^?1). However, the method does not enable analysis of aspartate and overall homocystine, present at very low concentrations, in all plasma samples. This PTC–amino acid chromatographic method is inexpensive, reliable, and suitable for clinical research and therapeutic drug monitoring, but adaptation to dual on-line detection is required to improve its sensitivity.     

Electrical and optical properties of ITO and ITO/Cr-doped ITO films

In this paper we report on the effects of the insertion of Cr atoms on the electrical and optical properties of indium tin oxide (ITO) films to be used as electrodes in spin-polarized light-emitting devices. ITO films and ITO(80 nm)/Cr-doped ITO(20 nm) bilayers and Cr-doped ITO films with a thickness of 20 nm were grown by pulsed ArF excimer laser deposition. The optical, structural, morphological and electrical properties of ITO films and ITO/Cr-doped structures were characterized by UV–Visible transmission and reflection spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Hall-effect analysis. For the different investigations, the samples were deposited on different substrates like silica and carbon coated Cu grids. ITO films with a thickness of 100 nm, a resistivity as low as ～4×10^?4 Ω?cm, an energy gap of ～4.3 eV and an atomic scale roughness were deposited at room temperature without any post-deposition process. The insertion of Cr into the ITO matrix in the upper 20 nm of the ITO matrix induced variations in the physical properties of the structure like an increase of average roughness (～0.4–0.5 nm) and resistivity (up to ～8×10^?4 Ω?cm). These variations were correlated to the microstructure of the Cr-doped ITO films with particular attention to the upper 20 nm.     

An approach for decomposition of finite rotations

Based on Lie groups theory, this work considers the problem of decomposition of a given rotation into three successive finite rotations with prescribed in advance axes. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanism of the hydroxycarbonylation of 1-hexene catalyzed by immobilized rhodium complexes of pyridine ligands

Summary In this work, a mechanistic study of the hydroxycarbonylation of 1-hexene to heptanoic acid and the water gas shift reaction (WGSR) catalyzed by the rhodium(I) complexes, [Rh(COD)(amine)₂](PF₆) (COD = 1,5-cyclooctadiene, amine = 4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) immobilized on poly(4-vinylpyridine) in contact with water under CO is discussed. Catalytic cycles for these reactions bearing common Rh-H catalytic species are proposed.     

Hydroformylation of 1-Hexene Catalyzed by [Rh(COD)(2-Picoline)2]PF6 Immobilized on Poly(4-Vinylpyridine) Under Water Gas Shift Reaction Conditions

Reported here is the influence of the reaction conditions variation (1-hexene/rhodium content (S/C) = 16 - 105, temperature (T) = 70 - 110 °C and carbon monoxide pressure (P(CO)) = 0.6 - 1.8 atm) on the catalytic hydroformylation of 1-hexene to aldehydes (heptanal and 2-methyl-hexanal) by the rhodium(I) complex, [Rh(COD)(2-picoline)₂]PF₆ (COD = 1,5-cyclooctadiene)immobilized on poly(4-vinylpyridine) in contact with 10 mL of 80% aqueous 2-ethoxyethanol, under water gas shift reaction condition. This revised version was published online in June 2006 with corrections to the Cover Date.