Michael additions of benzoins versus Michael-Stetter additions of aldehydes

Triethylamine catalyzed Michael additions of benzoins to chalcone can prevail over the expected Michael-Stetter additions when certain thiazolium ion conjugate bases - prepared $\text{in situ}$ from the pertinent thiazolium salts and triethylamine- are used as catalysts.     

Macrocyclic ligands with potential axial interactions. The preparation of copper(II), nickel(II) and cobalt(III) complexes of 7,14-o-hydroxyphenyl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene

Summary The new macrocyclic ligand 7,14-o-hydroxyphenyl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene (1=L) has been prepared and complexes with copper(II), nickel(II) and cobalt(III) characterised. The nickel(II) complex is a yellow square-planar species, while the purple-red copper(II) complex is probably tetragonal in both the solid state and solution. The complexes appear to have an N-meso arrangement of the chiral nitrogen centres with the HOC₆H₄ groups occupying equatorial sites so that axial interactions with the metal do not occur. A variety oftrans-[CoLX₂]ClO₄ complexes (X=Cl, Br, NO₂, or N₃) have been characterised.     

Chemistry of Acyl(imidoyl)ketenes: IX. Synthesis and Thermolysis of 3-Aroyl-8-chloro-1,2-dihydro-4<Emphasis Type="Italic">H</Emphasis>-pyrrolo[2,1-<Emphasis Type="Italic">c</Emphasis>][1,4]benzoxazine-1,2,4-triones

Reactions of 3-Z-aroylmethylene-6-chloro-3,4-dihydro-2H-1,4-benzoxazine-2-ones with oxalyl chloride afford 3-aroyl-8-chloro-1,2-dihydro-4H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones and Z-3-(2-aryl-2-chlorovinyl)-6-chloro-2H-1,4-benzoxazine-2-ones. Aroyl(imidoyl)ketenes generated by decarbonylation of pyrrolobenzoxazinetriones undergo dimerization through [4+2]-cycloaddition to form 4-aroyl-3-aroyloxy-2-(2-oxo-2H-1,4-benzoxazin-3-yl)-1H, 5H-pyrido[2,1-c][1,4]benzoxazine-1,5-diones.     

Observation of difluorinated higher fullerene anions by Knudsen cell mass spectrometry and determination of electron affinities of C60F2 and C70F2

Difluorinated higher fullerenes have been studied by Knudsen cell mass spectrometry. Thermal negative ions C_nF₂⁻ (n=60, 70, 72, 74, 76 and 78) were produced inside the effusion cell as well as the neutral molecules C₆₀F₂ and C₇₀F₂. From the equilibrium constants for the electron exchange reactions between difluorinated fullerenes and their parents electron affinity values were derived for C₆₀F₂ (2.74 eV) and C₇₀F₂ (2.80 eV).     

Kinetics and mechanism of a trans-tetraazamacrocyclic chromium(III) complex oxidation by hexacyanoferrate(III) in strongly alkaline media

Oxidation of the trans-[Cr(cyca)(OH)₂]⁺ complex, where cyca = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by [Fe(CN)₆ ]^3- ion in strongly alkaline media, leading to [Cr^V O(cyca_ox )]³⁺ ion, has been studied using electronic and e.p.r. spectroscopy. The kinetics of the Cr^III → Cr^IV transformation have been studied using a large excess of the reductant and OH^- ion over the oxidant. The reaction is a second order process: first order in [Cr^III] and [Fe^III] at constant [OH^-]. The second order rate constant is higher than linearly dependent on the OH^- concentration. The mechanism of the reaction has been discussed. A relatively inert intermediate chromium(V) species was detected based on characteristic bands in the visible region and the e.p.r. signal at g_iso = 1.987 for the systems where an excess of oxidant was used. The hyperfine structure of the main e.p.r. signal is consistent with the d¹ -electron interactions with four equivalent nitrogen nuclei and [Cr^V = O(cyca_ox)]³⁺ formula, where cyca_ox = oxidized cyca, can be postulated for the intermediate Cr^V complex.     

Absorption properties of körbl-catalyst and manganese dioxide

Summary Körbl-catalyst and manganese dioxide absorb chlorine and bromine quantitatively at room temperature. This property is applied to simultaneous microanalytical determination of carbon, hydrogen and chlorine or bromine in compounds containing carbon, hydrogen, oxygen, chlorine or bromine, but not nitrogen or sulphur.

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Zusammenfassung Der Körbl-Katalysator und Mangandioxid absorbieren Chlor und Brom bei Raumtemperatur quantitativ. Sie wurden daher zur gleichzeitigen Bestimmung von C, H sowie Cl oder Br in Verbindungen verwendet, die C, H, O, Cl (oder Br), nicht aber N oder S enthalten.

     

Effects of Photobiomodulation on Daphnia magna Straus and their Sensitivity to Toxicant

This paper deals with the effect of photobiomodulation (PBM) on Daphnia magna S. and their sensitivity to cadmium sulfate, a known high toxic pollutant. In a first series of experiments, the effect of different He-Ne laser fluences irradiation (range 0.9-4300 mJ cm⁻²) on the fertility of both parent and filial generations (F1–F3) of the crustacean was studied. It was found that PBM in some cases significantly influenced the fertility of both irradiated crustaceans and their nonirradiated offspring. By selecting two fluences (9 ± 2 mJ cm⁻² reducing fertility and 4.3 ± 0.9 J cm⁻² increasing it), the effect of these on toxicity of cadmium sulfate was evaluated. These experiments have shown that prior irradiation with low-intensity light of a helium–neon laser with 632.8 nm wavelength can change the sensitivity of aquatic organisms to toxin cadmium sulfate. The degree and direction of changes depend on the toxicant concentration and the irradiation dose.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

Destructive adsorption of CCl4 over lanthanum-based solids: linking activity to acid-base properties

The relative activities of a low-surface crystalline and high-surface amorphous LaOCl, further denoted as S1 and S2, have been compared for the destructive adsorption of CCl4. It was found that the intrinsic activity of S2 is higher than that of S1. Both samples were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2-physisorption, and Raman and infrared (IR) spectroscopy. IR was used in combination with CO2, CO, and methanol as probe molecules. The CO2 experiments showed that different carbonate species are formed on both materials. For S1, a high surface concentration of bidentate carbonate species and a lower concentration of monodentate carbonate were observed. In the case of S2, bulk carbonates were present together with bridged carbonates. CO adsorption shows that S2 and S1 have very similar Lewis acid sites. However, methanol adsorption experiments showed that S2 had a higher number of stronger Lewis acid sites than S1 and that twofold coordinated methoxy species were more strongly bound than threefold coordinated methoxy species. Because of the analogy between methanol dissociation and the removal of the first chlorine atom in the destructive adsorption of CCl4, the sites enabling twofold coordination were likely to be the same Lewis acid sites actively involved in the destructive adsorption of CCl4. La2O3 was less active than the two LaOCl materials, and therefore, the intrinsic activity of the catalyst increases as the strength of the Lewis acid sites increases. S2 contains more chlorine at the surface than S1, which is expressed by the higher number of sites enabling twofold coordination. Moreover, this explains the difference in destructive adsorption capacity for CCl4 that was observed for the samples S1 and S2. Since LaCl3, being the most acidic phase, is not active for the destructive adsorption of CCl4, basic oxygen atoms, however, remain needed to stabilize the reaction intermediate CCl3 as La-O-CCl3.     

Structure, stereochemistry, and biological activity of integramycin, a novel hexacyclic natural product produced by Actinoplanes sp. that inhibits HIV-1 integrase

[structure: see text] HIV-1 integrase is a critical enzyme for viral replication, and its inhibition is an emerging target for potential antiviral chemotherapy. We have discovered a novel inhibitor, integramycin, from screening of fermentation extracts using an in vitro assay. Integramycin possesses a hexacyclic ring system and exhibited an IC50 value of 4 microM against HIV-1 integrase (strand transfer). The isolation, structure elucidation, stereochemistry, conformation, and biological activity has been described.