On the occurrence and role of SnO2, SnS and FeSn2 in coal hydroliquefaction experiments using tin-based catalysts

Mössbauer Spectroscopy, X-Ray Diffraction and Electron Microscopy were applied to the study of solid residues of coal hydroliquefaction, for which tin-based catalysts were used. In the general case hydroliquefaction runs were performed in the presence of added sulphur and of finely dispersed SnO₂ as a catalyst precursor. The only observed tin species were SnO₂ and SnS, the former with percentages higher than expected from XRD, due to its large f factor, the latter as a symmetric doublet, which suggests that any asymmetry should be ascribed to small particle sizes rather than to structure. When the S content was only that of coal and the catalyst precursor β-Sn, FeSn₂ occurred together with Sn sulfides and oxides, while no β-Sn was detected. The main catalytic role is ascribed to SnS.     

Direct synthesis of new arylanthranilic acids via a Suzuki cross-coupling reaction from iodoisatins

Direct synthesis of new arylanthranilic acids via a Suzuki cross-coupling reaction with iodoisatins as key intermediates is described. A ‘one pot’ procedure is proposed.     

Direct determination of calcium,copper, iron,magnesium, manganese and zinc in amniotic fluid samples using inductively coupled plasma-atomic emission spectrometry

An inductively coupled plasma-atomic emission spectrometric method is reported for the determination of calcium, copper, iron, manganese, magnesium and zinc. Samples are introduced directly when a sheath gas device is used. An external calibration procedure is used. The standards are prepared in a matrix composed of 0.5% (w/v) albumin and 0.76% (w/v) sodium chloride. The procedure was evaluated with a standard reference material (NBS SRM 909 Human Serum); all the values obtained are in agreement with the certified values. Results obtained for the determination of zinc, calcium, magnesium, copper, iron and manganese in amniotic fluid samples are reported.     

Diastereoselective carbonyl phosphonylation using chiral N,N′-bis-[(S)-α-phenylethyl]-bicyclic phosphorous acid diamides

Addition of aldehydes to the P-anion derivatives of chiral phosphorous acid diamides (1S,2S,1′S,1″S)-2 and (1R, 2R,1′S,1″S)-2 in THF gave α-hydroxyphosphonamides in good yield (64-100%) and moderate diastereoselectivities.     

1H and 13C NMR characterization of hemiamidal isoniazid-NAD(H) adducts as possible inhibitors of InhA reductase of Mycobacterium tuberculosis

Isoniazid (INH) is easily oxidized with manganese(III) pyrophosphate, a chemical model of the KatG protein involved in activation of INH inside the bacteria Mycobacterium tuberculosis. Performed in the presence of NAD(+), this oxidation generates a family of isomeric INH-NAD(H) adducts, which have been shown to be effective inhibitors of InhA, an enzyme essential in mycolic acid biosynthesis. In this work, we fully characterized by (1)H and (13)C NMR spectroscopy four main species of INH-NAD(H) adducts that coexist in solution. Two of them are open diastereoisomers consisting of the covalent attachment of the isonicotinoyl radical at position four of the nicotinamide coenzyme. The other two result from a cyclization involving the amide group from the nicotinamide and the carbonyl group from the isonicotinoyl radical to give diastereoisomeric hemiamidals. Although an INH-NAD(H) adduct with a 4S configuration has been characterized within the active site of InhA from Xray crystallography and this bound adduct interpreted as an open form (Rozwarski et al., Science 1998, 279, 98-102), it is legitimate to raise the question about the effective active form(s), open or cyclic, of INH-NAD(H) adduct(s). Is there a single active form or are several forms able to inhibit the InhA activity with different levels of inhibitory potency?     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution

Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical ^.CHMeCO₂(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.     

Synthese de pyrrolo[1,2-a]quinoleines

A-Acetoxypyrrolo[1,2a]quinolines 26-30 were synthesized by cyclization of 2-(1-pyrroly)phenylacetic acids 21-25 with acetic anhydride. The structures of the new compounds were determined by ¹H-nmr spectroscopy.     

Thienopyrrolizines: New condensed triheterocyclic systems

Cyclization of 3-(1-pyrrolyl)thiophene-2-carboxamide derivatives of methyl 3-(1-pyrrolyl)-2-thiophenecarboxylate afforded imminium salts and resulted in the formation of thieno[2,3-b]pyrrolizine derivatives.     

The cyano nitronyl nitroxide radical: experimental and theoretical evidence for the fourth case of the McConnell-I mechanism

The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m space group with a=7.4050(7), c=8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two-dimensional square array of spin S=1/2 antiferromagnetically coupled (J=-10 cm(-1) and g=2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively.     

Efficient and simple synthesis of 3-aryl-1H-pyrazoles

Efficient preparation of 3-aryl-1H-pyrazoles by reaction of 1-protected-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazoles with (het)aryl halides is described. The choice of THP protecting group is discussed.