Successive intramolecular transiminations in an iron (II) complex with chiral tridentate ligands

Two molecules of S-2-pyridylmethylidene-1-(2-pyridyl)ethylamine coordinated to an iron(II) undergo successive transiminations yielding bis[1-(2-pyridyl)ethylidene-2-pyridylmethylamine]iron(II) in acetonitrile.     

Selective dehydrogenation of amines with respect to coordination geometry: different oxidation products of tricyano[bis(2-pyridylmethyl)amine]ferrate(II) between mer- and fac-isomers

Both the fac- and mer-isomers of tricyano[bis(2-pyridylmethyl)amine = 2-DPA]ferrate(II) were isolated and their spectroscopic properties compared. The fac-isomer was converted to the corresponding iron(III) complex under acidic conditions. Oxidation of the ferrate(II) complexes with ammonium peroxodisulfate yielded the mer-isomer of the dehydrogenated ferrate(II) compound, but only the metal-oxidized iron(III) complex for the fac-isomer was produced under neutral or basic conditions. Electrochemical measurements confirmed this difference in the oxidation behavior, in which the nature of the coordination governs the ease of oxidative dehydrogenation.     

Superconducting state of the organic conductor (TMTSF)2ClO4

(TMTSF)2ClO4 is a quasi-one-dimensional organic conductor and superconductor with Tc=1.4 K, and one of at least two Bechgaard salts observed to have upper critical fields far exceeding the paramagnetic limit. Nevertheless, the 77Se NMR Knight shift at low fields reveals a decrease in spin susceptibility chi(s) consistent with singlet spin pairing. The field dependence of the spin-lattice relaxation rate at 100 mK exhibits a sharp crossover (or phase transition) at a field Hs approximately 15 kOe, to a regime where chi(s) is close to the normal state value, even though Hc2> Hs.     

Metastable ion study of organosilicon compounds. Part V—tetramethoxysilane and trimethoxymethylsilane

The fragmentations of tetramethoxysilane ((CH₃O)₄Si (1)) and trimethoxymethylsilane ((CH₃O)₃SiCH₃ (3)) induced by electron impact were investigated by mass-analysed ion kinetic energy (MIKE) spectrometry and a deuterium-labelling study. These molecular ions begin to fragment by the loss of CH₃ or CH₃O. These fragmentations are followed by the loss of an aldehyde molecule (H₂CO), as commonly observed in the mass spectra of alkoxysilanes. Almost complete scrambling of the methoxy hydrogens takes place in the metastable molecular ion, [1]⁺˙, prior to the decomposition. On the other hand, a moderate extent of scrambling of the hydrogens takes place in [3]⁺˙. The fragmentations of [1]⁺˙ and [3]⁺˙ were compared with those of the corresponding carbon analogues, tetramethoxymethane ((CH₃O)₄C (2)) and 1,1,1-trimethoxyethane ((CH₃O)₃CCH₃ (4)), respectively.     

Synthesis of alkenylsilanes via palladium(0)-catalyzed silylation of alkenyl iodides with hydrosilane

Various alkenyl iodides were silylated with hydrosilanes in the presence of KOAc and a catalytic amount of Pd₂(dba)₃·CHCl₃ to afford the corresponding regio- and stereodefined (E)-alkenylsilanes in high yields.     

Phase segregation of LixMn2O4 (0.6<x<1) in non-equilibrium reduction processes

Chemical synthesis routes to Li_xMn₂O₄ (0.15≤x≤1) in non-equilibrium reduction processes were developed to carry out detailed structural analysis. Non-equilibrium Li_xMn₂O₄ (0.15≤x≤1) samples were prepared by chemical lithiation of λ-MnO₂ with LiI for 24 h; longer than 1 week was needed to reach true equilibrium at room temperature. The samples were characterized by X-ray diffraction analysis. The phase diagram was different from that in the equilibrium state; three cubic phases (phases A, B and C) were observed for Li_xMn₂O₄ (0.15≤x≤1). There were two regions of two-phase coexistence: the region of 0.25<x<0.55 (phase B+phase C) and 0.6<x<1.0 (phase A+phase B). In the compositional range of 0.6<x<1.0, the lattice constants of phases A and B change with the lithium composition, this indicates that it is a structural anomaly with a metastable two-phase character in non-equilibrium reduction processes.     

Asymmetric synthesis of 3-substituted 3,4-dihydroisocoumarins via stereoselective addition of laterally lithiated chiral 2-(o-tolyl)oxazolines to aldehydes followed by diastereomer-selective lactonization

Lateral lithiation of (S)-4-isopropyl-2-(o-tolyl)oxazoline in diethyl ether followed by the reaction with aldehydes in the presence of TMEDA produced the addition products with stereoselectivities up to 84% de. Utilization of TMEDA as a ligand is essential for the good selectivity. Rationale for the stereoselectivity is proposed based on ab initio calculation of the lateral lithio species. The major (S,S)-products lactonized faster than the minor (S,R)-products to the corresponding 3,4-dihydroisocoumarins under acidic conditions. Thus, (3S)-3,4-dihydroisocoumarins were obtained in good optical purities up to 97% ee by sequential application of these matched stereoselective reactions.     

Enhanced percutaneous penetration of flufenamic acid using lipid disperse systems containing glycosylceramides

The usefulness of lipid disperse systems, containing soybean phosphatidylcholine (PC) and glycosylceramide (GC) as lipid components, to enhance the percutaneous penetration of flufenamic acid (FA) through rat abdominal skin was examined by both in vitro permeation and in vivo absorption studies. The penetration of FA from a simple buffer suspension (pH 3.0) containing no lipid component was poor, but was markedly enhanced when FA was incorporated in PC-dispersions. However, this enhancing effect disappeared when the PC concentration in the preparation exceeded 40 mumol/ml. Enhanced penetration of FA from PC-dispersions could also be recognized when 30% propylene glycol or 30% glycerol was used as the dispersing medium instead of the aqueous buffer solution. Addition of GC to the PC-dispersions brought further enhancement of FA penetration through the skin. The maximal effect was observed when FA was incorporated in a 10%-GC system, and the cumulative amount of FA penetrating through the skin in 24 h from this system was approximately 6-fold larger than that from the simple buffer suspension. Enhanced absorption of FA from lipid disperse systems was also confirmed by in vivo application of these preparations.     

Determination of dextromethorphan in human plasma using pipette tip solid-phase extraction and gas chromatography-mass spectrometry

Dextromethorphan was extracted from human plasma samples (100 μL) using MonoTip C₁₈ tips, which are packed with C₁₈-bonded monolithic silica gel that is attached to the inside of the tip. The samples, which contained dextromethorphan and trimeprazine as an internal standard (IS), were mixed with 200 μL of distilled water and 50 μL of 1 mol/L glycine–sodium hydroxide buffer (pH 10). The mixture was extracted to the C₁₈ phase of the tip by 20 sequential aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C₁₈ phase were then eluted with methanol by five sequential aspirating/dispensing cycles. The eluate was injected directly into a gas chromatograph and detected by a mass spectrometer with selected ion monitoring in positive electron ionization mode. An Equity-5 fused silica capillary column (30 m × 0.32 mm i.d., film thickness 0.5 μm) gave adequate separation of the dextromethorphan, IS, and impurities. The recoveries of dextromethorphan and the IS spiked into plasma were >87.4%. The regression equation for dextromethorphan showed excellent linearity from 2.5 to 320 ng/mL of plasma, and the limit of detection was 1.25 ng/mL of plasma. The intraday and interday coefficients of variation were less than 10.5% and 14.7%, respectively. The accuracy ranged from 91.9% to 107%. The validated method was successfully used to quantify the plasma concentration of dextromethorphan in a human subject after oral administration of the drug.