Intercalating lithium into the lattice of silver nanoparticles boosts catalytic hydrogenation of carbon–oxygen bonds

Coinage metal nanoparticles with high dispersion can serve as highly efficient heterogeneous catalysts. However, owing to their low melting point, poor thermal stability remains a major obstacle towards their application under reaction conditions. It is a common practice to use porous inorganic templates such as mesoporous silica SBA-15 to disperse Ag nanoparticles (NPs) against aggregation but their stability is far from satisfactory. Here, we show that the catalytic activity for hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) over Ag NPs dispersed on SBA-15 silica can be further promoted by incorporation of alkali metal ions at small loading, which follows the inverse order of their cationic size: Li⁺ > Na⁺ > K⁺ > Rb⁺. Among these, 5Ag₁–Li_0.05/SBA-15 can double the MG yield compared to pristine 5Ag/SBA-15 under identical conditions with superior thermal stability. Akin to the effect of an ionic surfactant on stabilization of a micro-emulsion, the cationic charge of an alkali metal ion can maintain dispersion and modulate the surface valence of Ag NPs. Interstitial Li in the octahedral holes of the face center packed Ag lattice is for the first time confirmed by X-ray pair distribution function and electron ptychography. It is believed that this interstitial-stabilization of coinage metal nanoparticles could be broadly applicable to multi-metallic nanomaterials for a broad range of C–O bond activating catalytic reactions of esters.

Coinage metal nanoparticles with high dispersion can serve as highly efficient heterogeneous catalysts.     

Electron spin-spin contact interaction in many-electron atoms

A general formulation has been developed for the evaluation of the total electron spin-spin contact interaction in many-electron atoms, including both the intra- and inter-shell contributions. Calculations have been carried out, using existing analytical Hartree-Fock functions, for the positive ions, neutral systems, and negative ions for all the atoms from He to Kr.

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Zusammenfassung Es wird ein allgemeiner Formalismus zur Berechnung der gesamten Elektronen-Spin-Spin-Kontakt-Wechselwirkung in Vielelektronen-Atomen angegeben, der sowohl die Anteile der Wechselwirkung innerhalb einer Schale als auch zwischen einzelnen Schalen berücksichtigt. Berechnungen wurden unter Benutzung vorhandener analytischer Hartree-Fock-Funktionen für die positiven Ionen, die neutralen Systeme und die negativen Ionen aller Atome von He bis Kr durchgeführt.

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This work has been supported in part by the National Research Council of Canada.     

Closed‐form rectangular atomic wave functions of an N‐dimensional atom

A closed‐form expression has been derived to obtain the N‐dimensional rectangular atomic wave functions. The wave functions can be obtained straightforwardly with the knowledge of the angular momentum quantum numbers and the dimension and there is no need to employ recursive methods as in previous works. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 263–274, 2002     

Simultaneous determination of berberine in rat blood,liver and bile using microdialysis coupled to high-performance liquid chromatography

High-performance liquid chromatography coupled to microdialysis was used for the simultaneous determination of unbound berberine in rat blood, liver and bile for a pharmacokinetic study. Microdialysis probes were simultaneously inserted into the jugular vein toward the right atrium, the median lobe of the liver, and the bile duct of male Sprague-Dawley rats for biological fluid sampling after administration of berberine (10 mg/kg) through the femoral vein. Berberine and dialysates were separated using a Zorbax SB-phenyl column and a mobile phase comprised of acetonitrile-methanol-20 mM monosodium phosphate (pH 3.0) (35:20:45, v/v) together with 0.1 mM 1-octanesulfonic acid. The detection limit for berberine was 10 ng/ml. The concentration-response relationship was linear (r2 > 0.995) over the concentration range 0.05-50 microg/ml; intra-assay and inter-assay precision and accuracy for berberine fell within predefined limits. The disposition of berberine in the blood, liver and bile fluid suggests that berberine might be metabolized in the liver and undergo hepatobiliary excretion.     

Effects of fatty acids on growth and poly-3-hydroxybutyrate production in bacteria

The effects of saturated and unsaturated fatty acids (lauric acid, palmitic acid, steric acid, oleic acid, linoleic acid, soybean oil) on Sphaerotilus natans, 0B17 (Pseudomonas sp.), and recombinant Escherichia coli DH5(/pUC19/CAB were studied. Oleic acid enhances Poly-3-hydroxybutyrate (PHB) production in these three bacterial strains, suggesting that the single double bond of the acid activates the polyhydroxylkanoate accumulation enzymatic reaction. Under the effect of lauric acid and linoleic acid, the growth of S. natans and 0B17 were totally inhibited. However, the enhanced PHB accumulation in recombinant E. coli was observed.     

Eta6-mesityl,eta1-imidazolinylidene-carbene-ruthenium(II) complexes: catalytic activity of their allenylidene derivatives in alkene metathesis and cycloisomerisation reactions

The reaction of electron-rich carbene-precursor olefins containing two imidazolinylidene moieties [(2,4,6-Me(3)C(6)H(2)CH(2))NCH(2)CH(2)N(R)Cdbond;](2) (2a: R=CH(2)CH(2)OMe, 2 b R=CH(2)Mes), bearing at least one 2,4,6-trimethylbenzyl (R=CH(2)Mes) group on the nitrogen atom, with [RuCl(2)(arene)](2) (arene=p-cymene, hexamethylbenzene) selectively leads to two types of complexes. The cleavage of the chloride bridges occurs first to yield the expected (carbene) (arene)ruthenium(II) complex 3. Then a further arene displacement reaction takes place to give the chelated eta(6)-mesityl,eta(1)-carbene-ruthenium complexes 4 and 5. An analogous eta(6)-arene,eta(1)-carbene complex with a benzimidazole frame 6 was isolated from an in situ reaction between [RuCl(2)(p-cymene)](2), the corresponding benzimidazolium salt and cesium carbonate. On heating, the RuCl(2)(imidazolinylidene) (p-cymene) complex 8, with p-methoxybenzyl pendent groups attached to the N atoms, leads to intramolecular p-cymene displacement and to the chelated eta(6)-arene,eta(1)-carbene complex 9. On reaction with AgOTf and the propargylic alcohol HCtbond;CCPh(2)OH, compounds 4-6 were transformed into the corresponding ruthenium allenylidene intermediates (4-->10, 5-->11, 6-->12). The in situ generated intermediates 10-12 were found to be active and selective catalysts for ring-closing metathesis (RCM) or cycloisomerisation reactions depending on the nature of the 1,6-dienes. Two complexes [RuCl(2)[eta(1)-CN(CH(2)C(6)H(2)Me(3)-2,4,6)CH(2)CH(2)N- (CH(2)CH(2)OMe)](C(6)Me(6))] 3 with a monodentate carbene ligand and [RuCl(2)[eta(1)-CN[CH(2)(eta(6)-C(6)H(2)Me(3)-2,4,6)]CH(2)CH(2)N-(CH(2)C(6)H(2)Me(3)-2,4,6)]] 5 with a chelating carbene-arene ligand were characterised by X-ray crystallography.     

Cytotoxic Components from the Leaves of Schefflera Taiwaniana

The isolation and identification of eighteen components from the leaves of Schefflera taiwaniana are presented. Their structures were determined on the basis of spectral data as well as direct comparison with authentic samples. These compounds include two polyacetylenes, one carotenoid‐like, three sesquiterpenes, one diterpene, four triterpenes, two tocopherols, and five alkyl 4‐hydroxycinnamate mixtures. Among these, 4‐hydroxy‐trans‐cinnamic acid docosyl ester and 4‐hydroxy‐cis‐cinnamic acid tetracosyl ester are new compounds. Some of these components exhibit cytotoxic activity.     

Construction of recombinant Escherichia coli strais for production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate)

Plastic wastes constitute a worldwide environmental problem, and the demand for biodegradable plastics has become high. One of the most important characteristics of microbial polyesters is that they are thermoplastic with environmentally degradable properties. In this study, pUC 19/PHA was cloned and transformed into three different Escherichia coli strains. Among the three strains that were successfully expressed in the production of polyhydroxyalkanoates (PHA), E. coli HMS174 had the highest yield in the production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[HB-HV]). The cell dry weight and PHA content of recombinant HMS174 reached as high as 10.27 g/L and 43% (w/w), respectively, in fed-batch fermentor culture. The copolymer of PHA, P(HB-HV), was found in the cells, and the biopolymers accumulated were identified and analyzed by gas chromatography, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. We demonstrated clearly that the E. coli host for PHA production has to be carefully selected to obtain a high yield. The results obtained indicated that a superior E. coli with high PHA production can be constructed with a desirable ratio of P(HB-HV), which has potential applications in industry and medicine.     

Coordination properties of a diarylaza crown ether appended with a luminescent [Ru(bipy)3]2+ unit

The [Ru(bipy)(2)(1)](PF(6))(2) (bipy refers to 2,2'-bipyridine) complex, comprising a ruthenium(II) tris(2,2'-bipyridine) luminophore covalently linked to a di[(o-triethyleneglycoxy)phenyl]amine crown ether 1, has been synthesized and fully characterized. The photophysical properties of this metal complex have been examined in solution at ambient temperature. Luminescence from the metal complex is enhanced significantly in the presence of various adventitious cations, including protons. In particular, Li(+) cations bind to the crown ether, as evidenced by (1)H NMR and luminescence spectroscopy. Cation binding serves to decrease the rate of reductive quenching of the triplet state of the metal complex, thereby increasing the extent of luminescence. The solution-phase conformation of [Ru(bipy)(2)(1)](PF(6))(2), with and without encapsulated Li(+), has been examined by 2-D NMR and by molecular dynamics simulations.     

Etude des propriétés cristallographiques,diélectriques et d'optique non linéaire de quelques nouvelles phases de composition BaxLi5−2xNb5(1−y)Ta5yO15 et de structure bronzes oxygénés de tungstène quadratiques

Two series of phases with tetragonal bronze-like structure and composition Ba_xLi_5?2xT₅O₁₅ (T = Nb, Ta) have been isolated in the systems BaNb₂O₆LiNbO₃ and BaTa₂O₆LiTaO₃. All these phases show ferroelectric-paraelectric transitions. The Curie temperature increases with the lithium content. The value of T_C for Ba_2.03Li_0.94Nb₅O₁₅ is the highest ever observed for this type of structure: the obtained phases are potentially good materials for the harmonic generation of the 0.53-μm radiation. The optical yield of the niobate Ba_2.14Li_0.71Nb₅O₁₅ is about 2.5 times that of Ba₂NaNb₅O₁₅ and 250 times that of the K.D.P. The crystallographic and dielectric data of the system Ba_2.14Li_0.71Nb₅O₁₅Ba_2.14Li_0.71Ta₅O₁₅ characterize three domains, which are respectively antiferroelectric, ferroelectric, and paraelectric. The Curie temperature and the optical yield decrease with increasing tantalum content.