A catalytic one-step process for the chemo- and regioselective acylation of monosaccharides

An organocatalytic method for the chemo- and regioselective acylation of monosaccharides has been developed. Treatment of octyl beta-D-glucopyranoside with isobutyric anhydride in the presence of 10 mol % of a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at -50 degrees C gave the 4-O-isobutyryl derivative as the sole product in 98% yield. Thus, chemoselective acylation, favoring a secondary hydroxyl group in the presence of a free primary hydroxyl group, and regioselective acylation, favoring one of three secondary hydroxyl groups, took place with perfect selectivity. A competitive acylation between octyl beta-D-glucopyranoside and a primary alcohol (2-phenylethanol) with 1.1 equiv of isobutyric anhydride in the presence of 1 gave the 4-O-isobutyrate of octyl beta-D-glucopyranoside with 99% regioselectivity in 98% yield, which indicates that acylation of the secondary hydroxyl group at C(4) of the carbohydrate proceeds in an accelerative manner. A possible mechanism, involving multiple hydrogen-bonding between 1 and the monosaccharide, is proposed for the chemo- and regioselective acylation.     

Dimerization of mono-ruthenium substituted alpha-Keggin-type tungstosilicate [alpha-SiW11O39RuIII(H2O)]5- to micro-oxo-bridged dimer in aqueous solution: synthesis, structure, and redox studies

We report the dimerization of a mono-ruthenium(III) substituted alpha-Keggin-type tungstosilicate [alpha-SiW(11)O(39)Ru(III)(H2O)](5-) to a micro-oxo-bridged dimer [{alpha-SiW(11)O(39)Ru(m)}2O](n-) (m = III, n = 12; m = IV/III, n = 11; m = IV, n = 10). Single crystal X-ray structure analysis of Rb(10)[{alpha-SiW(11)O(39)Ru(IV)}2O].9.5H2O (triclinic, P1, with a = 12.7650(6) A, b = 18.9399(10) A, c = 20.2290(10) A, alpha = 72.876(3) degrees, beta = 88.447(3) degrees, gamma = 80.926(3) degrees, V = 4614.5(4) A(3), Z = 2) reveals that two mono-ruthenium substituted tungstosilicate alpha-Keggin units are connected through micro-oxo-bridging Ru-O-Ru bonds. Solution (183)W-NMR of [{SiW(11)O(39)Ru(IV)}2O](10-) resulted in six peaks (-63, -92, -110, -128, -132, and -143 ppm, intensities 2 : 2 : 1 : 2 : 2 : 2) confirming that the micro-oxo bridged dimer structure is maintained in aqueous solution. The dimerization mechanism is presumably initiated by deprotonation of the aqua-ruthenium complex [alpha-SiW(11)O(39)Ru(III)(H2O)](5-) leading to a hydroxy-ruthenium complex [alpha-SiW(11)O(39)Ru(III)(OH)](6-). Dimerization of two hydroxy-ruthenium complexes produces the micro-oxo bridged dimer [{alpha-SiW(11)O(39)Ru(III)}2O](12-) and a water molecule. The Ru(III) containing dimer is oxidized by molecular oxygen to produce a mixed valence species [{alpha-SiW(11)O(39)Ru(IV-III)}2O](11-), and further oxidation results in the Ru(IV) containing [{alpha-SiW(11)O(39)Ru(IV)}2O](10-).     

Asymmetric hydrogenation of aryl ketones mediated by a copper catalyst

[reaction: see text] A novel asymmetric hydrogenation protocol using a copper catalyst is reported. A Cu(I) complex in the presence of nonracemic BDPP hydrogenates aryl ketones with moderate to high enantioselectivity.     

Molecular dynamics simulation of an archaeal lipid bilayer with sodium chloride

We have performed molecular dynamics simulations of a bilayer formed by the synthetic archaeal lipid, diphytanyl phosphatidylcholine, in NaCl electrolyte solution at four different concentrations (0-4 M) to investigate how structural and dynamic properties of the model archaeal membrane are changed due to the ionic strength of the solution. The archaeal lipid bilayer shows minor changes in their physical properties, indicating the unusual high stability of the membrane against salt, though small reductions of molecular area and lateral diffusion of the lipid are detected at the highest electrolyte concentration of 4 M. Sodium ions penetrate to the ether-rich region, where the ions are likely bound to the ether oxygen in the sn-1 chain rather than to that in the sn-2 chain. The observed salt bridges among two or three neighboring lipids account for the small reduction in the molecular area. The bound ions together with the counter (chloride) ions give rise to a diffusive electric double layer; as a result, the membrane dipole potential is slightly increased with increasing NaCl concentration.     

Regio- and enantioselective hydroamination of dienes by gold(i)/menthol cooperative catalysis

Alcohol is key: Regio- and enantioselective hydroamination of 1,3-dienes has been achieved with the dinuclear catalyst (R)-DTBM-SEGPHOS. The rate and selectivity of the reaction are enhanced by alcohol additives like menthol, which coordinates the cationic gold(I) to generate a Br?nsted acid that can participate in catalysis. Mbs=p-methoxybenzenesulfonyl.     

The active site structure of nitrided and oxynitrided graphite as a cathode catalyst in a fuel cell

The first-principles studies were performed for the modified graphites with various edge conformations, which revealed that the NH edge facilitates easy transfer of an electron into the adsorbed O(2).     

Hexameric subphthalocyanine rosette

A highly congested hexameric subphthalocyanine array was synthesized by axial chlorine-to-phenoxy substitution of a hexakis(4-hydroxyphenyl)benzene based subphthalocyanine, and photoinduced symmetry-breaking charge separation was demonstrated in polar solvent.     

A characterization of extended monotone metrics

Classical information geometry has emerged from the study of geometrical aspect of the statistical estimation. Cencov characterized the Fisher metric as a canonical metric on probability simplexes from a statistical point of view, and Campbell extended the characterization of the Fisher metric from probability simplexes to positive cone . In quantum information geometry, quantum states which are represented by positive Hermitian matrices with trace one are regarded as an extension of probability distributions. A quantum version of the Fisher metric is introduced, and is called a monotone metric. Petz characterized the monotone metrics on the space of all quantum states in terms of operator monotone functions. A purpose of the present paper is to extend a characterization of monotone metrics from the space of all states to the space of all positive Hermitian matrices on finite dimensional Hilbert space. This characterization corresponds quantum modification of Campbell’s work.