Polymerization-induced phase separation in silica sol-gel systems containing formamide

Silica gels with well-defined pores both in micrometer and nanometer ranges were obtained by acid-catalyzed hydrolysis and polymerization of tetramethoxysilane in the presence of formamide. The micrometer-range structures of these gels are studied in terms of the phase diagram of the quasi two-component system, namely solvent-rich and silica-rich end compositions. The resulting interconnected structures and aggregates of particles are related to the occurrence of spinodal phase separation. The composition region that gave interconnected structures for the present system was much more limited and their characteristic sizes were much smaller than those for the previously reported systems containing an organic polymer. These results could be explained qualitatively by the effect of the degree of polymerization on the Flory-Huggins' type free energy change of mixing.     

Stoichiometry,product and kinetics of catalytic oxidation of 2,6–dimethylphenol by bromo(N,N′- diethylethylenediamine)copper complexes in methylene chloride

Copper(I) dimer [(DEED)CuBr]2 (4, DEED=N,N-diethylethylenediamine) is rapidly oxidized by O2 to mixed valence peroxocopper complex [(DEED)CuBr]4O2 (1) in CH2Cl2 at –50 to 30°C. The long half- life for conversion of (1) into oxocopper(II) complex [(DEED)]CuBr]2O (3) allows (1), (3) and their carbonato derivative of [(DEED)CuBr]2CO3 (5) to be compared as oxidants of 2,6–dimethylphenol (DMPOH) to the corresponding diphenoquinone (DPQ) over a range of concentrations and temperatures. DPQ production is: 1)less than stoichiometric with deficits or slight excesses of DMPOH, but 2) mildly catalytic at moderate [DMPOH], as found with tetranuclear oxo-halo(pyridine)copper(II) oxidants. This behaviour is attributed to 1) co-product water destruction of initiators, and 2) inhibition by water of copper(I) reoxidation to complete the catalytic cycle. These inhibiting factors apparently are ameliorated by water incorporation in hydrogen-bonded phenol clusters in aprotic solvents. Initial rate measurements show that (1), (3) and (5) form monophenolate complexes with DMPOH in methylene chloride. The rate-determining step for conversion of these complexes to DPQ is fastest for oxocopper(II) complex (3) which is expected to be the strongest proticbase. Highest rates with (3) and activation parameter comparisons suggest that the ability of phenolatocoppercomplexes to accept protons from coordinated phenolate is an important factor in determining overall copper- catalyzed phenolic oxidative coupling rates.     

Novel transformation of 2-substituted alkyl 1-indanone-2-acetates to 6-substituted 3,4-benzotropolones through sequential reduction and oxidation processes using Sm(II) and Ce(IV) salts

When 2-substituted alkyl 1-indanone-2-acetates 1 were treated with samarium diiodide, 3-substituted 2-hydroxy-2,3-methano-1-oxo-1,2,3,4-tetrahydronaphthalenes 4 were obtained. The reaction is proposed to proceed through a rearrangement initiated by intramolecular ketone–ester coupling. Oxidation of these products 4 or their silyl ethers 13 by ceric(IV) ammonium nitrate involving regioselective bond cleavage of their bicyclo[4.1.0]-rings produced the corresponding benzotropolone derivatives 10.     

Preparation of 4-pentenoic acid ester of Neu5Ac and 4-pentenyl glycoside of Neu5Ac and their application to glycosylation

Novel sialosyl donors, 4-pentenoic acid ester of N-acetylneuraminic acids (Neu5Ac) and 4-pentenyl glycoside of Neu5Ac were successfully prepared from the corresponding per-O-acetylated 2-hydroxy and 2-chloro derivatives of Neu5Ac, respectively and applied to the synthesis of O-sialosides.     

Recent advances in the biosynthesis and accumulation of anthocyanins

This review describes biochemistry, molecular biology and regulation of anthocyanin biosynthesis, with particular emphasis on mechanistic features and late steps of anthocyanin biosynthesis including glycosylation and vacuolar sequestration. The literature from 1997 to the beginning of 2002 is reviewed, and 163 references are cited.     

Design of Dual‐Emission Chemosensors for Ratiometric Detection of ATP Derivatives

Nucleoside pyrophosphate (nucleoside PP) derivatives are widespread in living cells and play pivotal roles in various biological events. We report novel fluorescence chemosensors for nucleoside PPs that make use of coordination chemistry. The chemosensors, which contain two Zn^II–dipicolylamine units, bind strongly to nucleoside PPs (K_app>10⁶ M ^?1) in aqueous solution and sense them by a dual‐emission change. Detailed fluorescence and UV/Vis spectral studies revealed that the emission changes of the chemosensors upon binding to nucleoside PPs can be ascribed to the loss of coordination between Zn^II and the acridine fluorophore. This is a unique sensing system based on the anion‐induced rearrangement of the coordination. Furthermore, we demonstrated the utility of these chemosensors in real‐time monitoring of two important biological processes involving nucleoside PP conversion: the apyrase‐catalyzed hydrolysis of nucleoside PPs and the glycosyl transfer catalyzed by β‐1,4‐galactosyltransferase.     

High-performance liquid chromatographic enantioseparations on capillary columns containing monolithic silica modified with cellulose tris(3,5-dimethylphenylcarbamate)

Monolithic capillary columns containing native silica gel were modified with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and used for enantioseparations in capillary liquid chromatography. The method adopted for in situ enantioselective modification of monolithic fused silica capillary columns by coating with CDPMC appears to be fairly simple and fast. High efficiency enantioseparations of test racemic compounds and s(everal chiral drugs were achieved in a short time. It was possible to increase the amount of chiral selector present by multiple coating of monoliths with CDMPC. The baseline enantioseparation of 2,2,2-trifluoro-1-(9-anthryl)ethanol was achieved in an analysis time less than 30 s with this capillary column. In addition, reproducible enantioseparations were obtained when the chiral selector was removed from the monolithic column by flushing it with appropriate solvent and the column recoated.     

Membrane Emulsification Using Sol-Gel Derived Macroporous Silica Glass

A macroporous silica glass membrane with continuous cylindrical pores was prepared by a sol-gel process using phase separation. The applicability of the sol-gel derived macroporous silica to the membrane emulsification process was evaluated in comparison with a conventional SPG (Silasu Porous Glass) membrane.Aqueous colloidal silica in one side of the membrane was emulsified through the pores under an applied pressure to a toluene bath containing surfactant. With the sol-gel and SPG membranes with respective median pore diameters of 0.6 and 1.0 m, emulsions with almost the same droplet size centered around 3 m were obtained. The permeation rate of the sol-gel derived membrane was about 1.6 times faster than SPG, which reflected higher pore volume of the former one.     

Langmuir monolayers of cerebroside originated from Linckia laevigata: binary systems of cerebrosides and phospholipid

The surface pressure (pi)-area (A), the surface potential (DeltaV)-A and the dipole moment (mu( perpendicular))-A isotherms were obtained for six cerebrosides of LLC-2, LLC-2-1, LLC-2-8, LLC-2-10, LLC-2-12, and LLC-2-15, which were isolated from Linckia laevigata, and two-component monolayers of two different cerebrosides (LLC-2 and LLC-2-8) with phospholipid of dipalmitoylphosphatidylcholine (DPPC) on a subphase of 0.15 M sodium chloride solution as a function of cerebroside compositions in the two-component systems by employing the Wilhelmy method, the ionizing electrode method, and the fluorescence microscopy. The new finding was that LLC-2 showed a stable and liquid expanded type film. Four of them (LLC-2-8, -10, -12, and -15) had the phase transition from the liquid-expanded (LE) to the liquid-condensed (LC) states at 298.2 K. The apparent molar quantity changes (Deltas(gamma), Deltah(gamma), and Deltau(gamma)) on their phase transition on 0.15M at 298.2 K were calculated. The miscibility of cerebroside and phospholipid in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the cerebroside molar fraction (X(cerebroside)), using the additivity rule. From the A-X(cerebroside) and DeltaV(m)-X(phospholipid) plots, a partial molecular surface area (PMA) and an apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible systems. Judging from the two-dimensional phase diagrams, these were found to be one type, a positive azeotropic type; all the cerebrosides were miscible with DPPC. Furthermore, assuming a regular surface mixture, the Joos equation for the analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltavarepsilon) between the cerebrosides and DPPC. The miscibility of cerebroside and phospholipid components in the monolayer state was also supported by fluorescence microscopy.     

Silica monolithic membrane as separation medium. Summable property of different membranes for high-performance liquid chromatographic separation

We studied an applicability of a silica monolithic membrane as separation medium for high-performance liquid chromatography (HPLC). We prepared porous monolithic silica membranes having a three-dimensional network structure to cut and shape into a membrane separation medium. We evaluated chromatographic properties of a variety of solutes using a column containing the membranes with HPLC to elucidate summable property of the membrane separation media. In addition, we made brief study on separation of HbA1c in whole blood with the stacked" membranes having different surface characteristics in one column, which is a membrane column. We confirmed that the membrane column was able to separate HbA1c from other matrix in whole blood to some extent, and it also had an excellent ability for hydrophobic and ion exchange adsorption.