Diffusion coefficients of metal acetylacetonates in supercritical carbon dioxide

Binary diffusion coefficients, D₁₂, of the metal acetylacetonates, palladium(II) acetylacetonate and cobalt(III) acetylacetonate, were measured from 308.2 to 343.2 K over the pressure range from 9 to 40 MPa at infinite dilution in supercritical carbon dioxide using the chromatographic impulse response method. The effects of pressure, temperature, density, and viscosity on D₁₂ values were examined. It was observed that the D₁₂ values of palladium(II) acetylacetonate and cobalt(III) acetylacetonate were larger than those of lipids with similar molecular weights, such as arachidonic acid and monoolein, respectively. Furthermore, the measured D₁₂ data of each metal acetylacetonate were well correlated by the hydrodynamic equation D₁₂/T as a function of carbon dioxide viscosity.     

Enzyme-catalyzed resolution of 3,8-dioxatricyclo[3.2.1.0]octane-6-carboxylic esters and the application to the synthesis of 3-epishikimic acid

3,8-Dioxatricyclo[3.2.1.0^2,4]octane-6-carboxylic acid, whose racemic form is readily available on a large scale, is a versatile starting material for the synthesis of carbasugars and carbocyclic biologically active natural products. In this study, the enzyme-catalyzed kinetic resolution was attempted on a variety of corresponding carboxylic esters. The hydrophobic and hydrophilic properties of ester substituents greatly affected the rate of reaction and the enantioselectivity. Hydrolysis of the corresponding 2′-chloroethyl ester with pig liver esterase worked well in a highly enantioselective manner (E = 116) to give the hydrolyzate (90.6% ee) and unreacted ester recovery (99.4% ee). The hydrolyzate is a precursor for (−)-oseltamivir phosphate, and a route to (3S,4S,5R)-(−)-3-epishikimic acid was developed from the recovered ester.     

Preferential 5‐Methylcytosine Oxidation in the Linker Region of Reconstituted Positioned Nucleosomes by Tet1 Protein

Tet (ten–eleven translocation) family proteins oxidize 5‐methylcytosine (mC) to 5‐hydroxymethylcytosine (hmC), 5‐formylcytosine (fC), and 5‐carboxycytosine (caC), and are suggested to be involved in the active DNA demethylation pathway. In this study, we reconstituted positioned mononucleosomes using CpG‐methylated 382 bp DNA containing the Widom 601 sequence and recombinant histone octamer, and subjected the nucleosome to treatment with Tet1 protein. The sites of oxidized methylcytosine were identified by bisulfite sequencing. We found that, for the oxidation reaction, Tet1 protein prefers mCs located in the linker region of the nucleosome compared with those located in the core region.     

Modification of interlayer space of kanemite with trimethylsilyl groups: structure and adsorption properties

Interlayer hydroxyl groups of layered silicate kanemite have been modified with trimethylsilyl groups by the reaction between the hydroxyl groups and trimethylchlorosilane. Expansion of the interlayer space by intercalation of dimethyldialkylammonium ions into the silicate layers enables the silylating reagent to access the hydroxyl groups. An increase in specific surface areas was observed with increasing concentration of trimethylsilyl groups. This result suggests that the interlayer space of kanemite can be used as an effective molecular adsorption space by weakening the interaction between the interlayer hydrogen bonds of hydroxyl groups. The modification of kanemite with trimethylsilyl groups restricted the adsorption of water below a monolayer capacity and was favorable for benzene adsorption.     

Amperometric measurement of ds-DNA content using a peroxidase-modified electrode

An enzyme electrode with a chemically amplified response for methylene blue (MB) was constructed from a glassy carbon electrode and a layer containing immobilized horseradish peroxidase (HRP). MB is reduced on the electrode but regenerated through the HRP-catalyzed reaction in the presence of H(2)O(2). The electroreduction/regeneration cycle for MB resulted in an amplified electrode response. The enzyme electrode was applied to the highly sensitive measurement of ds-DNA. The current for MB decreased in association with its complexation with DNA, and the current response caused by DNA was also amplified through the recycling processes. The detection limit of ds-DNA (from salmon testes) was as low as 5 ng ml(-1).     

Interlayer interaction of two-dimensional layered spin crossover complexes [FeIIH3L(Me)][FeIIL(Me)]X (X-=ClO4-, BF4-, PF6-, AsF6-, and SbF6-; H3L(Me)=tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A series of two-dimensional (2D) spin crossover complexes, [FeIIH3L(Me)][FeIIL(Me)]X (X-=ClO4-, BF4-, PF6-, AsF6-, SbF6-) 1-5, have been synthesized, where H3L(Me) denotes an hexadentate N6 tripodlike ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. Compounds 1-5 exhibit a two-step (HS-[FeIIH3L(Me)](2+) + HS-[FeIIL(Me)]-) <--> (HS-[FeIIH3L(Me)](2+) + LS-[FeIIL(Me)]-) <--> (LS-[FeIIH3L(Me)](2+) + LS-[FeIIL(Me)]-) spin-transition. The crystal structure of [FeIIH3L(Me)][FeIIL(Me)]PF6 (3) was determined at 295, 200, and 100 K. The structure consists of homochiral extended 2D puckered sheets, in which the complementary [FeIIH3L(Me)](2+) and [FeIIL(Me)]- capped tripodlike components, linked together by imidazole-imidazolate hydrogen bonds, are alternately arrayed in an up-and-down mode. The Fe-N bond distances and angles revealed that the FeII sites of both constituting units are in the high-spin (HS) state at 295 K; at 200 K, the FeII sites of [FeIIH3L(Me)](2+) and [FeIIL(Me)]- are in the HS and low-spin (LS) states, respectively. The FeII sites of both constituting units are in the LS state at 100 K. The size of the counteranion affects significantly the intra- and interlayer interactions leading to modifications of the spin crossover behavior. The onset of the second spin-transition of the ClO4- (1) and BF4- (2) salts adjoins the first spin-transition, while a mixed (HS-[FeIIH3L(Me)](2+) + LS-[FeIIL(Me)]-) spin-state spans a temperature range as wide as 70 K for salts 3-5 with larger counteranions, PF6-, AsF6-, and SbF6-, respectively. Compounds 1 and 2 showed remarkable LIESST (light induced excited spin state trapping) and reverse-LIESST effects, whereas 3-5 showed no remarkable LIESST effect. The interlayer interaction due to the size of the counteranion is an important factor governing the spin crossover behavior and LIESST effect.     

Laser-induced oxidation reactions in supercritical ethane---O2 mixtures

The laser-induced oxidation of ethane by O₂ at 318 K was investigated with varying the pressure between 12–91 atm. The reaction condition was regarded as the supercritical phase above 50–60 atm, depending on the O₂ fraction. Ethanol, acetaldehyde, and CO₂ were mainly produced at any reaction conditions, together with small amounts of C₁ compounds and formic esters. The kinetic discussion for the time dependence indicated that the consecutive photolysis of primary products takes place during the subsequent laser irradiation period. The branching ratio to CO₂ formation in the primary process in the supercritical phase is much smaller than that in the gas phase, and the selectivities for ethanol and acetaldehyde show a discontinuous change near the critical point. These facts show that the supercritical phase affects this complex radical reaction system. The primary photoabsorption process is also discussed.     

A generalized Born formalism for heterogeneous dielectric environments: application to the implicit modeling of biological membranes

Reliable computer simulations of complex biological environments such as integral membrane proteins with explicit water and lipid molecules remain a challenging task. We propose a modification of the standard generalized Born theory of homogeneous solvent for modeling the heterogeneous dielectric environments such as lipid/water interfaces. Our model allows the representation of biological membranes in the form of multiple layered dielectric regions with dielectric constants that are different from the solute cavity. The proposed new formalism is shown to predict the electrostatic component of solvation free energy with a relative error of 0.17% compared to exact finite-difference solutions of the Poisson equation for a transmembrane helix test system. Molecular dynamics simulations of melittin and bacteriorhodopsin are carried out and performed over 10 ns and 7 ns of simulation time, respectively. The center of melittin along the membrane normal in these stable simulations is in excellent agreement with the relevant experimental data. Simulations of bacteriorhodopsin started from the experimental structure remained stable and in close agreement with experiment. We also examined the free energy profiles of water and amino acid side chain analogs upon membrane insertion. The results with our implicit membrane model agree well with the experimental transfer free energy data from cyclohexane to water as well as explicit solvent simulations of water and selected side chain analogs.     

Fabrication of solid-state fuel cell based on DNA film

We have fabricated a fuel cell based on the DNA film (DNAFC) and examined its properties under various humidity conditions at room temperature. The open-circuit voltage of a DNAFC is generated by supplying H₂ gas to the anode. The open-circuit voltage strongly depends on the humidity conditions, and in a DNA film, the optimum condition in which the open-circuit voltage attains a value as high as 0.55 V is achieved under the relative humidity condition of 55%. Furthermore, the cell voltage of the DNAFC decreases with an increase in current density, as observed in fuel cells such as proton exchange membrane fuel cell, solid oxide fuel cell, and several others. These results indicate that DNA film can be used as the fuel cell electrolyte under approximately 55% humidity condition.     

Experimental evidence for the hydrogen evolution site in photocatalytic process on Pt/TiO2

A hydrogen-deuterium isotope effect on the title reaction is observed. The separation factor of the reaction is found to be 5.3 ± 0.5, which is similar to the separation factor reported on Pt electrode, but different from that observed on TiO₂ electrode. The Pt sites are assigned to the reduction site on the catalyst.