Lower critical solution temperature type of phase separation in aqueous mixture of polyelectrolytes

Phase separation behavior in aqueous mixture of different polyelectorolytes having like charges has been investigated as functions of concentration and charge density. When the charge densities of both polyelectorolytes were equally high, the compatibility between different polyelectorolytes was relatively good and the phase separation behavior was a normal upper critical solution temperature (UCST) type. With decreasing the charge density of one polyelectorolyte keeping the charge density of another polyelectrolyte unchanged, the compatibility between different polyelectorolytes became poorer. When the charge density of one polyelectorolyte was lowered below a certain value, the phase separation behavior suddenly changed from the UCST type to a lower critical solution temperature (LCST) type.     

Neocrocin A: a novel crocetin glycoside with a unique system for binding sugars isolated from gardenia yellow

A novel crocetin glycosyl ester, neocrocin A (2), was isolated from gardenia yellow. The structure of 2 was elucidated as that of an all-trans-crocetin beta-D-gentiobiosyl beta-D-glucopyranosyl-(1-->6)-D-2-deoxy-glucopyranos-2-yl diester based on chemical and spectral data. The findings provide evidence that the binding system of crocetin glycosides is not limited to the anomeric position.     

Cowaniin, a C-glucosidic ellagitannin dimer linked through catechin from Cowania mexicana

A new complex tannin, cowaniin (1) was isolated from the leaves and stems of Cowania mexicana (Rosaceae), and its structure was characterized as novel C-glucosidic tannin dimer linked through (+)-catechin on the basis of spectral and chemical evidence. The inhibitory effect on activation of the Epstein-Barr virus early antigen was assessed for cowaniin. Six known polyphenols and related compounds, including a nitrile glucoside, purshianin, were also characterized.     

Formation of fractal porous silica by hydrolysis of TEOS in a bicontinuous microemulsion

Mesoporous silica particles have been prepared by hydrolysis of TEOS (Si(OC₂H₅)₄) in bicontinuous microemulsions containing polyoxyethylene (POE) dodecylether, isooctane and water. TEOS was dissolved in a continuous water phase and hydrolyzed by the dispersed water at around the phase inversion temperature (60°C). Undulating solid materials with layered mesostructures were produced from middle-phase microemulsions in the three phase region (o/w=0.2–0.7). On the other hand, the solids obtained from the lower aqueous phase in the three phase region were found to have a heterogeneous disordered structure. Measurements of the fractal dimensions were performed in the macropore region using a box-counting method for the outline of the SEM texture. We found that the macropore size distribution in the particles prepared from the middle-phase microemulsion follows the fractal rule with a dimension of 1.7. From the results of nitrogen adsorption/desorption curves on the silica, a steep increase in the adsorption amounts was observed at a relative pressure below 0.2, and adsorption/desorption hysteresis was also observed at a relative pressure between 0.3 and 0.5. These studies suggest that the silica synthesized in the bicontinuous microemulsion mesostructure has a very broad size range from micro to macropores with a fractal distribution.     

Visualization of Magnetization Transfer Effect in Polyethylene Glycol Impregnated Waterlogged Wood

To visualize the condition of impregnation of polyethylene glycol (PEG) in waterlogged wood, we demonstrated magnetic transfer (MT) magnetic resonance imaging (MRI) through a series of process of PEG impregnation. Three different samples were examined; reference wood, 10 cm cut wood, and 5 cm cut wood. During this study, the upper section sample was kept immersed in water, for the middle and lower sections the concentration of PEG solution was changed at 20 wt% intervals from 20 to 100 wt%. The impregnated periods of each PEG solution concentration were 14 days. Then, MR imaging were performed with/without MT pulse. The MTR value for both 10 cm- and 5 cm-samples were shown to decrease at 20 wt% PEG at peak concentration. When the sample volume was large, e.g., 10 cm-sample, the MTR value decreased to 100 wt% PEG concentration. In contrast, when a sample volume was small, e.g., 5 cm-sample, MTR value decreased to 60 wt% PEG concentration. In conclusion, MTR analysis makes it possible to nondestructively visualize and evaluate the inner condition concerning the PEG impregnation method for waterlogged wood.     

Highly Diastereoselective Addition of Allyltitanocenes to Ketones

A route with less congestion : A practical method for the highly diastereoselective preparation of anti tertiary homoallylic alcohols has been developed. The reaction of allyltitanocenes, generated by the reductive titanation of various allylic substrates with a titanocene(II) species, with a variety of ketones produced the anti tertiary homoallylic alcohols in good diastereoselectivity, even when using sterically less congested ketones (see scheme; Cp: cyclopentadienyl; Piv: pivaloyl).

     

Two-dimensional structure control by molecular width variation with metal coordination

The self-assembled monolayer of bipyridine derivative 1, which has two alkyl chains on each end, at the HOPG/1-phenyloctane interface was studied by in situ scanning tunneling microscopy (STM). The detailed mechanism of a spontaneous change in the monolayer packing pattern by Pd coordination was studied. Uncomplexed 1 existed in a bent form in the monolayer, and the alkyl chains were interdigitated, whereas Pd-complexed 1 was in a straight form and the alkyl chains were not interdigitated. An intermediate state of 1 was successfully observed during metal coordination. The structure was the bent form with noninterdigitated alkyl chains. Equilibrium intermolecular distances reported from ab initio calculations indicate that the molecular width of the central aromatic part of uncomplexed 1 (7.5 A) is substantially smaller than that of the peripheral alkyl chain part (9.2 A). The bent form was suitable for covering up the surface to maximize the packing density. However, the molecular width of the aromatic unit of Pd-complexed 1 (9.1 A) was almost identical to that of the alkyl chain unit (9.2 A). Therefore, Pd-complexed 1 took the straight form in the monolayer. The observation of surface coverage by STM suggests that the bent form increases the packing density by as much as 16% compared with that of the straight form. These results indicate that the control of molecular width can be used to design molecular templates for nanostructure formation.     

Diastereoselective addition of allyltitanocenes to cyclic enones

The reaction of allyltitanocenes with five- to seven-membered cyclic enones proceeded with good to high diastereoselectivity depending on the ring size of enones. The stereochemistry of the major isomers produced by the reaction of cinnamyltitanocene was opposite to that of crotyltitanocene.