Velocity measurement of start-up flow of polymeric solutions in a planar contraction channel

The start-up flow of polymeric solutions in an abrupt contraction channel with a rectangular cross-section was experimentally studied. Aqueous solutions with 0.2 wt% and 1.0 wt% of polyacrylamide were used as test fluids. Temporal changes in velocity were measured with a laser Doppler velocimeter. The velocity overshot just after the onset of the flow. The changes in velocity caused by the rearrangement of the velocity distribution were observed. A three-dimensional flow structure and the development of a vortex region were found near the entrance to the contraction. A decrease in the axial velocity just upstream from the contraction was observed. The velocity profile is related to the three-dimensional nature of the flow and the elongational rheological properties of the test fluid. The experimental results indicate that three-dimensional analysis of viscoelastic flows is required especially for the flow in rectangular channels. Received: 6 July 1998 Accepted: 1 December 1998     

In‐situ Fabrication of Functional Materials inside Porous Fiber using Microwave Selective Heating

We developed a simple fabrication method, which can emplace functional materials inside porous fibers. In contrast to conventional impregnation methods or surface coating, various functions can be included inside of natural or synthetic fibers. This fabrication method has three steps. First, the raw material solution is absorbed to the fiber. Then the fiber is immersed and pressurized in immiscible liquids with the raw material solution. Finally, the functional particles are fabricated in‐situ inside of the fiber by a chemical reaction such as microwave selective heating. As a model reaction, we fabricated silver‐nanoparticle‐containing cotton fiber. The elemental silver was distributed inside of the fiber in a cross‐sectional distribution as confirmed by SEM‐EDS. Furthermore, we fabricated fibers with zeolite particles inside of porous PTFE fibers.     

Comprehensive 3D-RISM analysis of the hydration of small molecule binding sites in ligand-free protein structures

Hydration is a critical factor in the ligand binding process. Herein, to examine the hydration states of ligand binding sites, the three-dimensional distribution function for the water oxygen site, g_O( r ) , is computed for 3,706 ligand-free protein structures based on the corresponding small molecule–protein complexes using the 3D-RISM theory. For crystallographic waters (CWs) close to the ligand, g_O( r ) reveals that several CWs are stabilized by interaction networks formed between the ligand, CW, and protein. Based on the g_O( r ) for the crystallographic binding pose of the ligand, hydrogen bond interactions are dominant in the highly hydrated regions while weak interactions such as CH-O are dominant in the moderately hydrated regions. The polar heteroatoms of the ligand occupy the highly hydrated and moderately hydrated regions in the crystallographic (correct) and wrongly docked (incorrect) poses, respectively. Thus, the g_O( r ) of polar heteroatoms may be used to distinguish the correct binding poses.     

New solanocapsine-type tomato glycoside from ripe fruit of Solanum lycopersicum

A new solanocapsine-type tomato glycoside, a novel and interesting natural steroidal glycoside, was isolated from a mini tomato, Solanum lycopersicum L. The chemical structure of the new minor glycoside, esculeoside B-5 (3), was determined to be (5S,22R,23S,24R,25S)-22,26-epimino-16β,23-epoxy-3β,23,24-trihydroxycholestane 3-O-β-lycotetraoside.     

Four new iridoid glucosides from Ajuga reptans

Four new iridoid glucosides were isolated from the whole plant of Ajuga reptans L. (Labiatae) along with four known iridoid glucosides, one known diterpenoid glycoside, one known aliphatic alcohol glycoside, and three known ecdysteroids. Their chemical structures were determined on the basis of spectroscopic data and chemical evidence. The diterpenoid glycoside exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and H?O? scavenging activities.     

Synthesis of non-stoichiometric (LaO)CuS thin films by pulse laser deposition

We have attempted to control the photoluminescence spectrum of transparent p-type semiconductor (LaO)CuS to check possibilities of phosphor application using non-stoichiometric thin films prepared by pulse laser deposition method. Two kinds of samples are examined, one is the samples that contain the excess S and the other is the excess Cu. All samples are a single phase without impurities, regardless of heavily doping. Lattice constants for all samples don’t depend on the concentration of excess atoms. Perhaps, this is due to the nature of the layered materials. Introduction of excess atoms leads to change the photoluminescence spectra. The excess S and Cu have much effect on the red and the blue luminescence bands, respectively. We have succeeded in the tuning luminescence band of photoluminescence spectra.     

Single probe nucleic acid immobilization on chemically modified single protein by controlling ionic strength and pH

In an effort toward determining the feasibility of single molecule analysis, we describe a case whereby the binding of one biotinylated DNA to one streptavidin molecule via electrostatic interactions was controlled by altering in pH 4.0-9.0 and 0.16 of the ion strength. The quantitative analysis of immobilized probe ssDNA was realized in real-time via a quartz crystal microbalance (QCM) and electrochemical (EC) measurement in the range 100 pM to 50 μM of probe oligonucleotide concentration. The variation amount of biotinylated ssDNA immobilized on the streptavidin-modified surface at pH 7.5 was about 0.16 pmol, giving a ratio of streptavidin to biotinylated ssDNA of about 1:1.1. On the other hand, at pH 4.9, it was immobilized about 0.29 pmol. From the shape of the Langmuir plot and QCM, the immobilization efficiency of biotinylated DNA via streptavidin at pH 4.9 was approximately twofold that at pH 7.5. In view points of the reaction velocity, it was increased with decreasing buffer solution pH, indicating a strong interaction of negatively charged probe DNA with the positively charged streptavidin. And also the EC response value of ΔI/I_streptavidin for the immobilized biotinylated ssDNA in pH 4.9 was about 49%, while the corresponding value for the pH 7.5 was approximately 34%. As DNA molecules possess negative charges, electrostatic repulsion occurred between streptavidin and biotinylated ssDNA at pH 7.5. At pH 4.9, the attraction between the biotinylated ssDNA and streptavidin resulted in increased adsorption which has an isoelectric point of about 5.9. It was deduced that the binding of biotinylated ssDNA to one or two of the four binding sites of streptavidin can be controlled by adjusting the pH-controlled electrostatic interaction.