Takahide Kimura

A standard method to calibrate sonochemical efficiency of an individual reaction system.

Fricke reaction, KI oxidation and decomposition of porphyrin derivatives by use of seven types of sonochemical apparatus in four different laboratories were examined in the range of frequency of 19.5 kHz to 1.2 MHz. The ultrasonic energy dissipated into an apparatus was determined also by calorimetry. Sonochemical efficiency of Fricke reaction and KI oxidation was defined as the number of reacted molecule per unit ultrasonic energy. The sonochemical efficiency is independent of experimental conditions such as the shape of sample cell and irradiation instruments, but depends on the ultrasonic frequency. We propose the KI oxidation dosimetry using 0.1 moldm(-3) KI solution as a standard method to calibrate the sonochemical efficiency of an individual reaction system.

Standardization of ultrasonic power for sonochemical reaction

Abstract The calorimetric method and the Weissler reaction were reevaluated as a means to standardize the ultrasonic power of individual ultrasonic devices. Results showed that the Weissler reaction, which can be regarded as a chemical dosimeter for measuring acoustic energy, was directly and linearly related to the calorimetrically determined ultrasonic power; the latter was independent of the volume and shape of a vessel, even if ultrasound was introduced using different devices. The additional description of either the calorimetrically determined power or the chemical yield of the Weissler reaction as one of the reaction conditions to ascertain the level of ultrasonic power in the research report is proposed.

Damage to the cytoplasmic membrane of Escherichia Coli by catechin-copper (II) complexes

In the presence of a nonlethal concentration of Cu(II), washed Escherichia coli ATCC11775 cells were killed by (-)-epigallocatechin (EGC) and (-)-epicatechin (EC). Cell killing was accompanied by a depletion in both the ATP and potassium pools of the cells, but the DNA double strand was not broken, indicating that the bactericidal activity of catechins in the presence of Cu(II) results from damage to the cytoplasmic membrane. Induction of endogenous catalase in E. coli cells increased their resistance to being killed by the combination of catechins and Cu(II). In all cases studied, EGC and EC with Cu(II) were found to generate hydrogen peroxide, but its concentration was too low to account for the bactericidal activity. The bactericidal activity of EGC in the presence of Cu(II) was completely suppressed by ethylenediaminetetraacetate, bathocuproine, catalase, superoxide disumutase (SOD), heated catalase, and heated SOD, but not by dimethyl sulfoxide. When catalase, either heated or unheated, was added to the cells incubated with EGC in the presence of Cu(II), it completely inhibited further killing of the cells. These findings suggest that recycling redox reactions between Cu(II) and Cu(I), involving catechins and hydrogen peroxide on the cell surface, must be important in the mechanism of the killing.

DNA CLEAVAGE REACTION AND LINOLEIC ACID PEROXIDATION INDUCED BY TEA CATECHINS IN THE PRESENCE OF CUPRIC ION

Tea catechins with cupric ion promoted extensive DNA cleavage and fatty acid peroxidation in vitro under aerobic conditions. Neither cupric ions nor polyphenolic compounds including catechins alone induced DNA cleavage. While catalase significantly inhibited the DNA cleavage induced by catechins-Cu2+, superoxide dismutase (SOD) did not, indicating that H2O2 is probably involved in the DNA cleavage. These results suggest that the pro-oxidant property of catechins, which are generally considered to be anti-oxidants and anticarcinogens, is responsible for the O2 reducing ability of catechins catalyzed by cupric ion.

Simultaneous Discrimination of Handedness and Diameter of Single-Walled Carbon Nanotubes (SWNTs) with Chiral Diporphyrin Nanotweezers Leading to Enrichment of a Single Enantiomer of (6,5)-SWNTs

Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT-SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT-SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.

A facile and scalable process for size-controllable separation of nanodiamond particles as small as 4 nm.

Interest in nanometer-sized particles has increased in recent years, especially from the viewpoint of nanobiology and nanomedicine. Among them are gold, silver, and silica nanoparticles, quantum dots, magnetic beads, carbon nanotubes, and nanodiamond (ND) particles. Since the physical properties of these nanoparticles are largely dependent on their size and shape, control of their structure is vital for advancing both fundamental studies and technological applications. In this context, sizeselective preparation has been established for gold, silver, and silica nanoparticles, quantum dots, and magnetic beads (iron oxide). We have also investigated structure-based separation of single-walled carbon nanotubes by using molecular recognition or ultrasonic atomization. Quite recently, shape, as well as size, was successfully controlled in the preparation of silver and gold nanoparticles. The availability of a wide spectrum of nanoparticle size and shape enables precise investigation of their effects in biological systems. In contrast, the size and shape control of ND is much less developed than that of other nanoparticles. This restricts the potential applications of ND particles, in spite of their many prominent physical properties. Although the biological and medicinal applications of ND have been extensively investigated quite recently due to its biocompatibility, it is somewhat difficult to fully investigate the effect of its size in,

Fluoride-alumina reagents: the active basic species

Abstract Comparison of KF and NaF impregnated on active alumina shows that the formation of strong base by fluoride reaction with alumina cannot totally explain the extremely high reactivity of KF-alumina as a heterogeneous base for catalytic as well as non-catalytic reactions. At least three mechanisms apparently give rise to the high basicity.

Prooxidative Activities of Tea Catechins in the Presence of Cu2

The ability of various tea catechins to generate H2O2 and the hydroxyl radical in the presence of the Cu2+ ion was investigated and compared with the effect of iron ions. The presence of Cu2+ accelerated the generation of H2O2 by EGC, while EGCg with Cu2+ generated a little H2O2. The presence of iron ions inhibited the generation of H2O2 by EGC. EGC and EC with Cu2+ generated the hydroxyl radical, while EGCg and ECg with Cu2+ did not. The fact that EGCg showed less prooxidative activity than EGC can be explained by the chelating ability of catechin gallates to metal ions under the experimental conditions.

Sonochemical switching from ionic to radical pathways in the reactions of styrene and trans-β-Methylstyrene with lead tetraacetate

Abstract The reactions of styrene and trans-β-methylstyrene with lead tetraacetate in acetic acid are greatly influenced by ultrasonic irradiation to give products resulting mostly from radical chain pathways, whereas mechanical agitation gives products only from ionic processes.

Diameter-based separation of single-walled carbon nanotubes through selective extraction with dipyrene nanotweezers

We have been developing host–guest methodology for the separation of single-walled carbon nanotubes (SWNTs) according to handedness and diameter with gable-type chiral diporphyrins. The diporphyrins, designated as porphyrin nanotweezers, consist of two porphyrins and rigid spacer in between. As an extension of our strategy, novel nanotweezers having two pyrenes instead of porphyrins have been designed, because pyrene is known to have high affinity toward SWNT surface. The pyrene nanotweezers presented here consist of two 1- or 2-pyrenes and 3,6-carbazolylenes with various N-substituents. For the extraction of SWNTs, the 1- and 2-pyrene nanotweezers show a marked contrast: 1-pyrene nanotweezers selectively extract SWNTs with diameters ranging from 0.84 nm to 0.97 nm, while 2-pyrene nanotweezers are not able to extract SWNTs at all.