Influence of Microbubbles on Free Radical Generation by Ultrasound in Aqueous Solution: Dependence of Ultrasound Frequency.

The influence of microbubbles on sonochemical efficiencies has been investigated under 28, 45, and 100 kHz ultrasound irradiation. For the 28 and 100 kHz ultrasound frequencies, microbubbles suppressed the I3(-) formation from KI solution as well as the 7-hydroxycoumarin formation from coumarin solution caused by the ultrasonic irradiation. On the other hand, for the 45 kHz ultrasound frequency, microbubbles enhanced the I3(-) formation from KI solution as well as 7-hydroxycoumarin formation from coumarin solution caused by the ultrasonic irradiation. Detection of H2O2 after the irradiation of ultrasound in the presence or absence of microbubbles was also performed, and it was found that H2O2 formation was enhanced only when microbubbles were introduced under the 45 kHz ultrasonic irradiation, which was in good agreement with the results of KI oxidation dosimetry measurements and of coumarin fluorescent probe measurements. Based on these present results, plausible mechanisms that explain the dependence of the ultrasound frequency on the enhancement and suppression of free radical formation in the presence of MBs were proposed.

Removal of high concentration dimethyl methylphosphonate in the gas phase by repeated-batch reactions using TiO2.

The aim of our study is to develop apparatuses that use TiO(2) for effective decontamination of air contaminated by Sarin gas. We performed photocatalytic decomposition of gaseous dimethyl methylphosphonate (DMMP) by TiO(2) and identified the oxidization products. The high activity of TiO(2) (0.01 g) was observed under UV-light irradiation and high concentration DMMP (33.5 microM) was removed rapidly. On the other hand, DMMP was not decreased under UV-light irradiation without TiO(2). This indicates that photocatalytic treatment is very effective for the removal of DMMP. Methanol, formaldehyde, formic acid, methyl formate, CO, CO(2) and H(2)O were detected as the primary products. In the gas phase, no highly poisonous substances were detected. In order to examine the performance of photocatalytic activity during long-term reactions, we performed photocatalytic decomposition by repeated-batch reactions using TiO(2). High photocatalytic activities decreased gradually. Meanwhile, the strong adsorption of TiO(2) against DMMP was observed as photocatalytic activities decreased. During the repeated-batch reactions with the sample scaled up (TiO(2): 0.1g), the total amount of removed DMMP reached 968.5 microM by both photocatalytic decomposition and the strong adsorption of TiO(2). These results suggest the possibility of removing large amounts of DMMP.

[Decontamination of chemical warfare agents by photocatalysis].

Photocatalysis has been widely applied to solar-energy conversion and environmental purification. Photocatalyst, typically titanium dioxide (TiO(2)), produces active oxygen species under irradiation of ultraviolet light, and can decompose not only conventional pollutants but also different types of hazardous substances at mild conditions. We have recently started the study of photocatalytic decontamination of chemical warfare agents (CWAs) under collaboration with the National Research Institute of Police Science. This article reviews environmental applications of semiconductor photocatalysis, decontamination methods for CWAs, and previous photocatalytic studies applied to CWA degradation, together with some of our results obtained with CWAs and their simulant compounds. The data indicate that photocatalysis, which may not always give a striking power, certainly helps detoxification of such hazardous compounds. Unfortunately, there are not enough data obtained with real CWAs due to the difficulty in handling. We will add more scientific data using CWAs in the near future to develop useful decontamination systems that can reduce the damage caused by possible terrorism.

DNA methylation profile of tissue-dependent and differentially methylated regions (T-DMRs) in mouse promoter regions demonstrating tissue-specific gene expression.

DNA methylation constitutes an important epigenetic regulation mechanism in many eukaryotes, although the extent of DNA methylation in the regulation of gene expression in the mammalian genome is poorly understood. We developed D-REAM, a genome-wide DNA methylation analysis method for tissue-dependent and differentially methylated region (T-DMR) profiling with restriction tag-mediated amplification in mouse tissues and cells. Using a mouse promoter tiling array covering a region from -6 to 2.5 kb ( approximately 30,000 transcription start sites), we found that over 3000 T-DMRs are hypomethylated in liver compared to cerebrum. The DNA methylation profile of liver was distinct from that of kidney and spleen. This hypomethylation profile marked genes that are specifically expressed in liver, including key transcription factors such as Hnf1a and Hnf4a. Genes with T-DMRs, especially those lacking CpG islands and those with HNF-1A binding motifis in their promoters, showed good correlation between their tissue-specific expression and liver hypomethylation status. T-DMRs located downstream from their transcription start sites also showed tissue-specific gene expression. These data indicate that multilayered regulation of tissue-specific gene function could be elucidated by DNA methylation tissue profiling.

Charge separation and catalytic activity of Ag@TiO2 core-shell composite clusters under UV-irradiation.

Photocatalytic properties of Ag@TiO2 composite clusters have been investigated using steady state and laser pulse excitations. Photoexcitation of TiO2 shell results in accumulation of the electrons in the Ag core as evidenced from the shift in the surface plasmon band from 460 to 420 nm. The stored electrons are discharged when an electron acceptor such as O2, thionine, or C60 is introduced into the system. Charge equilibration with redox couple such as C60/C60*- shows the ability of these core shell structures to carry out photocatalytic reduction reactions. The charge separation, charge storage, and interfacial charge-transfer steps that follow excitation of the TiO2 shell are discussed.

Photovoltaic cells using composite nanoclusters of porphyrins and fullerenes with gold nanoparticles.

Novel organic solar cells have been prepared using quaternary self-organization of porphyrin (donor) and fullerene (acceptor) units by clusterization with gold nanoparticles on nanostructured SnO2 electrodes. First, porphyrin-alkanethiolate monolayer-protected gold nanoparticles (H2PCnMPC: n is the number of methylene groups in the spacer) are prepared (secondary organization) starting from the primary component (porphyrin-alkanethiol). These porphyrin-modified gold nanoparticles form complexes with fullerene molecules (tertiary organization), and they are clusterized in acetonitrile/toluene mixed solvent (quaternary organization). The highly colored composite clusters can then be assembled as three-dimensional arrays onto nanostructured SnO2 films to afford the OTE/SnO2/(H2PCnMPC+C60)m electrode using an electrophoretic deposition method. The film of the composite clusters with gold nanoparticle exhibits an incident photon-to-photocurrent efficiency (IPCE) as high as 54% and broad photocurrent action spectra (up to 1000 nm). The power conversion efficiency of the OTE/SnO2/(H2PC15MPC+C60)m composite electrode reaches as high as 1.5%, which is 45 times higher than that of the reference system consisting of the both single components of porphyrin and fullerene.

Photoinduced electron storage and surface plasmon modulation in Ag@TiO2 clusters.

The reversible charging and discharging effects associated with photoexcitation of a TiO2 shell in a Ag@TiO2 composite are described. The photoinduced charge separation in the TiO2 shell is followed by electron injection into the silver core. Interestingly, the charging of the silver core is associated with the shift in the surface plasmon band from 460 to 430 nm. The stored electrons are discharged upon exposure of the charged Ag@/TiO2 composite to an electron acceptor. As the electrons from the silver core are discharged, the original surface plasmon absorption of the Ag core is restored.