Comparison of radioactive and stable cesium uptake in aquatic macrophytes affected by the Fukushima Dai-ichi Nuclear Power Plant accident

Concentrations of ^134+137Cs and ¹³³Cs in aquatic macrophytes, water, and sediment were measured in samples collected from Fukushima Prefecture, Japan. The concentrations of ¹³⁷Cs in submerged and floating-leaved plants were higher than the values for emergent plants according to their main Cs uptake mode. The geometric mean water-to-plant concentration ratio for ¹³⁷Cs and ¹³³Cs was comparable observed in submerged and floating-leaved plants, while the geometric mean sediment-to-plant concentration ratio for ¹³⁷Cs in emergent plants was higher than that of ¹³³Cs, which suggest that the mobility of Fukushima accident-derived ¹³⁷Cs is not in steady state 4–5 years after the accident.

     

Mechanistic studies of hydrogen-peroxide-mediated anthocyanin oxidation

The oxidation of cyanidin-3-O-glucoside by hydrogen peroxide was investigated in a range of solvents. The reaction products had chemical structures identical to those formed by the reaction of this compound with the alkylperoxyl radical 2,2?-azobis(2,4-dimethyl)valeronitrile. A plausible oxidation mechanism was proposed based on the obtained reaction products, and this mechanism was confirmed by HPLC–MS experiments using ¹⁸O-labeled reagents. Further, the reaction conditions were found to influence both the reaction rate and the products formed during the transformation, which validated the proposed mechanism.     

Determination of trace silica in highly purified water based on delayed quenching of Rhodamine B through nanoparticle formation with molybdosilicate

The development of a highly sensitive analytical method for trace silica is an urgent necessity for the real-time monitoring of highly purified water used in the semiconductor industry. However, there are no reports of a simple yet sensitive method for the determination of trace silica. Here we describe the delayed quenching phenomenon of Rhodamine B cation caused by nanoparticle formation with molybdosilicate ions in aqueous solution and its application to the one-step determination of trace silica at ppt to low ppb levels. We found that the quenching takes place over several minutes and the quenching time is dependent on the concentration of silica. The measurements made by a dynamic light scattering particle size analyzer indicated that the diameter of the particles were at nanometer levels. The detection limit was found to be 34 ng dm(-3) Si (1.2 x 10(-9) mol dm(-3)). The average quenching time for 1 microg dm(-3) was 239 s with an RSD of 2.2% (n= 7). The proposed method has been successfully applied to distilled and highly purified water samples. There was good agreement between the results obtained by the proposed method and those by ICP-three dimensions quadrupole MS/MS with 11-fold evaporation concentration. The main point of this method is that in the trace determination of silica, the signal is larger at lower concentrations. The advantages of the proposed method are that it can be used as real-time monitoring for trace silica in highly purified water, and will be a great aid to industries in which the quality control of water is crucial.     

Alkali metal and alkali metal hydroxide intercalates of 2s-tantalum disulfide

The alkali metal intercalates of the layered compound 2s-tantalum disulfide were prepared from the respective hexamethylphosphoric triamide solutions of the metals. The c-lattice parameters of the intercalates increased with increase in the crystallographic radii of the metals. All intercalates prepared were superconductors, and the transition temperatures increased as the crystallographic radii of the metals became larger. The intercalates reacted with water to produce hydrogen gas and changed to different intercalates. These had properties similar to those of the corresponding alkali metal hydroxide intercalates prepared from aqueous solutions of the metal hydroxides. The alkali metal hydroxide intercalates, on the other hand, were found to be classified into two groups in terms of the c-lattice parameters; one having c-lattice parameters around 23.8 Å and the other 18 Å. Lithium and sodium hydroxide intercalates belong to the former type, and potassium, rubidium and cesium hydroxide intercalates, including ammonium hydroxide, to the latter. Dried lithium and sodium hydroxide intercalates were also classified in the latter group. In the former case the disulfide was found to intercalate the cations, conserving the ice-like structure of the surrounding water molecules. In the latter, the cations were intercalated in their naked or primary hydrated states, and the interlayer distances were governed by cointercalated hydroxide ions. The observed superconducting transition temperatures were similar for the intercalates with c-lattice parameters around 18 Å irrespective of the particular cation.     

STM studies of photochemistry and plasmon chemistry on metal surfaces

We review our recent studies of photochemistry and plasmon chemistry of dimethyl disulfide, (CH₃S)₂, molecules adsorbed on metal surfaces using a scanning tunneling microscope (STM). The STM has been used not only for the observation of surface structures at atomic spatial resolution but also for local spectroscopies. The STM combined with optical excitation by light can be employed to investigate chemical reactions of single molecules induced by photons and localized surface plasmons. This technique allows us to gain insights into reaction mechanisms at a single molecule level. The experimental procedures to examine the chemical reactions using the STM are briefly described. The mechanism for the photodissociation reaction of (CH₃S)₂ molecules adsorbed on metal surfaces is discussed based on both the experimental results obtained with the STM and the electronic structures calculated by density functional theory. The dissociation reaction of the (CH₃S)₂ molecule induced by the optically excited plasmon in the STM junction between a Ag tip and metal substrate is also described. The reaction mechanism and pathway of this plasmon-induced chemical reaction are discussed by comparison with those proposed in plasmon chemistry.     

Stepwise controlled immobilization of colloidal crystals formed by polymer-grafted silica particles

Colloidal crystals formed by polymer-grafted silica particles were immobilized by a stepwise procedure consisting of gelation by radical copolymerization followed by solidification by ring-opening radical polymerization. In the first step, the poly(methyl methacrylate) (PMMA)-grafted silica colloidal crystal suspension was incorporated into the gel without altering the crystal structure by copolymerization of cross-linker, 1,2-dimethylacryloyloxyethane (DME) and methyl methacrylate (MMA). In the second step, ring-opening radical polymerization was performed after substituting the solvent with vinylidene-1,3-dioxolane. By this two-step procedure, the silica particle array of colloidal crystals was immobilized and made into durable material.     

Preparation of poly(methyl methacrylate) films containing silica particle array structure from colloidal crystals

The incorporation of monodisperse, polymer-modified silica into poly(methyl metharylate) to prepare polymer films containing particle array structure was investigated. The preparation was carried out by a two-step radical polymerization for gelation and solidification. The colloidal crystallization of poly(methyl metharylate)-modified silica, in 78 nm size, in acetonitrile and successive copolymerization of methyl methacrylate and 1,2-dimethacryloylethane by UV light irradiation gave the polymer gel containing the colloidal crystal structure. The exchange of acetonitrile in the gel with methyl methacrylate and further photo-radical polymerization gave the durable polymer film composed of silica particle array.     

T cell response in rheumatic fever: crossreactivity between streptococcal M protein peptides and heart tissue proteins

Molecular mimicry between streptococcal and human proteins has been proposed as the triggering factor leading to autoimmunity in rheumatic fever (RF) and rheumatic heart disease (RHD). In this review we focus on the studies on genetic susceptibility markers involved in the development of RF/RHD and molecular mimicry mediated by T cell responses of RHD patients against streptococcal antigens and human tissue proteins. We identified several M protein epitopes recognized by peripheral T cells of RF/RHD patients and by heart tissue infiltrating T cell clones of severe RHD patients. The regions of the M protein preferentially recognized by human T cells were also recognized by murine T cells. By analyzing the T cell receptor (TCR) we observed that some Vbeta families detected on the periphery were oligoclonal expanded in the heart lesions. These results allowed us to confirm the major role of T cells in the development of RHD lesions.