Two novel highly water-soluble tetrazolium salts, WST-1 (4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt) and WST-8 (4-[3-(2-methoxy-4-nitrophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt) were applied to the assay of superoxide dismutase (SOD). The superoxide anion generated by xanthine/xanthine oxidase (XO) reduced WST-1 and WST-8 to water-soluble formazans which exhibited absorbance maxima at 438 and 460 nm, respectively. The rates of reduction were linearly related to the XO activity, and reduction was inhibited by SOD. Complete inhibition by SOD of the reduction of both WST-1 and WST-8 was achieved, suggesting that these WSTs were not reduced with XO. WST-1 was found more useful than WST-8 because it had shown higher sensitivity which was apparently not dependent on the assay pH value in the range pH 8.0-10.2. These properties of WST-1 are ideal for the spectrophotometric assay of SOD in an aqueous system.
The directed self-assembly (DSA) of block co-polymers (BCPs) can realize next-generation lithography for semiconductors and a variety of soft materials. It is imperative to simultaneously achieve many requirements such as a high resolution, orientation control of micro-domains, etch selectivity, rapid and mild annealing, a low cost, and compatibility with manufacturing for developing suitable BCPs. Here, we describe a new design for modified polysiloxane-based BCPs targeted for sub-10-nm-wide lines, which are able to form perpendicularly oriented lamellar structures in thin films. The hydroxyl groups in the side chains introduced in the polysiloxane block provide a good balance with the polystyrene surface free energy, thereby leading to the perpendicular orientation. Moreover, this orientation can be completed in only one minute at 130 °C in an air atmosphere. Oxygen plasma etching for the thin films results in the achievement of a line width of 8.5 nm.
A poly(4-hydroxystyrene) (PHS) backbone polymer and a tetramethylammoniumhydroxide (TMAH) aqueous developer are typically combined to form a positive chemically amplified resist. We investigated the dissolution kinetics of PHS with different molecular weights and molecular weight dispersions and different concentrations of TMAH by quartz crystal microbalance (QCM) measurement. QCM graphs showed different dissolution rates and forms for different concentrations. We attempted to explain the dissolution kinetics by introducing a dissolution index calculated from swelling and dissolving factors. These factors were calculated using a penetrating factor (water or TMAH molecules) and a disentanglement factor. It is considered that the dissolution index depends on the molecular weight distribution because polymers with different molecular weight distributions have different voids in their bulk and different tendencies of disentanglement. Our results suggest that dissolution can be controlled by adjusting the molecular weight distribution, which will lead to reduced defect generation during the fabrication of fine structures.
The radiation-induced reactions of ligands play an important role in the sensitization of metal oxide nanocluster resists. However, the details in the radiation chemistry of ligands for metal oxide nanocluster resists are still unknown. In this study, the radiation-induced reactions of carboxylic acid ligands were investigated using a pulse radiolysis method. The rate constants for the reactions of molecular and ionic forms of tiglic, angelic, otoluic, and p-toluic acids with hydrated electrons were determined. The rate constants for the reactions of tiglic, angelic, benzoic, o-toluic, and ptoluic acids with dodecane radical cations were also determined. The radical ions of tiglic and angelic acids were more unstable than those of benzoic, o-toluic, and p-toluic acids. The results obtained in this study indicate that the molecular structures of ligands affect their reactivity to cationic and anion species and the stability of their radical cations and anions.
A flow-injection analysis (FIA) for superoxide dismutase (SOD) activity was developed based on the use of tetrazolium salt, WST-1 (4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt) and an enzyme reactor packed with Sepharose 4B on which xanthine oxidase (XO) and catalase were co-immobilized. WST-1 is highly water-soluble, and no adhesion of the reduced form to the FIA line was observed during continuous operation for 3 months. As optimized conditions, a sample (9 vol) was mixed with a reagent solution (1 vol) containing 3 mM hypoxanthine and 2 mM WST-1, and the mixed solution (20 µl) was injected into a carrier stream of 50 mM carbonate buffer (pH 10.2) at a flow rate of 0.4 ml/min. Under the conditions, the concentration of the SOD preparation giving 50% inhibition (IC50) was 2.7 µg/ml and the sampling frequency was 30 samples/h. When the SOD activity in erythrocytes of rats was determined by the present FIA method, the values were linearly related to those obtained by the conventional nitroblue tetrazolium (NBT) assay (r =0.975; n =18). The enzyme reactor was stable for at least 200 repetitive injections.
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