Takushi Yokoyama

One-Pot Synthesis of Indoles and Aniline Derivatives from Nitroarenes under Hydrogenation Condition with Supported Gold Nanoparticles

One-pot sequences of hydrogenation/hydroamination to form indoles from (2-nitroaryl)alkynes and hydrogenation/reductive amination to form aniline derivatives from nitroarenes and aldehydes were catalyzed by Au nanoparticles supported on Fe(2)O(3). Nitro group selective hydrogenations and successive reactions were efficiently catalyzed under the conditions.

Simultaneous determination of arsenic and arsenious acids in geothermal water

Abstract A flow system using ion-exclusion chromatography and continuous hydride/atomic absorption spectrometry was developed for the simultaneous determination of arsenious acid (As(III)) and arsenic acid (As(V)) in geothermal water at the ppm level. The precision (C.V.) was ±2.4 and ±1.1% for As(III) and As(V) (1 ppm As each), respectively. The sampling rate was 5.5 samples hr−1. The arsenic species could be measured in the concentration range 0.01–10 ppm As by changing the injection volume of geothermal water. Total concentration of As in geothermal waters collected from geothermal fields in Kyushu, Japan, and Wairakei, New Zealand, was in the range of 0.5–4.6 ppm As. The arsenic was mostly present as As(III) in the geothermal waters directly discharged from geothermal wells through the water-vapor separator, but the As(III) was rapidly oxidized to As(V). This contrasts with slow oxidation of As(III) in standard solutions, which suggests that a catalyzer (probably Fe or Mn compounds) accelerating the oxidation reaction of As(III) to As(V) is present in the geothermal waters. For the speciation of As(III) and As(V), it was found that the geothermal water sample should be acidified with hydrochloric acid to pH 2 immediately after sampling to preserve the state of As.

Silicon enhances growth independent of silica deposition in a low-silica rice mutant, lsi1

To examine whether silica bodies are essential for silicon-enhanced growth of rice seedlings, we investigated the response of rice, Oryza sativa L., to silicon treatment. Silicic acid treatment markedly enhanced the SPAD (soil plant analytical development) values of leaf blades and the growth and development of leaves and lateral roots in cvs. Hinohikari and Oochikara, and a low-silicon mutant, lsi1. Combination of ethanol–benzene displacement and staining with crystal violet lactone enabled more detailed histochemical analysis to visualize silica bodies in the epidermis under bright-field microscopy. Supply of silicon induced the development of motor cells and silica bodies in epidermal cells in Hinohikari and Oochikara but not or marginal in lsi1. X-ray analytical microscopy detected silicon specifically in the leaf sheath, the outermost part of the stem, and the leaf blade midrib, suggesting that silicon is distributed to tissues involved in maintaining rigidity of the plant to prevent lodging, rather than being passively deposited in growing tissues. Silicon supplied at high dose accumulated in all rice seedlings and enhanced growth and SPAD values with or without silica body formation. Silicon accumulated in the cell wall may play an important physiological role different from that played by the silica deposited in the motor cell and silica bodies.

Effect of aluminum on the deposition of silica scales in cooling water systems

The mechanism of formation of silica scales from cooling water was studied by chemical analyses of the cooling water and silica scales, characterization of the aluminum in the silica scales by 27Al magic angle spinning NMR, the relationship between size distribution of particles in the cooling water and their Al/Si atomic ratios and zeta potentials, and the adsorption properties of the particles on the surface of silica gel powder as a mimic of silica scale. From our results, we determined that aluminum is concentrated from the cooling water into silica scales during their formation, 6-coordinate aluminum is preferentially adsorbed on the surface of the solid, and various particles with differing sizes, surface charges, and Al/Si atomic ratios are formed in the cooling water after addition of polyaluminum chloride. The formation mechanism for silica scales in the cooling water system is proposed based on the electrostatic interaction. The formation of aluminum hydroxide particles smaller than 0.2 microm with positive charges, consisting of 6-coordinate aluminum, and their subsequent adsorption on the surface of the solid are the most important factors contributing to the formation of silica scales.

Bio-deposition of Amorphous Silica by an Extremely Thermophilic Bacterium, Thermus spp.

The bio-deposition of amorphous silica, which occurred in vitro by exposure to the extremely thermophilic bacterium Thermus spp. began from the latter part of the exponential phase of growth of the bacteria. The concentration with which the deposition occurred exceeded the solubility of amorphous silica of neutral pH at the temperature 60~85°C. Our observations suggest that Thermus spp. promotes the formation of siliceous minerals in a geothermal environment.

Acceleration effect of sulfate ion on the dissolution of amorphous silica

The dissolution rate of amorphous silica is enhanced by sulfate ions. The zeta potential for silica particles in Na(2)SO(4) solution was lower than that in NaCl solution with the same ionic strength. These facts indicate that the specific adsorption of sulfate ions occurred by overcoming repulsion between negative charges of the SO(4)(2-) ion and SiO(-) on the surface of silica. The dissolution rate of amorphous silica may be accelerated by the specific adsorption of SO(4)(2-) ions because of a decrease in the strength of the [triple bond]Si-O-Si[triple bond] bond in amorphous silica due to donation of electron density from the adsorbed SO(4)(2-) ions.

Retarding and accelerating effects of aluminum on the growth of polysilicic acid particles

Abstract Retarding and accelerating effects of aluminum on the growth of particles of polysilicic acids were studied in the pH range 7–9 at 50°C by gel chromatography, spectrophotometry, and 27 Al NMR. The effects depended on the pH and aluminum concentration. The greater retarding effect was observed at lower pH, while the greater accelerating effect at higher pH. It was concluded that the retarding effect is due to the formation of a negatively charged aluminosilicate site by substitution of aluminum for 4-coordinated silicon on polysilicic acid, and that the accelerating effect is due to the formation of unidentified aluminum species, which could not be detected by 27 Al NMR, on the surface of polysilicic acid.

Stimulation of Expression of a Silica-Induced Protein (Sip) in Thermus thermophilus by Supersaturated Silicic Acid

ABSTRACT The effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan, were examined at 75°C. At concentrations higher than the solubility of amorphous silica (400 to 700 ppm SiO2), a silica-induced protein (Sip) was isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the molecular mass and pI of Sip to be about 35 kDa and 9.5, respectively. Induction of Sip expression occurred within 1 h after the addition of a supersaturating concentration of silicic acid to TM broth. Expression of Sip-like proteins was also observed in other thermophiles, including T. thermophilus HB8 and Thermus aquaticus YT-1. The amino acid sequence of Sip was similar to that of the predicted solute-binding protein of the Fe3+ ABC transporter in T. thermophilus HB8 (locus tag, TTHA1628; GenBank accession no. NC_006461; GeneID, 3169376). The sip gene (987-bp) product showed 87% identity with the TTHA1628 product and the presumed Fe3+-binding protein of T. thermophilus HB27 (locus tag TTC1264; GenBank accession no. NC_005835; GeneID, 2774619). Within the genome, sip is situated as a component of the Fbp-type ABC transporter operon, which contains a palindromic structure immediately downstream of sip. This structure is conserved in other T. thermophilus genomes and may function as a terminator that causes definitive Sip expression in response to silica stress.

Effect of aluminium on the polymerization silicic acid in aqueous solution and the deposition of silica of silica

Abstract The effect of aluminium on the polymerization of silicic acid was studied at pH 7, 8 and 9 in the aluminium concentration range of 0–26 ppm (Al) by spectrophotometry, gel chromatography and 27 Al NMR. Retarding and accelerating effects of aluminium on the growth of polysilicic acid particles and on the reaction between monosilicic acid and polysilicic acid were observed by changing the pH. It is suggested that the accelerating effect on the reaction between polysilicic acid particles is due to the formation of aluminium hydroxide on the surface of polysilicic acid. The rate of decrease in the monosilicic acid concentration in the presence of aluminium was faster than that in the absence of aluminium at pH 9, because monosilicic acid could be adsorbed rapidly on the aluminium hydroxide. From the results it was presumed that the formation of aluminium hydroxide on the solid surface may accelerate the deposition of silicic acid from geothermal water.

Thermus thermophilus TMY isolated from silica scale taken from a geothermal power plant

Aims:  To identify an extreme thermophile, strain TMY, isolated from silica scale from the geothermal electric power plant and to examine microdiversity of Thermus thermophilus strains.