Yoshihiro Okaue

Stabilization of Atomic Hydrogen in Both Solution and Crystal at Room Temperature

Atomic hydrogen has been stably encapsulated in both solution and crystal at room temperature. Upon γ-ray irradiation of [(CH3)3Si]8Si8O20, which is the trimethylsilylated derivative of the silicate anion with a double four-ring (D4R) cage, electron spin resonance (ESR) spectra revealed that a single hydrogen atom is encapsulated in the center of the D4R cage and is stable for periods of many months. Attack by chemically reactive species such as oxygen was prevented by the D4R cage, but the ESR signal of the hydrogen atom was sensitive to the magnetic interaction caused by the presence of the O2 molecule near the cage.

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.

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.

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.

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.

Formation conditions and stability of a toxic tridecameric Al polymer under a soil environment

It is important to study the formation conditions and the stability of the tridecameric Al polymer (Keggin-type Al(13) polycation, [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+), known as Al(13)) due to its strong toxicity to living organisms of a soil environment. In order to examine the pH range where toxic Al(13) can exist in aqueous solution, (27)Al NMR spectra for sample solutions containing Al(3+) ions with various pH (pH 3.5-6.1) were measured. The results show that the peak due to Al(13) (peak due to 4-coordinated Al around 63 ppm) appeared at pH 3.6-5.7 and the peak intensity was relatively high at pH 4.1-4.8, suggesting that Al(13) can be formed at pH 3.6-5.7, while it can exist dominantly at pH 4.1-4.8. It was also found that Al(13) can stably adsorb onto a chelate resin, Chelex 100, by weak electrostatic interaction. The Chelex 100, with iminodiacetate groups, served as a model compound for surfaces of microbes covered with carboxyl groups and for surfaces of soil particles covered with humic substances having many carboxyl groups. Additionally, decomposition of Al(13) did not occur even after adsorption, and its pH stability range was wide compared to that in aqueous solution.

The inhibition abilities of multifunctional polyelectrolytes for silica scale formation in cooling water systems: role of the nonionic functional group.

The abilities of multifunctional polyelectrolytes to enhance aluminum hydroxide dispersion and inhibit silica scale formation were examined in a pilot cooling water system. The following multifunctional polyelectrolytes were studied: a terpolymer of acrylic acid (AA), 2-acrylamide-2-methyl propane sulfonic acid (SA) and N-vinylpyrrolidone (NVP) (P(AA/SA/NVP)), acrylic acid homopolymer (P(AA)) and a copolymer of AA and SA (P(AA/SA)). The order of inhibition ability was P(AA/SA/NVP)>P(AA/SA)>P(AA), and was consistent with that of the dispersing ability for aluminum hydroxide. Other terpolymers incorporating different nonionic monomers were also examined and factors affecting their inhibition abilities were investigated, based on interaction energies calculated by density functional theory. Based on the correlation between scale inhibition abilities and interaction energies, we elucidated that the effective nonionic monomer of terpolymer for silica scale inhibition had low affinity for aluminum hydroxide and high affinity for H(2)O and Si(OH)(3)O(-). The affinities of nonionic monomer for aluminum hydroxide and H(2)O suggested that there was proper conformation of polyelectrolyte adsorbed for effectively dispersing aluminum hydroxide. Also, high affinity of nonionic monomer for Si(OH)(3)O(-) suggested that interacting Si(OH)(3)O(-) is an important role of inhibition of silica scale formation.

Effects of Adsorption Conformation on the Dispersion of Aluminum Hydroxide Particles by Multifunctional Polyelectrolytes

The influence of multifunctional polyelectrolytes on the dispersion of aluminum hydroxide particles was studied, in particular the influence of monomer units acting as functional groups, with respect to particle size and zeta potential. The conformation of polyelectrolytes adsorbed on aluminum hydroxide particles, which affects their dispersion abilities, was investigated via their adsorption isotherms and (1)H NMR spectral analysis. Furthermore, the functions of monomer units were evaluated by the calculation of the interaction energies between each monomer unit and aluminum hydroxide or H(2)O by density functional theory. Three multifunctional polyelectrolytes were compared: a terpolymer of acrylic acid (AA), 2-acrylamide-2-methyl propane sulfonic acid (AMPS), and N-vinylpyrrolidone (NVP) (P(AA/SA/NVP)), acrylic acid homopolymer (P(AA)), and a copolymer of AA and AMPS (P(AA/SA)). The most effective dispersant was P(AA/SA/NVP), which prevented further coagulation among the initial particles and shifted the zeta potential to the most negative value. The conformations of the adsorbed polyelectrolytes exhibited the following order of extended conformation (larger loops and longer tails): P(AA) > P(AA/SA/NVP) > P(AA/SA). From these results, we reasonably concluded that the prominent dispersing capability of P(AA/SA/NVP) was due to its preferred extended conformation on the particle surface due to a subtle balance between the moderate affinity of NVP and the relatively higher affinities of AA and AMPS for aluminum hydroxide in an aqueous solution and the hydrophobicity of the amide groups of AMPS.

Adsorption kinetics of silicic acid on akaganeite.

As part of a series of studies on the interaction between ferric ions and silicic acid in the hydrosphere, the adsorption of silicic acid on akaganeite was investigated kinetically at various pH values. The adsorption of silicic acid increased with increasing pH over an initial pH range of 4-11.5. In the kinetic experiment, the Cl(-) was released from akaganeite much faster than silicic acid was adsorbed. From this result, we concluded that chloride ions bound on the surface of akaganeite are released and Fe-OH or Fe-O(-) sites are formed, which then acts as an adsorption site for silicic acid. The uptake mechanism of silicic acid by akaganeite is significantly different from that by schwertmannite, despite the presence of the same tunnel structure.

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust

It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth’s continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2− complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2− and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.