Shigeru Shimomura

Detection of oxovanadium (IV) and characterization of its ligand environment in subcellular fractions of the liver of rats treated with pentavalent vanadium(V).

Abstract Tetravalent oxovanadium(IV) was detected in subcellular fractions of liver by ESR spectroscopy after i.p. injection of pentavalent vanadium(V) as sodium vanadate into rats for three days. This indicates that the metal ion was reduced from the pentavalent state to oxovanadium(IV). The ligand environment around this oxovanadium center was characterized using ESR parameters (g o and A o ) and the empirical bonding coefficients calculated from the ESR parameters. These values indicate that most of the ligand atoms around the oxovanadium(IV) are oxygens and that the metal may exist in a protein-bound form.

Atomic fluorescence spectrometry of mercury: principles and developments

Abstract Atomic fluorescence spectrometry (AFS) of mercury is very sensitive and the AFS system is an excellent detector for mercury analysis. The first part of this review covers the principles of determination of mercury by AFS. The second part delineates the loss and increase of mercury through its transfer between the gas and solution phases. The third part addresses some possible interferences in the determination of mercury by AFS. The fourth part describes preconcentration techniques for mercury species. In the fifth part, methods for total and selective determination of mercury are described. In the sixth part, various types of automated and semi-automated procedures for the determination of mercury are summarized. Finally, representative biological and environmental certified reference materials (CRMs) for mercury analysis are presented and the availability of CRMs in checking the accuracy and precision of the methodologies is briefly described.

ATP(adenosine triphosphate)-vanadyl complex.

Abstract Owing to the significance of inhibitory effect of vanadium ion to Na, K-ATPase, a complex formation between ATP and vanadyl ion was investigated over a wide pH range. Formations of two types of complex are observed : a blue complex formed in acidic and neutral pH regions and a green complex at higher than pH 11. On the basis of the results on potentiometric titration, optical and EPR spectra and empirical bonding coefficients calculated from the EPR parameters, two characteristic types of coordination environment are proposed for the ATP-vanadyl complex : a blue 1:1 complex is a relatively weak complex including a phosphate-vanadyl coordination mode, whereas a green 2:1 complex is much stronger complex including a vanadyl-oxygen coordination contributed from a deprotonated hydroxyl group of the ribose moiety of ATP.

Determination of germanium in different media by atomic absorption spectrometry with electrothermal atomization

Abstract Effectsof acids, alkalis or salts on the atomic absorption spectrometry (electrothermal atomization) of germanium are described. Most of the species tested interfere with the absorption. The mechanisms of the interferences were investigated by using tantalum-coated and standard graphite tubes. The results showed that positive interferences are due to inhibition of the reaction of germanium dioxide with carbon to form volatile GeO 3 and that suppressive interferences are due to physical occlusion effects. The addition of sodium hydroxide to the sample solution provides a very sensitive analysis (0.004 ppm for 1% absorption) for germanium without matrix interferences. This is probably due to the formation of stable Na 2 GeO 3 during the ashing step in the presence of sodium hydroxide.

31p- and 13C-NMR study of the ATP(adenosine triphosphate)-vanadyl complex.

Abstract The state of existence of cytoplasmic vanadyl ion is known to be important: the vanadyl ion forms complexes with ATP and the vanadate form inhibits its (Na++K+-ATPase. Therefore, the formation of complexes between ATP and vanadyl ion was investigated by 31P- and 13C-NMR spectrometry. From the present and previous results, it was concluded that three characteristic types of ATP-vanadyl complex are formed in aqueous solution: a blue 1:1 complex formed in the acidic pH region ATP has coordination sites between β- and γ-phosphates, a ribose 3′-protonated hydroxyl oxygen and adenine N-3 nitrogen and the vanadyl ion; a blue 1:1 complex formed in the neutral pH region contains coordination sites for vanadyl ion at β- and γ-phosphates and ribose 2′- and 3′-protonated hydroxyl oxygens; a green 2:1 complex at alkaline pH has binding sites between two sets of ribose 2′-protonated and 3′-deprotonated hydroxyl oxygens and vanadyl ion.

Glutathione-hemin complex as a cytochrome P-450 model characterization of the complex and its aromatic oxidation activities

Abstract A new cytochrome P-450 model that simulates the unusual spectral and substrate-oxidation properties of cytochrome P-450 is proposed. The complex, consisting of glutathione(GSH), hemin and pyridine(py), exhibits similar optical and EPR spectra to cytochrome P-450 in ferric low-spin state. On omission of py, a ferric high-spin state was produced. On exposure of the GSH-hemin-py complex to CO, a characteristic absorption band appeared at 450nm, like that typical of cytochrome P-450. Two types of spectral changes were observed when aminopyrine or phenobarbital (Type I) and aniline or quinoline (Type II) were added to the GSH-hemin complex. Hydroxylation, dealkylation and aromatic methyl migration activities were observed with the GSH-hemin complex.

Absorption of mercury by solutions containing oxidants

Abstract The transfer of mercury vapor into solutions containing mercury(II) ions and/or oxidants (dichromate, permanganate, cerium(IV) sulfate, silver nitrate) is investigated. The rate of absorption increases with increasing Hg 2+ concentration and with increasing oxidation potential of dichromate solutions in sulfuric acid. A mechanism is proposed for the transfer.

Flow Injection Analysis of Mercury/Cold Vapor Atomic Fluorescence Spectrophotometry

Abstract A new flow injection system for the determination of mercury by the cold vapor atomic fluorescence method is described. A sample solution (64 μ1) is injected into a stream of 0.1 M hydrochloric acid, which is mixed with a stream of 3% tin (II) chloride solution in a mixing joint. The combined stream is carried through a reaction coil for reduction of Hg (II) to Hg (0) and subsequently introduced into a specially designed gas-liquid separation vessel. Then the vaporized mercury is swept into a flow type fluorescence cell with a continuous flow of argon after removal of water in the gas phase through a condenser. Mercury is excited with an electrodeless discharge lamp as a source and the mercury fluorescence at both 184.9 and 253.7 nm is measured with a solar-blind photomultiplier. This method allows about 35 determinations of mercury in aqueous samples per hour. The calibration curve is linear over the 0–20 ppb range of mercury. The limit of detection (S/N = 3) is 0.008 ng (0.12 ppb × 64 μ1) and t...

Interrelationships between the concentration of magnesium, calcium, and strontium in the hair of Japanese school children

Inductively coupled atomic emission spectrometry was used for the determination of magnesium, calcium and strontium in the hair of Japanese school children (7-15 years of age, 158 males and 184 females). Sex-related differences in the levels of the three alkaline earth metals were observed (T-test, p less than 0.001). Geometric means (SD) of the concentrations of magnesium, calcium and strontium were 30.40 (1.42), 326.3 (1.62) and 0.509 (2.04) micrograms g-1 for males and 61.21 (1.73), 643.4 (1.57) and 2.749 (2.14) micrograms g-1 for females. For both sexes, significant positive correlations were observed between all concentration pairs of the three elements. The concentration ratios between any two of the three elements were also determined. The geometric mean of the concentration ratio of calcium to magnesium for males [10.73 (1.54)] is not significantly different from that for females [10.51 (1.40)] (T-test, p greater than 0.05). On the other hand, concentration ratios of magnesium to strontium [59.71 (1.99)] and calcium to strontium [640.9 (1.74)] for males are significantly higher (T-test, p less than 0.01) than those for females [22.27 (1.60) and 235.9 (1.65)]. The logarithmic-transformed ratio of magnesium to strontium has a strong positive correlation with the transformed ratio of calcium to strontium [r = 0.9529 (p less than 0.001) for males and r = 0.7284 (p less than 0.001) for females].

Determination of germanium and some other elements in hair, nail, and toenail from persons exposed and unexposed to germanium

Inductively coupled atomic emission spectrometry was used for the determination of germanium in hair, nail, and toenail. The levels of germanium in three individuals administered a high concentration of a germanium preparation daily for about 12-16 months were very high: 56.4-173.7; 5.4-35.0; and 14.0-15.8 micrograms g-1 in hair, nail, and toenail, respectively. The levels for normal or unexposed persons are very low and were not detected by the method.