Hiroki Asami

Diversity of 2,3-dihydroxybiphenyl dioxygenase genes in a strong PCB degrader, Rhodococcus sp. strain RHA1

Two 2,3-dihydroxybiphenyl (23DHBP) dioxygenase genes, bphC1 and etbC involved in the degradation of polychlorinated biphenyl(s) (PCBs) have been isolated and characterized from a strong PCB degrader, Rhodococcus sp. RHA1. In this study, four new 23DHBP dioxygenase genes, designated as bphC2, bphC3, bphC4, and bphC5 were isolated from RHA1, and their nucleotide sequences were determined. Based on amino acid sequence similarities, all of the newly isolated bphC genes could be categorized into type I along with BphC1 and EtbC [Eltis, L.D. and Bolin, J.T., J. Bacteriol., 178, 5930-5937 (1996)]. Six bphC genes, including bphC1, etbC, and four new genes, were expressed in Escherichia coli to determine their substrate specificity. The activities of BphC2, BphC3, BphC4, and BphC5 were found to be specific to 23DHBP, while BphC1 and EtbC exhibited activities towards compounds other than 23DHBP, including catechol (CAT) and 3-methylcatechol (3MC). RNA slot blot hybridization analysis indicated that only bphC5 was transcribed among the newly isolated bphC in RHA1 cells grown on biphenyl and ethylbenzene. The nucleotide sequence of the flanking region of each bphC revealed a homolog of the 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (HOPD) hydrolase gene, bphD, just upstream of bphC5. The bphC5 and putative bphD genes may constitute an operon and play a role in the degradation of biphenyl and PCBs together with bphC1 and etbC. In contrast, the bphC2, bphC3, and bphC4 genes may not be involved in biphenyl and PCB degradation.

Hardness Optimization of (Cr,Mg)(N,O) Thin Films Prepared by Pulsed Laser Deposition

Chromium magnesium oxynitride ((Cr,Mg)(N,O)) thin films have been prepared by pulsed laser deposition (PLD) method with changing the surface area ratio of Mg target (SR) from 0 to 100 %. As a result of the analysis by energy dispersive X-ray spectroscopy (EDX), it was found that magnesium content in the total metallic elements (Cr1-x, Mgx) are controlled by changing SR from 0 to 100 % to be the x ranging from 0 to 1.0. Since the crystal structure of main phase in all thin films was found to be NaCl type, the XRD results showed that the thin films were mainly consisted of (Cr,Mg)(N,O). The hardness of (Cr,Mg)(N,O) thin films were increased almost linearly up to SR = 50 %, above which it decreases rapidly. The maximum Vickers hardness (HV) of 3600 was obtained for the thin film which was prepared by SR = 50 %, and the minimum HV of 1650 was obtained for the thin film which was prepared by SR = 100 %.

Fourier-Transform Infrared Absorption Spectroscopy of Chromium Nitride Thin Film

Chromium nitride thin films were deposited by RF reactive unbalanced magnetron sputtering on (100) Si single-crystal or glassy carbon substrates. The characteristics of the thin films were measured by Rutherford backscattering spectroscopy, X-ray diffractometry, and scanning electron microscopy. From the results of the above measurements, it was found that our samples were stoichiometric chromium nitride thin films. The chemical bonding state was estimated using the results of the Fourier-transform infrared spectroscopy. A peak attributed to the Cr–N bond was observed at around 380 cm-1, and it could be obtained with any beam splitter and atmosphere. Furthermore, the influence of residual stress was also investigated. Residual stresses of CrN thin films, which were calculated from their strains, were quite low.

Material Design of Transition Metal Nitrides for Hard Coatings by Metal and Nonmetal Atom Substitution

Cr-Me-N-O (Me; Ni, Cu and Mg) thin films have been designed and successfully prepared by the pulsed laser deposition (PLD) method. It was found that Me, which form the monoxide MeO, are effective for hardening the Cr(N,O) thin films.

Preparation and Characterization of Cr–Zn–N–O Thin Films Deposited by Pulsed Laser Deposition

Cr–N–O, Cr–Zn–N–O, and Zn–O thin films were prepared by pulsed laser deposition. The compositional analysis of the Cr–Zn–N–O thin films by Rutherford backscattering spectroscopy revealed that they are ternary compounds of the Cr–Zn–N–O system. Their Vickers hardness was about 4200 kgf/mm2. X-ray diffraction indicated that the Cr–N–O and Cr–Zn–N–O thin films have the NaCl-type structure (B1), the same as CrN. Transition electron microscopy observation indicated that a grain of the (Cr,Zn)(N,O) phase existed, on the basis of which it could be considered as a solid solution of B1-CrN and a high-pressure phase of ZnO with the B1 structure.

(Ni,Cu)O Phase in Thin Films Prepared by Pulsed Laser Deposition

Nickel copper oxide [(Ni1-xCux)O] thin films in which Cu content x was changed from 0 to 1 were prepared by pulsed laser deposition. The copper content of the thin films was determined by energy-dispersive X-ray analysis with scanning electron microscopy. Transmission electron microscope observation of the thin films with x = 0.37 revealed that the thin films contained grains consisting of Ni, Cu, and O. Both interplanar distances and lattice constant increased with increasing copper content. The (Ni1-xCux)O phase with 0 < x < 0.27 has a B1 structure.

OXIDATION PROPERTIES OF Cr(N,O) THIN FILMS SYNTHESIZED BY PULSED LASER DEPOSITION

Chromium oxynitride (Cr(N,O)) thin films have been successfully prepared by using pulsed laser deposition. The oxygen content in the thin films ( x ) was controlled by changing experimental conditions. From the results of oxidation tests, the B1 (NaCl type) phase in Cr(N,O) thin films with x = 3 at. % exists up to T = 600 °C, whereas Cr(N,O) thin films with x = 30 at. % contain B1 phase at T = 800 °C. As one of the reasons to explain this fact, the existence of the oxide layer formed on the Cr(N,O) crystallites surface by the oxygen atoms dissolved in B1 structure is considered.