Change of phase transformation and bond strength of Y-TZP with various hydrofluoric acid etching.

OBJECTIVES: The purpose of this study was to quantify phase transformation after hydrofluoric acid (HF) etching at various concentrations on the surface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), and to evaluate changes in bonding strength before and after thermal cycling. MATERIALS AND METHODS: A group whose Y-TZP surface was treated with tribochemical silica abrasion (TS) was used as the control. Y-TZP specimens from each experimental group were etched with 5%, 10%, 20%, and 40% HF solutions at room temperature for 10 minutes. First, to quantify the phase transformation, Y-TZP specimens (n = 5) treated with TS, 5%, 10%, 20% and 40% HF solutions were subjected to X-ray diffraction. Second, to evaluate the change in bond strength before and after thermal cycling, zirconia primer and MDP-containing resin cement were sequentially applied to the Y-TZP specimen. After 5,000 thermal cycles for half of the Y-TZP specimens, shear bond strength was measured for all experimental groups (n = 10). RESULTS: The monoclinic phase content in the 40% HF-treated group was higher than that of the 5%, 10%, and 20% HF-treated groups, but lower than that of TS-treated group (p < 0.05). The 40% HF-treated group showed significantly higher bonding strength than the TS, 5%, and 10% HF-treated groups, even after thermal cycling (p < 0.05). CONCLUSIONS: Through this experiment, the group treated with SiO2 containing air-borne abrasion on the Y-TZP surface showed higher phase transformation and higher reduction in bonding strength after thermal cycling compared to the group treated with high concentration HF.

Unilamellar nanosheet of layered manganese cobalt nickel oxide and its heterolayered film with polycations.

The exfoliation of layered Li[Mn(1/3)Co(1/3)Ni(1/3)]O(2) into individual monolayers could be achieved through the intercalation of quaternary tetramethylammonium (TMA(+)) ions into protonated metal oxide. An effective exfoliation occurred when the TMA(+)/H(+) ratio was 0.5-50. Reactions outside this range produced no colloidal suspension, but all the manganese cobalt nickel oxides precipitated. Atomic force microscopy and transmission electron microscopy clearly demonstrated that exfoliated manganese cobalt nickel oxide nanosheets have a nanometer-level thickness, underscoring the formation of unilamellar nanosheets. The maintenance of the hexagonal atomic arrangement of the manganese cobalt nickel oxide layer upon the exfoliation was confirmed by selected area electron diffraction analysis. According to diffuse reflectance ultraviolet--visible spectroscopy, the exfoliated manganese cobalt nickel oxides displayed distinct absorption peaks at approximately 354 and approximately 480 nm corresponding to the d-d transitions of octahedral metal ions, which contrasted with the featureless spectrum of the pristine metal oxide. In the light of zeta potential data showing the negative surface charge of manganese cobalt nickel oxide nanosheets, a heterolayered film of manganese cobalt nickel oxide and conductive polymers could be prepared through the successive coating process with colloidal suspension and polycations. The UV--vis and X-ray diffraction studies verified the layer-by-layer ordered structure of the obtained heterolayered film, respectively.

Electronic structure and local atomic arrangement of transition metal ions in nanoporous iron-substituted nickel phosphates, VSB-1 and VSB-5.

The electronic structure and local atomic arrangement of transition metal ions in nanoporous iron-substituted nickel phosphates VSB-1 and VSB-5 have been investigated using X-ray absorption near-edge structure (XANES) spectroscopy at Fe K- and Ni K-edges. The Fe K-edge XANES study clearly demonstrated that substituted iron ions were stabilized in octahedral nickel sites of nanoporous nickel phosphate lattice. A comparison with several Fe-references revealed that the substituted irons have mixed Fe2+/Fe3+ oxidation state with the average valence of +2.8-3.0. According to the Ni K-edge XANES analysis, the aliovalent substitution of Ni2+ with Fe2+/Fe3+ induced a slight reduction of divalent nickel ions in VSB-5 to meet a charge balance. On the contrary, Fe substitution for the VSB-1 phase did not cause notable decrease in the oxidation state of nickel ions, which would be related either to the accompanying decrease of pentavalent phosphorus cations or to the increase of oxygen anions. In conclusion, the present findings clearly demonstrated that the nanoporous lattice of nickel phosphate can accommodate effectively iron ions in its octahedral nickel sites.

Soft-chemical exfoliation route to layered cobalt oxide monolayers and its application for film deposition and nanoparticle synthesis.

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau-like height profile with nanometer-level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross-confirmed by X-ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in-plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected-area electron diffraction and Co K-edge X-ray absorption near-edge structure analysis. The zeta-potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of approximately 10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.

Influence of synthesis temperature on the crystal structure and electrode property of sulfur-doped manganese oxide nanowires.

Sulfur-doped manganese oxide 1D nanostructures with controllable crystal structures and crystallite dimensions have been synthesized via one-pot non-hydrothermal solution route. Powder X-ray diffraction analysis clearly demonstrated that the crystal structures of the sulfur-doped manganates can be tailored by the change of reaction temperature; layered delta-MnO2-structured material was obtained at 60 degrees C while the reaction at 90 degrees C produced tunnel alpha-MnO2 structured material. According to field emission-scanning electron microscopy, both sulfur-doped manganates possess 1D nanostructure-type morphology with the diameter of approximately 20 nm and the length of approximately 1 microm for delta-MnO2-type material, and the diameter of approximately 100 nm and the length of approximately 800 nm for alpha-MnO2-type material, respectively. From X-ray photoelectron and X-ray absorption spectroscopic analyses, sulfur ions exist as highly oxidized sulfate cluster on surface or grain boundary of the manganate crystallite whereas manganese ions are stabilized in octahedral geometry with the mixed oxidation state of Mn+3/Mn+4. Of special importance is that both sulfur-doped manganate nanowires show promising electrode performances for lithium secondary batteries.

Diffusion changes suggesting predominant vasogenic oedema during partial status epilepticus.

Diffusion-weighted imaging (DWI) has demonstrated a focal area of cytotoxic oedema during partial status epilepticus (PSE). However, vasogenic oedema related to the breakdown of the blood-brain-barrier (BBB) and ictal hyperperfusion could be the predominant DWI findings in the epileptogenic area during PSE. We report a case of PSE with ictal aphasia, right hemiparesis, and repetitive focal motor seizure of the right side. T2-weighted image (T2WI) and apparent diffusion coefficient (ADC) maps obtained during PSE showed an increased signal in the left temporo-parietal area, indicative of vasogenic oedema. EEG documented the ictal activities and single photon emission tomography (SPECT) showed asymmetrically increased perfusion in the corresponding area. Follow-up T2WI, DWI, and ADC maps obtained 3 months later showed the disappearance of the previous abnormalities. However, T2WI showed cortical atrophy and newly developed white matter changes in the corresponding area. This case shows that DWI findings may be variable during PSE, dependent on the predominance of cytotoxic and vasogenic oedema.

The caudal homeodomain protein activates Drosophila E2F gene expression.

The Drosophila caudal homeobox gene is required for definition of the anteroposterior axis and for gut development, and CDX1 and CDX2, human homologs, play crucial roles in the regulation of cell proliferation and differentiation in the intestine. Most studies have indicated tumor suppressor functions of Cdx2, with inhibition of proliferation, while the effects of Cdx1 are more controversial. The influence of Drosophila Caudal on cell proliferation is unknown. In this study, we found three potential Caudal binding sequences in the 5'-flanking region of the Drosophila E2F (DE2F) gene and showed by transient transfection assays that they are involved in Caudal transactivation of the dE2F gene promoter. Analyses with transgenic flies carrying an E2F-lacZ fusion gene, with and without mutation in the Caudal binding site, indicated that the Caudal binding sites are required for expression of dE2F in living flies. Caudal-induced E2F expression was also confirmed with a GAL4-UAS system in living flies. In addition, ectopic expression of Caudal with heat-shock promotion induced melanotic tumors in larvae. These results suggest that Caudal is involved in regulation of proliferation through transactivation of the E2F gene in Drosophila.

The caudal-related homeodomain protein CDX1 activates proliferating cell nuclear antigen expression in hepatocellular and colorectal carcinoma cells.

Cdx1 and Cdx2 are known as Caudal-related homeodomain transcription factors important in the early differentiation and maintenance of intestinal epithelial cells. Cdx1 and Cdx2 are expressed in the small intestine and colon of fetus and adult. Most previous studies suggested that Cdx2 inhibits proliferation. Several target genes of Cdx2 have been identified. However, the effect of Cdx1 on cell proliferation is currently controversial and its target genes except for Hox-A7 remain unknown. In this study, we found several potential Caudal-related homeodomain binding sequences in the 5'-flanking region of human PCNA gene. Cotransfection experiments, using human PCNA reporter plasmid and CDX1 and CDX2 expression plasmids, showed that CDX1 transactivates human PCNA gene promoter activity in hepatocellular cell line (HepG2) and colorectal carcinoma cell lines (Colo320HSR and HCT116), while CDX2 does not. CDX1-induced PCNA expression was also detected in immunoblot and cytochemistry experiments. In BrdU incorporation experiments, CDX1 enhanced the incorporated BrdU. Taken together, our results suggest that CDX1 have a pro-proliferative effect on proliferation through transactivation of PCNA promoter activity.