ABSTRACT
In this study, we demonstrate for the first time the hydrothermal synthesis of yttria-stabilized zirconia (YSZ) nanocrystals with controlled yttria content (x = 3-12 mol %; xYSZ) with negligible aggregation from aqueous solution. The nanocrystals were grown via the hydrothermal treatment of basic Zr(IV) and Y(III) carbonate complex aqueous solutions in the presence of a cationic ligand, N(CH3)4(+). The nanocrystals were characterized in detail by dynamic light scattering, ζ-potential measurement, X-ray diffraction, specific surface area measurement based on the Brunauer-Emmett-Teller theory, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Shorter reaction times and higher Y2O3 content produce aqueous solutions with higher transparencies containing nanocrystals with sizes of 10 nm or less. Nanocrystals with the target composition were obtained by hydrothermal reaction for longer than 3 h, regardless of the Y2O3 content. The main phase is tetragonal for (3-6)YSZ and cubic with disordered oxygen vacancies for (8-12)YSZ. The characteristics of the nanocrystalline material synthesized are consistent with those of bulk YSZ crystals, indicating the growth of high-quality nanocrystals.
ABSTRACT
In humans and animals, intestinal flora is indispensable for bile acid transformation. The goal of our study was to establish gnotobiotic mice with intestinal bacteria of human origin in order to examine the role of intestinal bacteria in the transformation of bile acids in vivo using the technique of gnotobiology. Eight strains of bile acid-deconjugating bacteria were isolated from ex-germ-free mice inoculated with a human fecal dilution of 10(-6), and five strains of 7alpha-dehydroxylating bacteria were isolated from the intestine of limited human flora mice inoculated only with clostridia. The results of biochemical tests and 16S rDNA sequence analysis showed that seven out of eight bile acid-deconjugating strains belong to a bacteroides cluster (Bacteroides vulgatus, B. distasonis, and B. uniformis), and one strain had high similarity with Bilophila wadsworthia. All five strains that converted cholic acid to deoxycholic acid had greatest similarity with Clostridium hylemonae. A combination of 10 isolated strains converted taurocholic acid into deoxycholic acid both in vitro and in the mouse intestine. These results indicate that the predominant bacteria, mainly Bacteroides, in human feces comprise one of the main bacterial groups for the deconjugation of bile acids, and clostridia may play an important role in 7aplha-dehydroxylation of free-form primary bile acids in the intestine although these strains are not predominant. The gnotobiotic mouse with bacteria of human origin could be a useful model in studies of bile acid metabolism by human intestinal bacteria in vivo.