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[Ba2CuO2(CO3)]m[ACuO2]n(A=Sr) superlattices containing oxycarbonate blocks as charge reservoir have been prepared on SrTiO3 using the molecular beam epitaxy technique. First, thin films of the oxycarbonate cuprate Ba2CuO2(CO3) have been prepared on SrTiO3(001) using NO2 gas as an oxidant and CO2 gas. The films have been grown at 500°C. At higher substrate temperature or at lower CO2 pressure Ba2CuO3 was formed instead of Ba2CuO2(CO3), and the films becomes amorphous at lower temperature. X-ray diffraction and reflection high-energy electron diffraction observations indicated that (BaxSr1−x)2CuO2(CO3) grew along the  crystal orientation on SrTiO3(001) with the following epitaxial relationship: Ba2CuO2(CO3)//SrTiO3 and Ba2CuO2(CO3)//SrTiO3 . Depth profile of secondary ion mass spectrometry signals indicated the incorporation of carbon into the films. Secondly, the oxycarbonate cuprates and infinite layers have been alternately stacked. It was confirmed that Ba2CuO2(CO3)was inserted between several unit cells of SrCuO2. Electrical measurements show the as grown films to have a semiconducting behavior.
Generation of RNA dimeric form of the human immunodeficiency
virus type 1 (HIV-1) genome is crucial for viral replication.
The dimerization initiation site (DIS) has been identified
as a primary sequence that can form a stem-loop structure
with a self-complementary sequence in the loop and a bulge
in the stem. It has been reported that HIV-1 RNA fragments
containing the DIS form two types of dimers, loose dimers
and tight dimers. The loose dimers are spontaneously generated
at the physiological temperature and converted into tight
dimers by the addition of nucleocapsid protein NCp7. To
know the biochemical process in this two-step dimerization
reaction, we chemically synthesized a 39-mer RNA covering
the entire DIS sequence and also a 23-mer RNA covering
the self-complementary loop and its flanking stem within
the DIS. Electrophoretic dimerization assays demonstrated
that the 39-mer RNA reproduced the two-step dimerization
process, whereas the 23-mer RNA immediately formed the
tight dimer. Furthermore, deletion of the bulge from the
39-mer RNA prevented the NCp7-assisted tight-dimer formation.
Therefore, the whole DIS sequence is necessary and sufficient
for the two-step dimerization. Our data suggested that
the bulge region regulates the stability of the stem and
guides the DIS to the two-step dimerization process.
Apparent stability constants of Eu(III)- and Am(III)-humates determined at various pH (4.8 to 8) and supporting electrolyte concentration (0.02 to 1 mol/1), indicate that the humate complexes may be dominant species in the aquifer. Distribution coefficients of Eu(III) and Am(III) between kaolinite and solution phase were affected strongly by the presence of humic acid in the solution. Adsorption of humic acid may be an important factor controlling fixation of actinides(III) on mineral surfaces.
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