Spontaneous formation of polymer nanoparticles by good-solvent evaporation as a nonequilibrium process

In recent years, polymer nanoparticles have been investigated with great interest due to their potential applications in the fields of electronics, photonics, and biotechnology. Here, we report the spontaneous formation of polymer nanoparticles from a clear solution containing a nonvolatile poor solvent by slow evaporation of a volatile good solvent. During evaporation of the good solvent, the solution gradually turns turbid. After evaporation, polymer nanoparticles of homogeneous shape and size are dispersed in the poor solvent. Homogeneous nucleation and successive growth of polymer particles takes place during the dynamic nonequilibrium process of solvent evaporation. The size of the particles, ranging from tens of nanometers to micrometer scale, depends on both polymer concentration and the solvent mixing ratio. Because of the physical generality of the particle formation mechanism, this procedure is applicable to a wide variety of polymers with suitable combinations of solvents. Here, we also show unique features, surface structures and surface properties of polymer nanoparticles prepared by this method.     

Singlet energy migration and excimer formation in polymers of 2-tert-butyl-6-vinylnaphthalene

The homopolymer of 2-tert-butyl-6-vinylnaphthalene (BVN) and its copolymers with styrene were prepared to examine the effects of the bulky tert-butyl groups on singlet energy migration and excimer formation among the naphthalene chromophores. The intensity of naphthalene excimer emission relative to that of monomer emission was found to depend linearly on the concentration of the potential excimer forming site, i.e., the BVN dyad fraction of the polymer. The rate of fluorescence quenching by biacetyl, on the other hand, increased only slightly with the increase in the BVN content. These results are consistent with the slow energy hopping model and suggest that the neighboring naphthalene chromophores are virtually isolated from one another owing to the unfavorable interactions of the tert-butyl groups.     

Deprotection of dithioacetals using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide

Dithioacetals can be deprotected to afford carbonyl groups using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Myocardial imaging with thallium-201--subtraction imaging with 201TlCl and 99mTcO4- for the visualization of the right ventricle--(author's transl)

The dual radioisotope techniques with 201TlCl and 99mTcO4- were performed in 30 cases inclusive of various heart and lung diseases, using a scintillation camera coupling to a small digital computer. The scintigraphic procedures were started about 5 minutes after intravenous injection of 201TlCl. The myocardial images such as anterior, 60 degrees left anterior oblique, and left lateral view, were obtained. Next, 30 degrees left anterior oblique view was taken and radionuclide angiogram with 99mTcO4- was done in the same position too. This joint use of the myocardial imaging and radionuclide angiography could increase diagnostic reliability. Superimposing the image as iso-count map extracted out of radionuclide angiogram to the brightness image of 201TlCl, the anatomic orientation of the image of 201TlCl was improved. Subtracting the blood pool image with 99mTcO4- or radionuclide angiogram, which showed visualization of the right ventricle, lungs and left ventricle, from the image of 201TlCl, the subtraction image was obtained. The right ventricle was visualized more clearly on this subtraction image than the original image of 201TlCl. Good visualization of the right ventricle was shown in 25 cases on the subtraction image, and in 17 cases on the original image of 201TlCl.     

Long-Lived Radionuclides in Sea Sediments Around Kashiwazaki-Kariwa Nuclear Power Station

Natural and artificial radionuclide concentrations in sea sediments around Kashiwazaki-Kariwa nuclear power station have been investigated with respect to the particle size distributions and the ignition losses during assay. Plutonium concentrations around the south and north discharge area, ranged from 0.054 to 0.24 Bq·kg^-1 (average 0.145) and 0.15 to 0.25 Bq·kg^-1 (average 0.213), respectively. Plutonium concentrations were significantly related to erosion and accumulation processes of sediments in both south and north discharges. Additionally, the ratios of ²³⁹Pu to ²⁴⁰Pu were evaluated with ICP-MS to determine the origin of the Pu-isotopes. Uranium-238, ²³²Th and ⁴⁰K were found in concentration range of 7.3–67, 12–100 and 260–560 Bq·kg^-1 with mean concentrations of 20, 29 and 390 Bq·kg^-1, respectively. It is assumed that the relatively high concentrations of the natural radionuclides such as U and Th are due to the presence of minerals (the south discharge regions). On the basis of these results, the origin of the Pu-isotopes was assumed to be derived from fallout of the past atmospheric nuclear tests.     

A C4N4 Diaminopyrimidine Fluorophore

A new scaffold for producing efficient organic fluorescent materials was identified: 2,5-diamino-4,6-diarylpyrimidine featuring a C4N4 elemental composition. Single-step installation of two aryl groups at the 4,6-positions of the pyrimidine core delivered fluorescent organic materials in a modular fashion. A range of fluorescent compounds with distinct absorption/emission properties was readily accessed by changing the aromatic attachments. A generally high absorption coefficient and quantum yield were observed, including C4N4 derivatives that could fluoresce even in the solid state. The two amino groups at the 2,5-positions of the pyrimidine were essential for intense fluorescence with a large Stokes shift, which was corroborated by structural relaxation to a p-iminoquinone-like structure in the excited state. Besides live-cell imaging capabilities, fluorescent labeling of a protein involved in autophagy elucidated a new protein–protein interaction, supporting potential utility in bioimaging applications.     

Radiative X(3872) Decays in Charmonium-Molecule Hybrid Model

We study the radiative decays of the X(3872) in the charmonium-molecule model combined with the quark potential model. We obtain \({\Gamma(X(3872) \to J/\psi \, \gamma) = 29.2\,{\rm keV}}\) and \({\Gamma(X(3872) \to \psi' \, \gamma) = 6.3\,{\rm keV}}\) . The ratio of these two is 0.22, which is much smaller than the BABAR observation. We find that the result is very sensitive to the amount of the \({\chi_{c1}(1P)}\) component in the X(3872).