Determination of selenium and tellurium in silver chloride and uranium oxide

Methods are described for the determination of selenium and tellurium in crude silver chloride produced as a by-product of the refining of gold, and in high-purity uranium oxide. Selenium and tellurium are separated from one another as well as from the numerous other substances in the sample before they are extracted into organic solvents and determined spectrophotometrically. For the determination of selenium 3,3'-diaminobenzidine is used and for tellurium, sym-diphenylthiourea. A minimum of 2 ppm of each element may be determined in silver chloride and 0.3 ppm in uranium oxide. Statistical data are given to show the precision and accuracy of the methods.     

Synthesis and biological evaluation of integrin antagonists containing trans- and cis-2,5-disubstituted THF rings

The synthesis of a series of RGD mimetics is described. All compounds consist of a central 2,5-disubstituted tetrahydrofuran core, a variable linker to a guanidino group, and a beta-amino alanine unit to mimic the carboxylic acid. Three types of linkers were investigated: a simple four-atom methylene chain (type A, compounds 14, 15, 16, and 17), a four-atom methylene chain with an additional chiral center, and a nitrogen substituent (type B, compounds 38, 39, and 40), and an amide linker of different length with an additional chiral center (type C, compounds 59, 60, 61, and 62). A variety of compounds were tested as potential integrin antagonists in a receptor binding assay (alphaIIbbeta3, alphavbeta3, and alphavbeta5). The relative and absolute configuration of the chiral centers at the THF ring had a pronounced effect on the binding activity and selectivity. Compound 14 proved to be a selective inhibitor of alphaIIbbeta3 (IC50=20nM), whereas compound 40 exhibited high activity for binding of alphaIIbbeta3 (IC50=67nM) and alphavbeta3 (IC50=52nM).     

Synthesis of 6-formylsalicylates based on regioselective [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 1,1-dichloro-4-ethoxy-3-buten-2-ones

6-Formylsalicylates are prepared by regioselective [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 1,1-dichloro-4-ethoxy-3-buten-2-ones and subsequent transformation of the dichloromethyl into a formyl group.     

Das rasche Vergilben des Papieres im Lichte

Ohne Zusammenfassung     

Relative Quantum Yield Measurements of Coumarin Encapsulated in Core-Shell Silica Nanoparticles

Fluorescent silica nanoparticles encapsulating organic fluorophores provide an attractive materials platform for a wide array of applications where high fluorescent brightness is required. We describe a class of fluorescent silica nanoparticles with a core-shell architecture and narrow particle size distribution, having a diameter of less than 20 nm and covalently incorporating a blue-emitting coumarin dye. A quantitative comparison of the scattering-corrected relative quantum yield of the particles to free dye in water yields an enhancement of approximately an order of magnitude. This enhancement of quantum efficiency is consistent with previous work on rhodamine dye-based particles. It provides support for the argument that improved brightness over free dye in aqueous solution is a more general effect of covalent incorporation of fluorescent organic dyes within rigid silica nanoparticle matrices. These results indicate a synthetic route towards highly fluorescent silica nanoparticles that produces excellent probes for imaging, security, and sensing applications.     

Ultrasmall Sub-10 nm Near-Infrared Fluorescent Mesoporous Silica Nanoparticles

Ultrasmall sub-10 nm nanoprobes and carriers are of significant interest due to their favorable biodistribution characteristics in in vivo experiments. Here we describe the one-pot synthesis of PEGylated mesoporous silica nanoparticles with a single pore, tunable sizes around 9 nm and narrow size distributions that can be labeled with near-infrared dye Cy5.5. Particles are characterized by a combination of transmission electron microscopy, dynamic light scattering, fluorescence correlation spectroscopy, optical spectroscopy, nuclear magnetic resonance spectroscopy, and nitrogen sorption/desorption measurements. The possibility to distinguish an "inside" and "outside" may render these particles an interesting subject for further studies in sensing, drug delivery, and theranostics applications.     

Paradox of stability of nanoparticles at very low ionic strength

The scaling of electrical double layer interaction energy from a plate-plate system to a sphere-plate system was reexamined, and it was found that accurate scaling without resorting to the Derjaguin approximation theoretically predicts the destabilization of nanoparticles in water depleted of added electrolyte and, consequentially, a maximum stability at a moderate ionic strength. This theoretical feature re-emphasizes the dual-role nature of added electrolyte that was supported by experimental results of direct surface force measurement but not by those of colloidal stability of nanoparticle deposition/aggregation. Inconsistences between the theoretical prediction and the experimental observation and between experimental observations in different systems were discussed. Possible reasons leading to the inconsistences were explored, including the effect of curvature, the contribution from counterions, the mode of interaction, and the applicability of an equilibrium model to describe the colloidal interaction of a nanoparticle suspension.