Regiospecific synthesis of 6-halouridine derivatives: An effective method for coupling sterically hindered pyrimidine bases to ribose

6-Halouridine derivatives were synthesized regiospecifically through the coupling of N3-protected 6-halouracil to a ribose derivative. The combination of the silylating reagent N,O-bis(trimethylsilyl)acetamide and Lewis acid catalyst trimethylsilyl trifluoromethanesulfonate is unique in their ability to facilitate the coupling of sterically hindered pyrimidine bases to ribose to form nucleoside derivatives.     

Size-controlled synthesis of monodisperse core/shell nanogels

Small, monodisperse nanogels (∼50-nm radius) were synthesized by free-radical precipitation polymerization and were characterized using a suite of light scattering and chromatography methods. Nanogels were synthesized with either N-isopropylacrylamide or N-isopropylmethacrylamide as the main monomer, with acrylic acid or 4-acrylamidofluorescein as a comonomer and N,N′-methylenebis(acrylamide) as a cross-linker. By varying the surfactant and initiator concentrations, particle size was controlled while maintaining excellent monodispersity. An amine-containing shell was added to these core particles to facilitate subsequent bioconjugation. Successful conjugation of folic acid to the particles was demonstrated as an example of how such materials might be employed in a targeted drug delivery system.     

An experiment in chaotic scattering using repulsive magnetic forces

We consider the scattering of a particle injected into a system of three coplanar potentials that give rise to inverse square law repulsive forces. Most of the parameter space defined by the combination of injection energy and impact parameter is found to be associated with geometrically simple input–output trajectories. These regions in parameter space are separated by narrow ridges which correspond to chaotic scattering. Experimental data are also reported for the scattering of a magnetic puck propelled into the domain of three fixed magnets.