Abstract
Materials Science![Figure][1] CREDIT: GE ET AL., NANO. LETT. 11 , 10.1021/NL201303Q (2011) Nanoparticles formed from mixtures of proteins and synthetic polymers are of interest for applications such as protein delivery. Ge et al. examined the surface evolution of particles comprising conjugates of bovine serum albumin (BSA) and poly(methyl methacrylate) (PMMA). They first added 51 acryloyl groups to each denatured BSA molecule and then initiated radical polymerization at each site. Nanoparticles varying in BSA content from 4 to 82% by weight resulted from injection of an acetonitrile solution of these conjugates into phosphate-buffered saline. At the highest BSA content, the nanoparticles were well dispersed but the otherwise uniform surface of PMMA was covered with islands of BSA (as shown above). These islands grew over 2 weeks' time from surface patches to surface bumps in the buffered saline, but were unchanged if the nanoparticles remained in acetonitrile. The authors present a model in which PMMA, which is better solvated in acetonitrile, forms the main shell at the outset; over time in the aqueous medium, the more hydrophilic BSA then migrates to the surface. Nano. Lett. 11 , 10.1021/nl201303q (2011). [1]: pending:yes
Highlights
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Summary
Like many groups of organisms in the Amazonian tropical rainforest, hylid tree frogs show very high diversity. There is strong variation in local diversity, with some localities and regions having much higher density of species than others. Wiens et al take a phylogenetic approach to the question of the cause of this local variation. Their analysis indicates that there is little or no relationship between variation in local species richness and climate variables such as temperature and precipitation. Diversity is related to the length of time that hylids have occupied a region. Even though diversification rates slow down when multiple clades occupy a region, species continue to accumulate with the length of time that the region has been occupied: The highest diversity occurs where the largest number of clades have coexisted for longest.
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