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nanotimes News in Brief

Researchers presented in PNAS numerical simulati- ons that show that multivalent nano-particles can be designed such that they approach the “on-off” bin- ding behavior ideal for receptor-concentration se- lective targeting. They proposed a simple analytical model that accounts for the super selective behavior of multivalent nano-particles. The model shows that the super selectivity is due to the fact that the number of distinct ligand-receptor binding arrange- ments increases in a highly nonlinear way with re- ceptor coverage. Somewhat counterintuitively, their study shows that selectivity can be improved by ma- king the individual ligand-receptor bonds weaker. © PNAS

Francisco J. Martinez-Veracoechea and Daan Frenkel: Designing super selectivity in multivalent nano-particle binding, In: PNAS Early Edition, June 20, 2011, DOI: 10.1073/pnas.1105351108: http://dx.doi.org/10.1073/pnas.1105351108

11-06/07 :: June/July 2011

Various ratios of rhenium were added to WB4 in an attempt to increase hardness. © PNAS

Reza Mohammadia, Andrew T. Lech, Miao Xie, Beth E. Weaver, Michael T. Yeung, Sarah H. Tolbert, and Richard B. Kaner: Tungsten tetraboride, an inexpensive super- hard material, In: PNAS Early Edition, June 20, 2011, DOI:10.1073/pnas.1102636108: http://dx.doi.org/10.1073/pnas.1102636108

Tungsten tetraboride (WB4) is an interesting can- didate as a less expensive member of the growing group of superhard transition metal borides. WB4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthe- sized material is phase pure. The zero-pressure bulk modulus, as measured by high-pressure X-ray diffraction for WB4, is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 ± 2.9 GPa under an applied load of 0.49 N.

The world’s first three-dimensional plasmon rulers, capable of measuring nanometer-scale spatial changes in macromolecular systems, have been de- veloped by researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with re- searchers at the University of Stuttgart, Germany. These 3D plasmon rulers could provide scientists with unprecedented details on such critical dynamic events in biology as the interaction of DNA with enzymes, the folding of proteins, the motion of pep- tides or the vibrations of cell membranes.

“We’ve demonstrated a 3D plasmon ruler, based on coupled plasmonic oligomers in combination with high-resolution plasmon spectroscopy, that enables us to retrieve the complete spatial configuration of complex macromolecular and biological processes, and to track the dynamic evolution of these pro- cesses,” says Paul Alivisatos, director of Berkeley