Calixarene-Modified Nanoparticles

Modifying the surface of metal nanoparticles with organic ligands can enhance the particles’ catalytic properties. Ligands can stabilize neighboring particles against agglomerating into large clumps and burying active sites, and they may also serve as electron donors to activate metal catalysts. But finding suitable ligands and ensuring that they do not render the metal surface inaccessible to would-be reagents are formidable challenges. Alexander Katz of the University of California, Berkeley, reported that his group has developed a method for bonding calixarenes, a type of macrocyclic chelating agent, to gold nanoparticles. The group also developed a spectroscopic procedure for analyzing the extent to which the metal surface remains accessible (Langmuir, DOI: 10.1021/la9013174). Jeong-Myeong Ha, Andrew Solovyov, and Katz found that solutions of calixarene-modified particles remain stable against agglomeration for months. In contrast, particles treated with other compounds, for example, surfactants, are unstable. In addition, by using a naphthalene thiol probe molecule that fluoresces in solution but does not fluoresce when adsorbed on a surface, the team showed quantitatively that decorating the particles with bulky calixarenes leaves much of the metal surface accessible to bind small molecules—the first step toward surface catalysis.