The atomic structure of anisotropic titanium dioxide nanoparticles is characterized by HRTEM to identify coordination defects at the tip surfaces of the nanorods (see figure). At the tip regions of the nanoparticles, the titanium metal-metal atom spacings extend between the (001.) planes and demonstrate site-specific chemical reactivity towards surface modifiers. The observed reactivity of the nanorod tip is reminiscent of selectivity found in organic and biological self-organizing systems.