Carboxylated Nanospheres Using Cyclic Dipeptides as Removable Templates for Cation Binding

Carboxylated nanoparticles play an important role in separation technology, catalysis, proton conduction, water purification, ion transport, and gas separation. Reported herein are small cyclic dipeptide templates appended with monomeric norbornene units for obtaining robust carboxylated nanospheres. The stereochemistry of the dipeptides dictates the size of the resulting nanoassembly. The exposed monomeric units on the nanospheres are polymerized to covalently capture the self-assembly. Removal of the peptide template via ester hydrolysis results in carboxylated polymeric spheres. Polymer cross-linking enhances the thermal stability of the spherical assembly, while the five-membered ring obtained after norbornene polymerization retains its shape even after removal of the template. The ability of these charged spheres to bind cations is illustrated by the binding of a positively charged chloride-sensing lucigenin dye. The chloride-sensing ability of the bound dye is not compromised, illustrating the utility of these nanospheres as potential chloride sensors. One can also envision extending this concept for binding and separating other charged species of interest.