Acylpyrazolones: Synthesis, Self-Assembly and Lanthanide Metal Ion Separation
The central hypothesis that nanoscale self-assemblies can provide excellent metal ion recognition has been substantiated by employing acylpyrazolones and trivalent lanthanide metal ions as model systems. Several novel acylpyrazolones and their amphiphilic analogs have been designed, synthesized, and characterized. Their lanthanide metal ion recognition efficacies have been demonstrated through baseline separations of a mixture of light, middle, and heavylanthanide metal ions by employing them in the aqueous mobile phase of high performance liquid chromatography (HPLC) with octadecylsilanized silica (ODS) as the stationary phase. The complex separation mechanism is influenced by the structures of acylpyrazolone and amphiphilic moieties, and spontaneous self-assembly of the ligand in the aqueous and on the stationary phases. Transmission electron microscopy (TEM) studies of the ligand self-assemblies in the aqueous phase in the absence and presence of lanthanide metal ions reveal spherical, dendritic, and linear (nanofibers, nanorods, and nanotubes) nanoscale structures. Such structures have also been observed when chloromethylated acylpyrazolones are stimulated to self-assemble by a base in nonaqueous solvents and when silica nanoparticles derivatized with them spontaneously self-assemble in aqueous and nonaqueous solvents.