Characterization of Starburst Dendrimers by the EPR Technique. Copper(II) Ions Binding Full-Generation Dendrimers

Cu(II) was used as a probe to investigate the structure and ion binding ability of full-generation poly(amidoamine) starburst dendrimers (nSBDs). Computer-aided analysis of the EPR spectra provided information on the formation of copper complexes in various internal or external locations of the dendrimers, as well as the nSBD structure as a function of the size (generation) of the dendrimers, pH, temperature, Cu(II) concentration, and aging of the samples. At low pH, Cu2+ competes with protons for binding with external amino groups, which become available for complexation at pH > 3.5. The Cu(H2O)62+ complexes are localized in proximity to the SBD surface, where structural modifications of the water solution prevented the occurrence of a freezing transition. A portion (about 20%) of Cu(H2O)62+ resides in the water pools in the open structure of the earlier generation dendrimers (G < 4) and are capable of undergoing a freezing transition. Progressive penetration of Cu2+ ions into the SBD structure occurs wi...