CHARACTERIZATION OF STARBURST DENDRIMERS BY EPR .4. MN(II) AS A PROBEOF INTERPHASE PROPERTIES

Mn(II) has been used as a probe to investigate the interacting abiliti es of the various ligand sites at the surface of starburst dendrimers (SBDs) at different protonation conditions, and as a function of gener ation (G), both for half- and full-generation SBDs (n.5-SBDs and n-SBD s, respectively). The computer-aided analysis of the electron paramagn etic resonance (EPR) spectra of Mn(II) provided information on the loc ation of Mn(II) in the hydration layers of the internal and external S BD surface and on the physical status of water inside the dendrimer st ructure and at the surface/solution interface. Mn(II) did not show any interaction with the full-generation dendrimers and only interacted, at the second-third solvation shells, with the surface carboxylate gro ups (SBD-COO-) of n.5-SBDs. Two main components were identified in the EPR spectra: (1) a minor component due to Mn(II) that is localized in the solvation layers of the internal and external SBD surface and is in fast exchange with the bulk solution. This Mn(II) fraction underwen t a freezing transition at about 255 K; (2) a major component arising from complexation of Mn(II) with SBD-COO- groups at the second solvati on shell of the ions. The portion of solution that contained the Mn(II ) complexes underwent a glass transition with a decrease in temperatur e. The complexation of Mn(II) was favored for later generation dendrim ers (G > 4.5), at high pH and low Mn(II) concentrations.