Synthesis and Characterization of Carboxymethylated Polyethylenimines

As potential paramagnetic metal ion complexing macromolecular ligands, carboxymethylated polyethylenimines (CM-PEIs) were successfully prepared from polyethylenimine (PEI) with 2-chloroacetic acid (CA) in an alkaline medium. SEC, pH-potentiometry, DLS, and multinuclear and multidimensional NMR techniques were used to determine the degree of functionalization, size, and possible structure of the modified polymers. By varying the amount of CA, functionalization degrees of 7–67% relative to the theoretical maximum were achieved. Diffusometry shows that the PEI and CM-PEIs are highly hydrated. The CM-PEIs are larger molecules than the parent PEI, although their hydrodynamic size decreases with higher degrees of functionalization. CM-PEIs are isostable except for the most highly substituted derivative. CM-PEIs form complexes with Cu(II) and efficiently decrease the rate of the copper-mediated oxidation of ascorbic acid. The good affinity toward cations of CM-PEI functionalized at 67% is further demonstrated by its capacity to bind even sodium ions. These properties show that CM-PEIs are promising metal-chelating polymers for diagnostic or theranostic purposes.