Potentiometric response characteristics of polycation-sensitive membrane electrodes toward poly(amidoamine) and poly(propylenimine) dendrimers

The potentiometric response characteristics of polycation-sensitive membrane electrodes toward two classes of polycationic dendrimers are examined. Using appropriately formulated polymer membrane electrodes composed of a dinonylnaphthalenesulfonate (DNNS) salt in a plasticized polyurethane matrix, it is shown that poly(amidoamine) (PAMAM) and poly(propylenimine) (PPI) dendrimers are readily detected at submicrogram per milliliter levels via a nonequilibrium response mechanism. The relationship between the total EMF response (at equilibrium) and the specific dendrimer structure is also examined. For both the PAMAM and PPI species, it is shown that the total EMF response does not change significantly with dendrimer generation number; however, the nonequilibrium analytically useful response curves are shifted to higher mass concentrations as the generation number is increased. The relative contributions of the terminal primary amines and the interior tertiary amines of the dendrimers to the observed EMF response are investigated by synthesis of various dendrimer derivatives (acetylated, quaternized, etc.). By comparing the total EMF responses for these derivatives as a function of sample pH, it is demonstrated that the lipophilic cation exchanger (DNNS) within the membrane phase can likely interact electrostatically with both protonated forms of the terminal primary amines and interior tertiary amines of the dendrimer structures. The practical application of the nonequilibrium potentiometric detection of dendrimers for monitoring their interaction with DNA is also demonstrated.