Although it is an advantage when the carrier is non-toxic, it is well known that carriers that are characterized by neutral charge are not suitable to deliver negatively charged genetic material. It is also true in the case of the pyrrolidone modified DAB-core PAMAM G4 dendrimer. Cu(II) and Zn(II) form labile complexes with amines and we had previously characterized the Cu(II)-complexes with pyrrolidone modified PAMAM G4 dendrimer with ESR. This is not possible with Zn(II), which is diamagnetic.