Using Ethidium Bromide To Probe the Interactions between DNA and Dendrimers†

Investigations have been carried out to probe the interactions between double-stranded DNA and amineterminated, ethylenediamine core polyamidoamine starburst dendrimers generation 2 (G2), generation 4 (G4), and generation 7 (G7). Ethidium bromide is used as a fluorescent probe for this study. Under our experimental conditions, the results show that there is mainly one binding mode between ethidium and DNA-dendrimer complexes and that dendrimers bind to DNA sufficiently strongly that they cannot be displaced by ethidium. In the proposed binding model for DNA-dendrimer complexes, the DNA wraps around G7 dendrimers while the wrapping of DNA does not occur for G2 and G4 dendrimers. DNAdendrimer interactions display little preference on DNA base components. The influence of pH and ionic strength is in agreement with electrostatic interactions as the major binding force for DNA-dendrimer complexes.