Amine terminated G-6 PAMAM dendrimer and its interaction with DNA probed by Hoechst 33258

Fluorescence characteristics of Hoechst 33258 bound to G-6 dendrimer, to the DNA-G-6 dendrimer complex, and to DNA were compared with that in an aqueous solution. The spectral properties including fluorescence emission spectrum, accessibility of anionic quencher, as well as the fluorescence decay time of the Hoechst 33258 are different for all three conditions, indicating that the environments in these conditions are different. Close analysis of the fluorescence properties led us to suggest that Hoechst 33258 located at or near the contact area of the dendrimer and DNA in the DNA-G-6 complex. In the complex, in the absence of Hoechst 33258, the shape of the circular dichroism in the DNA absorption region remained, indicating that DNA is in B form in the complex. On the other hand, the magnitude of linear dichroism (LD) decreased upon DNA-G-6 dendrimer complex formation. The decrease in LD magnitude reflects the shortening of the DNA contour length, which is expected from the fact that a large part of linear DNA is required to wrap the surface of G-6 dendrimer.