DNA binding of a spermine derivative: spectroscopic study of anthracene-9-carbonyl-N1-spermine with poly[d(G-C).(d(G-C)] and poly[d(A-T).d(A-T)]

The binding of polyamines, including spermidine (1) and spermine (2), to poly[d(G-C).d(G-C)] was probed using spectroscopic studies of anthracene-9-carbonyl-N1-spermine (3); data from normal absorption, linear dichroism (LD), and circular dichroism (CD) are reported. Ligand LD and CD for transitions located in the DNA region of the spectrum were used. The data show that 3 binds to DNA in a manner characteristic of both its amine and polycyclic aromatic parts. With poly[(dG-dC).(dG-dC)], binding modes are occupied sequentially and different modes correspond to different structural perturbations of the DNA. The most stable binding mode for 3 with poly[d(G-C).d(G-C)] has a site size of 6 +/- 1 bases, and an equilibrium binding constant of (2.2 +/- 1.1) x 10(7) M-1 with the anthracene moiety intercalated. It dominates the spectra from mixing ratios of approximately 133:1 until 6:1 DNA phosphate: 3 is reached. The analogous data for poly[d(A-T).d(A-T)] between mixing ratios 36:1 and 7:1 indicates a site size of 8.3 +/- 1.1 bases and an equilibrium binding constant of (6.6 +/- 3.3) x 10(5) M-1. Thus, 3 binds preferentially to poly[d(G-C).d(G-C)] at these concentrations.