Binding of [Pt(1C3)(dien)]2+ to the duplex DNA oligonucleotide 5′-d(TGGCCA)-3′: the effect of an appended positive charge on the orientation and location of anthraquinone intercalation

The binding of a platinum intercalator complex [Pt(1C3)(dien)]²⁺ (1C3 = 1-[(3-aminopropyl)amino]-anthracene-9,10-dione, dien = 3-azapentane-1,5-diamine) to DNA and to the self-complementary oligonucleotide 5′-d(TGGCCA)-3′ has been investigated by UV-visible spectrophotometry and 2D NMR spectroscopy, respectively. The uncomplexed anthraquinone, 1C3, has an apparent DNA binding constant of 1.4 × 10 ⁴, similar to that of ethidium bromide. Addition of the coordinatively saturated {Pt(dien)} moiety increases the binding constant to 3.7 × 10⁵ M^-1, showing the effect of the increased positive charge introduced by this moiety. Multiple binding modes are evident from the lack of isosbestic points in the titration spectra and the non-linear nature of the half-reciprocal plot used to calculate the binding constant. [Pt(1C3)(dien)]²⁺ forms a 2: 1 adduct with 5′-d(TGGCCA)- 3′ and is shown by 2D NMR to intercalate primarily in the TG:CA base pairs at the ends of the oligonucleotide with the side chain and {Pt(dien)} situated in the minor groove.