Coil-globule structure transition and binding characteristics of DNA molecules induced by isoquinoline-based photoactive ionic liquid surfactant

The photodynamic therapy and gene transportation across cell membrane are closely related with the binding behavior of the photoactive vectors on DNA. Here, the binding characteristics of an isoquinoline-based photoactive ionic liquid surfactant, lauryl isoquinolinium bromide ([C(12)iQuin] Br), with DNA was investigated for the first time by various analytical techniques. It was found that the DNA molecules are strongly compacted at a low [C(12)iQuin] Br concentration, and then undergo a complete coil-to-globule structure transition upon further addition of [C(12)iQuin] Br, which was verified by cryo-TEM. Based on the H-1 NMR and 2D NOESY spectra, it can be concluded that the photoactive [C(12)iQuin] Br is an AT-specific minor groove binder. At a lower [C(12)iQuin] Br concentration, the isoquinolinium ring of [C(12)iQuin] Br would be arranged facing to the plane of the minor groove of DNA, and the hydrophobic tails of [C(12)iQuin] Br would be arranged parallel to the minor groove. The hydrophobic interaction between the hydrocarbon chains of the bound [C(12)iQuin] Br and DNA bases provides the dominate driving force in the binding process. The unique binding mode of [C(12)iQuin] Br on DNA causes the formation of the new photoactive structures of [C(12)iQuin] Br-DNA complexes, which would promise the novel applications in the photodynamic therapy or the gene transportation.