94 The investigation of Hoechst 33258 interaction with DNA in aqueous solutions of dimethylsulfoxide

Abstract

The melting of DNA complexes with Hoechst 33258 (H33258) has been carried out in both presence and absence of dimethylsulfoxide (DMSO) to reveal the effect of the mentioned compound on melting parameters of DNA-H33258 complexes at r = 0.1, where r = [H33258]/[DNA] and at 0.02 M Na⁺ ion concentration. It is known that the structural–functional changes of macromolecules take place in aqueous solutions of DMSO (Markarian et al., 2006). It has been shown earlier that DNA hydration degree increase results in sharp changing of the binding mechanism of H33258 to DNA: AT-specific mode of binding disappears and ligand molecules start to intercalate into DNA at r ⩽ 0.1 (Vardevanyan et al., 2008). Moreover, the increase of T _m of complexes is higher compared to the case of relatively low hydration degree of DNA. This is conditioned by the fact that at DNA hydration, increasing the intercalation becomes more preferable since in this case hydrophobic ligand molecules are shielded from water more effectively. The results obtained confirm that with the increasing of DMSO content in solution the melting temperature, T _m, decreases. Moreover, denaturation of complexes leads to the decrease of the fluorescence intensity of ligand molecule. We suggest that the observed phenomenon happens due to the structural change of solution which promotes dissociation of ligand molecules bound to DNA, and hence a facilitated denaturation of DNA-H33258 complexes occurs.