Spectroscopic Studies of the Interaction of some Monomer and Homodimer Styrylcyanine Dyes with DNA.

The interaction of the monomer dyes Sbt ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]thiazol-3-ium iodide), Sbo((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]oxazol-3-ium iodide), Sil((E)-2-(4-(dimethylamino)styryl)-1,3,3-trimethyl-3 H-indolium perchlorate) and their homodimers Dbt-10, Dbo-10, Dil-10 with salmon DNA were studied using steady-state and time-resolved fluorescence spectroscopic methods. A significant increase in the quantum yield was observed for homodimer dyes upon binding to DNA. Quantum chemical calculations show the formation of the non-emissive TICT state in these dyes. The increase in fluorescence quantum yield upon dye binding to DNA is associated with the restriction of the dye fragments rotations relative to one another in the excited state. For these dyes, the binding constant (Kb) to DNA were determined. Binding affinity depends on molecular structure of studied dyes. It was found that the addition of NaCl to a DNA solution leads to the formation of H-aggregates on the nucleic acid surface. Theoretical modeling shows that monomer and homodimer dyes bind to DNA in the minor groove via hydrogen bonds, Van der Waals and hydrophobic forces, that are main factor in the interaction of probe molecules with nucleic acid.