Synthesis of tetra(trimethylammonio)phthalocyanato zinc tetraiodide, [ZnPc(NMe3)4]I4, and a spectrometric investigation of its interaction with calf thymus DNA

The phthalocyanine salt [ZnPc(NMe₃)₄]I₄ was synthesized from 4-nitrophthalonitrile using a three-step procedure. The interaction of [ZnPc(NMe₃)₄]⁴⁺ with calf thymus DNA (CT DNA) has been investigated by UV-vis and fluorescence spectrometric methods. [ZnPc(NMe₃)₄]⁴⁺ exists in a non-monomeric form, proposed to be a dimer, in phosphate buffer solution (pH 6.82). Spectral changes show that in the presence of high concentrations of CT DNA added to the solution, [ZnPc(NMe₃)₄]⁴⁺ is bound in a monomeric state with evidence suggesting it is located in a DNA groove. At lower concentrations of DNA there is evidence of stacking of non-monomeric [ZnPc(NMe₃)₄]⁴⁺ onto the DNA. Two intrinsic binding constants for the interaction of [ZnPc(NMe₃)₄]⁴⁺ with CT DNA, 1.33 × 10⁵ and 2.56 × 10⁴ M^-1 have been obtained. Electrostatic binding is shown to play an important role in the interaction of [ZnPc(NMe₃)₄]⁴⁺ with nucleic acids.