Synthesis of quaternized zinc(II) and cobalt(II) phthalocyanines bearing pyridine-2-yl-ethynyl groups and their DNA binding properties

The synthesis and biological properties of tetra-substituted zinc and cobalt phthalocyanines bearing ethynylpyridine units on the periphery and their quaternized derivatives have been reported. The binding of quaternized ZnPc and CoPc (Q-ZnPc and Q-CoPc) with calf thymus DNA was investigated by UV-Vis spectrophotometric methods and thermodynamics. The mixtures of Q-ZnPc or Q-CoPc and DNA solutions were used to determine the change in the thermal melting temperature of DNA with the thermal denaturation profile. Thermodynamic parameters that show the spontaneity of the reactions between DNA and the quaternized phthalocyanines were investigated. K_b binding constants at a degree of 10⁵ and 10⁶ for Q-ZnPc and Q-CoPc, respectively, showed that the phthalocyanines bound to DNA fragments efficiently and thermodynamic data proved that the binding process was spontaneous and entropy-driven. The interactions between Q-ZnPc and Q-CoPc and DNA in an aqueous environment corresponded to electrostatic attractions and nonspecific binding.