Thermodynamic study of interaction between phthalocyanines with calf thymus DNA

Abstract

The experimental determination of formation constant for interaction of two water soluble phthalocyanines,<br />Cobalt (II) 4,4',4",4'"-tetrasulpho phthalocyanine (CoTsPc ) and Manganese(II) 4,4',4",4"-tetrasulpho<br />phthalocyanine (MnTsPc ) , with calf thymus DNA have been studied by UV-Vis spectrophotometric method<br />at lrnM phosphate buffer , pH 7.4 and at 5 different temperatures 20,25,30,35 and 400CC . The changes of Uv-<br />Vis absorption spectra during the titration of these phthalocyanines with calf thymus DNA revealed a large<br />hypochromicity (up to 45%) of the phthalocyanines maximum bands, usually considered as proof of<br />phthalocyanine intercalation in to DNA. The calculated formation constants, Ks , according to the<br />SQUAD software were in the range of 104-105 M-1.By using the Van't Hoff equation. The values of enthalpy<br />and entropy changes associated to the (CoTsPc +DNA) and<br />(MnTsPc+DNA) were determined .Then by using AG°=-RTLIIK, we calculated the values of AG° at considered<br />temperatures. Our results showed strong electrolytic effects on phthalocyanines behavior and increasing<br />NaCl concentration induced self-aggregation of the CoTsPc and MnTsPc.