Thermodynamic study of interaction between phthalocyanines with calf thymus DNA

Document Type : Research Paper




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