Correlation of thermochemical and spectral characteristics as a method for determining the type of binding of porphyrins to nucleic acids

Abstract

The work is devoted to the analysis and generalization of the thermochemical and spectral characteristics of complexes of porphyrins with synthetic oligonucleotides poly[d(AT)₂], poly[d(GC)₂] and calf thymus DNA of solutions, studied in our laboratory. The interactions of nucleic acids (NA) with cationic porphyrins containing indole (PorIn), caffeine (PorCofe), adenine (PorAd) and guanine (PorGu) residues as substituents were studied by spectrophotometric titration. The calorimetric method was used for measuring the temperature dependences of the heat capacity of solutions of cationic porphyrins, NA, as well as complexes. A correlation relationship was obtained for the temperature dependence of the specific heat capacity of NA-porphyrin-buffer. It was found that there is a correlation between the heat capacity of solutions of the complexes at 25 °C, the ratio of hypochromic effect to the shift of the maximum of absorption of the band Sore and the way of binding of NA to cationic porphyrins. Spectral methods for recording changes in the photophysical properties of chromophore ligands made it possible in most cases to reveal the mechanism of binding of porphyrins to NA. Thermochemical studies provided the evaluation of the structural consequences of the complexation process and clarification of the method of porphyrins binding to NA. The perspectives of joint application of the results of thermochemical and spectral studies to elucidate the structural aspects of the formation of complexes NA-porphyrin are discussed in this paper.