| Abstract: | The spectral properties of the actinocin derivative ActII in complexes with DNA were studied by UV visible spectrophotometry. Two binding models with one and two binding sites for competitive binding with different values of parameters were considered. To choose an optimal model of complexation, the optimization program of spectrophotometric concentration dependencies DALSMOD was used. Using this program, it was concluded that at least three complexes with different absorption spectra are present in the system ActII-DNA. The logarithms of K2 and K3 for DNA-ActII mixtures, calculated for models I and II at different sodium ion concentrations, were in good agreement with predictions of the counterion condensation theory. The analysis of the absorption spectra of ActII-DNA mixtures at different temperatures made it possible to obtain the values of deltaH and deltaS for each type of complexes. The values of entropy deltaS were positive in the 0.02 M NaCl solution and negative in the 0.15 M NaCI solution. |
