Thermodynamics of the interaction of berberine with DNA

The interaction of berberine [7,8,13,13a-tetrahydro-9-10-dimethoxy-2,3-(methylene dioxy)-berberinium] with calf thymus DNA has been studied by spectrophotometry in buffers of various salt concentrations and temperatures. Binding parameters obtained are best fit by the neighbour exclusion model. The salt and temperature dependence of the binding constants are used to estimate thermodynamic parameters involved in the complex formation of berberine with DNA. The binding process is exothermic over the entire range and the values of enthalpy and entropy change are strongly dependent on the salt concentration. The negative enthalpy and positive entropy changes compensate one another to produce a relatively small Gibbs' free energy change. Possible molecular contribution to the enthalpy and entropy changes is discussed.