Drug Binding, Order-Order and Order-Disorder Transitions in DNA Triple Helices

Zimm and Bragg theory for helix to coil transition has been suitably amended and applied to explain the two step transition in DNA triplex. The experimental measurements reported by G. E. Plum et al. and Y. W. Park et al. have been interpreted. The order-order and order-disorder transitions associated with the melting of DNA triple helix, with and without netropsin binding, have been characterized by the nucleation parameter, enthalpy change, sharpness of transition, and heat capacity. The destabilization of the triplex and stabilization of duplex on netropsin binding are reflected in these characteristic parameters.