Microscopical approach to the helix–coil transition in DNA

A model Hamiltonian for double-strand polynucleotides is suggested to describe the phenomenon of helix–coil transition. The Hamiltonian is constructed using solely the microscopical, pure physical quantities, characterizing the molecular chain, namely the energy of hydrogen-bond formation and the number of conformations of repeated unit. Realistic constraints are imposed on the conformations of chain in the case of loop formation. The advantage of the suggested approach is that the parameters of the model can be obtained from independent calculations or experiments. It is shown that with the approximation of neglecting the effect of large loops, the model of DNA is reduced to the generalized microscopical model of polypeptide chain.