A significant equilibrium distinguishing DNA/RNA-like phases in 2T SAW model on Husimi tetrahedron lattice

Abstract

A modified two-tolerate (2T) SAW polymer model is carried on the Husimi tetrahedron lattice to describe the DNA/RNA-like biomacromolecules. With a simplified assemble of configurations to catch the zipping/unzipping feature of intra-pair-able polymer chains, the thermodynamics are exactly derived via the recursive property of Husimi lattice. The probability(density) of monomers in single and paired strands, and solvent are calculated from recursive partial partition functions to characterize the phase diagrams. The model is found to be a practical setup fitting both DNA- and RNA-like polymers, with rich phase diagrams presenting the DNA/RNA-like regions and the unwinding/polymerase transitions. An intriguing equilibrium is found to separate DNA- and RNA-like regions with a particular parameters setup, where the single and double strands co-exist in the system with constant densities regardless of temperature.