DNA Melting in Poor Solvent

Abstract

The melting phase diagram of a double-stranded DNA in poor solvent, which promotes condensation, is studied using the pruned and enriched Rosenbluth method on a simple cubic lattice. For slightly poor solvent, melting temperature decreases linearly with a change in the solvent quality, which later changes slope and starts increasing as the melting line approaches the tricritical collapse curve. First-order melting transition, as in good solvent, gives way to continuous transition, and then to further broadened transitions where the order parameter smoothly becomes zero, for sufficiently poor solvent. This change in the melting behavior is accompanied by a continuously varying critical exponent along the second-order transition line, hinting at a non-universal nature of the melting transition. Further, we show that an unbound phase can be achieved just by changing the solvent quality. Importantly, our results conform to the experimental findings qualitatively.