A thermodynamic view of polymer degradation, and its application to extensive sonication of DNA

A simple thermodynamic theory is developed, which predicts (in agreement with a wide variety of other theoretical approaches and experimental results) that for simple polymers the most probable Schulz distribution of fragments will be obtained in a polymer degradation process that is allowed to proceed to a dynamic equilibrium. When the same method is applied to a double-stranded polymer like DNA, however, it predicts that some narrowing of this distribution may occur in conjunction with a limited amount of base unpairing at the fragment termini. The compatibility of this prediction with the experimental results of long-time sonication of DNA is considered.