Examining the Effect of DNA Flexibility in Complex Coacervates

Complex coacervation, the phase separation driven by electrostatic associations of a polyanion and polycation, has been extensively studied by varying the charge structure of the macromolecules or by adjusting solution conditions. However, there is a lack of understanding of how internal flexibility of the constituents affects the process. To vary flexibility, we exploit the programmable nature of DNA specifically studying the coacervation of single-strands, double-strands, and hairpins complexing with poly-l-lysine. We measure the DNA versus salt concentration phase diagrams of these varying structures by fluorescently tagging the DNA and using confocal microscopy to quantify the concentration in the dense and dilute phase via fluorescence intensity. We discuss how DNA secondary structure impacts phase behavior, including the critical salt and DNA concentration in the dense phase. We expect our work will lead to a better understanding of how the individual molecular properties affect the formation and composition of biomolecular condensates.