A thermodynamic study of cationic polymer-plasmid DNA complexes by highly-sensitive differential scanning calorimetry.

The characteristics of polymer-DNA complexes formed by positively-negatively charged interaction have a great influence on their transfection potential. Since the limit changes in thermal transitions which were hardly measured in conventional calorimetry, now in this study they have been successfully carried out by highly-sensitive differential scanning calorimetry for better understanding the pDMAEMA-plasmid DNA complexing process. Thermal behaviors of plasmid DNA, polymer and their formed complexes were recorded to give insights into their conformational changes when temperature was raised. In results, the supercoiled or open-circular plasmid DNA is not thermal reversible indicated by the decrease of denaturation peak and disappearance of DNA conformational transition related to its twist status at 50-70 degrees C. The cationic polymer is thermally stable by showing reversible transition peaks after two heating processes. For the cationic polymer-plasmid DNA complexes, electrostatic forces lead to a higher denaturation temperature of plasmid DNA and transition temperature of polymer. Also, heat can cause a topological change in plasmid DNA and then change their mutual complexation capacity.