| Abstract
| - The cooperative condensation of DNA and cationic liposomes to form ordered aggregates in aqueoussolution is associated with the release of partially bound counterions. We directly determine the extentof counterion release by separating the supernatant from the precipitated condensates, measuring theconductivity of the solution before and after the phase transition. The extent of counterion release iscalculated for a range of lipid/DNA concentration ratios based on the nonlinear Poisson−Boltzmann theory.Both experiment and theory show maximal, essentially complete, release of counterions at the isoelectricpoint, where the positive (lipid)/negative (DNA) charge ratio is 1:1. Furthermore, at this point the entropiccontribution to the condensation free energy is maximal and dominant.
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