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pH change obtained from titration of (a) 20 mM PEI (pH 7) into 1.5 mM DNA in water (pH7), and (b) 20 mM PEI (pH 6, 7, and 8) into 1.5 mM DNA in 0.1 M NaCl. The data points are mean ± SD of (a) four measurements and (b) duplicate measurements.
