Figure 2. PBAEs exhibit diversity in pK_a and cooperativity of deprotonation.

A) PBAE (0.6 mg/mL) was titrated with 0.1 N NaOH. pK_a was based on calculating the half equivalence point, using the first derivative of the titration curve to find the equivalence point (Figure S5). Normalized volume was derived from dividing by the initial volume of PBAE solution. B) Superimposed titration curves for the four polymers with normalization of titration coordinate to a measure of the degree of deprotonation (θ). Approximate pH range of the endocytic process denoted with shading. Unshaded regime: above physiologic pH, dark green shaded regime: extracellular space to early endosomal pH, light green shaded regime: late endosomal to lysosomal pH. C) Conversion of titration coordinate diagram to a log-transformed measurement of deprotonation against pH normalized to pK_a. Equation based on a cooperativity modification of the Henderson-Hasselbach equation. D) The linear region of log(θ/1−θ) versus pH-pK_a was used to determine n_hill, which represents the cooperativity and anti-cooperativity that occurs in the titration of polyamines. 95% confidence interval of the n_hill parameter is shown.