Fig 5.

(A) Comparison of the experimental pH profile of TPT release half-lives () to model fits that account for the kinetics of lactone-carboxylate interconversion () or assume lactone-carboxylate equilibrium (). The equilibrium model was unable to account for the steep changes in half-life in the neutral pH region. The blue section highlights the pH region in which release was slowed by greater than 25% due to rate-limiting ring-closure. (B) The biphasic release profile observed at pH 7.04 and the fits of models that either include interconversion kinetics () or assume interconversion equilibrium ().