Fig. 2. Dissociation constants K_D (mM) of boronic esters obtained from catechols 1–9 and boronic acids 10–12 in MeOH/H₂O 3 : 1 (100 mM HEPES, pH 7.8); from changes in absorption upon direct titration (1, 3, 4 and 6) or reverse titration with 4 (2, 5, 7–9).