Fig. 2: Chemical modification of the phenaline-1,3-dione scaffold yields fluorogenic probes for detecting sulfenic acid.

a Rate constants were measured under pseudo-first-order conditions with small-molecule sulfenic acid model, CSA, in excess over phenaline-1,3-dione nucleophiles. b k_obs (s⁻¹) for compounds 1 through 8 were determined by curve fitting to a single exponential function. Second-order rate constant, k is extrapolated from k_obs divided by the concentration of the limiting agent. Bars denote ±SEM. c Absorption and emission spectra of 7 and isolated CSA-7 (250 µM) in PBS:ACN (9:1) pH = 7.4. d Absorption and emission spectra of 8 and isolated CSA-8 (250 µM) in PBS:ACN (9:1) pH = 7.4. e Fluorescence intensity monitored over time for the reaction between 7 (5 to 100 µM) and CSA (1 mM) after excitation at 443 nm (left). Fluorescence intensity (15 min) is plotted versus the concentration of 7 (right). N = 3 independent experiments. f Fluorescence intensity monitored over time for the reaction between 8 (5 to 100 µM) and CSA (1 mM) after excitation at 447 nm (left). Fluorescence intensity (15 min) is plotted versus the concentration of 8 (right). N = 3 independent experiments. g, h Rate constants were measured under pseudo-first-order conditions with CSA in excess over phenaline-1,3-dione nucleophiles. A representative trace from these reactions is shown. Linear fit of k_obs (min⁻¹) plotted versus CSA concentration gives 91 ± 3 and 105 ± 2 M⁻¹ s⁻¹ for 7 and 8, respectively (inset). N = 3 independent experiments. i, j Box and whisker plot of normalized fluorescence intensity (F/F₀) for reaction between 7 or 8 (50 µM) and various analytes (500 µM) after 1 h. Box plots show center line as median, whiskers show maxima and minima, and box limits show upper and lower quartiles. N = 4 independent experiments.