Fig. 9. Ratio of emission intensities at 525 nm upon excitation at 480 and 510 nm after 30 and 60 minutes of incubation of probes 4–6 with GSH at various pH (5.0–8.0) and without GSH after 60 minutes. Probe 4 (A); probe 5 (B); probe 6 (C) (5 μM probe 4–6, 5 mM glutathione; DMSO/HEPES buffer 2 : 1, 0.1 M, 37 °C).