“…4CN has been used as a histochemical stain for neutrophils and MPO ex vivo 13 . [ 14 C]1-naphthol is oxidized and trapped on proximate proteins or macromolecules, including the ROS-producing enzymes [14][15][16] . Significantly, the redox potential of 1-naphthoxy radical is 0.59 V, which is well above hydrogen peroxide (1e − ) and NO but below MPO/compound 1 and high-energy effectors, tuned for selective reactivity with innate immunity (Table 1).…”